“Monsoon evolution and tectonics-climate linkage in Asia”

Koshiba Hall, University of Tokyo

7-3-1 Hongo, Tokyo, Japan

Final International Symposium of IGCP-476

Program and Abstracts

December 6-8, 2007

Final International Symposium of IGCP-476

"Monsoon evolution and tectonics-climate linkage in Asia"

Program and Abstracts

Tokyo, Japan

December 6-8, 2007

IGCP-476 Japan Local Organizing Committee: Ryuji Tada (University of Tokyo) Tomohisa Irino (Hokkaido University) Ken Ikehara (AIST) Yusuke Yokoyama (University of Tokyo) !

Host Organization: Department of Earth and Planetary Science, University of Tokyo

Sponsors: UNESCO-IGCP (International Geoscience Program) 21st Century Earth Science COE program, University of Tokyo J-DESC (Japan Drilling Earth Science Consortium)

! "

Program

Final International Symposium of IGCP-476

"Monsoon evolution and tectonics-climate linkage in Asia"

Date: December 6!to 8, 2007

Place: Koshiba Hall, University of Tokyo, 7-3-1 Hongo, Tokyo, Japan

Organizer: IGCP-476 Japan Local Organizing Committee!(Ryuji Tada, Tomohisa Irino, Ken Ikehara, Yusuke Yokoyama)

Sponsors: UNESCO-IGCP, 21 Earth Science COE Program!of University of Tokyo, J-DESC (Japan Drilling Earth Science Consortium).

Meeting Schedule: Dec. 6th afternoon:!IGCP-476 Workshop Dec. 7th: Fifth international symposium of IGCP-476 (Koshiba Hall) Dec. 7th evening: Reception Dec. 8th morning: Fifth international symposium of IGCP-476

(continue) Workshop Program:

15:00-17:00 Registration (In front of Rm 336)

15:30-17:30 IGCP-476 Workshop!(Rm 336)

IODP Update (Soh and CDEX) About next phase of IGCP-476 (Zheng)

Symposium Program: 1st day (December 7th)

8:30-15:00 Registration (In front of Koshiba Hall)

8:50-9:00 Opening

! #

Session 1: Monsoon evolution: (Chair: Clift and Zheng) 1) 9:00-9:50 History of the Asian monsoon climate as documented by

the loess-soil sequences in China and other geological evidence Zhentang GUO (China; keynote)

2) 9:50-10:30 Onset and evolution of dust emission from deserts in East Asia and its possible linkage with uplift of northern Tibet Ryuji TADA (Japan)

10:30-10:50 <Coffee Break>

3) 10:50-11:40 Plio-Pleistocene Evolution of the Indo-Asian Monsoon

Systems Steven CLEMENS (USA; keynote) 4) 11:40-12:20 Marine Geological Records of East Asian Monsoon

Variability over the past 5Myr Min Te CHEN (Taiwan)

12:20-13:20 <Lunch> <Afternoon: Session 1 continues> 5) 13:20-14:00 Evolutional history of Indian monsoon from terrestrial

record Rajiv SINHA (India) Session 2: Tectonic evolution and erosional history of the Himalaya-

Tibetan Plateau: (Chair: Khim and Irino) 6) 14:00-14:40 Extrusion of Himalayan metamorphic nappe: Its

significance in uplift and tectonic evlution of the Himalaya Harutaka SAKAI (Japan)

14:40-15:00 <Coffee Break> 7) 15:00-15:50 Stable isotopic evidence for Himalayan-Tibet Uplift in the

Tertiary Jay QUADE (USA; keynote) 8) 15:50-16:30 Evolution of the Cenozoic Yecheng foreland basin in

southern Tarim and tectonic and paleoenvironmental implications

Hongbo ZHENG (China)

! $

9) 16:30-17:10 Erosional response of the western Himalaya to Holocene monsoon intensification: Implications for the origin of the Greater Himalaya

Peter CLIFT (U.K.)

17:10-17:45 2 min. presentation on posters 17:45-18:30 Poster Session

18:30-20:00 Reception

2nd day (December 8th) 10) 9:00-9:50 CO2 sink potential of Himalaya-Tibet weathering and

erosion Youngsook HUH (Korea; keynote) Session 3: Tectonics-climate linkages, perspective from climatic

simulations: (Chair: Yokoyama) 11) 9:50-10:50 Effect of topographic uplift on monsoon evolution Akio KITOH (Japan; keynote) 12) 10:50-11:30 Subarctic Pacific sea-ice formation due to Central

American Seaway closure and its influence on East Asian winter monsoon

Tatsuo MOTOI (Japan) 11:30-11:50 <Coffee Break> Session 4: General Discussion and Conclusion 11:50-12:50 General Discussion i) What do paleoclimate people want from tectonics and modeling

people? Lead by Tada ii) What do tectonics people want from paleoclimate and modeling

people? Lead by Clift iii) What do modeling people want from paleoclimate and tectonics

people? Lead by Motoi iv) Toward the next phase of the project Lead by Tada

12:50-13:00 Concluding Remark

! %

Poster Session

1. Kan AOIKE (Japan): A few remarks on paleoceanographic history of offshore Shimokita Peninsula over the past 600,000 years from primary analyses on cores of D/V CHIKYU shakedown cruises

2. Rie FUJII (Japan): Middle to late Pleistocene terrestrial record of Indian monsoon reconstructed by pollen analysis of lacustrine sediments in the Kathmandu Basin, Central Nepal Himalaya

3. Hitoshi HASEGAWA (Japan): Evolution of East Asian Monsoon: New Insights from Desert Deposits in the Southwest China (Preliminary Report)

4. Ken IKEHARA(Japan): Rapid retreat of seasonal sea-ice margins in the western NW Pacific margin and Japan Sea during the last deglaciation

5. Tomohisa IRINO (Japan): Variation of eolian dust contribution to the Japan Sea sediments during the last 800 kyr deduced from major element composition

6. Takuya ITAKI (Korea): The late Pleistocene radioralians in the Bering Sea

7. Upali de Silva JAYAWARDENA (Sri Lanka): A Note on the deposits of older lacustrine sediments and younger glacial sediments in Sri Lanka

8. Boo Keun KHIM (Korea): Late Quaternary paleoceanographic conditions in the northeastern Japan Basin, East Sea (Sea of Japan)

9. Sunghan KIM (Korea): Millennial-scale paleoceanographic changes in the central Bering Sea during the late Pleistocene

10. Seung-Il NAM (Korea): Organic-gechemical proxy from the western margin of the East Sea/Japan Sea and its paleoceanographic implications

11. Testuya SAKAI (Japan): Simultaneous monsoon development in Himalaya and East Africa recorded in the terrrestrial successions in Siwalik Hills and Kenya Rift

12. Hisami SUGA (Japan): Paleohydrology of Japan Sea during the Last 48 KYR: A Ultra-High Resolution Record from NE Japan Sea

13. Yusuke SUGANUMA (Japan): Rock magnetic record of Southeast Asian monsoon variability during the past 800 kyr

14. Naomi SUGIURA (Japan): Uplift of Kunlun Mountains and the formation of Taklimakan Desert

15. Yaspal P. SUNDRIYAL (India): Palaeomonsoonal and palaeoseismic implications of landslide induced lakes: Evidence from the Lesser Central Himalaya, Uttrakhand, India

16. Shin TOYODA (Japan): ESR signals in quartz as indicators of provenance of aeolian dust

17. Pai-Sen YU (Taiwan): Late Quaternary planktic foraminifer fauna and monsoon upwelling records from the western South China Sea, near the Vietnam margin (IMAGES MD012394)

! &

Session 1

Monsoon evolution

! '

History of the Asian monsoon climate as documented by the loess-soil sequences and other

geological records Zhengtang Guo, Qingzhen Hao, Yansong Qiao, Shuzhen Peng and Tungsheng Liu

(Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029,

China)

There are still considerable disagreements about the onset, subsequent evolution and

underlying causes of the monsoon-dominant climate in Asia. Here, we address the Cenozoic history

of the Asian monsoon climate based on various geological records and the loess-soil sequences in

China.

Examinations on the spatial distribution of the Paleocene, Eocene and Oligocene

environmental indicators define roughly EW zonal climate patterns in Asia throughout the

Paleogene. These are attributable to the dominance of a Planetary Wind System (PWS). A major

reorganization occurred near the Miocene/Oligocene boundary, characterized by the replacement of

the zonal PWS by a monsoonal pattern similar to that of the present day.

The history of eolian dust deposition in northern China has been traced back from ~8 Ma to 22

million years ago (Myr). Eolian deposits in the region now include the well-known loess-soil

sequences of the last 2.6 Myr, containing more than fifty loess and soil layers, the Hipparion Red-

Earth, also referred to as Red-Clay (2.6-8.0 Myr) of eolian origin in the eastern Loess Plateau and

the Miocene-Pliocene loess-soil sequences (3.5-22 Myr) in the western Loess Plateau that contain

more than three hundred pairs of loess/soil layers. The eolian origin of the newly found Miocene

and Pliocene eolian sequences are evidenced by (1) their wide distribution mantling the broad

highlands; (2) the spatially correlative stratigraphy, magnetic susceptibility and grain-size timeseries;

(3) the presence of several hundred of paleosols with the interbedded loess layers also being

affected by pedogeneses; (4) the fine silty textures throughout the ~16 Myr sequence with the

maximum grain-size mostly < 120 µm; (5) the similarity of quartz grain morphology and

geochemical properties to Quaternary loess, (6) the well-preserved and abundant land snails and

lack of aquatic and amphibian species throughout the sequences; and (7) the cyclical changes of

various climate proxies along the sequences, similar to those in the Quaternary loess-soil sequences

in China.

The onset of eolian deposition is thus roughly consistent with the major reorganization of

climate pattern in Asia near the Oligocene/Miocene boundary. The numerous alternations of loess

and soil layers indicate the existence of sizeable deserts in the Asian inlands as dust sources, the

winter monsoon as dust carrier, and an energetic summer monsoon as a supply of moisture.

Recently, several lines of climate proxies have been developed from parallel eolian sections. These

provide a near complete history of continental aridity in the Asian inlands, Asian summer and

winter monsoons.

! (

For the early and middle Miocene portion, loess accumulation rates and eolian grain-size show

rough-coeval changes and indicate moderate levels of aridity and winter monsoon strength. Their

variations are significantly different from those of the marine oxygen isotope records, suggesting

rather weak impacts of the ongoing global cooling. On the contrary, global cooling and the

consequent expansion of Arctic sea-ice/ice sheets have strongly modulated the inland aridity and

winter monsoon since the Late Miocene. Some of the events also coincide with proposed uplift of

portions of the Tibetan Plateau.

Several soil, chemical and mineralogical parameters are used to document the effects of the

summer monsoon. Strongest effects are observed for the early Miocene, then progressively decline

during the Neogene. The drastic strengthening of summer monsoon at ~8-7 Ma, as inferred by the

cold foraminifera species in the Arabian Sea, is not obvious in the loess records in China. The cause

is enigmatic and their explanation would require invoking combined effects of multi-factors

associated with the Neogene global cooling and tectonic changes.

! )

Onset and evolution of dust emission from deserts in East Asia and its possible linkage with

uplift of northern Tibet

Ryuji Tada, Yuko Isozaki, Naomi Sugiura

Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,

Tokyo 113-0033, Japan

Hongbo Zheng

Department of Marine Geology, Tongji University, 1239 Siping Road, Shanghai, China

Youbin Sun

State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Ac

ademy of Sciences, Xi’an 710075, China

Shin Toyoda

Department of Applied Physics, Okayama University of Science, Okayama 700-0005, Japan

Desert areas in East Asia, such as Taklimakan, Gurbantunggut, Badain Juran, Tengger sa

nd deserts!and Gobi deserts in northwestern China and southern Mongolia are characterized

by their relatively high latitude!compared to other deserts in the world that develop under s

ubtropical highs. Climatic simulations predict such shift in deserts position toward higher la

titude is the result of uplift of Himalaya and Tibet and intensification of Asian monsoon th

at caused northward migration of the dry areas. Thus, to specify the onset timing and evol

ution process of these deserts are critical to understand the linkage between tectonics and cl

imate in East Asia.

Most of previous studies examining the onset timing of formation and subsequent evoluti

on of East Asian deserts are based on loess and paleosol records of Chinese Loess Plateau

(CLP) or pelagic sediment records of central North Pacific. The record of these fine-graine

d eolian deposits has been traced back to ca. 8 Ma by a decade ago, and now seems to be

traced back to ca. 23 Ma. However, their provenance is still poorly understood, and it is

not necessary clear from which area the eolian sediments are derived, since no good proven

ance indicators are developed so far.

Recently, we introduced new provenance tracing proxies, electron spin resonance (ESR) s

ignal intensity and crystallinity index (CI) of quartz in the eolian sediments. We applied th

ese proxies to the Red Clay Formation and Loess-Paleosol sequence in central CLP. The r

esult suggests that provenance before 4.3 Ma can be explained by contribution from Altai

Mountains or eastern part of Tianshan Mountains. Contribution from Taklimakan Desert are

a gradually increased from 4.3 to 1.1 Ma and became maximum during 1.1 to 0.4 Ma. Fi

nally, contribution from Tengger Desert became significant since 0.4 Ma.

Information on the onset timing and evolution process of the Taklimakan Desert can als

! *

o be obtained from fluvial deposits exposed on the southwestern margin of the Taklimakan

Desert, where fluvial sequence is continuously exposed since ca. 35 Ma till 1.6 Ma. The u

pper part of the fluvial sequence intercalates fine-grained eolian deposit similar to loess, of

which deposition started at ca. 4.6 Ma and its accumulation rate drastically increased betwee

n 3.6 and 1.6 Ma. Deposition of so-called “mountain loess” on the hills in front of Kunlu

n Mountains started after 1.6 Ma and probably around 1 Ma, although the exact timing is

not yet specified.

The onset timing of eolian dust deposition coincides with the first appearance of conglo

merate beds derived from the Kunlun Mountains at ca. 4.6 Ma and the start of increase in

its accumulation rate from 3.6 Ma coincides with the time of rapid tilting along the northw

estern margin of Kunlun Mountains from 3.7 to 2.7 Ma. These agreements in timing sugge

st casual linkage between tectonic uplift of Kunlun Mountains, its erosion and production of

abundant detrital material, and emission of eolian dust from Taklimakan Desert area.

!"+

PLIO-PLEISTOCENE EVOLUTION OF THE INDO-ASIAN MONSOON SYSTEMS

Clemens Steven, Prell Warren (Brown University, Providence, RI, 02912-1846, USA)

Sun Youbin (Institute of Earth Environment, Xi’an 710075, China)

Liu Zhengyu, Chen Guangshen (University of Wisconsin-Madison, Madison, WI, USA)

Indian monsoon records from the Arabian Sea and East Asian monsoon records from the South

China Sea and Chinese Loess Plateau are all linked either directly or empirically to the global marine oxygen isotope stratigraphy (global ice volume). In turn, the global ice volume record is theoretically and empirically linked to orbital forcing in what is commonly known as the ‘marine oxygen isotope chronostratigraphy’. We attempt to synthesize and interpret Plio-Pleistocene changes in summer- and winter-monsoon circulation from these regions relative to the evolution of global ice volume and orbital insolation forcing.

Between 5 and 2.75 Ma, when southern hemisphere (SH) ice volume dominated, strong summer and winter monsoons were in phase (occurred at the same time) at both the obliquity and precession bands. At the precession band, summer- and winter-monsoons were strong at precession minima (June 21 perihelion), consistent with direct northern hemisphere (NH) insolation forcing, and at precession maxima (December 21 perihelion), consistent with SH latent heat forcing from the Indian Ocean. This interpretation assumes a fundamental change in the global marine isotope chronology prior to 2.75 Ma such that ice-volume minima lag SH summer insolation forcing. This proposed change is entirely consistent with the SPECMAP paradigm linking changes in ice volume to insolation forcing in the hemisphere where dominant ice volume resides. At the obliquity band, summer- and winter-monsoon winds in East Asia were strongest at obliquity minima. Time-dependant Fast Ocean Atmosphere Model (FOAM) results suggest the possibility that this non-intuitive phase result is linked to increased surface temperatures and precipitation at obliquity minima, and seems to be related to the seasonal as well as annual mean insolation changes.

Near 2.75 Ma, as NH ice volume gains dominance, the phase of global ice volume at the precession band shifts nearly 180°, to a position slightly lagging NH summer insolation forcing. Between 2.75 and 1.25 Ma, at both orbital bands, the phase of SM proxies begin to drift toward ice minima while the phase of WM indicators begin to drift toward ice maxima; these drifts indicate that increased glacial boundary conditions tend, on average, to strengthen the winter monsoon while increased interglacial boundary conditions tend, on average, to strengthen the summer monsoon.

Between 1.25 Ma and present, the phase of the SM proxies reside between ice minima and precession maxima (Indian Ocean latent heat export); direct NH sensible heating appears to play a lesser role. At the obliquity band the phase of the SM proxies reside between and ice minima and obliquity maxima (NH sensible heat and SH latent heat maxima); all three factors appear to be important in driving SM circulation. For both the obliquity and precession bands, the WM proxies reside between ice maxima and obliquity maxima (NH sensible heat mimima).

In summary, prior to the development of significant NH ice volume, Pliocene SM and WM proxies tend to cluster at extremes of the orbital cycles (obliquity maxima, precession maxima, and precession minima) indicating that the monsoons are sensitive to fast-physics aspects of the climate system such as direct sensible and latent heating. As NH ice volume grows, the phase of strong winter monsoons tend to drift toward the phase of ice maxima while the phase of strong summer monsoons tend to drift toward ice minima indicating that the development high latitude NH glacial boundary conditions impact the strength and timing of low-latitude monsoon circulation.

!""

Marine Geological Records of East Asian Monsoon Variability over the past 5Myr

Min-Te Chen

Institute of Applied Geosciences, National Taiwan Ocean University, Keelung 20224, Taiwan

! The East Asian Monsoon (EAM) is a globally significant climate system with links to the climate systems of the high latitudes, as well as major elements of the general atmospheric circulation system dominating the tropics such as ENSO. Climatologically, monsoon regions are the most convectively active areas on Earth and account for the majority of global atmospheric heat and moisture transport. The EAM, as an modern active component of climate system of the East Asia, determines most of the variability of SST (Sea Surface Temperature) and SSS (Sea Surface Salinity) of the western tropical Pacific over seasonal to interannual time scales. Understanding how the EAM would have been evolved over more longer time scales (>Myr) is still a scientifically challenging question. The long-term evolution of the EAM could be reconstructed by using loess, stalagmite and marine sediment records, while this study focuses on synthesizing the EAM history of the past 5Myr based on data from published and on-going works of marine sediment cores mostly from the South China Sea (SCS). Though recent studies of terrestrial-based evidence of EAM monsoon evolution suggest that the EAM would have been initiated in much earlier time of ~22 Myr ago, marine records of the EAM are still too short to document the long-term initiation of the EAM. Microfossil evidence suggests that the increased strength of summer monsoon upwelling or thermocline deepening might have been evolved in the SCS since ~8-6 Ma. Between 4.6-3Ma, the gradual closures of the Panama Isthmus and Indonesian Seaways might have provided a “pre-condition” of more tilted thermocline or SST gradients across the equatorial Pacific, and in turn shifted the Pacific climate into more “La Niña”-like condition that was involved in the early development of EAM. Increased of surface water freshness in the SCS and more frequent alternations of humid and dry intervals observed in loess profiles in central China of ~3.6-2.6Ma suggest an intensification of the EAM. The timing of the EAM intensification appears to be too early to the initiation of the North Hemisphere glaciation in ~2.75Ma, and also to the final establishment of western Pacific warm pool or the ‘Walker Circulation” in ~1.7Ma, therefore the cause for the EAM intensification has been attributed to other mechanism such as the mountain uplifting of the northern Tibet. In the past 1.7Myr EAM history, the most dominant factors determining the timing and strength of the EAM variability over orbital to millennial time scales appear to be insolation and glaciation-related. Evidence from recent published IMAGES records suggests that the EAM would have been an important agent in controlling the SST, SSS, mixed-layer depth, and productivity as well as most hydrographic gradients in the SCS. The glacial stages are characterized by stronger winter EAM and the interglacial stages are more affected by summer EAM. Precession cycles have been dominant in most late Quaternary marine EAM records, while the timing of the stronger EAM appears to be varied depending on the methods and proxies for the reconstructions. I will present some examples of this type of discrepancy and propose the direction of future studies.

!"#

Evolutionary History of the Indian Monsoon from Terrestrial Records

Rajiv Sinha

Engineering Geosciences Group, Department of Civil Engineering

Indian Institute of Technology Kanpur 208016, India (rsinha@iitk.ac.in)

The evolution of the southwest Indian monsoon is considered to be strongly linked to the uplift of

the Himalaya beyond a critical height about 20 Ma ago (Early Miocene). A reasonably good record

of monsoonal fluctuations since Miocene exists from marine records from northwest Arabian Sea

suggesting that monsoonal upwelling conditions were established in this region about 8 Ma ago.

However, the terrestrial records of monsoonal variations in Pre-Quaternary times are rather

fragmentary. Fluvial sediments of Siwalik succession in the Himalayan Foreland Basin (HFB) form

the most important continental archive for reconstructing monsoonal fluctuations during Miocene-

Late Pleistocene. The Siwalik deposits started accumulating in the HFB ~20 Ma ago deposited by

large rivers and the post-Siwalkis fluvial deposition in the HFB has continued through the

Quaternary without any break. A number of proxy records including, paleosols, pedogenic

carbonates, pollens, microfossils, paleomagnetism and general sedimentation pattern have been used

to decipher the changes in the SW Indian monsoon from Siwalik sediments. The !18O variations of

soil carbonates suggest multiple phases of monsoonal intensification with peaks at 10.5 and 5.5 Ma

after which it decreased to modern day values with minor fluctuations1. A major change in

sedimentation pattern and drainage reorganization at 10 Ma and 5 Ma have been recorded2 and a

vegetational shift from C3 to C4 type occurred at 6 Ma coinciding with the monsoonal

intensification1. Paleosol records suggest warm and humid climate during 5.6-2.6Ma manifested as

red Alfisols with soil carbonate and Fe nodule and strong Bt horizon3 (Thomas et al., 2002). A great

diversification of murid rodent species around 2.5 Ma has also been documented4 once again

suggesting monsoonal intensification. After 2.6 Ma, a cooler and drier climate prevailed as indicated

by poorly developed yellow soils and common nodular soil carbonates and calcitic groundmass.

Further pollen records suggest four major stages of vegetation during the last 4 Ma: dry grassland,

wet and marshy grassland, marshy-ponding, and wet open and mixed in response to climatic shifts5.

Still more arid climate has been inferred around 0.9 Ma from the gravity flow deposits, weaker soils

and higher rate of sedimentation3.

For the Quaternary period, continental records from northern and western India have been studied

extensively and intensively as response systems to shifts in the monsoonal regimes, both in terms of

magnitude and in the zone of influence. Major areas of interest include the Himalaya, the Ganga

Basin, the Thar Desert, and the southwestern (Gujarat) and northeastern margin (Haryana) of the

Thar Desert. A variety of archives such as peat, loess, alluvial sediments, playas, lake sediments,

!"$

dunes, tree-rings, calcretes, and speleothems have been used to generate climate proxy data. In a

regional appraisal of the response of the Ganga river system, it has been demonstrated that climate

related signals propagate downstream and show tight coupling between source area, catchment basin

and coastal and marine depocenters6. Detailed evaluation of Late Quaternary interfluve stratigraphic

development in the Ganga plains showed that interfluve areas near the major rivers aggraded

periodically between 27 and 90 ka (MIS 3-5)7. They subsequently degraded or accumulated

sediment only locally, probably reflecting decreased monsoonal precipitation around the LGM (MIS

2). Increased precipitation during the 15 to 5 ka period of monsoon recovery probably increased

discharge and promoted incision and widespread badland formation. Calcrete records from Ganga

plains spanning over 60 ka suggest monsoon-induced vegetational shifts from C3-to C4-dominated

types8,9.

The fluvial successions in western India record a systematic variation of the sedimentation p

attern in response to the late Quaternary climate changes. The phases of aggradation and inc

ision occurred around the same times in the lower reaches of the three river basins, the Lun

i, Mahi and Sabarmati10. Variations in fluvial styles in different regions are apparently a fun

ction of precipitation gradient which is observed even today. Some attempt has also been m

ade to develop a preliminary chronometric framework for the Quaternary calcretes of Rajasthan11.

Large variations in oxygen stable isotope data (up to 4.4 %o) have been interpreted as representing

non-monsoonal 18O encircled “normal continental” waters during climatic phases when the monsoon

weakened12. The dunal formation in Thar Desert goes back to over >150 ka, and the Thar has gone

through various phases of expansion and contraction in response to monsoonal fluctuations13. Spatial

trends in dune formation are recognized on multi-millennial time scales (10-2ka) from Gujarat to

Rajasthan13.

The Holocene records from western Rajasthan suggest maximum lake level in the Lunkaransar14 at

6300 14C years B. P and complete desiccation around 4800 14C years B.P. An attempt was made to

extend the palaeoclimate record of the Sambhar15 playa to ~30,000 years and it was concluded that

the Sambhar did not show any desiccation phase throughout its history unlike Didwana and

Lunkaransar which desiccated completely between Ca 3 and 4 ka. Although the LGM aridity is

recorded at Sambhar, a shallow lake was maintained during this period15. AMS 14C dates of >15 ka

BP on pollen also reveal that the Bap-Malar playa possibly existed during the LGM and millennial

scale differences are recognized in spatially separated playas in the Thar16. Further east in the Ganga

plains, a dry phase in the Sanai Lake has been recognized between 11.5-10.5 ka and a climatic

optimum (~10-5.8 14C yr BP) during Early to Mid-Holocene17.

!"%

It is clear that the present knowledge of monsoonal reconstruction in the Indian sub-continent from

terrestrial records is extremely widespread and there are very few records which extend to the full

duration of even Late Quaternary time period. Similarly, high-resolution studies backed by high

quality chronometric data are also limited. A critical evaluation of chronological dates needs to be

undertaken to establish secure proxy-climatic indicators in the Indian-subcontinent.

References cited:

1. Sanyal, P. et al., 2004, Palaeogeog. Palaeoclim. Palaeoecol., 205, 23-41.

2. Kumar, R. et al., 2003, Sed. Geol., 158, 209-234.

3. Thomas, J.V. et al., 2002, Sed. Geol., 150, 343-366.

4. Patnaik, R., 2003, Palaeogeog. Palaeoclim. Palaeoecol., 197, 133-150.

5. Phadtare, N.R. et al., 1994, Himal. Geol., 15, 69-82.

6. Goodbred, S. L., Jr. 2003. Sed. Geol., 162, 83-104.

7. Gibling, M. R. et al., 2005, Jour. Sed. Res., 75, 373-389.

8. Srivastava, P., 2001, Palaeogeog. Palaeoclim. Palaeoecol., 172: 207-222.

9. Sinha, R., et al., 2006. Palaeogeog. Palaeoclim. Palaeoecol., 242/3-4 pp 214-239.

10. Jain, M. and Tandon, S.K. 2003 Quat. Sci. Rev. 33, pp. 2223-2235.

11. Dhir, R. P. et al. 2004 Proc. Ind. Acad. Sci. (Earth & Planetary Sci.), 113, No. 3, pp.

473 – 515

12. Andrews, J.E., et al. 1998. Quaternary Research, 50, 252-260.

13. Singhvi, A. K., & Kar, A. 2004. Proc. Ind. Acad. Sci. (Earth & Planetary Sci.), 113

(3), 371-401.

14. Enzel, Y. et al. (1999). Science, 284, 125 – 128.

15. Sinha, R., et al., 2005. Palaeogeog. Palaeoclim. Palaeoecol., 233/3-4, 252-270.

16. Deotare, B. C. Et al. 2004. Proc. Ind. Acad. Sci. (Earth & Planetary Sci.), 113 (3), 403

– 425.

17. Sharma, S., et al. 2004. Quat. Sci. Rev., 23, 145-159.

!"&

Session 2

Tectonic evolution and erosional history

of the Himalaya-Tibetan Plateau

!"'

EXTRUSION OF HIMALAYAN METAMORPHIC NAPPE: ITS SIGNIFICANCE IN

UPLIFT AND TECTONIC EVOLUTION OF THE HIMALAYA

Harutaka Sakai (Kyoto University, Kyoto, Japan, 606-8502), Tohru Danhara, Hideki Iwano (Kyoto

Fission-Track Co. Ltd) and Yutaka Takigami (Kanto-gakuen University)

We have been studying on the tectonic and thermal history of the Himalayan metamorphic

neppe, which extensively covers the Lesser Himalayan autochthonous sediments, extending more than

100 km from the northern slope of Mount Everest to the southern margin of the Mahabharat range in

eastern Nepal. On the basis of thermo -chronological study by means of fission-track dating of detrital

zircon and apatite and 40Ar-39Ar dating of mica in metamorphic nappe and underlying weakly

metamorphosed early Miocene fluvial sediments called the Dumri Formation, we reconstructed the

following scenario on the advancement and cooling history of the metamorphic nappe (Sakai, 2005); the

metamorphic nappe started its extrusion at ~14.4 Ma and moved southward at 3-4 cm/yr, tectonically

covering the floodplain deposits of the Dumri Formation, and finally stopped its movement at ~11 Ma

(Fig. 1). Tectonic overriding of metamorphic nappe more than 10 km thick on the floodplain must have

brought about the birth of the Higher Himalaya by 14 Ma. Our thermo-chronological data demonstrate

that inner part of the metamorphic nappe kept ~240 , till 6-4 Ma and cooled down below ~120 , by

3-0.8 Ma, whilst surficial part rapidly cooled down after extrusion.

In order to examine whether or not our model is applicable to other region, we performed the

preliminary thermo-chronological study on the Kathmandu nappe, central Nepal and the Karnali klippe,

western Nepal. In this paper, we present our research results, and discuss on their significances in tectonic

uplift and erosion history of the Himalaya.

Fission-track dating of pilot samples from the Kathmandu nappe indicates that the nappe has a

similar cooling history to that in eastern Nepal. The Bhainsedobhan Marble and Chisapani Quartzite

exposed along the southern margin of the metamorphic nappe show FT age of zircon at 11.3-0.4 Ma and

11.9-0.8 Ma, respectively. They are similar FT ages of zircon from gneiss in southern margin of the

metamorphic nappe in eastern Nepal. The Dunga Quartzite underlying the metamorphic nappe and is

exposed near the Main Boundary Thrust (MBT) shows FT age of zircon at 10.3-0.3 Ma, which is the

same age of metamorphosed Dumri Formation in eastern Nepal. Furthermore, the Markhu Formation at

the top of the metamorphic sequence and possible southern continuation of the Yellow Band in Mount

Everest yielded FT age of zircon at 13.7-0.7 Ma. This age is nearly the same age as 14.4-0.9 Ma from

the Yellow Band (Sakai et al., 2005).

Mylonitic granetiferous schist of the Radwa Formation, just over the Mahabharat Thrust (MT:

southern extension of the Main Central Thrust), shows FT age of zircon at 14.0 -1.4 Ma .

Metamorphosed gabbro of the Robang Formation, just below the MT shows FT age of apatite at 13.5-2.2

Ma. These data suggest that metamorphic rocks of the Kathmandu nappe also extruded on the earth

!"(

surface at around 14 Ma and has undergone rapid cooling, like as in eastern Nepal.

In western Nepal, the Karnali klippe, consisting of the high-grade metamorphic rocks and underlying

low-grade thrust-sheet of the Kuncha Formation, tectonically covers the Lesser Himalayan autochthon,

extending about 120 km in N-S directions. Zircon and apatite grains from mylonitic biotite granite in the

southern part of the Kuncha thrust-sheet yielded FT ages of 14.7-0.5 Ma and 10.3-0.5 Ma, respectively.

The former corresponds to rapid cooling age of the Yellow Band at the top of the metamorphic sequence

and the latter coincides with metamorphic age of the fluvial Dumri Formation, which was interpreted to

the youngest age of termination of nappe movement. The detrital zircon grains from the Dumri Formation

under the Karnali klippe show partially annealed age of 12.4-0.6Ma.

As mentioned above, those new age data suggest that ductile extrusion and southward advancement

of metamorphic nappe simultaneously took place in allover the Nepal Himalaya, extending about 800 km

in E-W directions. Termination of nappe movement and cooling of metamorphic rocks below a ductile-

brittle boundary at ~250 , at about 11 to 10 Ma correspond to timing of rapid increase of sedimentation

rate at Bengal submarine fan as well as timing of initiation of faulting activity along the Main Boundary

Thrust system.

Fig. 1 Our schematic model of ductile extrusion of Himalayan metamorphic nappe. !

!")

Stable isotopic evidence for Himalayan-Tibet Uplift in the Tertiary J. Quade, P.G. DeCelles, J. Saylor, and P. Kapp Department of Geosciences, University of Arizona, Tucson, Arizona 85721 USA

Stable isotopic approaches to paleoelevation reconstruction have undergone major advances and refinements over the past decade, involving variety of archives and old and new isotopic systems. Such work is making a significant contribution to our understanding of the recent growth of the world’s major orogens. I will begin with reviewing what is currently known about the uplift history of the Himalayan-Tibetan orogen from stable isotopic evidence, and finish with examining the potential of some unexploited isotopic archives.

Over the last ten years there has been major progress in reconstructing the rise of southern Tibet during the late Neogene (Quade et al., 2007). Key studies in the southern plateau—mainly in the Tethyan Himalaya and Lhasa terranes— include Thakkola (7-11 Ma: Garzione et al., 2000), Zada (3-9 Ma; Saylor et al., submitted), Giryong (7 Ma; Wang et al., 2006), Namling (16 Ma; Currie et al., 2005); and Lunpola (Rowley and Currie, 2006; Rowley and Garzione, 2007). Most, but not all (see Wang et al., 2006), isotopic evidence from these studies suggests that much of this large region stood at least as high as today since 10-15 Ma. Other work from the northern Lhasa terrane suggest that high elevations may have been attained as early as the Eocene (Rowley and Currie, 2006), and certainly no later than 26 Ma (DeCelles et al., 2007), at least for central Tibet.

There is much less known about the history of elevation change of the southern Tibetan Plateau prior to the Miocene, and very scanty direct evidence from any time period for the northern plateau. Work of Cyr et al. (2005) suggests possible high elevations by 35 Ma near Xoh-Xil, whereas that of Graham et al. (2005) just north of the plateau points to an elevated plateau by Eocene-Oligocene, and a continuously high NE plateau since 29 Ma (Dettman et al., 2003).

In general, the pre-Miocene record from anywhere on the plateau is far too thinly documented in time and space to draw firm conclusions on the uplift history in the first 20 million years after collision at 55 Ma. However, the geology of Tibet is rich and varied and will lend itself well to further work using both old and new isotopic approaches. For example, Mulch et al. (2006), building on Friedman et al. (1993), demonstrates the large potential of using !D of waters of hydration in glass to reconstruct !D of meteoric water in the past, and hence paleoelevation. This approach has great potential application in southern Tibet in volcanic rocks of the Linzizong Formation (69 to 47 Ma. !D analysis of these rocks using volcanic glass could resolve the issue of how much elevation was inherited from the pre-collision “Lhasaplano” (Kapp et al., 2005) and how much elevation, if any, was added post-collision. Other examples include the use if mylonitic micas, again to reconstruct !D values, of meteoric water (Morrison et al, 1998; Mulch et al. 2004). Our pilot data from three core complexes indicates high elevations comparable to today since 10 Ma. Finally, the use of mass-47 for estimating paleotemperature to reconstruct paleoelevations holds enormous potential (Ghosh et al., 2006; Eiler et al., 2007). To realize this potential, we are conducting studies of modern soils to understand the relationship between air temperature and soil temperature estimated from mass-47 measurements.

References cited:

Currie, B.S., Rowley, D.B., and Tabor, N.J. (2005) Middle Miocene paleoaltimetry of southern

Tibet: implications for the role of mantle thickening and delamination in the Himalayan orogen. Geology 33(3): 181-184.

!"*

Cyr, A.J., Currie, B.S., and Rowley, D.B. (2005) Geochemical evaluation of Fenghuoshan Group Lacustrine carbonates, north-central Tibet: implications for paleoaltimetry of the Eocene Tibetan Plateau. J Geol 113, 517-533.

DeCelles, P.G., Quade, J, Kapp, P., Fan, M., Dettman, D.L., Ding, L. (2007) High and dry in central Tibet during the late Oligocene. Ear Planet Sci Lett 253, 389-401.

Dettman, D. L., Fang, X., Garzione, C. N., Li, J. (2003) Uplift-driven climate change at 12 Ma: a long !18O record from the NE margin of the Tibetan Plateau. Ear. Planet. Sci. Lett. 214, 267-277.

Eiler, J.M. (2007) “Clumped-isotope” geochemistry—The study of naturally occurring, multiply substituted isotopologues. Earth and Planetary Science Letters 262: 309-327.

Friedman, I, Gleason, J, Warden, A. Cerling, T. E. and Quade, J (1993) Ancient climate from deuterium content of water in volcanic ash, in (P. Swart, J. A. McKenzie, K. C. Lohman Eds.), Continental Indicators of Climate, Proceedings of Chapman Conference, Jackson Hole, Wyoming, American Geophysical Union Monograph 78, 309-319.

Garzione, C.N., Quade, J, DeCelles, P.G., English, N.B. (2000) Predicting paleoelevation of Tibet and the Himalaya from !18O versus altitude gradients in meteoric water across the Nepal Himalaya. Earth Planet Sci Lett 183: 215-229.

Ghosh, P., Eiler, J.M. and Garzione, C. (2006) Rapid uplift of the Altiplano revealed in abundances of 13C—18O bonds in paleosol carbonate. Science 311: 511-515.

Graham, S. A. and eight others (2005) Stable isotope records of Cenozoic climate and topography, Tibetan Plateau and Tarim Basin. American Journal of Science 305, 101-118.

Kapp, P., Yin, A., Harrioson, T. M., Ding, L. (2005) Cretaceous-Tertiary shortening, basin development, and volcanism in central Tibet. Geol. Soc. Am. Bull. 117, 865-878.

Morrison, J., and Anderson, J. L. (1998) Footwall refrigeration along a detachment fault: implications for thermal evolution of core complexes. Science 279, 63-66.

Mulch, A., Teyssier, C., Cosca, M.A., Vanderhaeghe, O., Vennemann, V. (2004) Reconstructing paleoelevation in eroded orogens. Geology 32: 525-528.

Mulch, A., Sarna-Wodjicki, A. M., Perkins, M. E., and Chamberlain, C. P. (2006) A Miocene to Pleistocene Sierra Nevada rain shadow? Evidence from hydrogen isotopes in hydrated volcanic glass. American Geophysical Union, Fall Meeting, abstract #T23G-04.

Quade, J., Garzione, C., and Eiler, J. (2007) Paleosol carbonate in paleoelevation reconstuction, in M. Kohn, ed, Paleoaltimetry: Geochemical and Thermodynamic approaches. Reviews in Mineralogy and Geochemistry, Mineralogical Society of America Bulletin, v. 66, p. 53-87.

Rowley, D.B. and Currie, B.S. (2006) Palaeo-altimetry of the late Eocene to Miocene Lunpola basin, central Tibet. Nature 439: 677-681.

Rowley, D.B., 2007, Stable Isotope-Based Paleoaltimetry: theory and validation, in M. Kohn, ed, Paleoaltimetry: Geochemical and Thermodynamic approaches. Reviews in Mineralogy and Geochemistry, Mineralogical Society of America Bulletin, v. 66, p. 23-52.

Rowley, D.B. and Garzione, C.N., 2007, Stable isotope-based paleoaltimetry: Annual Review of Earth and Planetary Sciences (in press).

Wang, Y., Deng, T., and Basatti, D. (2006) Ancient diets indicate significant uplift of southern Tibet ca. 7 Ma. Geology 34, 309-312.

!#+

Evolution of the Cenozoic Yecheng foreland basin in southern Tarim and tectonic and

paleoenvironmental implications

Hongbo Zheng

School of Ocean and Earth Science, Tongji University, 1239 Siping Rd., Shanghai, 200092, China

zhenghb@mail.tongji.edu.cn

The Yecheng profile, lying in the southwest Tarim Basin at the northern foot of the West

Kunlun Mountains, comprises 4.5 km of conformable Miocene to Pliocene strata. The lower part of

the section, the Wuqia Group, is composed of interbedded red mudstone and pale-coloured fine

sandstone with a thickness of 1700 m. The Artux Formation is 800 m thick and composed of

mudstone, sandstone with thin gravel and conglomerate beds. The upper part of the section, known

as the Xiyu Formation, consists of 2000 m of cobble and boulder conglomerate intercalated with

massive siltstone lenses.

Compositional study of the sandstones in the Wuqia Group and Artux Formation indicate that

they were sourced from low relief areas of the Kunlun region, and probably further south from Tibet.

The provenance of the conglomerate in the Xiyu Formation is the West Kunlun Mountains.

Compositional trends within the conglomerate indicate that Upper Palaeozoic marine, and Mesozoic

to Tertiary terrestrial silicic rocks were eroded first, along with the Proterozoic to Lower Palaeozoic

Proto-Tethys metasedimentary rocks. Erosion into deeper levels of the Kunlun Mountains provided

igneous and high-grade metamorphic sediment, which first appears 640 m above the base of the

Xiyu Formation.

Lithofacies change from fine-grained mudstone and sandstone to coarse clasts coincides

with the onset of aeolian sedimentation, indicating major shift of regional paleoclimatic regime.

Although climatic changes may have played an important role in controlling the sedimentary regime

world-wide, our study of the lithostratigraphy and petrography of the Yecheng section suggests that

the lithofacies change recorded the progressive unroofing history of the source rocks in the West

Kunlun Mountains.

The Late Pliocene to Early Pleistocene Xiyu Formation is dominated by pebble to boulder

conglomerate typical of alluvial-fan debris flow deposits. Sedimentological investigation, together

with grain size and chemical analyses of siltstone bands intercalated with sandstone and

conglomerate in the Xiyu and Artux Formations, point to an aeolian origin, suggesting desertic

conditions in the Tarim Basin by the Early Pliocene. The onset of aeolian sedimentation in the

southern Tarim Basin coincided with uplift of the northern Tibetan Plateau inferred from the

lithofacies change from fine-grained mudstone and sandstone to coarse clasts. Tibetan Plateau uplift

resulted in the shift of sedimentary environments northwards into the southern Tarim Basin, and

could well have triggered the onset of full aridity in the Taklimakan region as a whole.

!#"

The late Miocene onset of the Indian monsoon and the late Miocene and middle Pliocene

enhancement of the East Asian monsoon appear to be the result of coeval uplift episodes in the

Himalayan-Tibetan region. A decrease of the abundance ratio of planktonic foraminifera G.

sacculifer/G. ruber and increase of Neogloboquadrina approximately 8 Myr at ODP site 1146 in the

South China Sea indicate lowering of the surface temperature and increased productivity, which are

interpreted to have been caused by an intensified influence of the East Asian winter monsoon winds.

In the Arabian Sea, monsoon-driven upwelling indicated by the appearance and abundance of

planktonic foraminifera G. bulloides and radiolaria increased remarkably at ~ 8 Myr. Wind-blown

sediment started to accumulate over a wide area of the Chinese Loess Plateau at ~ 8 Myr, about the

same time as a pronounced pulse of eolian dust to the North Pacific, as revealed at ODP site 885/886,

indicating onset of widespread aridity in the Asian interior. At 3.6 Myr the accumulation of eolian

sediment increased by about an order of magnitude, both at proximal settings in China and in the

distal North Pacific Ocean. The planktonic foraminifera Neogloboquadrina also underwent a further

increase in abundance in the South China Sea at this time.

Existing evidence from inland Asia and the surrounding seas suggests a late Miocene onset (or

significant intensification) of the East Asian and Indian monsoons, the reason being their link with

the uplift of the Himalayas and the Tibetan Plateau. The first increase in mean sediment flux to the

Indian Ocean at 11 Myr and strong peak beginning between 9 and 8 Myr indicates the rising of the

Himalayas. That rise could have reached sufficient height to produce a rain shadow in Central Asia,

causing aridity and providing a source of dust to be transported eastwards into north China and the

North Pacific. Further rapid uplift of the entire Tibetan Plateau at 3.6 Myr, as evidenced by the

extensive conglomerates of that age on the north flank of the Plateau, resulted in further aridity in the

basins of central and eastern Asia, an enhanced East Asian monsoon, and a second, late Pliocene,

pulse of terrigenous sedimentation in the Indian Ocean.

Key words: Tibetan Plateau, Taklamakan Desert, Cenozoic, foreland basin, Asian monsoon

!##

Erosional response of the western Himalaya to Holocene monsoon intensification: Implications

for the origin of the Greater Himalaya

Peter Clift, Anwar Alizai

School of Geosciences, University of Aberdeen, Meston Building, Kings College, Aberdeen, AB24

3UE, United Kingdom

Kip V. Hodges

School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ

85287-1404, USA

Liviu Giosan, Jerzy Blusztajn

Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA

Ian H. Campbell, Charlotte Allen

Research School of Earth Sciences, Australian National University, Canberra, A.C.T. 0200, Australia

Ali R. Tabrez, Mohammed Danish, M.M. Rabbani

National Institute for Oceanography, Clifton, Karachi 75600, Pakistan

Climate is one of the principal controls setting rates of continental erosion. We have made a

provenance analysis of Holocene sediments from the Indus delta, in order to assess climatic controls

on erosion over millennial timescales. Bulk sediment Nd isotope analysis reveals a number of

changes during the Late Pleistocene and early Holocene (at 14–20, 11–12 and 8–9 ka) away from

erosion of the Karakoram and toward more sediment flux from the Himalaya. Radiometric Ar-Ar

dating of muscovite and U-Pb dating of zircon sand grains indicates that the Lesser Himalaya eroded

relatively more strongly than the Greater Himalaya as global climate warmed and the summer

monsoon intensified after 14 ka. Monsoon rains appear to be the primary force controlling erosion

across the western Himalaya, at least over millennial timescales. This variation is preserved with no

apparent lag in sediments from the delta, but not in the deep Arabian Sea, due to sediment buffering

on the continental shelf.

Over longer timescales rapid erosion of the frontal Himalayan ranges would result in

focused exhumation and may be one of the primary controls on the orogenic evolution. Although

India-Eurasia continental collision began roughly 45–50 Ma, the architecture of the Himalayan

orogen is dominated by deformational structures developed in the Neogene Period (<23 Ma). The

stratigraphic record and thermochronometric data indicate that erosion of the Himalayan orogenic

hinterland intensified soon after this constructional phase began, remained high from ~23.0 to ~10.5

!#$

Ma, slowed gradually from ~10.5 Ma to ~2.5 Ma, and then began to increase once again in the late

Pliocene and Pleistocene Epochs. New weathering records from the South China Sea, Bay of Bengal

and Arabian Sea, which permit Asian monsoon climate to be reconstructed back to the earliest

Neogene, indicate both a strong coupling between East and South Asian monsoon intensity over

tectonic time periods and a strong correlation between the rate of Himalayan exhumation and

intensity of the Asian monsoons. We interpret this as evidence of a dynamic coupling between

Neogene climate and both erosion and deformation in the Himalaya.

!#%

CO2 SINK POTENTIAL OF HIMALAYA-TIBET WEATHERING AND EROSION Huh Youngsook Seoul National University, Seoul, Korea, 151-747

The Himalayas and the Tibetan Plateau (HTP) constitute one of the most significant topographic features on Earth today, and several major rivers originate there – the Huang He, Chang Jiang, Mekong, Salween, Ganges-Brahmaputra, and Indus. Since the first systematic study of the fluvial geochemistry of the Ganges (Sarin and Krishnaswami, 1984), several research groups worldwide have been analyzing the river waters for major elements as well as isotopic ratios of strontium. An important impetus for this concerted effort was the Tectonic Uplift hypothesis (Raymo and Ruddiman, 1992) which linked the uplift of the Himalayas with increased weathering of silicates and hence consumption of atmospheric CO2 and Cenozoic cooling of global climate. Two and a half decades after the original study of the Ganges, the geochemical community has expanded the database spatially to cover all the major rivers draining the HTP, and perhaps now is a good point in time to review the current rate of CO2 uptake by silicate weathering in the HTP region and evaluate the Raymo and Ruddiman hypothesis. A complication in trying to estimate the long-term CO2 uptake rates from dissolved major element composition of rivers is how to selectively account for the fraction from silicate weathering. Since carbonates occur ubiquitously in many drainage basins and since they weather faster than many silicates, this is a nontrivial task. Two methods are frequently used: a forward model where one sequentially subtracts the contribution from atmospheric, evaporite, silicate and carbonate sources based on a priori estimates of reservoir elemental compositions and the inverse model where one iteratively calculates the best fit starting from initial reservoir compositions. In my research group we have been carrying out such calculations for the rivers originating from the eastern Tibetan Plateau, and we combined our results with the literature dataset on other HTP rivers. The major conclusions are as follows. (1) The CO2 consumption rates range from 100-570 "103 mol#km-2#yr-1. The two Himalayan syntaxes are locations of extreme silicate weathering and CO2 consumption. However, the HTP basins in general are not very different from other orogenic regions, e.g. the Andes or the Rockies, though they have higher rates than shield or platform regions. (2) The extremely radiogenic Sr isotope ratios observed initially by Palmer and Edmond (1992) and Krishnaswami et al. (1992) for the Ganges headwaters are local to the Lesser Himalayas and are not representative for the HTP as a whole. In the upper Brahmaputra and Indus river basins, unradiogenic Sr isotope ratios are observed. The CO2 consumption rates quoted above come with large uncertainties. (1) The variability in runoff (or water discharge) is estimated to be at least 20%. Most river studies are based on one-time sampling for chemical composition, usually during the rising or falling stage, and the runoff values are multi-annual averages at select stations. In a few cases where time series both of runoff and geochemical measurements are available, using the rising or falling stage chemical composition and annual average runoff or using pre-monsoon, monsoon, and post-monsoon values of runoff and geochemistry give results that are accurate to within ~20%. (2) The acid source for chemical weathering is assumed to be atmospheric carbon dioxide. However, if there are other sources of acid available, e.g. sulfuric acid from weathering of sulfide minerals, dissolved cations were generated without consuming atmospheric CO2 and this fraction needs to be subtracted. The quantification of weathering of sulfide minerals is difficult, because sulfate ions can originate also from gypsum. Because in many basins SO4 concentrations are less than HCO3, this is a minor uncertainty. (3) In both forward and inverse models but especially for the forward model, accurate estimation of the

!#&

reservoir elemental composition is important. The difficulty here is that since the basins are often quite large, it is difficult to come up with a representative chemical composition for the rocks being weathered. In some remote regions bedrock studies are absent altogether. (4) The final calculated CO2 uptake rate represents the aggregate effect of tectonic history, geomorphology (elevation, relief), lithology (metamorphosed, recycled, primary igneous, ophiolites, age), climate (runoff, temperature), vegetation, etc. So far, GIS studies do not point toward any one parameter exercising overarching control on the CO2 uptake rates.

!

References

Krishnaswami S., Trivedi J. R., Sarin M. M., Ramesh R., and Sharma K. K. (1992) Strontium

isotopes and rubidium in the Ganga-Brahmaputra river system: Weathering in the Himalaya, fluxes

to the Bay of Bengal and contributions to the evolution of oceanic 87Sr/86Sr. Earth Planet. Sci. Lett.

109, 243-253.

Palmer M. R. and Edmond J. M. (1992) Controls over the strontium isotope composition of river

water. Geochim. Cosmochim. Acta 56, 2099-2111.

Raymo M. E. and Ruddiman W. F. (1992) Tectonic forcing of late Cenozoic climate. Nature 359,

117-122.

Sarin M. M. and Krishnaswami S. (1984) Major ion chemistry of the Ganga-Brahmaputra river

systems, India. Nature 312, 538-541.

!#'

!#(

Session 3

Tectonics-climate linkages,

perspective from climatic simulations

!#)

EFFECT OF TOPOGRAPHIC UPLIFT ON MONSOON EVOLUTION

Kitoh A

Meteorological Research Institute, Tsukuba, Ibaraki, 305-0052, Japan

The role of large-scale orography on climate is investigated by a series of topographic uplift experiments. We used a coupled atmosphere-ocean general circulation model (AOGCM) as well as an atmosphere only model (AGCM) so that response of the atmosphere, ocean and atmosphere-ocean coupled phenomena can be assessed. We used eight different mountain heights: 0% (no mountain, NM), 20%, 40%, 60%, 80%, 100% (control run, M), 120%, and 140%. Land-sea distribution is the same for all experiments and all mountains in the world are uniformly varied.

A north-south jump of the 500 hPa zonal wind axis around the longitude of the Tibetan plateau is found with mountain height higher than 60% between the winter and summer season. On the other hand the jet axis stayed in the northward position all the year round in the experiments with lower mountains. Figure 1(left) shows the annual mean precipitation difference between the control run (M) and no-mountain run (NM). Summertime precipitation is confined in the deep tropics around 10N in the no-mountain case, but it moves inland on the Asian continent with mountain uplift. Associated with this, an intensification of the Pacific subtropical anticyclone and trade winds is found. The Baiu-like precipitation belt in East Asia clearly appeared at mountains higher than 60%. Figure 1(right) shows the differences in annual range of monthly mean surface air temperature, i.e. warmest month temperature minus coldest month temperature, between M and NM. The annual temperature range over the continent is larger in M than in NM except in South Asia. Over South and East Asia, warmest month temperature in M is lower than in NM mainly due to summer monsoon precipitation changes. Opposite changes occur in mid-continent due to decrease in precipitation. Coldest month temperature in M is lower than in NM almost all over land. Signal over the Indian Ocean comes from differences in coldest month temperature.

!

Fig. 1. Differences in (left) annual mean precipitation and (right) annual range of monthly mean surface

air temperature between mountain (M) case and no-mountain (NM) case.

!#*

!Fig. 2. Monsoon intensity index at the surface for NM and M.

Figure 2 displays the monsoon intensity index after Liu and Yin (2002). The index is defined

where the differences between winter and summer mean surface wind directions are greater than 90 degree. The index is larger where the average wind velocity is higher and the wind direction differences are larger. A clear contrast of the monsoon region as well as monsoon intensity is found. In NM, monsoon region is confined within deep tropics, and the north Arabian Sea is not a monsoon area due to non-westerly winds in summer. It is also found that the monsoon region extends into the western Pacific in NM, while not in M where trade winds prevail year round.

Systematic changes in sea surface temperature (SST) are also obtained with progressive mountain uplift. In NM, the local SST maximum above 29°C is centered near the date line, while SST below 26°C is found in the eastern Indian Ocean and the eastern Pacific Ocean. Over the equatorial Indian Ocean, the SST gradient is reversed between NM and M. Summertime southwesterly monsoon flow does not cover the northernmost Arabian Sea region so that upwelling is inactive all the year round when mountain is lower than 40%. The location of warm pool shifts westward with progressive mountain uplift; in the cases with mountains higher than 80% of the control, the maritime continent becomes the region of the maximum SST.

The western Pacific warm pool and El Nino/Southern Oscillation (ENSO) also systematically changed. We have demonstrated that model ENSO exists in all the experiments. However, ENSO characteristics (pattern, amplitude and frequency) are different from those in the control experiment with mountain. The experiments have revealed that the intensity of the North Pacific subtropical anticyclone and associated trade winds becomes stronger and the location of maximum easterly winds in the central Pacific is closer to the equator with mountain height. Accordingly, the western Pacific warm pool and ENSO systematically change by mountain height. When the mountain height is low, a warm pool is located over the central Pacific due to weak trade winds in the Pacific, while it moves towards the maritime continent by mountain uplift. The model El Niño is strongest, frequency is long and most periodic in the 0% run. They become weaker, shorter and less periodic when the mountain height increases.

Representation of orography is highly dependent on model's horizontal resolution. Therefore, we started to use a high-resolution AGCM with 120-km mesh and a very high-resolution AGCM with 60-km mesh to investigate resolution dependency on the effect of topography on monsoon evolution. Preliminary results with 120-km mesh AGCM will be shown.

!$+

SUBARCTIC PACIFIC SEA-ICE FORMATION DUE TO CENTRAL AMERICAN SEAWAY

CLOSURE AND ITS INFLUENCE ON EAST ASIAN WINTER MONSOON

Motoi T (Meteorological Research Institute, Tsukuba, Ibaraki, Japan, 305-0052)

Chan W-L (Frontier Research Center for Global Change, Japan Agency for Marine-

Earth Science and Technology, Yokohama, Kanagawa, Japan, 236-0001)

The influence of the closure of the Central American Seaway on the East Asian w

inter monsoon is investigated by a series of closed (CE), open (OE) and re-closed (RCE) seaway experiments with a coupled ocean-atmosphere general circulation model. It is found that a permanent halocline forms in the subarctic Pacific due to the lack of saline water transport through the seaway in the cases of closed and re-closed seaway (CE and RCE). Figure 1 (left) shows the vertical section of 100-year averaged zonal mean salinity in the North Pacific Ocean for (a) CE, (b) OE and (c) RCE. A permanent halocline in the subarctic Pacific, similar to present-day observation in CE (Fig.1 (a)), is represented. In OE (Fig.1 (b)), the halocline in the subarctic Pacific disappears due to deep convection, which is caused by saline water transport from the subtropical Atlantic to the subarctic Pacific through the seaway. A permanent halocline reappears due to re-closing of the seaway in RCE (Fig.1 (c)) although its intensity is weaker than that in the initial, closed seaway experiment.

Fig.1. Left: Vertical section of 100-year averaged zonal mean salinity (psu) in the North Pacific Ocean

for (a) closed (CE), (b) open (OE) and (c) re-closed (RCE) seaway. Right: Seasonal variation of sea-ice thickness (cm) and sea surface temperature (oC) at 60oN 170oW. CE: dashed line OE: solid line RCE: dotted line.

Efficient wintertime cooling by shallow convection, owing to stratification of the permanent

halocline in CE and RCE, results in sea-ice formation in the Okhotsk and Bering Seas as shown in Fig.1 (upper right panel). On the other hand, in OE, deep convection by saline water pumps heat

!$"

from the deeper layer up to the surface in the subarctic Pacific, keeping the sea surface temperature there above 1oC throughout the winter (Fig.1, lower right panel), prohibiting sea-ice formation.

In Fig. 2, the geographical distribution of the differences in surface air temperature (left) and wind vectors (right) in February for closed minus open (CE-OE) and re-closed minus open (RCE-OE) is shown in order to detect the influence of the seaway closure easily. In CE and RCE, surface air temperatures over sea ice, which appears in the Okhotsk and Bering Seas due to closure of the seaway, are significantly lower (5 to 7 degrees lower in the Bering Sea and 1 to 3 degrees lower in the Okhotsk Sea) than those in OE because of high sea-ice albedo and insulation effects. Cooler air over the sea ice produces higher surface air pressure with clockwise wind anomalies. The East Asian winter monsoon is influenced by the seaway closure. Southeasterly wind anomalies, associated with the appearance of sea-ice in the Okhotsk Sea due to closure of the seaway, are detected around the Japanese archipelago in the East Asian winter monsoon region (Fig.2, right). Surface air over the East Asian continent is warmer in CE and RCE than that in OE as shown in Fig.2 (left). These southeasterly wind and higher temperature anomalies indicate that the East Asian winter monsoon is weakened by closure of the seaway.

The intensity of the atmospheric response to the sea ice in CE and RCE depends on its thickness which is closely related to the strength of the permanent halocline. Thicker sea ice forms when the permanent halocline is stronger, and causes surface air to become cooler, which results in higher surface air pressure and clockwise intensification of winds in the northern hemisphere.

Fig.2. Geographical distribution of the differences (closed minus open: CE-OE and re-closed minus open:

RCE-OE) in surface air temperature (deg.) (left) and wind fields (ms-1) (right) in February.

!$#

!$$

Poster Session

!$%

A FEW REMARKS ON PALEOCEANOGRAPHIC HISTORY OF OFFSHORE SHIMOKITA

PENINSULA, JAPAN, FOR THE PAST 600,000 YEARS BASED ON PRIMARY ANALYSES ON

CORE SAMPLES OF D/V CHIKYU SHAKEDOWN CRUISES

Aoike K. (CDEX / JAMSTEC, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, Japan, 236-

0001)

CK05-04 and CK06-06 Shipboard Laboratory Members

D/V CHIKYU shakedown cruises involving

coring tests, CK05-04 Leg 2 (16 Nov. – 14 Dec.

2005) and CK06-06 (6 Aug. – 29 Oct. 2007), were

carried out offshore Shimokita Peninsula, northeast

Japan forearc. During these two cruises, core samples

of 47 m (Site C9001 Hole A), 71 m (Site C9002 Hole

A and B) and 365 m (Site C9001 Hole C) in

penetration depth with more than 100 % in average

recovery were taken mostly by means of Hydraulic

Piston Coring System (HPCS) from the subseafloor

at about 1200 m water depth. Primary processing and

measurements for the recovered cores were

performed onboard as a part of the laboratory system integration test (LSIT), principally aimed at

examining laboratory performance and training laboratory staffs. Data obtained through the LSIT in

conjunction with some shore-based preliminary analyses, however, provides several paleoceanographic

remarks.

The coring sites are located on a well-developed sedimentary basin under tectonic effects of both

subduction of the Pacific plate and arc-arc collision of the central Hokkaido, affected by fluctuation of the

water masses of the Oyashio and the Tsugaru currents as well in the oceanographic aspect. The cored

sediments down to 365 mbsf are chiefly composed of diatom-rich silty clay, divided lithostratigraphically

into four units in descending order: Unit A with common intercalations of tephra/sand and higher

magnetic susceptibility (MS); Unit B poor in tephra/sand with lower MS; Unit C composed of sand; and

Unit D with common intercalations of tephra/sand. Methane hydrates were contained locally below about

190 mbsf in Site C9001. Preliminary shore-based micropaleontological and tephrochronological

investigations and onboard paleomagnetic data give some control points of age, suggesting about 600 ka

as the age at 365 mbsf in Site C9001 and roughly constant but high average sedimentation rate of 62

cm/kyr. Relatively serene volcanic activities in the hinterland during approximately 550-250 ka, the

depositional duration of Unit B, are implied from its lithologic characteristics.

!$&

In the order of a few to tens of meters, the presence of two dominant types of clay repeatedly

alternating can be recognized from petrographic and physical property characteristics. Clay A is olive

black and relatively rich in diatoms with lower MS, natural gamma radiation (NGR) and bulk density

(BD), and higher electrical resistivity (ER)

and CIE a* (redness-greenness), considered

to have deposited during a period with high

biological productivity, where clastic grains,

such as quartz, clay minerals and magnetite,

were diluted relatively by diatoms. On the

other hand, Clay B is dark olive gray and

relatively rich in clastic grains with higher

MS, NGR and BD, and lower ER and CIE a*,

regarded as having been deposited in a period

where terrigenous clastic flux is higher. The

intervals of repetition calculated according to

the preliminary age model vary from several

thousand to 20,000 and/or 40,000 years,

possibly reflecting the Dansgaard-Oeschger

and Milankovitch Cycles. Establishment of a

robust age model by further shore-based

biostratigraphic and stable isotopic

investigations will allow frequency analyses

on each property profile and deconvolution of

the cycles and other forcing factors affecting

the expression of environmental variations in

the northwestern Pacific.!

!$'

MIDDLE TO LATE PLEISTOCENE TERRESTRIAL RECORD OF INDIAN MONSOON

RECONSTRUCTED BY POLLEN ANALYSIS OF LACUSTRINE SEDIMENTS IN THE

KATHMANDU BASIN, CENTRAL NEPAL HIMALAYA

Rie Fujii (Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kyoto,

Japan, 606-8502), Takeshi Maki (JAMSTEC) and Harutaka Sakai (Department of Geology and

Mineralogy, Graduate School of Science, Kyoto University)

Palynological and sedimentological studies on the sediment core from the Kathmandu Basin have

been carried out, in order to reconstruct terrestrial record of Indian monsoon during the middle to late

Pleistocene. In this paper, we show an outline of paleoclimatic changes during the last ca. 600 kyr and

millennial-scale climatic changes from ca. 15 kyr BP to 50 kyr BP. We also discuss on the differences of

Indian monsoon in glacial and interglacial periods, comparing with the studies from the deep-sea

sediments in the Indian Ocean and moraines and ice cores record from the Himalaya-Tibetan plateau.

The Kathmandu Valley is located on the southern slope of the central Himalaya and is under strong

influence of Indian monsoon. The climate in the valley is in subtropical to temperate, and the rainfall of

80% in the annual precipitation is brought by the Indian summer monsoon. The basin-fill sediments of the

Kathmandu Valley are mainly composed of Pleistocene thick lacustrine-fluvial sediments. The samples

for pollen analysis were obtained from a 218-m-long core at Rabibhawan in the western central part of the

Kathmandu Valley. It is lithologically divided into three parts: 1) 15 m thick gravelly mud at the basal part,

2) 187 m thick clayey and muddy lacustrine sediments in the middle, 3) 9 m thick sand bed at the top. The

samples used for pollen analysis were collected at one-meter intervals from 62 m to 218 m in depth, 50-

cm intervals from 45 m to 62 m in depth and 10-cm intervals from 7 m to 45 m in depth. The age of the

core was estimated to be from ca. 15 kyr BP to 600 kyr BP on the bases of magnetostratigraphic study

(Yahagi et al., 2003), AMS14C dating (Mampuku, 2007) and spectral analysis of several paleoclimatic

curves (Hayashi et al., submitted).

The pollen diagram of the core was characterized by predominance of Quercus, Pinus, Alnus,

Carpinus, Betula, Castanopsis and Mallotus of the arboreal pollen. Gramineae, Chenopodiaceae,

Artemisia were predominant in the nonarboreal pollen. The pollen diagram was divided into eighteen

pollen zones based on pollen assemblages and fluctuation of the ratio of arboreal and nonarboreal pollen.

As a whole, when the percentages of pollen of Castanopsis and Mallotus increase, those of Alnus, Betula,

Carpinus, arboreal pollen and the absolute pollen frequency tend to increase. On the other hands, when

the percentages of pollen of Pinus, Picea, Abies and Tsuga increase, those of Gramineae, Artemisia,

Chenopodiaceae and nonarboreal pollen tend to increase. Thus, in order to reconstruct the paleoclimatic

changes, we used the following genera as climatic indexes on the bases of the present distribution of

vegetation and vertical climatic zone in the valley and surrounded mountains: Pinus, Abies, Picea, Tsuga

!$(

for cold climate, Castanopsis and Mallotus for warm climate, Alnus, Betula, Carpinus for wet climate and

Gramineae, Chenopodiaceae, Artemisia for dry climate. Our results are as follows:

1. The pollen zones correspond to marine isotope stage 2 to 15 as shown in Fig.1.

2. The variation of the absolute pollen frequency is likely in harmony with that of Arabian Sea Summer-

Monsoon Factor during the last 350 kyr reported in Clemens and Prell (2003).

3. Interglacial periods of MIS5e, MIS9 and MIS11 were warmer than others. Especially in the periods of

MIS9 and MIS11, the Indian monsoon might have been stronger, because the absolute pollen frequency in

these periods was twice or more than the others.

4. In the early period of MIS3, rainfall was high, because the percentages of the wet index of pollen show

high value. It suggests that the timing of intensification of the Indian summer monsoon in MIS3

corresponds to the timing of glacial advance in the south of Mt. Everest (e.g., Finkel et al., 2003) as well

as that of increase of foraminiferal upwelling faunas and wet index of pollen in the deep-sea sediments

from the Arabian Sea (e.g., Prell & Van Campo, 1986).

5. The Indian summer monsoon was week in MIS2 in general, but we divided the climate in this period

into three stages: a cold-and-dry climate in ca. 24 kyr BP (first stage), but once the climate became little

warmer (second stage), and then the climate deteriorated in ca. 19 kyr BP (third stage). These results

support that the glaciation in the Himalaya was very restricted under a weaker monsoon cycle in MIS 2

(e.g., Owen et al., 2002).

!Fig. 1. Pollen diagram during the Middle to Late Pleistocene from the Kathmandu Valley, Central

Himalaya!

!$)

Evolution of East Asian Monsoon: New Insights from Desert Deposits in the Southwest China

(Preliminary Report)

Hasegawa H.1, Jiang X.2, Wu H.2, Tada R.1, and Suganuma Y.1 1 Department of Earth and Planetary Sciences, the University of Tokyo, Tokyo 113-0033, Japan 2 Chengdu Institute of Geology and Mineral Resources, Chengdu 610081, China

The onset and evolution of the East Asian Monsoon which may be triggered by the uplift of

the Himalayan-Tibetan plateau are currently debated, but the knowledge on the timing and process of the East Asian Monsoon evolution has not been sufficient (e.g., An et al., 2001). The recent intensive studies on loess sequences in north China revealed that aridification and enhancement of East Asian Monsoon in mid- to high latitudinal region in Asia occurred since at least 22 Ma (Guo et al., 2002). However, the exact timing of the East Asian Monsoon initiation has not been evidenced. Here we report the occurrences of the desert deposits during the Paleocene to Eocene times in Sichuan and Lanping-Simao basins, southwest China. The Liujia Formation in Sichuan basin consists of reddish colored massive sandstone and sandy mudstone (88m thick), which is considered to be Paleocene to Eocene in age (Hao et al., 2000). The Lijiang Formation in Lanping-Simao basin is composed of the reddish-colored sandstone (lower part: 300m) and alternating beds of sandstone and mudstone (upper part: 100m), which is considered to be middle-late Eocene in age (Hao et al., 2000). These sandstone beds (Liujia Fm and lower part of the Lijiang Fm) show large-scale cross-bedding structure indicating eolian dune origin, while alternating beds of sandstone and mudstone in the upper part of the Lijiang Fm are probably fluvio-lacustrine origin. The occurrences of these desert deposits are direct evidence of the dominance of subtropical arid climate zone in Southeast Asia before the uplift of the plateau, supporting previous climate modeling studies (e.g., Kitoh, 2005). Furthermore, the demise of these desert deposits in these regions during the latest Eocene time might have been affected by the onset and enhancement of the East Asian Monsoon. To determine the exact timing of this desert shrinkage in Southeast Asia, detailed geochronological work is now conducting. REFFERENCE

An, Z., Kutzbach, J.E., Prell, W.L., and Porter, S.C. (2001) Evolution of Asian monsoons and phased uplift of the Himaraya-Tibetan plateau since Late Miocene times; Nature, v.411: p. 62-66.

Guo, Z., Ruddiman, W.F., Hao, Q.Z., Wu, H.B., Qiao, Y.S., Zhu, R.X., Peng, S.Z., Wei, J.J., Yuan, B.Y., and Liu, T. (2002) Onset of Asian desertification by 22 Myr ago inferred from loess deposits in China; Nature, v.416: p.159-163.

Hao, Y., Su, D., Yu J., et al. (2000) The Cretaceous System of China, Beijing: Geological Publishing House: pp.162.

Kitoh, A. (2005) Climate model simulation on the role of mountain uplift on Asian monsoon; Journal of Geological Society of Japan, v.111: p.654-667.

!$*

RAPID RETREAT OF SEASONAL SEA-ICE MARGINS IN THE WESTERN NW PACIFIC

MARGIN AND JAPAN SEA DURING THE LAST DEGLACIATION

Ikehara K. (Geological Survey of Japan, AIST, Tsukuba, Ibaraki, Japan, 305-8567)

and Irino T. (Hokkaido Univ., Sapporo, Japan, 060-0810)

Ice-rafted debris (IRD) records in marine cores collected from the western NW Pacific

margin and Japan Sea suggested the rapid retreat of seasonal sea-ice margin during the last

deglaciation. IRD occurrence suggests the location of sea-ice margin along the NW Pacific margin

reached to 36 N at off Kashima during the last glacial maximum (LGM). Frequent occurrence of

IRD was recognized in cores collected from off Sanriku. IRD in these cores decreased at 13-15 ka

corresponding to Bolling-Allerod warm period. IRD disappeared at 11-12 ka in off Sanriku and off

Shimokita areas, but still remained in off Tokachi area. No IRD occurrence found at around 10 ka in

off Tokachi area. Disappearance of IRD was almost coincided with the decreasing of a deep-

dwelling radiolarian Cycladophora davisiana occurrence. Ohkushi et al. (2003) suggested that the

ventilation during the LGM to last deglaciation occurred in the Bering Sea from the radiolarian

records in the northwestern NW Pacific and its marginal seas, although modern (Holocene)

ventilation has occurred in the Sea of Okhotsk. Benthic foraminiferal assemblages of the cores in the

northwestern NW Pacific also suggested the change of source region of the intermediate water

between LGM and Holocene (Shibahara et al., 2007). Sea-ice formation might have a close relation

with the ventilation and intermediate water formation in the North Pacific. The coincidence of IRD

disappearance and C. davisiana decreasing might suggest change of area of sea-ice and intermediate

water formation in the NW Pacific. After the sea-ice retreat, the Uk37-derived sea surface

temperature increased both in off Sanriku (Minoshima et al., 2007) and off Tokachi areas (Inagaki et

al., submitted). On the other hand, the southern margin of sea-ice distribution was located at off

Oga Peninsula of 40 N in the LGM of the Japan Sea. IRD disappeared from the sites off central and

southern Hokkaido at 9 ka when the warm Tsushima Current started to flow into the Japan Sea

through the southern Tsushima Strait. Sea-ice still remained at 9 ka and disappeared at 8 ka in off

Soya Strait near Japan-Russia border according to migration of the warm surface water. These facts

indicate that the sea-ice retreat in the last deglaciation of the northwestern NW Pacific and the Japan

Sea has close relation with the surface water warming.

A part of this study is financially supported by the Sumitomo Foundation (No. 053321).

!%+

Variation of eolian dust contribution to the Japan Sea sediments during the last 800 kyr

deduced from major element composition

Tomohisa IRINO* (Hokkaido Univ.), Kana NAGASHIMA (JAMSTEC), Yoshiki KIDO (MWJ), and

Ryuji TADA (Univ. of Tokyo)

* irino@ees.hokudai.ac.jp

Major element composition of marine sediment is generally controlled by the mineral

composition which is also affected by sorting effect during their transport process. This feature can

be used for the variability of provenance and transport pathway of detrital fraction in the sediments

of the Japan Sea. Detrital fraction in the sediments collected from the abyssal part of the Yamato

Basin in the Japan Sea has been regarded as the mixture of aeolian dust and the detritus derived from

the Japan Arc (Irino and Tada, 2000; 2002). This knowledge was utilized to reconstruct the

millennial-scale aeolian dust variation in order to clarify the East Asian monsoon variability.

The sediment collected from the site closer to the Japan Arc is characterized by lower

Mg/Al and Ti/Al, and higher Na/Al than abyssal sediments, which suggests much less contribution

from aeolian dust. On the other hand, the difference in grain size of aeolian dust between the

northern and southern part of the Yamato Basin has been pointed out to indicate the relative

contribution of aerosols transported by westerlies in spring time vs. those transported by

northwesterly in winter (Nagashima et al., 2004).Therefore, at least three major source of detrital

material including two different aerosols and the Japan Arc derived detritus could be recognized

from the sediment in the Yamato Basin. Mixing ratio of these three detrital subcomponents in

sediment would be controlled by relative influences from summer precipitation in the central and

east Asia brought by summer monsoon, and wind strength of northwesterly promoted by winter

monsoon.

In order to establish the detailed occurrence of the central to east Asian monsoon variability

during the last 800 kyr, we will examine the major element composition of ODP Site 797 from

the Yamato Basin. If the temporal variation of detrital subcomponents from three sources mentioned

above are reconstructed, we will be able to give a strong constraint on the mechanisms controlling

the Milankovitch time-scale variabilities of the dust availability in the central Asia, strength of

northwestern winter monsoon, and runoff (~precipitation) on the Japanese islands.

!%"

The late Pleistocene Radiolarians in the Bering Sea

Takuya ITAKI 1*, Boo-Keun KHIM 1, Sunghan KIM 1, Masao UCHIDA 2, Kota KATSUKI 1, Ken’ichi OHKUSHI 3, Kana NAGASHIMA 4, Stephan RELLA 5 & Ryuji TADA 5

1 Division of Earth Environmental System, Pusan National University, Busan, 609-735 Korea * t-itaki@pusan.ac.kr 2 National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, 305-8506 Japan 3 Kobe University, Kobe, 657-8051 Japan 4 IORGC/JAMSTEC, Yokosuka, 237-0061 Japan 5 Department of Earth Planetary Sciences, University of Tokyo, Tokyo, 113-0033 Japan

Three piston cores were obtained from sites PC-23 (1,002 m), PC-24 (850 m) and PC-25 (1,156 m), respectively, located in the northern slope in the Bering Sea during the research cruise MR06-04 (August to September 2006) by R/V Mirai of JAMSTEC. The sediment cores were mainly composed of laminated diatomaceous ooze and homogeneous silty clay. Six radiocarbon ages based on planktonic foraminiferal tests from the core PC-23 indicate that the laminated layers were deposited during the deglacial period (ca. 11 to 15 ka). In the North Pacific, it has been known that two radiolarians Lychnocanoma nipponica sakaii and Amphimelissa setosa disappeared at 50 ka and 85 ka, respectively. In our cores, the former bio-event was recognized from all sites, and the latter was recorded only in the core PC-24. Thus, it seems that the bottom of core PC-24 reached at about 110 ka, and the cores PC-23 and PC-25 might be younger than 60 ka;. Radiolarian analysis revealed that an abundance of Cycladophora davisiana, an intermediate-water species, changed significantly throughout core PC-23, and its variation seemed centennial to millennial. The high abundance of C. davisianais is closely related to both (1) the well-ventilated intermediate water with low temperature and high oxygen content, generated by brine rejection due to the strong sea-ice formation, and (2) the enhanced supply of organic materials into the intermediate depth, resulting from increased primary production. This species is quite abundant in the modern Okhotsk Sea, where the intermediate water is observed. In contrast, very few occur in the present-day Bering Sea in spite of the subarctic marginal sea similar to the Okhotsk Sea. Therefore, high abundance of C. davisiana in the Bering Sea implies shallow ventilation, resulting in that the high organic matters can be supplied under the well-developed stratification same as the modern Okhotsk Sea.

!%#

A NOTE ON THE DEPOSITS OF OLDER LACUSTRINE SEDIMENTS AND YOUNER

GLACIAL SEDIMENTS IN SRI LANKA

Jayawardena U.de S ( Department of Civil Engineering, Faculty of Engineering, University of Peradeniya, Peradeniya, Sri Lanka) udsj@pdn.ac.lk Sri Lanka is a small island with many historical geologic records from the Gondwanaland Era. The studies on the paleomagnetic and geologic data have proved the relationship of India, Sri Lanka and Antarctica from the Proterozoic to middle Mesozoic era (Yoshida et al.1990). The occurrence of some marine and fluvial sedimentary rocks indicates the changes of the geologic structures, formation of tectonic lakes, deposition of marine and fluvial sediments and the sea level changes during Jurassic, Miocene, Quaternary and recent periods (Cooray, 1967). Another important study attempted to indicate the evidences for the deposition of varve-like glacial sediments underlain by Precambrian metamorphic rocks in a small valley of the central hilly region of the Island (Dahanayake and Dasanayake, 1981). The objective of this paper is to provide some additional evidences for the occurrence of tectonic activities before the deposition of glacial sediments at the same location namely Weuda (Fig.1). Figures 2 and 3 show a black color thick peaty clay deposit a few meters below the present ground surface. In most of places the thickness of this layer is more than a meter. The laboratory experiments indicated the organic content of this peaty clay varies between 1.7% and 8.2%. Varve-like sedimentary layers occur above this black layer and the boundary between these two formations is very sharp. The peaty clay or mud layer should be a deposit of lacustrine sediments. High organic percentages in different samples of it show the mixture of ancient plant remains transported by flood water or decayed plants in a lake or marshy or swampy area in this hilly region. Later this layer had been subjected to the surface erosion processes after the exposure to the atmosphere probably due to the effect of some earth tectonic activities. Varve-like sediments which may be glacio-fluvial have been deposited over the eroded lacustrine deposit in a later period. The stratigraphy change in this small valley indicates a possible tectonic activities and change of two sedimentary environments in the land area of Sri Lanka within a shorter geological time period. References Cooray, P.G., 1967, An introduction to the Geology of Ceylon, Ceylon National Museums Dept,

Colombo. Kapila Dahanayaka and D.M.S.N.Dasanayake, 1981, Glacial sediments from Weuda, Sri Lanka,

Sedimentary Geology 30, Elsevier, p1-14. Yoshida M, M Funaki and P.W.Vitanage , 1990, Study of geologic correlation between Sri Lanka

and Antarctica, Interim report of Japan-Sri Lanka joint research, edited by Hiroi Y and Y. Motoyoshi. P151.

!

!%$

!

!%%

LATE QUATERNARY PALEOCEANOGRAPHIC CONDITIONS IN THE

NORTHEASTERN JAPAN BASIN, EAST SEA (SEA OF JAPAN)

Khim, B.K. (Division of Earth Environmental System, Pusan National University, Busan, 609-735

Korea), Ikehara, K. (Geological Survey of Japan, AIST, Central 7, Higashi 1-1-1, Tsukuba, 305-8567

Japan), Irino, T. (Graduate School of Environmental Earth Science, Hokkaido University, Sapporo,

060-0810 Japan), Itaki, T. (Division of Earth Environmental System, Pusan National University,

Busan, 609-735 Korea), and Tada, R. (Department of Earth Planetary Sciences, University of Tokyo,

Tokyo, 113-0033 Japan)

The East Sea (Sea of Japan) is famous for its paleoenvironmental variations between interglacial

and glacial stages, which is mainly controlled by the glacio-eustatic sea-level fluctuations during the

late Quaternary. The temporal and spatial paleoceanographic variations in the East Sea (Sea of

Japan) seem to be uniformly synchronous, in spite of a little local discrepancy. However, most of

investigated areas were limited to the southern half of the East Sea (Sea of Japan) due to the political

affairs and lack of investigations in the northern region, mostly consisted of the Japan Basin. Here

we documented some paleoceanographic data from three sediment cores collected from the Japan

Basin. Two gravity cores (GH99-1239 and GH99-1246) were collected during cruise GH99 by the

R/V Hakurei-Maru of the Geological Survey of Japan in 1999. Core GH99-1239 (44°48.07'N,

139°42.05'E) was collected from the western slope (water depth of 840 m) of the Musashi Bank in

the northeastern Japan Basin. Core GH99-1246 (43°46.19'N, 138°49.86'E) was also obtained from

the northeastern margin of the Japan Basin (water depth: 3435 m). The third piston core KR05-

09PC-1 (41°41.95'N, 139°04.98'E) was taken from the Matsumae Plateau (water depth of 1,764 m)

of the northeastern Japan Basin during cruise KR05-09 through the R/V Karei-Maru by University

of Tokyo in July, 2005. A variety of analytical approaches including geochemical, elemental and

isotopic measurements were applied to these sediment cores to verify the orbital- and millennial-

scale paleoceanographic changes during the late Quaternary. The age models for these cores were

!%&

established using diverse methods such as AMS 14C dates, identification of known tephra layers,

stratigraphic correlation of TL layers with well-dated core MD01-2407 which was obtained from the

Oki Ridge in the southern East Sea (Sea of Japan). Based on the geochemical and isotopic properties

of these sediment cores, the orbital- and millennial-scale paleoceanographic variations were

observed clearly in the Japan Basin, similar to those of other areas. This results in a conclusion that

the sea-level fluctuations have induced the unique and basin-wide paleoenvironmental changes in the

East Sea (Sea of Japan). However, the spatial variability should be emphasized with respect to the

interaction between the surface and bottom waters.

!%'

Millennial-scale paleoceanographic changes in the central Bering Sea during the late

Pleistocene

Sunghan KIM 1, Boo-Keun KHIM 1*, Takuya ITAKI 1, Kota KATSUKI1, Masao UCHIDA 2, Ryuji

TADA3

1 Division of Earth Environmental System, Pusan National University, Busan 609-735, Korea *E-mail: bkkhim@pusan.ac.kr

2 National Institute for Environmental Studies, Onogawa 16-2, Tsukuba 305-8506, Japan 3 Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan

During MR06-04 cruise of R/V Mirai, an 18 m long piston core (PC23A) was obtained from the

northern slope area (60o09.52’N, 179o27.82’W, 1002 m deep) in the central Bering Sea. The age of

the upper part of core was decided by planktonic foraminifera AMS 14C dates which were measured

in National Institute for Environmental Studies in Japan. The presence of L. nipponica sakaii and

absence of A. setosa constrain the age of lowermost of core younger than 60 kyr. The precise age

model will be provided using more planktonic foraminifera AMS 14C dates. The sedimentation rate

of core PC23A is high up to 30 cm/kyr which seems to be expected enough to preserve the short-

term paleoclimatic events. The overall CaCO3 contents are generally low (less than 10 %) and lower

than opal contents (less than 20 %), confirming that the modern Bering Sea is typical of a silica

ocean. It is interesting that the downcore variation of geochemical values (CaCO3 and opal) and

microfossil assemblage data shows glacial-interglacial changes throughout the core as well as the

distinct millennial-scale signals during the last glacial period. The high geochemical values (CaCO3,

opal, and TOC) in the upper part of core correspond to the deglacial laminated sediments. At this

interval, sea-ice indicator diatom as Fragilariopsis cylindrus and well ventilated intermediate water

indicator radiolarian as Cycladophora davisiana rapidly increased. These results are attributed to

high primary production [during deglaciation due to the ice edge bloom] which develops in surface

meltwater layer at the early spring, and the seasonal sea-ice produced the cold and ventilated

intermediate water mass during this time. In addition, a series of prominent CaCO3 peaks during the

last glacial can be clearly correlated with Dansgaard-Oeschger events. The increased CaCO3 values

may result either from enhanced productivity, causing the expansion or migration of oxygen

minimum zone or from the reduction in intermediate-water ventilation of the North Pacific,

enhancing degree of CaCO3 preservation potential.

!%(

Organic-geochemical proxies from the western part of the East Sea/Japan Sea

and its paleoceanographic implications

S.I. Nam (Korea Institute of Geoscience & Mineral Resources, 305-350 Daejeon, Korea), J.J.

Bahk, J.H. Jin, B.K. Khim (Pusan National University, Busan 609-735, Korea), Y.H. Park

Several AMS-14C age dating, stable oxygen and carbon isotopes of the planktonic foraminifera N.

pachyderma sin., and detailed organic-geochemical analyses (e.g., carbon and nitrogen isotopes of

organic matters and opal) were performed on several marine sediment cores recovered from the

western margin of the East Sea/Japan Sea. The main objective of this study is to reconstruct

paleoceanographic changes of the western margin of the East Sea/Japan Sea during the late

Quaternary glacial-interglacial cycles. The multi-proxy data obtained from the western margin are

compared with those previously published in the central and eastern parts of the East Sea/Japan Sea.

In particular, organic-geochemical multi-proxies are used to understand characteristics and origin of

organic matter deposited along the East Sea/Japan Sea western margin.

There are a couple of peaks with relatively increased supply of marine organic matter during the

MIS 4, 3 and 2, probably indicating to some extent enhanced productivity of the surface water during

the interstadials. A gradual shift towards heavy !13Corg and !15N values along with high biogenic

opal during the last deglaciation (T1) indicates enhanced primary production within the sub/surface

water due to inflow of the Tsushima warm current and increased nutrient supply from the deep water.

However, core GCRP-21 (recovered from the South Korea Plateau) is characterized by cyclic peaks

with distinctly increased TOC contents during the last 190 ka. These TOC peaks are well correlated

with high C/N ratios >15 and depleted !13Corg (< -24‰) and !15Norg (<4‰) values, strongly

indicating enhanced input of terrigenous organic matter to the East Sea/Japan Sea during stadials as

well as glacial periods.

!%)

Simultaneous monsoon development in the Himalaya and East Africa recorded

in terrestrial successions in the Siwalik Hills and the Kenya Rift

Sakai, T. (Shimane Univ., Matsue 690-8504, Japan), Gajurel, A.P., Ulak, P.D. (Tribhuvan Univ.,

Nepal), Gautam, P. (Hokkaido Univ. Japan), Sawada, Y. (Shimane Univ.), Saneyoshi, M.

(Hayashibara Museum, Japan), Nakatsukasa, M., Kunimatsu, Y. (Kyoto Univ., Japan), and Nakaya,

H. (Kagoshima Univ., Japan)

We evaluated the timing of monsoon intensification in both the Himalaya (Siwalik Hills) and

Kenya Rift based on fluvial facies analysis. The onset of intensification of the Indian Monsoon has

long been discussed using various climatic proxies derived, in particular, from sediment successions

in the Siwalik Hills. However, the specific timing of this onset is still under debate due to differences

in the resultant timing among areas and proxies. The effect of local climate influenced by

topography is a possible cause of the variable timing between areas. The climatic proxies commonly

used, such as C-O isotope ratios and plant fossils, are strongly related to water discharge to the basin.

For precise determination of monsoon intensification, we therefore need to find successions that

accumulated in basins where the water discharge was controlled by the regional climate, rather than

by local factors. In this study we analyzed Siwalik successions in western and central Nepal inferred

to have been deposited in the basins with the largest catchments, hence minimizing local climatic

effects. The climate of East African has been affected by both the Indian and African Monsoons, but

its history in the Miocene period (particularly around 10 Ma) is also still unclear.

The Nepal study areas were selected based on petrographic information, to identify the basins in

the early phase of the Siwalik Group that had the most extensive catchments in the Himalaya. The

Chisapani (western Nepal) and Butwal (central Nepal) areas were selected. Previously evaluated

sedimentation rates in both areas are almost identical. A distinct change in floodplain facies from red

soils (drier climate) to frequent interbedded flood-flow deposits in floodplain mudstones (wetter

climate) has already been reported from the Butwal area. This change occurred around 9.9 Ma.

Similar change was found in the Chisapani area, occurring around 9.7 Ma. The persistence of red

soils through to a higher stratigraphic position in the Chisapani area implies a drier climate in

western Nepal than in central Nepal.

The succession studied in the Kenya Rift (Aka Aiteputh and Namurungule Formations) is exposed

in the Samburu Hills, filling a small half-graben. Intense volcanic activity around the Samburu Hills

was lacking at that time, suggesting absence of higher mountains around the basin, similar to the

present day. Petrographic study of the lower Namurungule Formation shows that the sediments

consist only of volcaniclastic detritus transported from the adjacent area by streams or from the far

south by pyroclastic falls. These features suggest that in the early phase of basin formation its

!%*

catchment was limited in extent. The absence of high mountains and the small catchment imply that

water was brought to the basin by air passing over it, and the climatic record from this basin thus

represents the regional climate of northern Kenya. A change from a red soil-dominant facies to

fluvio-lacustrine deposition occurred around 9.6 Ma, reflecting the onset of wetter climate. The

combination of mammal fauna suggesting an open-grassland environment (drier climate) during the

Namurungule phase and change to fluvio-lacustrine facies implies climatic seasonality strengthened

around 9.6 Ma.

The present wet season in Kenya is brought mainly by the westerly (African) monsoon, whereas

the Indian monsoon wind brings dry air. Assuming this climate system was present around 10 Ma,

the strengthened seasonality at that time may have been induced by intensification of both wind

systems. The climate change detected from the Kenya Rift and Nepal may imply linkage of the

Indian and African Monsoons around 10 Ma.

!&+

PALEOHYDROLOGY OF JAPAN SEA DURING THE LAST 48 KYR: A ULTRA-HIGH

RESOLUTION STUDY OF SEDIMENTS FROM NE JAPAN SEA

SUGA Hisami (Institute for Research on Earth Evolution (IFREE), Japan Agency for Marine-Earth

Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka 237-0061, Japan),

YOKOYAMA Yusuke (Department of Earth and Planetary Sciences University of Tokyo,

IFREE/JAMSATEC), OGAWA O. Nanako, KASHIYAMA Yuichiro, CHIKARAISHI Yoshito,

KITAZATO Hiroshi and OHKOUCHI Naohiko (IFREE/JAMSTEC)

Japan Sea!is a marginal sea connected to the open ocean through four shallow straits

(<140 m). Hence the global sea-level should have strongly constrained the influx of the seawater

into Japan Sea, leading to drastic hydrological variations during the late Quaternary. In this study, we

report analytical results of sediments recovered from northeastern Japan Sea (39.5°N, 139.4°E, water

depth of 860 m, core length of 7.37 m) during R/V Kaiyo KY04-09 cruise in 2004. The sediment is

characterized by alternating laminated dark and massive light layers, which have been widely

observed in Japan Sea (e.g. Oba et al.,1991). The chronology of the sediment was determined by 14

radiocarbon dates of mostly single species planktonic foraminifera. It indicates that the core covers

last 4.8 cal. kyr BP with mean sedimentation rate of 15.1 cm kyr-1. We determined oxygen and

carbon isotopic compositions for both planktonic and benthic foraminiferal tests in every 0.5-1 cm

throughout the core. Total number of sliced sediments is as much as 870, which corresponds to time

interval of ca. 70 years. The lightness of the core (L*) showed large fluctuations in Marine Isotope

Stage (MIS) 3, which mimics Dansgaard/Oeschger (DO) Events!recorded in Greenland ice cores.

This pattern was originally suggested by Tada et al. (1999). Correlation of L* with oxygen isotopic

record of GISP2 indicates that both peaks coincide with age difference by 0.1 to 1.1 kyr. Total

organic carbon and nitrogen contents in the sediment also show the DO-like fluctuations.

Nevertheless, even in the laminated sediments, several species of benthic foraminifera were

observed, suggesting the dissolved oxygen content in the bottom water was abundant enough for

benthic foraminifera to survive. Carbon isotopic composition of benthic foraminifera and oxygen

isotopic compositions of both planktonic and benthic foraminifera little vary along the DO-like

events. Therefore, lamina formation during the MIS-3 should have been controlled by delicate

balance of oxygen supply and consumption in the deep water. This balance could have been

controlled by mechanism(s) sensitively modulated with the teleconnection of North Atlantic climate.

Reference

Oba, T., Kato, M., Kitazato, H., Koizumi, I., Omura, A., Sakai, T., Takayama, T., 1991.

Paleoceanography 6 (4), 499-518.

Tada, R., Irino, T., Koizumi, I., 1999. Paleoceanography 14 (2), 236-247.

!&"

!&#

ROCK MAGNATIC RECORDS OF SOUTHEAST ASIAN MONSOON

VARIABILITY DURING THE PAST 800 KYR

Suganuma Y (University of Tokyo, Tokyo Japan, 113-0033)

Yamazaki T (Geological survey of Japan, AIST) and Kanamatsu T (IFREE, JAMSTEC)

Rock magnetic investigations were carried out on a sedimentary core taken from the Ninety-

east ridge, the eastern equatorial Indian Ocean in order to reconstruct the South Asia monsoon

variability during the past 800 kyr. A 10.2 m long piston core “MR0503-PC3” was recovered in

August 2005 during the R/V Mirai MR0503 cruise. The core site is located in the western flank of

the Ninety-east ridge (113.2'N, 8826.0'E), and water depth is 4400 m. In order to develop an age

model for the MR0503-PC3 core, a relative paleointensity record (NRM30mT/IRM30mT) obtained

from the core is correlated with the global stack of relative paleointensity records, “Sint-800”

(Guyodo and Valet, 1999). Based on the developed age model, the age of the bottom of the

MR0503-PC3 core is ca. 800 ka and an average sedimentation rate is 1.3 cm/kyr.

A suite of rock magnetic parameters (Magnetic Susceptibility, IRM, ARM, Mrs/Ms, and S-

ratio) was obtained from discrete samples collected from the half-split of the core. Magnetic

Susceptibility, IRM, and ARM are used as proxies for magnetic mineral flux. Mrs/Ms and S-ratio

are used as proxies for mean grain size and magnetic mineralogical, respectively. The results show

that magnetic mineral flux increases during warmer periods, whereas the flux decreases during

colder periods. On the other hand, magnetic grain size increases during colder periods and

decreases during warmer periods. These indicate that a supply of fine-grained magnetite (or

maghemite), probably originated from pedogenesis, increases during warmer periods, suggesting

intense precipitation related to the South Asian summer monsoon. During MIS 15 to 11, stepwise

increases of the magnetic mineral flux accompanied with sudden drops of S-ratios are recognized.

The sudden drop of S-ratio is related to intense inputs of coarse-grained hematite and maghemite,

probably originated from the chemical weathering of the Himalaya-Tibet plateau. This feature

suggests that intensification of the South Asian monsoon from MIS 15 to 11. This intensification of

the South Asia monsoon may be related to the climate shift during the mid-Brunhes chron observed

from several regions of the western Eurasia (e.g., Chinese Loess plateau and lake Baikal).

!&$

Uplift of Kunlun Mountains and the formation of Taklimakan Desert

Naomi Sugiura, Ryuji Tada, Hitoshi Hasegawa, Yuko Isozaki

Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,

Tokyo 113-0033, Japan

Hongbo Zheng, Yan wecheng

Department of Marine Geology, Tongji University, 1239 Siping Road, Shanghai, China

Youbin Sun

State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Ac

ademy of Sciences, Xi’an 710075, China

East Asian Monsoon was considered to have been enhanced by the uplift of the Himala

ya – Tibetan Plateau. The Kunlun Mountains fringes northern edge of the Tibetan Plateau, a

nd formed at the final stage of the uplift of the Tibetan Plateau and still continue to rise.

The Tarim Basin is surrounded by the Kunlun Mountains to the south and the Tian Shan M

ountains to the north, and is largely covered by the Taklimakan Desert, the world’s second l

argest sand desert. It is suggested that the Taklimakan Desert is one of the major sources

of aeolian sediments in Chinese Loess Plateau which record the evolution and variability of

East Asian Monsoon. Thus, knowledge on the timing and mode of emergence and evolutio

n of the Taklimakan Desert will provide useful information for understanding the linkage bet

ween mountain building and evolution of East Asian Monsoon as well as aridification in inl

and Asia.

In order to examine the sedimentary record on the evolution of Taklimakan Desert since

10Ma, we conducted field survey at Yecheng located in the southwestern margin of the Ta

rim Basin, where more than 3 km thick fluviao-eolian depositional sequence of late Cenozoi

c age is continuously exposed (Zheng et al., 2000). Our survey revealed that accumulation o

f fine-grained yellowish silt deposit, which is interpreted as aeolian deposits (Zheng et al., 2

003), started around 4.6 million years ago and accumulation rate increased from 3.6 to 1.6

million years ago. This timing coincides with the onset of thick conglomerate deposition an

d acceleration of tilting of strata!in the area that commenced around 3.6 million years ago.

This observation suggests the linkage between mountain uplift, enhanced deposition of fluvi

al sediments, and increased dust production/emission, and accumulation of sand in the Takli

makan Desert.

!&%

PALAEOMONSOONAL AND PALAEOSEISMIC IMPLICATIONS OF LANDSLIDE

INDUCED LAKES: EVIDENCE FROM THE LESSER CENTRAL HIMALAYA,

UTTRAKHAND, INDIA.

Sundriyal Y P (Department of Geology, HNB Garhwal University, Srinagar, Uttarakhand, India-

246174)

Chaudhary Shipra and Sati S P

In lesser Himalaya, tectonics, lithology and southwest monsoon play a major role in

landscape evolution particularly formation of temporary lakes. We report for the first time evidence

of post glacial slope activation leading to the development of temporary lakes have been found

around the out of sequence North Almora Thrust (NAT) in the Lesser Himalayan domain of the

Alaknanda basin (Lat. 30°15'-30°18'32''nd Long 78°42'-78°50'). Morphometric analyses of the

drainage basins show that the 2nd or 3rd order ephemeral streams having catchment areas of ~ 300 m2

were blocked by landslides at the knick points developed on the crumpled and fractured phyllite

rocks. The obstruction thus facilitated the development of temporary ponds in which sand; silt and

clay of varying thickness (few to tens of cm) were deposited. Considering that these lakes were

formed in the vicinity of the NAT, we attribute them to the paleoseismic activity along the NAT and

its sympathetic NW-SE lineaments (Fig.1).

Optical dating of the lake sediments indicate that landslide activity probably occurred around

the Last Glacial Maximum (>14 ka) where as the lacustrine environment persisted during 14 ka to

around 5 ka. We interpret the lacustrine sedimentation to the post glacial reestablishment of the

southwest monsoon in the region which continued (impersistently) till the Mid Holocene. Absence of

lake sediments and large-scale colluvial deposition in the region is attributed to the weakening of the

southwest monsoon and onset of the Mid Holocene aridity.

In addition to this, presence of seismically induced deformation in the lake deposits implied

that the terrain was seismically active at least between 14 ka to 5 ka (Fig.2).

In this presentation an attempt would be made to evaluate these results in regional perspective

in order see if there existed in the synchronicity in the post glacial monsoon variability.

!&&

_____________________________

For correspondence ypsundriyal@yahoo.co.in

!&'

!Fig. 1 The number of oxygen vacancies in quartz is correlated with the ages of the host granites (Toyoda, 1992)

ESR SIGNALS IN QUARTZ AS INDICATORS OF PROVENANCE OF AEOLIAN DUST

Toyoda, S. (Okayama University of Science, Okayama, 700-0005, Japan), Nagashima, K. (Ja

pan Agency for Marine-Earth Science and Technology, Yokosuka, 237-0061, Japan), Isozaki,

Y. (University of Tokyo, Tokyo, 113-0033, Japan), Sun, Y. (Institute of Earth Environment,

Chinese Academy of Sciences, Xian, P. R. China) Tada, R. (University of Tokyo, Tokyo, 11

3-0033, Japan)

Large amounts of aeolian dust are transported from dried areas in Eurasian contine

nt to the Japan Sea and the Japanese islands through the westerly jet. We have investigated

the history of the provenance of quartz grains in aeolian dust which indicates the history of

the variation of the westerly jet, by using the ESR (electron spin resonance) signals observ

ed in quartz and the Crystalinity Index measured by X ray diffraction.

The E1’ center is a paramagnetic center in quartz with an unpaired electron at an

oxygen vacancy. Based on the study investigating the process that oxygen vacancies turn E1’

centers, Toyoda and Ikeya (1991) proposed a protocol to estimate the total number of the

oxygen vacancies by observing the ESR intensity of the E1’ center, which is gamma ray irra

diation to more than 200 Gy followed by heating at 300"C for 15 minutes. A correlation w

as found between the number of oxygen vacancies in natural quartz and the ages of their h

ost granites in the range of 10 Ma and 1 Ga as shown in Fig. 1 (Toyoda, 1992; Toyoda an

d Hattori, 2000). The number of the oxygen vacancies in quartz of loess in Japanese Islands

were systematically measured based on the above findings. It was shown that the amount i

n Japanese loess is about the same with

that in Chinese loess plateau in MIS 1,

being consistent with the satellite obser

vation. On the other hand, in MIS 2, th

e case also applies to the loess samples

in southern Japan while the amounts ar

e systematically larger in those in northe

rn Japan, implying that aeolian dust from sources which have derived from older basement rocks, possibly Precambrian rocks in Siberia, has contributed the loess deposited in northern Japan in

!&(

!Fig. 2 The contributions from eolian dusts from Taklamakan and Siberia to sediment in Japan sea as a function of the deposition age, being consistent with the climate change (Nagashima et al., 2007)

MIS 2 (Naruse et al, 1997; Ono et al., 1998; Toyoda and Naruse, 2002).

Nagashima et al. (2007a, b) proposed that the Crystalinity Index (CI) measured by

X ray diffraction is another proxy to reveal the source of the aeolian dust. They calculated

the ratios contributed from the three sources, Taklamakan, Siberia, and Japanese river, to the

sediments taken from a core in Japan Sea down to 150 ka. It was found that the contribut

ion from Taklamakan dominates in warmer period while that from Siberia is larger in colder

period (Fig. 2).

The next step of this provenance study requires more detailed specification of the d

ust sources as well as precise values of the contribution. Other ESR signals, such as parama

gnetic centers due to impurities in quartz, would be such useful additional proxies. We inves

tigated the ESR intensities of impurity centers (Al, Ge, and Ti-Li centers) produced by unit

gamma ray dose (the slopes of the dose responses) in quartz of three desert samples (TG: T

enger, HB: Hobi, and Tak: Taklamakan) and of Chinese loess plateau (YL2). As shown in F

ig.3, it was found that these three deserts can be distinguished while YL2 is close to TG, i

ndicating that these ESR signals could be additional useful proxies.

TG

TG

HB HB

Tak

Tak

Fig. 3 The ESR intensities produced by unit dose of gamma ray irradiation, together with the number of oxygen vacancies. The samples were heated at 400"C for 1 hour to erase the natural signals before irradiation for the measurements of impurity centers. It was found that the three deserts can be distinguished while YL2 is close to TG in both diagrams.

!&)

LATE QUATERNARY PLANKTIC FORAMINIFER FAUNA AND MONSOON

UPWELLING RECORDS FROM THE WESTERN SOUTH CHINA SEA, NEAR THE

VIETNAM MARGIN (IMAGES MD012394)

Yu Pai-Sen (Institute of Applied Geosciences, National Taiwan Ocean University, Keelung 20224,

Taiwan, ROC)

Mii Horng-Sheng (Department of Earth Sciences, National Taiwan Normal University, Taipei,

Taiwan, ROC)

Masafumi Murayama (Center for Advanced Marine Core Research, Kochi University, Kochi, Japan)

Chen Min-Te (Institute of Applied Geosciences, National Taiwan Ocean University, Keelung 20224,

Taiwan, ROC)

Marine sediment core MD012394 from the Vietnam coastal upwelling area in the western

South China Sea was investigated in order to reconstruct the last Quaternary monsoon upwelling

based on planktic foraminifer fauna assemblages and fauna-based sea surface temperature (SST)

estimates. The age model of core MD012394 was constructed using oxygen isotope stratigraphy of

the planktic foraminifer G. sacculifer, with 10 accelerator mass spectrometry (AMS) 14C dating of

planktic foraminifers from the sediment samples. Our studies on the relative and absolute

abundances of planktic foraminifer assemblages reveal eight dominant species in core MD012394: N.

dutertrei + N. pachyderma (right coiling), G. ruber, G. glutinata, G. sacculifer, P. obliquiloculat

a, G. menardii + G. tumida, G. calida, and G. inflata. In a Q-mode factor analysis of the fauna

abundance data, the fauna factors show variations that do not parallel the glacial/interglacial changes

throughout the last 135 kyr. The relative abundance patterns of G. inflata and N. dutertrei (including

N. pachyderma-R) are interpreted as hydrographic proxies for East Asian summer and winter

monsoon, respectively, in the current study. We calculated the fluctuations in the SST using the

Revised Analog Method (RAM) in MD012394 and found that the abundance changes of the summer

monsoon upwelling indicator G. inflata were similar and nearly synchronous. This suggests that the

summer monsoon-driven upwelling signal was strong near the local summer insolation maximum,

which induced low SSTs, particular around ~11, 33, 59, and 83 kya. Our studies support the view

that the strengths of both summer insolation and the East Asian summer monsoon have determined

the relative abundance of planktic foraminifers and the SSTs in the western SCS during the last 135

kyr.

!&*

Figure 1

Figure 2

!'+