investigation of late-quaternary … of... · istituto di geologia marina, cnr, bologna, tech. rep....

INVESTIGATION OF LATE-QUATERNARY SEDIMENTS FROM THE SOUTH YELLOW SEA

AND THE YANGTZE RIVER DELTA

Maurizio Bonardi*, Luigi Tosi*, Jeanne Percival**, Chen Lirong*** and Andrea Zanucco****

* Consiglio Nazionale delle Ricerche, Istituto per 10 Studio della Dinamica delle Grandi Masse, San Polo 1364, 30125 Venezia (Italy).

** Geological Survey of Canada, 601 Booth St., Ottawa, Ont., K1A OE1 Canada.

*** Institute of Oceanology, Academia Sinica, 7 Nan-Hai Road, Qingdao, 266071 China.

* .. * Universita' di Padova, Dipartimento di Mineralogia e Petrologia, C.so Garibaldi 37,35137 Padova (Italy)

Abstract

The results of a study to determine the geochemical, mineralogical, magnetic and textural characteristics done on Late-Quaternary sediments from drill cores from the South Yellow Sea (core H106) and the Yangtze River Delta (core LA) (China) are reported. The Late-Pleistocene continental sedimentation is represented by clayey silt and hard clay layers, while the marine Holocene sediments consist mainly of clay (H106) and sand and clay layers (LA).

Introduction

Reported here are the results of a mineralogical, geochemical, paleomagnetic and textural investigation carried out with the purpose of characterizing Late-Quaternary sediments from two different depositional environments: the South Yellow Sea and the Yangtze River Delta.

The imprinting of the climatic conditions that characterised the Last WOrmian phase are recognitiable in the overconsolidated clay layer that marks the Pleistocene/Holocene boundary.

Particle size distribution was determined using a Brinkmann Particle Size Analyzer (Model 2010). The mineralogy of bulk materials and their clay-size separates were determined by X-ray powder diffraction analysis (XRD).

South Yellow Sea, Core H106

Fifty-five clay and clayey silt samples representative of the last 20.000 years of sedimentation, were taken from a 600 cm-Iong core (H106), in 70 m of water (Figg. 1 J 2).

18

Bonardi, M., Tosi, L., Percival, J., Lirong, C., Zanucco, A. 1995. Investigation of Late Quaternary sediments from the South Yellow Sea and the Yangtze River Delta. In: (Marabini, F. Editor) Italian Contribution to the China-Italy Bilateral Seminar on Marine Geology, 4-6 October 1994, Qingdao, China. Istituto di Geologia Marina, CNR, Bologna, Tech. Rep. 40, 18-24.

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Fig. 1

Fig. 2

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80

120

160

200

240

280

320

360

400 399

440

480 76

520

560

~

~ Litho-2 U5 Description

~ ~ Clay

a

Clayey silt

Grain Size ("!oj

25 50 75

.............. ............... .. ... .. .. .. .. .. .............. .............. ............... ------............. -................ .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..

Heavy Mineral

("!oj

Ca Ca + Fe

20 '0 '02 03 04

Location: 35° 30' N 123°E

o Marine Facies

Continental Facies D. Hard Clay o Clayey Silt

Clay 50

50 Sand

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Pollen 5 Assemblage

en ., '0

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Detailed mineralogical analyses show that the ,samples are dominated by Quartz with subordinate Plagioclase, Chlorite and Mica (Muscovite/Biotite) and minor to trace amounts of K-Feldspar and Calcite (Fig.3).

40 Q) 35 u c eel 30 -0 c 25 :::l .0 20 « Q) 15

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Sample Depth (cm)

, . ...... Quartz _ .•. - Calcite ---,Ir- Total Feldspars'

Fig. 3

Trace amounts of Smectite, Illite/Smectite mixed-layer mineral, Dolomite and Hornblende are also present and related to the magnetic (Fig. 4).

60 140 Q) u 50 c eel 'U

40 c ::J .0 til 30 Q)

. ~ ro 20 C3 a: 10 ~

120 ..... 0.. <D

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Fig. 4

In bulk samples, Calcite is more abundant from top of the core down to about 275 cm and is notably absent from 305 to 445 cm.

In the clay-size fraction, Calcite occurs in minor to trace amounts in most of the marine facies samples, is notably absent in the hard clay samples, and occurs in trace amounts in the lower continental unit samples,

The concentration of clay minerals Chlorite, Mica and Smectite is enhanced in the clay-size fraction, Chlorite and Mica occur in abundant to minor amounts in both units. Smectite is more abundant in the continental unit relative to the marine unit.

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The concentration of heavy minerals (see Fig. l)decreases with depth within the marine unit. The change in concentration of heavy minerals in the upper vs. lower marine units suggests a change in provenance of the sediments. Provenance includes both the Yellow and Yangtze Rivers.

Yangtze River Delta, CORE LA1

Twenty-one samples were taken from Core LA 1 30 m-Iong, in the Yangtze River Delta; stratigraphy and depositional environments are reported in Fig. 5.

~1l:Jr -:.:-:-:-:-: LawTl~ ~ALfLA:

5 -:.:-:- suaT1Q4 •• ' ''; (,SAKO)

2.0---

~

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~ - - ~,(t'EN ~ - - - STIFF-'-' _ - _ - _ (.J..AY

~ 2S - )'fU-O"", '" - _-_- MowN U'. - - - STlH ~ _-_-_ CLAY

Fig. 5

..... . ·. 0 ..

CZJ SAND

The Late-Pleistocene "Stiff Clay" layer in the Yangtze Delta area is a paleosol (personal communication by Baozhu Liu, Tongji University, Shanghai), moreover it is considered as "meadow-soil-type".

The average relative persentage of the Silicates, for the bulk samples, is always higher than the Carbonates.The trend of the Silicates shows a constant high percentage for the continental samples, a constant low values for the neritic facies (base of Holocene transgression) and percentages that decrease from a high value in correspondance of the subtidal facies to a low value at the tidal flat sedimentation (Fig. 6).

Similarly, the relative abundance variation of the clay minerals for the claysize fraction can be related to different paleoenvironmental depositions (Fig. 7).

The sand samples of the Upper Holocene sedimentation, from subtidal to low-, mid- and high tidal flats (Upper Holocene) show a mineralogical composition variation that, as for the clay sediments, may well be correlate to different depositional environments (Fig. 8).

The magnetic susceptibility variations, as indicated if Figg. 6, 7, 9, can be also correlated to mineralogical composition variations due to different facies.

21


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Fig. 6

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0 5 10 15 20 25 30

Sample depth (m)

• Magn.Suscept. - .•. - Total Carbonates ....... Total Silicates

.. -II ,

• . -. . ........ ~ ..

.'. • ....•. _~. II",

.' II, ... .. .#

\' .. .... ....... - ......... -' -' - ............. - .... -+-- .....

-+-.... ·r ~-.. ..... o~~----~·~~~~--~--~·~~~~--~~~--~~~~~~~

o 5 10 15

Sample depth (m)

20 25 30

_ .•. - Quartz ....... Chl.+Sm+MI+Mus. _. A-' Carbonates • Magn. Suscept.

Fig. 7

9 - 8 eft. -Gl 7 0 c 6 ca '0 5 c :J ..0 4 <t Gl 3 > :;: 2 ca

Cii 1 a: 0

Fig. 8

2.5 3.8 5.5 7

Samples Depth (m)

22

8.5 10

o Opaques

• Apatite

IIIJEpidotes

13 Pyroxenes

Ira Amphiboles


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Fig. 9

o 2 3 4 5 6 7 0+-__ ~-r----~------+-~ __ -+------r-----~-----4

5

10

15

20

25

~

'II..- ...... ... -- _____ II..--~

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• Magnetic Susceptibility (X *10-1 )

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-. -Sand: % Amphib.+Pyrox.

30~--------------------------------------------~

Conclusions

The study has evidenciated the different mineralogical and sedimentological characteristics of Cores H106 and LA 1, that can be attributed to source areas and depositional paleoenvironments differences.

Nevertheless, a detailed interpretation of the mineralogical composition variations for each of the two cores, indicates that these changes were related to the same paleoclimatic events.

The results obtained with this and similar studies (see references) has indicated that this analytical approach offers the possibilty to correlate in a regional scale global climatic events.

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Bibliography

BONARDI M. & CARBOGNIN L. (1992): Late Quaternary sediments differentation and characterization by EMPA-EDS mineral assemblage study. Electron Microscopy 92, Proc.of the 10th EUREM 92, Vol. 2, p. 603, Granada. BONARDI M. & TOSI L. (1994): I sedimenti tardo-quaternari del cordone litoraneo della Laguna di Venezia: Ie sabbie. Istituto Studio Dinamica Grandi Masse, Techn. Rep. 184, Venezia. BONARDI M., SOCCORSO C. & ALDIGHIERI F. (1992): A new approach to the study of the sediments of the Lagoon of Venice (Italy). Marine Geoscience, Vol. 4, No 1, p.36-39. BONARDI M.& TOSI L. (1994): Climatic and sea level fluctuations evidenced in the mineralogical composition of Late Quaternary sediments from the Venetinan Littoral (Italy). Proc. of the 14th International Sedimentological Congress, Recife, Brazil, E5. BONARDI M. & TOSI L. (1994): Effects of Late Quaternary climatic changes on an exposed clay layer in the Lagoon of Venice (Italy). Proc. of the 14th International Sedimentological Congress, Recife, Brazil, 017. CHEN Z. & STANLEY D.J., (1993): Yangtze delta, eastern China: 2. Late Quaternary subsidence and deformation. Mar. Geol., 112: 13-21. CONGXIAN L. & PING W., (1991): Stratigraphy of the Late Quaternary barrierlagoon depositional systems along the coast of China. Sediment. Geol., 72: 189-200. GATTO P. & PREVIATELLO P. (1974): Significato stratigrafico, comportamento meccanico e distribuzione nella laguna di Venezia di un argilla sovraconsolidata nota come 'caranto' . C.N.R., Istituto Studio Dinamica Grandi Masse, Techn. Rep. 70, Venezia. PUZHI Y., (1989): The Nature and Evolution of Tectonics in the Bohai Sea, the Yellow Sea and the East China Sea. Marine Sciences, Vol. 1, No.2. Oct.1989 pp.99-112. QIN Y., ZHAO Y.,CHEN L. & ZAO S., (1990): Geology of Bohai Sea. China Ocean Press, Beijing. QIN YUNSHAN & ZHAO SONGLING (1991): Quaternary coastline changes in China. XIIIINQUA Congress, China Ocean Press Beijing. STANLEY D.J. & CHEN Z., (1993): Yangtze delta, eastern China: 1. Geometry and subsidence of Holocene depocenter. Mar. Geol., 112, 1-11. TOSI L. (1993): Caratteristiche geotecniche del sottosuolo del litorale veneziano. C.N.R. Istituto per 10 Studio della Dinamica delle Grandi Masse, Tech. Rep., 171, Venezia. TOSI L. (1994): Rapporto e prime interpretazioni sulle analisi paleontologiche condotte su campioni tardo-quaternari del sottosuolo del litorale veneziano. C.N.R. Istituto per 10 Studio della Dinamica delle Grandi Masse, Tech. Rep., 182, Venezia.

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investigation of late-quaternary … of... · istituto di geologia marina, cnr, bologna, tech. rep....

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