storm and recovery stage sedimentation records in...
TRANSCRIPT
Journal of Geosciences, Osaka City University
Vol. 44, Art. 8, p. 163-171, March, 2001
Storm and Recovery Stage Sedimentation Records in theShoreline Deposits of the Miocene T6gane Formation I
Southwestern Japan
Wataru MAEJlMA 1, Takeshi NAKANISHI 2 and Takeshi NAKAJ03
lDepartment of Geosciences, Osaka City University, Sugimoto 3-3-138, Sumiyoshi-ku, Osaka
558-8585, Japan (E-mail: [email protected] p)
2Japan National Oil Corporation, Uchisaiwaicho 2-2-2, Chiyoda-ku, Tokyo 100-8511, Japan
Present address: National Center for Petroleum Geology and Geophysics, University of
Adelaide, Thebarton, South Australia 5005, Australia (E-mail: nakanish @ncpgg.adelaide.
edu. au)
30saka Museum of Natural History, Nagai Park 1-23, Higashisumiyoshi-ku, Osaka 546-0034,
Japan (E-mail: [email protected])
Abstract
Wave-work processes originated the shorel ine facies on the margi n of the progradi ng fan-delta plai n
In the Kanaso Conglomerate and Sandstone Member of the Middle Miocene Togane Formation,
Shimane Prefecture, southwestern Japan. The shoreline deposits, up to 3 m thick, are subdivisible into
the lower, cross-stratified sandstone unit and the upper, planar-stratified sandstone unit. The lower
unit is attributed to upper shoreface sedimentation and is characterized by complex interfingering of
gently inclined, thin conglomerate layers deposited on the erosional surface as a coarse lag in a peak stage
of major storms; onshore-di ppi ng, planar cross sets representing land ward migration of longshore bars;
and longshore trough fills revealing along-shore direcrted, trough cross stratification. The upper,
planar stratified unit is dominated by seaward dipping, low-angle cross-sets, implying deposition chiefly
in a foreshore.
Gravels on the fan-delta plain or on the marginal beach were removed by storm waves, swept into
the shoreface by the backwash action of storm waves or by storm-enhanced rip currents, and deposited
as a coarse lag on the erosion surface produced by waves or wave-induced strong currents in the peak
stage of a storm. During the declining and following stage of storms, long-period swells resulted in the
development of a longshore bar system. Bars migrated onshore and climbed over the lag conglomerate
resting on the erosional surface. With the development and onshore migration of the longshore bars,
the longshore trough became distinct and active sedimentation took place in the troughs as waves were
still powerful enough to generate strong longshore currents in the declining and following stage of
storms. The longshore bars did not fi nally weld to the beach face and the nearshore morphology of a
barred system was not replaced by a non-barred reflective system duri ng the period between storms.
Key words: Barred system, Sedimentary facies, Storm, Togane Formation, Upper shoreface.
Introduction
Storms are an important mechanism for the depo
sition of clastic sediments in shallow marine environ-
ments. Many works on storm sedimentation have
been concerned with the shelf and lower shoreface
sequences, which commonly show storm-generated
sandstones interbedded with fair-weather mudstone
and amalgamated storm sandstones respecti vely (efr.
164 Storm and Recovery Stage Sedimentation Records in the Miocene Shoreline Deposits
50km
SETOUCHI PROVINCE,
133°E 134°E
ISAN-IN -HOKURIKU PROVINCE
o
35°N--t----------3Ild~.._I
SAlKAI PROVINCE
Fig. I Index map of the western Setouchi Geologic Province showing distribution of the Mioceneformations.
Hamblin and Walker, 1979; Dott and Bourgeois,
1982; Brenchley, 1985; Brench ley et aI., 1986;
N0ttvedt and Kreisa, 1987; Cheel and Leckie, 1993).
In the shelf and lower shoreface depths, limited or no
influences modify the storm deposits during the
fair-weather periods, and storm depositional records
tend to be selectively preserved in the successions
originating in these depths. The effects of storms in
shallow marine environments also involve coastal
erosion by wave attack and landward sediment trans
port d uri ng wani ng storms or post-storm recovery
stages. These processes are most sign ificant in an
upper shoreface environment. Being different from
the shelf and lower shoreface, fair-weather wave and
current processes are much more intense in this zone,
resulting in reworking and modification of storm
related deposits. Hence, in general, the upper shore
face successions in geologic records consist of materials
deposited between the times of greatest storm erosion
and greatest fair-weather buildup and, thus, include
materials deposited during waning storms or post
storm recovery stages as well as during the following
fair-weather periods (Hunter et al., 1979). Fair
weather sedimentation records probably dominate in
the upper shoreface deposits of high wave-energy seas.
On the other hand, records during waning storms or
post-storm recovery stages should tend to have high
preservation potential in the upper shoreface deposits
of low to moderate wave-energy seas because of limited
influences of fair-weather wave and current processes.
Such deposits reveal successive sedimentation records
from a peak stage of a storm through a waning or
recovery stage to a fair-weather period and their
responsibility for upper shoreface facies organization.
This paper describes and interprets facies of the
shoreline deposits in the Miocene T6gane Formation
to the north of Hamada, Shimane Prefecture, south
western Japan (Fig. 1). The rocks under study
provide a good example of successive sedimentation
records between the times of greatest storm erosion and
greatest fai r-weather bui Id upin an upper shoreface
zone.
Geologic Setting
The T6gane Formation is one of the early Middle
Miocene formations in the western part of the Setouchi
Geologic Province of southwestern Japan (Fig. I).
w. MAEJlMA, T. NAKANISHI and T. NAKAJO 165
oI
N
o
DD··. . .
~
T6gane
SOOmI
Alluvium
Plio-Pleistocene & Holocene sed. cover
Fault
f:=:=::'1t.:.:..:Jr·::,~"."..
UIIID
~--- .. ..
-
-- ..
T6gane Formation ---Miocene
Kanas6 Congl. & Sst. Member
Kokufu Volcanic Rocks --Paleogene
Fig. 2 Geologic map of the northern Hamada area showing distribution of the KanasoConglomerate and Sandstone Member of the Togane Formation. Numerals indicate the localities of measured sections shown in Fig. 4
These Miocene formations fill the basins that are
thought to have developed due to regional downwarp-·
ing in the Setouchi Province (Huzita, 1962; Shibata,
1985). Basin subsidence was slow, and the resultant
basin-fills are represented by a relatively thin
sequence, some 200 m thick, of clastic sediments.
The successions are dominated by shallow marine
deposits and consistently show gradual deepening of
the water depth (Shibata and ltoigawa, 1980; Shibata,
1985) .
The T6gane Formation crops out in a small area
to the north of Hamada (Figs. I, 2). The formation
rests unconformably on the Paleogene Kokufu Vol-
canic Rocks and is, in turn, unconformably covered
by both the Pliocene-Pleistocene Tsunozu and the
Holocene Kokubu Groups (Fig. 2). The T6gane
deposits appear to infill a N-S oriented depression in
the basement rocks (N akajo et a!., 1993a, b). The
lower part of the formation abuts against the base
ment. The structural dip is commonly less than IS".
The T6gane Formation is 200 m thick, and shows, as
a whole, a transgressive stratigraphy, like the equiva
lent formations in the western Setouchi Provi nee.
Continental deposits in the lower part of the formation
grade upward into shallow maflne sandstones
(Okubo, 1982; Nakajo et a!., 1993a, b). The for-
166 Storm and Recovery Stage Sedimentation Records in the Miocene Shoreline Deposits
:cC : : :
Fig. 3 Generalized sequence and stratigraphic subdivision of the T6gane Formation.
Facies of Shoreline Deposits
documented in the shoreline deposits in the Kanas6
Conglomerate and Sandstone Member. The Kanaso
Member has been attributed to deposition in an allu
vial fan-fan delta system (Nakajo et a!., 1993a;
Maejima and Nakanishi, 1994). The alluvial fan
prograded northward into a standing body of shallow
water of a low to moderate wave-energy sea (Maejima
and Nakanishi, 1994). Sediment delivered by the
alluvial fan was deposited mostly subaqueously as the
fan delta. The resultant sequence of the Kanaso
alluvial fan-fan delta system shows a remarkable
lateral facies change in a N-S direction (Fig. 4).
Subaerial alluvial-fan conglomerates in the south pass
northward, within a short distance, into subaqueous
(delta front) deposits and associated subaerial (delta
plain) and transitional (shoreline) deposits. The
delta plain and shoreline deposits form two prominent
tongues projecting northward into subaqueous
deposits of fan-delta front origin. These tongues
demonstrate that the relative sea-level rise episodically
lost balance with the rate of sediment supply. The
conglomeratic fan-delta plain deposits rest erosively on
the accompanying shoreline deposits and have locally
incised into the fan-delta front deposits. Such an
erosional contact is highly suggestive of control by
relative sea-level change rather than by an increase in
the rate of sediment supply. The rate of relative rise
in sea level significantly diminished and the sea level
may have even fallen to some degree. Consequently,
the alluvial fan rapidly prograded over the fan-delta
front, resulting in development of an extensive fan
delta plain. The shoreline deposits represent signifi
cant reworking of the fan-derived sediments by waves
and wave-generated currents. A beach and shoreface
developed on the margin of the fan-delta plain and
prograded northward, accompanied by episodic,
basinward extension of the fan-delta plain (Fig. 4).
Preservation of the shoreline deposits may reflect a
diminished fluvial agency as a result of extension of the
fan-delta plain. Fluvial processes, although power
ful enough to produce conglomeratic fan-delta plain
deposits, was probably overpowered by moderate
energy wave processes acting on the margin of the
fan-delta plain (Maejima and Nakanishi, 1994).
Kanaso Conglomerateand Sandstone Member
Tatamigaura SandstoneMember
Toganegawa MudstoneMember
KOKUFU VOLCANIC ROCKS
200----r."'"=====~-----------,-----,
\\\\i\\i\l\l\\\\!ii\!!!!lli::!\\\\\:::::::: :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
l\llllll\lllllllllllllllllllllllill
100
mation is subdivided into four members (Nakajo et
a!., 1993b), named, in ascending order: Toganegawa
Mudstone, Anegahama Sandstone, Kanaso Conglom
erate and Sandstone, and Tatamigaura Sandstone
Members (Fig. 3). The Toganegawa Mudstone con
tains some freshwater molluscan fossils (Tsuru,
1983), whereas in the lower part of the Anegahama
Sandstone, brackish-water molluscs have been report
ed (Okubo, 1982). Marine molluscs, sharks teeth
and foraminifers are found higher up in the formation
(Okubo, 1982; Tsuru, 1983), specifically in the
Anegahama and Tatamigaura Sandstones.
Depositional Background
The storm and recovery stage sedimentation
records in an upper shoreface environment are well
DescriptionThe shoreline deposits of the Kanaso Member
consist dominantly of fine- to coarse-grained sand
stone, with intercalations of thin conglomerate. The
w. MAEJlMA, T. NAKANISHI and T. NAKAJO 167
m40
4Tatamigaura Sandstone Member
....Q).DEQ)
~Q)coen
"0cctl
(f)
"0CctlQ)
~Q)
E.2OJco()<0(f)
ctlcctl~
Anegahama Sandstone Member
8
TR: Transgressive DepositsSL: ShorelineOF: Fan-Delta FrontDP: Fan·Delta PlainAF: Alluvial Fan
--,--- --
~ "-..
§ Mudstone
CJ Sandstone
~ Conglomerate
o
30
20
10
Fig. 4 Measured sections of the Kanaso Conglomerate and Sandstone Member showing lateral andvertical facies relationships and occurrence of shoreline deposits under study. Location ofeach section is shown in Fig. 2.
shoreline sandstones gradationally overlie the fan-delta
front deposits and are, in turn, covered by the
fan-delta plain conglomerates with a sharp and erosive
contact. The sequence of the shoreline deposits, up
to 3 m thick, is conveniently subdivisible into the
lower, cross-stratified sandstone unit and the upper,
planar-stratified sandstone unit.
The lower, cross-stratified sandstone unit, com
monly I to 2 m thick, is characterized by complex
interfingering of trough and planar cross-sets and thin
conglomerate layers (Fig. 5A). The conglomerate
layers, up to 20 cm thick, are usually poorly to
moderately sorted, and have an erosional surface at
the base. They are gently inclined northward with
gradual decrease in inclination in the down-dip direc
tion (Fig. 5A). Individual conglomerate layers tend
to thin out and to be better sorted up-dip southwards
into one-clast thick layers. Clasts frequently show
well-developed imbrication, dipping either northward
or southward. The planar cross-sets of sandstone are
up to 60 cm thick. They commonly climb up the
gently dipping conglomerate layers and wedge out
southwards. Foresets consistently dip to the south
(Fig. 6) at angles of 10· to 25". Trough cross-sets
with local pebbles are 10 to 40 cm thick, either iso
lated or grouped in up to I m thick cosets. Pebbles
tend to be segregated on the basal surfaces of troughs.
Foreset dip azimuths are bi-directional, oriented
either to the west or to the east (Fig. 6). Biological
influences are not common throughout this unit.
Burrows, however, are locally 0 bserved at the top of
the planar cross-sets and in the trough cross-sets.
The upper, planar-stratified sandstone unit is I m
or so th ick. The sandstones are fi ne-grai ned and well
sorted. Planar stratification is characteristic through
out the sandstone of this unit (Fig. 5B). Lamina
tions are subhorizontal or dip gently to form low angle
cross-beds. The inclination direction of laminae is
bi-directional, with a dominant mode to the north and
a distinct secondary mode to the south (Fig. 6). The
sandstones are free from biological influences, apart
from sparse burrows in the uppermost part of this unit.
The planar-stratified sandstones generally rest on the
cross-stratified sandstones of the lower unit. Locally,
however, the planar-stratified sandstone passes later
ally to the north into the trough cross-stratified sand
stone of the lower unit (Fig. 5B).
168 Storm and Recovery Stage Sedimentation Records in the Miocene Shoreline Deposits
------
1m
Fig. 5 Field sketches of the shoreline deposits which are erosively covered by fan-delta plain conglomerates,viewed normal to the paleo-shoreline (land to right). A) Upper shoreface deposits at the south ofsection 7. Onshore-dipping planar cross-sets climb up the gently seaward-dipping thin conglomeratelayer and interfinger with trough cross sets. B) Lateral transition of planar stratified foreshore sandstones with longshore-directed trough cross-sets of longshore trough origin, section 8.
Interpretation
The variability in textural and stratification char
acteristics in the shoreline deposits of the Kanas6
Member reflects complex hydraulic processes related to
wave and wave-generated current activities on the
coast. The shoreline was approximately oriented
east-west with the seaward side to the north. This
paleogeography is inferred from consistently
northward-flowing paleocurrents in the alluvial and
fan-deltaic deposits (Maejima and Nakanishi, 1994)
and lateral facies relationships revealing transition
from the alluvial fan conglomerates in the south to the
subaqueous fan-delta front deposits in the north (Fig.
4) .
The planar-stratified sandstones of the upper unit
are interpreted as beach deposits. Subhorizontal or
gently dipping planar laminations composed of
well-sorted sand are documented from many present
day beach deposits (Clifton et al., 1971; Howard and
Rei neck, 1981, among others), and are explai ned by
processes of swash action. Dominantly seaward dip
ping, low-angle cross-sets imply deposition chiefly in
a foreshore. The oppositely dipping laminae are
attributed to deposition in a backshore which is flatter
or even slopes very gently landward.
The lower, cross-stratified sandstone unit is inter
preted as an upper shoreface deposit, because of the
predominance of cross-stratification, variability of
W. MAEJIMA, T. NAKANISHI and T. NAKAJO 169
Planar crossstratification
20 %
Trough crossstratification
20 %
Planarstratification
N-8
periods when the shore profile was of fair-weather
form. Long-period swells following storms were
probably responsible for the development of a bar
system. Deposition in longshore troughs in such a
barred shore is represented by trough cross-stratified
sandstones. The trough sets show dominantly
eastward- or westward-flowing paleocurrents (Fig.
6), parallel to the inferred shoreline orientation.
This indicates that these trough sets were deposited
from dunes migrating in an along-shore direction in
the longshore troughs.
Fig. 6 Rose diagrams summarizing dip directions ofplanar and trough cross sets in the uppershoreface deposits and planar stratification offoreshore deposits.
foreset azimuths and occasional burrows (cL Clifton,
1976; Hunter et al., 1979; Howard and Reineck,
1981). An upper shoreface interpretation is further
suggested by the local, landward transition with the
planar-stratified sandstone of beach origin (Fig. 58) .
The conglomerate layers in the lower unit represent a
record of intensive storm sedimentation on the upper
shoreface. During major storms, waves or wave
induced strong currents tend to erode the shore-zone
materials and sweep them into a deeper area (Elliot,
1986). The erosional surface at the base of gently
seaward-dipping conglomerate layers represents the
record of the peak of such events (Massari and Parea,
1988) and shows that the upper shoreface profile was
planed off. Clasts were probably emplaced on the
erosional surface as a coarse lag. 8i-directional
clast-imbrication is suggestive of oscillatory storm
wave motion. The conglomerate layers become thin
ner and better segregated into one-clast thick layers
landward, implying intense winnowing of finer frac
tions towards the toe of the beachface.
As storms wane, shoaling waves rework the sedi
ment previously swept offshore and return the mate
rials landward in the form of a longshore bar (Davis et
aI., 1972; Hunter et aI., 1979, Elliot, 1986). The
onshore-dipping, planar cross-stratified sandstones
represent deposition from such landward-migrating
longshore bars (Massari and Parea, 1988). Individ
ual planar cross-sets tend to climb and wedge out over
the gently seaward-dipping, upper shoreface slope that
had planed off during the storm (Fig. 5A). This
suggests that bar growth and landward migration was
most significant during waning storms or post-storm
recovery periods as well as during the following
Conclusions and Discussion
The shoreline deposits that originated on the
margin of the fan-delta plain of the Kanas6 Conglom
erate and Sandstone Member record storm and recov
ery stage processes in an upper shoreface environment.
During major storms, the shore zone is subjected to
erosion that affects not only the beach face but also the
upper shoreface (Elliot, 1986). Erosion of the shor
eface substrate due to storms is well documented by
gently seaward-dipping, thin conglomerate layers hav
ing the erosional surface at the base. Gravels on the
fan-delta plain or on the marginal beach were removed
by storm waves, swept into the shoreface by back wash
action of storm waves or by storm-enhanced rip cur
rents, and deposited as a coarse lag on the erosion
surface produced by waves or wave-induced strong
currents during the peak stage of a storm. Finer
materials would have been transported further off
shore. Following storm erosion, the bed materials
could have been reworked to make the erosion surface
obscure. A veneer of lag conglomerate, however,
prevented later-stage modification of a storm erosion
surface on the upper shoreface bed. Intensive oscil
latory water-motion due to storm waves was respon
sible for to and fro rolling of clasts on the sea bed,
producing both offshore- and onshore-dipping clast
imbrication. Winnowing of finer fractions took
place also under intense storm-wave agitation, espe
cially towards the toe of the beachface, resulting in
thinning and increased segregation of a conglomerate
layer landward.
Duri ng the declj nj ng and followi ng stage 0 f
storms, long-period swells rework much of the sedi
ment previously eroded in the shore zone and transpor
ted offshore, tend to selectively remove fi ner mate
rials, and transport them onshore, leavi ng behind
coarse particles (Clifton, 1981). Through this proc
ess, a longshore bar system develops and bars migrate
170 Storm and Recovery Stage Sedimentation Records in the Miocene Shoreline Deposits
towards the shore. The profile of bars is modified as
they migrate shoreward and becomes sharply asym
metrical with a steep slip face on the landward slope
(Davis et aI., 1972). The sedimentation record
during such waning storms or post-storm recovery
stages is represented by landward-dipping, planar
cross-stratified sandstones, which are interpreted as
bar lee deposits marking net onshore-migration of the
longshore bar system. Climbing of planar cross-sets
over the lag conglomerate resting on the gently
seaward-dipping, erosional surface demonstrates land
ward migration of the bar onto the upper shoreface
slope that had planed off during the peak stage of
storms. The development of the longshore bar system
and its onshore migration probably took place within
a rather short time after the erosion of the upper
shoreface substrate in a peak stage of storms. At the
depth of the upper shoreface, high orbital velocities
and high orbital asymmetry capable of onshore sedi
ment transport are prod uced by long-period waves,
and probably not by short-period waves (Clifton and
Dingler, 1984). In the low to moderate wave-energy
sea, in which the Kanaso fan-delta was built (Mae
jima and Nakanishi, 1994), long-period waves would
have been most significant in the waning stage of
storms and have been uncommon in the fair-weather
periods that occupy the great intervals between storms.
Such an interpretation is consistent with direct cover
ing of planar cross-sets of a bar slip-face origin on the
lag conglomerate without any intervening deposits and
with indications of faunal activity suggesting a
fair-weather, calm condition (Fig. 5A).
With the development and onshore migration of
the longshore bar, the longshore trough becomes
distinct. Under the wan ing stage of storms, waves
would have been still powerful enough to generate
strong longshore currents in the trough. Consequent
ly active sedimentation took place in the longshore
trough through this stage, depositing trough cross sets
having along-shore paleocurrent directions. After
the establishment of the distinct longshore trough,
wave-driven longshore currents were probably capable
of depositing cross sets even in the fair-weather period,
as suggested by local lateral transition of the trough
cross sets with the planar stratified, beach deposits that
are most likely the fair-weather products (cf. Komar,
1976; Hunter et al., 1979; Maejima, 1983). The
planar cross-sets commonly wedge out into the trough
cross-stratified sandstones of a longshore trough origin
(Fig. 5A) and are separated from the beach depsoits.
This implies that the longshore bars did not finally
weld to the beachface. The nearshore morphology of
the barred system was not replaced by a non-barred
reflecti ve system and was basically mai ntai ned d uri ng
the period between storms.
Acknowledgments
We thank journal reviewers, K. Hisatomi (Wa
kayama University), T. Kawabe (Yamagata Univer
sity) and A. Yao (Osaka City University), for their
cri ticism of the man uscri pt. Financial su pport was
provided to WM by Grants-in-Aid for Scientific
Research (C) from the Ministry of Education, Sci
ence, Sports and Culture (No. 08640579) and from
the Japan Society for the Promotion of Science (No.
11640457) .
References
Brench ley, P. J. (1985) Storm infl uenced sandstone
beds. Modern Geol., 9, 369-396.
Brenchley, P. J., Romano, M. and
Gutierrez-M arco, J. C. (1986). Proximal and
distal hummocky cross-stratified facies on a wide
Ordovician shelf in Iberia. In: Shelf Sands andSandstones (Knight, R. J. and McLean, J. R.,
eds.), Can. Soc. Petrol. Geol, Mem. No. II,
241-255.
Cheel, R. J. and Leckie, D. A. (1993) Hummocky
cross-stratification. Sedimentology Review, 1,
103-122.
Clifton, H. E. (1976) Wave-formed sedimentary
structures-a conceptual model. In: Beach andNearshore Sedimentation (Davis, R. A. Jr. and
Ethington, R. L., eds.), Spec. Pub. Soc.
Econ. Paleontol. Mineral., No. 24, 126-148.
Clifton, H. E. (1981) Progradational sequences in
Miocene shoreline deposits, southeastern Caliente
range, California. Jour. Sed. Petrol., 51, 165
184.
Clifton, H. E., Hunter, R. E. and Phillips, R. L.
(1971) Depositional structures and processes in
the non-barred high-energy nearshore. Jour.Sed. Petrol., 41, 651 -670.
Clifton, H. E. and Dingler, J. R. (1984)
Wave-formed structures and paleoenvironmental
reconstruction. Marine Geol., 60, 165-198.
Davis, R. A. Jr., Fox, W. T., Hayes, M. O. and
Boothroyd, J. C. (1972) Comparison of ridge
and runnel systems in tidal and non-tidal environ
ments. Jour. Sed. Petrol., 42, 413-421.
W. MAEJlMA, T. NAKANISHI and T. NAKAJO 171
Dott, R. H. Jr. and Bourgeois, J. (1982) Hummocky
stratification: significance of its variable bedding
sequences. Bull. Geol. Soc. Am., 93,663-680.
Elliot, T. (1986) Siliciclastic shorelines. In: Sedimen
tary Environments and Facies (Reading, H. G. ,
ed.), Blackwell Sci. Pub., London, 155-188.
Hamblin, A. P. and Walker, R. G. (1979)
Storm-dominated shallow marine deposits: the
Fernie-Kootenay (Jurassic) transition, southern
Rocky Mountains. Can. Jour. Earth Sci., 16,1673- 1690.
Howard, J. O. and Reineck, H. E. (1981) De
positional facies of high-energy beach-to-offshore
sequence: comparison with low-energy sequence.
Am. Assoc. Petrol. Geol. Bull., 65, 807-830.
Hunter, R. E., Clifton, H. E. and Phillips R. L.
(1979) Deposi tional processes, sed imentary struc
tures, and predicted vertical sequences in barred
nearshore systems, southern Oregon coast. Jour.
Sed. Petrol., 49, 711-726.
Huzita, K. (1962): Tectonic development of Median
Zone (Setouchi) of Southwest Japan, since the
Miocene. Jour. Geosci., Osaka City Univ., 6,103-144.
Komar, P. D. (1976) Beach Processes and Sedimen
tation. Prentice-Hall, 429p.
Maejima, W. (1983) Prograding gravelly shoreline
deposits in the Early Cretaceous Yuasa Forma
tion, western Kii Peninsula, Southwest Japan.
Jour. Geol. Soc. Japan, 89, 645-660.
Maejima W. and Nakanishi T. (1994) Middle
Miocene alluvial fan-fan delta sedimentation:
the Kanaso Conglomerate and Sandstone Member
of the Togane Formation to the north of
Manuscript received August 30, 2000.Revised manuscript accepted December 6, 2000.
Hamada, Southwest Japan. Jour. Geosci.,Osaka City Univ., 37, 55-75.
Massari, F. and Parea, G. C. (1988) Prograding
gravel beach sequences lJ1 a moderate- to
high-energy, microtidal marine environment.
Sedimentology, 35, 881-913.
Nakajo, T., Maejima, W. and Nakanishi, T.
(l993a) Basin evolution of the Middle Miocene
Togane Formation in the Hamada area, Shimane
Prefecture, Southwest Japan. Proc. KansaiBranch, Geol. Soc. Japan, No. 116,3-4.
Nakajo, T., Nakanishi, T. and Maejima, W.
(1993b): The Middle Miocene Togane Formation
in the north of Hamada area, Shimane Prefecture,
Southwest Japan. Earth Sci. (Chikyu Kagaku) ,47, 473-484.
N0ttvedt, A. and Kreisa, R. D. (1987) Model for
the combined-flow origin of hummocky
cross-stratification. Geology, 15, 357-361.
Okubo, M. (1982) Miocene fossil assemblages at
Tatamigaura area, Hamada City, Shimane Prefec
ture. Mem. Fac. Sci., Shimane Univ., 16,113-123.
Shibata, H. (1985) Miocene history of the Setouch iProvince, Southwest Japan. Assoc. Geol. Col
laboration Japan, Mem., No. 29,15-24.
Shibata, H. and Itoigawa, J. (1980) Miocene
paleogeography of the Setouchi Province, Japan.
Bull. Mizunami Fossil Mus., No.7, 1-49.
Tsuru, T. (1983) Middle Miocene molluscan fauna
from the Togane Formation in Hamada City,
Shimane Prefecture, Southwest Japan. Bull.
Mizunami Fossil Mus., No. 10, 41-84.