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: maejima@sci.osaka-cu.ac.j 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: nakajo@mus-nh.city.osaka.jp)

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.