tis

aki1-7

a r t i c l e i n f o

Available online 23 July 2009

Keywords:CalcreteFloodplain depositKanmon GroupLower Cretaceous

a b s t r a c t

variations in oodplain deposition (Kraus and Aslan, 1993; Kraus,1996; McCarthy et al., 1998); indeed, previous studies have soughtto clarify the spatial and temporal development of oodplainpaleosols (Kraus, 1997; McCarthy et al., 1998). Knowledge of the

CO217003200 ppmV based on the stable isotopic composition of thecalcretes. However, the formative process of these paleosols has yetto be considered.

The aim of the present study is to characterize the developmentof the oodplain paleosol proles preserved in the ShiohamaFormation. Furthermore, we seek to reconstruct the formationprocess of the calcretes, based on their mode of occurrence, and toidentify the relation between rate of sediment supply andpedogenesis.

* Corresponding author.

Contents lists availab

Cretaceous

els

Cretaceous Research 30 (2009) 13131324E-mail address: hori-yu@geol.tsukuba.ac.jp (Y. Horiuchi).1. Introduction

A paleosol is a soil that formed on a landscape of the past (Ruhe,1965; Retallack, 2001). Soils that develop in alluvial sequences maybe preserved within oodplain sediments as paleosols (Miall,1996). The development of soils in alluvial sequences is a commonphenomenon because the rate of sedimentation on oodplains isgenerally slow enough to allow sediments to be pedogenicallymodied (Wright, 1986). Paleosols preserved in oodplain depositscommonly show complex proles because of spatial and temporal

relationship between pedogenic and sedimentologic features canhelp in estimating the rate of sediment supply.

Details of themode of occurrence of paleosols in Japanwere rstreported by Lee and Hisada (1997) in a study of the ShiohamaFormation of the Lower Cretaceous Kanmon Group, southwestJapan. The paleosols in the Shiohama Formation are developed inoodplain deposits within an alluvial fan setting (Lee and Hisada,1997, 1999; Horiuchi et al., 2008). Lee and Hisada (1999) describedcalcretes from these paleosols, focusing mainly on a chemicalanalysis of calcrete, and estimated paleoatmospheric P to bePaleosolShiohama Formation0195-6671/$ see front matter 2009 Elsevier Ltd.doi:10.1016/j.cretres.2009.07.009Japan. The paleosol proles in the Shiohama Formation are compound and complex, characterized by thepresence of abundant calcrete horizons. An analysis of these proles reveals that the oodplain uponwhich the Shiohama Formation was deposited was part of an unstable aggradation system characterizedby the intermittent inux of sediments and occasional erosion. Furthermore, the mean annual range ofprecipitation was less than about 30 mm, suggesting only minor seasonal change between wet and dryconditions during deposition of the Shiohama Formation. The microstructures of the observed calcretesinclude dense microfabric, oating detrital grains, micronodules, circum-granular cracks, and complexcracks. These features formed by chemical precipitation under dry conditions, with little bioactivity. Thecalcrete horizons are classied into seven types (IVII) based on their modes of occurrence. Twoprocesses of carbonate accumulation can be identied based on the size and abundance of nodules: VIVIII(II)I and VI(V)IVIII. These processes represent the development of calcrete horizons from theearly to late stages of calcretization. Type I represents the most highly developed stage of calcretization.Calcretes within the Lower Member sequence of the Shiohama Formation show repetitions of type I andtypes II and III. Thus, it is interpreted that the frequency of sediment supply to the oodplain changedrepeatedly over time.

2009 Elsevier Ltd. All rights reserved.Received 2 March 2009Accepted in revised form 16 July 2009This paper describes the pedogenic features of paleosols in the upper Lower Cretaceous ShiohamaFormation, the lowest unit of the Shimonoseki Subgroup, in Yoshimi, Yamaguchi Prefecture, southwestArticle history:Paleosol proles in the Shiohama FormaGroup, Southwest Japan and implication

Yu Horiuchi a,*, Ken-ichiro Hisada a, Yong Il Lee b

a Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibarb School of Earth and Environmental Sciences, Seoul National University, NS80, Seoul 15

journal homepage: www.All rights reserved.on of the Lower Cretaceous Kanmonfor sediment supply frequency

305-8572, Japan47, Korea

le at ScienceDirect

Research

evier .com/locate/CretRes

2. Geological setting

Cretaceous red beds are widely distributed throughout East Asia(Miki, 1992). In Japan, their occurrence is restricted to the InnerZone of Southwest Japan, where their presence is attributed to thisregion having been either emergent or in a shallow-sea environ-ment under a hot arid/humid climate during the Cretaceous (Mikiand Nakamuta, 1997).

The Cretaceous Kanmon Group, characterized by intercalationsof red beds, is widely distributed throughout westernmost Honshuand northern Kyushu Islands (Fig. 1). The Kanmon Group dis-conformably overlies the Jurassic marine Toyora and ToyonishiGroups, and also unconformably overlies the Sangun high P/Tmetamorphic rocks and granitic rocks (Okada and Sakai, 1993).

Fig. 2 shows the age and stratigraphy of the Kanmon Group. Thegroup is subdivided into the Wakino and Shimonoseki Subgroupsbased on lithology (Matsumoto, 1951). The Wakino Subgroup ischaracterized by clastic sediments intercalated with minor felsictuff and tuffaceous sediments, whereas the Shimonoseki Subgroup

assigned to the AptianAlbian based on ssion track ages of zircon

Formation conformably overlies the Upper Wakamiya Formation ofthe Wakino Subgroup. The strata in this section strike NESW anddip to the SE at 4050. Fig. 3 also shows a columnar section of theShiohama Formation in the studied section, subdivided into Lower,Middle and Upper Members (Horiuchi et al., 2008).

The Lower Member is characterized by abundant red beds. Themember is about 80 m thick, and is composed of conglomerate,sandstone, and mudstone. The conglomerates generally show thecharacteristics of sediment gravity-ow deposits, and the sand-stones and mudstones are indicative of oodplain deposits, withsome paleosol features. Sediment gravity-ow deposits are thoughtto represent components of debris-ow-dominated alluvial fans,whereas oodplain deposits with abundant paleosols are inter-preted to represent the distal part of a sheet-ooding-dominatedalluvial fan or the overbank nes of an alluvial plain (Horiuchi et al.,2008).

The paleosols within the Lower Member contain numerouscalcareous nodules known as calcrete (Wright and Tucker, 1991).The paleosols also locally contain slickensides and are mottled.Calcrete within paleosols is a feature of arid environments (Wrightand Tucker, 1991). The uppermost part of each reddish sandstonebed in the Lower Member preserves parallel laminations disturbedby burrows and surfaces with raindrop imprints. Although beddingplanes within these oodplain deposits are sometimes obscured bypedogenesis, a number of calcrete horizons can be recognized.

TheMiddle Member (about 60 m thick) is characterized by thickconglomerate with intercalated thin sandstone and mudstone beds

140Valanginian

Berriasian

Fig. 2. Stratigraphy and age of the Kanmon Group. Compiled from Hase (1958).Absolute age is cited from Sakai and Okada (1997).

Y. Horiuchi et al. / Cretaceous Res1314in acidic tuff (Murakami, 1985) and K-Ar dating of hornblende involcanic rocks (Imaoka et al., 1993). The Shimonoseki Subgroup issubdivided into the following four formations (in ascendingstratigraphic order): the Shiohama, Kitahikoshima, Sujigahama,and Fukue Formations (Fig. 2; Ueda, 1957; Hase, 1960).

The present study area, the Yoshimi area, is located upon Aji-ronohana headland, Shimonoseki City (Fig. 3). The sequence of theShiohama Formation, about 350 m thick, is well exposed along therocky coast, although the upper contact of the formation is not seen.

3. Stratigraphy and depositional environments

Fig. 3 shows a route map of the Yoshimi area. The studiedsection extends for about 500 m along the coast-line, where-conglomerate, sandstone, and mudstone of the Shiohama Forma-tion are exposed. In the northern part of this section, the Shiohama

KOREA

JAPAN

Kanmon

Group

Fig. 3

126 E 132 E

36 N

32 N

Honshu

KyushuJejuis characterized by large volumes of andesitic to dacitic volcani-clastic sediment.

The Shimonoseki Subgroup, about 3,000 m thick, dis-conformably overlies the Wakino Subgroup, and unconformablyoverlies older basement rocks. The Shimonoseki Subgroup iscomposed of conglomerate, sandstone, shale, tuff, tuff breccias, andlavas of andesite, dacite, and rhyolite. This subgroup has beenFig. 1. Distribution of the Kanmon Group, southwest Japan.Perio

d

Age

Ma

Early

Cre

tace

ous

100

110

120

130

Albian

Aptian

Barremian

Hauterivian

Stratigraphy

Fukue Fm.

Shiohama Fm.

Kitahikoshima Fm.

Sujigahama Fm.

Upper Wakamiya Fm.Lower Wakamiya Fm.

Nyoraida Fm.Sengoku Fm.

Shim

onos

eki S

ubgr

oup

Wak

ino

Subg

roupK

an

mo

n G

ro

up

earch 30 (2009) 13131324(less than 50 cm thick). Sediment gravity ows are the main

er Fo

s ResUpp

N

Upp

er M

embe

r

Y. Horiuchi et al. / Cretaceoudepositional mode in this member (Horiuchi et al., 2008). Thesedeposits indicate the progradation of alluvial fans.

The Upper Member, which occurs in the southern part of thestudied section and is more than 40 m thick, is characterized bythick conglomeratic sandstone containing volcanic rock fragments.The conglomeratic sandstone, which is massive or contains hori-zontal bedding, is indicative of deposition by high-velocity ow orsediment gravity ow. Paleosols in this member are less developedthan those in the Lower Member, and are commonly covered bysheet sandstones deposited from plane-bed ows. The UpperMember was deposited on the middle part of a sheet-ooding-dominated alluvial fan (Horiuchi et al., 2008). The middle andupper parts of the Upper Member contain several beds of volca-niclastic breccia and conglomerate. In the lower and middle parts,

0

20m

0

red bed mudstonesandstone conglomerfault inferred fault

conglomerate

mudstonesandstone

detailedcolumn

in Fig. 6

Shio

ham

a Fo

rmat

ion

Mid

dle

Mem

ber

Low

er M

embe

r

Upper Wakamiya Formation

Calc

rete

hor

izon

Legends

Fig. 3. Columnar section and rout40

46

4349

Lower Member

Wakamiyarmation

earch 30 (2009) 13131324 1315sandstones show a gradational upward change in color from palegreen to reddish, followed by an abrupt change from reddish to palegreen or grayish. Calcretes are only developed in red-colored layers,which are interpreted as a oodplain paleosol developed on a fansurface, although the calcretes are developed in fewer horizonsthan in the paleosols within the oodplain deposit of the LowerMember.

4. Occurrence of calcretes

Paleosols in the Shiohama Formation are characterized byabundant calcretes. Lee and Hisada (1997, 1999) suggested that thecalcretes observed in the Shiohama Formation are pedogenic inorigin, based on the following observations: (1) the presence of

43

100

9080

70

60

50

40

30

20

47

46

35

Middle Member

Upper Member

Ajironohana50 m

ateconglomeratic sandstone

strike & dip of bedding plane

strike & dip of fault plane46

e map of the studied section.

Calcretes occur within about 110 horizons in the Shiohama

commonly oriented parallel to bedding in ne-grained sandstone

s Resor mudstone. Most are white to pale red in color. Tables 1 and 2 listthe shape, abundance, and size of calcretes in each horizon, as wellas the distinctness of the boundary between calcrete and the hostmaterial, and the contrast in color between calcrete and hostmaterial. The calcrete horizons are classied into seven types(IVII) based on the abundance and size of calcrete nodules (Fig. 4).Each of these types is briey described below.

The type I horizons are characterized by abundant nodules, andshow layering dened by concentrations of nodules. Nodules rangein size from 5 cm across, although it is sometimes difcultto identify nodule boundaries because they coalesce with eachother to dene individual layers. Type I is developed only in theLower Member.

In calcrete horizons of type II, calcrete is abundant as individualnodules larger than 1 cm across on average. This is the mostcommon type, and differs from type I in that calcrete nodules havea scattered distribution (without dening layers) and their outlinesare distinct. This type occurs in both the Lower and UpperMembers.

Type III is also characterized by abundant small nodules, but isdistinguished from type II based on the size of nodules, beingsmaller than 1 cm across on average. This type occurs only in theFormation in the studied section (Fig. 3). Among these, the calcreteswithin 64 horizons are clearly observable and are described in thisstudy; the other horizons are unsuitable for detailed observationsbecause of poor exposure. Of the 64 studied horizons, 53 (Sh0153)are in the Lower Member and 11 (Sh5464) in the Upper Member.The calcrete horizons are commonly parallel to bedding and areoccasionally truncated by overlying channel sediments. Most ofthese calcretes occur in the oodplain paleosols. The averageinterval between successive calcrete horizons is 20 cm, and thehorizons are generally less than 20 cm thick.

4.2. Mode of occurrence of calcretes

The calcretes in the studied section are nodular in shape and arecalcareous root traces and rhizoliths, (2) poor stratication of thenodule-bearing overbank nes, (3) the presence of purple-coloredhorizons, (4) the diffuse lower boundaries of limestone beds(Esteban and Klappa, 1983; Retallack, 1988), and (5) carbonatenodule- and lens-bearing horizons are cut by overlying channeldeposits. It is generally accepted that calcrete is composed mainlyof calcium carbonate, although there exists no uniform denition ofthe term calcrete in the literature (Quast et al., 2006). The term iscommonly used for carbonates from the vadose zone, but also forgroundwater carbonate precipitated in the phreatic soil zone (e.g.,Wright and Tucker, 1991; Quast et al., 2006; Stokes et al., 2007). Inthe present paper, the term calcrete is used to refer to carbonatenot only from the vadose zone but also from the phreatic soil zone.

The precipitation of carbonate occurs via several mechanisms,including evaporation, evapotranspiration, the degassing of CO2,the common ion effect, and biological activity (Wright and Tucker,1991). Calcrete formation is also inuenced by climate, especiallythe amount of rainfall (Khadkikar et al., 2000; Retallack, 2005).Previous studies have classied calcretes based on theirmorphology, and have reconstructed their stages of development(e.g., Gile et al., 1966; Alonso-Zarza, 2003).

4.1. Distribution of calcrete horizons within the ShiohamaFormation

Y. Horiuchi et al. / Cretaceou1316Lower Member.Type IV horizons contain small numbers of nodules that are>1 cm across on average. Only one horizon of type IV is recognized,in the Upper Member.

Type V horizons also contain relatively few nodules, but differfrom type IV in containing smaller nodules,

s ResTable 1Description of calcretes in the Shiohama Formation

No. type shape distinctness

Sh01 I d very sharpSh02 V rod, disc, irregular diffuse

Y. Horiuchi et al. / CretaceouThis microstructure is observed in most of the calcrete horizons(Table 3). There are two types of cracks in micrite (Khadkikar et al.,2000): those that represent the shrinkage planes of clay mineralsformed by alternating dry and wet conditions, cemented by pore-lling sparite; and channels formed by rootlets, lled with micro-sparite. In the case of the Shiohama Formation, it seems that most

Sh03 I d very sharp, diffuseSh04 I sphere? sharpSh05 I d very diffuseSh06 V sphere, disc sharpSh07 II sphere, disc very diffuseSh08 II irregular, disc very sharpSh09 II irregular very sharpSh10 I irregular sharp-diffuseSh11 III irregular very sharpSh12 II irregular very diffuseSh13 II irregular very diffuseSh14 II sphere, irregular very diffuseSh15 I rod, irregular very diffuseSh16 I irregular, disc sharpSh17 II sphere, irregular diffuseSh18 II sphere, irregular, rod sharpSh19 II irregular, rod sharpSh20 VII d diffuseSh21 III sphere sharp-diffuseSh22 II disc, sphere sharpSh23 II irregular sharp, very diffuseSh24 VII irregular very diffuseSh25 II sphere/irregular diffuseSh26 III irregular, rod, disc sharpSh27 III disc sharpSh28 III irregular-disc sharpSh29 III irregular, rod sharpSh30 III sphere, disc sharpSh31 I disc sharpSh32 III disc, irregular sharp-diffuseSh33 III irregular diffuseSh34 III irregular sharp-diffuseSh35 VII very diffuseSh36 II irregular, sphere diffuseSh37 II disc very sharpSh38 III irregular-sphere sharpSh39 III irregular-sphere diffuseSh40 I d diffuseSh41 I d very diffuseSh42 I d sharpSh43 I sphere very sharpSh44 I d very diffuseSh45 I irregular sharpSh46 I d sharp-diffuseSh47 I sphere sharp-diffuseSh48 I sphere sharp-diffuseSh49 II irregular-rod diffuseSh50 II irregular diffuseSh51 II sphere sharpSh52 I irregular sharp-very diffuseSh53 II irregular-rod diffuseSh54 II disc? very sharpSh55 VI ? very diffuseSh56 II sphere, irregular, rod diffuseSh57 VII sphere, irregular very diffuseSh58 VI ? very diffuseSh59 V sphere, disc, rod very diffuseSh60 II ? very diffuseSh61 II irregular very diffuseSh62 II irregular sharpSh63 II irregular sharpSh64 IV irregular, sphere diffuse

Terms used in this table are listed in Table 2.contrast abundance size

prominent dense 30 cm?prominent sporadic large-medium

earch 30 (2009) 13131324 1317of these cracks originated by the former process, as they containmany offshoots. Sparry-calcite crystals tend to be larger toward theinner parts of the observed cracks. It is known that rapid precipi-tation occurs in cracks in which processes of evaporation anddegassing are enhanced (Wright and Tucker, 1991). Stokes et al.(2007), however, reported sparite and microsparite originating

prominent dense 020 cmprominent dense 010 cmprominent dense 4010 cmprominent sporadic medium-smallmoderate scattered small-largeprominent scattered largeprominent scattered medium-largeprominent dense large-mediumprominent scattered medium-smallprominent scattered large-mediumprominent scattered largemoderate scattered small-largemoderate dense medium-ne/5 cmprominent dense large-mediumprominent scattered medium-largeprominent scattered small-largeprominent scattered small-largeprominent scattered 510 cmprominent scattered small, 05 cmprominent scattered medium-largeprominent scattered medium-large, 010 cmprominent scattered 010 cmprominent scattered small/largeprominent scattered small-largeprominent scattered small-largeprominent scattered medium-largeprominent scattered small-mediumprominent scattered small-mediumprominent dense small-mediumprominent scattered small-mediummoderate scattered small-mediummoderate scattered small-mediummoderate dense 1030 cmprominent scattered large-smallmoderate scattered large-mediummoderate scattered medium-largemoderate scattered medium-largeprominent dense 1015 cmprominent dense 2030 cmprominent dense 020 cmprominent dense mediummoderate dense 015 cmprominent dense large-mediumprominent dense 010 cmprominent dense medium-largeprominent dense medium-largeprominent scattered medium-largeprominent scattered mediumprominent scattered largeprominent dense largeprominent scattered largeprominent scattered largefaint d dprominent scattered medium-largemoderate dense medium, 03 cmfaint d 010 cm?moderate sporadic small-largemoderate scattered large-mediumprominent scattered large-mediumprominent scattered medium-largemoderate scattered medium-largemoderate sporadic medium-large

from groundwater in an alluvial fan setting, and proposed that theearly phase of calcrete formation is characterized by pedogenicprocesses, involving increasing groundwater calcretization overtime.

Returning to the Shiohama Formation, Lee and Hisada (1999)stated that the origin of sparry calcite was different from that of

stable isotope analyses. Hence, the authors inferred that the sparrycalcite was precipitated during a later phase of calcretization, fromdifferent water to that from which the surrounding micrite wasprecipitated.

The micromorphology of calcretes can be classied into two endmembers (alpha and beta) controlled by climate (Wright andTucker, 1991). Beta-type calcretes form by bioactivity, and aredeveloped in semi-arid to sub-humid areas covered by vegetation.In contrast, alpha-type calcretes form by chemical precipitationassociated with evaporation, evapotranspiration, and degassing.Compared with beta-type calcretes, alpha-type calcretes occur inrelatively arid climates with little bioactivity (Wright and Tucker,1991).

The calcretes of the Shiohama Formation show the character-istics of alpha-type calcretes (i.e., dense microfabric, oatingdetrital grains, micronodules, circum-granular cracks, and complexcracks); thus, they are interpreted to have formed under dryconditions with little vegetation cover. In terms of carbonatemorphology, it is generally noted that relatively complex later-stage carbonate horizons contain relict carbonate forms fromearlier stages (Gile et al., 1966). However, the various stagesinvolved in the development of carbonate microstructure remainpoorly understood, because it is difcult to determine the origin ofindividual microstructures, such as micronodules and complexcracks (Alonso-Zarza, 2003). In the Shiohama Formation, themicrostructures of type I calcretes show relatively prominent densemicrofabric, but other microstructures occur in similar proportionsamong the different types of horizons (Table 3). This ndingsuggests that the dense microfabric formed during the develop-ment stage of calcretization. It is inferred that the dense micro-fabrics of type IIVII calcrete were precipitated during the early

Table 2Terms for description of calcretes

Aspect Category Description

shape sphere spherical shapeirregular irregular shapedisc discoidal shaperod rod shape

distinctness very sharp transition to matrix in less than 1 mmsharp transition to matrix over about 1 mmdiffuse transition to matrix over 1-5 mmverydiffuse

transition to matrix over more than 5 mm

contrast faint recognizable only on close inspectionmoderate readily seen, differing by at least two Munsell hues,

chromas or valuesprominent obvious, with hue, chroma or value several Munsell units

apart

abundance sporadic less than 2% of exposed surfacescattered 2-20% of exposed surfacedense more than 20% of exposed surface

size small less than 5 mm in diameter on exposed surfacemedium 5-15 mm in diameterlarge more than 15 mm in diameter(cm) thickness of layer

Y. Horiuchi et al. / Cretaceous Research 30 (2009) 131313241318micrite, which formed by pedogenic processes, as indicated by

type I(Sh04)

(Sh62) (Sh06)

(No.)

IV

sporadic, medium to largenodule

picture

occurrences of calcrete

stratigraphic position

Upper Member

V

dense, coalesced nodule,a single layer

sporadic, small to medium nodule

Lower Member

Lower and Upper Members

Fig. 4. Occurrence of calcretes in the Shistage of calcretization, whereas dense microfabrics of type I

(Sh08) (Sh26)

(Sh35)(Sh58)

III

VII

scattered, small to mediumnodule

partly diffuse, difficult to identify

Lower and Upper Members

II

VI

scattered, medium to largenodule

very diffuse, difficultto identify

Lower and Upper Members

Upper Member

Lower Memberohama Formation, southwest Japan.

grain

s Rescalcrete were precipitated during the early to later stages. Types IIII are commonly observed in the Shiohama Formation. Thus, type Icalcretes represent the last stage of calcretization among theseprominent types IIII. Types II and III contain similar proportions of

Table 3Microstructure of calcretes

No. type dense microfabric oating detrital

Sh01 I A CSh03 I A CSh04 I A CSh05 I A VRSh15 I A VRSh16 I A VRSh31 I C dSh41 I A CSh46 I C CSh47 I A dSh48 I C CSh52 I A ASh07 II C RSh17 II C CSh19 II R dSh23 II A RSh51 II R ASh53 II A ASh62 II VR dSh63 II d dSh27 III R VRSh28 III R CSh29 III C CSh30 III R CSh32 III C CSh34 III C ASh39 III A CSh02 V A ASh06 V R CSh20 VII A C

A: abundant, C: common, R: rare, VR: very rare,d: non-developed.

Y. Horiuchi et al. / Cretaceouvarious microstructures. It is therefore likely that types II and IIIformed during similar stages of the development of calcretes.

6. Repeated Bk horizons in the Shiohama Formation

The oodplain deposit in the Shiohama Formation is charac-terized by the presence of abundant calcrete horizons. Asmentioned above, these calcretes formed by pedogenesis andgenerally occur within a specic horizon in the soil prole. Thishorizon is usually recognized as the Bk horizon in the soil prole.The prole consists (from top to bottom) of the near-surface A,subsurface B (including Bk), and weathered parent material Chorizons. In Fig. 6, the calcrete horizons labeled Sh1441 representthe Bk horizon. The depth to the top of the Bk horizon is generallydependent on the mean annual precipitation: the Bk horizon iscloser to the surface in drier climates (Retallack, 1997, 2005). It isdifcult to identify the paleo-surface at the time when each Bkhorizon formed in the Shiohama Formation, because of the scarcityof surcial root traces and relicts of ped structures, and becausebedding planes are obscured by pedogenesis.

There exists a strong correlation between the thickness of soilbearing carbonate nodules and the mean annual range of precipi-tation (Retallack, 2005). As mentioned above, the thickness of thecalcrete horizon in the Shiohama Formation is usually less than20 cm; accordingly, the mean annual range of precipitation isestimated to be less than about 30 mm. On this basis, it is inferredthat only minor seasonal change occurred in the amount ofprecipitation at the time the Shiohama Formation was deposited.However, wetdry cycles are essential for pedogenesis (Breeckeret al., 2009). High CO2 concentrations during wet periods of theyear are responsible for carbonate dissolution and the mobilizationof Ca, whereas the reduced concentrations of CO2 associated withwarm, dry periods are responsible for carbonate precipitation(Breecker et al., 2009). It has also been noted that the paleoatmo-spheric P was signicantly overestimated in previous studies

s micronodule grain coating complex cracks

VR R CVR VR AC C CC R Rd VR Cd VR Cd d CVR R Ad C CVR VR VRVR VR AVR A CVR VR Cd C CC d dC R CVR A CC A CVR VR Rd d CC VR CR d Cd C CC C dC C VRd VR VRVR C CVR R RC VR VRVR R A

earch 30 (2009) 13131324 1319CO2based on the d13C values of paleosol carbonate (Breecker et al.,2009). Though the paleoatmospheric PCO2 in the ShiohamaFormation has been estimated to be about 17003200 ppmV, basedon the stable isotopic composition of calcretes (Lee and Hisada,1999), this estimation also requires a downward revision.

Paleosols preserved inoodplain deposits are commonly complexdue to spatial and temporal variations in deposition upon theoodplain (Kraus and Aslan, 1993; Kraus, 1996; McCarthy et al.,1997a,b). It is rare that an individual paleosol prolewith a completeABC type horizon sequence is recognized in aggradational regimes(McCarthy et al., 1998). After the formation of the complete ABCtype horizon sequence, subsequent erosion and sedimentation mayoccur, meaning that the new parent material is superimposed on theolder paleosol, and subsequently modied by new pedogenesis. Thispattern of erosion, sedimentation, and soil development may resultin a compound-type prole (e.g., BCBC) or a complex-type prole(e.g., BBBB) (Fig. 7; McCarthy et al., 1997b,1998). Such compoundand complex proles have been reported from several alluvialsections, and have been used to interpret past rates of sedimenttransport, storage, and deposition (McCarthy et al., 1998; Daniels,2003). Such proles are developed within an unstable aggradationsystem subjected to the intermittent inux of sediments and occa-sional erosion (McCarthy et al., 1998).

The oodplain paleosol prole in the Shiohama Formationincludes repeated Bk horizons, corresponding to a complex and/orcompound prole (Fig. 7). Parts of the oodplain deposit containshort intervals of calcrete horizons, whereas other parts containlong intervals marked by erosional surfaces, probably correspond-ing to complex and compound proles, respectively. Thus, it isinterpreted that the oodplain of the Shiohama Formation devel-oped within an unstable aggradation system (Fig. 7).

s ResY. Horiuchi et al. / Cretaceou1320Lee et al. (2003) reported a non-marine sedimentary sequencewith cyclic tuffpaleosol intervals in the Cretaceous Mifune Group,southwest Japan. The sequence shows several cycles of paleosoldevelopment and contains well-developed Bk and clay-rich Bthorizons. The amount of sediment supplied during each cycle in theMifune Group was probably larger than that supplied in the Shio-hama Formation, because in the Mifune Group paleosol formation

Fig. 5. Microstructures of calcretes. A. Dense microfabric and complex cracks (Sh07).B. Floating detrital grains and calcite grain coatings (Sh17). C. Micronodule (Sh03).Scale bar is 1 mm long.calcrete horizonSh41Sh40

earch 30 (2009) 13131324in each overlying cycle did not affect the underlying cycle, thusresulting in the development of compound proles.

7. Pedogenesis in the Shiohama Formation

The 64 calcrete horizons analyzed in the present study werecategorized into seven types (Tables 1 and 2; Fig. 5). Types IVIIcontain 18 (28%), 24 (38%), 12 (19%), 1 (2%), 3 (5%), 2 (3%), and 4 (6%)

1 mSh14Sh15Sh16Sh17

Sh18Sh19Sh20Sh21Sh22Sh23Sh24Sh25Sh26

Sh39

Sh38Sh37

Sh36Sh35Sh34Sh33Sh32Sh31Sh30Sh29Sh28Sh27

ConglomerateSandstoneMudstone

Fig. 6. Example of a oodplain deposit with abundant calcrete horizons in the LowerMember of the Shiohama Formation, southwest Japan.

BB

C

C

BBC

dim

rosioime

dim

rosiime

nt a

s ResB

BBB

A

A

C

C

C C

Sediments

BBBB

AA

C CC

Sediments

soildevelopment

soildevelopment

soildevelopment

erosion + sedimentation

Se

esed

soildevelopment

erosion + sedimentation

Se

esed

Fig. 7. Generation processes of oodplain paleosol proles. Repetition of soil developme

Y. Horiuchi et al. / Cretaceouof the total horizons, respectively (Fig. 8); types IIII are thereforethe dominant types.

Gile et al. (1966, 1981) divided the process of carbonate accu-mulationwithin non-gravellymaterial into four stages based on themorphology of the carbonate horizon: I: few laments or faintcoatings, II: scarce to common nodules, III: many nodules and inter-nodular llings, and IV: laminar horizon overlying a pluggedhorizon. Most of the calcrete horizons in the Shiohama Formationcorrespond to stage II or III (Table 4). Stage III develops from stage IIvia an increase in the number of nodules (Gile et al., 1966, 1981).

We propose two processes of carbonate accumulation in theShiohama Formation, based on the size and abundance of nodules(Fig. 9): VIVIII(II)I and VI(V)IVIII. These processes repre-sent the development of calcrete horizons from the early to latestages of calcretization. Both processes lead to a progressiveincrease in the number of nodules, although with contrastingnodule sizes.

Retallack (2005) examined the relationship between nodule sizeand radiocarbon age, nding that nodule size increases over time.On this basis, it is expected that the size of nodules in the ShiohamaFormation increases from types V to IV and from types III to II.However, it may be unlikely that small nodules form after largenodules, as mixtures of large and small nodules are rarely observedin the Shiohama Formation. It is probable that nodule size iscontrolled by physical factors such as grain size, uniformity ofsorting, sedimentary structures, development of crumb structure,and density of cracks made by roots and organisms, as waterbehavior is important for carbonate precipitation.

The paleosols in the Shiohama Formation formed withinoodplain deposits in an alluvial fan or alluvial plain setting(Horiuchi et al., 2008). The maturity of paleosols in alluvial fan

The differences of these proles are dependent on amount of sediments. Complex procesubsequent pedogenesis, whereas compound one remains erosional surfaces. The prolesproles.B

B

B

A

C

C

C

Time

Time Compound

BA

C

BBBB

Complex

ents

BB

BC

n + ntation

A

soildevelopment

soildevelopment

ents

on + ntation

B

B

B

A

C

C

C

nd erosion sedimentation results in complex (upper) and compound (lower) proles.

earch 30 (2009) 13131324 1321deposits reects factors such as the degree of channel entrench-ment and climate (Wright and Alonso-Zarza, 1990). It is acceptedthat calcrete development upon alluvial fan sediments reectsa marked decrease in detritus supply to a previously sedimenta-tion-dominant part of the fan surface (Wright, 1992). The rela-tionship between detritus supply and soil maturity is the basis ofthe pedofacies concept proposed by Bown and Kraus (1987). Apedofacies is a laterally contiguous body of sedimentary rock thatdiffers from adjacent units in terms of its laterally contiguouspaleosols, reecting differences in the distance to areas of relativelyhigh rates of sediment accumulation (Bown and Kraus,1987). In thecase of a oodplain within an alluvial plain system, immature soilsoccur on the alluvial ridge, whereas the most mature soils occur onthe distal oodplain (Bown and Kraus, 1987). This pedofaciesconcept suggests that the interval between periods of sedimentsupply to the oodplain controls the type of calcrete horizon. In theShiohama Formation, it is possible that type II and III calcretehorizons occur in soils of similar maturity, given the similarity inmicrostructure and timing of development. That is, the intervalsbetween periods of sediment supply to type I horizons are longerthan those between periods of sediment supply to type II and IIIhorizons.

Fig. 8 and Table 1 show the stratigraphic distributions of type IV horizons in the Shiohama Formation. The formation can bedivided into ve units based on the dominant type of calcretehorizon: Sh0105 (dominantly type I), Sh0639 (types II and III),Sh4048 (type I), and Sh4953 (type II) in the Lower Member, andSh5464 (type II) in the UpperMember. The sequence of types I to IIand III horizons observed in the Lower Member representsa repeating pattern in the frequency of sediment supply to theoodplain over time.

ss has less amount of sediments and the original erosional surfaces are modied byof the Shiohama Formation are represented by both types of complex and compound

s ResLower MemberMaturity

highLow

V III

Y. Horiuchi et al. / Cretaceou1322The calcrete horizons in the Upper Member are dominantly typeII, possibly reecting the heterogeneous coarse-grained hostmaterial. The number of calcrete horizons in the Lower and UpperMembers with diffuse to very diffuse distinctness from the hostsediment and moderate to faint contrast with the host sediments is8 (15%) and 6 (55%), respectively (Table 1). In other words,compared with the Lower Member, a higher proportion of the

Legends conglomerate

conglomeratic sandstone

conglomerate

mudstone dominatedsandstone dominated

calc

rete

hor

izon

occ

urr

ence

of c

alcr

etes

IV,

II, I

Fig. 8. Distribution of calcretes horizon types in the Lower and UUpper MemberMaturity

highLow

, V III

earch 30 (2009) 13131324calcretes in the Upper Member have diffuse and low-contrastboundaries with the host sediment. This nding probably reectsthe fact that calcium carbonates percolated and precipitated moreeasily in the pores between grains in the Upper Member than in theLower Member. Calcretes generally formmuchmore rapidly withincoarse-grainedmaterials than in ner materials (Gile et al., 1966). Itis likely that the paleosol in the Upper Member is less mature than

mudstonesandstone

0

20 m

IV II, I

Type

occurrence of calcretes

IIIIIIIVVVIVII

total

1824121324

64

(28.1 %)(37.5 %)(18.8 %)(1.6 %)(4.7 %)(3.1 %)(6.3 %)

the number of horizons

percentage (approx.)

pper Members, the Shiohama Formation, southwest Japan.

s ResTable 4Occurrence mode of calcrete horizons in the Shiohama Formation and its corre-spondence to stage of development in Gile et al. (966, 1981)

type description Gile et al. (1966, 1981)

I dense, coalesced nodule, a single layer stage III or IIII scattered, medium to large nodule stage IIIII scattered, small to medium nodule stage IIIV sporadic, medium to large nodule stage IIV sporadic, small to medium nodule stage IIVI very diffuse, difcult to identify stage IVII partly diffuse, difcult to identify stage II or III?

Y. Horiuchi et al. / Cretaceouthat in the Lower Member. Accordingly, it is concluded that sedi-ment was supplied more frequently to the oodplain of the UpperMember than to that of the Lower Member.

8. Conclusions

The paleosols in the Shiohama Formation are characterized byabundant calcretes. It is inferred that deposition of the ShiohamaFormation was accompanied by minor seasonal changes in precip-itation, as deduced fromthe thicknesses of the calcretehorizons. Theoodplain paleosol proles in the Shiohama Formation arecompound and complex types. Based on these proles, it is inferredthat the oodplain was part of an unstable aggradation system

I

IIIII

IVV

VI

Num

ber o

f nod

ules

Size of nodules

Fig. 9. Occurrence modes of calcretes of the Shiohama Formation and its developmentprocess. Solid-white and bold arrows show nodule formation and increase the numberof nodules, respectively. Middle arrows from left to right show increase the size ofnodules.subjected to intermittent inuxesof sediments andperiodic erosion.The size and abundance of nodules indicates two processes ofcarbonate accumulation in the Shiohama Formation. The paleosol inthe Lower Member of the formation shows repeated patterns ofchange in maturity, reecting repeated changes in the rate of sedi-ment supply to theoodplain. The paleosols in theUpperMemberofthe formation are less mature than those in the LowerMember, andthe rate of sediment supply to the oodplain of the Upper Memberwas higher than that to the oodplain of the Lower Member.

Acknowledgements

The rst author (Y.H.) is grateful to Prof. Kenshiro Ogasawaraand Dr. Isao Motoyama of the University of Tsukuba for theirvaluable suggestions, to Dr. Tatsuo Hamano (University ofTokushima) and Dr. Hoi Jeong Yang (Gwacheon National ScienceMuseum, Korea) for assistance in the eld, and toMr. YongWoo Leefor providing helpful advice during laboratory work. We thankDr. Hidetoshi Hara and Dr. Koichi Okuzawa for correcting an earlyversion of the manuscript. Y.I. Lee was supported by a grant fromKOSEF (R01-2008-000-20056-0).

References

Alonso-Zarza, A.M., 2003. Palaeoenvironmental signicance of palustrine carbon-ates and calcretes in the geological record. Earth Science Reviews 60, 261298.

Bown, T.M., Kraus, M.J., 1987. Integration of channel and oodplain suites: I.Development sequence and lateral relations of alluvial paleosols. Journal ofSedimentary Petrology 57, 587601.

Breecker, D.O., Sharp, Z.D., McFadden, L.D., 2009. Seasonal bias in the formation andstable isotopic composition of pedogenic carbonate in modern soils fromcentral New Mexico, USA. Geological Society of America Bulletin 121, 630640.

Daniels, J.M., 2003. Floodplain aggradation and pedogenesis in a semiarid envi-ronment. Geomorphology 56, 225242.

Esteban, M., Klappa, C.F., 1983. Subaerial exposure environments. In: Scholle, P.A.,Bebout, D.G., Moore, C.H. (Eds.), Carbonate Depositional Environments, vol. 33.American Association of Petroleum Geologists Memoir, Tulsa, OK, pp. 196.

Gardner, R.A.M., McLaren, S.J., 1994. Variability in early vadose carbonate diagenesisin sandstones. Earth-Science Reviews 36, 2735.

Gile, L.H., Peterson, F.F., Grossman, R.B., 1966. Morphological and genetic sequencesof carbonate accumulation in desert soils. Soil Science 101, 347360.

Gile, L.H., Hawley, J.W., Grossman, R.B., 1981. Soils and geomorphology in the Basinand Range area of southern New MexicodGuidebook to the Desert Project.New Mexico Bureau of Mines and Mineral Resources, Memoir 39, 222 p.

Given, K.R., Wilkinson, B.H., 1985. Kinetic control of morphology, composition andmineralogy of abiotic sedi-mentary carbonates. Journal of SedimentaryPetrology 55, 109119.

Goudie, A.S., 1983. Calcrete. In: Goudie, A.S., Pye, K. (Eds.), Chemical Sediments andGeomorphology. Academic Press, London, pp. 93131.

Hase, A., 1958. The Stratigraphy and Geologic Structure of the Late MesozoicFormations in Western Chugoku and Northern Kyushu. Geological report of theHiroshima University 6, 150 [in Japanese, English abstract].

Hase, A., 1960. The Late Mesozoic Formations and their Molluscan Fossils in WestChugoku and North Kyushu, Japan. Journal of Science of Hiroshima UniversitySeries C 3, 281342.

Horiuchi, Y., Hisada, K., Lee, Y.I., 2008. Paleosol, Facies and Paleoenvironment of theCretaceous Shiohama Formation, Kanmon Group, SW Japan. Journal of theGeological Society of Japan 114, 447460 [in Japanese, English abstract].

Imaoka, T., Nakajima, T., Itaya, T., 1993. K-Ar ages of hornblendes in andesite anddacite from the Cretaceous Kanmon Group, Southwest Japan. Journal ofMineralogy, Petrology and Economic Geology 88, 265271.

James, N.P., Choquette, P.W., 1984. Diagenesis 9. Limestonesdthe meteoric diage-netic environment. Geoscience Canada 11, 161194.

Khadkikar, A.S., Chamyal, L.S., Ramesh, R., 2000. The character and genesis of cal-crete in Late Quaternary alluvial deposits, Gujarat, western India, and itsbearing on the interpretation of ancient climates. Palaeogeography, Palae-oclimatology, Palaeoecology 162, 239261.

Kraus, M.J., 1996. Alluvial deposits in lower Eocene alluvial rocks, Bighorn Basin,Wyoming. Journal of Sedimentary Research 66, 354363.

Kraus, M.J., 1997. Lower Eocene alluvial paleosols: pedogenic development, strati-graphic relationships, and paleosol/landscape associations. Palaeogeography,Palaeoclimatology, Palaeoecology 129, 387406.

Kraus, M.J., Aslan, A., 1993. Eocene hydromorphic paleosols: signicance for inter-preting ancient oodplain processes. Journal of Sedimentary Petrology 63,453463.

earch 30 (2009) 13131324 1323Lee, Y.I., Hisada, K., 1997. Characteristics of alluvial deposits and paleosols of theCretaceous Shimonoseki Subgroup in Yoshimi area, westernmost Honshu,

Japan. Annual Report of the Institute of Geoscience, University of Tsukuba 23,2933.

Lee, Y.I., Hisada, K., 1999. Stable isotopic composition of pedogenic carbonates of theEarly Cretaceous Shimonoseki Subgroup, western Honshu, Japan. Palae-ogeography, Palaeoclimatology, Palaeoecology 153, 127138.

Lee, Y.W., Lee, Y.I., Hisada, K., 2003. Paleosols in the Cretaceous Goshoura andMifune groups, SW Japan and their paleoclimate implications. Palaeogeography,Palaeoclimatology, Palaeoecology 199, 265282.

Longman, M.W., 1980. Carbonate diagenetic textures from near-surface diageneticenvironments. AAPG Bulletin 64, 461487.

Matsumoto, T., 1951. The Yezo Group and the Kwanmon Group. The Journal of theGeological Society of Japan 57, 9598 [in Japanese, English abstract].

McCarthy, P.J., Martini, I.P., Leckie, D.A., 1997a. Anatomy and evolution of a LowerCretaceous alluvial plain: sedimentology and paleosols in the upper BlairmoreGroup, southwestern Alberta, Canada. Sedimentology 44, 197220.

McCarthy, P.J., Martini, I.P., Leckie, D.A., 1997b. Pedosedimentary history andoodplain dynamics in the Lower Cretaceous upper Blairmore Group, south-western Alberta, Canada. Canadian Journal of Earth Sciences 34, 598617.

McCarthy, P.J., Martini, I.P., Leckie, D.A., 1998. Use of micromorphology for inter-pretation of complex alluvial paleosols: examples from the Mill Creek Forma-tion (Albian), southwestern Alberta, Canada. Palaeogeography,Palaeoclimatology, Palaeoecology 143, 87110.

Miall, A.D., 1996. The geology of uvial deposits: sedimentary facies, basin analysisand petroleum geology. Springer Verlag, New York, 582 p.

Miki, T., 1992. Sedimentologic and paleoclimatic classication of Cretaceous redbeds in East Asia: a general view. Journal of Southeast Asian Earth Sciences 7,179184.

Miki, T., Nakamuta, Y., 1997. Sedimentary petrography of Cretaceous red beds inCentral Kyushu, Japan. Memoirs of the Geological Society of Japan 48, 110119.

Murakami, N., 1985. Late Mesozoic to Paleogene igneous activity in West Chugoku,Southwest Japan. Journal of the Geological Society of Japan 91, 723742 [inJapanese, English abstract].

Okada, H., Sakai, T., 1993. Nature and development of Late Mesozoic and EarlyCenozoic sedimentary basins in southwest Japan. Palaeogeography, Palae-oclimatology, Palaeoecology 105, 316.

Quast, A., Hoefs, J., Paul, J., 2006. Pedogenic carbonates as a proxy for palaeo-CO2 inthe Palaeozoic atmosphere. Palaeogeography, Palaeoclimatology, Palaeoecology242, 110125.

Retallack, G.J., 1988. Field recognition of paleosols. In: Reinhardt, J., Sigleo, W.R.(Eds.), Paleosols and Weathering through Geologic Time: Principles andApplications. Geological Society of America, pp. 120. Special Paper no. 216.

Retallack, G.J.,1997. A colour guide to paleosols. JohnWiley and Sons, Chichester,175 p.Retallack, G.J., 2001. Soils of the past. An Introduction to Paleopedology. Blackwell,

Oxford, 404 p.Retallack, G.J., 2005. Pedogenic carbonate proxies for amount and seasonality of

precipitation in paleosols. Geology 33 (4), 333336.Ruhe, R.V., 1965. Quaternary paleopedology. In: Wright, H.E., Frey, D.G. (Eds.),

The Quaternary of the United States. Princeton University Press, New Jersey,pp. 755764.

Sakai, T., Okada, H., 1997. Sedimentation and tectonics of the Cretaceous sedi-mentary basins of the Axial and Kurosegawa Tectonic Zones in Kyushu, SWJapan. Memoirs of the Geological Society of Japan 48, 728.

Stokes, M., Nash, D.J., Harvey, A.M., 2007. Calcrete fossilisation of alluvial fans in SESpain: the roles of groundwater, pedogenic processes and fan dynamics incalcrete development. Geomorphology 85, 6384.

Tandon, S.K., Friend, P.F., 1989. Near surface shrinkage and carbonate replace-ment processes, Aran Cornstone Formation, Scotland. Sedimentology 36,11131126.

Tandon, S.K., Gibling, M.R., 1997. Calcretes at sequence boundaries in UpperCarboniferous cyclothems of the Sydney Basin, Atlantic Canada. SedimentaryGeology 112, 4367.

Ueda, Y., 1957. Geology of the Shimonoseki district with special reference to theKwanmon Group. Journal of the Geological Society of Japan 63, 2634 [inJapanese, English abstract].

Wieder, M., Yaalon, D.H., 1982. Effect of matrix composition on carbonate modulecrystallisation. Geoderma 11, 95121.

Wright, V.P., 1986. The role of fungal biomineralization in the formation of earlyCarboniferous soil fabrics. Sedimentology 33, 831838.

Wright, V.P., 1992. Paleopedology: stratigraphic relationships and empirical models.In: Martini, I.P., Chesworth, W. (Eds.), Weathering, Soils and Paleosols. Elsevier,Amsterdam, pp. 475499.

Wright, V.P., Alonso-Zarza, A.M., 1990. Pedostratigraphic models for alluvial fandeposits: a tool for interpreting ancient sequences. Journal Geological SocietyLondon 147, 810.

Wright, V.P., Tucker, M.E.,1991. Calcretes: an introduction. In:Wright, V.P., Tucker, M.E.(Eds.), Calcretes. IAS Reprint Series, vol. 2. Blackwell, Oxford, pp. 122.

Y. Horiuchi et al. / Cretaceous Research 30 (2009) 131313241324

Paleosol profiles in the Shiohama Formation of the Lower Cretaceous Kanmon Group, Southwest Japan and implications for sediment supply frequencyIntroductionGeological settingStratigraphy and depositional environmentsOccurrence of calcretesDistribution of calcrete horizons within the Shiohama FormationMode of occurrence of calcretes

Microstructure of calcretesRepeated Bk horizons in the Shiohama FormationPedogenesis in the Shiohama FormationConclusionsAcknowledgementsReferences