Sequence Stratigraphic Analysis of the Mixed Siliciclastic-Carbonate Sediments (Middle Jurassic) of...

GEOLOGICAL SOCIETY OF INDIA SPECIAL PUBLICATIONNo. 1, 2013, pp.57-77

Sequence Stratigraphic Analysis of the

Mixed Siliciclastic-Carbonate Sediments (Middle Jurassic)

of the Patcham Island, Kachchh, Western India:

An Ichnological Approach

SATISH J. PATEL1, JAQUILIN K. JOSEPH

1 and NISHITH Y. BHATT2

1Department of Geology, The M. S. University of Baroda, Sayajiganj, Vadodara - 390 0022Department of Geology, M.G. Science Institute, Navrangpura, Ahmedabad - 380 009

E-mail: [email protected]

Abstract : The Middle Jurassic (Bajocian to Callovian) sequence of the Patcham Island, Kachchh, comprises mixed siliciclastic-carbonate sediments displaying transgressive-regressive cycles that record changes in the relative sea level condition. Thesemixed siliciclastic carbonate sediments are of varying composition representing six sedimentary facies namely, micritic sandstone,allochemic sandstone, sandy allochem limestone, sandy micrite, muddy micrite, and micritic mudrock along with the greyshale, allochemic limestone and ferruginous sandstone facies. These sedimentary facies are bioturbated with a total of 65ichnospecies of 42 ichnogenera which are recurring throughout the sequence. The trace fossils are further grouped into ninetrace fossil assemblages based on environmentally related traces based on diversity, frequency and preservational aspects (viz.,Arenicolites, Asterosoma, Gyrochorte, Ophiomorpha, Planolites/Palaeophycus, Phycodes, Rhizocorallium, Skolithos andThalassinoides assemblages). The sedimentary units (packages) coupled with ichnoassemblages reveal three transgressive systemtracts (TST) and four regressive system tracts (RST) separated by flooding surfaces representing 3rd order transgressive-regressive(T-R) cycles bounded by regressive surfaces. In the T-R cycle, presence of the Rhizocorallium ichnoassemblage (TRC-II) andArenicolites, Thalassinoides with Planolites-Palaeophycus assemblages (TRC-III) mark the flooding surfaces while the Skolithos

assemblage with the Planolites-Palaeophycus assemblage (TRC-I), Arenicolites assemblage (TRC-II) and Planolites-

Palaeophycus assemblage (TRC-III) mark the regressive surfaces. These soft ground ichnoassemblages mark the Skolithos andCruziana ichnofacies conditions developed in progradational and retrogradational sequences and indicate cyclic changes inbathymetry within shoreface-offshore settings. An integrated sedimentological and ichnological approach has allowed therecognition of the internal organization of the sequence in absence of significant physical expressions of discontinuity surfacesat the T-R cycle scale.

Keywords: Sequence stratigraphy, mixed siliciclastic-carbonate, Patcham Island, Kachchh, India.

INTRODUCTION

The Kachchh basin, situated at the western margin ofthe Indian plate, opened into the Malagassy Gulf, a southernextension of the Tethyan Ocean during Jurassic time (Fürsichet al, 2004). The sedimentation started in the basin during theMiddle Jurassic and reached up to 750m in thickness, whichwas exposed as the six uplifts of the Kachchh basin during theTertiary. The Patcham Island (Fig.1) is part of the island beltregion, which was uplifted along with the other highlands ofthe basin (Biswas, 1977). This Island represents the earlyMiddle Jurassic (i.e., Bajocian) sediments of the Kachchh basin(Fürsich et al., 2004).

The concept of sequence stratigraphy, originallydeveloped by the Exxon research group in the 1980s (e.g.,Baum and Vail, 1988; Donovan et al., 1988; Haq et al., 1987;Loutit et al., 1988) emerged as an important tool over the pastfew years and the integrated studies on the sedimentologicaland ichnological aspects have helped immensely inunderstanding the depositional environment (MacEachern etal., 2007). Although various workers have worked on thepalaeontological aspects in the Mesozoic rocks of the Kachchhbasin (Pandey and Fürsich 1993, 1998; Fürsich and Heinze1998; Fürsich et al., 2000; Jaquilin et al., 2012), these studiesare only based on the sequence stratigraphy of the UpperJurassic-Lower Cretaceous based on the shell concentrations

GEOL. SOC. INDIA, SPEC. PUBL. No. 1, 2013

58 SATISH J. PATEL AND OTHERS


(Fürsich and Pandey, 2003) and the Middle Jurassic of KuarBet based on the ichnological aspects (Patel et al., 2010).Detailed sequence stratigraphic studies of the Middle Jurassicrocks of the Patcham island have not yet been attempted.

The present study focuses on understanding thesignificance of trace fossil assemblages within thetransgressive-regressive cycles and to analyze the sedimento-logical-ichnological aspects in order to determine thedepositional environment and sea level changes during theMiddle Jurassic period in the Kachchh Basin. This integratedstudy helps in enhancing and refining the schematicrepresentation of the transgressive and regressive cycles inthe T-R sequence stratigraphic paradigm.

GEOLOGICAL FRAMEWORK

The Kachchh basin began rifting along the Delhi trendduring the Late Triassic (Kosal, 1984) and is also related tothe breakup of eastern Gondwanaland from westernGondwanaland in the Late Triassic/Early Jurassic (Norton andSclater, 1979). This rifting resulted into the inundation of theTethyan Sea into the Kachchh basin (Fürsich et al., 2004),which later initiated the marine sedimentation during theBajocian or possibly Alenian time (Pandey and Dave, 1993)and continued until the basin filled up during the Cretaceous(Biswas, 1977). During the Tertiary period, tectonic activityof the Mesozoic sediments exposed six major uplifts of the

Kachchh basin, including the Island belt (Biswas, 1977).Patcham Island is the westernmost island of this island beltregion, separated from the Mainland of Kachchh by the banniplain. It exposes the oldest sedimentary rocks of Bajocian toCallovian age of the Mesozoic era and Miocene sedimentsfringe the border of the island (Biswas, 1977).

Lithostratigraphically, the Mesozoic rocks of the PatchamIsland are divided into two Formations: Lower, KaladongarFormation and Upper, Goradongar Formation (Biswas, 1977).Accordingly, the Kaladongar Formation is further subdividedinto three members, namely, Dingy Hill member, KaladongarSandstone member and Babia Cliff Sandstone member. TheGoradongar Formation is subdivided into four members;Goradongar Flagstone member, Gadaputa Sandstone member,Raimalro Limestone member and Modar Hill member.

METHODS AND MATERIALS

Ten localities were analyzed for this study: the ChapparBet, Dingy Hills, Kuran village, Babia cliff, Modar Hill, andHills near the villages of Juna, Tuga, Paiya and Dhorawar,and the Raimalro Hills of the Patcham Island (Fig. 1). Theselocalities were studied, described and measured and a lithologof each section prepared along with their physical, biologicaland biogenic entities. The samples were collected bed-by-bedand the trace fossils observed, photographed and collectedwherever possible. The lithologs of different sections were

Fig. 1. Location and geological map of the study area

SEQUENCE STRATIGRAPY OF MIXED SILICICLASTIC-CARBONATE SEDIMENTS 59


correlated and a composite litholog was generated for the wholeisland. The petrographic and ichnological analyses of thesediments were carried out in order to identify the nature ofsedimentary deposits, ichnoassemblages, ichnofacies and thedepositional environment. This dataset was subjected tosequence stratigraphic analysis to evaluate the depositionaltrends, stratigraphic surfaces and sedimentary cycles and theirrelationship with the observed ichnoassemblages (Fig. 2). Ageneralized schematic diagram depicting the sequencestratigraphic sequences of the Patcham Island was produced.

FACIES AND TRACE FOSSIL DISTRIBUTION

The Kaladongar and Goradongar Formations are exposedalong the northern cliff of the Kaladongar Hill and theGoradongar Hill ranges. These sequences display vertical aswell as the lateral variations exhibited by sedimentarycharacteristics (textures and structures) and bedform geometry.The field observation and the petrographic study reveal thatthe sequence comprises of mixed siliciclastic-carbonatesediments intercalated with shales, sandstones, limestones andconglomerates. The sandstones, carbonates and the mixedsiliciclastic-carbonate sediments are classified based on Dott(1964), Folk (1959) and Mount (1985). These mixed sedimentscontain varying proportions of siliciclastic and carbonatematerials which are categorized on the basis of fourcomponents: (1) siliciclastic sands (sand-sized quartz, feldspar,etc); (2) mud (mixture of silt and clay); (3) allochems(carbonate grains such as peloids, ooids, bioclasts andintraclasts > 20µm in size); and (4) carbonate mud or micrite(< 20µm in size). A total of ten sedimentary facies wereidentified, including a) six mixed siliciclastic-carbonate faciesnamely, micritic sandstone, allochemic sandstone, sandyallochem limestone, micritic mudrock, sandy micrite andmuddy micrite; and b) ferruginous sandstone, allochemiclimestone, grey shale and conglomerate facies (Fig. 2). Eachof the sedimentary facies is briefly described along with itsphysical, biogenic and petrographic characters (Table.1).

In the studied sedimentary successions of the PatchamIsland, the majority of the succession consists of mixedsiliciclastic-carbonate sediments, which contain varyingproportions of trace fossils. A total 65 ichnospecies of 42ichnogenera are identified and their frequency is marked ineach member of the Kaladongar and Goradongar Formations(Table 2). At certain levels, these trace fossils are recurring,but their proportions, diversity and density vary. Trace fossilsare further classified according to ichnofossil associations andnamed based on the most dominant ichnofossils. Nineichnoassemblages can be distinguished namely, Skolithos,

Arenicolites, Ophiomorpha, Planolites-Palaeophycus,

Thalassinoides, Gyrochorte, Asterosoma, Phycodes andRhizocorallium assemblages. The trace fossil assemblages aredescribed with respect to their T-R cycles and the utility ofichnoassemblages in identifying sequence surfaces is discussedin section 5.

SEQUENCE STRATIGRAPHY

The elevation of the stratigraphic surface to sequenceboundary is attempted for the relatively conformablesuccession of the Patcham Island, and hence, a modeldependent workflow is considered for sequence stratigraphicanalysis (Catuneanu et al., 2009). The exposed sequence is+462 m thick and mainly consists of a relatively conformablesuccession of mixed siliciclastic-carbonate sediments. It alsodisplays cyclic patterns of shallow marine deposits, whichformed in the upper shoreface to offshore region. The thicksuccession also indicates the high rate of subsidence followedby intermittent tectonic quiescence, which has createdaccommodation space for basin-fill (Martins-Neto andCatuneanu, 2010). The tectonic quiescence further invokedby the eustatic sea-level changes in space createdaccommodation for sediments of respective levels (high/low).For this reason, transgressive-regressive (T-R) sequences,proposed by Embry and Johannessen (1992) and Catuneanuet al., (2009) are used to define the sequential filling of thispart of the Kachchh basin. Based on the stratigraphicarchitecture of this succession, four asymmetrical shallowingand deepening upward T-R cycles were identified. Each cycleconsists of two parts: 1. Transgressive system tract (TST),characterized by low terrigenous influx and high carbonateproductivity that marked an increase in the accommodationspace. 2. Regressive system tract (RST) characterized by highterrigenous influx and low-carbonate productivity marked bya decrease in the accommodation space and separated by theflooding surfaces.

Transgressive Regressive Cycle (TRC) - I

The TST deposits of the T-R cycle-I are not observed inthe sequence, which may be either due to the erosion of thethin transgressive bed, or may be undifferentiated from theobserved RST-I or present in the subsurface.

RST-I: The Regressive system tract-I is characterizedby the +76.35m thick coarsening and shallowing upwardsedimentary cycles consisting of mixed siliciclastic-carbonatesequence of the Dingy Hill member (Fig. 2a) of the KaladongarFormation. These sediments contain common trace fossils likeArenicolites, Chondrites, Daedalus, Didymaulichnus,

Gyrochorte, Lockeia, Monocraterion, Ophiomorpha,

Planolites, Palaeophycus, Phoebichnus, Protovirgularia,



(2a)

Fig. 2a, b & c. Composite litholog shows the sedimentary facies and occurrence of trace fossils, the extent of trace fossil assemblages andtransgressive-regressive cycles. (Legend continued in 2a and 2b).



(2b)




(2c)


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Table 1. Sedimentary facies, sedimentology and characteristics trace fossils of Patcham Island

FerruginousSandstone

AllochemicSandstone

MicriticSandstone

MicriticMudrock

SandyAllochemicLimestone

Red to brown coloredferruginous Sandstone;X cross bedded and ripples.

Pale to dark brown colored;X-bedded & ripple marks.

Brown to red colored, finegrained fossiliferous &bioturbated; X-bedding,planar laminations &linguoid ripple mark;occasionally corals, fossilwood & fossil bones

Yellow to brown colored;planar laminations.

Dark brown to black colored,highly fossiliferous &bioturbated; planarlaminations.

SedimentaryCharacteristics Petrography Trace fossils

Facies

Quartz (95-98%),

feldspar (0-2%)

Quartz (65-70%), Calcite(7-10%), Feldspar (2-5%),Mica (0-1%) withAllochems - (10-15%)consisting of bioclastpellets, corals and algae ina Micritic matrix (5-10%)

Quartz (80-82%),Feldspar (3-5%),Recrystallized calcite (2-5%), Allochems (0-5%)Micrites (8-10%)

Quartz (60-65%) Calcite(2-5%) Allochems (0-5%)consisting of oolites,pellets and algae inmicritic matrix (25-30%)

Quartz (25-30%) Calcite(20-25%) Allochems (30-35%) like bioclasts;oolites; pellets andforaminifers in a sparrymatrix (15-20%)

Arenicolites carbonarius, Asterosoma radiciforme, Beaconites coronus,

Bifungites isp, Circulichnus montanus, Cochlichnus isp, Dactylophycus

isp, Didymaulichnus lyelli, Diplocraterion parallelum, Gordia arcuata,

Gyrochorte comosa, Gyrolithe isp, Hartsellea sursumramosa,

Ichnocumulus isp, Lockeia siliquaria, Margaritichnus, Ophiomorpha

nodosa, Palaeophycus alternates P. striatus, P. tubularis, Phoebichnus

trochoides, Phycodes palmatum, Pilichnus isp, Planolites beverleyensis,

Plug shaped form, Protovirgularia dichotoma, P. isp, Rhabdoglyphus

isp, Rhizocorallium jenense, R. irregularre,, Skolithos linearis,

Taenidium serpentinum, Thalassinoides suevicus, T. horizontalis, T. isp,& Walcottia devilsdingli

Arenicolites carbonarius, A. statheri, Chondrites targionii, Gyrochorte

comosa, Laevicyclus isp, Lockeia amygdaloides, L. siliquaria,

Monocraterion tentaculatum, Ophiomorpha nodosa, Palaeophycus

striatus, P. tubularis, Planolites beverleyensis, Protovirgularia

dichotoma, Rhizocorallium jenense, R. irregularre, Skolithos linearis,

Taenidium serpentinum & Thalassinoides suevicus.

Arenicolites carbonarius, Asterosoma radiciforme, Didymaulichnus

lyelli, Diplocraterion parallelum, Gyrochorte comosa, Lockeia

siliquaria, Phycodes palmatum, Planolites beverleyensis,

Rhizocorallium jenense, R. irregulare, & Thalassinoides suevicus

Arenicolites carbonarius, A statheri, Chondrites intricatus, Daedalus

verticalis, Diplocraterion parallelum, Gordia arcuata, Gyrochorte

comosa, Lockeia siliquaria, Monocraterion tentaculatum, Nereites

missourienses, Ophiomorpha nodosa, Palaeophycus tubularis, P. isp,

Phoebichnus trochoides, Phycodes palmatum, Planolites beverleyensis,

Rhizocorallium irregularre, Scolicia prisca, S.isp, Skolithos linearis,

& Thalassinoides suevicus.

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Sandy Micrite

MuddyMicrite

AllochemicLimestone

Grey Shale

Conglomerate

SedimentaryCharacteristics Petrography Trace fossils

Facies

Arenicolite statheri, A. carbonarius, Aulichnites parkerensis,

Beaconites coronus, Bichordites isp., Cochlichnus isp. Diplocraterion

parallelum, Gyrochorte comosa, Helicolithus isp. Ophiomorpha

nodosa, Planolites beverleyensis, Rhizocorallium jenense, R.

irregularre, Rodoglyphus modari, Skolithos linearis, Taenidium baretti

& T. serpentinum

Arenicolites carbonarius, Beaconites coronus, Chondrites targionii,

Ophiomorpha nodosa, Paleophycus tubularis, Planolites beverleyensis,

Rhizocorallium irregularre, Skolithos linearis, Taenidium baretti & T.

satanassi

Arenicolites carbonarius, Gyrochorte comosa, Laevicyclus isp,

Lockeia siliquaria, Palaeophycus tubularis, Planolites

beverleyensis, Rhizocorallium irregularre, R. jenense,

Thalassinoides suevicus

Planolites beverleyensis & Rhizocorallium irregularre

Quartz (35-40%) Calcite(2-5%) with allochems(5-10%) consisting of thepellets and bioclasts inmicritic matrix (50-55%)

Quartz (35-40%) Calcite(4-8%) grains in amicritic matrix (55-60%)and devoid of allochems

Brown to light browncolored, medium grained,bioturbated but poorlyfossiliferous.

Light brown to browncolored, very fine grained,hard, poorly fossiliferous &bioturbated.

Yellowish to dark browncolored, highlyfossiliferous & bioturbatedlimestone.

Dark to light grey color todull yellowish colored,poorly bioturbated shale.

Grey, brownish & blackcolored embedded by subangular quartz grains, flatpebbles of lithoclasts, largebroken pieces of bivalves &fossil wood.

Table 1. Continued .....



Table 2. Trace fossil frequency in the Middle Jurassic rocks of the Patcham Island (VR-very rare, < 3 specimen; R-rare, when 3-9 specimen; C-common, 10-25 specimen and A-abundant, >25 specimen)



Rhizocorallium, Skolithos, and Thalassinoides. The lower partof the RST-I consists of an intercalated micritic sandstone-shale sequence characterized by mainly horizontal traces ofChondrites and Planolites, Palaeophycus, Rhizocorallium. Theupper part of this interval is marked by FS-Ii (Fig. 2a) andvertical structures like Arenicolites, Monocraterion, Skolithos,

and Thalassinoides. The upper part of the RST-I consists ofmassive thick micritic sandstones with abundant burrows ofSkolithos and Ophiomorpha with few horizontal structures ofPlanolites and Protovirgularia. These sediment characteristicsand trace fossils of RST-I mark a gradual upward shallowingfrom middle to upper shoreface environments. Late regressiveconditions are represented by the amalgamated micriticsandstone bed, which records aggradational condition in theregressive phase. These regressive deposits are separated fromthe transgressive deposits by regressive surface (RS)-Ii, whichmark the maximum regressive surface (MRS)-I in thesuccession (Fig. 2a).

Transgressive Regressive Cycle (TRC) -II

TST-II: The transgressive system tract-II is characterizedby a ~63m thick deepening and fining upward sequence ofmixed siliciclastic carbonate sediments of the Dingy Hillmember of the Kaladongar Formation. The sediments consistof trace fossils such as Nereites, Rhizocorallium and Scolicia.TST-II consists of micritic mudrock and sandy allochem

limestone differentiated by the transgressive surface (TS-II).The percentage of carbonate, including allochems, increasesupwards. Sandy allochem limestone of the TST-II isbioturbated and consists of horizontal crawling traces with afew isolated feeding burrows. The litho units of the TST-IIshow a major transgression in the retrograde deposits. Thesedimentary features and trace fossils suggest a significantchange in bathymetry and indicate the deepening of the basin.Transgressive conditions are represented by retrogradationaldeposits above the regressive phase and the top of the TST-IIis represented by the flooding surface (FS)-IIi (Fig. 2a).

RST-II: Regressive system tract-II is represented by~259m thick coarsening and shallowing upward sequence ofmixed siliciclastic carbonate sediments from the Dingy Hill,Kaladongar Sandstone and Babia Cliff Sandstone membersof the Kaladongar Formation. These sediments containcommon trace fossils like Arenicolites carbonarius,

Asterosoma radiciforme, Beaconites, Berguaria, Cochlichnus,

Dactylophycus, Didymaulichnus lyelli, Diplocraterion

parallelum, Gordia arcuata, Gyrochorte comosa, Halopoa isp,

Lockeia siliquaria, Ophiomorpha nodosa, Planolites

beverleyensis, Palaeophycus tubularis, Phycodes palmatum,

Phoebichnus trochoides, Pilichnus dichotoma, Rhizocorallium

irregulare, Rhizocorallium jenense, Skolithos linearis,

Taenidium, Teichichnus, Thalassinoides horizontalis andThalassinoides suevicus. Sedimentary structures include cross-

Table 2. continued...



bedding and ripple marks in the Dingy Hill and Babia CliffSandstone members. Bivalve and gastropods shells, echinoidstests and their spines are observed in the Babia Cliff Sandstonemember, whereas only bivalve shells are observed in DingyHill and Kaladongar sandstone members.

The onset of the regressive phase is indicated by theflooding surface (FS)-IIi marked by sandy allochem limestone.The initial phase of the RST-II consists of micritic mudrock(silt size quartz ~60%), which progressively changes toallochemic sandstone is overlain by micritic mudrock, the baseof which is marked by RS-IIi. The micritic mudrockprogressively changes to thick micritic sandstone, which showstextural variations and physical structures (e.g., cross-beddingand wave ripples). The micritic sandstone of the Dingy Hillmember marks the stratigraphic surface RS-II(ii- iv) that indicatesthe upward shallowing sequence capped by RST-II which alsoincludes relatively thin beds of sandy allochem limestone,micritic mudrock and muddy micrite with ethologically diversegroups of trace fossils that mark this minor transgressions.The micritic sandstone indicates shoal deposits in theprograding environment of the upper offshore/transitional tomiddle shoreface zone.

Transgressive Regressive Cycle (TRC) –III

TST-III: This cycle is characterized by ~31m thickupward fining and deepening sequence of the Babia CliffSandstone, Goradongar Flagstone, Gadaputa Sandstone andRaimalro Limestone members. These sediments containbivalve shells, echinoid spines and common trace fossils likeArenicolites isp., Arenicolites statheri, Asterosoma radiciforme,

Beaconites coronus, Bifungites, Chondrites intricatus,

Circulichnus montanus, Cochlichnus isp, Diplocraterion

parallelum, Diplocraterion isp, Gyrochorte, Hartsellea

sumsumramosa, Laevicyclus, Lockeia amygdaloides, Lockeia

siliquaria, Ophiomorpha nodosa, Palaeophycus alternatus,

Palaeophycus striatus, Palaeophycus tubularis, Phoebichnus

trochoides, Phycodes palmatum, Pilichnus dichotoma,

Planolites beverleyenis, Protovirgularia dichotoma,

Rhabdoglyphus, Rhizocorallium irregularre, Rhizocorallium

jenense, Skolithos linearis, Taenidium serpentinum,

Thalassinoides horizontalis, Thalassinoides isp,

Thalassinoides suevicus, and Walcottia devilsdingli. Themaximum regressive surface (MRS-II) delineates thetransgressive deposits TST-III from the regressive deposits ofRST-II. The geometry of the beds, sediment characteristicsand presence of trace fossils suggest deposition in the lowershoreface to offshore region. The later phase of TST-III showsmajor retrogradation in the retrogradation-aggradationalsequence and the top allochemic (oolitic) limestone (RaimalroLimestone member) marks the drowning unconformity (DU)-

IIIii /flooding surface (FS)-IIIi, which marks the maximumflooding surface in the 2nd order sequence.

RST-III: This system tract is characterized by a ~74.5m thick upward coarsening and shallowing sequence of mixedsiliciclastic-carbonate rocks with thin bands of ferruginoussandstone and allochemic limestone (Fig. 2 b & c). The mixedsiliciclastic-carbonate sediments are moderately bioturbatedand contain trace fossils (e.g., Rhizocorallium irregularre,

Arenicolites carbonarius, Diplocraterion parallelum,

Planolites beverleyensis, Taenidium serpentinum, Gyrochorte

comosa and Palaeophycus tubularis). The maximum sedimentflux for the regressive part is represented by the siliciclasticsediments (sandstone) at the lower part of the sequence of theModar Hill member, which may indicate a sudden drop of thebase level due to tectonism or eustatic changes. The rise of thebase level or decreased clastic influx is suggested by thelimestone near the top of the regressive sequence RS-IIIi (Fig.2c). These sediments show retrogradation and aggradation inthe major prograding sediments, which suggests theenvironmental influence in the stacking pattern (Potma et al.,2001). The aggradational deposits show ~ 50 m thick micriticsandstone indicative of the intervening sea level stand-still.The top of the prograding RST-III is marked by the maximumregressive surface (MRS-III).

Transgressive Regressive Cycle (TRC) -IV

TST-IV: These systems tract deposits are comprised of~ 15.7 m upward fining intercalated sandy allochem limestone-shale to limestone-shale sequence. The TST-IV records theincrease of carbonate-rich sediments and their increasedthickness in upsection represents the aggradational patternwithin the retrogradation deposits. The allochemic limestonesare devoid of oolites but dominated by bioclastic mudstone/wackestone. This succession marks many flooding surfacesand the top is marked by the flooding surface FS-IVi, whichalso represents the drowning unconformity DU-IVi in thetransgressive sediments of the TST-IV in Patcham Island(Fig. 2c).

RST-IV: Sediments of RST-IV are characterized by ~2.2m of upward coarsening and shallowing mixed siliciclastic-carbonate sediments. The base of this system tract isrepresented by micritic mudrock above the flooding surfaceFS-IVi / Drowning unconformity DU-IVi. The presence ofripple marks and the cross-bedding in the overlying micriticsandstone suggest tidally influenced lower shoreface condition.The top of the RST-IV is represented by sandy micrite, cappedby muddy micrite - a transgressive deposit that may indicatean end of the regressive phase at the surface RS-IVi and anonset of the transgressive phase, which is not observed in thesediments of the Patcham island due to the stratigraphic gap.



IMPLICATIONS OF TRACE FOSSIL

ASSEMBLAGES FOR T-R SEQUENCE

Sequence stratigraphy involves the recognition andinterpretation of genetically related stratigraphic packages ofa variety of scales (Van Wagoner et al., 1990). In recent time,the application of ichnology is focused on sea-level dynamicsin the context of the sequence stratigraphic analysis (Savrda,1991; MacEachern et al., 1992a; Pemberton et al., 1992a;Taylor and Gawthorpe, 1993). Moreover the ichnofaciesconcept of Seilacher (1967) is used for recognizing regionalstratigraphic discontinuities and delineation of stratigraphicsurfaces (Pemberton and MacEachern, 1992).

The ichnoassemblages of the Kaladongar andGoradongar Formations are recurring in time and space, andshow a wide range in their occurrence throughout the sequence.Their development displays substrate controlled ichnofaciesand reflects the response of animal to sea-level dynamics andvarious factors, such as oxygen, substrate condition,bathymetry and nutrient levels. The recurring ichno-assemblages represent the Skolithos and Cruziana ichnofacies,which is comparable to the classical ichnofacies concept ofSeilacher (1967). Although Middle Jurassic deposits of thePatcham Island were deposited in the upper shoreface-offshoreregion, not all are typified by the Skolithos and Cruziana

ichnofacies. The intermittent deposition of sediments showsmixed Skolithos-Cruziana ichnofacies, which is not a part ofthe classical ichnofacies scheme. This mixed kind ofichnofacies indicates a sudden change in energy conditionsand substrate consistency and thus exhibits the developmentof stressed environmental conditions. The ichnoassemblagesdominated by Skolithos or Cruziana ichnofacies proved to begood indicators of bathymetric trends/change within theshoreface to offshore region (Fig.3), and also helped indifferentiating system tracts and stratigraphic surfaces withinthe transgressive-regressive cycles of the Patcham Island. Eachof these ichnoassemblages and their occurrences within theaforementioned four T-R cycles are discussed below from theshallowest to the deepest:

1. Skolithos assemblage: The Skolithos assemblagemostly consists of trace fossils, such as Skolithos

linearis (Fig. 7b & c), Arenicolites carbonarius,

Rhizocorallium irregulare, Planolites beverleyensis,

Beaconites coronus, Circulichnus montanus,

Ophiomorpha nodosa and Rhizocorallium jenense.

The commonly associated trace fossils areDiplocraterion parallelum, Gyrochorte comosa,

Monocraterion tentaculatum, Palaeophycus

tubularis, Palaeophycus striatus, Taenidium

serpentinum (Fig. 7d & e) and Thalassinoides

suevicus. This assemblage is observed in the RST-I in micritic sandstone of the Dingy Hill member,in RST-II in Sandy allochem limestone of theKaladongar Sandstone member, and in RST-IV inmicritic sandstone, sandy micrite and muddy micriteof the Modar Hill member. This is significantlyobserved with regressive phases of T-R cycles I, IIand IV. The presence of this ichnoassemblage inthe Mesozoic successions of the Patcham Islandmarks the regression. It also indicates the high levelof wave or current energy of the tide influencedshoreface environment and shoal deposits of theoffshore region.

2. Arenicolites assemblage: The Arenicolites

assemblage consists of trace fossils, such asArenicolites carbonarius (Fig. 4a), Arenicolites

statheri, Arenicolites isp., Chondrites intricatus,

Chondrites targionii (Fig. 4b & c), Diplocraterion

parallelum, Gyrochorte comosa, Helicolithus

sampelayoi, Ophiomorpha nodosa, Planolites

beverleyensis, Rhizocorallium irregularre,

Rhizocorallium jenense, Skolithos linearis,

Taenidium serpentinum and Thalassinoides

suevicus. This assemblage recurs in the KaladongarFormation in the micritic sandstone but in micriticmudrock of Goradongar Flagstone member,allochemic sandstone of Gadaputa Sandstonemember, sandy allochem limestone of RaimalroLimestone member and sandy micrite and muddymicrite of Modar Hill member in the GoradongarFormation. This assemblage occurs in transgressive,regressive and transgressive deposits of TRC- II,III and IV, respectively. This assemblage indicatesthe high wave and current energy conditions of theshoreface region, whereas the occurrence in thesandy allochem limestone, muddy micrite and sandymicrite indicates the intermittent high and lowenergy events in the subtidal region.

3. Ophiomorpha assemblage: The Ophiomorpha

assemblage is characterized by numerous tracefossils, such as Ophiomorpha nodosa (Fig. 5a &b), Arenicolites carbonarius, Arenicolites statheri,

Aulichnites parkerensis, Beaconites antarcticus,

Beaconites coronus, Bichordites isp, Chondrites

targionii, Circulichnus montanus, Cochlichnus isp,

Diplocraterion parallelum, Gordia arcuata,

Gyrochorte comosa, Helicolithus sampelayoi (Fig.5c), Palaeophycus alternatus, Palaeophycus

striatus, Palaeophycus tubularis, Phoebichnus

trochoides, Phycodes palmatum, Pilichnus

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Fig. 3. An ichnological-sedimentological model for mixed siliciclastic-carbonate sediment dominated shoreface deposits of the middle Jurassic of Patcham Island (Modified afterMacEachern et al., 1999).



Fig. 4. a. Arenicolites isp, Sandy micrite facies, Modar Hill member, Goradongar Formation. Coin diameter = 2.4 cm; b. Chondrites targionii,

Muddy micrite facies, Modar Hill member, Goradongar Formation. Bar scale = 2 cm; c. Chondrites targionii, Micritic sandstone facies,Dingy Hill member, Kaladongar Formation. Coin diameter = 2.4 cm; d. Asterosoma radiciforme, Allochemic sandstone facies, BabiaCliff Sandstone member, Kaladongar Formation. Coin diameter = 2.4 cm; e. Gyrochorte comosa, Allochemic sandstone facies, DingyHill member, Kaladongar Formation. Coin diameter = 2.4 cm; f. Gyrochorte comosa, Sandy allochem limestone facies, Babia cliffsandstone Member, Kaladongar Formation. Coin diameter = 2.4 cm; g. Walcottia devilsdingli, Allochemic sandstone facies, Raimalrolimestone member, Goradongar Formation. Bar scale = 2 cm; h. Walcottia devilsdingli, Allochemic sandstone facies, Dingy Hill member,Kaladongar Formation. Bar scale = 2 cm.



dichotomus, Planolites beverleyensis,

Protovirgularia dichotoma (Fig. 5d),

Rhizocorallium irregulare, Rhizocorallium jenense,

Rodoglyphus isp, Skolithos linearis, Taenidium

baretti, Taenidium satanassi, Taenidium

serpentinum, Thalassinoides horizontalis, andThalassinoides suevicus (Fig. 2). The assemblageoccurs in RST-II in the sandy allochem limestone(Babia Cliff Sandstone member), in TST-III inallochem sandstone (Babia Cliff Sandstone andGadaputa Sandstone members), and in RST-IV inmicritic sandstone, sandy micrite and muddy micrite(Modar Hill member). The presence of thisassemblage indicates tidally influenced high energyconditions where the opportunistic organismscolonized during the regressive cycles.

4. Planolites-Palaeophycus assemblage: ThePlanolites-Palaeophycus assemblage consists oftrace fossils, such as Planolites beverleyensis,

Palaeophycus tabularis (Fig. 6a), Palaeophycus

alternatus (Fig. 6b), Palaeophycus striatus (Fig. 6c),Rhizocorallium irregulare, Lockeia siliquaria (Fig.6d), Skolithos linearis, Cochlichnus montanus,

Ophiomorpha nodosa and Thalassinoides suevicus.

This assemblage occurs in RST-I in the micriticsandstone (Dingy Hill member), in RST-II inallochemic sandstone (Dingy Hill member), sandyallochem limestone (Kaladongar Sandstone

member), allochemic sandstone (Babia CliffSandstone member), in TST-III in limestone ofGoradongar Flagstone member, micritic sandstoneand allochemic sandstone of Gadaputa Sandstonemember, and in sandy allochem limestone andlimestone of Raimalro Limestone member, in RST-III in sandy micrite and micritic sandstone of ModarHill member; and in RST-IV in muddy micrite andsandy micrite of Modar Hill member. Developmentof this ichnoassemblage is very conspicuous andusually associated with repetitive regressive phasesof TRC-I, II, III and IV. This assemblage representsthe transitional zone to a lower shorefaceenvironment and somewhat quieter offshoreconditions, which are probably correlative with thelowest energy levels (Fürsich and Heinberg, 1983).However, the presence of opportunistic structuresof Skolithos linearis and Ophiomorpha nodosa mayindicate intermittent moderate energy conditions inlower shoreface environments.

5. Thalassinoides assemblage: The Thalassinoides

assemblage is characterized by Thalassinoides

suevicus (Fig. 7f), T. horizontalis, andThalassinoides isp., commonly associated withRhizocorallium irregulare, Arenicolites

carbonarius, Planolites beverleyensis,

Rhizocorallium jenense Gyrochorte comosa,

Skolithos linearis, Thalassinoides horizontalis,

Fig. 5. a. Ophiomorpha nodosa, Allochemic sandstone facies, Babia Cliff Sandstone member, Kaladongar Formation. Coin diameter= 2.4 cm;b. Ophiomorpha nodosa, Allochemic sandstone facies, Babia Cliff Sandstone member, Kaladongar Formation. Coin diameter= 2.4 cm; c.

Helicolithus sampelayoi, Sandy micrite facies, Modar Hill member, Goradongar Formation. Coin diameter = 2.5 cm; d. Protovirgularia

dichotoma, Micritic sandstone facies, Dingy Hill member, Kaladongar Formation. Coin diameter = 2.4 cm; e. Phycodes palmatum,

Micritic sandstone facies, Dingy Hill member, Kaladongar Formation. Bar scale = 2 cm; f. Phycodes circinnatum, Micritic sandstonefacies, Dingy Hill member, Kaladongar Formation. Bar scale = 2 cm.



Fig. 6. a. Palaeophycus tubularis, Allochemic sandstone facies, Babia Cliff Sandstone member, Kaladongar Formation. Bar scale = 2 cm; b.

Palaeophycus alternatus, Allochemic sandstone facies, Gadaputa Sandstone member, Goradongar Formation. Bar scale = 2 cm; c.

Palaeophycus striatus, Allochemic sandstone facies, Babia Cliff Sandstone member, Kaladongar Formation. Bar scale = 2 cm; d. Lockeia

siliquaria, Allochem limestone facies, Raimalro Limestone member, Goradongar Formation. Bar scale= 2 cm; e. Rhizocorallium irregularre,

Sandy allochem limestone facies, Kaladongar Sandstone member, Kaladongar Formation. Bar scale = 2 cm; f. Rhizocorallium irregularre,

Sandy allochem limestone facies, Kaladongar Sandstone member, Kaladongar Formation. Coin diameter = 2.4 cm; g. Rhizocorallium

irregularre, Micritic sandstone facies, Kaladongar Sandstone member, Kaladongar Formation. Bar scale = 2 cm; h. Rhizocorallium

jenense, Sandy allochem limestone facies, Dingy Hill member, Kaladongar Formation. Coin diameter = 2.4 cm; i. Beaconites antarcticus,

Sandy micrite facies, Modar Hill member, Goradongar Formation. Coin diameter = 2.4 cm; j. Beaconites coronus, Muddy micrite facies,Modar Hill member, Goradongar Formation. Coin diameter = 2.4 cm; k. Nereites missouriensis, Sandy allochem limestone facies, DingyHill member, Kaladongar Formation. Bar scale = 2 cm; l. Phoebichnus trochoides, Allochem sandstone facies, Gadaputa Sandstonemember, Goradongar Formation. Coin diameter = 2.5 cm.

Palaeophycus striatus and Diplocraterion

parallelum. This assemblage is observed in RST-IIin micritic sandstone (Dingy Hill member); and inTST-III in limestone (Goradongar Flagstone andRaimalro Limestone members), allochemicsandstone (Goradongar Flagstone, GadaputaSandstone and Raimalro Limestone members) and

in sandy allochem limestone (Raimalro Limestonemember). This assemblage crosses theenvironmental gradients and is developed mainlywith vertical structures in the regressive phase andwith horizontal structures in the transgressive phase.The association with dominant horizontal feedingstructures in the transgressive phase suggests low



Fig.7. a. Arenicolites isp. and Rhizocorallium jenense, Micritic sandstone facies, Gadaputa Sandstone member, Goradongar Formation. Coindiameter = 2.4 cm; b. Skolithos linearis, Micritic sandstone facies, Dingy Hill member, Kaladongar Formation. Coin diameter = 2.4 cm;c. Skolithos linearis, Sandy allochem limestone facies, Kaladongar Sandstone member, Kaladongar Formation. Coin diameter = 2.4 cm;d. Taenidium serpentinum, Sandy micrite facies, Modar Hill member, Goradongar Formation. Coin diameter = 2.4 cm; e. Taenidium

serpentinum, Allochemic sandstone facies, Babia Cliff Sandstone member, Kaladongar Formation. Coin diameter = 2.4 cm; f. Thalassinoides

suevicus, Sandy allochem limestone facies, Raimalro Limestone member, Goradongar Formation. Coin diameter = 2.4 cm.

to moderate energy conditions of soft, unconsoli-dated substrate while vertical structures indicate thesoft, unstable unconsolidated substrate of theshoreface environment and the shoal deposits of theoffshore region.

6. Gyrochorte assemblage: The Gyrochorte

assemblage is characterized by trace fossils likeDidymaulichnus lyelli, Gyrochorte comosa (Fig. 4e& f), Planolites beverleyensis, Rhabdoglyphus isp.,and Walcottia devilsdingli (Fig. 4g & h). Sedimentsconsist of micritic mudrock of the Babia CliffSandstone member representing the regressivedeposits of TRC-II and the sandy micrite andallochem limestone of Modar Hill member thatrepresent regressive and transgressive deposits ofthe TRC-III and TRC-IV, respectively. Thisassemblage is typically developed at regressivesurfaces of TRC II. Development of this assemblagesuggests intermediate to low energy conditions ofthe transitional zone between the lower shorefaceand shoreface to low energy offshore regions.

7. Asterosoma assemblage: This assemblage ischaracterized by Asterosoma ludwigae, Asterosoma

radiciforme (Fig. 4d), Gyrochorte comosa,

Phycodes palmatum, Protovirgularia dichotoma,

Rhizocorallium irregulare and Thalassinoides

suevicus. It occurs in the Allochemic Sandstone(Babia Cliff Sandstone member) and allochemlimestone (Goradongar Flagstone member) in TST-II. Recurrence of this assemblage in transgressivephases of T-R cycle II indicates that the sequence isdeveloped in the transition zone between the lowershoreface to upper offshore zone.

8. Phycodes assemblage: This assemblage representsan association of trace fossils including Phycodes

palmatum (Fig. 5e), Phycodes circinnatum (Fig. 5f),Asterosoma ludwigae, Asterosoma radiciforme,

Beaconites coronus, Cochlichnus anguineus,

Gordia arcuata, Gyrochorte comosa, Ophiomorpha

nodosa, Pilichnus dichotomus, Rhizocorallium

irregulare, Rhizocorallium jenense, Scolicia strozzi

and Thalassinoides suevicus. This assemblageshows a predominance of deposit feeders over thesuspension feeders. The assemblage recurs in RST-II in micritic sandstone of the Dingy Hill member,allochem sandstone of the Babia Cliff Sandstonemember) and allochem limestone and micriticmudrock of the Goradongar Flagstone member. Theassociation of the Phycodes assemblage in micriticsandstone and allochem sandstone of the regressive



phase of TRC-II and in allochem limestone andmicritic mudrock of the transgressive phase of TRC-III marks minor eustatic changes. It also indicatesfluctuating energy conditions from low tointermittent moderate energy in offshore totransition-shoreface environments.

9. Rhizocorallium assemblage: This assemblage ischaracterized by diverse trace fossils includingRhizocorallium irregularre (Fig. 6 e, f & g),Rhizocorallium jenense (Fig. 6h), Rhizocorallium

uraliense, Gyrochorte comosa, Arenicolites

carbonarius, Arenicolites statheri, Asterosoma

lugwigae, Asterosoma radiciforme, Beaconites

antarcticus (Fig. 6i), Beaconites coronus (Fig. 6j),Bifungites, Chondrites targonii, Circulichnus

montanus, Cochlichnus anguineus, Diplocraterion

parallelum, Gordia arcuata, Hartsellea

sumsumramosa, Helicolithus isp, Laevicyclus isp.,

Nereites missouriensis (Fig. 6k), Ophiomorpha

nodosa, Palaeobullia isp., Palaeophycus striatus,

Palaeophycus tubularis, Phoebichnus trochoides

(Fig. 6l), Phycodes palmatum, Pilichnus

dichotomus, Planolites beverleyensis, Scolicia

prisca, Scolicia strozzi, Skolithos linearis,

Taenidium serpentinum, Teichichnus rectus,

Thalassinoides horizontalis, Thalassinoides isp andThalassinoides suevicus. The assemblage isrecurrent throughout the sequence and consists ofimprints of each environmentally related trace fossiland, hence, shows the maximum diversity in theircontent.

This ichnoassemblage occurs in the RST-I in micriticsandstone and sandy allochem limestone of DingyHill member, in TST-II in the sandy allochemlimestone of Dingy Hill member, in RST-II inmicritic sandstone (Dingy Hill member), sandyallochem limestone (Kaladongar sandstone memberand Babia Cliff Sandstone member) and sandymicrite (Kaladongar Sandstone member), in TST-III in micritic mudrock (Goradongar Flagstonemember) allochemic sandstone (GoradongarFlagstone member) and limestone (GoradongarFlagstone member and Raimalro Limestonemember), and in micritic sandstone (GadaputaSandstone member), and in RST-IV in sandy micriteand muddy micrite of Modar Hill member. TheRhizocorallium ichnoassemblage is mostconspicuous and developed in transgressive andregressive phases of all T-R cycles. The trace fossilRhizocorallium jenense reflects a generalized

suspension-feeding mode of life (Rodri´guez-tovarand Pérez-valera, 2008) and is usually related tounstable sedimentary environments (Fürsich 1975).It is associated with Arenicolites carbonarius (Fig.7a) and can be related to more intermediate shorefacedepths (Worsley & Mork 2001) while R. irregulare

has a deposit-feeding mode of life (Rodri´guez-tovarand Pe´rez-valera, 2008) and suggests low tomedium energy conditions. Furthermore, it is alsofound in all types of mixed siliciclastic-carbonatesediments, which have been deposited in low tomoderate wave and current energy of tidallyinfluenced shoreface and transition offshore regions.

DISCUSSION

The trace fossils are classified under nine ichno-assemblages: Skolithos, Arenicolites, Ophiomorpha,

Planolites-Palaeophycus, Thalassinoides, Gyrochorte,

Asterosoma, Phycodes and Rhizocorallium. These assemblagesare studied in order to unravel the relationship with thesedimentary packages and stratigraphic surfaces (Fig. 8). Inthe context of sequence-stratigraphic analyses, Diplocraterion

parallelum has been linked to transgressive and marineflooding surfaces (Dam, 1990; Taylor and Gawthorpe, 1993;Goldring et al., 1998) as well as to sequence boundaries(Olo´riz and Rodrý´guez-Tovar, 2000). Rhizocorallium jenense

is generally related to transgressive surfaces produced duringa period of non-deposition before and at the beginning of thesubsequent deposition (Uchman et al., 2000). The absence ornon-preservation of hardground Glossifungites ichnofacies inthe sequence makes the identification of the boundariesdifficult on the basis of trace fossils (Pemberton andMacEachern, 1992). However, the present study incorporatesthe possibility that sedimentary layers coupled withichnoassemblages can be very useful in identifying thesequence stratigraphic surfaces and sequence boundaries.

The transgressive-regressive sequence of the PatchamIsland comprises sediments displaying depositional trends ofprogradation, retrogradation and aggradation, which representfour 3rd order transgressive-regressive cycles (RST-I, II, III,IV & TST- II, III,) bounded by three regressive surfaces (MRS-I, II and III, Fig.3). Each of these system tracts shows thepresence of particular ichnoassemblages that distinguish them.These sedimentary packages show frequent and abundantrecurrence of Planolites/Palaeophycus and Rhizocorallium

assemblages in the regressive deposits, whereas Planolites/

Palaeophycus, Rhizocorallium, Gyrochorte and Asterosoma

assemblages seem to recur in the transgressive deposits.Arenicolites, Skolithos, Ophiomorpha and Thalassinoides



Fig. 8. Schematic cross section of a shoreface-offshore region shows the spatial relationships of different ichnoassemblages with variousflooding and regressive surfaces in T-R cycles. Note: Numbers on left side in the diagram indicate the ichnoassemblages number followedin the text.

assemblages are representing the intermittent high-energyconditions and/or opportunistic environments in the regressiveas well as in transgressive deposits.

The Rhizocorallium ichnoassemblage (Cruziana

ichnofacies) recurs conspicuously in the sequence and marksthe flooding surface FS-II, whereas Arenicolites and Skolithos

ichnoassemblages (Skolithos ichnofacies) associated with thePlanolites-Palaeophycus assemblage (Cruziana ichnofacies)seem to mark the regressive surfaces MRS-I & II.

The transgressive phase of TRC-III and IV showspresence of limestone with mixed siliciclastic carbonatesequence, which may develop during an offshore siliciclasticsediment starvation (Brett, 1995) or form during thedevelopment of the conditions responsible for the increase incarbonate production (Lukasik and James, 2003; Pomar andKendall, 2007). The allochemic carbonates represent the keep-up margin formed at the platform while the micrite-richcarbonate sequences suggest the catch-up carbonate highstandrepresenting a relatively slow rate of accumulation (Sarg,

1988). This change in the depositional system (depositionalbias) as well as environmental changes strongly influencedthe sequence patterns (Tucker et al., 1990). This also explainsthe aggradational or even retrogradational deposition in theregressive system tracts of TRC-II & III (Potma et al., 2001)and the drastic reduction in the carbonate productivity indicatedby the drowning unconformities (Schlager, 1992).

CONCLUSION

The sedimentary sequence of the Patcham Island chiefly

comprises highly bioturbated mixed siliciclastic-carbonate

sediments and consists of 65 ichnospecies of 42 ichnogenera.

Based on sedimentological and ichnological data, four phases

of 3rd order T-R cycles (RST-I, II, III, IV & TST- II & III)

bounded by three regressive surfaces MRS-I, II and III were

identified. A strong influence on the sequence patterns

(progradation, retrogradation and aggradations) is reflected

by changes in the depositional system (depositional bias) in



shoreface to offshore environmental conditions. Recurring

trace fossil assemblages help understanding their nature and

occurrence in depositional system tracts. The soft substrate

trace fossil assemblages in specific depositional environments

delineate specific stratigraphic surfaces (FS, DU and RS) and

suggest new proxies in resolving the difficulty of identifying

surfaces/discontinuities in T-R sequences. More detailed work

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Acknowledgment : The present research work issupported under a DST Research Project No. SR/S4/ES-350/

2008.

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