Ichnology of the Callovian-Oxfordian rocks of the Katrol hill range,Kachchh, western India

On the basis of distinct lithologic features such as composition, grain size, bedding characteristics and sedimentary structures, six facies were identified in Callovian to Oxfordian rocks exposed southwest of Bhuj, Kachchh. They are interbedded calcareous shale-siltstone (ICSSF), limestone (LF), ferruginous sandstone (FerSF), felspathic sandstone (FelSF), grey shale (GSF) and oolitic limestone (OLF) facies. The rich and highly diversified trace fossils reveal a wide range of animal behaviours represented by dwelling, feeding, crawling and resting structures. Horizontal feeding structures are found abundantly in all lithofacies indicating low wave and current energy and deposition of poorly sorted muddy to sandy sediments. A few coarse layers containing Arenicolites, Ophiomorpha and Skolithos indicate the presence of opportunistic animals (due to their first appearance under harsh conditions) under -intermittently moderate wave and current energy or storm wave conditions (due to coarse grain size and dominance/presence of only vertical trace fossils) in the shoreface zone. Taenidium occurs mainly in the lower shoreface to transitional zone suggesting low to moderate energy conditions. Thalassinoides occurs in middle to lower shoreface settings under relatively low-energy conditions. Zoophycos represents offshore environment, where it occupies the deepest bioturbation levels.The characteristic lithofacies and assemblages of trace fossils in the rocks of the Chari/Jumara Formation indicate a depositional environment fluctuating from the upper shoreface to offshore zone.     

Trace fossil assemblages in mixed siliciclastic-carbonate sediments of the Kaladongar Formation (Middle Jurassic), Patcham Island,Kachchh, Western India

The Middle Jurassic rocks of the Kaladongar Formation well exposed in the Kaladongar Hill range of the Patcham Island and Kuar Bet of the Northern Kachchh comprises of ∼450 m thick sequence of mixed siliciclasticcarbonate sediments intercalated with shales. These Mixed siliciclastic-carbonate sediments show wide variation in textural and mineralogical composition and represent genetically related six rock types: micritic sandstone, allochemic sandstone, sandy allochemic limestone, micrtic mudrock, sandy micrite and muddy micrite; which are highly bioturbated and show behaviourally diverse groups of trace fossils. Total 34 ichnogenera are identified, which includes, Arenicolites, Asterosoma, Beaconites, Bergaueria, Chondrites, Cochlichnus, Dactylophycus, Daedalus, Didymaulichnus, Diplocraterion, Gordia, Gyrochorte, Gyrolithes, Ichnocumulus, Laevicyclus, Lockeia, Margaritichnus, Monocraterion, Nereites, Ophiomorpha, Palaeophycus, Phoebichnus, Phycodes, Pilichnus, Planolites, Plug Shaped Form, Protovirgularia, Rhizocorallium, Scolicia, Skolithos, Taenidium, Teichichnus, Thalassinoides and Walcottia. These trace fossils are classified into six morphological groups namely, circular and elliptical structures; simple structures; branched structures; rosette structures; spreiten structures; and winding and meandering structures. These trace fossils are further group into eight assemblages which occurred together into mixed siliciclastic-carbonate sediments, include, Asterosoma assemblage, Gyrochorte assemblage, Rhizocorallium assemblage, Thalassinoides assemblage, Planolites-Palaeophycus assemblage, Phycodes assemblage, Ophiomorpha assemblage and Skolithos assemblage. The recurring pattern of these assemblages through the sequence displays the development of Skolithos and Cruziana ichnofacies and at places the mixed Skolithos-Cruziana ichnofacies which suggest a low wave and current energy conditions with intervening period of high wave and current energy conditions and an intermediate period of stressful environments, respectively. Sedimentological and ichnological data suggest that the deposition of the mixed siliciclastic-carbonate sediments of the Kaladongar Formation took place in the foreshore to offshore environment under fluctuating wave and current energy condition.     

Facies controlled synaeresis cracks in mixed siliciclastic-carbonate sediments of Middle Jurassic of Patcham Island, Kachchh, Western India

Synaeresis cracks are observed at different stratigraphic levels in shallow marine mixed siliciclastic-carbonate sediments of the Middle Jurassic rocks of the Patcham Island, Kachchh, Western India. Cracks are preserved as cast or grooves in micritic sandstone of the Kuar bet member of Kaladongar Formation and sandy allochem limestone of the Raimalro Limestone member of Goradongar Formation. It bear distinct morphology of simple, straight to gently curved, spindle-shaped, irregular, unbranched to branched at acute angle; interconnected curlicue forms of non-orthogonal pattern. The X-radiography shows sharp margin and tapering twigs which support to nullify the possible biogenic origin. These cracks are developed at sediment-water interface and sediment-sediment interface in aqueous conditions, where partial dewatering of sediments causes reduction of sediment volume and loss of plasticity. Formation of cracks are also post-depositional phenomenon operated during initial phase of diagenesis where induced stress is generated due to compaction of sediments and neomorphism/recrystallisation of the susceptible carbonate grains.     

Miocene bryozoa from the Kachchh Offshore Basin,Western India

The present paper records for the first time the bryozoan fragments from 4 m core of the Godhra Formation (early Miocene) and from 4m core and 5 m core of the Chhasra Formation (early middle Miocene) of the Kachchh Offshore Basin, Western India. The Godhra Formation has presence of three bryozoans, viz., ?Crassimarginatella sp., Thalamoporella sp. and Vincularia sp. while the Chhasra Formation has presence of four bryozoans, namely, ?Margaretta sp., Steginoporella sp., ?Thalamoporella sp. and Vincularia sp.     

Petrofacies, provenance and diagenesis of the dhosa sandstone member (Chari Formation) at Ler, Kachchh sub-basin, Western India

The sandstones of the Dhosa Sandstone Member of Late Callovian and Early Oxfordian age exposed at Ler have been analyzed for their petrofacies, provenance, tectonic setting and diagenetic history. These sandstones are fine to medium grained and poorly- to well sorted. The constituent mineral grains are subangular to subrounded. These sandstones were derived from a mixed provenance including granites, granite–gneisses, low- and high-grade metamorphic and some basic rocks of the Aravalli Range and Nagarparkar Massif. The petrofacies analysis reveals that these sandstones belong to the continental block-, recycled orogen- and rifted continental margin tectonic regime.The imprints of early and deep burial diagenesis of these sandstones include different stages of compaction, cementation, change in crystal boundaries, cement–cement boundaries, chertification and neomorphism. The sequence of cementation includes precipitation of calcite and its subsequent replacement by Fe calcite and silica cements. The typical intermediate burial (2–3 km depth) diagenetic signatures of these sandstones are reflected in the formation of suture and straight-line boundaries, and triple junctions with straight-line boundaries. The depositional environment, relatively low-energy environment that was below storm wave base but subjected to gentle currents, of the Dhosa Sandstone Member controlled the early diagenesis, which in turn influenced the burial diagenesis of these sandstones.     

Paleoecological significance of the trace fossils of Dhosa Oolite Member (Jumara Formation), Jhura dome,Mainland Kachchh,Western India

Dhosa Oolite Member of the Jumara Formation comprises alternating bands of oolitic limestones and shales, exposed in Jhura dome of Mainland Kachchh, Western India. This sequence is highly bioturbated and exhibits a moderate diversity and behaviourally complex assemblage of ichnospecies. The rhythmically bedded sequence shows three different levels of preservation of traces. Epichnial tiering consists of moderately bioturbated oolitic limestone exhibiting horizontal or low-angle protrusive/retrusive biogenic laminae, commonly dominated by feeding structures like Rhizocorallium jenense, R. irregulare, Zoophycos brianteus and Zoophycos isp. The endichnial structures within the oolitic limestone can be separated into two different preservational trace fossil suites. The endichnial shallow suites consist chiefly of deposit feeders like Chondrites intricatus, C. targionii, Planolites beverleyensis, Taenidium cameronensis, Thalassinoides isp., Z. brianteus, Z. cf circinnatus and Zoophycos isp. and few suspension feeder forms like Palaeophycus tubularis; while endichnial deep suites consist of Chondrites intricatus, Skolithos linearis and Zoophycos isp. Hypichnial structures consists abundant, cylindrical, branched, horizontal, large-sized three dimensional feeding burrows of Thalassinoides isp. and somewhat irregular, obtuse angle ramification burrows of Phycodes isp., which are attached to the lower surface of the casting medium. The trace fossil association indicates Cruziana ichnofacies and abundance of Zoophycus species below the fair weather wave base level is largely a preservational artifact. The preservational processes of the trace fossils indicate soft substrate and diversity and their abundance reflects the other palaeoecological parameters of the open shallow marine environments.     

Ichnology of Bhuban and Boka Bil Formations,oligocene-miocene deposits of Manipur Western Hill,Northeast India

Oligocene-Miocene deposits of Bhuban and Boka Bil Formations, Surma Group, Manipur Western Hill consist of well preserved ichnofossil assemblages. These formations are represented by eight lithofacies such as Massive sandstone (Sm), Rippled marked argillaceous sandstone (Sr), Wavy laminated sandstone-siltstone-silty shale (Sw), Laminated shale (Fl), Massive mudstone (Fm), Trough cross-bedded sandstone (St), Lenticular laminated sandstonesiltstonesilty shale (Sll) and Laminated to massive sandstone-siltstone (Ssc). Fifteen ichnospecies were identified, which further categories into Skolithos, Cruziana, and Skolithos/Cruziana ichnofacies. Overall distribution pattern and behavioural nature of the ichnoassemblage and sedimentological attributes suggests that the sediments of Bhuban and Boka Bil Formations were deposited under frequent fluctuating sea level, moderate to strong energy condition, subtidal to lower intertidal environment, rich in organic nutrients.     

Morphotectonic control on Quaternary sedimentation and landscape evolution,Pachham Island,Kachchh, Western India

Pachham Island is the westernmost island in a chain of four rocky islands within the Great Rann of Kachchh that are bounded in the north by the Island Belt Fault (IBF). The island is characterized by two parallel and structurally controlled Kaladungar hill range and Goradungar hill range separated by a synclinal central valley. The central valley has acted as a sink for the Quaternary sediments. The island is transversely traversed by a N-S trending basement high termed as Median high that shows pronounced geomorphic and drainage anomaly. The Quaternary sediments comprise coarse-grained colluvio-fluvial deposits, miliolite, and sandy alluvium. The coarse-grained Quaternary deposits were primarily derived from the colluvium generated due to the uplift of the Kaladungar hill range and Goradungar hill range along the IBF and Goradunagar Fault, respectively. The colluvial debris were subsequently reworked, transported down slope and deposited in the central valley. The presence of the deeply incised valleys in Quaternary sediments, two levels of terrace surfaces over the Median high, and the raised Rann floor surrounding the island suggest a dominant role of neotectonics in the landscape evolution and Quaternary sedimentation.     

Burrowing activities of goby fish in the recent intertidal mud flats along the Navinal coast,Kachchh, Western India

Behavioural activities of the goby fish-Periophthalmodon septemradiatus were observed in the intertidal zone around Navinal coast in the Gulf of Kachchh, western India. Intertidal zone is broad, and comprise of creeks, which are muddy and vegetated by mangrove on eastern side and ridge runnel systems on western side of the study area which are hospitable for the goby fish. Different types of biogenic activities are observed such as crawling, pellet making, grazing and burrowing. The crawling activity is part of movement of the goby fish from one burrow to another burrow and pellet making activity is part of burrow modification. The grazing activity is feeding on the surface mud after receding of tide and exposure of the tidal flat by left and right movement of the front part of the body. The most conspicuous activity is burrowing, they construct unlined, vertical to incline ‘I’, ‘J’ and ‘Y’ shaped branched, circular to oval burrows with varying diameter and depth. In the muddy sediments goby fish produced circular to oval rimmed muddy lumps as surfacial expression around the burrows and further produced funnel shape depression and downward extended cylindrical holes, while in the runnels burrows are usually small and simple. The trail is consisting of fin marking on either side of the tail marks (grooves) which are radiate around the burrows. Occasionally burrows are interconnected in more than one burrow system which is nested within single funnel structure on the surface. The burrow systems of the goby fish in the intertidal sediments serves for protection and dwelling purpose and most importantly these burrows are irrigated by water which supply the oxygen and keep body surface wet. The overall dimensions of the burrow decrease towards the lower intertidal zone. In all, behavioural structure produced by the goby fish marks the combined activity of dwelling, feeding and grazing. The complex behavioural mechanisms have helped the goby fish to survive and flourish in the harsh intertidal environments along the Navinal Coast, in the Gulf of Kachchh.     

Animal-sediment relationship of the crustaceans and polychaetes in the intertidal zone around Mandvi,Gulf of Kachchh,Western India

Animal-sediment relationships of two benthic communities (Crustaceans and Polychaetes) were studied around Mandvi coast in the Gulf of Kachchh, Western India. This coast consists of many micro-geomorphic landforms in which benthic communities are inhabited and select their niches and produce endemic biogenic structures. Five intertidal subfacies have been described and four types of grounds are identified, based on substrate consistency. 18 species of crustaceans, 15 species of polychaetes and unsegmented worm nemertea have been identified. Crustacean behavioural activities were observed in dunes, beaches and ridge-runnel in the form of burrowing, pellet making, feeding and crawling traces. Pelleted wall lining burrows of the suspension feeder stomatopodean species of Oratosquilla striata are also abundant in runnels. Motile, deposit feeder polychaetes are abundant on the ridges and are occasionally found on the lower reaches of the beaches, while suspension and filter feeders are found in the runnels. Lagoons consist of mainly grouped funnel branched burrows of Oniphus eremita which is identical to ichnogenus Balanoglossites. Nemertea, which are opportunistic algal grazers, have exploited restricted niches for dwelling-feeding purposes and constructed vertical burrow with pentamerous conical mound. The shore platform consists of cemented, calcareous tubes of filter feeder Serpula along with symbiotic encrusters like Ostrea and barnacles. Ichnocoenoses are discussed and three-dimensional ichno-sedimentologic models are reconstructed for Beach, Ridge, Runnel and Lagoon of the Mandvi intertidal zone.     

The Effects of Diagenesis on the Reservoir Characters in Ridge sandstone of Jurassic Jumara dome,Kachchh, Western India

Ridge sandstone of Jurassic Jumara dome of Kachchh was studied in an attempt to quantify the effects of diagenetic process such as compaction, cementation and dissolution on reservoir properties. The average framework composition of Ridge sandstone is Q₈₀F₁₇L₃, medium-to coarse grained and subarkose to arkose. Syndepositional silty to clayey matrix (3% average) is also observed that occurs as pore filling. The diagenetic processes include compaction, cementation and precipitation of authigenic cements, dissolution of unstable grains and grain replacement and development of secondary porosity. The major cause of intense reduction in primary porosity of Ridge sandstone is early cementation which include silica, carbonate, iron, kaolinite, illite, smectite, mixed layer illite-smectite and chlorite, which prevents mechanical compaction. The plots of COPL versus CEPL and IGV versus total cement suggest the loss of primary porosity in Ridge sandstone is due to cementation. Cements mainly iron and carbonate occurs in intergranular pores of detrital grains and destroys porosity. The clay mineral occurs as pore filling and pore lining and deteriorates the porosity and permeability of the Ridge sandstone. The reservoir quality of the studied sandstone is reduced by clay minerals (kaolinite, illite, smectite, mixed layer illitesmectite, chlorite), carbonate, iron and silica cementation but on the other hand, it is increased by alteration and dissolution of the unstable grain, in addition to partial dissolution of carbonate cements. The potential of the studied sandstone to serve as a reservoir is strongly related to sandstone diagenesis.     

Nongeniculate coralline algae from early middle Miocene offshore sequence of Kachchh basin,Western India: Paleoenvironmental significance

The present paper reports five nongeniculate coralline algal species, viz., Lithothamnion valens Foslie, Mesophyllum roveretoi Conti, Phymatolithon calcareum (Pallas) Adey and Mckibbin, Melobesioideae gen. et spec. indet. and Lithoporella melobesioides Foslie form the early middle Miocene Chhasra Formation of Offshore Sequence of Kachchh basin, western India. The present day depth distribution of Lithothamnion and Mesophyllum and growth forms of five nongeniculate coralline algal species points that the two cores belonging to the Chhasra Formation of offshore sequence of Kachchh basin were deposited in inner shelf environment at 60-100m depth in moderate-energy conditions.     

Ichnological analysis of transgressive marine tongue in prograding deltaic system: Evidences from Ukra Hill Member, Western Kachchh, India

The Ukra Hill Member exposed only in Western part of Kachchh basin comprises of fossiliferous shales, limestones and glauconitic sandstones in between thick unfossiliferous sandstone. The present study documents abundance of trace fossil Teredolite, occurring as driftwood and bedload log ground as well as re-worked log ground from the basal part of the Ukra Hill Member. These Teredolite bearing horizons are underlain by coarse grained cross bedded sediment with monodominant Psilonichnus tubiformis, while abundant Gyrolithes cycloides along with Rhizocorallium irregulare, R. Jenense occurs in overlying horizons. Three ichnofabrics recognized within the Ukra Hill Member are inferred to represent near shore high energy conditions (Psilonichnus ichnofabric), transgressive condition with subsequent erosion (Teredolites Ichnofabric) and shelf environment (Gyrolithes-Rhizocorallium Ichnofabric). TheTeredolite bearing horizons also occurs with abundant belemnites Neohibolithes ewaldi, which is considered to be index fossil for the Early Aptian sediments. Thus, based on the ichnofabric analysis, the basal part of the Ukra Hill Member represents an Early Aptian transgressive event in Kachchh basin.     

dC Variations in Late Jurassic Carbonates, Jaisalmer Formation, Western India

The carbon isotope measurements, carried out on subsurface carbonate samples from Oxfordian Jaisalmer Formation, western India, yield positive d¹³C values up to +3.17%. The most positive Oxfordian C-isotope value corresponds to the carbon isotope excursion measured in samples from from other late Jurassic basins of world. The latest Oxfordian C-isotope values of Jaisalmer Basin fluctuate around 2% while the C-isotope values of 1.50% mark the base of Kimmeridgian. The Oxfordian C-isotope excursion appears to correspond to a time of overall increased organic carbon burial triggered by increased nutrient transfer from continents to oceans during a time of rising global sea level.     

Characterization of organic carbon in black shales of the Kachchh basin,Gujarat, India

Thirty-three black shale samples from four locations on the onland Kachchh basin, western India were analyzed to characterize organic carbon (OC), thermal maturity and to determine the hydrocarbon potential of the basin. Upper Jurassic black shales from the Jhuran Formation (Dhonsa and Kodki areas) are characterized by the presence of chlorite, halloysite, high \(T_{\mathrm{max}}\), low OC, low hydrogen index and high oxygen index. These parameters indicate the OC as type IV kerogen, formed in a marine environment. The rocks attained thermal maturity possibly during Deccan volcanism. Early Eocene samples of the Naredi Formation (Naliya-Narayan Sarovar Road (NNSR) and the Matanomadh areas) are rich in TOC, smectite, chlorite and framboidal pyrite, but have low \(T_{\mathrm{max}}\). These indicate deposition of sediments in a reducing condition, probably in a lagoonal/marsh/swamp environment. Organic carbon of the Naredi Formation of NNSR may be considered as immature type III to IV kerogen, prone to generate coal. Core samples from the Naredi Formation of the Matanomadh area show two fold distribution in terms of kerogen. Organic carbon of the upper section is immature type III to IV kerogen, but the lower section has type II to III kerogen having potential to generate oil and gas after attaining appropriate thermal maturity.     

High energy transgressive deposits from the Late Jurassic of Wagad,Eastern Kachchh,India

The whole sedimentary succession (ca 600 m thick) of Wagad area ranging in age from Callovian to Early Kimmeridgian has been divided in to three Formations namely Washtawa, Kanthkot and Gamdau in ascending order. Prograding Kanthkot Formation was frequently interrupted by transgressions. Field and petrographic investigations revealed that the Kanthkot Formation represents three fossiliferous marker beds corresponding to Transgressive sequence I; Transgressive sequence II and Transgressive sequence III. These transgressive sequences are composed of two lithounits: medium to coarse grained/gritty, graded to massive, sheetlike, fossiliferous calcareous sandstone (storm lag unit I) and fossiliferous mudrocks (swell lag unit II). The thickness of the unit I varies from 5 to 75 cm and contains mostly convexly oriented shell fragments and whole shell of Pelecypods, Cephalopods and Brachiopods. Unit II (5–15 cm) is distinguished by sheetlike, massive or laminated, yellowish colour, soft fossiliferous mudrocks. This unit is intercalated with moderately bioturbated sandy siltstone. Unit I is dominant over Unit II in the sequences.Study suggests that the transgressive units were deposited close to wave base by high energy storm flows followed by low energy marine swells during transgression. The intense storms played a major role in the distribution of siliciclastics and nonclastic materials. Storms are evidenced by the occurrence of two distinctly different types of units (storm lags and swell lags). High energy levels are characterized by sand dominated sequence, abundance of reworked sediment particles, high proportion broken shells with convex up orientation and erosional and sharp nature of basal contacts of units together with well preserved bioclasts. Sudden short term changes from high to low energy during transgression are explained by the occurrence of medium to coarse grained siliciclastics interbedded with moderately bioturbated mudrocks. Moderately bedded individual strata, high content of coarse clastics along with polished granule size quartz and abundance of comminuted shells indicate a significant change in depositional setting, possibly closure approach of the source of terrigenous fraction or source uplift. Synrift sedimentation in the present study is documented by an abundance of coarse clastics and an over all aggradational nature of transgressive sequences.     

Upper Callovian-Middle Oxfordian belemnite assemblage from Jara Dome,Western Kachchh

Belemnites and ammonites were collected from the Dhosa Oolite beds of Jara Dome in Kachchh. The Dhosa Oolite is an important marker of the Mesozoic sediments exposed in the Kachchh Basin. Nine belemnite species are reported belonging to four genera Belemnopsis, Demubelus, Hibolithes and Conodicoelites. These include Belemnopsis cf. moluccana Boehm, B. calloviensis Oppel, Demubelus weberi Stolley, Hibolithes boloides Stolley, H. longiscissus Stolley, H. cf. compressus Stolley, H. jumarensis Waagen, H. budhaichus Stoliczka and Conodicoelites cf. abadi Challinor. Besides the belemnites, diagnostic ammonoid fauna are also recorded from the studied section enabling better controlled stratigraphic resolution and biostratigraphic correlation. Taxonomic studies on the different belemnite species are presented with illustration for reference.