Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

S. J. Patel ¹, B. G. Desai ¹, A. D. Vaidya ¹, R. Shukla ¹

Affiliations
1 Department of Geology, M S University of Baroda, Vadodara-390 002, IN

Abstract

Middle Jurassic rocks of the Habo Dome consist of well-preserved abundant trace fossil genera. These are described from the black limestone of Jhuno Formation and overlying thick classic sequence which is capped by thin bands of oolitic limestone of Jumara Formation. Total 30 ichnospecies of 23 ichnogenera are identified and their preservational aspects, ecological observations, producers and behavioural aspects are discussed. The trace fossils are found in subtidal sequences i.e. sandstone-siltstone-shale partings, thick, massive and cross-Bedded sandstones and in shelf sequences i.e. black limestone which consists of abundant Chondrites species with resting traces (Lockeia). The clastic sequence exhibits poorly sorted and intensely bioturbated cross-bedded sandstone, ripple-marked ferruginous sandstone and laminated shale-siltstone lithofacies which consist of three dimensional buiTow systems of Ophiomorpha, Thalassinoides and Spongeliomorpha, feeding burrows (Rhizocoralhum, Chondrites, Halymenidium, Gordia, Rutichnus, Planobtes) and crawling traces (Scolicia, Gyrochorte) Massive sandstone facies is moderately bioturbated while shale, conglomerate, shell bed and oolitic limestone lithofacies are poorly bioturbated (Thalassinoides). Wave and current energy, substrate consistency, food supply and bathymetry may have influenced the distribution of trace fossils m the shallow marine environments of the Middle Jurassic rocks of the Habo Dome.

Keywords

Trace Fossil, Lithofacies, Environment, Middle Jurassic, Habo Dome, Mainland Kachchh, Gujarat.

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S. J. Patel ¹, N. Y. Bhatt ², B. G. Desai ³

Affiliations
1 Department of Geology, M S University of Baroda, Vadodara -390002, IN
2 M. G. Science Institute, Navarangpura, Ahmedabad-380009, IN
3 Department of Geology, M. S. University of Baroda, Vadodara-390002, IN

Abstract

Trace fossil of ichnospecies Asteriacites quinquefolius- QUENSTEDT 1876, of the pentamerous star tish is recorded for the first time from the Central Mainland Kachchh, Western India It occuis in the lower part of Bhuj Formation, on thin slabs of fine grained sandstone that intercalate with siltstone, along with symmetrical ripple surface covered by mud drapes Two different types of behavioural activities are found (i) solitary and isolated deep impression of the traces, on account of their resting structures and (n) composite, overlain structure indicating the movement of arms for preying activities The occurrence of Asteriacites traces in the Lower Bhuj Formation indicates tidal-subtidal condition in a fully marine environmental set up.

Keywords

Asteriacites, Asteroid (star-fish), Trace fossil, Marine environment, Bhuj Formation, Kachchh, Gujarat.

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S. J. Patel ¹, B. G. Desai ², R. Shukla ³

Affiliations
1 Department of Geology, M.S. University of Baroda, Vadodara - 390 002, IN
2 Institute of Petroleum Technology, Pandit Deendayal Petroleum University, Gandhinagar - 382 009, IN
3 Wadia Institute of Himalayan Geology, 33, Gen. Mahadeo Singh Road, Dehra Dun - 248 001, IN

Abstract

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.

Keywords

Oolitic Limestone, Trace Fossils, Preservation, Palaeoecology, Jurassic, Kachchh, Gujarat.

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