DOI: 10.5176/2251-3361_GEOS12.31
Authors: Nishith Y. Bhatt,Satish J. Patel and Jaquilin K. Joseph
Abstract: The Callovian-Oxfordian sediments, exposed in the Gangeshwar dome, SE of Bhuj (Kachchh), represent 247 m thick highly bioturbated sequence, comprising of sandstone, siltstone, shale and limestone. The presence of trace fossils suites, reflecting the characteristics of the behavioral patterns, are intimately related to the depositional processes that helped in identifying depositional facies associations viz., Middle Shoreface (A), Lower Shoreface (B) and Offshore (C) facies. This has also helped in sequence stratigraphic analysis for identifying two 3rd order transgressive-regressive cycles (TRC); regressive system tract (RST-I) and transgressive system tract (TST-II); wherein the TST-I is unexposed. The trace fossils show a change from the proximal Cruziana to Skolithos ichnofacies in the regressive phase while from the mixed Cruziana-Skolithos to distal Cruziana ichnofacies in the transgressive phase and also marked the regressive surface and the transgressive surface of erosion. The trace fossils at the base of the TST-II and the transgressive lag deposits in the retrograding deposits suggested the still stand in the relative sea level. The sedimentary facies associations and associated trace fossils reflecting the nature of transgressive-regressive cycles, controlled by either regional tectonic or sea level rise, coincides with the eustatic sea level changes of the Callovian-Oxfordian times. 1
Keywords: T-R cycle; shoreface-offshore zone; Gangeshwar dome; Kachchh; India
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