Bhawanisingh G. Desai

Ichnology of the Early Cambrian Tal Group, Nigalidhar Syncline, Lesser Himalaya, India

Though trace fossils have been recorded from the Tal Group of the Krol-Tal Belt by earlier workers, most of the records are at generic level only. This paper describes, in detail, 24 ichnospecies from 20 ichnogenera, some of which are being reported for the first time, from the Ganog and Koti Dhaman sections of the Nigalidhar Syncline, H.P. Based on the ichnostratigraphic and ichnofabric analyses these ichnofossils have been categorized into three ichnoassemblages, namely Palaeophycus-Phycodes, Daedalus-Phycodes, and Cruziana Ichnoassemblages. An attempt has also been made for correlation of the Tal sections with other Precambrian-Cambrian sections of the world.

Significance of the trace fossil Balanoglossites Mägdefrau, 1932 from the Lower Cretaceous Guneri member (Bhuj formation) of the Guneri dome, Kachchh, India

The Guneri dome, situated in the Western Kachchh, is famous for its prominent exposures of Lower Cretaceous sandstone-dominated Guneri member belonging to the Bhuj formation. The ichnogenus Balanoglossites Mägdefrau, 1932 is reported for the first time from the Indian subcontinent and is represented by B. triadicus and B. ramosus, occurring in association with the tear-shaped boring Gastrochaeonolites. These trace fossils occur as a part of two, laterally extensive Glossifungites ichnofacies surface, representing omission suite assemblage. The detailed analysis of the trace fossil Balanoglossites along with lithofacies analysis suggests that it belongs to the Glossifungites ichnofacies surface and this trace fossil bearing surface corresponds to the Lower Cretaceous regressive phase that marks the unconformity of other parts of the Kachchh basin.

Ichnofabric analysis of the Tithonian shallow marine sediments (Bhadasar Formation) Jaisalmer Basin, India

The shallow marine sedimentary sequence of the Jaisalmer Basin exhibits one of the important and well-developed Tithonian sedimentary outcrops for western India. The ichnology and ichnofabric of the lower part of Bhadasar Formation (i.e., Kolar Dongar Member) belonging to Tithonian age are presented and discussed. The Kolar Dongar Member represents a shallow marine succession that contains 16 ichnotaxa: Ancorichnus ancorichnus, Conichnus conicus, Gyrochorte comosa, cf. Jamesonichnites heinbergi, Imponoglyphus kevadiensis, Laevicyclus mongraensis, Monocraterion tentaculatum, Ophiomorpha nodosa, Palaeophycus tubularis, P. bolbiterminus, Phycodes palmatus, Planolites beverleyensis, Rhizocorallium isp., Rosselia rotatus, R. socialis, and Teichichnus rectus. The ichnofabric analysis divulges five distinct ichnofabrics, each typifying distinct depositional environment within shallow marine conditions. The ichnofabric Ophiomorpha 1 with syn-sedimentary faulting exemplifies high energy conditions typical of lower shoreface environment, whereas the Ophiomorpha 2 ichnofabric typifies upper shoreface environment. The Ancorichnus ichnofabric reflects lower offshore condition of deposition. The high ichnodiversity Ancorichnus–Rosselia ichnofabric is indicative of inner shelf conditions, while low ichno-diversity Teichichnus ichnofabric indicates prevalence of low energy brackish bay environment. Thus, Tithonian Kolar Dongar Member indicates depositional environment ranging from shoreface to offshore to inner shelf and finally to brackish bay environment.

Palaeocommunity Dynamics and Behavioral Analysis of Conichnus: Bhuj Formation (Lower Cretaceous),Kachchh-India

A palaeocommunity of large Conichnus conicus, a conical, cone-in-cone shaped burrow, created by sea anemones, occurs in medium-grained, crossbedded, well-sorted sandstone in the middle part of the Cretaceous Guneri Member of the Bhuj Formation in India. The trace fossil Conichnus is considered to be a common element of the Skolithos ichnofacies and is interpreted to reflect equilibrium movement in response to substrate aggradation. In the present study, three different varieties of Conichnus conicus are distinguished based on morphology and internal fabric. Community dynamics and burrowing behavior are revealed by inter-burrow relationships, burrow initiation levels and sedimentology. Three types of behavior are envisaged: retrusive equilibrium, protrusive equilibrium response, and escape behavior. Palaeocommunity dynamics show that the tracemakers consisted of only adult organisms that initiated burrows during neap tides and are adapted to feed effectively during weak flow conditions. The occurrence of Conichnus palaeocommunity in the Guneri Member indicates the tidal conditions in a fully marine setting. Results presented herein may aid in the understanding of palaeocommunity dynamics in other shallow marine sequences.

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.

Dwarf megateuthidid belemnites from the Bathonian of Kachchh (India: Gujarat) and their significance for palaeobiogeography

We describe in detail new finds of dwarf megateuthidid belemnites from the Middle–Late Bathonian of Kachchh (Western India), previously only rarely mentioned in the literature. The material is assigned to a new genus and species, Challinoria challinori gen. et sp. nov. Extensive morphological comparison together with analysis of the biogeographical distribution of comparable taxa suggests affinity of the newly described taxon with Early Bajocian megateuthidids from South America, showing the existence of a previously unknown megateuthidid habitat area in the Southern Hemisphere during the Bajocian and Bathonian. The biogeographical patterns and trans-equatorial migration routes of Middle Jurassic megateuthidids are discussed. The occurrence of the newly described taxon in the Bathonian of India, along with the lack of Mediterranean and Indo-Pacific records of similar age, may be connected with the short-term opening of a marine trans-Gondwanan seaway. http://zoobank.org/References/urn:lsid:zoobank.org:pub:F5F7B7E6-ABA2-4EAF-A56C-9025075428A0

Ichnological analysis of the Pleistocene Dwarka Formation, Gulf of Kachchh: tracemaker behaviors and reworked traces

Complex interaction among trace fossils are important in understanding organisms niche preference for foraging in ancient rock records. There exist well-recorded examples of compound trace fossils. However, such compound traces rarely exhibit exploitation of burrow wall and fill sediments for feeding. In recent sediments, several examples are well documented for feeding on burrow wall and burrow fills because of nutrient enrichments in them. Such type of complex interactions occur in the shallow marine Pleistocene age sequences exposed in island in Gulf of Kachchh, India. These deposits are known as ‘Shankhodhar Sand Clay Member’ of Dwarka Formation. Trace fossils recorded are Chondrites, Chomatichnus, Gyrolithes, Ophiomorpha, Rhizocorallium, Schaubcylindrichnus, Sinusichnus, Spongeliomorpha, Taenidium and display three Ichnoassemblages. Three types of complex interactions are suggested: (1) Burrow architecture modification, (2) feeding on burrow walls and burrow fills and (3) acute angle branching. Thus, the trace fossil association indicates selective preference of trace maker for their foraging activities in shallow marine Shankhodhar Sand Clay Member of Pleistocene age.