Sabyasachi Shome

Geological Survey of India | GSI

Brachiopods are common in the Middle Jurassic in the Kachchh and Jaisalmer basins of India but show a decline at the Oxfordian-Kimmeridgian boundary. After an absence in the Kimmeridgian, two brachiopod taxa suddenly appear in the Tithonian in both areas but does not continue afterwards. The two species, Somalithyris lakhaparensis n. sp. and Acanth...

The phosphatized globular to sub-oval metazoan eggs with distinctively ornamented covering and phosphatized polar lobe forming embryos are recorded for the first time from the black phosphatic chert lenticles and bands of early Cambrian Chert Member of Deo ka Tibba Formation, Tal Group, Uttarakhand Lesser Himalaya. Similar metazoan eggs have been r...

Recently collected specimens of Umiaites from the latest Jurassic of Kutch, have facilitated a better understanding of this endemic genus. Two previously described species, Umiaites rajnathi and U. Minor, appear to be conspecific, and the former name is retained. An attempt has been made to characterize the sexual dimorphism between Proniceras and...

Three of Kitchin's (1903) trigomid species, Trigonia trapeziforms, T spissicosiata, and T cardiniiformis, have been frequently examined taxonomically, but their phylogenetic relationships remain uncertain. Taxonomic designations have ranged from grouping them within a single subgenus to separating them into different subfamilies. Principal factors...

The Late Tithonian ammonite-bearing horizons have very limited geographic occurrence in Kutch, being restricted only to the western part of the mainland. A 15 m thick sequence consisting mainly of oolite-shale alternations and coarse grained sandstone yields the terminal Tithonian faunal assemblages. The previous comprehensive report comes from Spa...

A new species of Erymnoceras, Erymnoceras washtawaensis sp. nov., from Wagad, eastern Kutch is described. The genus is a time-diagnostic fleeting taxon and is found elsewhere only from the upper Middle Callovian. This record allows a precise dating of the Middle Callovian sequence in this region, which in turn assists intra- and interprovincial cor...

The present find is the first record of Pterolytoceras from Kutch. The species in question i.e., Pterolytoceras sutile (Oppel) has been found from the Late Tithonian horizon. Stratigraphic distribution of the genus has been discussed in detail and it has been shown that Pterolytoceras is restricted only within the Tithonian. Palaeobiogeographic ana...

Some ammonites provide high time resolution and some others record precise palaeolatitudinal position of the sedimentary basins which harboured them. The Late Jurassic fossil record in Kutch was poor until recently. The present discovery of four genera, viz. Micracanthoceras, Spath, 1925; Durangites, Burckhardt, 1912; Corongoceras, Spath, 1925 and...

The general opinion is that hummocky cross-stratification is generated from superposition of storm waves on a unidirectional current. However, constraints on the type of the current field have not been clearly established. Sedimentary structures preserved in rocks of the Tithonian-Neocomian Umia Member, Kutch, India, indicate hummocky cross-stratif...

In marginal marine environments facies mosaics become complicated through time as and when the regular autocyclic changes are frequently intervened by allocyclic changes. The facies mosaic of the marginal marine Tithonian Ghuneri Member (476 m thick) exposed in western Kutch, India, is likewise fairly complex with frequent lateral as well as vertic...