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

Subhendu Bardan ¹, Kalyanbrata Datta ¹

Affiliations
1 Department of Geological Sciences Jadavpur University, Calcutta 700 032, IN

Abstract

A biostratigraphic subdivision has been proposed in 210 metres-thick Jurassic Chari Pormation exposed around Keera, Kutch. Evaluation of the relevant pieces of earlier works and new findings emerged in course of present study allow establishment of six distinctive assemblage-zones especially on the basis of rich cephatopod biota. These biozones are largely facies transgressive and hence are often not correlatable with lithofacies distribution. A possible correlation between these biozones at Keera and those established in the type section at Jumara, Kutch from the earlier work has also been attempted.

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Debasish Bhaumik ¹, Kalyanbrata Datta ², Sudipta Kumar Jana ¹, Subhendu Bardhan ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta 700 032, IN
2 Oil & Natural Gas Commission, Ankleshwar 393 020, IN

Abstract

Macrocephalites Zittel, 1884, an important genus in Kutch biostratigraphy, shows considerable diversity at species level. Macrocephalites formosus (Sowerby) is one species which shows a wide range of variability of different morphological characters. A detailed statistical analysis of the principal biocharacters of 140 individuals collected from different localities of Kutch was made to assess quantitatively the range of variation of the species.  "Macrocephalites chariensis (Waagen)", which was previously designated as a separate species, is demonstrated here to be a variant of Macrocephalites formosus and is incorporated into the latter species. An attempt is made to delineate the generic characters of Macrocephaliles and describe the diagnostic characters of the species M. formosus in detail. The variability of the species has no obvious adaptive significance.

Keywords

Ammonoidea, Jurassic, Kutch, Palaeontology.

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