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

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Characterization of Dichotomoceras in the Oxfordian of Kachchh


Affiliations
1 Department of Geology, Banaras Hindu University, Varanasi - 221 005, India
     

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We report here the first Dichotomoceras of the Indian subcontinent at Kantkote (Wagad) in the proximal most exposed part of the Kachchh Basin. This is further addition to the significant enlargement of the Oxfordian ammonoid record made earlier (Krishna et al. 1994, 1995, 1998, 2000). Near continuous presence of ammonoids has been recorded in ca 55 m thick succession, almost immediately above the Schilli Subzone, that was considered ammonoid devoid earlier. The ammonoid density, diversity and frequency in this just discovered ca 55 m thick column are much scarcer in comparison to the underlying 10 m thick ammonoid abundant Schilli Subzone.

Examples of Dichotomoceras are determined almost throughout the said interval which in our preliminary taxonomic evaluation appear identical or close to D. rotoides (Ronch.), D. stenocycloides (Siem.), D. bifurcatus (Quenst.) and D. crassus Enay. It thus suggests the characterization of the Rotoides Subzone of the Transversarium Zone and the superjacent Bifurcatus Zone of the column at least up to the early Late Oxfordian.


Keywords

Ammonoids, Dichotomoceras, Jurassic, Oxfordian, Kachchh, Gujarat.
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  • Characterization of Dichotomoceras in the Oxfordian of Kachchh

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Authors

Jai Krishna
Department of Geology, Banaras Hindu University, Varanasi - 221 005, India
Bindhyachal Pandey
Department of Geology, Banaras Hindu University, Varanasi - 221 005, India
Deo Brat Pathak
Department of Geology, Banaras Hindu University, Varanasi - 221 005, India

Abstract


We report here the first Dichotomoceras of the Indian subcontinent at Kantkote (Wagad) in the proximal most exposed part of the Kachchh Basin. This is further addition to the significant enlargement of the Oxfordian ammonoid record made earlier (Krishna et al. 1994, 1995, 1998, 2000). Near continuous presence of ammonoids has been recorded in ca 55 m thick succession, almost immediately above the Schilli Subzone, that was considered ammonoid devoid earlier. The ammonoid density, diversity and frequency in this just discovered ca 55 m thick column are much scarcer in comparison to the underlying 10 m thick ammonoid abundant Schilli Subzone.

Examples of Dichotomoceras are determined almost throughout the said interval which in our preliminary taxonomic evaluation appear identical or close to D. rotoides (Ronch.), D. stenocycloides (Siem.), D. bifurcatus (Quenst.) and D. crassus Enay. It thus suggests the characterization of the Rotoides Subzone of the Transversarium Zone and the superjacent Bifurcatus Zone of the column at least up to the early Late Oxfordian.


Keywords


Ammonoids, Dichotomoceras, Jurassic, Oxfordian, Kachchh, Gujarat.

References