A B C D E F G H I J K L M N O P Q R S T U V W X Y Z All
Krishna, Jai
- Refinement of Time in the Indian Geological Record: Case-Sheet of the Jurassic in Kachchh
Authors
1 Department of Geology, Banaras Hindu University, Varanasi - 221 005, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 63, No 1 (2004), Pagination: 120-123Abstract
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- Characterization of Dichotomoceras in the Oxfordian of Kachchh
Authors
1 Department of Geology, Banaras Hindu University, Varanasi - 221 005, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 74, No 4 (2009), Pagination: 469-479Abstract
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
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- Development of Oxfordian (Early Upper Jurassic) in the Most Proximally Exposed Part of the Kachchh Basin at Wagad Outside the Kachchh Mainland
Authors
1 Department of Geology, Banaras Hindu University, Varanasi 221005, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 52, No 5 (1998), Pagination: 513-522Abstract
Over a century and half the Kachchh Oxfordian ammonoid record has remained restricted to Early and early Middle Oxfordian, that too in extremely condensed/reworked/starved sedimentary facies. In this backdrop we here discuss the Middle and Late Oxfordian ammonoid faunas recently discovered in Wagad (Krishna et al. 1994a, b). Among these the mid Middle Oxfordian stratigraphic interval is found exceptionally rich in ammonoids at Kantkote - the richest ever discovered in the Kachchh basin. It is made up of a 10m thick succession of 13 ammonoid levels. Farther up after a thick ammonoiddevoid sediment interval appear again a few rather ammonoid scarce levels of late Late Oxfordian age with doubtful extension into early Early Kimmeridgian. The Oxfordian/Kimmeridgian boundary may be included in the latter of the two ammonoid bearing intervals in the Orthosphinctes/Lithacosphincteslevels. The rich mid Middle Oxfordian anunonite fauna inspite of being known for over a century from loose imprecise, unlocalised collections has been stratigraphically precise and dated for the first time in the relatively unexplored. stratigraphic section of Wagad.The anunonoid abundant mid Middle Oxfordian Transversarium Zone succession in addition of the restricted Indo-East African mayaitins and widely distributed perisphinctins includes a few examples of the Mediterranean Gregoryceras gr. fouquei, Euaspidoceras and Taramelliceras and suggests maximum flooding and eustatic rise in the Kachchh Mesozoic in the Middle Oxfordian Schilli Subzone of the Transversarium Zone. Another significant aspect of this fauna is the marked continuous presence of the compressed platyconic densely costate lithacoceratins (Larcheria and Discosphinctes) stocks in parallel with the true perisphinctin and mayaitin lineages almost althrough the Middle Oxfordian (Krishna et al. 1994a. b, 1995, 1996a). The mayaitins are for the first time precisely ranged up to the Transversarium Zone.
The basin margin Oxfordian ammonoid succession at Wagad shows recurrence only of small portion in its basal part of the previously known Oxfordian section of the Kachchh Mainland (e.g. the common Perisphinctes-Epimayaites assemblage of bed G Lakbapur). The remainder ca 200 m thick Oxfordian at Wagad is interpreted here to correspond to the non-depositional submarine stratigraphic gap elsewhere in the relatively deeper parts of the basin from the later part of the Middle Oxfordian Plicatilis Zone to the early Early Kimmeridgian Hypselocyclum Zone.