Brachiopod migration and palaeosea temperatures: A case study from the Jurassic of Western India

摘要

The Middle Jurassic brachiopod record show a distinction of the Tethyan and Boreal faunas maintained in the Northern Hemisphere, with the differentiation of an Ethiopian fauna in the Southern Tethys. The Bathonian-Callovian-Oxfordian sediments of Kachchh and Jaisalmer depict wide taxonomic diversity of the brachiopods, characterised by endemic species of Kutchithyris, Kutchirhynchia.Cryptorhynchia etc., together with cosmopolitan species like Eudesia multicostata, Aulacothyris pala which are typically known from Mediterranean Province and North East European Province. Recent findings of Boreal, European brachiopods Plectoidothyris and Aulacothyris in the Bathonian - Callovian of Kachchh and Jaisalmer posed questions regarding the possible environmental trigger for the migration events.To understand the causes of such migration events and the apparent faunal disjunctive distribution patterns, stable isotopic studies of brachiopods from the Kuldhar Member (Callovian-Oxfordian) of Jaisalmer Formation, Jaisalmer basin were conducted and palaeo- temperatures estimated. The result shows that during the Middle Jurassic the Kachchh and Jaisalmer basin had warm palaeosea temperature. The Boreal - sub Boreal regions became cooler during Bathonian - Callovian which might have triggered migration events from the higher latitudes to the sub-tropical waters of the Kachchh - Jaisalmer sea.