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Black Shale in Late Jurassic Jhuran Formation of Kutch: Possible Indicator of Oceanic Anoxic Event?

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Title Black Shale in Late Jurassic Jhuran Formation of Kutch: Possible Indicator of Oceanic Anoxic Event?
 
Creator ARORA, A
BANERJEE, S
DUTTA, S
 
Subject CENTRAL INDIA
SEQUENCE STRATIGRAPHY
VINDHYAN SUPERGROUP
CRETACEOUS MOOSEBAR
KATROL FORMATION
ISOTOPE RECORD
GAS HYDRATE
BASIN
CARBON
KACHCHH
Black shale
Basalt
Jurassic
Kutch
Gujarat
 
Description This paper reports the results of sedimentary facies analysis and organic geochemical investigations of the middle Member of the Jurassic Jhuran Formation of Kutch which is conspicuous by the occurrence of organic-rich shales. Five lithofacies have been identified for lower part of the Middle Member, e.g. Facies A: Black shale, Facies B: Black shale with siltstone inter-bedding, Facies C: shale and siltstone alternations with minor sandstones, Facies D: siltstone-sandstone alternations and Facies E: plane laminated and hummocky cross-stratified sandstone. The average TOC content of the shales decreases from facies A (av. TOC- 3.4%), to facies D (av. 0.6%) through facies B (av. 1.75%) and facies C (av. 1.34%). The Facies E comprises dominantly of hummocky cross-stratified sandstones. The facies study indicates storm-influenced, shallow marine depositional conditions. Organic geochemical study of shale samples collected from several outcrops from Bhuj to Zara suggests a mixture of type III and type IV kerogen, supplied from higher plant sources. Although most organic matters are mildly matured (av. Tmax c. 427 degrees C), some of the samples reflect overheating related to extrusion of Deccan basalt (av. Tmax c. 604 degrees C). V, Ni, and Co concentrations are indicative of anoxic condition within the depositional settings. The Ni/Co ratio (av. 2.5) and V/(V+Ni) ratio (av. 0.82) as well as size of pyrite framboids (7 to 20 micron), advocates intermittent anoxic and sulfidic conditions in the depositional setting. Black shales within the Jhuran Formation possibly suggest intermittent anoxia related to late Jurassic Oceanic anoxic event (OAE). Detailed investigations are needed to explain the factors causing anoxia in shallow marine conditions.
 
Publisher SPRINGER INDIA
 
Date 2016-01-14T12:43:00Z
2016-01-14T12:43:00Z
2015
 
Type Article
 
Identifier JOURNAL OF THE GEOLOGICAL SOCIETY OF INDIA, 85(3)265-278
0016-7622
0974-6889
http://dx.doi.org/10.1007/s12594-015-0215-6
http://dspace.library.iitb.ac.in/jspui/handle/100/17526
 
Language en