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Facies and diagenetic evolution of the Bathonian-Oxfordian mixed siliciclastic-carbonate sediments of the Habo Dome, Kachchh Basin, India

Ahmad A. H. M., Irshad R., Bhat G. M.

Volumina Jurassica

2015

Vol. 13, no. 1

83--104

This paper examines the depositional environment and diagenetic aspects of the exposed Patcham and Chari formation within the Habo Dome. The Patcham Formation is represented by the Black Limestone Member. The Chari Formation is represented by two distinct sedimentary successions: (i) shale and carbonates, and (ii) coarse clastics. The paper describes eleven lithofacies from these successions. The depositional framework constituents of these facies have been greatly modified by diagenetic evolution through time. Two main depositional environments, i.e. foreshore intertidal and shoreface (subtidal), have dominated during their deposition. The diagenetic signatures observed within these sediments suggest early or syndepositional changes in marine phreatic and burial environments. Two phases of early mechanical compaction have largely governed porosity evolution within the limestone facies. Micritization of the allochems was caused by endolithic algae prevalent within the restricted lagoon environments with stagnant marine phreatic zone conditions. Random dissolution of microcrystalline grains has created vugs with patchy distribution reflecting neomorphism within the meteoric vadose zone. The types of cements within the sandstone facies include silica, calcite, and its replacement by Fe-calcite cement. The sandstones were deposited in a relatively low energy environment below storm wave base. The depositional conditions have controlled the early diagenesis of the sandstones which in turn have influenced their burial diagenesis.

Temporal facies and diagenetic evolution of the mixed siliciclastic-carbonate Jajiya Member (Callovian–Oxfordian), Jaisalmer Formation, West India

Bhat G. M., Ahmat A. H. M.

Volumina Jurassica

2013

Vol. 11, no. 1

147–-162

Three broad lithofacies – bioturbated packstone- to rudstone, calcareous sandstone and cross-bedded rudstone to packstone are recognized within the Jajiya Member. The facies architecture and stalking pattern suggests deposition related to TST, HST and TST events punctuated by MFZ events in sequence stratigraphic terms. The 11.4 m thick sequence represents two fining upward and three coarsening upward cycles representing bar-bank depositional settings. The framework constituents of these facies were mainly controlled by the depositional conditions through space and time and have greatly influenced their diagenetic evolution. The main diagenetic features observed within the facies include compaction, early cementation and porosity reduction, micritization and neomorphism representing early or syn-depositional and post-depositional changes. Two phases of early mechanical compaction have largely governed porosity development in these facies. However, cementation, micritization and neomorphism have also contributed significantly in this respect. Evidence suggests that marine phreatic and fresh water phreatic environments dominated the diagenetic evolution of these facies. Calcite cementation was first formed, followed by iron oxide, while silica cementation occurred probably at a late stage.