Depositional environments and sources for the middle Eocene Fulra Limestone Formation, Kachchh Basin, western India: Evidences from facies analysis, mineralogy, and geochemistry

Abstract

The middle Eocene Fulra Limestone Formation of the Kachchh Basin, western India was investigated to interpret depositional environments and sources of limestones based on facies analysis, mineralogy, and major, trace, and rare earth elements (REEs) geochemistry. Facies stacking pattern of the Fulra Limestone Formation exhibits an overall shallowing-upward sedimentary succession developed in the middle to inner ramp to lagoonal set-up. Staining of the thin sections and X-ray diffraction patterns show dominance of calcite mineral. The CaO, ranging from 40.45% to 49.69%, is the dominant oxide among the major oxides followed by SiO 2 (4.04-10.3%). The dominance of CaO over MgO suggests that the major mineral phase has been calcite and no dolomitization occurred during the deposition of the Fulra limestone. The low proportion of SiO 2 and Al 2 O 3 suggests low siliciclastic input during the precipitation of the Fulra limestone that is confirmed by the positive correlation of ∑REE with Al 2 O 3 , Fe 2 O 3 , Ni, Th, Sc, and Y and the negative correlation of SiO 2 , Al 2 O 3 , and Sr with CaO. The average value of REE contents in the Fulra Limestone Formation are lower (*16.02 ppm) than the average value of typical marine carbonates (*28 ppm). The Post-Archean Australian Shale-normalized REE + Y patterns of the Fulra limestone exhibit seawater like shale-normalized REE + Y pattern, whereas slightly lower average value of Y/Ho ratio (34.60) than the typical seawater value (~44-74) suggests modification of the seawater, to some extent, by input of freshwater in a coastal environment. The REEs of the Fulra Limestone Formation have similarity with the carbonates of the Arabian Sea and/or shallow marine carbonates with exception of a few elements. It is envisaged from this study that the Fulra limestone was deposited in a shallow marine to coastal set-up where mixing of the continental material in seawater was feasible.

Microfacies, diagenesis, and stable isotope analysis of the Jurassic Jumara Dome carbonates, Kachchh, Western India: Implications for depositional environments and reservoir quality

“…The total area of the basin is about 71,000 km 2 of which the onshore area is 43,000 km 2 and offshore area is 28,000 km 2 (Merh, ). The basin was formed due to rifting of Africa and India in the late Triassic time, during the fragmentation of the Gondwana superplate (Biswas, ) and experienced periodic carbonate sedimentation from middle Jurassic to Neogene time (Srivastava & Singh, ). It is bordered by Nagar Parker Fault in the north (Figure ), Radhanpur–Barmer Arch in the east, and Kathiawar Fault towards the south (Biswas, ).…”

“…The concentration of whole brachiopods shells and ooids in the oolitic bar to bank system suggests their adaptation to high‐energy conditions but were partially scattered by currents and tides. Fine detrital quartz grains occur throughout the bioclastic bar system (Srivastava & Singh, ; Srivastava & Singh, ). Pellets and infaunal association (represented by whole‐fossil wackestone, bioclastic wackestone, sponge spicule wackestone, and bioclastic packstone microfacies) occurs in open marine areas of low‐energy conditions with restricted circulation.…”

Petrographical, mineralogical, and geochemical characteristics of the Palaeocene lateritic bauxite deposits of Kachchh Basin, Western India

“…The Matanomadh Formation is overlain by the early Eocene lignite deposits of the Naredi Formation in the western part of the study area (Biswas, ), where these lignite deposits are being mined by the Gujarat Mineral and Development Corporation at Matanomadh and Panandhro localities. The Naredi Formation, a shale‐ and limestone‐dominated succession, is in turn, overlain by shale–limestone–evaporite‐ and limestone–dolostone‐dominated Harudi and Fulra limestone formations, respectively, in the western mainland of Kachchh (Biswas, ; Srivastava & Singh, , b, ; Srivastava, Singh, & Kanhaiya, ; Srivastava et al, ).…”

Sedimentological and geochemical characteristics of the late middle Eocene dolostone succession, Kachchh, western India

“…It has preserved almost a complete sequence from Middle Jurassic to Recent, punctuated by several stratigraphic breaks between transgressive cycles (Biswas, ). There are extensive and nearly semi‐circular patterns of the Tertiary rocks exposed in the mainland Kachchh (Biswas, ; V. K. Srivastava & Singh, , , ; V. K. Srivastava, Singh, & Kanhaiya, ; V. K. Srivastava, Singh, & Patra, ).…”

“…The middle Eocene Fulra Limestone Formation is areally the most extensive Formation among the Paleogene succession of Kachchh, which shows continuous presence from Lakhpat in the north to Harudi in the south (Biswas, ; V. K. Srivastava & Singh, ). It mainly consists of carbonate facies that are formed through biochemical precipitation and contains larger benthic foraminifers, such as Nummulites , Discocyclina , Alveolina , Asterocyclina , and Lepidocyclina , along with rich assemblages of smaller benthic and planktic foraminifers, bivalves and echinoids (Jauhri, ; Kachhara, Jodhawat, & Bigyapati Devi, ; Samanta, ; Samanta, Bandopadhyay, & Lahiri, ; Saraswati, Patra, & Banerji, ; D. K. Srivastava, Gupta, & Jauhri, ; V. K. Srivastava & Singh, ; Tandon & Srivastava, ). Besides, it also contains calcareous nannofossils and calcareous algae (for details, see Rai, ; P. Singh & Singh, ; S. K. Singh, Kishore, Misra, Jauhri, & Gupta, ).…”