Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

D. R. Gadekar ¹

Affiliations
1 Dept. of Geology, M. S. University of Baroda, Baroda 390002, IN

Abstract

The supra-Trappean Broach Group of Tertiary sediments show evidences of a variety of diagenetic changes. The arenaceous sediments of the Vagalkhod Formation contain proofs of recrystallisation of sparry and micrite cement indicating pore-filling and shallow depth of burial. The calcareous sediments of the Bhilod Formation (Nummulitics) show limonitisation suggesting low temperature metasomatism and precipitation in shallow waters. The argillaceous rocks of the Tarakeshwar Formation reveal authigenic sparite, also indicative of shallow burial. Silica cementation, authigenesis and limonitisation are some of the important diagenetic changes discernible in the overlying rudaceous Babaguru Formation. These changes suggest redoxomorphic stage, precipitation from gel and epidiagenesis. The calcareous sediments of the Kand Formation reveal recrystallisation of spa rite from micrite, which may suggest diagenetic transformation. The arenaceous sediments of the Jhagadia Formation bear evidence of the activity of carbonate cementation ~nd replacement, which may perhaps indicate locomorphic stage of diagenesis.

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D. R. Gadekar ¹

Affiliations
1 Department of Geology, Maharaja Sayajirao University of Baroda, Baroda 390 002, IN

Abstract

Tertiary rocks are exposed around Tarakeshwar, Surat district, Gujarat. These are mainly Eocene sediments which are predominantly clastic and are overlain by carbonate sediments. Several interesting sedimentary structures are revealed by calcareous claystones associated with fossiliferous limestones; among them concretions, septarian nodules and imatra stones are striking. These secondary sedimentary structures are developed due to chemical changes effected during diagenesis of the fine grained detrital sediments, probably involving precipitation of calcium carbonate in the pores of silt beds. The sediments were deposited in a near-shore environment of a shallow Eocene sea.

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D. R. Gadekar ¹

Affiliations
1 Department of Geology, M. S. University of Baroda, Baroda 390002., IN

Abstract

Planar cross stratification, trough cross stratification, imbricate structure and channel structure observed in Jhagadia, Babaguru and Tarakeshwar Formations indicate fluvial depositional environment. Oscillation ripple marks preserved in the Kand Formation suggest transitional conditions. Graded bedding seen in Jhagadia, Tarakeshwar and Vagalkhod Formations indicate deposition by turbidity currents. Convolute laminations and ball and pillow structure by sediments belonging to Babaguru Formation indicate intrastratal deformation and slumping, perhaps on a delta. Colour banding observed in the sandstones of the Babaguru Formation suggests oxidising environment in a tranquil water body.

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