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

Abstract

A 40m thick Early Miocene sequence occurring near Naliya has been investigated for its sedimentary facies and benthic foraminiferal biofacies. The changing depositional environments of the sequence have been interpreted to represent (a) supratidal to (b) supratidal-intertidal and (c) subtidal (limited clastic influx) to ultimately subtidal (increased clastic influx) palaeoenvironments. The lowest part of the section shows evidence of emergence which together with benthic foraminiferal population dominated by Pararotalia nipponica - Loxostomwn lobatwn (water depths of 05-10m) suggests a supratidal environment.

The middle part of the stratigraphic interval has been subdivided into a lower and upper part on the basis of an intervening calcrete (calcretised shell limestone) horizon. The lower part of this interval represents lagoonal and high intertidal environments.

The upper part of this interval shows development of cross bedded and wave-rippled sandstones representing beach ridge-tidal inlet sequence. Other lithofacies include shell layers having predominance of one kind of organism. Some of these shell banks are wave sorted. Biofacies II -Hanzawaia nipponica - Cibicides lobatulus characterises this part of the section and indicates water depths of - 5Om.

The upper part of the sequence is composed of silt which contains Ammonia beccarii -Pseudorotalia gaimardi in abundance. This interval is frequently interspersed by oyster-Pecten beds and indicates subtidal environment with increased influx of siliciclastics.

The changing depositional environments show that these Early Miocene rocks represent a transgressive, tide-dominated, storm affected sequence.

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