Abstract
The sedimentary sequence exposed in the erstwhile Tiruchirapalli district hosts a more or less complete geological record of the Upper Cretaceous-Tertiary period. Systematic field mapping, collation of data on the micro-meso scale lithology, sedimentary structures, petrography, faunal assemblage and facies relationships of these rocks, in the light of modern stratigraphic concepts, helped to enumerate the lithostratigraphic setup and depositional history of the basin. Spatial and temporal variations of the lithologies and revised stratigraphic units are presented in this paper. Many high frequency sea level cycles (presumably fourth or higher order) which stack up to form third order sea level cycles (six in number), which in turn form part of second order cycles (two in number), including seven eustatic sea level peaks, have been recorded in this basin. Trend analysis of sea level curves indicates a gradual increase of the sea level from Barremian to Coniacian and a gradual decrease from Coniacian to Danian. Such lasting sea level trends had their influence on the sedimentation pattern and facies association. It is inferred that depositional bathymetry was maintained at a shallow-moderate level, primarily influenced by a lack of major subsidence during the depositional history of this basin. The study also revealed a prevalent simple basin filling process and dominant control by sea level changes, rather than tectonic movements over the depositional regime.
Highlights
The Cauvery Basin, the southernmost basin (Fig. 1) in the Indian peninsular shield of the NE–SW trending Late Jurassic–Early Cretaceous rift basins (POWELL et al, 1988) was created during the fragmentation of the supercontinent (JAFER, 1996)
While the present study enables the exposed strata to be defined into 22 members and 9 formations, it was not felt possible to “accommodate” them into groups, as the existing terminologies of groups are either non-relevant or rest over Archaen rocks
While TEWARI et al (1996) eliminated the use of the term Trichinopoly on the grounds that it is far from the exposed area and rests over Archaen rocks, they themselves termed the Dalmiapuram and Garudamangalam Formations as the “Uttatur” Group after the village name “Uttatur”, which in turn rests over Archaen rocks
Summary
The Cauvery Basin, the southernmost basin (Fig. 1) in the Indian peninsular shield of the NE–SW trending Late Jurassic–Early Cretaceous rift basins (POWELL et al, 1988) was created during the fragmentation of the supercontinent (JAFER, 1996). The goals of this study were: to present a workable lithostratigraphy with detailed lithological profiles, including recognisable units so as to produce a realistic mesomicro scale lithological column. This was necessary, primarily because recognition and fixation of any biostratigraphic or chronostratigaphic boundaries rely mostly on the correct recognition of lateral and vertical spatial relationships of the strata, and to enumerate the depositional history of the basin with a view of singling out the controls of the depositional and stratigraphic continuum and breaks in order to deduce the differential roles of geological agents and processes
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