A foraminiferal zonal scheme for the mid-Cretaceous sediments of the Cauvery Basin, India

Abstract

One hundred and sixty-two species of foraminifera have been identified from the mid-Cretaceous sediments (including the Dalmiapuram and Uttattur Formations) of the Cauvery Basin. Among these, 133 species are benthonic while the remaining 29 are planktonic. On the basis of the distribution of the planktonic foraminifera, a zonal scheme has been established. It consists of nine zones, of which five are Total Range Zones and four are Partial Range Zones. These zones in ascending order are as follows: Ticinella roberti Total Range Zone (latest Aptian-early Albian), Hedbergella planispira Partial Range Zone (middle Albian), Planomalina buxtorfi Total Range Zone (late Albian), Rotalipora evoluta Total Range Zone (early Cenomanian), Rotalipora reicheli Partial Range Zone (middle Cenomanian), Rotalipora cushmani Total Range Zone (late Cenomanian), Whiteinella archaeocretacea Partial Range Zone (earliest Turonian), Helvetoglobotruncana helvetica Partial Range Zone (early to middle Turonian), Marginotruncana sigali Total Range Zone (early late Turonian). Among these, the Ticinella roberti Zone and Whiteinella archaeocretacea Zones are recognized for the first time in this area. Several subzones and an assemblage zone proposed by earlier workers are elevated to zonal status. The probably stratigraphic age of the proposed zones and their correlation are given. The boundary problems/intervals of the mid-Cretaceous of the Cauvery Basin are discussed using stratigraphically important world-wide zonal markers.