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Introduction
The low-field anisotropy of magnetic susceptibility (AMS) technique is increasingly used in geological sciences to study the magnetic fabric in igneous, sedimentary and metamorphic rocks (Nagata 1961; Rees 1965; Ellwood 1980; Knight and Walker 1988; Ernst and Baragar 1992; Tarling and Hrouda 1993; Borradaile and Henry 1997; Cañón-Tapia 2000). Ising (1942) and Graham (1954) were the first to propose the application of AMS in geological studies and since then it has emerged as a successful tool in determining the petrofabric and paleocurrent directions of unconsolidated sediments and sedimentary rocks (Jackson 1991; Schieber and Ellwood 1993; Park et al.2000; Baas et al.2007; Parés et al.2007; Veloso et al.2007). During the deposition of sediments, the magnetic particles (ferrimagnetic, paramagnetic and diamagnetic) align to ambient geomagnetic field at that time, which is not isotropic and varies with direction, grain size, shape and preferred orientation (Tarling and Hrouda 1993). The results of AMS are usually represented by second-rank tensor, which can be depicted as an ellipsoid with mutually perpendicular principle axes, i.e., K1 ≥ K2 ≥ K3 representing maximum, intermediate and minimum susceptibility axes, respectively (Rochette et al.1992). The study of magnetic mineralogy and its orientation is a primary step to understand the fabric and paleocurrent directions. The AMS study of sediments (sands and sandstones) is suggested to be a reliable tool to identify the paleoflow directions (e.g., Hamid Reza Bakhtari et al.1998; Baas et al. 2007). In the past, limestone received less attention in AMS studies than any other sedimentary rock type since their remanent intensities are very weak. Recent development of advanced magnetometers made possible accurate measurement of all weakest remanent magnetizations (Lowrie and Heller 1982). In this study, the preliminary AMS results obtained from the sandstones and limestones of Ariyalur Group of Cauvery Basin, India, have been presented to understand the magnetic fabrics and their paleocurrent directions.
Geological setting
The Cauvery Basin is a pericratonic basin located along the southeast coast of India (figure 1a). It was developed as a consequence of the break-up of Gondwanaland during the Late Jurassic (Rangaraju et al. 1993). The outcrop area comprises part of the western margin of the basin from Pondicherry in the north to Sivaganga in...