Analysis of paleocurrent directions of sedimentary rocks using anisotropy of magnetic suscetibility (AMS) from talchir and barakar formations in Damodar Valley

Abstract

Magneto-mineralogy and Anisotropy of Magnetic Susceptibility (AMS) data of rocks from Lower Gondwana succession, Damodar Valley, Maithon region, are investigated to determine the paleocurrent direction of sedimentary formations using the magnetic fabrics. The main aims of this work are to study the magneto mineralogical characters of rocks and to investigate the behaviours of Magnetic Fabrics of the studied rocks using Anisotropy of Magnetic Susceptibility (AMS) data. The studied rock samples do not exhibit any evidence of high temperature oxidations of Fe-Ti oxides. Considering the textural relationship in rocks from different sampling sites, at least three generations of ferromagnetic mineral assemblage are distinguishable. The earliest one is the primary homogeneous titanomagnetite suffering different stages of low temperature oxidations. These are medium sized irregular grains occurring separately or associated with silicate grains. The second generation consists of Ultra-fine grains of hematite and pigmentary hematite. The last generation is the ultra-fine grains or droplets of secondary magnetite occur along the grain boundary of silicate minerals. This type of secondary magnetite can be generated during long term diagenesis processes after deposition. All the features are suggested that the studied rocks exhibit some important magnetic signatures, which will be more useful for the identification palaeo-pole positions to fix the Damodar Valley in Gondwana time. So these types of studied rocks must be the suitable samples for the through palaeomagnetic measurements by which we can construct the APWPs of the continental blocks to unravel tectonic history of Gondwana Successions in India. The results derived from the statistical parameters (especially the q-factor), the shapes of the susceptibility ellipsoids and directional data of the AMS indicate that the magnetic fabrics within the studied units are primary (depositional) and are correlatable form the paleoenvironmental features. The orientation of the maximum (K1), intermediate (K2) and minimum (K3) susceptibility axes is dispersed on the lower hemisphere equal area diagram rather than strong clusters which is not because of secondary (tectonic) influence but due to the moderate to high energy environment of deposition of the sediments in the studied units. Based on the q-factor (which is 0.581 <0.7), it is suggested the AMS indicates that the imbrication of the K1axis is the indicator of paleocurrent. Also, the magnetic foliation (average value = 1.255) exceeds the magnetic lineation (average value = 1.107) and the shape parameter exceeds 0 in most cases pointing towards an oblate fabric. However, apart from this precise paleocurrent direction, there exists a certain degree of randomness of the susceptibility axes which are very clear indication of corresponding depositional environments.