INITIAL PALEOMAGNETIC ANALYSIS OF THE MARWAR BASIN, RAJASTHAN, INDIA

The Marwar Supergroup refers to the 1000-2000m thick marine and coastal sequences that cover a vast area of the Rajasthan shelf in NW-India. The Marwar Basin uncomformable overlies the well-dated ~750 Ma rocks of the Malani Igneous province and is therefore believed to be Late Neoproterozoic to Early Cambrian in age. The adjacent Upper Vindhyan sequence has long been assumed to be the same age as the Marwar basin. In older publications the Marwar sedimentary rocks were referred to as the ‘Trans-Aravalli Vindhyans”. Detrital zircon populations of the Marwar and Upper Vindhyan sequences show some similarity in the older populations, but the Vindhyan sequence shows no zircons younger than 1000 Ma whereas samples taken from the Marwar Basin show distinctly younger zircons. This may indicate that either the Vindhyan ceased sedimentation prior to the closing of the Marwar, or that more significant differences exist between the two basins than previously believed.

We have collected paleomagnetic data from samples collected in the Marwar basin. Previous paleomagnetic studies of Marwar basinal sediments are problematic and have been misinterpreted (see Poornachandra-Rao et al., 2007) to correspond with the Upper Vindhyan sequence. The vast majority of our samples are consistent with previously published studies that show only a recent field overprint (Torsvik et al., 2005) in the region; however, a small subset of hematite-bearing rocks exhibit directional data that is distinct from the Upper Vindhyan sediments and may offer additional support for temporally distinct episodes of sedimentation in these proximal regions.