Palaeomagnetism of Mesoproterozoic limestone and shale successions of some Purana basins in southern India

The 'Purana' basins were long considered Neoproterozoic basins until geochronology and palaeomagnestism showed parts of the Chattisgarth and lower Vindhyan basins to be a billion years older. Historically, the successions in the Chattisgarth Basin are correlated with similar successions in the Pranhita-Godavari and Indravati basins. In India, differentiating between early-late Mesoproterozoic rocks and those spanning the Mesoproterozoic-Neoproterozoic boundary is possible by comparing magnetic declination and inclination; palaeomagnetism is therefore a very useful correlation tool. Here we report a new Stenian-aged palaeopole (50.1 degrees N, 67.4 degrees E, radius of cone of 95% confidence A(95) = 12.4 degrees, precision K = 30.1) from carbonate and shale successions of the Pranhita-Godavari and Chattisgarth basins (the C+/-magnetization). In addition, an early diagenetic remagnetization (component A) was identified. No primary or early diagenetic magnetizations were identified from the Indravati Basin. Here, as well as in stratigraphically higher parts of the other two successions, widespread younger magnetic overprints were identified (B+ and B-magnetic components). Our C+/-palaeopole is constrained by palaeomagnetic stability field tests, is different from known 1.4 Ga and 1.0 Ga Indian palaeopoles, but similar to a 1.19 Ga palaeopole. Penganga Group (Pranhita-Godavari Basin) deposition was probably initiated at around 1.2 Ga. A similar palaeomagnetic signature confirms its correlation with the Raipur Group (Chattisgarth Basin), of which the deposition spans most of the Stenian period (c. 1.2-1.0 Ga). Sedimentation in these groups began significantly later than c. 1.4 and c. 1.6 Ga, as suggested by ages reported from below the Raipur and Penganga groups, respectively.