An alternate perspective on the opening and closing of the intracratonic Purana basins in peninsular India

Abstract

Purana basins in India are Proterozoic in age, filled with mostly marine, deltaic, and fluvial sediments, with some alluvial fan deposits in the basin margins. The basin fill is largely undeformed and unmetamorphosed, and the basins occur in many shallow (<5 km), large and small depressions in the Archean-Paleoproterozoic cratons in peninsular India. An understanding of the reasons for the opening and closing of these intracratonic basins is elusive, far more so than that of the better-studied Phanerozoic intracratonic basins in the world. On the basis of meager, but robust new data, published in this century on the Purana basins and their host cratons’ lithostratigraphy, paleomagnetism, seismic images, geochronology, and paleontology, we propose a scenario of their opening and closing related to the assembly and disassembly of the supercontinents Kenorland, Columbia, and Rodinia. The Marwar and the Bundelkhand cratons occur in the western and northern Indian blocks, respectively. The southern Indian Block consists of the Singhbhum, Bastar, Eastern Dharwar, and Western Dharwar cratons; these had amalgamated by ca. 2.5 Ga, but split and re-amalgamated along the western margin of the Bastar craton ca. 1.6 Ga. These three blocks, and East Antarctica, were assembled ca. 1000 Ma along the Aravalli-Delhi Fold Belt, Central Indian Tectonic Zone, and the Eastern Ghats Mobile Belt, as part of Rodinia. There are three sets of Purana basins. The oldest set (Papaghni-Chitravati; Kaladgi-Badami; Lower Vindhyan; Gwalior-Bijawar-Sonrai) opened diachronously after 2.0 Ga and closed by 1.55 Ga. Others (Chhattisgarh; Indravati; Khariar;Ampani;Albaka; Mallampalli; Kurnool; Bhima; etc.) opened after the 1.6 Ga amalgamation event in the southern Indian block, and closed shortly after the 1000 Ma collision of East Antarctica with India. In the northern Indian block, the upper Vindhyan basin likely opened after 1.4 Ga. Sedimentation lingered in some of these basins for some time after 1000 Ma but ceased at the latest by 900 Ma. The Marwar basin in the western Indian block opened ca. 750 Ma, after the emplacement of the Malani Igneous Suite, and sedimentation ceased by 520 Ma, before the Cambrian Explosion. We propose that the three crustal blocks were largely separate between ca. 2.0 and 1.0 Ga but may have collided with and separated from each other from time to time. Minor fracturing in the cratons, entirely within the crust, caused them to have uneven topography. The resulting depressions were filled with sediments as sea level rose; they sagged under the sediment load and as a result of far-field effects of packing and unpacking of large landmasses (Kenorland, Columbia, and Rodinia). Ensuing dynamic topography and sea level fluctuations gave rise to the opening and closing of the Purana basins and their sediment fills.