Search

The late Mesoproterozoic to Neoproterozoic sedimentary successions on the southern Indian craton are described from the Dharwar and Bastar cratonic blocks and the intervening Pranhita-Godavari rift valley. These successions include a characteristic lime-mudstone-shale assemblage that has been deposited in a deep-water cratonic depositional setting beyond the reach of coarser detritus. The Kolhan Group occurring on the Singhbhum craton at the northeastern corner of the southern Indian craton also includes similar lime-mudstone and shale deposits that can be lithologically correlated with the late Meso-Neoproterozoic successions from other cratonic blocks of the peninsula. The correlation attempted here, based on the lithology and depositional setting, leads to the reconstruction of a major deep-water basin on the southern Indian craton during the late Mesoproterozoic to Neoproterozoic transition. The large-scale subsidence of the Indian craton leading to the development of a vast deep-water cratonic basin is likely to be related to terminal Mesoproterozoic fragmentation of parts of the supercontinent Rodinia. [ABSTRACT FROM AUTHOR]

Singhbhum Craton (>3500 Ma), the Archean continental nuclei of eastern India, preserves on its southern margin coexisting deep crustal granulites and shallow crustal metasedimentary lithologic units that were juxtaposed through complex transpressional tectonics. U-Pb detrital zircon ages were obtained from five samples of widely separated locations of two parallel belts, which are known as the Northern and the Southern Supracrustal Belts. In addition, zircon grains from a pegmatite from the central gneissic complex were also dated. The LA-ICP-MS derived U-Pb age data from these samples lead to the estimation of age of sedimentation and the thermal events in the provenance. The U-Pb age from these samples yielded younger than 2235 ± 28 Ma for Northern Supracrustal Belt, while that of the Southern Supracrustal Belt is consistently younger (<1835 Ma). Development of these basins at the southern margin of the Singhbhum Craton was associated with four cycles of sedimentation at ca. 3100–2800 Ma, ca. 2800–2450 Ma, ca. 2450–2235 Ma and ca. 2235–1835 Ma. These cycles resulted in the southward growth of the Singhbhum Craton through successive opening and closing of basins. The ca. 2540–2480 Ma zircon population of the Northern Supracrustal Belt has no proven source from the Singhbhum Craton, but distal cratonic blocks might have provided the detritus. The provenance of the sediments could also be traced in the transcontinental pre-existing cratonic block, e.g. East Antarctica. [ABSTRACT FROM AUTHOR]

The article discusses research being done on oxygenation of Earth's atmosphere. It references the study "Oxygenation of the Archean Atmosphere: New Paleosol Constraints From Eastern India," by Joydip Mukhopadhyay et al. in the 2014 issue. Topics discussed include the presence of pyrophyllite-quartz horizon in the Singhbhum Craton, the redox state of the atmosphere and oceans, and the enrichment of heavy rare earth elements (HREE).