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Geology Notes On – Phanerozoic Rocks Of India – For W.B.C.S. Examination.
The northern margin of the Indian plate bears a sequence of Tethyan sediments of platform facies ranging in age from Vendian to Cretaceous punctuated by a series of breaks in sedimentation. There are about five transgressive-regressive cycles until the Tethys got eventually closed after the end of Cretaceous.Continue Reading Geology Notes On – Phanerozoic Rocks Of India – For W.B.C.S. Examination.
The Palaeozoic stratigraphy was somewhat confused due to the mis-reporting of fauna supposedly of late Silurian and Devonian ages. This has been cleared now and it is seen that there are two major breaks in Palaeozoic viz, Late Cambrian—Early Ordovician and Late Silurian-Devonian.
The Mesozoic sequence represents deposition on a passive continental margin with slow subsidence. The pattern was, however, entirely different along the northern boundary close to the Indus-Tsangpo Suture where an arc-trench system developed in Mesozoic times resulting in the deposition of wildflysch and generation of island arc volcanism.
The geology of India is diverse. Different regions of India contain rocks belonging to different geologic periods, dating as far back as the Eoarchean Era. Some of the rocks are very deformed and altered. Other deposits include recently deposited alluvium that has yet to undergo diagenesis. Mineral deposits of great variety are found in the Indian subcontinent in huge quantity. Even India’s fossil record is impressive in which stromatolites, invertebrates, vertebrates and plant fossils are included. India’s geographical land area can be classified into the Deccan Traps, Gondwana and Vindhyan.
The understanding of the Earth’s processes in the geologic past has advanced due to the ability to resolve geologic time in the rock records at progressively higher levels of time resolution. The rock records are now being probed to decipher short-term processes of palaeobiological and palaeoclimatic interests operating at a few tens of kyr to centennial and decadal scales.
How good are the stratigraphic records to answer such questions? The fragmentary nature of the stratigraphic records is well recognized, and it is best summed up by the catchphrase “more gaps than record” or “a set of frozen accidents” of some leading stratigraphers. Quantitative analysis of sedimentary records in the 1980s and taphonomic studies supported by radiometric dating of shells in 1990s gave insight into an estimation of temporal resolutions of rock records. Two distinct types of resolutions are recognized, stratigraphic resolution (among strata) and palaeontological resolution (within stratum). The stratigraphic resolutions in 106-years scale can be achieved by biostratigraphy alone in the Cenozoic, and it can be raised to 105 to 104-years scale when integrated with as many means as magnetostratigraphy, radiometric dating, and cyclostratigraphy.
Taphonomic processes deteriorate the palaeontological resolutions, and it is of major concern in bridging the gap between 104-years scale resolutions in the geological records and the human-life observations. The palaeobiological and palaeoclimatic processes at this scale may require exceptional records and rigorous approach to demonstrate that the requisite time-resolution is achievable in the investigated rock record.
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