Kasturi Bhattacharyya
The age of the Kolhan Basin was mysterious. Careful literature review and logical constraints from available data in literature can constrain the age. The maximum age of Kolhan Basin (closing) is 1531 Ma from whole rock Rb/Sr age of Kolhan shale [1] and opening of basin corresponds to Dalma plume (1600 Ma) [2,3]. Hence the duration or life of Kolhan Basin corresponds to 30 Ma. The Dalma plume magmatism was possibly part of a 1600 Ma global tectono-thermal event. This is synchronous to the existence of the Columbia supercontinent. The implied age directly gives the tectonic implication of the basin.\
The Kolhan basin in Singhbhum district is unique in many respects. Its narrow strip-like outcrop pattern, controlled by the NE_SW trend of the much older Iron-Ore Formation synclinorium abuts against the Singhbhum Granite in the east of a greater portion of its trend. A part of eastern and entire western boundary is in contact (fault) with the Iron-Ore Formation rocks. Its age, stratigraphic relationship and tectonic framework is still controvertial. The Kolhan Shale Formation is of course definitely younger than the Iron-Ore Formation as originally suggested by Dunn and is also younger than the Singhbhum Granite as is clear from the field relations.
The Kolhan Basin is set in a diversified lithological provenance, so that it exhibits the development of a rudaceous, arenaceous, calcareous and an argillaceous facies within only a few hundred feet of thickness. The various members of the Formation of the formation dip in general uniformly low to the west away from the contact with the Singhbhum Granite.
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