Tattekere conglomerate-quartzite association: origin and stratigraphic position of a disputed Archean formation in the supracrustals of Karnataka, India
The origin and stratigraphic interpretation of the conglomerate-quartzite rocks occurring in and around Tattekere and Kumkumna Hosuru villages in the Holenarsipur Supracrustal Belt, is an important aspect of the Precambrian Geology of Karnataka, India. Due to the controversy regarding its origin and stratigraphic status, the geology of the Holenarsipur Supracrustal Belt has been interpreted by previous workers in different ways. In the present work, attempts have been made to resolve the controversy based on recent observations and analytical results. The petrographic characteristics of conglomerates and quartzites, the occurrences of primary sedimentary structures and their similarity to proven sedimentary quartzites in the northern sector, along with the chemical composition of the quartzites point to a sedimentary origin for this association. The heavy mineral and chemical composition of the quartzites suggest a major source rock contribution from a granitic terrain with subordinate contributions from metamorphic and/or metasedimentary rocks. Al 2O 3 and Cr enrichment in quartzites resulted from deposition of Al 2O 3-rich chromite grains derived from isolated exposures of ultramafic rocks. Possible K-metasomatism has also been inferred from the chemical composition of the quartzites. From field distributions, petrographic characteristics, chemical compositional data and inferred source rock contribution, it may be inferred that the conglomerate-quartzite association occurring in and around Tattekere and Kumkumna Hosuru villages in the Holenarsipur Supracrustal Belt represents a single horizon with a near-basal position in the stratigraphic sequence. This suggests a basal/near-basal unconformity in the stratigraphic succession of Holenarsipur Supracrustal Belt.