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Early diagenetic glauconitization of feldspar grains in a middle Proterozoic tidal-flat complex

A. K. Chaudhuri
Early diagenetic glauconitization of feldspar grains in a middle Proterozoic tidal-flat complex
AAPG Bulletin (May 1980) 64 (5): 691


Extensive glauconitization of feldspar grains exists in arkosic sedimentary rocks of a middle Proterozoic carbonate tidal-flat sequence in the Godavari valley, south India. Glauconitized sedimentary rocks occur as (1) well-defined thick layers, (2) small lenses at different stratigraphic levels, and (3) infilling in the intercolumnar areas of SH-stromatolite structures, in colonies of SS-type structures, and shrinkage cracks in algal mats. Glauconite replaces potash feldspar and plagioclase along cleavage and fractures. Varying degrees of replacement from incipient to complete are observed. Petrographic studies reveal two phases of glauconitization. The major phase, affecting detrital grains, is early diagenetic and is almost syndepositional. A second phase, affecting authigenic feldspar overgrowth, follows silicification. Primary structures and sediment characters of glauconitized sandstones indicate that glauconite formed in varying conditions of turbulence and bathymetry. A glauconitic layer in Ramgundam (18 degrees 45'N, 79 degrees 26'E) appears to have formed in a quiet environment, at moderate depth below wave base, during brief periods of transgression. Large bed forms in a thick layer near Manthani (18 degrees 33'N, 79 degrees 40'E), indicate a turbulent environment. Small sand lenses within carbonate rocks reflect rapid deposition by high-velocity currents. Close association of glauconite with SH and SS-type stromatolites indicates origin in agitated environments at very shallow depth, and supratidal origin is implied by its presence in shrinkage cracks within algal mats. Evidence of organic activity to aid glauconitization is absent. Even if blue-green algae might have effected glauconitization of detritus associated with stromatolites by providing small areas of reducing environment within a strongly oxidizing macroenvironment, glauconitization in the thick, sandy zones appears to be independent of biochemical processes.

ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 64
Serial Issue: 5
Title: Early diagenetic glauconitization of feldspar grains in a middle Proterozoic tidal-flat complex
Author(s): Chaudhuri, A. K.
Pages: 691
Published: 198005
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
Meeting name: AAPG-SEPM-EMD annual meeting
Meeting location: Denver, Colo., USA, United States
Meeting date: 19800608June 8-11, 1980
Summary: Y
Accession Number: 1981-002962
Categories: Sedimentary petrology
Document Type: Serial Conference document
Bibliographic Level: Analytic
N18°00'00" - N19°00'00", E79°00'00" - E80°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 1981
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