Mg-rich ferric illite in marine transgressive and highstand systems tracts: Examples from the Paleoproterozoic Semri Group, central India

Abstract

This paper focusses upon two glauconitic sandstones in the Paleoproterozoic Deoland Formation and Chorhat Sandstone, both belonging to the Semri Group, central India. In both the cases glauconitic minerals occur in sandstones deposited in the marine realm, within a transgressive systems tract (TST) for the former unit and within a highstand systems tract (HST) for the latter. The proportion of glauconitic minerals increases in the paleo-offshore direction. Petrography reveals selective early glauconitization of detrital K-feldspars along their fringes, cleavages and the fractures created by volume expansion during progressive alteration, leading to the generation of peloids with small relics of the precursors. XRD and mineral chemistry reveal a structure typical of glauconite, and more akin to Mg-rich ferric illite. The mineral chemistry of the glauconitic mineral phases remains the same whether the glauconitization process was incipient or at an advanced stage.These findings contrast with the previously held belief that ferric illite is confined to terrestrial or marginal marine sediments, and concurs with recent observations that the mineral can form in the open sea, but with high Mg. Since there are no ferro-magnesian minerals in association with these Vindhyan glauconitic sandstones, the seawater appears

Substrate control on formation and maturation of glauconites in the Middle Eocene Harudi Formation, western Kutch, India

“…10). This is in accordance with the earlier observations that AlFe 3þ substitution is predominant in glauconitic minerals (Odin and Matter, 1981;Velde, 1985;Dasgupta et al, 1990;Amorosi et al, 2007;Banerjee et al, 2008). All data occupy the true glauconite field of Odin and Matter (1981) in K 2 O vs. total Fe 2 O 3 plot (Fig.…”

“…Glauconite pellets are known to occur in marine sedimentary rocks ranging in age from Palaeoproterozoic to recent (Odin and Matter, 1981;Dasgupta et al, 1990;Amorosi, 1994;Chafetz and Reid, 2000;Lee et al, 2002;El Albani et al, 2005;Meunier and El Albani, 2007 and references therein; Amorosi et al, 2007;Bandopadhyay, 2007;Banerjee et al, 2008;Chattoraj et al, 2009). Glauconite is generally considered as common authigenic product of marine environment and is indicative of low sedimentation rate (Amorosi, 1995(Amorosi, , 1997Ghibaudo et al, 1996;Kitamura, 1998;Amorosi and Centineo, 2000;Harris and Whiting, 2000;Giresse and Wiewióra, 2001;Hesselbo and Huggett, 2001;Banerjee et al, 2008;Chattoraj et al, 2009).…”

“…Glauconite is generally considered as common authigenic product of marine environment and is indicative of low sedimentation rate (Amorosi, 1995(Amorosi, , 1997Ghibaudo et al, 1996;Kitamura, 1998;Amorosi and Centineo, 2000;Harris and Whiting, 2000;Giresse and Wiewióra, 2001;Hesselbo and Huggett, 2001;Banerjee et al, 2008;Chattoraj et al, 2009). Most of these studies highlight sedimentation rate as the most crucial factor involved in formation and maturation of glauconite.…”

Glauconites from the Late Palaeocene — Early Eocene Naredi Formation, western Kutch and their genetic implications

“…Glauconitic minerals are reported from various sedimentary rocks ranging in age from Palaeoproterozoic to Recent (Odin and Matter, 1981;Amorosi, 1994;Lee et al 2002;Bandopadhyay, 2007;Banerjee et al 2008). They have two end members, glauconitic mica or true glauconite and ferric illite (Odin and Matter, 1981;Velde, 1985).…”

“…They form either as cements or by the diagenetic alteration of host minerals like quartz, feldspar, calcite and micaceous minerals. The stratigraphic significance of the glauconitic minerals lies in the fact that these are indicative of low sedimentation rate and therefore can be considered as one of the key elements in sequence stratigraphy (Amorosi, 1995(Amorosi, , 1997Amorosi and Centineo, 1996;Kitamura, 1998;Banerjee et al 2008).…”