On the occurrence of caliche pisolites from the Western continental shelf of India

Abstract

Pisolitic limestones collected from the western continental shelf of India, at a depth of 60 m, showed characters similar to caliche pisolites. Low-magnesium calcite and quartz are the major minerals in the pisolites. Polished sections show downward thickening of pisolites with intermittent macro- and microfractures. Micrite showing clotted and pelloidal texture is the dominant component of the pisolites. They further consist of calcite crystal structures resembling Microcodium, root voids filled with sparry calcite and reddish brown peloids. Spherulitic structures exibiting radial patterns of calcite formed by the neomorphism of Microcodium have been identified. Fibrous calcite cement occurs as replacement after prismatic calcite and as terminal expansion of prism faces. Acicular calcites, flower spar calcites and dendritic calcites which owe their origin due to intense evaporation are also found. The environmental conditions for the formation of caliche pisolites are discussed. It is suggested that these caliche pisolites represent continental conditions of the shelf during the Holocene and are formed by pedogenic soil processes in association with a semi-arid climate and moderate rainfall.