Deposition of calcium sulfate from sea water

Abstract

SHORTER COMMUNICATIONS 395 have formed under oxidizing, evaporitic, low energy, protected conditions. Presently they from in (i) tidal channels, lagoon, playa lakes, and mud flats within the area of intertidal influence, and (ii) in supratidal environments. Fossils are rare and confined to some localized bands. Gypsum crystals are formed within the sediments after their deposition and are therefore postdepositional. Thin laminations of gypsum are formed in sediments of deeper parts of the playa lakes or lagoon. On the basis of the present study it is interesting to speculate on the origin of some older deposits of Kutch. It is suggested that the unfossiliferous sections of 'Gypseous Shale' sequence (Mohan and Gupta, 1968) of the Tertiary, which closely resemble the Rann deposits, had a similar mode of origin during regressive cycles. The intercalated fossiliferous bands are perhaps thin records of short spells of marine transgressions. Similarly, the unfossiliferous yellow-grey gypseous clays of Katrol series were probably formed under much the same conditions as the Rann sediments. Acknowledgements: The author is thankful to his colleague Mr. S. K. Biswas for discussions on some aspects of this subject, and to Mr. Madan Mohan for critical comments on the draft of this paper.