Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

C. Gundu Rao ¹, Dwijendra K. Sharma ¹

Affiliations
1 Department of Geology, Dharam Samaj College, Aligarh 202 001, IN

Abstract

The dun pink micritic limestone and purple shale alternations unit resemble the deeper Water carbonates. The dull pink micritic limestones of the unit give a weak 1:4 dilute acid reaction and negative test for Mann's stain solution for dolomite. Despite this, the samples showon XRD Charts, a prominent peak for ordered dolomite (104) 2.88 Å to the total exclusion of calcite. The important point of the present example is, despite complete dolornitisation, the resulting dolostone neither shows change in porosity nor in size and shape of the micritic particles. The kind and intensity of dolomitisation observed in the present example are difficult to explain in terms of the existing dolomitisation models for deeper water limestones.

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C. Gundu Rao ¹, Dwijendra K. Sharma ¹, Sunil Kumar ¹

Affiliations
1 Department of Geology, D. S. College, Aligarh 202001, IN

Abstract

The pink Quartzarenite Unit 3 (Q₃) of Larji Window Section (Lesser Himalaya), Kulu District, Himachal Pradesh, India, shows a lower thickness of continuous, undisturbed, uniform, horizontal laminations followed by a zone of flat stratification and this in turn by cross-bedded layers. Horizontal stratification is referred to as due to high flow regime conditions and the cross stratification to moderately shallow upper part of low flow regime conditions. Flat stratification (crenulated or wavy laminations of low amplitudes and broad wave lengths) are commonly observed in flume experiments as a function of low flow regime in shallow water formed by the migration of very small ripples or very shallow sand waves but rarely reported from the stratigraphic record. The only known two instances are from Bull Run Formation (Triassic) of Northern Virginia and Duncannon Formation (Devonian) of south-central Pennsylvania. In this connection, reporting the occurrence of flat stratification from such an ancient quartzarenite unit (Lower Upper Proterozoic) as of Larji Window may be of considerable interest from the point of view of Dynamic Stratigraphy.

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