Granulometric Analysis of Rajmahal Inter-Trappen Sedimentary Rocks (Early Cretaceous), Eastern India, Implications for Depositional History

Abstract

Rajmahal trap along with its Inter-trappean sedimentary rocks is found exposed in the eastern part of India (24°00'E - 25°15'N; 87°20'E - 87°15'E). Ten representative samples of Inter-trappean sandstone selected from the study area have been subjected to granulometric analysis. The result of the grain size analysis indicates that these sandstone specimens are very fine to fine grained with unimodal grain size distribution. They are dominantly fine skewed and generally mesokurtic in nature. The linear discriminant function plots of various grain size parameters suggest that these sandstones appear to have been deposited either in shallow marine or lacustrine environment. On multigroup multivariate discriminant functions V1 - V2 diagram majority of the samples fall in the beach depositional environment, indicating that most of the sediments were reworked by wave processes before deposition. The C-M pattern diagram shows that the sediment deposition took place in beach environment by rolling or suspension of sediments; hence the clastics were deposited in low energy condition.