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

Aparna Sinha,Sarwar Rais

doi:10.4236/ijg.2019.103015

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.

Highlights

Grain size is the most fundamental feature and important descriptive property of siliciclastic rocks
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; the clastics were deposited in low energy condition

Summary

Introduction

Grain size is the most fundamental feature and important descriptive property of siliciclastic rocks. Rajmahal volcanic rocks of Early Cretaceous age are part of Upper Gondwana Group These volcanics along with Inter-trappean strata occur in eastern parts of Eastern Indian Shield [5] [6] [34]. Lower one-third part of Rajmahal lava contains Inter-trappean beds whereas upper two-thirds of the rock succession consists of subaerial fine grained basalt without any Inter-trappean beds [7]. These Inter-trappeans are made up of both clastic and volcanoclastic rocks. The clastic rocks occur in the form of thin or thick [7] beds of sandstone, black or grey shale/mudstone and lenses and pockets of bentonite, pyroclasts and oolites [7]

Methods

Results

Conclusion