Depositional mechanism of Fort Member Sandstone (Early-Late Bathonian), Jaisalmer Formation, Western Rajasthan: insights from granulometric analysis

Abstract

Granulometric analysis is an imperative tool used to reveal the hydrodynamic conditions, mode of transportation and deposition of siliciclastic sediments. Forty-two samples of Fort Member Sandstone of the Jaisalmer Formation, Western Rajasthan were selected and studied with the help of detailed granulometric analysis which include both graphical as well as mathematical moment methods. Micro textures were recognized as chatter marks, curved and straight steps, grooves, upturned plates in association with V impact pits and triangular solution pits suggesting the predominance of mechanical activities over the chemical dissolution. The analysis shows the sandstone is coarse-grained, very well sorted, very fine to fine skewed and very platykurtic to platykurtic in nature. The dominance coarse grains give an indication of high energy level and almost stable as there is not much variation in the grain-size. Bivariate plots show that the sediments were deposited in beach sub-environment which was also confirmed by the linear and multigroup discriminant analysis. C-M plot shows that the sediments were transported by rolling and log-log plot also confirms the transportation by the traction processes. These features describe the sediments deposited by the fluvial process dominated by tractive current pattern in a shallow marine depositional environments.

Keywords

• granulometric analysis
• hydrodynamic condition
• depositional environment
• fort member
• jaisalmer formation