Depositional environments of the Bara formation sandstone from Lakhra areas Sindh, Pakistan

Abstract

Twenty four samples of the Bara formation from east and west sections of Lakhra areas have been investigated, to interpret the environments of deposition and to propose a suitable classification for the sandstones present in the studied sediments. Values of different statistical parameters of the studied sediments grain size data, for example mean, median; standard deviation, skewness, and kurtosis were determined for plotting the cumulative curves and histograms to analyse the data. Study of the shapes, roundness and the sphericity of the grains provided valuable information regarding the environment of deposition. The 92 percentage negative and 8 percentage positive values of skewness, respectively, indicated that the studied sediments are composed of coarse grained-fine grained sediments and deposited under the high-low energy conditions of fluviatile and beach environments. The presence of abundant amounts of Quartz and Si02 in the bulk-rock samples also suggested fluviatile/beach environments. The inclusive graphic standard deviation diagrams and the size distribution data also indicated that fine-medium grained sediments, were deposited in the study areas. Occurrence of three groups of sediments for example, sediments from lower lagoon; sediments from upper lagoon and river; and the sediments from the deadend marsh channels from the deeper parts of the basin of deposition, have been recognized. The kurtosis values indicated that studied sediments are composed of Platykurtic, Leptokurtic and Mesokurtic groups of sediments. The sandstones, present in the Bara formation of the Lakhra west and the east areas, showed the textural maturity, therefore, have been classified as sub-mature, and sub-mature to mature sandstones, respectively.