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Grain size distributions are widely used to describe sedimentary geochemistry, depositional environment, and sediment transportation. The objective of this study is to analyze grain size distributions of modern sandy beach sediments in Sri Lanka. Sediment samples (n = 90) were collected from beach berm, representing the entire coastline of Sri Lanka. Grain sizes were determined by the dry-sieving method. Statistical parameters such as mean size, sorting, skewness, and kurtosis were calculated using GRADISTATV9.1 software for all the sieved sediment samples. Grain size variations (108.2 – 609.8 µm) show that Sri Lanka mainly consists of medium sand, whereas the northeast part of the country mixes with fine sand due to the influence of Bengal fan sediments. The variations of skewness (-0.229 – 0.446) and sorting (1.305 – 2.436) indicate symmetrical distributed moderately sorted samples. These variations specify a moderate energy depositional environment/wave action around the coastline of Sri Lanka. In addition, grain size analysis confirmed relatively high and low energy deposition environments on the west and east coasts, respectively. Accordingly, the west coast is more vulnerable to coastal erosion compared to the east coast of Sri Lanka. Therefore, this study provides the baseline grain size distribution data that can be used in decision-making for coastal zone management by mitigating beach erosion.

Montmorillonite (MMT) is a layered aluminosilicate with a higher specific surface area. Montmorillonite is the most abundant of the smectite clays that have a spectrum of advanced applications. Characterization of Murunkan deposit (i.e. known as a potential for MMT clay) is poorly investigated. Therefore, the main objective of the current study is to characterize clay minerals present in the Murunkan area. Three core samples were collected from in and outside the Giant's Tank reservoir at Murunkan. Samples of each core were cut into 0.125 m intervals. Mineralogical and geochemical characteristics of the Murunkan clay deposit were evaluated using X-ray diffraction, Fourier Transform Infra-Red, and X-ray fluorescence techniques. X-ray diffraction analysis indicates almost similar patterns in each clay sample, dominated by MMT peaks in comparison with the Sigma-Aldrich commercial standard. Kaolinite and illite were also identified as potential clay minerals in the Murunkan area. Fourier Transform Infra-Red spectra of analyzed clay samples show transmittance bands mostly matching with the standard data of kaolinite and MMT. X-ray fluorescence results indicate that the average compositions of clay samples taken from Core 1 and Core 2 are comparable with that of the Sigma-Aldrich MMT clay. Geological observations of the core samples showed that the clay deposit was formed mainly due to in-situ weathering of bedrock and long-term accumulations of sediments. The washbasins/depressions in the Murunkan area can thus be identified as prospective locations for MMT clay.