Analysis of beachrock samples along Southern and Western coasts of Sri Lanka by spectroscopic methods

Abstract

Beachrocks are sedimentary structures commonly observed where there is warm sea water in tropical and subtropical regions as a result of cementation by CaCCb of coastal sediments in the tidal zone. Comprehensive studies have been carried out to determine the formation mechanisms of beachrocks specially Japan to improve an alternative countermeasure against erosion by man-made rocks. When focusing on formation mechanism of beachrocks elemental and mineralogical composition is vital. Considering this important application, we used spectroscopic techniques to understand composition of beachrocks in southern coastal region between Ahangama to Kaikawala and Uswetakeiyawa in the western coastal region of Sri Lanka. The presence of minerals in beach rock samples in southern coast were identified by FT-IR spectroscopic technique. The constituents of minerals present in the beach rocks are further confirmed by XRD technique. Elemental concentrations of beach rock samples have been analyzed using technique of WDXRF spectrometry. Uswetakeiyawa beachrock was mainly analyzed by using EDX in SEM. Beachrocks in southern coasts is comprise higher percentage of Aragonite which is the polymorph of CaCCb, frequently founded in most of the sites in the world. Further the composition shown similarities with Indian (Tiruchendru) and Japan (Okinawa) beachrock occurrences. Comparative to the composition of southern coast beachrock, XRD analysis did not indicate any CaC03 polymorphs Uswetakeyyawa, beachrocks. Instead it indicated the presence of Kutnohorite (Ca(Mn,Mg,Fe)(C03)2).