978-1-7281-3632-5/19/$31.00 ©2019 IEEE Elemental and Mineralogical Analysis of Beachrocks in Southern Coastal Region Sri Lanka ABN Dassanayake, CL Jayawardena, KVUI Edirisooriya, MADP Thilakarathna, V Thirunavukkarasu Department of Earth Resources Engineering University of Moratuwa, Katubedda 10400, Sri Lanka. anjula@uom.lk, chulanthaj@uom.lk, indiedirisooriya@gmail.com, darshanaprazad@gmail.com, vijiththa1994@gmail.com Abstract— Beachrock is coastal sediment that has been cemented primarily by calcium carbonate within the intertidal zone in tropical and subtropical regions. Considering that beachrock has the potential to inhibit coastal erosion, we performed laboratory tests to understand the formation mechanism of beachrocks in southern coastal regions of Sri Lanka. The mineralogical composition of beachrock samples were identified by FT-IR spectroscopic technique. The constituents of minerals present in the beachrocks were further confirmed by XRD analysis. Elemental concentrations of beachrock samples have been examined using WD-XRF spectrometry. The formative environment (sea water) was analyzed using EDTA titration, AAS, UV/Vis spectroscopy and Iron Chromatography. The results reveal the presence of minerals aragonite, calcite, orthoclase, quartz, albite, kaolinite and lime in the beachrocks. According to the results, there is a high probability to precipitate CaCO3 from the sea water in southern coastal regions indicating a positive formative environment for beachrocks. Hence, by appropriate regulation of the conditions could foster the development of manmade beachrocks to control the coastal erosion. Keywords—Beachrock, formation mechanism, mineralogical analysis, XRD I. INTRODUCTION Beachrock is the consolidated deposit that results of lithification of beach sand and gravels by calcium carbonate cementation. These are generally found in the sandy beaches of tropical and subtropical regions with tidal and intertidal zones. Beachrock is a sedimentary formation mainly consists with carbonate cement-aragonite or magnesium calcite [1], which most commonly appear as layered deposits inclined towards the sea. The natural factors of a beach, such as gentle slope of the foreshore, sufficient shell content and ground water temperature causes the formation of beachrocks [2]. These rocks in beaches act as a resistant barrier to protect the shore line from erosion. The cementation mechanism of beachrocks differ from one location to another and influenced by varying factors but primarily derived by physicochemical precipitation such as follows. Physicochemical precipitation of high-Mg calcite and aragonite from seawater resulted from high temperatures, is considered as the earliest approximation for cementation in beachrocks by Ginsburg, 1953 and Stoddart and Cann, 1965 [1, 3]. Later, Schmalz, 1971 proposed physicochemical precipitation of low-Mg calcite and aragonite by mixing of meteoric and fresh groundwater with seawater as the primary mechanisms for the origin of beachrock cements [4]. Thorstensen et al, 1972 and Hanor, 1978 favored the physicochemical precipitation of high-Mg calcite and aragonite by degassing of CO2 from beach sediment pore- water as the origin of beachrock cements [5][6]. In contrast, Taylor and Illing, 1969, Krumbein, 1979, Strasser et al 1989; Molenaar and Venmans,1993 and Bernier et al, 1997 reported precipitation of micritic calcium carbonate as a byproduct of microbiological activity as primary mechanisms for the origin of beachrock cements [7-10]. Studies conducted on beachrocks all over the world (Fig. 1) have shown that tropical and subtropical climates are more preferred for beachrock formation and over 90% of the occurrences are between 40 ⁰ N and Tropic of Capricorn [11]. Fig. 1. Beachrock occurrences in the world [11] Sri Lanka as a tropical country, favors the origin of beach rocks among the discontinuous reefs along the coast. These beachrocks are exposed in many places along the present coastline as reef-like patches and long reefs. Patches of calcareous algae occur on the surface of exposed beachrocks, and sometimes shells are found embedded on them. In many