Citation:
Saitis G, Koutsopoulou E, Evelpidou N, Kawasaki S. A comparative study of beachrock mechanism formation focusing on natural and artificial beachrocks: case of Diolkos, Corinth, Greece and Sumuide, Okinawa, Japan. RCG2019 “Geomorphology of Climatically and Tectonically Sensitive Areas”. 2019.
Abstract:
Beachrocks are a window in the past environmental, geological, sedimentological and geographical conditions that were dominant on the coastal zone. The minerochemical examination of cement and the sedimentological analysis are the most efficient methods for understanding the formation mechanism. However, the examination of beachrock samples have limitations and the evidence of formation mechanism are not enough. This study emphasizes on the beachrock formation mechanism through the comparison of cement characteristics, mineral chemistry and sedimentology of beachrock occurrences from different geological and geographical setting areas Diolkos, Corinth, Greece and Sumuide, Okinawa, Japan. Furthermore, in order to investigate the beachrock formation, artificial beachrock samples were created in-vitro using sand samples and ureolytic bacteria from Okinawa under accelerating conditions. Bulk samples were collected from the study areas in order to analyze their mineralogical (XRD and SEM-EDS) and chemical (XRF) composition. Microscopy studies (optical and SEM-EDS) revealed that the cement agent from Diolkos is mainly composed of High-Magnesian Calcite (HMC) in comparison to the Sumuide beachrock which is characterized by the presence of calcite and aragonite. Additionally, the analysis revealed clastic silicate and aluminosilicate minerals. The grain composition of Diolkos slab consists of
quartz, plagioclase, K-feldspar with 20% bioclasts compared to the Sumuide beachrock grains that consist of calcareous residuals from the local coral reef. The artificial beachrock investigation indicated that ureolytic bacteria that reside in the Sumuide beach sediment, are capable to precipitate aragonite coating the sediment grains and filing the pores. The cementation was most active in the top part of the samples than the bottom part. This is an indicator that the beachrock formation might occur in depths were these bacteria can be found. The artificial beachrock analysis included its physicochemical parameters using UCS
penetration, pH and Ca2+ measurements, X-Ray CT-scanning, petro-graphic polarized microscopy, XRD, and SEM-EDS.