Modern fringing reef carbonates from equatorial SE Asia: An integrated environmental, sediment and satellite characterisation study

Although field and satellite imagery observations reveal ten environmental facies, sedimentological characterisation results in a lower number of distinctive categories due to the similarity of many deposits. Foreshore/backshore and bare intertidal deposits are distinctive and are composed of reef-derived material that has been reworked shorewards. Seagrass-associated facies all show some fine silt-clay sized material (< 8%) with common imperforate foraminifera and pervasive micritisation, but also contain high abundances of reworked coral and shell allochems. Coral-associated reef flat facies are typically low in imperforate but high in perforate foraminifera, and show lesser effects of bioerosion and very low silt contents. The reef slope and crest are characterised by high abundances of gravel-sized fragmented corals with the highest abundances of echinoderm material and alcyonarian sclerites. Sediment samples across all fringing reef environments from the Kaledupa-Hoga transects are characterised almost exclusively by grain-rudstone textures, with < 2-5% silt and clay size fractions, and minor baffling of fines in seagrass-associated settings (grain-packstones). The paucity of fines across the fringing reef systems as a whole, and the degree of homogenisation of sediment characteristics across the different field- and satellite-identifiable environmental facies are attributed to: (1) high wave/current energies, (2) the small size of the islands rendering limited protection, (3) bidirectional monsoon winds and (4) the lack of reef rimmed margins built to sea level. Absent from these deposits are well developed high energy windward and low energy leeward deposit characteristics and/or an overriding hurricane influence that are commonly seen in fringing reef systems from other areas.