This study offers insights into the diagenetic alteration of coastal carbonates that formed coevally with nearly continuous siliciclastic influx in a humid equatorial setting. A multi-disciplinary petrographic, cathodoluminescent, stableisotope, trace-element and major-element investigation allowed characterization of diagenetic features, paragenetic sequencing, and an interpretation of diagenetic environments from Neogene patch reefs of the Samarinda region, Mahakam Delta, Borneo, SE Asia. Marine cements are absent from the patch reefs, with grain micritization the only marine diagenetic feature recognized. The predominant diagenetic feature within the patch reefs is pervasive neomorphic stabilization and cementation of aragonite reef components to calcite that pre-dates all compaction features. Meteoric aquifer flow derived from the adjacent landmass is inferred as the main parent diagenetic fluid, since d 18 O V-PDB values of calcite cements of 23.6 to 211.7% are consistent with precipitation from SE Asian freshwater, and inconsistent with a wholly marine origin. Late-stage fracturing, cementation, and chemical compaction are relatively minor features and attest to a changing paleohydrologic and diagenetic environment. Evidence for a shallow to moderate burial diagenetic regime for these later features are maximum temperature of 53 uC and burial depths , 1000 m inferred from stable-isotope values of calcite and late dolomite cements, dolomite crystal fabrics, the onset depth of stylolite or dissolution-seam formation, and regional geothermal gradients.
Fringing reefs of SE Asia may conservatively comprise ~30% of the world's coral reef area, but remain almost unstudied (White, 1987; Tomascik et al., 1997). This study provides insights into the primary sedimentological and early alteration characteristics of an isolated fringing reef system (Kaledupa-Hoga) from the Tukang Besi Archipelago, SE Asia. A combined multispectral satellite imagery, field and petrographic study allowed for the generation of an environmental facies map, which acts as a model for the distribution of primary sedimentological characteristics in relation to the primary environmental facies. The islands of the Tukang Besi Archipelago are mesotidal (<2 m) affected by strong diurnal and oceanic tidal currents, as well as high wave energy influenced by the bi-directional southeast Asian monsoon. An environmental facies map generated from Landsat-7 imagery and utilising field observations defines ten environmental facies. The facies map generated has a >71% accuracy when compared with field and sedimentary data. With the exception of the reef crest and reef slope that commonly have widths on a sub-imaging resolution (<30 m), the facies map accurately demonstrates the heterogeneous nature of the carbonate system. 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 gravelsized 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 (grainpackstones). 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 satelliteidentifiable 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.
Carbonate breccias dissociated from their platform top counterparts are little studied despite their potential to reveal the nature of past shallow-water carbonate systems and the sequential alteration of such systems. A petrographic and stable isotopic study allowed evaluation of the sedimentological and diagenetic variability of the Cenozoic Batu Gading limestone breccia of Borneo. Sixteen
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