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  • 1
    Publication Date: 2012-12-11
    Description: :  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, stable-isotope, 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 18 O V-PDB values of calcite cements of –3.6 to –11.7 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 °C 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. The humid tropical environment and "ever-wet" conditions on the island of Borneo together with rapid Cenozoic uplift likely led to paleoaquifer flow with fluids focused through adjacent deltaic units into the reef carbonates. In these coastal carbonates from the humid Samarinda region, continental groundwater flow has resulted in pervasive stabilization and calcitization, features rare in arid or temperate counterparts.
    Print ISSN: 1527-1404
    Topics: Geosciences
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  • 2
    Publication Date: 2014-05-03
    Description: Multiple bioclaustrations identified as possible Chaetosalpinx are reported from a stromatoporoid of Rhuddanian age from Hiiumaa Island, Estonia. This is the second record of symbiotic worm endobionts from the end-Ordovician mass extinction recovery fauna of Estonia. The end-Ordovician mass extinction did not terminate complex ecological relationships between at least some worm endobionts and their hosts.
    Print ISSN: 0883-1351
    Electronic ISSN: 0883-1351
    Topics: Geosciences
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  • 3
    Publication Date: 2015-02-27
    Description: A holistic approach is adopted here to evaluate basin-wide trends in carbonate systems, their subenvironments and the potential marine biodiversity partitioning between different habitats within the Coral Triangle biodiversity hotspot in central Southeast Asia. The Central Indonesian Kutai Basin is typical of many Cenozoic Southeast Asian basins in having extensive and varied carbonate systems, and is one of the few regions in the Coral Triangle with detailed systematic multitaxon evaluation of Oligo-Miocene deposits. The Kutai Basin may therefore provide data, when compared with other modern and global datasets, to better understand marine biodiversity development within the global diversity foci. Carbonate systems in the Kutai Basin included small-scale ephemeral features, such as delta-associated patch reefs, mixed carbonate-clastic shelves, and large-scale (〉 10 km) land-attached and isolated carbonate platforms affected by varied energy regimes. Twenty-five–plus subenvironments or habitats are spread across the different carbonate systems, with the large-scale platforms hosting over 12–15 different habitats. These subenvironments include clastic-influenced mesophotic coral reefs/carpets, nonclastic- and clastic-influenced sea-grass beds, downslope reworked coral rubble, and shallow low-energy inner platform areas, to name a few. Perhaps paradoxically, the systems that two decades ago were almost unstudied, the clastic-influenced coral reefs/carpets, are now the only ones in the region to have been systematically studied for their marine biota. Detailed biotic studies have therefore only investigated 〈 4 of the 25-plus potentially habitable carbonate subenvironments within the basin. This variability of carbonate systems and their subenvironments, but paucity of detailed biotic data is typical of many basins within equatorial Southeast Asia. It is recognized that detailed multitaxon biotic studies are in their infancy for Southeast Asia, and that there are challenges of taxonomic bias and/or preservation for many groups within the fossil record. Currently, however, we cannot evaluate marine biodiversity partitioning across the varied habitat mosaics of Southeast Asian carbonate systems with possible pathways discussed for furthering this field of research. It is likely that we are (?grossly) underestimating biodiversity on a basin-wide and probably a system-wide scale. It is hoped that studies of this type will contribute towards better understanding of equatorial marine carbonate systems, their biological inhabitants and producers, and the spatio-temporal development of global biodiversity hotspots.
    Print ISSN: 0883-1351
    Electronic ISSN: 0883-1351
    Topics: Geosciences
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