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2: Tectonic situation of the Bahamas (from James, 2009). Both streched continental crust and Jurassic oceanic crust (dark blue) occur in the Bahamas area.
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... the northern shoreline of Mayaguana. They include three distinctive units that will be formally described in a future work (Godefroid, in prep.). The lowermost unit is made of karstified foraminiferal packstone containing a rich assemblage of Miogypsinids typical of a shallow and energetic reefal environment, and indicating a Burdigalian age ( Fig. 1.12). This age is corroborated by an average 87 Sr/ 86 Sr ratio of 0.708546 corresponding to the early Miocene (18.4-18.7 Ma). The second unit consists of cross-bedded microsucrosic dolostone, likely deposited in a tidal environment. Sr-isotope analyses on this unit gave an average 87 Sr/ 86 Sr ratio of 0.708995 resulting in a late Miocene ...
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... will depend on their growth ability, which is species specific, but also upon local environmental conditions (i.e. water temperature, turbidity, nutrient content, etc.), and on the rate of sea-level rise or fall. Neumann and Macintyre (1985) and Woodroffe (2003) recognize five types of reef according to their response to sea-level changes ( Fig. 3.12). Keep-up reefs. These buildups are able to track sea level as it rises, maintaining a sufficient growth rate that enables the reef crest to remain at sea level. In the Caribbean region, Acropora palmata reefs have generally been able to keep up with fast rates of sea-level rise during the middle Holocene because such reefs can accrete ...
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... on arid tidal flats when desiccation cracks are filled by sediment and subsequent growth of cement pushes the dried, superficial sediment layers upwards (Fig. 5.11). (Wright and Burchette, 1996). In the fossil record, the above-mentioned sedimentary features allow distiguishing between tidal flats that formed in arid, semi-arid, and humid climate (Fig. 5.12). Evaporites are common in arid tidal-flat sediments. Many ancient tidal-flat deposits show signs of dolomitization. On recent tidal flats, dolomitization does not only occur in arid environments such as the Arabian Gulf ( Bontognali et al., 2010) but also in humid conditions. In the Bahamas, for example, incipient dolomite crusts have ...
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... by a erosional surface (ravinement surface). McKee and Ward (1983) identify a number of dune types (Fig. 6.11) that include transverse and barchanoid ridges as well as barchan and parabolic dunes. Dune type is related to the wind regime (uni-or bidirectional) and the importance of vegetation. In the Bahamas, transverse and "haystack" dunes ( Fig. 6.12) are most represented. Parabolic dunes (Fig. 6.13) have been identified in the late Pleistocene record (Kindler and Strasser, 2000), but this occurrence is subject to controversy ( ). The internal structure of coastal dune can be extremely complex due to the variability of wind strength in space and time. Large-scale cross beds are ...
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... CaCO 3 bioerosion is a dynamic process pertaining to complex ecological impacts within coral reefs [2]. The intensity and pace of bioerosion influences the cycling of biogenic CaCO 3 and supports the formation of sediment in large buildups such as carbonate platforms and reef structures [3][4][5]. From the reef ecosystem or colony scale, bioerosion, by way of endolithic (i.e. inside hard substrate) micro-and macrobioerosion, as well as epilithic (i.e. on hard substrate) attachment etching and grazing activity, effects the physical resistance of coral reef framework to extrinsic erosion such as storm surges, thereby further promoting sediment production [6]. ...
Coral reefs persist in an accretion-erosion balance, which is critical for understanding the natural variability of sediment production, reef accretion, and their effects on the carbonate budget. Bioerosion (i.e. biodegradation of substrate) and encrustation (i.e. calcified overgrowth on substrate) influence the carbonate budget and the ecological functions of coral reefs, by substrate formation/consolidation/erosion, food availability and nutrient cycling. This study investigates settlement succession and carbonate budget change by bioeroding and encrusting calcifying organisms on experimentally deployed coral substrates (skeletal fragments of Stylophora pistillata branches). The substrates were deployed in a marginal coral reef located in the Gulf of Papagayo (Costa Rica, Eastern Tropical Pacific) for four months during the northern winter upwelling period (December 2013 to March 2014), and consecutively sampled after each month. Due to the upwelling environmental conditions within the Eastern Tropical Pacific, this region serves as a natural laboratory to study ecological processes such as bioerosion, which may reflect climate change scenarios. Time-series analyses showed a rapid settlement of bioeroders, particularly of lithophagine bivalves of the genus Lithophaga/Leiosolenus (Dillwyn, 1817), within the first two months of exposure. The observed enhanced calcium carbonate loss of coral substrate (>30%) may influence seawater carbon chemistry. This is evident by measurements of an elevated seawater pH (>8.2) and aragonite saturation state (Ωarag >3) at Matapalo Reef during the upwelling period, when compared to a previous upwelling event observed at a nearby site in distance to a coral reef (Marina Papagayo). Due to the resulting local carbonate buffer effect of the seawater, an influx of atmospheric CO2 into reef waters was observed. Substrates showed no secondary cements in thin-section analyses, despite constant seawater carbonate oversaturation (Ωarag >2.8) during the field experiment. Micro Computerized Tomography (μCT) scans and microcast-embeddings of the substrates revealed that the carbonate loss was primarily due to internal macrobioerosion and an increase in microbioerosion. This study emphasizes the interconnected effects of upwelling and carbonate bioerosion on the reef carbonate budget and the ecological turnovers of carbonate producers in tropical coral reefs under environmental change.
