| Summary: | The Carambar scientific cruise along western Great Bahama Bank (GBB) and north of Little Bahama Bank has documented the abundance and rich diversity of cold-water coral mounds in the Florida-Bahamas region. During the cruise, two cores were taken in the area where Correa et al. (2012a) identified the largest mound (the Matterhorn) at GBB site 3 west of Bimini. By analyzing the cores, the nature of the cold-water coral mounds and their surrounding area are studied in great detail in terms of composition, internal structure and diagenesis. Both cores from the flank and base of the 110 m-tall Matterhorn mound prove the un-cemented nature of the mound situated in a high-energy environment. The first core (CARKS 15) from the Matterhorn can be divided into five sedimentary units based on the lithology and the different geophysical and geochemical properties. The succession is dominantly a coral floatstone with variable amounts of corals in a matrix of changing composition and grain size. The matrix of the coral floatstone is mainly composed of pteropods, planktonic and benthic foraminifera, with admixed coral fragments, sponge spiculae, mollusks, and echinoids. Tomogram (CT) scans reveal that the highest amount of coral, 49.1%, is in the interval where corals float within a fine-grained matrix. The cold-water corals grew during both glacial and interglacial times, but living conditions might be slightly better during higher sea levels. The decrease of aragonite and the coeval increase of lithification and low-Magnesium calcite document early diagenetic alterations within the mound. The most prominent diagenetic alterations observed in thin section are dissolution of coral fragments and neomorphism that characterized an early diagenesis in marine to marine burial environment. A second, 3.26 m long core (CARKS 16) that was taken in the sediments adjacent to the mound consists of a coarse-grained skeletal grainstone to rudstone. The skeletal components are predominantly pteropods, benthic and planktonic foraminifera. Portions of the core display inclined bedding and large-scale cross-bedding indicating the sedimentary record of the high-energy bi-directional tidal current regime in the Straits of Florida. In addition, both of the cores have been tied to a high-resolution geophysical dataset collected with an Autonomous Underwater Vehicle (AUV) providing information about morphology and facies distribution of the area around the Matterhorn.
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