Carbonate mounds in the Santaren Channel, Bahamas: A current-dominated periplatform depositional regime

T. Lüdmann, M. Paulat, C. Betzler, J. Möbius, S. Lindhorst, M. Wunsch, Gregor P Eberli

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

New hydroacoustic data, high resolution multichannel seismic reflection data, CTD casts and sampling document the dominance of bottom currents and the occurrence of carbonate mounds in the Santaren Channel off Great Bahama Bank and Cay Sal Bank. Based on these data sets, three types of carbonate mounds have been identified in water depths between 285 and 685. m. Their distribution is strongly related to the present current regime. Bank-driven sediments are caught up by the currents and redeposited mainly in the channel center, resulting in the accumulation of giant confined drifts flanked by moats. The moats at the banks toe-of-slope are formed by a southward and northward flowing water mass, respectively, mainly Antarctic Intermediate Water and Subtropical Underwater. The observed carbonate mounds are concentrated in these moats. Mound type 1 has an elongated shape parallel to the prevailing bottom current direction, a gently inclined flank facing the water flow and a steep flank in its current shadow. Its upstream flank is covered by a thin sediment wedge whereas the lee side is marked by a parabolic scour. Type 1 occurs at both bank margins but mainly off Great Bahama Bank, consisting of cold-water coral rubble floating in a sediment matrix and is, thus, interpreted as cold-water coral mound. By contrast, type 2 mounds are restricted to the Cay Sal margin and have a predominately conical outline. Bottom samples including living sessile crinoids show that its surface must be lithified and colonized by macroepibenthos, except corals. The mounds are situated in pockmark-like depressions that are underlain by fluid escape structures like pipes and chimneys. These fluid pathways are generated by a network of fractures. Mound type 2 is probably formed by abiotic carbonate precipitation; however, a chemoherm nature cannot be ruled out. Mound type 3 has a conical to polygonal shape and occurs off Cay Sal Bank and Great Bahama Bank. It is surrounded by a scour which is elongated in downcurrent and crescent in upcurrent direction. A sediment bulge formed at its front. This type is consistent with blocks and boulders colonized by macroepibenthos and related to gravity-controlled mass movements at the steep bank slopes.Principally, two habitats can be distinguished: the Great Bahama Bank periplatform deep-water province dominated by mound type 1 and the Cay Sal Bank slope to basin province occupied by mound type 2 that is associated with pockmark-like structures. Mound type 3 occurs in both habitats. Physical water mass properties for the existence of cold-water corals are limited to a depth range of ca. 430 to 685. m, with seawater densities (σ-θ) of 26.93 to 27.29. kg/m and temperatures below 13. °C. Their dominance off Great Bahama Bank might be addressed to a more effective food supply induced by local downwelling.

Original languageEnglish (US)
JournalMarine Geology
DOIs
StateAccepted/In press - Sep 21 2015

Keywords

  • Bottom current
  • Carbonate mound
  • Carbonate platform
  • Cold-water corals
  • Drift sedimentation
  • Great Bahama Bank
  • Oceanographic setting

ASJC Scopus subject areas

  • Oceanography
  • Geochemistry and Petrology
  • Geology

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