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Geomorphology of carbonate platform-marginal uppermost slopes: Insights from a Holocene analogue, Little Bahama Bank, Bahamas
Article first published online: 31 MAY 2012
© 2012 The Authors. Journal compilation © 2012 International Association of Sedimentologists
Volume 59, Issue 7, pages 2146–2171, December 2012
How to Cite
RANKEY, E. C. and DOOLITTLE, D. F. (2012), Geomorphology of carbonate platform-marginal uppermost slopes: Insights from a Holocene analogue, Little Bahama Bank, Bahamas. Sedimentology, 59: 2146–2171. doi: 10.1111/j.1365-3091.2012.01338.x
- Issue published online: 22 NOV 2012
- Article first published online: 31 MAY 2012
- Accepted manuscript online: 15 APR 2012 11:50PM EST
- Manuscript received 18 November 2011; revision accepted 11 April 2012
- Autonomous underwater vehicle;
- carbonate platform;
- last glacial maximum;
- mass transport complex
As the product of a variety of sediment sources and sedimentation (and re-sedimentation) and erosion processes, the geomorphology and sedimentology of carbonate slopes are highly variable. The purpose of this study is to describe sub-bottom profiles and side-scan sonar, multibeam and optical data acquired by an autonomous underwater vehicle to explore variability in geomorphological and sedimentological character of the present-day platform-marginal, uppermost slope environments (< 240 m water depth) on the north, open-ocean facing flank of Little Bahama Bank, Bahamas. Although at time scales of greater than 100 ka this margin is progradational, the data illustrate a complex juxtaposition of erosional and depositional processes and features. Erosion is evidenced by two prominent escarpments (70 m and 120 m) that expose eroded, bedded rocky outcrops. These escarpments are interpreted to represent relict features, related to past sea-level positions, although they still may be shedding debris. Aside from erosional remnants, sedimentation and active transport is indicated by several features, including active bedforms (especially above the 70 m escarpment, but ripples occur to depths of ca 200 m), several mass transport complexes that overlie and cover the lower escarpment, gravity flow deposits and rare slump features. Similarly, a thick (up to 20 m) onlapping sediment wedge, interpreted to be Holocene in age, suggests lateral accretion of the slope by more than 75 m in this period. Data illustrate that this open-ocean margin is distinct from windward margins in the Bahamas, which typically include near-vertical walls of erosion or bypass, flanked downdip by rubble and talus, and leeward margins, which have onlapping muddy wedges, but that lack marked terraces or escarpments. Collectively, the results provide perspectives into the nature and controls on complex geomorphological patterns of erosion and deposition in Holocene uppermost slope systems, concepts potentially applicable to ancient analogues.