DEEP CARBONATE BANK MARGIN STRUCTURE AND SEDIMENTATION IN THE NORTHERN BAHAMAS

Abstract

The deep 200 m carbonate bank margins in the northern Bahamas display complex and diverse seismic facies structure morphology and sedimentary facies On the basis of analysis of more than 1200 km of high frequency high resolution seismic reflection profiles and 149 bottom samples seven deep carbonate bank margin types have been recognized in the northern Bahamas I Type A Open Ocean Windward margin east of Little Bahama Bank LBB 2 Type B Open Ocean Windward margin north of LBB 3 Type C Extended deep bank margins off the northwest corners of both LBB and Great Bahama Bank GBB 4 Type D Open Seaway Leeward margin west of LBB and GBB 5 Type E Open Seaway Leeward margin south of LBB 6 Type F Open Seaway Windward margin north of GBB and 7 Type G Eroded margins along the mouth of the Northwest Providence Channel NWPC In general leeward deep bank margins tend to be steeper narrower more dissected and contain significantly greater amounts of coarse grained sediment than windward margins The processes most responsible for the development of deep carbonate bank margins include I basement faulting 2 direction and magnitude of off bank sediment transport 3 oceanic circulation 4 gravity and pelagic sedimentation 5 submarine cementation and 6 biological buildups Of these basement faulting is primarily responsible for the initiation of carbonate platform edges Offbank sediment transport is controlled by the physical energy flux winds waves storms at the sea surface and controls the availability of shallow water sediment for transport to the deep flanks Oceanic circulation bottom currents winnows and redistributes sediment and may aid in submarine cementation which appears responsible forthe stabilization of carbonate slopes through hardground development Pelagic carbonate sediments are ubiquitous in deep water carbonate environments but are volumetrically important only where they are not winnowed by bottom currents diluted by sediment gravity flow deposits or deposited below the CCD Much of the material deposited on carbonate slopes is allochthonous transported via a variety of sediment gravity flows including turbidity currents grain flows and debris flows Deep waterbiological buildups are locally important and may add to flank accretion Previous models of deep carbonate bank margins derived solely from analysis of the ancient appear to be oversimplifications A new knowledge of the diverse types of modern deep carbonate bank margins and an understanding of the processes that control their formation should aid in the interpretation of ancient deep water carbonate sequences as well as in theexploration forand exploitationof hydrocarbons from off platform carbonates