Depositional And Diagenetic History Of Pliocene-Pleistocene Carbonates Of Northwestern Great Bahama Bank; Evolution Of A Carbonate Platform

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Doctor of Philosophy (Ph.D.)


Cores from nine borings across Northwestern Great Bahama Bank provide the basis for the first subsurface cross section across a Bahamian platform. This cross section reveals that through the Pliocene-Pleistocene the Northwestern Great Bahama Bank has been a dynamic evolving carbonate platform. Through this period, during episodes of sedimentation, there has been an overall trend toward shoaling water depths and increasing restriction of circulation.On a gross level sedimentation has changed both on the margins and over the interior of the Bank. On the margins the most dramatic change has been from reefal to nonskeletal eolianite. Over the interior of the Bank deposition changed from predominantly poorly stratified marine-cemented skeletal packstone to mottled nonskeletal packstone. Laterally, grain-supported sediment is most widespread over the windward half of the Bank; mud-supported sediment over the leeward half.On a finer scale the sedimentary record is punctuated by subaerial discontinuity zones which form the boundaries between 19 discrete depositional units. Correlation of units between cores is based on comparison of sediments, sedimentary sequences, and depth. Based on similar sediments and thicknesses the units can be grouped to define three periods in the development of the Bank through the Plio-Pleistocene. These periods appear to correspond to changes in frequency and amplitude of the late Tertiary-Quaternary record of sea level fluctuations thus suggesting that changes in sea level was the underlying cause of the evolution of the Bank.The sediments of the Bank have been most altered by meteoric diagenesis. Equant spar is the most widespread cement fabric. Recrystallized marine cement is common in early Pliocene sediments across the interior of the Bank. It is virtually absent in borings from the margins.Porosity, mostly secondary below 10 m depth, remains about 35% in originally aragonitic deposits. Large-scale leaching is pervasive.Texture and fabric-preserving nonstoichiometric dolomite occurs in the basal section of one core on the windward margin. The upper two metres of the dolomitized section show partial and preferential dolomitization; below that the section is massive dolomite.



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