Carbonate preservation in Pliocene to Holocene periplatform sediments (Great Bahama Bank, Florida Straits)

Abstract

Decreasing temperatures and increasing pressure and CO2 enhance the dissolution of carbonate particles at the sediment-water interface in the deep sea. Moreover, dissolution processes are dependent of the saturation state of the surrounding water with respect to calcite or aragonite. It was suggested that significant dissolution also occurs in the water column or at the sediment-water interface above the lysocline. Despite the evidence for supralysoclinal dissolution in some areas of the worldà ´s ocean, the question still exists whether dissolution occurs above the lysocline in the entire ocean. The first part of this thesis seeks answers to this question. All samples located at the Bahamian platform are well preserved. In contrast, the samples from the Florida Straits show dissolution in 800 to 1000 m and below 1500 m water depth. Degradation of organic material and the subsequent release of CO2 probably causes supralysoclinal dissolution. Part two deals with the preservation of periplatform carbonate sediments around Great Bahama Bank (GBB). Carbonate nodules have been found in the sediments, which have formed during shallow burial diagenesis. The temporal distribution of these nodules shows how early diagenetic processes at these locations depend on the margin type, the bottom water velocity and the pore water chemistry. Coarser layers in the sediment facilitate the formation of nodules, and, on the other hand, the formation of nodules coarsens the sediment. These observations lead to a model, showing the alteration of different types of initial grain-size patterns due to the formation of nodules. The results of this study contribute to the understanding of general sedimentation processes in the periplatform realm: the preservation state of surface samples shows the influence of supralysoclinal dissolution due to the degradation of organic matter and due to the presence of corrosive water masses; the composition of the sand fraction shows the alteration of the carbonate sediment due to early diagenetic processes.