Impact of diagenesis on carbonate mound formation

Impact of diagenesis on carbonate mound formation This thesis is devoted to define the parameters influencing cold-water coral growth and therefore carbonate mound development with a focus on the impact of diagenesis on mound sediments. The first part of this thesis (Chapters 2 to 4) discusses the distribution and growth history of carbonate mounds, the sedimentary processes leading to sediment accumulation at mound sites and the primary sediment composition of cold-water coral carbonate mounds along the Irish margin. The second part of the thesis (Chapters 5 to 7) elaborates on the post-depositional processes (diagenesis) affecting mound sediments, the timing of these diagenetic processes and their impact on carbonate mound development. Piston cores obtained from mound summits were studied to determine paleo-environmental conditions influencing mound development. Component analysis, thin section petrography and X-ray fluorescence scanning revealed the impact of diagenesis in the form of dissolution and cementation of the coral framework. U-series dating of coral skeletons and stable isotope measurements on foraminifera provided us with a chrono stratigraphic framework for carbonate mound build-up. Coral ages showed that large hiatuses are present in the mounds, which can be linked to multiple phases of erosion or non-deposition in the mound history. In Chapter 2 the morphology and sedimentology of carbonate mounds from two mound provinces at the southeast and southwest margin of the Rockall Trough (RT) (NE Atlantic Ocean) are investigated. Cold-wat er coral mounds on both margins have a strongly different morphology. Single, isolated mounds occur on the SE RT margin and are mainly found on the upper slope between 650 and 900 m water depth, while large mound clusters are found on the SW RT margin in water depths between 600 and 1000 m, in a narrow zone almost parallel to the slope. Sedimentation rates on the mounds are higher than on the surrounding seabed as a result of baffling of biogenic carbonate debris and sediment particles by the coral framework. The three-dimensional coral framework and the presence of extensive hardgrounds and firmgrounds are considered to be responsible for the stability of the relatively steep slopes of the 2 Summary mounds. High current velocities in the intra-mound areas result in local non-sedimen-tation and erosion, as is shown by the presence of IRD lag deposits on the seabed and moats around some of the mounds. The morphology and sedimentology of cold-water coral (mainly Lophelia pertusa and Madrepora oculata) covered mounds on the …