The Middle Miocene Carbonate Crash:Relationship to Neogene Changes inOcean Circulation and Global Climate

Abstract

In this thesis a comprehensive data collection mainly from non-destructive XRF core scanner measurements and oxygen isotope data have been applied for reconstructing and interpreting paleoenvironmental changes in Neogene sediments of the South Atlantic. The obtained data document the geochemical reorganization in the world oceans across the middle to late Miocene transition (basin-to-basin fractionation) which mainly is contributed to the uplift of the Central American Seaway and expansion of the Antarctic ice-sheet. Detailed comparison of carbonate sedimentation patterns from different regions and different water depth clearly show that the carbonate crash events differ substantially in timing and magnitude. In addition, the congruent variability of shallow and deep water carbonate records contradict the assumed gradients between intermediate and deep-water masses as predicted by modeling studies. Furthermore, the present study suggests that interactions exist between the geochemical reorganization of the world oceans and climate events during the Neogene. For example, the close timing of aridification in South Africa and Patagonia, strengthening of the Antarctic Circumpolar Current, begin of Benguela upwelling, intensification of Southern Hemisphere winds and expansion of the Antarctic ice-sheet point to a common driving mechanism. The configuration of ocean gateways and sills (i.e. Central American Seaway, Greenland-Scotland Ridge) seem to play a key role in the observed changes in ocean chemistry. Other factors like the uplift of major orogenes (Andes, Himalayas) might have significant influence on the ocean geochemistry and therefore carbonate sedimentation pattern.