Abstract:
Preliminary analysis of magnetic susceptibility data coupled with visual analysis of Deep Sea Drilling Project (DSDP) Site 242 cores has helped to determine the changes in sedimentary characteristics through the late Paleogene. Significant climate perturbations took place during the Paleogene as the Earth shifted from greenhouse to icehouse states. DSDP Leg 25, Site 242 drilled to 676 m in the western Indian Ocean (Mozambique Channel). This site is located on the eastern flank of the Davie Ridge (15 degrees 50.65'S, 41 degrees 49.23'E) and presently at 2275m water depth. The sedimentary succession covers both the Eocene/Oligocene and Oligocene/Miocene boundaries. For this study, visual color changes (L*) and magnetic susceptibility data are a proxy for lithologic changes. Color variations (L*) in deep sea cores largely reflect variations in carbonate productivity and dissolution. Preliminary analysis of the Eocene/Oligocene and Oligocene/Miocene transitions by means of visual examination, core description, color imaging, reflectance spectrophotometry (L*), and magnetic susceptibility scans suggests that cyclic changes in percent carbonate might be present. Unlike what has been recorded in the equatorial Pacific Ocean (Site 1218), we do not see evidence for a two step transition in the calcite compensation depth (CCD). By documenting the carbonate changes at Site 242, we will determine the timing of changes in the CCD and look for cyclic changes in percent carbonate (%CaCO (sub 3) ). After completing our analysis of Site 242 we can gain a global perspective by comparing the site with the Pacific Ocean and provide data for future drilling in the Mozambique Channel. Future work will quantify the changes in percent carbonate through this critical interval and will examine the implications for the depth and fluctuations of the CCD through time. Further refinement of the planktonic foraminiferal biostratigraphy will also constrain the timing of the climatic events.