Grain size analysis and sedimentation rates of ODP Hole 175-1085A off the Namibian coast, supplement to: Roters, Bastian; Henrich, Rüdiger (2010): The middle to late Miocene climatic development of Southwest Africa derived from the sedimentological record of ODP Site 1085A. International Journal of Earth Sciences, 99(2), 459-471

• Main Authors: Roters, Bastian, Henrich, Rüdiger
• Format: Article in Journal/Newspaper
• Language: English
• Published: PANGAEA - Data Publisher for Earth & Environmental Science 2010
• Subjects: Drilling/drill rig; Leg175; Joides Resolution; Ocean Drilling Program ODP; Antarctic; The Antarctic; Antarc*
• Online Access: https://dx.doi.org/10.1594/pangaea.738695; https://doi.pangaea.de/10.1594/PANGAEA.738695

Sediments from the ODP Site 1085A were studied to investigate the impacts of global cooling in the Middle and Late Miocene on the climate in Southwestern Africa. The size composition of the sediment was analysed emphasising the silt fraction. A comparison with the modern grain size distribution and suitable transport processes made it possible to assign specific transport processes to the grain size composition. Three processes are considered for transport of terrigeneous silt: while there was no evidence found for (1) transport by ocean currents, the analyses showed signals of (2) wind transport indicating dry conditions associated with a cool climate and (3) fluvial transport that points to humid and warm conditions. Three climatic phases were defined. The first phase from 13.8 to 11.8 Myr reveals a stable humid climate in Southwest Africa independent of the Antarctic glaciations. During the second phase from 11.8 to 10.4 Myr the regional climate cooled considerably but was not drier. Additionally, the climate during this phase reacted to the Antarctic glaciations. This cooling-trend continued during phase 3 from 10.4 to 9.0 Myr with a significant increase in dust input, pointing to overall drier conditions. However, fluvial transport still remained as the main source.