NOAA/WDS Paleoclimatology - Gulf of Aden DSDP231 Plio-Pleistocene Tephra Shard Counts and Geochemistry

We reconstruct a Plio-Pleistocene microscopic tephrostratigraphy for DSDP Site 231 in the Gulf of Aden. Systematic microtephrostratigraphy increases the potential for identifying tephra horizons for regional stratigraphic correlation and age control, as well as providing information about eruptive histories. Microtephra reveal three main pulses of volcanism c. 4.0-3.2 Ma, 2.4 Ma and 1.7-1.3 Ma, corresponding to peaks in volcanic activity recorded in the East African Rift System. Previous studies of DSDP Site 231 have reported six visible tephra horizons (up to 25 cm thick) with geochemical compositions matching East African tuffs. We find 68 additional microtephra horizons through microscopic examination of 1050 samples (each integrating c. 3 ka) in over 200 m of marine sediments. We report the major and minor element geochemical compositions of individual glass shards in six of these microtephra horizons and establish a robust correlation at 168.73 m to the Lokochot Tuff (3.58 Ma), which together with previously identified tephra, provides a tightly constrained chronostratigraphy for the mid Pliocene.

本研究重建了亚丁湾深海钻探计划（Deep Sea Drilling Program, DSDP）231站位的上新世-更新世显微火山碎屑地层序列。系统开展的显微火山碎屑地层学研究，不仅可为识别用于区域地层对比与年代约束的火山碎屑层位提供可能，还能为火山喷发历史研究提供关键数据支撑。本次显微火山碎屑分析识别出三期主要的火山活动脉冲，分别对应约4.0~3.2 Ma、2.4 Ma及1.7~1.3 Ma，与东非裂谷系（East African Rift System）记录的火山活动峰值相吻合。此前针对DSDP 231站位的研究已报道6层可见火山碎屑层（最大厚度达25 cm），其地球化学组成与东非凝灰岩一致。本研究通过对200余米海洋沉积物中的1050个样品（每个样品对应约3 ka的沉积时段）开展显微分析，额外识别出68层显微火山碎屑层。本研究还报道了其中6层显微火山碎屑层中单颗玻璃碎屑的常量与微量元素地球化学组成，并建立了168.73 m处层位与3.58 Ma的洛科乔特凝灰岩（Lokochot Tuff）的可靠对应关系；结合此前已识别的火山碎屑层，该成果为中上新世地层建立了约束严谨的年代地层序列。