Annotated record of the detailed examination of Mn deposits from DSDP Site 113, Leg 12 (Cores 113-3, 113-11)

Seismic reflection profiles across the Labrador Sea by Vema-19 and Charcot-S had revealed a rugged basement topography almost entirely buried by sediments up to 2000 meters thick. It was first suggested that this was the median valley of a mid-Labrador Sea ridge where oceanic crust was generated during the last phase of opening of the Labrador Sea but which is now virtually inactive and covered by sediment. The choice of a site where basement could be dated by sampling sediments that were believed to be the same age as the basement was difficult. Site 113 was eventually chosen in a local valley 8 kilometers south of a small knoll believed, from the Vema-ll record, to be a basement high.由Vema-19号与Charcot-S号采集的横穿拉布拉多海的地震反射剖面（Seismic reflection profiles）显示，崎岖不平的基底地形几乎完全被厚度可达2000米的沉积物所覆盖。早期研究曾提出，该区域为拉布拉多海中部海岭的中央谷，拉布拉多海最后一期张开过程中生成的洋壳即形成于此，但如今该海岭已近乎停止活动，且被沉积物覆盖。要选取一处可通过采集被认为与基底形成年代一致的沉积物样本以测定基底年代的站位颇具挑战。最终，结合Vema-11号的观测记录，研究人员在一处被认定为基底隆起的小型海丘以南8公里的局部谷地中选定了113号站位（Site 113）。