Annotated record of the detailed examination of Mn deposits from DSDP Leg 76 (Hole 534A)

The continental edge of eastern North America is the passive margin with the oldest geological history available in the modern oceans. Rifting and seafloor spreading between the North American and African continents began in the late Triassic to Early Jurassic. A possible spreading-center jump and reorganization in spreading at the time of the Blake Spur Magnetic Anomaly (?Bathonian ) left some of the oldest crust on the western margin of the North Atlantic. Penetration and sampling of such old ocean crust and the immediately overlying pelagic sedimentary cover, consisting of Middle Jurassic and younger strata, has long been a key objective in oceanographic research. This objective was accomplished at Site 534.

北美东部大陆边缘是现代海洋中地质历史最为悠久的被动大陆边缘（passive margin）。北美与非洲大陆之间的裂谷作用与海底扩张（seafloor spreading）始于三叠纪晚期至侏罗纪早期。在布雷克海岭磁异常（Blake Spur Magnetic Anomaly，?巴通阶（Bathonian））时期，可能发生的扩张中心跃迁与扩张体制重组，造就了北大西洋西部边缘部分最古老的洋壳。对这类古老洋壳及其紧邻上覆的、由中侏罗统及更年轻地层构成的远洋沉积盖层（pelagic sedimentary cover）进行钻进与采样，长期以来都是海洋学研究的核心目标。该研究目标在534站位（Site 534）得以完成。