Annotated record of the detailed examination of a Mn deposits from the Carnegie Ridge in the Pacific Ocean

The Carnegie Ridge is a linear, aseismic, submarine ridge lying between the Galapagos Islands and the coast of South America. Surface ship, near bottom, and grain size studies from the saddle have been used to delineate the present geological environment and history of the ridge. Structurally the Carnegie Ridge is rather simple in profile, being bounded by east-west trending scarps which give the ridge a block-faulted appearance. Acoustic basement over the ridge appears smooth on reflection profiles and is composed of chert. The sedimentary sequence above the chert horizon contains a lower chalk unit overlain by calcareous ooze. Where erosion has exposed the chalk a karst-like micro-topography is present which is characterized by steep walled channels and cliffs and consolidated bed forms undergoing erosion and dissolution. The ridge crest has been stripped of almost its entire sediment cover. Thick sequences of sediment are found only in areas protected from north or south flowing bottom currents. Evidence of erosion is provided by extensive channeling on both the north and south flanks of the ridge. Near bottom observations in one channel on the north flank revealed a large field of sand dunes indicating northward, downslope sediment transport. These dunes are found on manganese-encrusted chalk which floors the channel.

卡内基海岭（Carnegie Ridge）是一条线性无震海底海岭，坐落于加拉帕戈斯群岛与南美大陆海岸之间。科研人员依托取自该海岭鞍部的海面观测、近底探测及粒度分析数据，阐明了该海岭当前的地质环境与演化历程。从构造剖面来看，卡内基海岭形态相对简单，其边界受东西走向的陡崖挟持，整体呈现断块抬升的地貌特征。海岭上方的声学基底在地震反射剖面中表现为平滑形态，其物质组成为燧石（chert）。燧石层位之上的沉积序列包含下部白垩单元，该单元之上又覆盖有钙质软泥。在侵蚀作用使白垩岩层出露的区域，可见喀斯特型微地貌，其以陡壁水道与悬崖为典型标识，同时存在正遭受侵蚀与溶蚀作用的固结床形体。海岭脊顶几乎被完全剥蚀了全部沉积盖层，厚层沉积序列仅见于受南北流向底流保护的区域。海岭南北两侧侧翼广泛发育的水道，为侵蚀作用提供了直接佐证。对北翼一处水道的近底观测显示，该处发育大型沙丘场，指示沉积物沿北坡向下搬运。这些沙丘发育于水道底部的覆锰白垩岩层之上。