(Figure 1, page 726) Thorium 230 excess values as a function of distance inside layers of a manganese nodule from DOMES Site B, Pacific Ocean

We report here that a manganese nodule from the Central Pacific manganese nodule province has been dated by fossil diatoms found in mud scraped from near the nodule's centre. The nodule was taken at DOMES Site B from Core B55-56 at 11°50.3'N and 137°28.2'W in a water depth of 4,892 m. It was resting on the sediment surface, with about 1.5 cm of the nodule bottom (of a total nodule height of 4.2 cm) buried in the mud. The top surface of the nodule was covered with a smooth manganese coating, but the bottom had a very rough, crusty texture. It was found that recent mud had leaked in through cracks in the nodule bottom, but that there were no pre-Pleistocene diatoms in this material. The date obtained was compared with the growth rate determined by the 230Th excess method and found to be in reasonable agreement. This study adds to the work of Harada1,2 on the biostratigraphy (mainly coccoliths) of manganese nodules.

本研究报道了一件采自中太平洋锰结核矿区的锰结核，通过对该结核中心附近刮取的沉积物中的化石硅藻进行分析，确定了其形成年代。该结核采自DOMES站点B的B55-56岩心，采样位置为北纬11°50.3′、西经137°28.2′，水深4892米。该结核静置在沉积物表面，结核总高4.2厘米，其底部约1.5厘米埋于沉积物中。结核顶面覆盖有光滑的锰质覆膜，底面则质地粗糙，呈硬壳状结构。研究发现，现代沉积物通过结核底部的裂隙渗入该区域，但该渗入物中未发现更新世之前的硅藻。所得定年结果与通过钍-230过剩法测定的结核生长速率进行比对，二者吻合度较好。本研究补充了Harada等人[1,2]针对锰结核生物地层学（以颗石藻为主）开展的相关研究工作。