Miocene to Holocene diatom biostratigraphy of ODP Leg 105 sites@en

Diatoms occur sporadically in lower Miocene to Holocene sediments recovered at ODP Site 645 and in upper Pliocene to Holocene sediments at ODP Site 646. The diatom assemblage at Site 645 contains rare stratigraphic indicators. Fragmentation of frustules and the occurrence of species characteristic of high-latitude shelf, upper-slope environments suggest current transportation from the shelf. The diatom abundance and preservation at Site 646 probably reflect climatic changes and are also affected by dissolution, but it is not possible to detect the dominant factor. Therefore, the stratigraphic ranges of the primary and secondary biostratigraphic indicators are often unreliable.硅藻在大洋钻探计划（Ocean Drilling Program, ODP）645站位钻取的早中新世至全新世沉积物中零星产出，同时在ODP 646站位的晚上新世至全新世沉积物中亦有分布。645站位的硅藻组合仅包含稀有的地层指示类群。硅质壳的破碎现象，以及高纬度陆架、上斜坡环境特征物种的出现，表明存在来自陆架的海流搬运作用。646站位的硅藻丰度与保存状况大概率反映了气候变化，同时也受到溶解作用的影响，但无法确定二者中的主导因素。因此，主要与次要生物地层标志的地层延限范围往往并不可靠。