Investigation of Quaternary diatoms in sediment core CRP-1 from the Ross Sea, Antarctica

In the first season of drilling, the Cape Roberts Project (CRP) recovered one drillcore (CRP-l) from Roberts Ridge in western McMurdo Sound, Ross Sea, Antarctica Diatom biostratigraphy places the upper six lithostratigraphic units (Units 1.1, 2.1, 2.2, 2.3, 3.1, and 4.1) of CRP-l (0.0 to 43.15 mbsf) within the Quaternary. Both non-marine and marine Quaternary diatoms occur in variable abundance in the Quaternary interval of CRP- 1 Biostratigraphic data resolve two Quaternary time slices or events within CRP-1. Marine diatom assemblages in Units 4.1 and 3.1 represent sedimentation within the diatom Actinocyclus ingens Zone (1.35 to 0.66 Ma). Further refinement of the age of Unit 3.l places deposition in the interval 1.15 to 0.75 Ma based on the common occurrence of Thalassiosira elliptipora and correlation to the Southern Ocean acme of this taxon The absence of ActiActinocyclus ingens and the presence ot Thalassiosira antarctica in Unit 2.2 require a younger zonal assignment for this interval, within the diatom Thalassiosira lentiginosa Zone (0.66 to 0.0 Ma). A new diatom species. Rouxia leventerae, is described from marine assemblages of Units 2.2, 2.3, 3.1, and 4.l. Lithostratigraphic Unit 3.1 (33.82 to 31.89 mbsf) is a bryozoan-dominated skeletal-carbonate facies. Low abundance of Fragilariopsis curta and Fragilariopsis cylindrus within this unit combined with the relatively high abundance of species associated with open water indicates deposition in waters that remained ice free for much or all of the year Diatom assemblages suggest carbonate deposition in Unit 3.1 is linked to a significant early Pleistocene event in McMurdo Sound, when elevated surface-water temperatures inhibited the formation of sea ice.

在首轮钻探季中，开普罗伯茨项目（Cape Roberts Project, CRP）从南极洲罗斯海麦克默多湾西部的罗伯茨岭获取了一根钻探岩芯（CRP-1）。硅藻生物地层学（diatom biostratigraphy）研究将CRP-1的上部6个岩石地层单元（单元1.1、2.1、2.2、2.3、3.1及4.1，对应海底以下0.0至43.15米，mbsf）归为第四纪。CRP-1第四纪层段中，陆相与海相硅藻均有分布且丰度存在差异。生物地层数据可明确区分出CRP-1内的两个第四纪时间切片或沉积事件。单元4.1与3.1中的海相硅藻组合对应强壮辐环藻带（Actinocyclus ingens Zone）的沉积过程，时代为1.35至0.66 Ma。基于椭圆海链藻（Thalassiosira elliptipora）的普遍产出，并结合该类群在南大洋的繁盛期对比，可将单元3.1的沉积时代进一步限定为1.15至0.75 Ma。单元2.2中未检出强壮辐环藻，但存在南极海链藻（Thalassiosira antarctica），因此该层段需划归更年轻的多疣海链藻带（Thalassiosira lentiginosa Zone），时代为0.66至0.0 Ma。本文描述了采自单元2.2、2.3、3.1及4.1海相组合中的硅藻新种——莱文特罗氏藻（Rouxia leventerae）。岩石地层单元3.1（海底以下33.82至31.89 mbsf）为以苔藓虫为主的骨骼碳酸盐相。该层段中短小脆星藻（Fragilariopsis curta）与圆柱脆星藻（Fragilariopsis cylindrus）丰度较低，而与开阔水域相关的硅藻物种丰度相对较高，指示其沉积环境为全年多数或全部时间无海冰覆盖的水域。硅藻组合特征表明，单元3.1的碳酸盐沉积与麦克默多湾内一次重要的早更新世（early Pleistocene）事件相关，当时表层海水温度升高抑制了海冰形成。