Oligocene and Lower Miocene Calcareous Nannofossil Biostratigraphy and Paleoceanography of the Ross Sea

罗斯海渐新世和下中新世钙质超微化石生物地层学和古海洋学

• 批准号: 0126170
• 负责人: David Watkins
• 金额: $ 9.02万
• 依托单位: University of Nebraska-Lincoln
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-02-01 至 2004-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0126170&HistoricalAwards=false
• 关键词: Oligocene; Lower; Miocene; Calcareous; Nannofossil

0126170WatkinsThis award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, provides funds for a study of calcareous nannofossils in cores from the Ross Sea. Much of the direct evidence of the early history of Cenozoic glaciation on Antarctica comes from cores that were drilled in the waters of the Ross Sea. One set of these cores was drilled by rigs mounted on the fast ice that rings the southern part of the Ross Sea, just to the north of the Ross Ice Shelf. These include the CIROS-1 hole and Cape Roberts Project (CRP) holes 2 and 3, which cored thick sections of Oligocene and lower Miocene sedimentary rocks deposited within about 15 km offshore of the glaciated coast of Victoria Land. These clastic rocks include sandstones, siltstones, mudstones, conglomerates and diamictite that indicate glaciers reached sea level by the Oligocene and were very close (or actually on top of) the site of deposition for all or part of the Oligocene and early Miocene. A second set of cores, drilled by the Deep Sea Drilling Project (DSDP) drilling vessel Glomar Challenger includes Site 270, located at the same latitude (77 degrees) as CIROS and CRP, but more than 300 km away from the nearest source of glacial sediment. The Oligocene - lower Miocene sedimentary sequence at this site is thinner and more fine-grained, but contains abundant evidence of nearby ice in the form of ice rafted debris (IRD). A second DSDP Site (274), located some 8 degrees latitude north, contains a Oligocene and lower Miocene dominated by diatomaceous sediment including mud and ooze, reflecting its largely open oceanic position. These four drill-holes form a latitudinal and paleoenvironmental transect to investigate the surface water history of the Ross Sea using calcareous nannofossils.Calcareous nannofossils, the fossil remains of coccolithophorid algae that secrete calcite skeletal plates, will be used in two ways to examine the Ross Sea: 1) Paleoceanographic reconstruction - The distribution of the coccolithophorid algae is strongly controlled by the thermal structure of the surface water mass, making their fossils sensitive indicators of past water mass temperature. This is especially useful in an area that is dominated by sediments with too little calcite to use isotopic methods of estimating water temperatures. Analysis of the calcareous nannofossils by statistical paleoecologic methods will provide a temperature history of the Ross Sea surface waters for a period of geological time characterized by fluctuating ocean temperatures and partial or ephemeral continental ice sheets. In addition, because of the sensitivity these phytoplankton are known to have to abnormal salinity, the analysis of the assemblages from deep ocean to the mouths of the Victoria Land glaciers may provide a new way to estimate the meltwater outflow of the evolving East Antarctic Ice Sheet. 2) Biostratigraphy - The rapid rate of evolution of the coccolithophorid algae through the mid-Cenozoic, coupled with their widespread distribution in the oceans, provides the means of age dating the sediments that contain their fossils. The numerical ages of extinction and speciation events have been well documented, providing a means to accurately and precisely date the sedimentary sequences in the Ross Sea and, thus, the events responsible for the deposition. Because of the excellent calibration of calcareous nannofossil biostratigraphy to the time scale, these fossils offer the possibility of constraining the paleomagnetic stratigraphy and other fossil biostratigraphies (such as the largely endemic Antarctic shelf diatoms) that occur in these Oligocene and lower Miocene sections. If successful, this work will have important, and wide reaching ramifications to paleoceanographic research that seeks to understand the role of the Antarctic ice sheet in global systems.

0126170沃特金斯该奖项由极地项目办公室南极地质和地球物理项目提供，为罗斯海岩芯中钙质超微化石的研究提供资金。南极洲新生代冰川作用早期历史的直接证据大多来自罗斯海沃茨钻探的岩芯。其中一组岩芯是由安装在环绕罗斯海南部的快冰上的钻井平台钻探的，就在罗斯冰架以北。其中包括CIROS-1孔和Cape Roberts项目（CRP）2号和3号孔，这些孔取芯了维多利亚地冰川海岸离岸约15公里范围内沉积的渐新世和下中新世沉积岩的厚段。这些碎屑岩包括砂岩、粉砂岩、泥岩、砾岩和杂砂岩，表明冰川在渐新世达到海平面，并且非常接近（或实际上位于）渐新世和早中新世全部或部分沉积地点。第二组岩心由深海钻探项目（DSDP）钻探船Glomar Challenger钻探，包括与CIROS和CRP位于同一纬度（77度）的270号地点，但距离最近的冰川沉积物源超过300公里。该地点的渐新世-下中新世沉积序列较薄且粒度较细，但包含大量以冰筏碎片（IRD）形式存在的附近冰的证据。第二个DSDP站点（274）位于北纬8度左右，包含渐新世和下中新世，主要是硅藻土沉积物，包括泥浆和软泥，反映了其基本上开放的海洋位置。这四个钻孔形成了一个纬度和古环境断面，利用钙质超微化石研究罗斯海的地表水历史。钙质超微化石是分泌方解石骨骼板的球石藻类藻类的化石遗骸，将以两种方式用于研究罗斯海：1）古海洋学重建-球石藻的分布强烈地受表层水团的热结构控制，使它们的化石成为过去水体温度的敏感指标。这是特别有用的，在一个地区，主要是沉积物与太少的方解石使用同位素方法估计水温。通过统计古生态学方法对钙质超微化石进行分析，将提供罗斯海表面沃茨在一段地质时期内的温度历史，其特征是海洋温度波动和部分或短暂的大陆冰盖。此外，由于这些浮游植物对异常盐度的敏感性，对从深海到维多利亚陆地冰川口的浮游植物组合的分析可能为估计东南极冰盖融水外流提供一种新的途径。2)生物地层学-颗石藻类藻类在新生代中期的快速进化，加上它们在海洋中的广泛分布，提供了测定含有其化石的沉积物年龄的手段。灭绝和物种形成事件的数字年龄已被很好地记录下来，提供了一种手段，以准确和精确的日期在罗斯海的沉积序列，从而，事件负责的沉积。由于钙质超微化石生物地层学的时间尺度的良好校准，这些化石提供了约束古地磁地层学和其他化石生物地层学（如主要是特有的南极陆架硅藻），发生在这些渐新世和下中新世部分的可能性。如果成功，这项工作将对古海洋学研究产生重要而广泛的影响，这些研究旨在了解南极冰盖在全球系统中的作用。