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

[126170 .沃特金斯]该奖项由极地项目办公室的南极地质与地球物理项目提供，为罗斯海岩心中钙质纳米化石的研究提供资金。关于南极洲新生代冰期早期历史的许多直接证据来自在罗斯海水域钻取的岩心。其中一组岩心是由安装在环绕罗斯海南部、罗斯冰架以北的快冰上的钻机钻取的。其中包括CIROS-1孔和罗伯茨角项目（CRP）的2孔和3孔，它们取心了离维多利亚地冰川海岸约15公里处沉积的渐新世和中新世下沉积岩的厚剖面。这些碎屑岩包括砂岩、粉砂岩、泥岩、砾岩和杂晶岩，它们表明冰川在渐新世达到海平面，并且在渐新世和中新世早期的全部或部分沉积地点非常接近（或实际上在上面）。第二组岩心由深海钻探项目（DSDP）的Glomar Challenger号钻井船钻探，包括Site 270，位于与CIROS和CRP相同的纬度（77度），但距离最近的冰川沉积物源超过300公里。渐新世-中新世下沉积层序较薄，颗粒较细，但含有大量冰筏碎屑（IRD）的证据。第二个DSDP遗址（274）位于北纬8度左右，包含渐新世和中新世下部，主要为硅藻质沉积物，包括泥和软泥，反映了其大部分开放的海洋位置。这四个钻孔形成了一个纬度和古环境样带，利用钙质纳米化石研究罗斯海的地表水历史。钙质纳米化石是分泌方解石骨板的球石藻化石遗骸，将从两个方面对罗斯海进行研究：1)古海洋学重建——球石藻的分布受地表水团热结构的强烈控制，其化石是过去水体温度的敏感指标。这在一个以方解石含量过少的沉积物为主的地区尤其有用，无法使用同位素方法估计水温。利用统计古生态学方法对这些钙质纳米化石进行分析，将提供一段以海洋温度波动和部分或短暂大陆冰盖为特征的地质时期内罗斯海表层水的温度史。此外，由于已知这些浮游植物对异常盐度的敏感性，从深海到维多利亚地冰川口的组合分析可能为估计正在演变的南极东部冰盖的融水流出量提供一种新的方法。为含有它们化石的沉积物提供年代测定方法。灭绝和物种形成事件的数字年龄已经被很好地记录下来，这提供了一种方法，可以准确地确定罗斯海沉积序列的年代，从而确定导致沉积的事件。由于钙质纳米化石生物地层学在时间尺度上的出色校准，这些化石提供了限制古地磁地层学和其他化石生物地层学（如大部分特有的南极陆架硅藻）发生在渐新世和中新世下剖面的可能性。如果成功，这项工作将对寻求了解南极冰盖在全球系统中的作用的古海洋学研究产生重要而广泛的影响。

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.