Palynostratigraphic and Paleoenvironmental Characterization of Upper Miocene Sediments from Western Ross Sea, Antarctica

南极洲西罗斯海上中新世沉积物的孢粉地层和古环境特征

• 批准号: 0230001
• 负责人: Sophie Warny
• 金额: $ 9.2万
• 依托单位: Louisiana State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-04-15 至 2005-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0230001&HistoricalAwards=false
• 关键词: Palynostratigraphic; Paleoenvironmental; Characterization; Upper; Miocene

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a project to investigate the interaction of the Antarctic ice sheet and the Southern Ocean during the late Miocene time period. Numerous lines of geological evidence show that the Earth climate system changed dramatically during the late Miocene. These changes include the largest pre-Pleistocene glacioeustatic sea-level low stands during the Cenozoic, a 300-km northward shift of the Polar Front, multiple pulses of ice rafting, a global carbon isotopic (d13C) shift, a global reduction in ocean salinity, and several episodes of Southern Ocean abyssal-plain erosion. Primarily on the basis of deep-sea proxy data, it has been inferred that late Miocene climatic changes were related to Antarctic glacial intensification.Although these proxy data interpretations are based on fundamentally sound geological and geochemical principles, the conclusions concerning linkages to the Antarctic cryosphere are equivocal because the specific environmental conditions at the Antarctic continental margins have not yet been established. The fundamental purpose of this palynological study is to address the following question: What were the environmental conditions (i.e. salinity, temperature, and sea ice-cover) during late-Miocene interglacials and glacials on the western Ross Sea inner and outer continental shelf?The secondary goals are to:1. Enhance the existing Ross Sea palynostratigraphy developed from the Cape Roberts Project.2. Determine if the major glacial advance to the Northern Basin shelf edge, described by Brancolini and colleagues in 1995 and Bart and colleagues in 2000, was indeed a late Miocene event, and if so, what were the environmental conditions existing during this glacial period.3. Determine the effect of Antarctic environmental changes on low-latitude climate change, focusing on linkage with the Messinian Salinity Crisis and the reason behind the global salinity reduction. Indeed, new palynological data from the Atlantic coast of the paleo-Gibraltar threshold suggests that a significant Antarctic-linked lowering of sea level occurred during the late Miocene, restricting Atlantic inflow into the Mediterranean Sea at the beginning of the crisis.In the first part of this study, the palynology of the well-dated, inner continental shelf cores DVDP 10 and 11 will be analyzed. Prior work by others showed, on the basis of benthic foraminifer and diatom distribution, that cycles of open-marine/glacial conditions existed on the Ross Sea inner continental shelf during the Mio-Pliocene. Dinocyst distribution should test this theory. In the second part of this study, a palynological analysis of previously acquired material from the Northern Basin outer continental shelf will be conducted. Recent seismic-stratigraphic analyses indicated that the sediments associated with a major late Miocene (?) glacial advance are exposed over a broad area, on the northwestern Ross Sea outer continental shelf. Palynomorphs contained in these sediments should test if indeed, the outcrops were deposited during the late Miocene. Because basic types of Antarctic and Arctic marine palynomorphs are similar, paleoenvironmental reconstruction will be based on existing ecological data from the Arctic, as well as that from Antarctic waters. The oxygen isotopic (d18O) record recently generated for DVDP sites 10 and 11 should provide a reasonable proxy for Antarctic ice-volume changes and evaluate if environmental changes were related to ice-volume changes. In addition to the environmental aspect, the biostratigraphic information generated by this study should provide improved chronostratigraphic support for future proposed Antarctic geological drilling programs, such as SHALDRIL and ANDRILL.

该奖项由极地方案办公室南极地质和地球物理方案提供，支持一项研究南极冰盖与南大洋在中新世晚期相互作用的项目。大量的地质证据表明，地球气候系统在中新世晚期发生了巨大变化。这些变化包括：新生代最大的前更新世冰川稳定海平面低位、极锋向北移动300公里、多次冰筏漂流、全球碳同位素(D13C)移动、全球海洋盐度下降以及几次南大洋深海-平原侵蚀。主要根据深海代理数据推断，晚中新世气候变化与南极冰川加剧有关。尽管这些代理数据的解释是基于基本合理的地质和地球化学原理，但关于与南极冰冻圈的联系的结论是模棱两可的，因为南极大陆边缘的具体环境条件尚未确定。这项孢粉学研究的基本目的是解决以下问题：罗斯海西部内外大陆架晚中新世间冰期和冰川的环境条件(即盐度、温度和海冰覆盖)是什么？次要目标是：1.加强从罗伯茨角项目发展而来的现有罗斯海孢粉地层。确定Brancolini及其同事在1995年和Bart及其同事在2000年描述的向北部盆地陆架边缘的主要冰川推进是否确实是中新世晚期事件，如果是，在这一冰期期间存在的环境条件是什么。确定南极环境变化对低纬气候变化的影响，重点是与梅西尼亚盐分危机的联系以及全球盐分减少的原因。事实上，来自大西洋沿岸古直布罗陀门槛的新孢粉学数据表明，与南极有关的海平面显著下降发生在中新世晚期，限制了大西洋在危机开始时流入地中海。在这项研究的第一部分，将分析测年准确的内陆架岩芯dvdp 10和dvdp 11的孢粉学。前人的工作表明，根据底栖有孔虫和硅藻的分布，罗斯海内大陆架在中上新世期间存在开阔海洋/冰川条件的旋回。双胞体的分布应该验证这一理论。在这项研究的第二部分，将对以前从北部盆地外大陆架获得的材料进行孢粉学分析。最近的地震地层学分析表明，这些沉积物与主要的晚中新世(？)冰川的推进暴露在罗斯海西北部外大陆架的大片区域内。这些沉积物中含有的孢粉形态应该测试露头是否确实是在中新世晚期沉积的。由于南极和北极海洋孢粉的基本类型相似，古环境重建将基于北极和南极水域现有的生态数据。Dvdp站点10和11最近产生的氧同位素(D18O)记录应该可以合理地替代南极冰量的变化，并评估环境变化是否与冰量变化有关。除了环境方面，这项研究产生的生物地层学信息应该为未来拟议的南极地质钻探计划，如SHALDRIL和ANDRILL提供改进的年代地层学支持。