Collaborative Research: Development of a Luminescence Dating Capability for Antarctic Glaciomarine Sediments: Tests of Signal Zeroing at the Antarctic Pennisula

合作研究：南极冰川沉积物发光测年能力的开发：南极半岛信号归零测试

• 批准号: 9909665
• 负责人: Glenn Berger
• 金额: --
• 依托单位: Nevada System of Higher Education, Desert Research Institute
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-09-15 至 2007-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9909665&HistoricalAwards=false
• 关键词: Collaborative; Research; Development; Luminescence; Dating

9909665BergerThis award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports project to test and develop approaches for using thermoluminescence techniques to determine the age of Antarctic marine sediments. Quaternary (last 2 million yrs) marine sediments surrounding Antarctica record the waxing and waning of ice shelves and ice sheets, and also other paleoclimatic information, yet accurate chronologies of these sediments are difficult to obtain. Such chronologies provide the essential foundation for study of geological processes in the past. Within the range of radiocarbon (14C) dating (less than 30-40 thousand yrs, note - "ka" below means 1000 yrs) 14C dates can be inaccurate because of a variable 14C reservoir effect, and beyond 30-40 ka few methods are applicable. Photon-stimulated-luminescence sediment dating (photonic dating) of eolian and waterlain deposits in temperate latitudes spans the range from decades to hundreds of ka, but marine sediments in and around Antarctica pose special difficulty because of the potentially restricted exposure to daylight (the clock-zeroing process) of most detrital grains before deposition. This proposal will test the clock-zeroing assumption in representative Antarctic glaciomarine depositional settings, and thereby determine the potential reliability of photonic dating of Antarctic marine sediments.Limited luminescence dating and signal-zeroing tests using glaciomarine and marine deposits have been conducted in the northern temperate and polar latitudes, but the effects on luminescence of the different glaciomarine depositional processes have never been studied in detail. Furthermore, the depositional settings around Antarctica are almost entirely polar, with consequent specific processes operating there. For example, transport of terrigenous suspensions by neutrally buoyant "cold-tongue" (mid-water) plumes may be common around Antarctica, yet the effect of such transport on luminescence zeroing is unknown. Typical marine cores near Antarctica may contain an unknown fraction of detrital grains from cold-tongue and near-bottom suspensions. Thus the extent to which the polar glaciomarine depositional processes around Antarctica may limit the potential accuracy of photonic dating of marine cores is unknown (age overestimates would result if grains are not exposed to daylight before deposition).This project will collect detrital grains from a variety of "zero-age" (modern) marine depositional settings within the Antarctic Peninsula, where representative Antarctic depositional processes have been documented and where logistics permit access. Suspensions will be collected from four fjords representing a transect from polar through subpolar conditions. Suspensions will be collected from two stations and from up to 3 depths (surface and 2 deep plumes) at each station. Sediment traps will be deployed at two of these fjord settings. As well, core-top sediments will be collected from several sites. All samples will be shielded from light and transported to Reno, Nevada, for luminescence analyses.Systematic study of the effectiveness of luminescence-clock-zeroing in Antarctic glaciomarine settings will determine if photonic dating can be reliable for future applications to Antarctic marine sediments. Refined sedimentological criteria for the selection of future samples for photonic dating are expected from this project. A photonic-dating capability would provide a numeric geochronometer extending well beyond the age range of 14C dating. Such a capability would permit answering a number of broader questions about the timing and extent of past glaciations near and on the Antarctic shelves.

9909665伯格该奖项由极地项目办公室南极地质和地球物理项目提供，支持测试和开发使用热释光技术确定南极海洋沉积物年龄的方法的项目。南极洲周围的第四纪（过去200万年）海洋沉积物记录了冰架和冰盖的消长，以及其他古气候信息，但这些沉积物的准确年代很难获得。这些年表为研究过去的地质作用提供了必要的基础。在放射性碳（14 C）定年范围内（小于3万至4万年，注-下面的“ka”表示1000年），14 C定年可能不准确，因为14 C储层效应可变，超过30-40 ka的方法很少适用。温带地区风成沉积物和水纹沉积物的光释光沉积物测年（光子测年）跨度从几十年到几百万年，但南极洲及其周围的海洋沉积物造成了特殊的困难，因为大多数碎屑颗粒在沉积前可能受到日光照射（时钟归零过程）的限制。该提案将在代表性的南极冰海沉积环境中检验时钟归零假设，从而确定南极海洋沉积物光子测年的潜在可靠性。在北方温带和极地纬度，利用冰海和海洋沉积物进行了有限的发光测年和信号归零测试，但不同的冰海沉积过程对发光的影响还没有详细的研究。此外，南极洲周围的沉积环境几乎完全是极地的，因此有特定的过程在那里运作。例如，中性浮力的“冷舌”（中层水）羽流对陆源悬浮物的输送在南极洲周围可能很常见，但这种输送对发光归零的影响尚不清楚。南极洲附近的典型海洋岩芯可能含有未知部分的冷舌和近底悬浮物的碎屑颗粒。因此，南极洲周围极地冰川海洋沉积过程可能限制海洋岩心光子定年的潜在准确性的程度是未知的（如果颗粒在沉积前没有暴露在日光下，会导致年龄被高估）。该项目将收集南极半岛内各种“零年龄”（现代）海洋沉积环境中的碎屑颗粒，在那里，有代表性的南极沉积过程已被记录在案，后勤允许进入。将从四个峡湾收集悬浮液，代表从极地到亚极地条件的横断面。悬浮液将从两个站点收集，每个站点最多从3个深度（表面和2个深层羽流）收集。将在其中两个峡湾设置沉积物收集器。此外，还将从几个地点收集岩心顶部沉积物。所有样品都将避光，运往内华达州的里诺进行发光分析，对南极冰川海洋环境中发光时钟调零的有效性进行系统研究，将确定光子测年法在南极海洋沉积物未来应用中是否可靠。预计该项目将为未来光子测年样品的选择提供精细的沉积学标准。光子测年能力将提供一种数字地质年代计，其范围远远超出14 C测年的年龄范围。这种能力将允许回答一些更广泛的问题，即南极大陆架附近和大陆架上过去冰川作用的时间和范围。