Collaborative Research: Testing The Tectonic Uplift-Weathering Hypothesis For The Late Ordovician Greenhouse-Icehouse Transition

合作研究：检验晚奥陶世温室-冰库转变的构造隆升-风化假说

• 批准号: 0745452
• 负责人: Matthew Saltzman
• 金额: $ 17万
• 依托单位: Ohio State University Research Foundation -DO NOT USE
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-03-15 至 2012-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0745452&HistoricalAwards=false
• 关键词: Collaborative; Research; Testing; Tectonic; Uplift

COLLABORATIVE RESEARCH: TESTING THE TECTONIC UPLIFT-WEATHERING HYPOTHESIS FOR THE LATE ORDOVICIAN GREENHOUSE-ICEHOUSE TRANSITIONMatthew Saltzman, Ohio State UniversityStephen Leslie, James Madison UniversityEAR-0745452, -0746181AbstractIt is widely accepted that the end of the Ordovician period (445-443 Ma) was a time of large continental ice sheets in polar regions. However, the circumstances surrounding the initiation of cooling and the transition from a greenhouse climate remains controversial. It has been proposed that cooling was brought about by a lowering of atmospheric carbon dioxide levels. Ordovician carbon dioxide could be lowered either by burial of organic carbon or by silicate weathering (burial of carbonate carbon). Our research will use multiple isotopic proxy records with different causal factors and response times (C, Sr, Nd) to investigate links between Ordovician climate and processes affecting the long term carbon cycle. PIs will obtain these coupled isotopic records primarily in thick stratigraphic sections preserved on opposite sides of low-latitude Laurentia that are well-dated by conodont biostratigraphy. Previous isotopic studies have identified significant changes in both strontium and carbon isotopes of carbonates through the Ordovician climate transition. PIs research aims to address the cause and consequences of the large drop in Sr isotopes in the Middle-Late Ordovician using neodymium isotope patterns in conodont apatite and C isotopes in organic matter. The 87Sr/86Sr of seawater is commonly used as a proxy for paleotectonic events because it is controlled by a balance between riverine inputs and seafloor hydrothermal alteration. Like Sr, the Nd isotopic composition of seawater can record changes in continental weathering. However, a key difference is that the oceanic inventory of Nd is not balanced by seafloor hydrothermal inputs. Thus, 143Nd/144Nd can provide independent constraints on the sources of seawater 87Sr/86Sr variations. PIs will also construct paired records of C isotopes in carbonate and organic matter that may potentially provide information on relative changes in atmospheric carbon dioxide that resulted from changes in silicate weathering or previously identified organic carbon burial events. In addition, by coupling C with Nd which has a residence time considerably shorter than interocean mixing times, it is possible to obtain local information on weathering patterns and nutrient cycling.

合作研究：测试已故的奥陶纪温室冰镇过渡室的构造隆起假设地区。但是，围绕冷却启动和从温室气候过渡的情况仍然存在争议。已经提出，通过降低大气二氧化碳水平的降低来进行冷却。奥陶纪二氧化碳可以通过埋葬有机碳或硅酸盐风化（碳酸盐碳）来降低。我们的研究将使用具有不同因果因素和响应时间（C，SR，ND）的多种同位素代理记录来研究奥陶纪气候与影响长期碳循环的过程之间的联系。 PI将获得这些耦合的同位素记录，主要是在较厚的地层截面中保存在低纬度月经laurentia的相对侧面，这些分层由Conodont BiostraTaphy良好地结实。以前的同位素研究已经通过奥陶纪的气候过渡确定了碳酸盐质和碳质同位素的显着变化。 PIS研究旨在通过使用有机物中牙形山磷灰石和C同位素中的Neododymium同位素模式来解决中级奥陶纪SR同位素大量下降的原因和后果。海水的87SR/86SR通常被用作古氏事件的代理，因为它受河流输入与海底水热改变之间的平衡来控制。像SR一样，海水的ND同位素组成可以记录大陆风化的变化。但是，一个关键的区别在于，海洋水热输入不平衡ND的海洋清单。因此，143/144nd可以对海水87SR/86SR变化的来源提供独立的约束。 PI还将构建碳酸盐和有机物中C同位素的配对记录，这些记录可能会提供有关硅酸盐风化或先前确定的有机碳埋葬事件的变化而导致的大气二氧化碳相对变化的信息。此外，通过与ND耦合C的停留时间比Interocean混合时间短得多，可以获得有关风化模式和营养循环的局部信息。