COLLABORATIVE RESEARCH: TESTING THE TECTONIC UPLIFT-WEATHERING HYPOTHESIS FOR THE LATE ORDOVICIAN GREENHOUSE-ICEHOUSE TRANSITION

合作研究：验证晚奥陶纪温室-冰室转换的构造抬升风化假说Matthew Saltzman，俄亥俄州州立大学Stephen Leslie，James麦迪逊大学-0745452，-0746181摘要人们普遍认为，奥陶纪末期（445-443 Ma）是极地地区大陆冰盖形成的时期。然而，围绕开始冷却和从温室气候过渡的情况仍然存在争议。有人提出，冷却是由于大气中二氧化碳含量的降低而引起的。奥陶纪二氧化碳的降低可能是由于有机碳的埋藏或硅酸盐风化作用（碳酸盐碳的埋藏）。我们的研究将使用多种同位素代用记录与不同的因果关系和响应时间（C，Sr，Nd），以调查奥陶纪气候和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，主要是在厚的地层剖面保存在低纬度劳伦的相对两侧，牙形石生物地层学的日期。以前的同位素研究已经确定了碳酸盐的锶和碳同位素在奥陶纪气候转变中的显着变化。PI研究的目的是解决的原因和后果的大幅度下降的Sr同位素在中晚奥陶世使用钕同位素模式牙形石磷灰石和C同位素的有机质。海水中的87 Sr/86 Sr通常被用作古构造事件的替代物，因为它受河流输入和海底热液蚀变之间的平衡控制。与Sr一样，海水Nd同位素组成可以记录大陆风化的变化。然而，一个关键的区别是，海洋库存的钕是不平衡的海底热液输入。因此，143 Nd/144 Nd可以提供独立的限制来源的海水87 Sr/86 Sr的变化。PI还将构建碳酸盐和有机物中C同位素的配对记录，这些记录可能提供有关大气二氧化碳相对变化的信息，这些变化是由硅酸盐风化或先前确定的有机碳埋藏事件引起的。此外，通过耦合C与Nd的停留时间大大短于interocean混合时间，它可以获得当地的风化模式和养分循环的信息。

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.