Carbon Stable Isotope Ratio Stratigraphy: A Test of the Method in Pennsylvanian Limestones

碳稳定同位素比地层学：宾夕法尼亚石灰岩方法的测试

• 批准号: 1038702
• 负责人: James Trexler
• 金额: $ 5.97万
• 依托单位: Board of Regents, NSHE, obo University of Nevada, Reno
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1038702&HistoricalAwards=false
• 关键词: Carbon; Stable; Isotope; Ratio; Stratigraphy

Carbon Stable Isotope Ratio Stratigraphy: A Test of the Method in Pennsylvanian LimestonesThis project tests the hypothesis that systematic excursions in limestone carbon stable isotope ratios can be used as a high-resolution stratigraphic correlation tool in carbonate-dominated basins. It is well known that carbonate components of limestone preserve the 13C/12C ratio in seawater. The reasons for this are complex, but the result is a record of isotopic ratios that vary at scales as short as 5th-order glacioeustatic sea-level changes (100,000 years). During ice-house Earth conditions, limestones record glacioeustatic cycles world-wide as repeated shallowing-upward lithologic cycles. Our data show that isotopic excursions mirror lithologic changes, and therefore can be used to correlate limestone sections within basins in great detail. Our target is the Pennsylvanian Ely Limestone and equivalent Bird Spring Formation that crop out throughout central, eastern, and southern Nevada. We refer to this collection of shallow-water carbonate basin(s) as the Ely-Bird Spring basin (EBSB). These strata were deposited during Morrowan and Atokan (Pennsylvanian) time at low latitudes on the open-marine shelf of western Laurentia, during Gondwanan glaciation. In order to develop the high-resolution isotopic stratigraphy of the EBSB we are measuring and sampling a number of closely and widely spaced sections which are known to be roughly time-equivalent based on biostratigraphic evidence (resolution ~2-5My). Large continental basins filled with shallow-water limestone are enigmatic, and they are common in the Carboniferous of western North America. These basins contain very thick sections of limestone, 1 to 3 kilometers in some examples. Based on our new data, a number of compelling questions can be asked about these carbonate basins. Detailed subsidence histories constrained by known water depth (near sea-level) and high-resolution relative timing reveal rates of subsidence. Comparing rates from different parts of the basin will result in three-dimensional basin evolution, and evidence of the tectonic forcing of sediment accumulation. We may also be able to contribute to more fundamental questions about climate change and ice-house Earth: What do the carbonate cycles tell us about ocean chemistry during glacial advance and retreat? How do water depth, limestone sedimentation, and transport energy interact at different scales in the basin? Can longer, 4th order, cycles of sea-level and marine water chemistry also be correlated? The tool we are developing to begin to answer these questions is carbon isotope correlation of cyclothemic limestone sections.

碳稳定的同位素比率地层学：宾夕法尼亚limestonesthis项目中该方法的测试检验了以下假设：石灰石碳稳定同位素比率可以用作高分辨率地层相关工具中的高分辨率地层相关工具。 众所周知，石灰石的碳酸盐成分保留了海水中的13c/12c比率。 原因是复杂的，但结果是同位素比的记录，其尺度的变化最短至5阶冰川化海平面变化（100，000年）。 在冰室地球条件下，石灰石在全球范围内记录了冰川化周期，这是反复的浅岩性周期。 我们的数据表明，同位素偏移反映了岩性的变化，因此可以用来详细介绍盆地内石灰石部分。我们的目标是宾夕法尼亚州的石灰石和等效的鸟类形成，它们在整个内华达州中部，东部和南部。 我们将此浅水碳酸盐盆地的集合称为Ely-Bird Spring盆地（EBSB）。 这些地层是在Morrowan和Atokan（宾夕法尼亚州）时期沉积的，该地层是在贡德瓦南冰川期间在劳伦西亚西部的开放式陆地架子上的低纬度地区沉积的。 为了开发EBSB的高分辨率同位素地层学，我们正在测量和采样许多紧密和广泛间隔的部分，这些部分已知基于生物地层学证据（分辨率〜2-5MY）大致相等。 充满浅水石灰石的大型大陆盆地是神秘的，它们在北美西部石炭纪很常见。 这些盆地包含非常厚的石灰石部分，在某些例子中有1至3公里。 根据我们的新数据，可以询问有关这些碳酸盐盆地的许多令人信服的问题。详细的沉降历史受已知水深度（靠近海平面）和高分辨率相对时机限制的历史表明沉降率。 比较盆地不同部分的速率将导致三维盆地的演变，以及沉积物积累的构造强迫的证据。 我们也许还能够为有关气候变化和冰室地球的更根本问题做出贡献：碳酸盐周期在冰川进展和撤退期间如何告诉我们有关海洋化学的信息？ 水深，石灰石沉积和运输能量如何在盆地的不同尺度上相互作用？ 还可以将更长的，第四阶，海平面和海水化学的周期循环是否相关？我们正在开发的工具开始回答这些问题是环状石灰石部分的碳同位素相关性。