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

碳稳定同位素比率地层学：宾夕法尼亚石灰岩中的方法测试该项目测试了石灰岩碳稳定同位素比率的系统偏移可以用作碳酸盐岩为主的盆地中的高分辨率地层对比工具的假设。 众所周知，石灰石的碳酸盐成分在海水中保持13 C/12 C比率。 其原因是复杂的，但结果是同位素比率的记录，其变化范围短至5级冰川海平面变化（10万年）。 在冰室地球条件下，石灰岩记录冰川海平面变化周期作为重复的浅向上的岩性循环。 我们的数据表明，同位素偏移反映岩性变化，因此可以用来关联石灰岩部分盆地内的非常详细。我们的目标是宾夕法尼亚州的伊利石灰岩和相当于鸟泉地层，它们遍布内华达州的中部、东部和南部。 我们将这些浅水碳酸盐盆地称为伊利伯德泉盆地（EBSB）。 这些地层沉积在Morrowan和Atokan（宾夕法尼亚州）时间在低纬度的开放海洋陆架的劳伦西亚西部，在冈瓦纳冰期。 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一些密集和广泛分布的剖面，这些剖面根据生物地层学证据（分辨率~2- 5 My）被认为大致与时间相当。 充满浅水石灰岩的大型大陆盆地是神秘的，它们在北美西部的石炭纪很常见。 这些盆地包含非常厚的石灰岩部分，在某些例子中为1至3公里。 根据我们的新数据，可以对这些碳酸盐盆地提出一些令人信服的问题。受已知水深（近海平面）和高分辨率相对时间限制的详细沉降历史揭示了沉降速率。 比较盆地不同部分的速率将得到三维盆地演化，以及沉积物堆积的构造强迫的证据。 我们还可能对有关气候变化和地球冰室的更基本问题做出贡献：在冰川进退期间，碳酸盐循环告诉我们海洋化学的什么？ 水深、石灰岩沉积和输送能量在盆地不同尺度上是如何相互作用的？ 海平面和海水化学的更长的四阶周期也可以相互关联吗？我们正在开发的开始回答这些问题的工具是循环灰岩剖面的碳同位素对比。

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.