POWRE: Strontium Isotopes to Gauge Climatic vs. Tectonic Effects on Carbonate Sedimentation in Continental Basins

0074647 Gierlowski-KordeschSr同位素是确定物源（源区）以了解盆地内沉积模式的有力工具;这些信息对于重建过去的历史以及资源勘探都很重要。 锶同位素在解决大陆地质问题中的作用，大部分应用于海洋领域，但尚未被地质界完全利用。 由于盆地沉积物中的Sr信号可以由源区的碳酸盐岩控制（没有明显的水文/气候变化），因此将该技术应用于陆相碳酸盐岩可以用来解决许多地质问题。 在大陆研究中，一个经常涉及的主题是沉积的主要控制因素的分化：气候与构造。 这已被证明是相当困难的，因为缺乏时间分辨率的大陆序列在一个盆地内的发展表明，构造是更重要的比气候在控制沉积物结构的盆地。 为了验证这一理论，可以用非海相碳酸盐岩中的Sr同位素来确定它们的起源。 有七种可能的机制产生原始的非海相碳酸盐沉积物。 通过推移质、悬浮物和溶解物（碎屑碳酸盐）的陆上搬运形成的碳酸盐的识别对于评估沉积物与其源区之间的联系至关重要。 硅质岩系中的碳酸盐岩层长期以来被认为是“干旱气候事件”。 然而，只要盆地的源区含有含钙岩石，特别是碳酸盐岩，就可以在任何气候条件下沉积大量的碳酸盐岩。 在岩石序列中碳酸盐岩层的出现可能与构造变化有关。 此外，碎屑碳酸盐岩的结构还能指示其沉积的气候类型。 通过比较层序内非海相碳酸盐的结构和稳定同位素，可以确定气候变化是否影响了整个层序的沉积。 如果不是，那么可以通过Sr同位素特征测试，通过与源岩的Sr信号比较，这些岩石是否确实直接来自流域盆地。 层序中碳酸盐岩层的出现可能表明源区的变化，而不是气候的变化;然后可以区分气候与构造的影响。 为了测试和改进这种技术，在应用于古代例子之前，将对现代例子进行严格的采样。 现代的例子是不列颠哥伦比亚省的凯利湖--一个含有碳酸盐岩阶的湖泊，与一条河流相连，河流直接从含有二叠纪石灰岩的源区排出。 古代的例子包括在北方阿巴拉契亚盆地发现的非海相碳酸盐，位于宾夕法尼亚纪的科内莫和莫农加希拉群内，是所谓的“旋回层”的组成部分，其源区假定为弗吉尼亚州的寒武-奥陶纪碳酸盐。 如果成功，这项技术可能会改变人们对沉积记录中非海相碳酸盐的看法和使用。

0074647Gierlowski-KordeschSr isotopes are a powerful tool in determining provenance (source area) for understanding sedimentation patterns within a basin; this information is important for reconstructing past history as well as resource exploration. Applied in large part to the marine realm, the usefulness of Sr isotopes in solving continental geologic problems has not been totally utilized by the geologic community. Because the Sr signal within basinal sediments can be dominated by the carbonate rocks in the source area (with no significant change in hydrology/climate), the application of this technique to nonmarine carbonates might be used to solve many geologic problems. A topic usually addressed in continental research is the differentiation of the main controlling factors in sedimentation: climate vs. tectonics. This has proven quite difficult to do because of the lack of time resolution across continental sequences within a basin development suggests that tectonics is more important than climate in controlling sediment architecture in basins. To test this theory, Sr isotopes from nonmarine carbonate rocks can be used to determine their origin. There are seven possible mechanisms to produce primary nonmarine carbonate sediments. The identification of carbonates formed from the overland transport of material through bedload, suspended load, and dissolved load (clastic carbonates) is crucial to assessing a link between a sediment and its source area. Layers of carbonate within siliciclastic sequences have long been identified as "arid climatic events". Large quantities of carbonates, however, can be deposited in any climate as long as the source area for the basin contains calcium-bearing rocks, especially carbonates. The occurrence of carbonate beds in a rock sequence may instead be linked to tectonic changes. In addition, the textures of a clastic carbonate rock are indicative of the type of climate in which it is deposited. Comparing the textures and stable isotopes of nonmarine carbonates within a sequence, one can determine whether climatic change affected deposition across a sequence. If not, then one could test through Sr isotopic signatures whether the rocks are indeed directly sourced from the drainage basin through comparison with the Sr signal of the source rocks. The appearance of a carbonate bed in a sequence might indicate a change in the source area, not in climate; the effects of climate vs. tectonics could then be differentiated. In order to test and refine this technique, a modern example would be sampled rigorously before application to an ancient example. The modern example is Kelly Lake in British Columbia - a lake containing a carbonate bench and associated with a river, which directly drains from a source area containing Permian limestones. The ancient example involves nonmarine carbonates found in the northern Appalachian basin within the Conemaugh and Monongahela Group of the Pennsylvanian, components of the so-called "cyclothems", with the source area postulated to be the Cambro-Ordovician carbonates if Virginia. If successful, this technique may change the perception and use of nonmarine carbonates in the sedimentary record.