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

sr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；这些信息对重建过去的历史和资源勘探具有重要意义。锶同位素主要应用于海洋领域，在解决大陆地质问题方面的作用尚未被地质界充分利用。由于盆地沉积物中的Sr信号可以由源区碳酸盐岩（水文/气候变化不明显）主导，因此将该技术应用于非海相碳酸盐岩可能用于解决许多地质问题。大陆研究中经常讨论的一个主题是沉积主要控制因素的区分：气候与构造。这已被证明是相当困难的，因为在盆地内缺乏跨大陆层序的时间分辨率。发展表明，在控制盆地沉积物结构方面，构造比气候更重要。为了验证这一理论，来自非海相碳酸盐岩的锶同位素可以用来确定它们的来源。原生非海相碳酸盐岩沉积的形成可能有7种机制。识别由物质通过层载、悬浮载和溶解载（碎屑碳酸盐）的陆上搬运形成的碳酸盐，对于评估沉积物与其源区之间的联系至关重要。碳酸盐层在硅屑层序中一直被认为是“干旱气候事件”。然而，只要盆地的源区含有含钙岩石，特别是含碳酸盐，那么在任何气候条件下都可以沉积大量的碳酸盐。相反，碳酸盐岩层在岩石层序中的出现可能与构造变化有关。此外，碳酸盐岩碎屑的结构还表明其沉积的气候类型。通过比较一个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，则可以通过Sr同位素特征与烃源岩的Sr信号对比，验证其是否直接来源于流域。层序中碳酸盐层的出现可能表明烃源区发生了变化，而不是气候的变化；这样就可以区分气候和构造的影响。为了测试和改进这种技术，在应用于古代的例子之前，将对一个现代的例子进行严格的抽样。现代的例子是不列颠哥伦比亚省的凯利湖，这是一个含有碳酸盐层的湖泊，与一条河流相连，直接从含有二叠纪石灰岩的源区流出。古代的例子包括在阿巴拉契亚盆地北部发现的非海相碳酸盐岩，位于宾夕法尼亚的Conemaugh和Monongahela群内，是所谓的“旋回岩”的组成部分，其来源假定是弗吉尼亚州的寒武纪-奥陶纪碳酸盐岩。如果成功，这项技术可能会改变沉积记录中对非海相碳酸盐的认识和使用。

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.