Small shelly fossils and carbon isotopes from the lower–middle Cambrian of Idaho (western USA)

寒武系是目前唯一一个没有正式国际划分的古生代。迄今为止，寒武纪第2、3、4期的基底尚未确定，传统的中寒武世基底-五柳庵期的陆间对比也不可能有足够的准确性。造成这些问题的原因之一是早寒武世和早中寒武世后生动物（特别是三叶虫和古囊虫）明显的地方性。摆脱这种痛苦的一种方法是生物地层学和化学地层学信息的结合。一个潜在的非传统生物地层学工具是小壳化石（SSF）。SSF广泛分布于早寒武世中晚期（寒武纪2-4期）和中寒武世（庙岭统）。特别是在沉积序列的特点是没有古细胞或很难提取三叶虫（如碳酸盐）SSF提供的唯一的生物地层信息。近20年来，人们对全球早-中寒武世（第二阶段-五柳庵阶段）地层层序的SSF潜力的认识有了根本性的提高。与此同时，很明显，关于劳伦西亚西部（加拿大西部和美国）SSF的数据库仍然很差。碳同位素地层学作为一种化学地层学信息，已成为寒武系地层对比的有力工具。但是，对于这个强大的标记几乎没有数据存在的早中寒武世西部劳伦。最重要的是，对于保存完好的爱达荷州早-中寒武世层序，既没有SSF的信息，也没有任何化学地层学数据。该项目的目的是首次对爱达荷州的SSF动物群和碳同位素进行调查（1）改进西劳伦蒂亚寒武纪的生物化学地层划分和对比（2）为寒武纪生态系统的生态和演化提供新的认识。

The Cambrian System is presently the only Phanerozoic period characterized by the lack of a formal international subdivision. Up to now, bases of Cambrian stages 2, 3, and 4 are not defined and an intercontinental correlation of the Wuliuan Stage (base of the traditional middle Cambrian) is not possible with sufficient accurateness. One of the reasons for these problems is a pronounced provincialism of early and early middle Cambrian metazoans (especially trilobites and archaeocyaths). A way out of this misery is the combination of bio- and chemostratigraphic information. A potential non-traditional biostratigraphic tool are small shelly fossils (SSFs). SSFs have a wide distribution during the mid and late parts of the early Cambrian (Cambrian stages 2–4) as well as of the middle Cambrian (Miaolingian Series). Especially in sedimentary successions characterized by the absence of archaeocyaths or where it is hard to extract trilobites (e.g. in carbonates) SSFs deliver often the only biostratigraphic information. During the last two decades the knowledge on the potential of SSFs of worldwide early–middle Cambrian (Stage 2–Wuliuan Stage) successions has been fundamentally increased. At the same time, it becomes obvious that the data base on SSFs of western Laurentia (western Canada and USA) is still very poor. Concerning a chemostratigraphic information, carbon isotope stratigraphy has emerged as a robust correlation method in Cambrian strata. But, also for this robust marker almost no data exist for the early–middle Cambrian of western Laurentia. Above all, neither information on SSFs nor any chemostratigraphic data exist for the well-preserved early–middle Cambrian successions of Idaho. Aim of the project is the first time investigation of SSF fauna and carbon isotopes of Idaho (1) to improve a bio-chemostratigraphic subdivision and correlation of the Cambrian of western Laurentia and (2) to shed new light on the ecology and evolution of Cambrian ecosystems.