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

寒武纪是目前唯一以缺乏正式国际分界为特征的显生宙时期。到目前为止，寒武系2期、3期和4期的基准面尚未确定，对传统中寒武统基准面--乌连期的洲际对比也不可能有足够的精度。造成这些问题的原因之一是寒武纪早期和中期早期后生动物(特别是三叶虫和古环虫)明显的地方性。摆脱这种痛苦的一种方法是结合生物和化学地层信息。一个潜在的非传统生物地层学工具是小壳化石(SSFS)。SSF广泛分布于早寒武世中晚期(寒武纪2-4期)和中寒武世(苗林组)。特别是在沉积序列中，其特征是没有古环藻或很难提取三叶虫(如碳酸盐)，SSF往往提供唯一的生物地层信息。近二十年来，人们对全球早、中寒武世(阶段2-五六期)沉积体系潜力的认识有了根本的提高。与此同时，显而易见的是，关于西部劳伦西亚(加拿大西部和美国)SSFS的数据基础仍然很差。作为一种化学地层学信息，碳同位素地层学在寒武纪地层中已成为一种强有力的对比方法。但是，对于这一强有力的标志，几乎没有关于西部劳伦西亚早-中寒武世的数据。最重要的是，爱达荷州保存完好的早中寒武世层序既没有关于SSFS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)改进西部劳伦西亚寒武纪的生物化学地层划分和对比，(2)对寒武纪生态系统的生态和演化有新的认识。

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.