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

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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.