The lowest occurrence of the conodont Eoconodontus notchpeakensis (Miller, 1969) has been proposed as the base of Cambrian Stage 10. The horizon is recognized in three sections in the House Range, western Utah, USA in the lower part of the Red Tops Member of the Notch Peak Formation. This horizon fits within a tightly integrated framework that includes conodont, trilobite, and brachiopod biozonations, as well as carbon-isotope stratigraphy and sequence stratigraphy. The proposed horizon is the base of the Eoconodontus conodont Zone. This horizon is in the lower part of the Saukiella junia Subzone of the Saukia trilobite Zone and is near the top of the Billingsella brachiopod Zone. The HERB Event is a high-amplitude, negative carbon-isotope excursion that has been identified in Laurentia, Australia, China, and Argentina. The start of the excursion is at a negative carbon-isotope peak that is less than half a metre above the base of the E. notchpeakensis Subzone, and the highest-amplitude peak of the HERB Event is near the middle of that relatively thin subzone. The HERB Event has been identified in strata with minimal faunal data, providing the possibility of identifying the base of Stage 10 in nearly unfossiliferous strata. The Notch Peak Formation has been divided into a detailed sequence-stratigraphic framework within a lithostratigraphic context, and some of the sequence boundaries have been identified in Australia and China. Conodonts diagnostic of the Eoconodontus Zone have been identified at 54 localities around the world, including in a succession of Cambrian deep-ocean radiolarian cherts. The Utah conodont zonation has been identified across Laurentia and in other parts of the world in facies ranging from continental slope to nearshore sandstone deposits. The variety of correlation tools and the integration of diverse data produce a superior framework for correlation of the proposed base of Stage 10 and for correlation of many horizons within Stage 10.
Miller, J. F., Ripperdan, R. L., Loch, J. D., Freeman, R. L., Evans, K. R., Taylor, J. F., & Tolbart, Z. C. (2015). Proposed GSSP for the base of Cambrian Stage 10 at the lowest occurrence of Eoconodontus notchpeakensis in the House Range, Utah, USA. Annales de Paleontologie, 101(3), 199–211. https://doi.org/10.1016/j.annpal.2015.04.008