The Cambrian Drumian carbon isotope excursion (DICE) in the Great Basin, western United States

Abstract

The Global boundary Stratotype Section and Point (GSSP) of the Cambrian Series 3 (formerly the Middle Cambrian) Drumian Stage is defined by the first appearance datum (FAD) of the agnostoid trilobite Ptychagnostus atavus in the deep-water Wheeler Formation of the Drum Mountains in Utah, USA. In the Great Basin (USA), China and Scandinavia the FAD of P. atavus is associated with transgression and with a negative carbon isotope excursion named the Drumian Carbon isotope Excursion (DICE). However, the relationship between the FAD of P. atavus, sea-level changes, and the DICE is tentative, mainly due to the paucity of biostratigraphic data in shallow-water sections that limit correlation between deep- and shallow-water chemostratigraphic sections. An integrated sequence and chemostratigraphic study across a platform-to-basin transect in western Utah and southern Nevada indicates that the DICE is stratigraphically located above the FAD of P. atavus, associated with retrogradation of the shallow-water carbonate platform and with stratigraphic condensation in the basin. The results suggest that in future global correlations, the DICE should be restricted to the negative carbon isotope anomaly slightly post-dating the Drumian GSSP.