The Late Cambrian Spice ({delta}13C) Event and the Sauk II-SAUK III Regression: New Evidence from Laurentian Basins in Utah, Iowa, and Newfoundland

摘要

Carbon isotope data from Upper Cambrian sections in three Laurentian basins in northern Utah, central Iowa, and western Newfoundland record a large positive 13C excursion (SPICE event) of up to + 5 Peak 13C ratios are well dated by trilobite collections to the middle of the Steptoean Stage (Dunderbergia Zone) and occur during maximum regression associated with formation of the Sauk II-Sauk III subsequence boundary on the North American craton. Maximum regression was marked by an influx of quartz sand into carbonate-platform settings in all three widely separated basins. In northern Utah, this quartz sand formed a thick sequence known as the Worm Creek Quartzite, which marks a conspicuous interruption of carbonate deposition during the Middle to Late Cambrian in the region. In western Newfoundland, the thickness of the quartz sand unit is much reduced but still marks a brief shutdown of the carbonate factory that is unique to the Cambrian shelf succession of the area. In the central Iowa area of the cratonic interior, an upward-shallowing carbonate succession culminates in cross-stratified trilobite grainstones at the peak of the SPICE in Dunderbergia Zone time, and the lowest point on the relative-sea-level curve is associated with the occurrence of coarse quartz sand derived from the encroaching shoreface.