We present the results of our integrated high-resolution Sr isotope and accommodation study of Middle to Late Cambrian (~ 10 to 12 m.y.) carbonates of the southern Great Basin. The well-defined relative sea-level history for this study area coupled with the excellent lateral (0.5 to > 1 km) and vertical (300 to 1200 m) stratigraphic continuity allowed for dm-scale vertical sampling and m-to km-scale collection of contemporaneous samples within a sequence stratigraphic framework. To evaluate the diagenetic history of marine components and the effect of contamination of ⁸⁷Sr/⁸⁶Sr by noncarbonate phases, all microsamples were submitted to rigorous petrographic and geochemical selection criteria and ion exchange pretreatment prior to Sr isotope analysis.

Our results significantly refine the structure of the previously existing Sr isotope curve by (1) constraining the highest seawater ⁸⁷Sr/⁸⁶Sr values (<0.7093) over the past 2 b.y. to the latest Middle Cambrian to earliest Late Cambrian, and (2) by partially bridging the gap in the apparent long-term increasing trend in seawater ⁸⁷Sr/⁸⁶Sr values beginning in Early Cambrian time (0.7082) and culminating in the latest Middle Cambrian to earliest Late Cambrian (0.7093). High-resolution (0.5 to 3 m.y.) changes in seawater ⁸⁷Sr/⁸⁶Sr values are superimposed on the longer-term trend for which we proposed a model that links changes in weathering rates and riverine Sr flux with variations in area of exposed pericratonic sediments governed by short-term sea-level events during greenhouse times. We are currently extending our integrated Sr isotope and accommodation study to latest Early Cambrian through early Late Cambrian carbonates of the southern Canadian Rockies and U.S. Great Basin.

At a higher resolution scale, the ⁸⁷Sr/⁸⁶Sr values from earliest Late Cambrian carbonates covary inversely with their d¹³C values, over a stratigraphic interval representing ~ 3 m.y. The d¹³C values of earliest Late Cambrian carbonates show a sharp increase in values (from <0 up to +2) relative to generally invariant d¹³C values of Middle Cambrian carbonates (-1.8 to -0.5). The associated decrease in ⁸⁷Sr/⁸⁶Sr values and abrupt increase in d¹³C values through earliest Late Cambrian time appears to be coincident with a relative increase in sea level. These relationships suggest a potential mechanistic link between processes controlling the strontium and carbon isotope composition of early Late Cambrian oceans and processes governing high-frequency sea level fluctuations during the Cambrian.