HIGH-RESOLUTION C-ISOTOPE STRATIGRAPHY FROM THE REED DOLOMITE, WHITE-INYO MOUNTAINS, CA

The Neoproterozoic Reed Dolomite, White-Inyo Mountains, California, is comprised of, in stratigraphic order, the Lower Member, the Hines Tongue, and the Upper Member. The Lower Member's basal contact is older than 548 Ma (ca. 580 Ma, but the age is not well constrained). In some locations the Lower Member indicates a tectonic influence on deposition, including carbonate breccia from the Lower Member itself and associated normal faulting. The Hines Tongue follows abruptly as a coarse, arkosic unit that pinches out from the southeast to the northwest and can be interpreted as recording a dramatic change in relative base level, possibly related to continuing tectonism. The Upper Member indicates deposition during tectonic quiescence, and is considered to be ca. 548 Ma. Interestingly, previous correlations have tied the Lower Member and Hines Tongue of the Reed Dolomite to the Rainstorm Member of the Johnnie Formation and the lower Stirling Quartzite from the Death Valley succession to the east, where workers have identified extensional tectonism that may be related to protracted continental rifting along the entire continental margin.

New high-resolution C-isotope data show an oscillatory, positive δ¹³C trend from approximately +1 per mil (VPDB) to +2 per mil (VPDB) through the Lower Member that rapidly climbs and maintains at +3 per mil (VPDB) with the onset of the Hines Tongue. These new data suggest increasing productivity and/or increasing organic carbon burial during Lower Member and Hines Tongue deposition. This could be consistent with thermal uplift in an extensional setting that would provide increased nutrients via increased weathering and erosion to spur productivity and/or greater sedimentation rates to sequester more organic carbon. Further, the Reed Dolomite positive excursion being of the rough duration of 10's of millions of years is most consistent with a tectonic time scale.