C-ISOTOPE STRATIGRAPHY OF THE REED DOLOMITE, WHITE-INYO MOUNTAINS, CALIFORNIA

From the Neoproterozoic succession in the White-Inyo Mountains, the Reed Dolomite is comprised of, in stratigraphic order, the Lower Member, the Hines Tongue, and the Upper Member. The Lower Member's basal contact is ca. 560 Ma. 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 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 decay of a thermal anomaly. The Upper Member indicates deposition during tectonic quiescence, and is considered to be ca. 548 Ma. 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, and then decreases to ~+1.5 per mil (VPDB) in the Upper Member. My preferred interpretation of these observations is extensional tectonism during Reed deposition. This interpretation is supported by the Lower Member breccia, thermal subsidence rates, dramatic lateral thickness variations in the Lower Member, and previous chemostratigraphic correlations tying the Lower Member of the Reed Dolomite to incision of the Johnnie Formation of the Death Valley succession to the east, where workers have identified extensional tectonism as well. Extensional tectonism in the Reed Dolomite suggests protracted rifting of the Laurentian margin following the breakup of Rodinia.