Two diamictites, two cap carbonates, two delta C-13 excursions, two rifts:The Neoproterozoic Kingston Peak Formation, Death Valley, California

Stratigraphic mapping of the Neoproterozoic glaciogenic Kingston Peak Forma tion (Death Valley, California) provides evidence for two temporally discre te extensional deformation episodes. These episodes are bracketed by the So urdough Limestone and Noonday Dolomite, the facies characteristics and delt a(13)C data (ranging between 2.15 and -2.56 parts per thousand and -1.88 an d -4.86 parts per thousand, respectively) of which make them equivalent to Sturtian and Varangian age cap carbonates, respectively. This constrains th e two extensional episodes along the southwestern margin of Laurentia to ca . 700 Ma and ca. 600 Ma. These observations and data show that the field ev idence for mid-Neoproterozoic breakup and the predictions from tectonic sub sidence curves for a latest Neoproterozoic breakup are both correct. Thus, Neoproterozoic plate reconstructions must account for two discrete rift epi sodes separated by 100 m.y. or more. Confining rifting to within the Kingst on Peak Formation thereby places the younger Proterozoic rocks of the south western Great Basin in the rift to drift tectonic phase.