Stratigraphic investigations of carbon isotope anomalies and Neoproterozoic ice ages in Death Valley, California

An unusual richness of biogeochemical events is recorded in Neoproterozoic– Cambrian strata of the Death Valley region, California, United States. Eight negative carbon isotope (d13C) excursions are found in carbonate units between 1.08 Ga and the Precambrian/Cambrian boundary; four of these excursions occur in carbonates that contain textural features similar to those found globally in postglacial ‘‘cap carbonates’’ (including one or more of the following: laminite with rollup structures, apparent ‘‘tube rocks,’’ seafloor precipitates, and sheet-crack cements). However, only two of these units, the Sourdough limestone member of the Kingston Peak Formation and the Noonday Dolomite, rest directly upon glacial strata. The basal Beck Spring Dolomite and the Rainstorm Member of the Johnnie Formation each contain negative excursions and cap-carbonate–like lithofacies, but do not rest on known glacial deposits. If the negative d13C excursions are assumed to record depositional processes, two equally interesting hypotheses are possible: (1) The Death Valley succession records four glacial pulses in Neoproterozoic time, but glacial units are not preserved at two stratigraphic levels. (2) Alternatively, other global oceanographic processes can cause negative excursions and cap-carbonate– like facies in addition to, or independent of, glaciation.