THE BEGINNING AND END OF A RIFT: THE INTIMATE ASSOCIATION BETWEEN NEOPROTEROZOIC GLACIATION AND RIFT-CONTROLLED ACCOMODATION SPACE

The Neoproterozic record from Death Valley, southeastern California, provides a well exposed and laterally extensive example of a glacial succession in which the mechanisms and characteristics of Neoproterozoic glaciation can be accessed and compared to other younger glacial epochs. Examination of the Neoproterozoic Kingston Peak Formation (KPF) in the southeastern Death Valley Region reveals: 1) a long-lived record of coupled tectonism and glaciation, 2) an active submarine biota during ice-sheet retreat, 3) evidence for an active hydrologic cycle, and 4) a record of glacial and interglacial phases implying strong climate variability.

The Kingston Peak Formation shows an intimate relationship between the glacial record and rift-controlled accommodation space. Deposition of glacigenic sediments in the lower KPF is synchronous with rift-related tectonism while initially dominated by a glacial signal. Evidence for glaciation is diminished upsection as local tectonic influence dominates sedimentation. Glacigenic sediments are present at the top of the Kingston Peak as glacioeustatic transgression flooded footwall highlands and provided accommodation space on horst tops. The end of glacial sedimentation is marked by the deposition of the Noonday Dolomite cap carbonate. Mapping of syn-depositional extensional faults show initiation of tectonic activity is synchronous with basal KPF coupled rift-glacial deposits and that rift-related tectonic activity is terminated within the Noonday Dolomite. The close association of glacial and rift deposits serves to illustrate the dominant control on the climate record in the Death Valley region is rift-related creation of accommodation space. The glacial record begins with the initiation of faulting and rifting, and ends with faulting and transgression in the Noonday Dolomite.

The record of glaciation is thus a function of the accommodation space and the timing of rifting. Correlation to diamictite deposits in the Panamint Range to the North suggests older intervals of diamictite deposition that are time equivalent to the KP1. In this region, rifting may have begun earlier. Whether these are discrete episodes or the continuation of a prolonged ice age with an incomplete record remains to be resolved.