PUDDINGSTONES OF THE KINGSTON PEAK FORMATION: SUBMARINE DEBRIS FLOWS ON A COLLAPSING CONTINENTAL MARGIN, CALIFORNIA, USA

Neoproterozoic Kingston Peak Formation, the uppermost unit of the Pahrump group, underlies several mountain ranges within the Death Valley and Mojave Desert region, California. The stratigraphy consists of a lower siltstone bed overlain by puddingstone, a mudstone containing pebbles, cobbles and boulders. Upper beds contain alternating coarse breccias, puddingstones, conglomeratic sandstones, and several enormous blocks and olistostromes from the underlying Pahrump group. Early workers have interpreted these deposits as: fanglomerates, Hewett, (1952); marine synsedimentary tectonic, Wright et al., (1974) and Schermehorn, (1977); and glacial marine, Miller, (1982).

Puddingstones and the coarse facies of the Kingston Peak Formation in the Kingston Range were the focus of this study, but outcrops in the Silurian Hills, Southern Salt Spring Hills, Avawatz Mountains and Saratoga Hills were also studied. Methods include: field mapping at bed contacts; measures of stratigraphic thickness and orientation of clasts; point counts and identification of pebbles, cobbles in puddingstone matrix; and petrographic analysis of mud matrix and clasts.

In the Kingston Peak Formation, all beds above the lower siltstone are conformable and graded, including the puddingstone unit. The plunge of long axes of cobbles is measurable, and displays imbrication suggesting a prevailing flow direction. Silt and sand frequency indicate poor to faint sorting. Strata are intimately associated with marine sedimentation. The giant blocks and olistostromes have sedimentary contacts indicative of mass flow processes driven by tectonic elevation of source area. Upper coarse beds are products of rapid sedimentation. They display gravity flow deposits in rhythmic fashion and contain beds of puddingstone meters thick, all very suggestive of debris flow processes. In summary, the most probable explanation of Kingston Peak puddingstones and related coarse debris are products of tectono-sedimentation during collapse of the continental margin.