ARCHITECTURE AND HIGH-RESOLUTION PROVENANCE OF ENIGMATIC SANDSTONE FACIES RESTING NONCONFORMABLY ON CRATONIC BEDROCK, MARBLE MOUNTAINS, CALIFORNIA, USA

Cambrian sandstones overlie Proterozoic basement across much of western Laurentia, including southeastern California, but do not record the same depositional processes or provenance signals. The basal ~2–10 meters of the Cambrian, Series 2, middle member of the Wood Canyon Formation (mmWCF) in the Marble Mountains represent sandstone facies deposited on the Laurentian craton after development of the Great Unconformity. Detrital zircon geochronology from other localities suggests some mmWCF is derived from uplifted rift-flank sources of the Texas Promontory. Sedimentary architecture of the subarkosic basal unit, Unit X, differs from superjacent fluvial strata typical of the mmWCF. Facies analysis and geochronologic testing of these enigmatic rocks can determine the likelihood that they preserve an older episode of deposition unrelated to Texas Promontory uplift.

Three Unit X facies are described in order of increasing stratigraphic height: Facies X1, a granular, coarse sandstone that ranges from absent to 1.3 meters in thickness; Facies X2, planar-bedded, medium sandstone that thins northward from 3.2 to 1.0 meters of strata; and Facies X3, a coarsening-upwards package overlying Facies X2 throughout the area. Facies X2 preserves plausible upper-stage planar bedding, stable antidunes, and in-phase asymmetrical ripples formed under a range of energy conditions. Coiled, sandy rip-ups, fragmented layers, and triradiate sand cracks provide physical evidence for subaerial, cohesion-enhancing microbial communities. In contrast to the perennial braidplain system of the overlying middle member, Facies X2 formed in a distinct environment of ephemeral fluvial discharge and potential nearshore-marine influence.

Inconsistencies in depositional process between studied strata and regional descriptions of the mmWCF, and sharp contacts between facies, permit that the mmWCF may contain one or more localized paraconformities in the Marble Mountains section. Utilizing U-Pb detrital zircon geochronology and textural analysis addresses whether Unit X is entirely part of the mmWCF or representative of a separate event correlated with older stratigraphic units in southeastern California.