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Evaluation Of Late Neogene Sediments On The Northern Flank Of The Central Coyote Mountains: Paleotopographic Setting And Sediment Sources Of The Late Miocene Latrania Formation During Initial Stages Of A Marine Incursion


During the late Miocene, initiation of motion on the West Salton detachment fault caused rapid subsidence of the Salton Trough region, resulting in a marine incursion between 6.3 and 4.3 Ma (Dorsey and others, 2011). Marine sediments of this age were deposited unconformably onto Paleozoic/Mesozoic metamorphic rocks and mid-Miocene nonmarine clastics and volcanics of the Split Mountain Group. In the central Coyote Mountains, located along the southern edge of the Salton Trough, the marine sedimentary rocks consist of the Miocene-Pliocene Latrania Formation, a thin sequence of locally derived fossiliferous immature conglomerates and sandstones, overlain by the Pliocene Deguyos Formation, a thick sequence of Colorado River-derived deltaic mudstones and fine mature sandstones. Progradation of the delta resulted in a return of nonmarine conditions, marked by the deposition of the Pliocene-Pleistocene Diablo Formation, a thick sequence of fine mature sandstones and mudstones. Around 1 Ma, the tectonic regime in the area changed, deposition of Colorado River-derived sedimentation ceased, and the right-lateral Elsinore fault formed, uplifting the range. Detailed geologic mapping on the north flank of the central Coyote Mountains reveals a network of faults kinematically compatible with the Elsinore Fault as well as a remarkably rugged paleo-topography along the unconformity between the marine sedimentary rocks and the metamorphic basement. This unconformity is locally so steep that it is easily mistaken for a fault. In these places, the Latrania Formation is absent; deltaic mudstones of the Deguyos Formation are plastered directly against paleo-cliffs of metamorphic rocks. In addition, the Latrania Formation appears to have been simultaneously deposited at varying depths–wherever the topography was gentle enough to retain sand. Specific focus on the depositional environment and provenance of the Latrania Formation has yet to be presented. Petrographic analyses of thin-sectioned samples and a proposed paleogeographic reconstruction of the studied area during Latrania deposition add to a growing understanding of the paleotopography and sediment sources associated with the initial stages of this marine incursion.