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A Southern Antler Foredeep Submarine Fan: The Mississippian Eleana Formation, Nevada Test Site
James H. Trexler, Jr., Patricia H. Cashman
Strata of the Eleana Formation in southern Nevada record the history of the Late Devonian through late Mississippian Antler foreland basin in southern Nevada. The Antler foredeep was created in latest Devonian or early Mississippian time, but did not receive significant sediments in southern Nevada until early-middle Mississippian (late Osagean) time. During late Osagean and Meramecian time, sediments deposited in the foredeep were dominantly mature, recycled siliciclastics derived from the uplifted Antler allochthon and foreland basin to the north in central Nevada. At the same time, a heterolithic sediment source, including mafic volcanic rocks and eroded, older limestones, supplied sediment intermittently and sparsely from the west-northwest. In late Mississippian (Chesterian) time siliciclastic sedimentation waned and deposition was dominated by fine-grained, carbonate- and siliciclastic-debris turbidity currents derived from an organically productive shelf or slope, probably to the north and northeast.
The Eleana Formation on the Nevada Test Site is preserved in at least two pre-Tertiary thrust sheets that are separated by a fault with potentially large horizontal displacement. Although palinspastic reconstruction is not yet possible, understanding of this thrust juxtaposition allows a preliminary reconstruction of the Eleana basin paleogeography. The stratigraphically lower part of this Mississippian submarine fan comprised mainly channel and interchannel deposits. More proximal fan deposits are found in the upper thrust plate of an east-vergent thrust system, indicating that the axis of the fan was to the west of the present exposures of the Eleana Formation.
The Antler foreland basin remained a basin in southern Nevada long after the Antler foredeep had filled in central Nevada. It may have been a peripheral deep marine basin that occupied either a reentrant in the old passive margin or a reentrant in the encroaching allochthon. Foredeep sediments were recycled down the basin axis from central Nevada south into the Eleana basin. Overlying allodapic limestone turbidites in the upper Eleana Formation were deposited as a transgressive deposit and are coeval with a known eustatic sea-level rise in Chesterian time.
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