Lacustrine, fluvial, and fan sedimentation; Quaternary climate change and tectonism, Pine Valley, Nevada

Pine Valley, an intermontane graben in the Basin and Range province, has trapped a unique record of Quaternary volcaniclastic fluviolacustrine sediments, largely exposed by late Pleistocene tectonism and erosion. These are analogous to Great Basin sediments spanning the Tertiary and which produce oil in Railroad Valley, Nevada, and Rozel Point, Utah, and gas in Carson Sink, Nevada. Three major facies in the 400+-m thick middle Pliocene to middle Pleistocene Hay Ranch formation are shallow lacustrine, fluviatile, and alluvial fan. Deposits from the fresh-water, quiet, alkaline, oxygenated lakes include tuffaceous calcilutite interlayered with rhyolitic vitric tuff, zeolite, silt, and clay. Organic content varies widely. Grading laterally and in places vertically are fluviatile lithofacies of thickening wedges of silt and sandstone. Sedimentary structures indicate episodic transport by anastomosing stream channels and spreading sheetflood, which grade into sand to cobble-fan-glomerates of valley-margin alluvial fan facies and include water-lain and debris-flow clasts. Middle Pleistocene to Holocene sediments are of unconsolidated fluvial and alluvial fan facies, with minor landslide, talus, and thin carbonate lake and welded tuff facies. The complexly interfingering facies and subfacies represent transgressing and regressing lake shorelines and variable fluvial input related to glacial climatic changes and are best illustrated with a series of time-sequential basin facies maps. Decreased evaporation and increased precipitation during glacial times, at least in winter, pulsed clastics to narrow basin-margin fans, and clay and silt to the lake center. Dry periods allowed thicker algal lime mud and ash to accumulate. Lack of paleosols, beaches, paludal facies, and lake shallowness preclude very wet conditions. Tectonism had a steady control on sedimentation. Growing horst relief maintained local stream gradients. Pleistocene epeirogenic uplift and tilting northward of the region reversed the flow of and entrenched Pine Creek; the new external drainage dissected Hay Ranch pediments and inhibited playa evaporite and perhaps beach deposition and preservation. Continued extension and slight south and east tilting of the graben, however, roughly kept pace with warping during Hay Ranch time.