Black Mats, Spring-Fed Streams, and Late-Glacial-Age Recharge in the Southern Great Basin☆

摘要: Black mats are prominent features of the late Pleistocene and Holocene stratigraphic record in southern Great Basin. Faunal, geochemical, sedimentological evidence shows that black formed several microenvironments related to spring discharge, ranging from wet meadows shallow ponds. Small land snails such asGastrocopta tappanianaandVertigo berryiare most common mollusk taxa present. Semiaquatic aquatic less abundant include Catinellids,Fossaria parva, Gyraulus parvus,and others living today around perennial seeps The ostracodesCypridopsis okeechobiandScottia tumida,typical low-discharge springs today, as well other typical wetlands, mats. Several new species lived saturated subsurface also present, but lacustrine ostracodes absent. δ13C values organic matter range −12 −26‰, reflecting contributions tissue both C3(sedges, shrubs trees) C4(saltbush, saltgrass) plants. Carbon-14 dates on humate fraction 55 fall between 11,800 6300 230014C yr B.P. modern. total absence our sample likely reflects increased aridity associated with mid-Holocene Altithermal. oldest date 11,800–11,60014C B.P., peak the14C mat distribution falls at ∼10,00014C As formation is related, their abundance refilling valley aquifers starting no later than peaking after 11,00014C Reactivation spring-fed channels shortly before 11,20014C apparent records Las Vegas Pahrump Valleys. This age suggests part may have response Younger Dryas (YD)-age recharge region. However, inception precedes YD by least 40014C yr, hydrological change gradual, not rapid.