In:
Quaternary Research, Cambridge University Press (CUP), Vol. 49, No. 2 ( 1998-03), p. 129-148
Abstract:
Black mats are prominent features of the late Pleistocene and Holocene stratigraphic record in the southern Great Basin. Faunal, geochemical, and sedimentological evidence shows that the black mats formed in several microenvironments related to spring discharge, ranging from wet meadows to shallow ponds. Small land snails such as Gastrocopta tappaniana and Vertigo berryi are the most common mollusk taxa present. Semiaquatic and aquatic taxa are less abundant and include Catinellids, Fossaria parva, Gyraulus parvus, and others living today in and around perennial seeps and ponds. The ostracodes Cypridopsis okeechobi and Scottia tumida, typical of seeps and low-discharge springs today, as well as other taxa typical of springs and wetlands, are common in the black mats. Several new species that lived in the saturated subsurface also are present, but lacustrine ostracodes are absent. The δ 13 C values of organic matter in the black mats range from −12 to −26‰, reflecting contributions of tissue from both C 3 (sedges, most shrubs and trees) and C 4 (saltbush, saltgrass) plants. Carbon-14 dates on the humate fraction of 55 black mats fall between 11,800 to 6300 and 2300 14 C yr B.P. to modern. The total absence of mats in our sample between 6300 and 2300 14 C yr B.P. likely reflects increased aridity associated with the mid-Holocene Altithermal. The oldest black mats date to 11,800–11,600 14 C yr B.P., and the peak in the 14 C black mat distribution falls at ∼10,000 14 C yr B.P. As the formation of black mats is spring related, their abundance reflects refilling of valley aquifers starting no later than 11,800 and peaking after 11,000 14 C yr B.P. Reactivation of spring-fed channels shortly before 11,200 14 C yr B.P. is also apparent in the stratigraphic records from the Las Vegas and Pahrump Valleys. This age distribution suggests that black mats and related spring-fed channels in part may have formed in response to Younger Dryas (YD)-age recharge in the region. However, the inception of black mat formation precedes that of the YD by at least 400 14 C yr, and hydrological change is gradual, not rapid.
Type of Medium:
Online Resource
ISSN:
0033-5894
,
1096-0287
DOI:
10.1006/qres.1997.1959
Language:
English
Publisher:
Cambridge University Press (CUP)
Publication Date:
1998
detail.hit.zdb_id:
1471589-2
detail.hit.zdb_id:
205711-6
SSG:
13
SSG:
14
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