LATE QUATERNARY PLUVIAL HISTORY OF NEWARK VALLEY, EAST-CENTRAL NEVADA

Mapping of landforms and Quaternary stratigraphy within Newark Valley, east-central Nevada, has resulted in the characterization of shorelines used for paleoclimatic interpretations in pluvial Lake Newark. Shorelines are differentiated into two age groups based on analysis of 28 soil profiles, 37 topographic profiles of beach barriers, along with preservation and surficial characteristics. The most prominent suite of shorelines reach an elevation of 1845m and are characterized by an A/Bwk/Coxk soil profile and profile development index (PDI) values ranging from 0.01 to 0.16, typically 0.07 to 0.16. Based on these parameters, the shorelines are correlated with a stage 2, Sehoo equivalent, pluvial lake. This is supported by an AMS 14C numerical age from a gyraulus sp. snail within the highstand beach barrier, yielding a maximum age of 13,780 +/- 50 radiocarbon years [16,550 +/-350 cal. yr B.P.]. The higher, less prominent, suite of shorelines reach an elevation of at least 1862m. These shorelines are characterized by an A/Bwk/Bkm or Km/Coxk soil profile and PDI values ranging from 0.20 to 0.34, typically 0.26 to 0.34. This suite of shorelines are correlated with a stage 6, Eetza equivalent, pluvial lake. Secondary carbonate and clay accumulation index values were calculated and individual soil properties analyzed. These data also support the favored interpretation of only two ages of shorelines. However, some scatter within the data exists, thus the possibility of additional shoreline ages are not ruled out.

These results, in combination with lake and drainage basin areas, indicate a relative decrease in effective moisture from stage 6 to stage 2. This is demonstrated by a decrease in hydrologic index (HI) values (Mifflin and Wheat, 1979) from 0.36 (stage 6) to 0.29 (stage 2). Limited evidence suggests that pluvial Lake Newark may have overflowed. The timing of this possible overflow is poorly constrained. Soil development into deposits on the potential sill preliminarily suggests a stage 6 age. However, the weak geomorphic expression and poorly preserved stratigraphy of potential shorelines at the sill elevation suggest an older age of overflow, possibly stage 16 (Reheis, 1999). This potential overflow elevation results in a lake elevation of 1890m with a minimum HI of 0.47, a 45% increase in effective moisture from stage 2 time.