The Quaternary pluvial history and paleoclimate implications of Newark Valley, east-central Nevada, derived from mapping and interpretation of surficial units and geomorphic features

Graduation Date

2003

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Environmental Systems: Geology, 2003

Committee Chair Name

R.M. Burke

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Paleoclimate, Nevada, Quaternary geology, Pluvial lakes, Humboldt State University -- Theses -- Geology, Newark Valley, Geomorphology, Soils

Abstract

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 and 37 topographic profiles of beach barriers, along with geomorphic preservation and surficial characteristics. The most prominent suite of shorelines reach an elevation of 1845 m 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 marine oxygen isotope stage (OIS) 2, Sehoo equivalent, pluvial lake. This is supported by an AMS 14C numerical age from a Gyraulus snail within the highest beach barrier of the younger suite of shorelines, yielding a maximum age of 13,780 +/- 50 14C yr B.P. [16,550 +/-350 cal yr B.P.]. The higher, less prominent, suite of shorelines reach an elevation of at least 1862 m. 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 is correlated with an OIS 6, Eetza equivalent, pluvial lake. Secondary carbonate and clay accumulation index values were calculated for 17 soil profiles and individual soil properties of 28 soil profiles were 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 is not ruled out. These results, in combination with lake and drainage basin areas, indicate a relative decrease in effective moisture from OIS 6 to OIS 2. This is demonstrated by a decrease in Hydrologic Index (HI) values (Mifflin and Wheat, 1979) from 0.36 (OIS 6) to 0.29 (OIS 2). Limited evidence suggests that the highest 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 minimum age of OIS 6 age. However, weak geomorphic expression, poorly preserved stratigraphy of potential shorelines at the sill elevation, and relation of the sill with mapped alluvial fans suggest an older age of overflow, possibly OIS 16 (Reheis, 1999). This potential overflow elevation results in a lake elevation of 1890 m with a minimum HI of 0.47, 45% greater effective moisture than in OIS 2 time. To augment estimates of shoreline ages based on geomorphology, preservation, and soil development, 14C AMS numerical age analyses and amino acid racemization (AAR) age estimates were used. Snail shells were collected from WSGP and Lone Mountain (LMt.) for 14C AMS and AAR analyses. Tufa was collected from three gravel pits near LMt. and the Diamond Peak Gravel Pit (DPGP) for 14C AMS analyses. 14C AMS analyses were performed by Beta Analytic and the USGS. AAR analyses used procedures outlined in Kaufman and Manley (1998) and were conducted by Darrell Kaufman and Ben Laabs of Northern Arizona University (NAU). These results show that the OIS 2 highstand of pluvial Lake Newark occurred ~13,780 +/-50 14C years ago, essentially coeval with the Lake Lahontan OIS 2 highstand. In addition, these numerical ages allowed a simple lake level curve to be constructed that describes fluctuations in Lake Newark from ~14,000 to ~12, 000 14C yrs B.P. To provide depositional context for these age estimations, stratigraphic sections were described from where the materials were sampled. As an outgrowth of mapping pluvial Lake Newark shorelines for paleoclimate study, surficial geologic and geomorphic maps were made of Quaternary deposits for parts of eight 71/2 Minute USGS Quadrangles in Newark Valley. These maps identify alluvial fans of three ages, which interact with two ages of shorelines. The timing of deposition of these alluvial fans exhibits a complex relation to shorelines thus, to climatic changes. Faults were identified and mapped that displace alluvial fans of three ages in the valley, and some that may displace shorelines. This reconnaissance investigation shows these faults exhibit progressive deformation, and a rough survey suggests slip rates may be on the order of 0.05 to 0.02 mm/yr. Attempts to use topographic surveys of fault scarps, both a general comparison with scarps of known ages in the Great Basin (Barnhard, 1985) and application of the Diffusion Equation (Hanks, 1998) were problematic and unsuccessful.

https://scholarworks.calstate.edu/concern/theses/7m01bp09z

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