Portland State University. Department of Geology
Richard E. Thoms
Term of Graduation
Date of Publication
Master of Science (M.S.) in Geology
Gabbs Formation (Nev.), Sunrise Formation (Nev.), Geochemistry -- Nevada, Stratigraphic correlation -- Nevada, Geology -- Nevada
1 online resource (98, 15 pages)
Trace and minor element geochemistry was determined using Instrumental Neutron Activation Analysis for ninety-six (96) limestone and calcareous siltstone samples from four stratigraphic sections in the Triassic-Jurassic age Gabbs and Sunrise formations of west central Nevada. Geochemical data support lithologic and faunal interpretations of relative basin positions of the Sunrise Formation stratigraphic sections, as well as basin development (including transgressive-regressive sequences) during deposition of the Gabbs and Sunrise formations at New York Canyon (Gabbs Valley Range). All sections show characteristics of both oceanic and continental island arc sources. Rare positive Eu anomalies relative to chondrites suggest that the Gabbs Formation at New York Canyon may have received occasional large oceanic island arc volcanic contributions, but that it is dominated by continental, andesitic elastics, as is the Sunrise Formation at all sections except Pamlico (Garfield Hills). Sunrise Formation sediments at Pamlico have varied Eu anomalies relative to chondrites, suggesting long-term, sporadic inclusion of oceanic island arc volcanic detritus. Na, Fe, Sc, and Co concentrations correspond with the Eu anomalies in the Pamlico sediments. The New York Canyon section appears to have undergone the most intense diagenesis, particularly at horizons associated with regressions. Similar Fe-As relationships throughout the section may indicate a post-diagenetic phase of low temperature, low water/rock alteration in which the entire section was affected.
Geochemical evidence supports suggestions by others of a period of extreme local and global sea level fluctuations during latest Triassic to earliest Jurassic time. Initiation of this phase may be represented by the topmost bed of the Mount Hyatt Member (Gabbs Formation) at New York Canyon. Sea level status and water redox conditions within the 5.5m Triassic-Jurassic boundary strata at New York Canyon, however, are indeterminate. Geochemical correlations of the four sections correspond with existing biochronologic correlations. On the basis of selected geochemical patterns, however, expansion of the upper stratigraphic limits is proposed for two Hettangian age zones within the Pamlico section and one within the New York Canyon section.
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Boelling, Karen Elizabeth, "Geochemical Characteristics and Correlations Within the Triassic-Jurassic Age Gabbs and Sunrise Formations of West Central Nevada" (1997). Dissertations and Theses. Paper 6286.