Characterization Of The Union Springs Formation, Finger Lakes Region, Ny: An Integrated High Resolution Facies, Geochemical And Sequence Stratigraphical Approach
The Devonian Marcellus "Shale" of the Appalachian Basin is a typical black shale formation with high concentrations of organic matter (maximum Total Organic Carbon, TOC, 14%). Early descriptions of black shales, including the Marcellus, emphasized their homogeneity, high organic matter content, very fine particle size and low energy depositional conditions. Mechanisms that lead to organic matter enrichment (i.e. anoxia, production and sedimentation rate) have been a scientific controversy. Recent studies show that these black shales are not homogenous and display a high degree of variability, and show current-induced deposition. Interdependent processes of preservation, production and sedimentation have been agreed upon rather than one or the other. This study attempts to document the heterogeneity of the Union Springs Formation (within the Marcellus Shale) and focuses on determining depositional conditions that resulted in organic matter enrichment. An integrated high-resolution microfacies, geochemistry and sequence stratigraphical approach is followed in order to achieve this goal. Details are documented in 32 samples collected from fresh, unweathered surfaces of an active rock quarry (Seneca Stone Co.) in Seneca Falls, NY. Utilizing a combination of outcrop observations, hand sample descriptions, optical and scanning electron petrography, and TOC, three lithofacies and thirteen microfacies have been identified based on their allochthonous, autochthonous and authigenic components. A geochemical proxy-based approach is followed to predict the bottom water anoxia, distance to detrital source, and biologic productivity. Results show that mechanisms that led to organic enrichment in the Union Springs Formation included the interdependent processes of preservation, production and sedimentation rate. High TOC values, high abundances of redox proxies (Mo, U, V, Cr) and high abundance of framboidal pyrite indicate anoxic to sulphidic bottom waters that lead to preservation of organic matter. Low Si/Al and Ti/Al are indicative of the absence of coarse grain detrital input to the system, which agrees with the petrographical observations. The main agent diluting the organic matter appears to be carbonates (styliolinids, brachiopods, calcisilt grains). During the deposition of the Union Springs Formation, primary biological production was high, as revealed by the prevalence of marine algal cysts in all of the organic-rich microfacies. A high-resolution sequence stratigraphic framework is established for the Union Springs Formation. Small-scale (<50 cm) stratigraphic stacking patterns are recognized based on the microfacies distribution (grain size distribution, shell bed distributions, black shale-carbonate concretion cycles, and diagenetic components). Based on the sequence stratigraphy, first deepening then shallowing base level is interpreted. The Union Springs Formation constitutes an interval of Transgressive Systems Tract and Highstand Systems. This interpretation agrees with the sequence stratigraphic models of the large-scale Devonian Appalachian Basin.
Marcellus Shale; Sedimentology; Microfacies
Jordan, Teresa Eileen
Allmendinger, Richard Waldron
M.S. of Geological Sciences
Master of Science
dissertation or thesis