Date of Graduation
Eberly College of Arts and Sciences
Geology and Geography
Amy L Weislogel
This dissertation presents new results of the linkages between primary productivity, bottom water redox conditions and clastic input associated with the Acadian orogeny of the Marcellus Shale.;Chapter 1 compares the isotopic and geochemical characteristics of sediments of a liquids-prone well (WV-7) in Wetzel County with a gas-prone well (WV-6) in Monongalia County, northern West Virginia. The difference in organic carbon isotopes indicates that the dominant organic matter preserved in each core is different: delta13Corg values are lighter on average in WV-6 compared with WV-7. A possible explanation is that a larger fraction of terrestrial organic matter was preserved in the WV-6 core, whereas WV-7 may contain a greater percentage of marine organic matter. Clastic-influx proxies (e.g. Ti/Al, Ca/Al and Mg/Al) also suggest that the WV-6 core site received a higher sediment input compared to WV-7, consistent with a more proximal location to dry land and the delivery of greater amounts of terrestrial organic matter. Depleted delta13C carb values, low concentrations of redox sensitive elements (e.g. V, Cr, Ni and U), and high variability delta15N values in the WV-6 core all suggest the presence of higher dissolved oxygen concentration and short term shifts in an oxic/anoxic boundary near the sediment-water interface during deposition. This indicates that the depositional conditions were favorable for the accumulation of predominantly gas-prone Type III kerogen in the Marcellus Shale at the WV-6 site. In contrast, the Marcellus Shale at the WV-7 site was deposited in a more distal area that received a low terrestrial sediment supply, organic matter primarily derived from marine algae, and bottom water conditions that were dominantly anoxic. Such conditions were favorable for the accumulation of Type II kerogen that has a greater capacity to generate liquid hydrocarbons.;Chapter 2 employs geochemical, isotopic in combination with petrographic analyses from a core of the Marcellus Shale obtained from Greene County, Pennsylvania, to understand the dominant controls on organic matter deposition in the black shale study units. This study suggests that the regeneration of nutrients, such as nitrogen (N) and phosphorous (P), may have played a key role in the formation of organic carbon (OC)-rich intervals in the Marcellus Shale. The ratios of Corg/Nbulk and Corg/P tot are significantly higher in the OC-rich zone of the core (i.e., defined as TOC > 4% and located between 2393 and 2406.5 m depth). The high Corg/Ptot and Corg/Nbulk ratios of the preserved organic matter may reflect the release of N and P by microbial processes, indicating the recycling of nutrients during deposition of the OC-rich interval. In addition, our data show a positive relationships between the Corg/Ptot and Corg/Nbulk ratios and the organic carbon content, which indicate that the recycled nutrients may have promoted primary productivity, resulting in higher OC accumulation in some intervals. The geochemical and stable isotopic results also suggest that the alternating redox conditions in the water mass were favorable for nutrient regeneration. Highly variable trace metal concentrations (e.g., U, Mo, V) in the OC-rich zone and a wide range of delta15N and delta 34Spyr values towards the top of the OC-rich zone suggest fluctuations between anoxic and suboxic water conditions. Finally, sedimentary features and agglutinated benthic foraminifera in the OC-rich zone support the existence of short-term fluctuations between suboxic and anoxic conditions near the sediment-water interface.;Chapter 3 reports trace and rare earth elements (REE) of the samples collected from a 30-m core of the Marcellus Shale obtained from Greene County, southwestern Pennsylvania. This study provides the direct links between organic matter enrichment trends in the Marcellus Shale with the Acadian orogeny. The Acadian orogen has been recognized as a main sediment source for the Marcellus Shale. Synthesis of tectonic history and recent ash bed geochronology, reveals that deposition of the organic carbon-rich (OR) zone (characterized by TOC >4%; located between 2393 m and 2406.5 m core depth) in the studied Marcellus Shale core was coincident with tectonically active and magmatic quiescent period of the Acadian orogeny (ca. 395--380 Ma). This time also corresponds to the period when mountain building in the Acadian orogen was at its highest rates. The light rare earth (LREE) and selected trace elemental (e.g., Ta, Cs) composition of the OR zone sediments is similar to that of the bulk continental crust, supporting the lack of magmatic activity in the source area (i.e. Acadian orogen). In contrast, subsequent deposition of the organic carbon-poor (OP) sediments (characterized by TOC <4%; located between 2376 m and 2393 m core depth) in the upper Marcellus Shale occurred synchronously with a magmatic active phase (ca. 380--370 Ma) during the Acadian orogeny. The OP zone sediments have LREE and trace elements composition similar to that of the upper continental crust. (Abstract shortened by UMI.).
Chen, Ruiqian, "Dominant controls on organic-rich shale deposition: Geochemical evidences from the Marcellus Shale in the Appalachian basin" (2016). Graduate Theses, Dissertations, and Problem Reports. 7070.