Provenance of the Hamilton Group: A Study of Source-to-Sink Relationships within the Middle Devonian Central Appalachian Basin

• Main Author: Hupp, Brittany N
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2017
• Subjects: Geochemistry; Geology; Petroleum Geology
• ISBN: 9780355153545; 0355153548

Little is known of the provenance of detrital clays in the Hamilton Group, which contains one of the most lucrative unconventional shale gas plays in the world. The Hamilton Group consists of both the organic-rich Marcellus Shale and the overlying, clay-rich Mahantango Formation. This research, in collaboration with the Marcellus Shale Energy and Environmental Laboratory (MSEEL) project, aims to constrain the provenance of the two units within the Hamilton Group and evaluate paleoclimate indicators in order to better understand the role of clastic influx on organic-matter production and preservation within the Middle Devonian Acadian foreland basin. Geochemical and petrographic analysis of 121 samples from two different wells in Monongalia Co., West Virginia indicate slight changes in provenance throughout the deposition of the Marcellus Shale into the Mahantango Formation. Major and trace element geochemistry indicates a felsic igneous, upper-continental crust sediment source of granodioritic composition with additional influx from a quartzose recycled sedimentary source. Nine samples throughout the Hamilton Group underwent Sm-Nd isotopic analysis, yielding ϵNd values ranging from –7.06 to –11.75 and Nd depleted mantle model ages (τNd) ranging from 1.63-1.85 Ga, with ages becoming younger up-section. Mineralogical data acquired from x-ray diffraction analysis found the dominant mineral phases to be illite, muscovite, and quartz with fairly consistent mineralogy found throughout the Mahantango Formation and slightly more heterogeneous mineralogy found throughout the Marcellus Shale. Weathering indices including the CIA, CIW, and ICV all indicate increased weathering throughout the deposition of the Marcellus Shale followed by constant moderate rates of weathering during deposition of the Mahantango Formation. These results suggest that the extrabasinal detrital sediments of the Hamilton Group came from a mixed sediment source with clay influx from both the Superior Craton to the north (τNd >2.7 Ga) and Grenville-sourced sediments of the adjacent Acadian fold-thrust belt to the east (~1.0–1.3 Ga). Older model ages, felsic composition, and evidence of sediment recycling suggest little to no influx from the Acadian volcanic arc, aside from the volcanic air fall tuffs of the Tioga Ashes. Model ages and trace element geochemistry indicate increased sediment influx from the fold-thrust belt during the deposition of the Hamilton Group, with the highest sediment influx having occurred during Mahantango Formation deposition. Petrographic and geochemical analyses suggest that variations in organic-content throughout the Hamilton Group is due to dilution of organic-matter by increased influx of detrital clays during its deposition, particularly within the Mahantango Formation. Consistent clay mineralogy and weathering indices suggest that this influx of detrital sediment is not a function of climate fluctuations at this time, but rather may be influenced by increased tectonic activity and fluvial progradation during the second tectophase of the Acadian Orogeny.