Date of Thesis
Bachelor of Science
Geology & Environmental Geosciences
Pennsylvania, geology, devonian, geochronology, muscovite, zircon
Foreland basin sediment deposition in North-Central Pennsylvania during Late Devonian time records erosion of hinterland source terranes exhumed during regional plate convergence, including the collisional Acadian orogeny. The Catskill clastic wedge preserves a coarsening-upwards stratigraphic succession from marine to fluvial environments associated with sediment progradation and sea-level regression, yet depositional timescales and quantitative provenance data are largely unconstrained.
Detailed facies analysis of eight outcrops spanning >2 km of stratigraphy in Lycoming Co., Pennsylvania documents distinct upsection changes, interpreted to reflect changes in depositional environments consistent with previous sedimentology of the Catskill clastic wedge. Stratigraphy displays a transition from nearshore marine and estuarine environments above the fairweather wave-base to fluvial channel-bar systems with poorly drained floodplains. New U/Pb detrital zircon ages (n=737) from six sandstones overlap with ages reported from exposed hinterland Appalachian bedrock sources. Taconic (440–490 Ma, 13%), Grenville (900–1200 Ma, 46%), and Pre-Grenville (1201–2950 Ma, 26%) age populations and synorogenic Acadian (350–420 Ma, 4%) ages make up the zircon age spectra. New 40Ar/39Ar detrital muscovite age populations (358–475 Ma, n=341) from three sandstones are chiefly Acadian (93%). The youngest population of detrital zircon ages from the lowermost sample indicates a maximum depositional age of ~369 Ma. The youngest population of detrital muscovite ages from the uppermost sample yields a maximum depositional age of ~361 Ma. These new age constraints, together with previously reported Late Devonian fossil vertebrates and palynomorphs, indicate deposition of the entire 2-km-thick succession in <14 m.y from <373 to ~359 Ma.
LA-ICP-MS geochemistry of detrital muscovite grains and muscovite within schistose lithic grains from eight sandstones implies mixed igneous and metamorphic provenance. This new data builds upon previous sandstone modal analyses inferring provenance from both recycled sedimentary and crystalline bedrock source terranes. Populations of detrital muscovite display significantly higher incompatible element concentration values relative to sampled muscovite within schistose clasts, and implies igneous provenance for most incompatible element-rich detrital muscovite grains. Overlapping incompatible element concentrations between detrital muscovite and schistose muscovite indicate metamorphic provenance for some the detrital muscovites.
Collectively, the new geochronologic and geochemical data from detrital minerals indicate erosion of igneous and metamorphic bedrock sources exposed >250 km to the east and transport westward into the foreland basin, consistent with previously reported west-directed paleocurrent indicators and westward-fining lithofacies trends. Specifically, the results presented herein are most consistent with sediment derivation from igneous and metamorphic source terranes analogous to those presently exposed in Connecticut, New Jersey, and Southeastern New York. The <6 m.y. lag time between cooling of Late Devonian detrital muscovite and deposition in Late Devonian sediments implies rapid exhumation/erosion; additional thermochronologic data are needed to estimate exhumation rates. This exhumation is consistent with muscovite cooling ages previously reported from hinterland bedrock sources and evidence for regional hinterland glaciation.
Gardner, Cole T., "Late Devonian Sedimentary Record Of Appalachian Tectonics And Erosion: Geochronology And Geochemistry Of Detrital Muscovite And Zircon From Central Pennsylvania Strata" (2019). Honors Theses. 507.