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Southwestern Alaska is a critically understudied region of Beringia, highlighted by the lack of paleoenvironmental reconstructions of the Yukon-Kuskokwim Delta (YK Delta). This sub-arctic region is a joint deltaic coastal lowland environment, home to 50 Yup’ik and Cup’ik communities. Anthropogenic climate change dramatically impacts the landscape. Increases in the intensity and occurrence of coastal flooding, the thaw of permafrost and tundra wildfire events have directly affected community resilience and their subsistence way of life. The YK Delta also contributes to the global atmospheric carbon budget as the region’s discontinuous permafrost thaws releasing stored carbon. These issues necessitate the filling of the regional paleoenvironmental knowledge to properly inform native populations and predict future changes to the landscape. Working with two communities on the outer YK Delta, namely, Kongiganak and Mekoryuk, this thesis presents initial paleoenvironmental studies which contribute to our understanding of the impacts of climate change on this region. The first effort documents the development of a loess plateau on the YK Delta during the Last Glacial Period (115,000 – 11,700 years ago), specifically during Marine Isotope Stage III (60,000 – 25,000 years ago), described in Chapter 2. This topic was developed from exposures at Kongiganak and Mekoryuk, and helps to refine the relative sea level history and aeolian processes of the YK Delta. Other efforts on Nunivak Island consist of preliminary results from the first late Holocene lacustrine reconstruction and the first attempt to provide context to coastal dune geomorphology, highlighted in Chapter 3. These efforts help to establish regional paleoenvironmental conditions in the late Holocene, methodology for future sampling, and provide important estimates of long-term coastal erosion.

Detection of large-magnitude coastal events, especially in wave-dominated retrograding barrier settings, has traditionally relied upon lithological evidence, such as distinct overwash sand layers within the muddy backbarrier sequences. In tide-dominated environments, unconformities in marsh stratigraphy have been interpreted as rapid drowning or erosion events caused by large storms. In transitional mixed-energy backbarrier environments, however, clearly identifiable event horizons are rare, due to unfavorable conditions for peat formation or to a lack of overwash. To address these challenges, the present study utilized X-ray fluorescence (XRF), magnetic susceptibility (MS), and X-ray diffraction (XRD) techniques to identify anomalies within 4-to-7-m-thick sequences recovered from Sewell Point, Cape May, New Jersey. In these cores, at least five peaks were identified that exhibit up to three-to-four-fold increase in Fe (up to 6.2%) and Ti (up to 0.5%) concentrations and a substantial increase in MS values (> 200 μSI). The sand fraction at these intervals exceeds 40% and is represented by moderately well-sorted, negatively-skewed, fine-grained sand (2.7 φ). Fe, Ti, and MS are positively cross correlated due to the relatively high content of sand-sized heavy minerals such as magnetite, rutile, ilmenite and biotite, as well as phlogopite and muscovite mica. These minerals were also identified using a Rigaku Dmax/B X-ray diffraction device. Seven radiocarbon-dated in situ samples of intertidal gastropods and the few available rhizomes indicate that the Sewell Point sequence accumulated over the past 900-1,000 years, at an average sedimentation rate greater than 4.5 mm/yr, which is consistent with its proximity to a historically active tidal inlet. Lithological anomalies at Sewell Point are interpreted as the signatures of episodic large-magnitude sediment fluxes into the paleo-lagoon. The calibrated ages of organic remains (mollusks and rhizomes) constrain chronology and allow interpretation of these stratigraphic layers as event horizons with historical storms of 1594, 1743 and 1821, along with pre-historic storms in the 11th-13th centuries. This research indicates that geochemically diagnostic intervals offer an effective tool for detection of event horizons and their regional correlation in mixed-sediment backbarrier settings. / Geology

The Upper Devonian Catskill Formation represents marginal marine and alluvial sediments which prograded into the Appalachian Basin during the Acadian Orogeny. Distributive fluvial systems (DFS) are prevalent in modern actively aggrading basins in all tectonic and climatic regimes and may be common in the rock record. In this study, I reinterpret the Catskill Formation as a prograding distributive fluvial system (DFS) on the basis of up-section variability in paleosols, channel sandstone textural trends, and alluvial architecture. At least three distinct pedotypes representative of prevailing soil forming conditions are identified during deposition of the Irish Valley, Sherman Creek, and Duncannon Members of the Catskill Formation. Increased paleosol drainage is inferred from an up-section transition from hydromorphic aqualfs within the Irish Valley Member to non-calcareous, uderts within the Duncannon Member. Qualitative field observations of channel sandstone morphology show an increase in channel size up-section. Channels occur as small isolated bodies at the base of the section, transitioning to relatively larger, amalgamated channels, and finally, large isolated channel bodies up-section. Sandstones are litharenites and coarsen-upward throughout the Catskill Formation overall. This coarsening upward trend results from increasing paleo-flow competency in larger channels up-section. These results are consistent with deposition of the Catskill Formation by DFS processes and demonstrate the utility of paleopedological analysis in interpreting alluvial depositional processes. Identifying DFS in the rock record has implications for paleosol-based paleoclimatic studies, as paleosols forming on prograding DFS have increased paleosol drainage up-section, which could potentially be misinterpreted as a shift from prevailing humid to arid paleoclimatic conditions. Recognition of DFS in the rock record also has implications for basin analysis and exploration of fluvial aquifers and hydrocarbon reservoirs, as the stratigraphic architecture of DFS are fundamentally different from tributary systems at the basin scale. / Geology