Department of Earth Sciences
Permanent URI for this community
The Earth Sciences Department is part of the College of Earth, Ocean, & Environment. We have an excellent faculty with research strengths in coastal and marine geology and geophysics, surface processes and geomorphology, hydrogeology, geomicrobiology, Quaternary geology, paleobiology and micropaleontology, and environmental geophysics.
Visit the Department's website for more information.
Browse
Browsing Department of Earth Sciences by Title
Now showing 1 - 20 of 95
Results Per Page
Sort Options
Item Alegria Canyon Terrace, Santa Barbara County, California(2012-05-15) Wehmiller, John F.Alegria Canyon Terrace, west of Santa Barbara, California. Modern terrace platform at sea level; Pleistocene (MIS 5) terrace at level of railroad tracks.Item Along-Shore Movement of Groundwater and Its Effects on Seawater-Groundwater Interactions in Heterogeneous Coastal Aquifers(Water Resources Research, 2021-12-14) Geng, Xiaolong; Michael, Holly A.Studies of coastal groundwater dynamics often assume two-dimensional (2D) flow and transport along a shore-perpendicular cross-section. We show that along-shore movement of groundwater may also be significant in heterogeneous coastal aquifers. Simulations of groundwater flow and salt transport incorporating different geologic structure show highly three-dimensional (3D) preferential flow paths. The along-shore movement of groundwater on average accounts for 40%–50% of the total flowpath length in both conduit-type (e.g., volcanic) heterogeneous aquifers and statistically equivalent (e.g., deltaic) systems generated with sequential indicator simulation (SIS). Our results identify a critical role of three-dimensionality in systems with connected high-permeability geological features. 3D conduit features connecting land and sea cause more terrestrial groundwater flow through the inland boundary and intensify water exchange along the land-sea interface. Therefore, conduits increase the rate of SGD compared to equivalent homogeneous, SIS and corresponding 2D models. In contrast, in SIS-type systems, less-connected high-permeability features produce mixing zones and SGD nearer to shore, with comparable rates in 3D and 2D models. Onshore, 3D heterogeneous cases have longer flowpaths and travel times from recharge to discharge compared to 2D cases, but offshore travel times are much shorter, particularly for conduit-type models in which flow is highly preferential. Flowpath lengths and travel times are also highly variable in 3D relative to 2D for all heterogeneous simulations. The results have implications for water resources management, biogeochemical reactions within coastal aquifers, and subsequent chemical fluxes to the ocean. Plain Language Summary: The findings of this study provide insight into the complex patterns of groundwater flow under the influence of geologic variability in coastal aquifers. In coastal regions, studies of solute transport processes mainly rely on an assumption of 2D groundwater flow and solute transport in the shore-perpendicular direction. Our results reveal that groundwater does not only flow toward the sea, it also can flow along-shore, especially in aquifers with features that connect the onshore and offshore. This affects exchange and mixing between fresh and saline groundwater, which can strongly impact delivery of contaminants and nutrients to sensitive nearshore marine ecosystems. Results highlight the importance of characterizing the geology of coastal aquifers and representing it in models of groundwater flow and contaminant transport.Item Amino acid racemization age estimates for Pleistocene marine deposits in the Eukeka-Fields Landing Area, Homboldt County, California(U.S. Department of the Interior Geological Survey, 1977) Wehmiller, John F.; Kennedy, George L.; Lajoie, Kenneth R.Amino acid enantiomeric (D/L) ratios in fossil Saxidomus samples from four localities in the Eureka - Fields Landing area of the Humboldt Bay region, California yield age estimates of 180,000 to 280,000 years for exposed and slightly deformed bay and estuarine deposits.Item Amino acid racemization dating of some coastal plain sites, southeastern Virginia and northeastern North Carolina(University of Delaware, Newark, DE, 1985) Mirecki, JuneBivalve mollusks (g. Mercenaria and g. Anadara) have been analyzed from 4 southeastern coastal plain sites using the amino acid racemization (AAR) technique for correlation and age estimate purposes. As seen previously (Wehmiller and Belknap, 1982), a conflict exists between age estimates obtained by AAR and V-series methods at the Norris Bridge, VA locality. Here, V-series dating of coral yields a 187 ±20 KA age, while AAR methods suggest a 400 to 500 KA age. The following methods are employed to understand this discrepancy at the Norris Bridge site: 1). Analysis of standard samples to ensure uniform sample preparation and system operation; 2). Quantification of variation in Mercenari'a and Anadara samples for each field site; 3). Qualitative comparison of AAR behavior between Mercenaria and Anadara to assess suitability of Anadara for dating purposes; 4). Aminostratigraphic correlation of field sites using both genera, and 5). Estimation of AAR ages using the the non-linear model of Wehmiller and Belknap (1982). Standard samples analyzed for this study show relatively good preCISIon. Coefficients of variation (CVs) of D/L leucine values are 5.7% (ILC-A) and 9.1% (ILC-B). Overall, both ILC-A and -B show accuracy within 6% when compared to other University of Delaware analyses. Several valves of each genus were analyzed from all sites to determine field site precision. CVs for multiple Mercenaria samples from each site are as follows: Gomez Pit, VA (5.2%); New Light Pit, VA (7.0%); Moyock Pit, N.C. (8.8%) and Norris Bridge, VA (4.4%). CVs for Anadara samples are slightly higher, but comparable for each field site. No Anadara were analyzed from the New Light Pit locality. On the basis of an identical order of racemization rates (i.e. ASP2:ALA> LEU>VAL) and similar ASP/LEU values in both genera, Mercenaria and Anadara qualitatively show similar racemization behavior. 3 clusters of DjL leucine values have been discerned from these field site analyses. These D/L leucine values are used to correlate fossiliferous strata in the southeastern Virginia and northeastern North Carolina Using the non-linear kinetic model, these Coastal Plain. D/L values suggest the following ages: 0.21 to 0.25 (75 KA) and 0.530 (approximately 400 KA). D/L values ranging between 0.33 and 0.38 are tentatively estimated to be 100 to 200 KA in age.Item Aminostratigraphy, geochronology and geochemistry of fossils from Late Cenozoic marine units in southeastern Virginia(University of Delaware, Newark, 1990) Mirecki, JunePaired Amino Acid Racemization (AAR) and Electron Spin Resonance (ESR) data have been obtained from individual mollusc valves (g. Mercenaria) collected from stratified nearshore deposits at three sites in southeastern Virginia (Gomez Pit, Norris Bridge and Yadkin Pit). AAR and ESR data are used here to define aminozones in the region, and to infer age relationships among these superposed aminozones. These data are compared to U-Th analyses of corals from both sites (Szabo, 1985). Age differences among aminozones are estimated using models of racemization kinetics. Previous workers have generally concluded that the lithologic section at Gomez Pit represents a single transgression followed by minor regression. However, AAR and ESR data indicate at least one unconformity in this transgressive sequence, representing approximately 100 ka. The uppermost aminozone lla is defined by a mean ALLO/ISO values of 0.141+/-0.026 (n = 55). Aminozone lla directly overlies aminozone llc (ALLO/ISO = 0.335+/-0.028; n = 19). Molluscs representing a third, lowest aminozone (lld; ALLO/ISO = 0.471+/-0.038; n = 9) are recognized, but taphonomic and ESR data suggest that lld molluscs in Gomez Pit may be reworked. At Norris Bridge, only aminozone lld (ALLO/ISO = 0.473+/-0.020; n = 5) is recognized. ESR age estimates for aminozone lla range from 93-125 ka (n = 4), in general agreement with a Stage 5 estimate of 75+/-5 ka from U-Th analyses of corals from the same unit. ESR age estimates of 220 and 262 ka were calculated from 2 shells showing ALLO/ISO = 0.33; these data support a Stage 7 or Stage 9 interpretation for aminozone llc. AAR kinetic models suggest an age $>$400 ka for aminozone lld shells, inconsistent with a 187+/-20 ka age from a solitary coral at Norris Bridge. Attempts to obtain age estimates using ESR have been unsuccessful. Shells representing excellent, good, fair and poor preservation conditions from Gomez Pit aminozone lla were compared to determine the effects of condition on precision of amino acid data. These data were used to test the hypothesis that leaching by groundwater selectively removes the most extensively epimerized (free) amino acids from the mollusc shell, thus lowering the ALLO/ISO value. No statistically significant difference in amino acid concentrations, amino acid fractions or ALLO/ISO values was found among these Gomez Pit shells representing different preservation characteristics.Item Aqueous Geochemical Controls on the Sestonic Microbial Community in Lakes Michigan and Superior(Microorganisms, 2023-02-17) Rani, Asha; Ranjan, Ravi; Bonina, Solidea M. C.; Izadmehr, Mahsa; Giesy, John P.; Li, An; Sturchio, Neil C.; Rockne, Karl J.Despite being the largest freshwater lake system in the world, relatively little is known about the sestonic microbial community structure in the Laurentian Great Lakes. The goal of this research was to better understand this ecosystem using high-throughput sequencing of microbial communities as a function of water depth at six locations in the westernmost Great Lakes of Superior and Michigan. The water column was characterized by gradients in temperature, dissolved oxygen (DO), pH, and other physicochemical parameters with depth. Mean nitrate concentrations were 32 μmol/L, with only slight variation within and between the lakes, and with depth. Mean available phosphorus was 0.07 μmol/L, resulting in relatively large N:P ratios (97:1) indicative of P limitation. Abundances of the phyla Actinobacteria, Bacteroidetes, Cyanobacteria, Thaumarchaeota, and Verrucomicrobia differed significantly among the Lakes. Candidatus Nitrosopumilus was present in greater abundance in Lake Superior compared to Lake Michigan, suggesting the importance of ammonia-oxidating archaea in water column N cycling in Lake Superior. The Shannon diversity index was negatively correlated with pH, temperature, and salinity, and positively correlated with DO, latitude, and N2 saturation. Results of this study suggest that DO, pH, temperature, and salinity were major drivers shaping the community composition in the Great Lakes.Item Assessing the use of a camera system within an autonomous underwater vehicle for monitoring the distribution and density of sea scallops (Placopecten magellanicus) in the Mid-Atlantic Bight(National Marine Fisheries Service., 2016-04-26) Walker, Justin H.; Trembanis, Arthur C.; Miller, Douglas C.; Justin H. Walker, Arthur C. Trembanis and Douglas C. Miller; Walker, Justin H.; Trembanis, Arthur C.; Miller, Douglas C.The sea scallop (Placopecten magellanicus) fishery in the Atlantic is assessed during annual surveys by using both dredging and surface-deployed imaging techniques. In this pilot study in the Mid-Atlantic Bight, we used an autonomous underwater vehicle (AUV) to photograph the seafloor and to evaluate its use for determining scallop density and size. During 22 surveys in 2011, 257 km of seafloor were photographed, resulting in over 203,000 color images. Using trained annotators and photogrammetric software, we determined scallop density and shell heights for 15,252 scallops. The inshore scallop grounds near Long Island (at depths <40 m) had a density of 0.077 scallops per m2, whereas the inshore grounds of the New York Bight had a density of 0.012 scallops per m2. Shell heights derived from images were found to agree well with measurements from scallops collected with a commercial dredge. We show that images obtained with an AUV can be used to reliably estimate both density and shell height consistent with direct sampling from the same area. Moreover, side-scan sonar images obtained with an AUV can be used to detect dredge scars and, therefore, can provide a simultaneous, relative estimate of fishing effort in that area. AUVs provide a highly accurate suite of data for each survey site and therefore allow the design of experimental studies of fishing practices.Item Caloosa Shell Pit, Florida(2012-05-15) Wehmiller, John F.Item Cape Blanco, Oregon(2012-05-15) Wehmiller, John F.Item Cape Hatteras and Core Banks, North Carolina beach shells(2012-05-15) Wehmiller, John F.Item Cedar Neck, Sussex County, Delaware(2012-05-15) Wehmiller, John F.Item Coastal topography and hydrogeology control critical groundwater gradients and potential beach surface instability during storm surges(Hydrology and Earth System Sciences, 2022-12-02) Paldor, Anner; Stark, Nina; Florence, Matthew; Raubenheimer, Britt; Elgar, Steve; Housego, Rachel; Frederiks, Ryan S.; Michael, Holly A.Ocean surges pose a global threat for coastal stability. These hazardous events alter flow conditions and pore pressures in flooded beach areas during both inundation and subsequent retreat stages, which can mobilize beach material, potentially enhancing erosion significantly. In this study, the evolution of surge-induced pore-pressure gradients is studied through numerical hydrologic simulations of storm surges. The spatiotemporal variability of critically high gradients is analyzed in three dimensions. The analysis is based on a threshold value obtained for quicksand formation of beach materials under groundwater seepage. Simulations of surge events show that, during the run-up stage, head gradients can rise to the calculated critical level landward of the advancing inundation line. During the receding stage, critical gradients were simulated seaward of the retreating inundation line. These gradients reach maximum magnitudes just as sea level returns to pre-surge levels and are most accentuated beneath the still-water shoreline, where the model surface changes slope. The gradients vary along the shore owing to variable beach morphology, with the largest gradients seaward of intermediate-scale (1–3 m elevation) topographic elements (dunes) in the flood zone. These findings suggest that the common practices in monitoring and mitigating surge-induced failures and erosion, which typically focus on the flattest areas of beaches, might need to be revised to include other topographic features.Item Comparison of approaches to dating Atlantic coastal plain sediments, Virginia Beach, Virginia(Washington, DC : U.S. Nuclear Regulatory Commission, 1998-03) Lamothe, Michel; Wehmiller, John F.; Noller, Jay S.Item Compilation of Florida Amino Acid Racemization Data(2014-07-24) Wehmiller, John F.Item Correlation and chronology of Pacific Coast marine terrace deposits of continental United States by fossil amino acid stereochemistry technique, evaluation, relative ages, kinetic model ages, and geologic implications(U.S. Department of the Interior Geological Survey, 1977) Wehmiller, John F.; Lajoie, Kenneth R.; Kvenvolden, Keith A.; Peterson, Etta; Belknap, Daniel F.; Kennedy, George L.; Addicott, Warren O.; Vedde, John G.; Wright, Robert W.Enantiomeric (D/L) ratios of six or more amino acids have been determined in Pleistocene mollusks from fifty-one terrace localities on the Pacific coast of the United States from Puget Sound, Washington, to San Diego, California. Samples have been selected for the purpose of evaluation of various aspects of the amino acid dating technique as well as for the application of the technique to unresolved chronologic problems. Samples with known stratigraphic relationships (upper and lower Pleistocene, Pliocene) have been examined to document the relationships between geologic age and extent of racemization. Most genera investigated exhibit the expected trend of increasing extent of racemization with increasing age, but some genera do not document this trend, probably because of contamination during diagenesis. Of all genera examined in this manner, the bivalve mollusk Saxidomus appears to be the most reliable.Item Critical facility accessibility and road criticality assessment considering flood-induced partial failure(Sustainable and Resilient Infrastructure, 2022-11-25) Gangwal, Utkarsh; Siders, A. R.; Horney, Jennifer; Michael, Holly A.; Dong, ShangjiaThis paper examines communities’ accessibility to critical facilities such as hospitals, emergency medical services, and emergency shelters when facing flooding. We use travel speed reduction to account for flood-induced partial road failure. A modified betweenness centrality metric is also introduced to calculate the criticality of roads for connecting communities to critical facilities. The proposed model and metric are applied to the Delaware road network under 100-year floods. This model highlights the severe critical facility access loss risk due to flood isolation of facilities. The mapped post-flooding accessibility suggests a significant travel time increase to critical facilities and reveals disparities among communities, especially for vulnerable groups such as long-term care facility residents. We also identified critical roads that are vital for post-flooding access to critical facilities. The results of this research can help inform targeted infrastructure investment decisions and hazard mitigation strategies that contribute to equitable community resilience enhancement.Item Davenport, California(2012-05-15) Wehmiller, John F.Item Descriptive text for Gomez Pit stratigraphy and geochronology(2013) Wehmiller, John F.Item Development of an amino acid racemization database for coastal plain sites in North Carolina(University of Delaware, 2004) Pellerito, VincentAn extensive collection of unpublished and published AAR, radiometric and taphonomic characteristic data for mollusk samples from coastal North and South Carolina have been arranged into a relational database. Organizing over two decades of regional AAR data is particularly important for ongoing chronostratigraphic studies of coastal North Carolina, where active study of an extensive Quaternary sequence is underway as part of the North Carolina Coastal Geology cooperative. A relational database design allows for integrated querying of multiple parameter datasets and ensures the database remains adaptable by removing any dependency on software. We also make use of current data sharing standards for the Microsoft® Windows® platform, employing data analysis software and GIS. Examination of this integrated dataset using advanced visualization techniques should improve understanding of the North Carolina coastal plain stratigraphy and help refine current chronostratigraphic estimates for the region. Furthermore, it builds on efforts to hone the accuracy and applicability of the AAR method as a chronological tool by incorporating numerous analyses over a thoroughly studied region such as the North Carolina coastal plain. Future endeavors such as web accessibility of the database and possible incorporation into a larger data repository is assisted with proper design early on. In addition, a user-friendly database interface has been developed for continued chromatographic data collection for an active AAR laboratory.Item Dynamic Steady State in Coastal Aquifers Is Driven by Multi-Scale Cyclical Processes, Controlled by Aquifer Storativity(Geophysical Research Letters, 2022-05-24) Paldor, Anner; Frederiks, Ryan S.; Michael, Holly A.Coastal aquifers supply freshwater to nearly half the global population, yet they are threatened by salinization. Salinities are typically estimated assuming steady-state, neglecting the effect of cyclical forcings on average salinity distributions. Here, numerical modeling is used to test this assumption. Multi-scale fluctuations in sea level (SL) are simulated, from tides to glacial cycles. Results show that high-frequency fluctuations alter average salinities compared with the steady-state distribution produced by average SL. Low-frequency forcing generates discrepancies between present-day salinities estimated with and without considering the cyclical forcing due to overshoot effects. This implies that salinities in coastal aquifers may be erroneously estimated when assuming steady-state conditions, since present distributions are likely part of a dynamic steady state that includes forcing on multiple timescales. Further, typically neglected aquifer storage characteristics can strongly control average salinity distributions. This has important implications for managing vulnerable coastal groundwater resources and for calibration of hydrogeological models. Key Points: - Average salinities in coastal aquifers are affected by low-frequency cyclical changes in sea level (SL) - High-frequency cyclical forcings generate episodic discrepancies in salinity when modeled with and without considering these processes - Under these multi-scale fluctuations in SL, dynamic steady states of coastal aquifers are affected by aquifer storage properties Plain Language Summary: Coastal communities rely heavily on groundwater for freshwater supply, and the primary risk for this vital resource is salinization. Multiple processes in the ocean-land interface control the salinity of coastal aquifers, and assessments of salinities typically neglect some of these processes. In this work, we show that some of the typically neglected processes may be responsible for large-scale, systematic discrepancies between actual and estimated salinities. This has important implications for the assessment of risks to coastal groundwater reservoirs and for the long-term management of these resources.