The Yorktown Formation: Improved Stratigraphy, Chronology, and Paleoclimate Interpretations from the U.S. Mid-Atlantic Coastal Plain

The Yorktown Formation records paleoclimate conditions along the mid-Atlantic Coastal Plain during the mid-Piacenzian Warm Period (3.264 to 3.025 Ma), a climate interval of the Pliocene in some ways analogous to near future climate projections. To gain insight into potential near future changes, we investigated Yorktown Formation outcrops and cores in southeastern Virginia, refining the stratigraphic framework. We analyzed 485 samples for alkenone-based sea surface temperature (SST) and productivity estimates from the Holland and Dory cores, an outcrop at Morgarts Beach, Virginia, and the lectostratotype of the Yorktown Formation at Rushmere, Virginia, and analyzed planktonic foraminferal assemblage data from the type section. Using the structure of the SST record, we improved the chronology of the Yorktown Formation by establishing the maximum age ranges of the Rushmere (3.3–3.2 Ma) and Morgarts Beach (3.2–3.15 Ma) Members. SST values for these members average ~26 °C, corroborating existing sclerochronological data. Increasing planktonic foraminifer abundance, productivity, and species diversity parallel increasing SST over the MIS M2/M1 transition. These records constitute the greatest temporal concentration of paleoecological estimates within the Yorktown Formation, aiding our understanding of western North Atlantic temperature patterns, seasonality and ocean circulation during this interval. We provide a chronologic framework for future studies analyzing ecological responses to profound climate change.

Biogeographic, stratigraphic, and environmental distribution of Basilosaurus (Mammalia, Cetacea) in North America with a review of the late Eocene shoreline in the southeastern coastal plain

A new specimen of Basilosaurus cetoides was discovered on the banks of the Flint River in Albany, Georgia, USA, in 2010. This fossil, which was the most complete specimen of the species from Georgia to date, consisted of five nearly complete and two partial post-thoracic vertebrae, tentatively identified as S4 through Ca6. During excavation, however, the site was looted and most of the specimen was lost to science. Nonetheless, we use this discovery as an opportunity to update the current state of knowledge on the stratigraphic, biogeographic, and environmental distribution of Basilosaurus in North America, as well as the position of the late Eocene shoreline in the southeastern United States. The results show that Basilosaurus was most abundant across the southeastern coastal plain during the early to middle Priabonian, coincident with the late Eocene maximum marine transgression. The decline in Basilosaurus localities is associated with the retreating shoreline of the terminal Eocene. The majority of Basilosaurus localities fall well south of the position of the late Eocene shoreline hypothesized in this study, suggesting the genus favored middle to outer neritic zones of the epicontinental sea. The comparatively low number of Priabonian specimens in the Atlantic Coastal Plain versus the Gulf Coastal Plain, then, suggests the presence of shallow zones in the Atlantic Coastal Plain that may have limited the distribution of Basilosaurus across the region. The hypothesized shoreline of this study ultimately differs from earlier reconstructions by extending the Mississippi embayment at the Bartonian/Priabonian boundary farther north than previously noted.

Landscape and climatic features drive genetic differentiation processes in a South American coastal plant

Background Historical and ecological processes shape patterns of genetic diversity in plant species. Colonization to new environments and geographical landscape features determine, amongst other factors, genetic diversity within- and differentiation between-populations. We analyse the genetic diversity and population structure of Calibrachoa heterophylla to infer the influence of abiotic landscape features on the level of gene flow in this coastal species of the South Atlantic Coastal Plain. Results The C. heterophylla populations located on early-deposited coastal plain regions show higher genetic diversity than those closer to the sea. The genetic differentiation follows a pattern of isolation-by-distance. Landscape features, such as water bodies and wind corridors, and geographical distances equally explain the observed genetic differentiation, whereas the precipitation seasonality exhibits a strong signal for isolation-by-environment in marginal populations. The estimated levels of gene flow suggest that marginal populations had restricted immigration rates enhancing differentiation. Conclusions Topographical features related to coastal plain deposition history influence population differentiation in C. heterophylla. Gene flow is mainly restricted to nearby populations and facilitated by wind fields, albeit without any apparent influence of large water bodies. Furthermore, differential rainfall regimes in marginal populations seem to promote genetic differentiation.

Using Convolutional Neural Networks for Detection and Morphometric Analysis of Carolina Bays from Publicly Available Digital Elevation Models

Carolina Bays are oriented and sandy-rimmed depressions that are ubiquitous throughout the Atlantic Coastal Plain (ACP). Their origin has been a highly debated topic since the 1800s and remains unsolved. Past population estimates of Carolina Bays have varied vastly, ranging between as few as 10,000 to as many as 500,000. With such a large uncertainty around the actual population size, mapping these enigmatic features is a problem that requires an automated detection scheme. Using publicly available LiDAR-derived digital elevation models (DEMs) of the ACP as training images, various types of convolutional neural networks (CNNs) were trained to detect Carolina bays. The detection results were assessed for accuracy and scalability, as well as analyzed for various morphologic, land-use and land cover, and hydrologic characteristics. Overall, the detector found over 23,000 Carolina Bays from southern New Jersey to northern Florida, with highest densities along interfluves. Carolina Bays in Delmarva were found to be smaller and shallower than Bays in the southeastern ACP. At least a third of Carolina Bays have been converted to agricultural lands and almost half of all Carolina Bays are forested. Few Carolina Bays are classified as open water basins, yet almost all of the detected Bays were within 2 km of a water body. In addition, field investigations based upon detection results were performed to describe the sedimentology of Carolina Bays. Sedimentological investigations showed that Bays typically have 1.5 m to 2.5 m thick sand rims that show a gradient in texture, with coarser sand at the bottom and finer sand and silt towards the top. Their basins were found to be 0.5 m to 2 m thick and showed a mix of clayey, silty, and sandy deposits. Last, the results compiled during this study were compared to similar depressional features (i.e., playa-lunette systems) to pinpoint any similarities in origin processes. Altogether, this study shows that CNNs are valuable tools for automated geomorphic feature detection and can lead to new insights when coupled with various forms of remotely sensed and field-based datasets.

Oxon Run Parkway: Paleontological resource inventory; supplement to the National Capital Parks-East paleontological resource inventory

Oxon Run Parkway (OXRN) is a 51-hectare (126-acre) natural area within Washington, D.C. administered by the National Park Service under National Capital Parks East (NACE). The original plan called for a road, slated to follow Oxon Run stream, but this never came to fruition; despite this, the moniker stuck. The majority of the original Oxon Run Parkway is managed by the District of Columbia. The section of Oxon Run Parkway under NPS jurisdiction contains wetlands and forests, as well as the only McAteean magnolia bogs still remaining in the District. The lower Cretaceous Potomac Group, known as one of the few dinosaur-bearing rock units on the east coast of North America, crops out within Oxon Run. One of the most prevalent fossil-bearing resources are the siderite, or “bog iron” sandstone slabs that sometimes preserve the footprints or trackways of various vertebrates, including dinosaurs. Such trackways have been reported from Potomac Group outcrops throughout the Atlantic Coastal Plain of Maryland and Virginia. In 2019, National Capital Parks-East took possession of such a track, referred to a dinosaur, collected by paleontologist Dr. Peter Kranz. This report was compiled after a paleontological survey of Oxon Run Parkway and is intended as a supplement to the National Capital Parks East Paleontological Resource Inventory (Nelson et al. 2019). This report contains information on the history of Oxon Run Parkway and its geology, as well as discussion of the fossil track.

Clear as mud: Clinoform progradation and expanded records of the Paleocene-Eocene Thermal Maximum

The mid-Atlantic coastal plain (eastern United States) preserves high-resolution records of the Paleocene-Eocene Thermal Maximum (PETM) and attendant carbon isotope excursion (CIE), though preservation is highly variable from site to site. Here, we use a dip transect of expanded (as much as 15 m thick) PETM sections from the New Jersey coastal plain to build a cross-shelf PETM depositional model that explains the variability of these records. We invoke enhanced delivery of fine-grained sediments, due to the rapid environmental changes associated with this hyperthermal event, to explain relatively thick PETM deposits. We utilize δ13Cbulk, percent CaCO3, and percent coarse fraction (>63 μm) data, supported by biostratigraphic records, to correlate sites along a paleoslope dip transect. Updip cores from Medford, New Jersey, preserve expanded sections of the initiation of the PETM and the earliest portion of the CIE. Medial sites (Wilson Lake, Millville) preserve an expanded CIE body, and downdip Bass River records the CIE recovery. We interpret this pattern to reflect the progradation of clinoform foresets across the paleoshelf via fluid mud, similar to modern high-sediment-supply rivers and adjacent muddy shelves (e.g., the Amazon, Mahakam [Indonesia], and Ayeyarwady [Myanmar] Rivers). Our subaqueous-clinoform delta model explains the pattern of the CIE records and provides a framework for future PETM studies in the region.

Redefining Waters of the US: A Case Study from the Edge of the Okefenokee Swamp

Defining the upslope extent of Federal Clean Water Act jurisdiction over wetlands and streams has been contentious since the passage of the Act but has large effects on the type, number, and area of wetlands that are protected by legislation. Federal guidance in the US has changed and evolved in response to scientific knowledge, Supreme Court decisions, and policy goals of Presidential Administrations. In 2020, the Trump administration replaced the Obama administration Clean Water Rule with the Navigable Waters Protection Rule with the goal of reducing jurisdiction over so-called isolated depressional wetlands and small streams. Here we use a case study of a titanium sands mining proposal on Trail Ridge southeast of Okefenokee Swamp to illustrate the large reduction in wetland and stream protection engendered by this policy change. Under the Navigable Waters Protection Rule, all seven wetlands within the 232 ha mining area, totaling 131 ha or 56% of the project area, were deemed non-jurisdictional and thus the project required no federal review or permitting. Under an earlier mining application under the Clean Water Rule, all of these wetlands were declared jurisdictional. Trail Ridge is located on the Atlantic Coastal Plain, an ecological province rich in depressional wetlands and ill-defined surface drainages. This case study shows that in such environments, the Navigable Water Protection Rule will allow destruction of large numbers and areas of ecologically significant wetlands.

Fundamental Resonant Frequencies Derived from Shallow Sediment Properties for the Charleston, South Carolina Area

Large historic earthquakes, low velocity near surface sediments, a poor understanding of earthquake sources, and a growing population base for the Charleston, South Carolina area suggest robust site response and active fault maps are needed. A Boise State University team acquired 14 km of new surface-based seismic data to obtain surface wave dispersion curves and reflection images for the southern isoseismal region of the 1886 earthquake. From these data, I generate shear wave velocity (Vs)-depth profiles through a grid search approach. I integrate my results with other published data to develop a soil thickness and high frequency fundamental resonance maps for the Charleston region. From the reflection data, I identify faults that may be Quaternary active, as they are co-located with surface deformation features observed in 1886. The Boise State University rapid seismic land streamer acquisition system produces robust dispersion and reflection data that may be applicable for other areas within the Atlantic Coastal Plain, where shallow high impedance boundaries and faults that offset Tertiary strata are common.

Dinosaurs from the Santonian–Campanian Atlantic coastline substantiate phylogenetic signatures of vicariance in Cretaceous North America

During the Cretaceous, diversifications and turnovers affected terrestrial vertebrates experiencing the effects of global geographical change. However, the poor fossil record from the early Late Cretaceous has concealed how dinosaurs and other terrestrial vertebrates responded to these events. I describe two dinosaurs from the Santonian to Early Campanian of the obscure North American paleolandmass Appalachia. A revised look at a large, potentially novel theropod shows that it likely belongs to a new clade of tyrannosauroids solely from Appalachia. Another partial skeleton belongs to an early member of the Hadrosauridae, a highly successful clade of herbivorous dinosaurs. This skeleton is associated with the first small juvenile dinosaur specimens from the Atlantic Coastal Plain. The tyrannosauroid and hadrosaurid substantiate one of the only Late Santonian dinosaur faunas and help pinpoint the timing of important anatomical innovations in two widespread dinosaur lineages. The phylogenetic positions of the tyrannosauroid and hadrosaurid show Santonian Appalachian dinosaur faunas are comparable to coeval Eurasian ones, and the presence of clades formed only by Appalachian dinosaur taxa establishes a degree of endemism in Appalachian dinosaur assemblages attributable to episodes of vicariance.