A new map on the Portal shows the approximate routes of infilled paleochannels, which are rivers that once flowed over the shelf beneath the Chesapeake Bay and Delmarva Peninsula and carved out deep shelf-edge canyons, such as Norfolk Canyon. This Paleochannels (Delmarva Area) layer can be found by clicking on the “Seabeds and Sediments” dropdown in the Habitat theme.
These paleochannels were shaped by Pleistocene rivers, primarily the ancestral Susquehanna system, when the sea level was lower on the Mid-Atlantic continental shelf during glacial periods. When the glaciers retreated, sea levels rose and the channels/valleys transformed into rivers, then progressively to an open-bay estuary, filling the channels over time with marine and estuarine sediments.
The estimated age of the channels shown in the map are as follows:
- Cape Charles: approximately 18,000-20,000 years ago
- Eastville: Late Pleistocene, approximately 150,000 years ago
- Exmore and Belle Haven: Middle Pleistocene, approximately 450,000 years ago
- Beaverdam: Early Pleistocene, approximately 550-650,000 years ago
- Persimmons Point and Ocean City: Early Pleistocene, approximately 1 million years ago
These paleochannels data were produced by Brothers et al. and appear in the following paper (Figure 9):
Brothers, L.L., Foster, D.S., Pendleton, E.A., Baldwin, W.E., 2020, Seismic Stratigraphic Framework of the Continental Shelf Offshore Delmarva, U.S.A.: Implications for Mid-Atlantic Bight Evolution since the Pliocene: Marine Geology, v. 428. doi.org/10.1016/j.margeo.2020.106287
Additional Information
Additional information was sourced from:
Colman, Steven M.; Halka, Jeffrey P.; Hobbs, C.; Mixon, Robert B.; and Foster, David S., Ancient channels of the Susquehanna River beneath Chesapeake Bay and the Delmarva Peninsula (1990). Geological Society of America Bulletin, 102, 1268-1279. doi.org/10.1130/0016-7606(1990)102%3C1268:ACOTSR%3E2.3.CO;2
Foster, D.S., Brothers, L.L., Baldwin, W.E., and Pendleton, E.A., 2023, Geospatial data layers of shallow geology from the inner continental shelf of the Delmarva Peninsula, including Maryland and Virginia state waters: U.S. Geological Survey data release, doi.org/10.5066/P9GQY0ZN
The age estimations for the paleochannels were published in:
Wehmiller, J. F., Brothers, L. L., Ramsey, K. W., Foster, D. S., Mattheus, C. R., Hein, C. J., & Shawler, J. L. (2021). Molluscan aminostratigraphy of the US Mid-Atlantic Quaternary coastal system: Implications for onshore-offshore correlation, paleochannel and barrier island evolution, and local late Quaternary sea-level history. Quaternary Geochronology, 66, 101177. doi.org/10.1016/j.quageo.2021.101177