Physical Sciences and Mathematics Commons^™

Postimpact Deformation Associated With The Late Eocene Chesapeake Bay Impact Structure In Southeastern Virginia, Gerald H. Johnson, Sarah E. Kruse, Allison W. Vaughn, John K. Lucey, C. Hobbs, David S. Powars

VIMS Articles

Upper Cenozoic strata covering the Chesapeake Bay impact structure in southeastern Virginia record intermittent differential movement around its buried rim. Miocene strata in a graben detected by seismic surveys on the York River exhibit variable thickness and are deformed above the crater rim. Fan-like interformational and intraformational angular unconformities within Pliocene–Pleistocene strata, which strike parallel to the crater rim and dip2°–3° away from the crater center, indicate that deformation and deposition were synchronous.Concentric, large-scale crossbedded, bioclastic sand bodies of Pliocene age within ~20 km of the buried crater rim formed on offshore shoals, presumably as subsiding listric slump blocks rotated …

Transport Of Particles Across Continental Shelves, Ca Nittrouer, Ld Wright

VIMS Articles

Transport of particulate material across continental shelves is well demonstrated by the distributions on the seabed and in the water column of geological, chemical, or biological components, whose sources are found farther landward or farther seaward. This paper addresses passive (incapable of swimming) particles and their transport across (not necessarily off) continental shelves during high stands of sea level. Among the general factors that influence across-shelf transport are shelf geometry, latitudinal constraints, and the timescale of interest. Research studies have investigated the physical mechanisms of transport and have made quantitative estimates of mass flux across continental shelves. Important mechanisms include …

Ancient Channels Of The Susquehanna River Beneath Chesapeake Bay And The Delmarva Peninsula, Steven M. Colman, Jeffrey P. Halka, C. Hobbs, Robert B. Mixon, David S. Foster

VIMS Articles

Three generations of the ancestral Susquehanna River system have been mapped beneath Chesapeake Bay and the southern Delmarva Peninsula. Closely spaced seismic reflection profiles in the bay and boreholes in the bay and on the southern Delmarva Peninsula allow detailed reconstruction of each paleochannel system. The channel systems were formed during glacial low sea-level stands, and each contains a channel-fill sequence that records the subsequent transgression. The trunk channels of each system are 2 to 4 km wide and are incised 30 to SO m into underlying strata; they have irregular longitudinal profiles and very low gradients within the Chesapeake …

Late Pleistocene Barrier-Island Sequence Along The Southern Delmarva Peninsula: Implications For Middle Wisconsin Sea Levels, Kenneth Finkelstein, Michael S. Kearney

VIMS Articles

Evidence for a middle Wisconsin sea-level high at or above modern limits along the east coast of the United States has long been controversial. Most reports have been dismissed as poorly dated or lacking unequivocal documentation of a marine transgression. We describe here a 14C-dated, middle Wisconsin transgressive sequence with an extant subaerial barrier facies along the southern Delmarva Peninsula. This sequence indicates that sea levels were near their present position between ca. 23 and 34 ka; it may correlate with other inferred similar-age littoral deposits of the area, and it suggests that the evidence for glacioeustatic fluctuations during the …

Consequences Of Sediment Flux: Escape Or Entrapment?, Maynard M. Nichols

VIMS Articles

Estuaries exhibit a full range of flux that extends from escape of sediment into the ocean to complete entrapment and storage within the system. The trapping efficiency of U.S. East Coast estuaries is compared with respect to long-term infilling and present- day flushing velocity , volumetric capacity , and circulatory mixing. It was found that entrapment prevails in many northern estuaries as a consequence of high volumetric capacity , low flushing velocity , and the nearly closed circulation. In many estuaries, channel deepening has reversed the " normal" trend of long-term infilling. Although dredging enhances circulatory entrapment, large-scale ocean dumping …

Optimized Measurements Of Discharge And Suspended Sediment Transport In A Salt Marsh Drainage System, John D. Boon

VIMS Articles

Detailed measurements of current speed and suspended sedlment concentration distributions in a channel cross-section of a tidal marsh creek were analyzed. Subsequent sampiing Intervals In time and space were selected to provide acceptable estimates of flood and ebb transport of water and suspended sediment post the cross sectlon. Data from eight 13-hour measurement runs taken at various times of the year seem to favor a net ebb resldual of suspended sedlment transport for the year In question.

A number of environmental factors appear to Influence suspended sediment trons· port in marsh channels.Residual transport of sediment In these systems is, however, …

Possible Late Pleistocene Uplift, Chesapeake Bay Entrance, W. Harrison, Rj Malloy, Ga Rusnak, J Terasmae

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Paleontological and lithological studies of engineering borings and boring logs subaerial erosion surface of Pliocene (?)-Pleistocene age cuts across clastic sediments of pre-Yorktownian Miocene age in the subsurface and subbottom of the lower Chesapeake Bay area. When the bore-hole data are coupled with the results of subbottom echo profiling and piledriving records, it is possible to construct accurate cross sections of the buried Miocene-Pleistocene contact. The cross sections show "lows" in the erosion surface that may be correlated with the buried channels of the Pleistocene Elizabeth, James, York, and Susquehanna river valleys. Probable channel depths below mean low water at …

Sea-Level And Crustal Movements Along The New England-Acadian Shore, 4,500-3,000 B.P, W. Harrison, C. J. Lyon

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Remains of three drowned forests have been investigated at Odiorne Point, New Hampshire, and Fort Lawrence and Grand Pre, west-central Nova Scotia. Carbon-14 ages and altitudes below mean tide levels were determined for four in-place stumps of white pine at each locality. Assuming that each dated stump was killed by rising salt water, and that its C14 age represented its true age at death, it was possible to construct curves showing the sequence of submergence and emergence at each site.

A continuous transgression of the sea, approximating 0.31 foot per century, is indicated for the period 4,500-3,200 B.P. This rate …