The Virginia Chesapeake Bay: recent sedimentation and paleodrainage

• Main Author: Carron, Michael J.
• Format: Others
• Language: English
• Published: W&M ScholarWorks 1979
• Subjects: Geology; Oceanography
• Online Access: https://scholarworks.wm.edu/etd/1539616599; https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=2167&context=etd

A comparison of the bathymetric surveys of the 1850-series and 1950-series indicated an average sedimentation rate for the Virginia Chesapeake Bay of 0.55 m (1.81 ft) for the last century. A statistically significant relationship between the depth of water and the rate of sedimentation was found where high rates of sedimentation exist in extremely shallow water (0 to 2 m) and in intermediate depths (6 to 13 m), while low rates exist between 2 m and 6 m, and in some cases in water deeper than 13 m. The results of 900 km of continuous seismic reflection profiles taken in the Virginia and lower-Maryland Chesapeake Bay indicate that the ancestral Rappahannock, Piankatank, York, and James rivers were not tributary to the ancestral Susquehanna River during the Wisconsin Glaciation as was previously believed. The ancestral Rappahannock, Piankatank, and York rivers converge and flow out of the present bay area through a paleochannel located under Tail of the Horseshoe Shoal on the south side of the Bay entrance. These combined rivers probably converged with the ancestral James River somewhere on the present continental shelf. A paleochannel in the Mainstem of the Bay north of the Potomac River mouth has an apparent thalweg depth of -42 m (-138 ft), whereas a much deeper channel at -61 m (-200 ft) has been reported by Ryan (1953) in the upper bay reaches. This suggests that the Susquehanna did not flow in the Mainstem region during the Wisconsinan Glaciation and most probably flowed in the Tangier Sound region. No evidence was found to support theories concerning the existence of significant Post-Tertiary crustal movement in the lower Bay region.