Stratigraphy and heavy mineral analysis in the lower Chesapeake Bay, Virginia

• Main Author: Berquist, C. R., Jr
• Format: Others
• Language: English
• Published: W&M ScholarWorks 1986
• Subjects: Paleontology
• Online Access: https://scholarworks.wm.edu/etd/1539616565; https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=2133&context=etd

Spatially continuous patterns of heavy mineral distributions in three dimensions characterized the sandy Holocene sediments of the lower Chesapeake Bay. A pilot study using Q-mode factor analysis on data from an earlier study determined mineral assemblages and mineral composition gradients; the gradients suggested that surficial sediments entered the Bay from offshore and from older deposits to the west. Principal components analysis of the same data indicated that the abundances of only 5 out of 21 minerals were adequate to explain most of the mineral variance. The mineralogy of 87 samples from cores defining two geologic cross-sections was added to the pilot study data and formed a new data set of 173 samples and 5 minerals. Q-mode factor analysis gave similar end-member compositions and mineral gradients as compared to the pilot study. Mineral gradients in the cross-sections show offshore sediment rich in amphibole, garnet, and pyroxene has entered the Bay mouth and presently overlies landward-derived sediment rich in zircon and epidote. The gradients depict tube- and tongue-shaped pathways located above paleodrainages. Surficial gradients support the notion of mutually evasive ebb and flood channels in the Bay entrance. Most of the Holocene sediment in the lower Bay appears to have originated from outside the Bay mouth, to include littoral drift from the north. The techniques used in this study may be useful in an attempt to subdivide a massive sandy lithosome by recognizing distinct stratigraphic units of different age or origin. A magnetohydrostatic mineral separator was constructed and tested.