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

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

Assessment of Economic Heavy Minerals of the Virginia Inner Continental Shelf

The Virginia Division of Mineral Resources and the Virginia Institute of Marine Science jointly made three cruises over the Virginia continental shelf in April and July of 1985 to sample known heavy-mineral sites for minerals of potential economic and/or strategic value. In addition to sampling, side-scan sonar and sub-bottom profiling surveys were performed at a site off Smith Island. At the Smith Island site, as many as four acoustic horizons were detected within the upper 6 meters of sediment. The uppermost seismostratigraphic layer consists of fine and very fine sand and contains the higher concentrations of heavy minerals. There are also higher concentrations of heavy minerals on the flanks of topographic ridges. The average content of heavy minerals for all samples collected is 8 percent by weight

Virginia Beach offshore sediment study

This investigation was initiated from discussions among members of the Minerals Management Service-Virginia Task Force in an effort to locate a nearby and offshore source of beach-quality sand for the resort strip at Virginia Beach. Because of the increasing difficulty of relying upon land-based material, attention has been focused on investigating offshore sources. Previous work (Kimball and others, 1991) suggests an offshore deposit of beach-quality sands is located on a shoal between 3 and 8 km east of Sandbridge. Planned vibracoring on this shoal during the fall of 1993 should establish the viability of the sand occurrence. Although material from this site could . be used to nourish the resort strip, the dredging and transportation costs for an offshore resource would be decreased if another source could be located closer to the strip

Heavy Mineral Variability And Provenance Of The Virginia Inner Shelf And Lower Chesapeake Bay

The mineral composition of the 3- to 4-phi (0.125 to 0.063 mm) size fraction of 49 surficial grab samples,located north and south of the entrance to Chesapeake Bay and of 38 surficial samples, located in the bay mouth, was determined during this study. Although up to 17 minerals were identified, principal components analysis indicated that seven minerals accounted for 96 percent of the composition variance in the bay samples. By using Q-mode factor analysis, three mineral composition end-members (factors) were selected from the sample data and provided an adequate description of the spatial variation in heavy-mineral composition. The end members suggest possible mineral sources.https://scholarworks.wm.edu/vimsbooks/1105/thumbnail.jp

A Procedure for Assessing Heavy Mineral Resources Potential

Supplies of placer heavy minerals, such as ilmenite, rutile, zircon, and monazite, are anticipated to be in short supply by early in the next century. The depletion of conventional onshore deposits coupled with the declaration of the Exclusive Economic Zone in 1983 have provided the impetus to assess the resource potential of heavy-mineral concentrations in U.S. Continental Shelf sediments as future sources for these mineral commodities. Mineralogically imprecise assessments of placer resources result from analyses of concentrates derived from small volume samples because of the particle-sparsity effect. The overall low grade of heavy minerals in Atlantic Continental Shelf sediments require the analysis of mineral concentrates from large volumes of bulk sample. A set of procedures to extract and analyze heavy minerals from large-volume samples is presented.https://scholarworks.wm.edu/vimsbooks/1103/thumbnail.jp

Sandy Estuarine Fill Transported into the Mouth of Chesapeake Bay

The landward flux of sand into an estuary is a process that is seldom documented or quantified, yet is important to the sedimentary dynamics of a maturing estuary. Data from three recent studies converge to demonstrate the transport of sand into Chesapeake Bay from the adjacent shelf. A 100- year sediment budget, distributions of heavy minerals, and seismic-reflection data all point to the bay mouth as a gate through which a significant quantity of sand enters the estuarine system.https://scholarworks.wm.edu/vimsbooks/1140/thumbnail.jp

Submarine Sand Resources, Southeastern Virginia - Contributions from Year Nine and Year Ten of Virginia’s Continental Margins Program

Virginia’s Year-Nine and Year-Ten funds from the Continental Shelf Program were used to supplement other work funded by the Minerals Management Service in an ongoing Cooperative Agreement focused on the area offshore of southeastern Virginia. Year-Nine and Year-Ten funds facilitated interpretation of subbottom profiles and the analysis of sediment samples from cores and grabs. On Virginia’s sediment-starved continental shelf, deposits of material potentially suitable for use as beach nourishment or, perhaps, as construction aggregate occur in three stratigraphic settings, each with specific characteristics of morphology, grain-size gradients, likelihood of discovery, and physical ease of exploitation. All must be verified with a careful program of coring. Modern shoals generally are easier to identify, prove, and access than either filled channels or lenticular facies. Shoals usually are identifiable on nautical charts and characteristically have a definite lower boundary that can be seen in subbottom profiles. In most cases, the base of the shoal coincides with the level of the surrounding sea floor. Filled channels are readily identifiable on subbottom profiles but may have a narrow, sinuous form and steep lateral gradients in sediment properties. Buried lenticular facies of good-quality sand usually are found only fortuitously. As the lateral and often vertical gradients in geotechnical properties usually are low, the lenticular facies can be mined with a lesser concern for the consequences of violating the deposit’s limits than with the other two types of deposit. (more ....)https://scholarworks.wm.edu/vimsbooks/1122/thumbnail.jp

Heavy Mineral Concentrations In Sediments Of The Virginia Inner Continental Shelf

The Virginia Division of Mineral Resources and the Virginia Institute of Marine Science investigated the occurrence of heavy minerals in the offshore sediments of Virginia. We began the project because earlier reconnaissance studies reported high heavy-mineral concentrations from several samples collected off the Eastern Shore of Virginia. Our work confirms the previously reported mineral values and locates additional high concentrations up to 20 nautical miles offshore. Furthermore, we show that potentially economic mineral values are not restricted no surficial sediments, but also are found in the upper 15 to 20 feet of inner continental shelf sediments. Several core samples indicate that potential economic values of heavy minerals are clustered offshore of Hog Island, Smith Island, Virginia Beach, and False Cape. These areas are likely targets for resource assessment studies of heavy minerals and construction or beach nourishment sand. The high heavy-mineral concentrations suggest that further investigations are warranted.https://scholarworks.wm.edu/vimsbooks/1104/thumbnail.jp