Shipboard magnetic field "noise" reveals shallow heavy mineral sediment concentrations in Chesapeake Bay

Marine Geology
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Abstract

Shipboard magnetic field data collected over Chesapeake Bay exhibit low-amplitude, short-wavelength anomalies that most likely indicate shallow concentrations of heavy mineral sediments. Piston core layers and black sand beach samples exhibit enhanced magnetic susceptibilities and carry remanent magnetization, with mineralogical analyses indicating ilmenite and trace magnetite and/or maghemite and hematite. The anomalies are subtle and would be filtered as noise using traditional approaches, but can instead be highlighted using spectral methods, thus providing nearly continuous coverage along survey tracks. The distribution of the anomalies provides constraints on relevant sorting mechanisms. Comparisons to sonar data and previous grab samples show that two of three areas surveyed exhibit short-wavelength anomalies that are clustered over sand-covered areas, suggesting initial sorting through settling mechanisms. This is supported by a correlation between core magnetic susceptibility and grain size. Near the Choptank River, where sediment resuspension is wave-dominated, anomalies show a sharp decrease with seafloor depth that cannot be explained by signal attenuation alone. In Pocomoke Sound, where both tidal currents and wave-action impact sediment resuspension, anomalies show a more gradual decrease with depth. Near the mouth of the bay, where there is a higher influx of sediments from the continental shelf, short-wavelength anomalies are isolated and do not appear to represent heavy mineral sand concentrations. These combined observations suggest the importance of further sorting by erosional processes in certain parts of the bay. Additionally, comparisons of these data to cores sampling pre-Holocene sediments suggest that the sorting of heavy minerals in higher energy, shallow water environments provides a mechanism for correlations between core magnetic susceptibility and sea-level changes.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Shipboard magnetic field "noise" reveals shallow heavy mineral sediment concentrations in Chesapeake Bay
Series title Marine Geology
DOI 10.1016/j.margeo.2012.02.006
Volume 303-306
Year Published 2012
Language English
Publisher Elsevier Scientific
Publisher location Amsterdam
Description 16 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Marine Geology
First page 26
Last page 41
Country United States
State Maryl;Virginia
Other Geospatial Chesapeake Bay