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N. T. DeWitt

Publications and source records attributed to N. T. DeWitt.

4 recordsLinked to original sources
USGS2011

Geophysical data from offshore of the Gulf Islands National Seashore, Cat Island to Western Horn Island, Mississippi

This report contains the geophysical and geospatial data that were collected along the western offshore side of the Gulf Islands of Mississippi on the research vessel Tommy Munro during two cruises in 2010. Geophysical data were collected by the U.S. Geological Survey in Woods Hole, Massachusetts, and St. Petersburg, Forida, in cooperation with the U.S. Army Corps of Engineers Mobile District. Bathymetric-sonar, sidescan-sonar, and Chirp seismic-reflection data were acquired with the following equipment, respectively: Systems Engineering and Assessment, Ltd., SwathPlus interferometric sonars; Klein 3000 and 3900 dual-frequency sidescan sonars; and an EdgeTech 512i Chirp sub-bottom profiling system. The long-term goals of this mapping effort are to produce high-quality, high-resolution geologic maps and interpretations that can be utilized to identify sand resources within the region, to better understand the Holocene evolution, and to anticipate future changes in this coastal system. Processed geospatial data files and the geophysical data provided in this report help attain these goals.

Mississippi↗
USGS2003

Patterns and controls of surface sediment distribution: West-central Florida inner shelf

The west-central Florida inner shelf represents a transition between the quartz-dominated barrier-island system and the carbonate-dominated mid-outer shelf. Surface sediments exhibit a complex distribution pattern that can be attributed to multiple sediment sources and the ineffectiveness of physical processes for large-scale sediment redistribution. The west Florida shelf is the submerged extension of the Florida carbonate platform, consisting of a limestone karst surface veneered with a thin unconsolidated sediment cover. A total of 498 surface sediment samples were collected on the inner shelf and analyzed for texture and composition. Results show that sediment consists of a combination of fine quartz sand and coarse, biogenic carbonate sand and gravel, with variable but subordinate amounts of black, phosphorite-rich sand. The carbonate component consists primarily of molluskan fragments. The distribution is patchy and discontinuous with no discernible pattern, and the transition between sediment types is generally abrupt. Quartz-rich sediment dominates the inner 15 km north of the entrance into Tampa Bay, but south of the Bay is common only along the inner 3 km. Elsewhere, carbonate-rich sediment is the predominate sediment type, except where there is little sediment cover, in which cases black, phosphorite-rich sand dominates. Sediment sources are likely within, or around the periphery of the basin. Fine quartz sand is likely reworked from coastal units deposited during Pleistocene sea-level high stands. Carbonate sand and gravel is produced by marine organisms within the depositional basin. The black, phosphorite-rich sand likely originates from the bioerosion and reworking of the underlying strata that irregularly crop out within the study area. The distribution pattern contains elements of both storm- and tide-dominated siliciclastic shelves, but it is dictated primarily by the sediment source, similar to some carbonate systems. Other systems with similar sediment attributes include cool-water carbonate, sediment-starved, and mixed carbonate/siliciclastic systems. This study suggests a possible genetic link among the three systems. ?? 2003 Elsevier B.V. All rights reserved.

Marine Geology↗
USGS2001

Overview of SAX99: Environmental considerations

A 1-km2 area located 2 km off the Florida Pan-handle (30??22.6???N; 86??38.7???W) was selected as the site to conduct high-frequency acoustic seafloor penetration, sediment propagation, and bottom scattering experiments [1]. Side scan, multibeam, and normal incidence chirp acoustic surveys as well as subsequent video surveys, diver observations, and vibra coring, indicate a uniform distribution of surficial and subbottom seafloor characteristics within the area. The site, in 18-19 m of water, is characterized by 1-2-m thick fine-to-medium clean sand and meets the logistic and scientific requirements specified for the acoustic experiments. This paper provides a preliminary summary of the meteorological, oceanographic, and seafloor conditions found during the experiments and describes the important physical and biological process that control the spatial distribution and temporal changes in these characteristics.

IEEE Journal of Oceanic Engineering↗