The Offshore Sand Resources Study
|contact: Stephen Van Ryswick (firstname.lastname@example.org)|
Our third objective in this study was to estimate the quantity and quality of sand in the shoals we identified as potential sand sources. To achieve this objective, four tasks were undertaken.
- construct a three-dimensional model of the shoals
- collect and analyze sediment samples from the shoals
- estimate the volume of sand available in each shoal
- map the sand resources
The three-dimensional shoal model consists of a bathymetric surface, which represents the present day ocean floor, and several underlying surfaces that define the base of the shoals and other stratigraphic structures. We constructed the bathymetric surface from National Ocean Service data. A bathymetric map was prepared from this data, which served both to locate the shoals and later to define shoal volumes. From the bathymetric model, we defined three shoal fields. Within these fields, 19 shoals were selected for seismic profiling surveys. Seismic profiles were used to determine the internal structure of the shoals and the geometry of underlying structures. Seismics also present clues to which sediment types might exist on and in the shoals. Sediment samples can be correlated to seismic data for stratigraphic analysis. We have at our disposal more than 1,500 km of seismic data taken from 1985 to 1995, during MMS and Army Corps projects. Seismic data were digitized and combined with the bathymetric data to construct the three-dimensional model of the shoals.
Based on seismic data, we selected eight shoals for coring. A total of 56 cores was taken from these shoals. We also have more than 200 archival cores with more than 3,000 sediment samples from the same MMS and Army Corps projects. Data from core samples were used to define shoal stratigraphy and determine grain size parameters. The following parameters were measured:
- percent sand/gravel/mud
- mean grain diameter and sorting (standard deviation) of the sand fraction
- Folk and Ward(1957), and Shepard(1954) sediment classifications
- vertical variations in these parameters throughout the core