Interpretation of the Surficial Geology in the Pulley Ridge Study Area

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What does this data set describe?

Interpretation of the Surficial Geology in the Pulley Ridge Study Area
Pulley Ridge is a series of drowned barrier islands that extends almost 200 km in 60-100 m water depths. This drowned ridge is located on the Florida Platform in the southeastern Gulf of Mexico about 250 km west of Cape Sable, Florida. This barrier island chain formed during the initial stage of the Holocene marine transgression. These islands were then submerged and left abandoned near the outer edge of the Florida Platform. The southern portion of Pulley Ridge hosts zooxanthellate scleractinian corals, green, red and brown macro algae, and a mix of deep and typically shallow-water tropical fishes. This reef community is in unusually deep water, and its extent and the controls on its distribution were unknown. To address these questions scientists from the U.S. Geological Survey Coastal and Marine Geology Program in cooperation with scientists from the University of South Florida Department of Marine Sciences have completed a detailed mapping of the southernmost 35 km of Pulley Ridge. The area was mapped using multibeam bathymetry, sidescan-sonar imagery, and high-resolution seismic-reflection profiling to define the geologic framework on which the reef is established. Submersible dives, remotely operated vehicle (ROV) transects, and transects of bottom photographs and video were collected to identify the corals and to map their distribution. This extensive suite of data has been compiled and preliminary analysis of the data suggests that the reefs are not tied to the ridge system, but instead are more broadly distributed. Whether reef distribution is controlled by oceanographic conditions or by subtle differences in the substrate that overlies the barrier island system is unclear, and are topics of continued research.
  1. How should this data set be cited?

    Twichell, David C. , 2005, Interpretation of the Surficial Geology in the Pulley Ridge Study Area:.

    Online Links:

    This is part of the following larger work.

    Cross, VeeAnn A. , Twichell, David C. , Halley, Robert B. , Ciembronowicz, Kate T. , Jarrett, Bret D. , Hammar-Klose, Erika S. , Hine, Al C. , Locker, Stan D. , and Naar, Dave F. , 2005, GIS Compilation of Data Collected from the Pulley Ridge Deep Coral Reef Region: Open-File Report 2005-1089, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Science Center, Woods Hole, MA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -83.768420
    East_Bounding_Coordinate: -83.599513
    North_Bounding_Coordinate: 24.996035
    South_Bounding_Coordinate: 24.665195

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Calendar_Date: 2004
    Currentness_Reference: publication date

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: vector digital data

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Vector data set. It contains the following vector data types (SDTS terminology):

      • G-polygon (41)

    2. What coordinate system is used to represent geographic features?

      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.000000. Longitudes are given to the nearest 0.000000. Latitude and longitude values are specified in Decimal degrees.

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.

  7. How does the data set describe geographic features?


    Internal feature number. (Source: ESRI)

    Sequential unique whole numbers that are automatically generated.

    Feature geometry. (Source: ESRI)

    Coordinates defining the features.

    Computer generated polygon ID number. (Source: Software.)


    Interpretation of the seafloor based on the sidescan-sonar mosaic. (Source: Scientist - David C. Twichell)

    character set

    The Interp attribute definitions are as follows:

    terraces: Alternating linear bands of high and low backscatter on the sidescan-sonar imagery. The high-backscatter stripes are interpreted to be reflections off rock surfaces while the low-backscatter stripes are either shadows cast by the terraces or areas where fine-grained sediment has covered parts of the terraces. The bathymetry shows that the terraces occur along the flanks of the narrow ridge that marks the crest of the ridge. Video observations show outcrops of hardgrounds in these areas.

    high-backscatter: The sidescan-sonar images were smoothed in PCI with a 7x7 average filter, and the areas with values mostly between 117 and 225 were mapped as areas of high backscatter. video observations indicate that these areas are a mix of exposed hardgrounds, carbonate rubble, and deep-water coral.

    broad lines: The sidescan sonar image shows subtle variations in backscatter intensity that coincide with low-relief ridges on the multibeam bathymetry.

    depression-large: Sub-circular depressions show on the multibeam bathymetry that have 30-200 m diameters and are less than 3 m deeper than the surrounding seafloor. Many of these depressions have low-backscatter floors on the sidescan-sonar imagery. Video observations indicate that the floors of these depressions are fine sand.

    mottled-mod: The sidescan-sonar image shows a mottled seafloor of moderate and low-backscatter patches that have dimensions of 50-200 m. The average backscatter values on the filtered image for these areas are mostly 110-120.

    mod-backscatter: More uniform in backscatter intensity than the mottled-moderate backscatter regions. These areas occur mostly around the edges of the ridge where the seafloor is smoother than it is on the ridge itself. Video observations from these areas show a sandy seafloor with some carbonate cobbles, but the cobbles are not as concentrated as they are on the ridge.

    mottled-low: Low backscatter areas that are interrupted by sub-circular moderate backscatter patches that are 20-100 m in diameter. The moderate backscatter patches commonly have a pit or mound near their centers. The background in these areas mostly has a DN value less than 100. The multibeam bathymetry shows that the seafloor in these areas is smooth, and video observations indicate that the seafloor is somewhat sandier than other parts of the study area.

    low-backscatter: Areas with a smooth seafloor with a low-backscatter (DN less than 105) appearance. the only part of the study area with this appearance is in the southernmost part of the area beyond the shelf on the uppermost slope.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    David C. Twichell
    U.S. Geological Survey
    384 Woods Hole Rd.
    Woods Hole, MA 02543-1598

    (508) 548-8700 x2266 (voice)
    (508) 457-2310 (FAX)

Why was the data set created?

Polygon shapefile indicating the interpretation of the sidescan-sonar mosaic.

How was the data set created?

  1. From what previous works were the data drawn?

  2. How were the data generated, processed, and modified?

    (process 1 of 1)
    Sidescan-sonar image mosaics were enhanced within PCI Geomatics software, using a linear stretch mapping the values between 80 and 140 across the entire 8-bit range (0-255). In addition, a 7x7 average filter was applied to smooth the images.

  3. What similar or related data should the user be aware of?

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

  2. How accurate are the geographic locations?

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

  5. How consistent are the relationships among the observations, including topology?

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: None.
The U.S. Geological Survey must be referenced as the originator of the dataset in any future products or research derived from these data.

  1. Who distributes the data set? (Distributor 1 of 1)

    David C. Twichell
    U.S. Geological Survey
    384 Woods Hole Rd.
    Woods Hole, MA 02543-1598

    (508) 548-8700 x2266 (voice)
    (508) 457-2310 (FAX)

  2. What's the catalog number I need to order this data set?

    Downloadable Data

  3. What legal disclaimers am I supposed to read?

    These data were prepared by an agency of the United States Government. Neither the United States government nor any agency thereof, nor any of their employees, make any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. Any views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Although all data published in this report have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and/or the functioning of the software. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of this data, software, or related materials.

  4. How can I download or order the data?

Who wrote the metadata?

Last modified: 12-May-2005
Metadata author:
VeeAnn A. Cross
U.S. Geological Survey
Marine Geologist
384 Woods Hole Rd.
Woods Hole, MA 02543-1598

(508) 548-8700 x2251 (voice)
(508) 457-2310 (FAX)

Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:

Generated by mp version 2.8.6 on Fri May 13 13:15:12 2005