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Open-File Report 2014–1018

Pubs Warehouse

### Sea-Floor Geology in Northwestern Block Island Sound, Rhode Island 

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## Sediments

| Title PageList of FiguresConversion FactorsAbstractIntroductionSettingMethodsBathymetrySidescan Sonar**Sediments**Bottom PhotographyGIS Data CatalogSummaryAcknowledgmentsReferencesContactsIndexClick on figures for larger images**Figure 19.**Map showing locations of sediment samples obtained during  U.S. Geological Survey cruise 2012-002-FA in the H12296 study area in northern  Block Island Sound. **Figure 20.**Photographs contrasting the sea floor at a station with  modern marine sediment and a station within a scour depression.Sediment Distribution
Just over half of the stations in the study area are sand,  and gravel or gravelly sediment was observed at the remaining stations (fig. 19).  No silty sand or finer grained muddy sediments were encountered; all samples  contained less than 4 percent mud. Sand is found in areas where modern marine  sediments cover the sea floor. Gravel and gravelly sediment are found in scour  depressions and areas where boulders are present. Scour depressions have  coarser mean-sediment sizes, that range from -2.06 to 1.30 phi and average  -0.04 phi, than the surrounding modern marine sediments, that range from 1.25  to 3.29 phi and average 2.36 phi (fig. 20). Scour depressions tend to have  poorly and very poorly sorted sediment, whereas most of the modern marine  sediment is moderately well sorted. Sample stations were occupied along several  transects that were oriented perpendicular to the shore, and efforts were made  to obtain samples from transects through large scour depressions and modern  marine sediments. We were able to obtain samples from only one transect in a  scour depression, which indicated sediment coarsening in an offshore direction with  a mean grain size of 1.30 phi at station NBIS60 close to shore, and a mean grain  size of 0.03 phi at NBIS57 further offshore. The samples from transects  crossing modern marine sediments did not show a trend of either fining or  coarsening offshore, although the finest sediment was often found in the middle  of the transect with coarser sediment close to shore, and the coarsest sediment  offshore, such as in stations NBIS49, NBIS48, and NBIS47. 
Sediment Data
The sediment grain-size dataset provided in this report  contains information on the collection, description, and texture of sediments  at the 43 stations in the study area. Sediments were sampled at only 27 of the  stations owing to either a coarse-grained sea floor or rough sea state that  prevented a sample from being acquired. Stations where samples could not be  obtained were visually classified based on video and still photography from the  station. These stations have no-data values (-9999) in the textural and statistical  sections of the sediment dataset. The basic structure of the dataset is laid  out in a matrix, where rows represent individual samples and columns (fields)  contain sample- and station-specific information. This matrix consists of 42  fields that are defined in the Data Dictionary below. 

 A .zip file in the Geographic Information System Data Catalog section contains  the sediment data in three formats (a shapefile, a Microsoft Excel spreadsheet,  and a comma-delimited ASCII text file) along with metadata. 
Data Dictionary 
An integral  part of any database is the dictionary that explains the structure and content.  It contains a list of the fields and definitions of parameters measured. Data  utilization is facilitated by reference to this compilation because it defines  abbreviations and lists field names. 

 LABNO - Unique  sample identifier assigned in the laboratory 

 STATIONID -  Sample name or number assigned in the field 

 PROJECT -  Project under which samples were taken or data were generated 

 CRUISEID - Name  or number of cruise on which the sample was collected or station was occupied 

 PRINCIPAL -  Name of the principal investigator 

 LATITUDE -  Latitude in decimal degrees (north latitudes are positive values) 

 LONGITUDE -  Longitude in decimal degrees (west longitudes are negative values) 

 DEPTH_M - Depth  of water overlying sediment at the time of sampling, measured by a hull-mounted  fathometer, corrected for draft, but not corrected for tides, in meters 

 T_DEPTH - Top  depth of the sample below the sediment-water interface, in centimeters 

 B_DEPTH -  Bottom depth of the sample below the sediment-water interface, in centimeters 

 DEVICE - Device  used to collect the sample 

 MONTH - Number  of calendar month during which the sample was collected 

 DAY - Calendar  day on which the sample was collected 

 YEAR - Calendar  year during which the sample was collected 

 WEIGHT - Dry  weight of sample, in grams 

 ZGRAVEL -  Gravel content in percent of dry weight of the sample (particles with nominal  diameters greater than 2 mm; -1 phi and larger) 

 ZSAND - Sand  content in percent of dry weight of the sample (particles with nominal  diameters less than 2 mm but greater than or equal to 0.0625 mm; 0 through 4  phi, inclusive) 

 ZSILT - Silt  content in percent of dry weight of the sample (particles with nominal  diameters less than 0.0625 mm but greater than or equal to 0.004 mm; 5 through  8 phi, inclusive) 

 ZCLAY - Clay  content in percent of dry weight of the sample (particles with nominal  diameters less than 0.004 mm; 9 phi and smaller) 

 SEDCLASS -  Sediment description based on a rigorous definition (Shepard, 1954; Schlee,  1973; Poppe and others, 2004) 

        For sediments with gravel equal to or greater than 10 percent: 

 GRAVEL - gravel equal to or greater than 50 percent 

 GRAVELLY SEDIMENT - gravel equal to or greater than 10 percent,  but less than 50 percent 

 For sediments with gravel less than 10 percent: 

 SAND - sand equal to or greater than 75 percent 

 SILTY SAND - sand less than 75 percent and equal to or greater  than 50 percent, silt is greater than clay, and clay less than 20 percent 

 CLAYEY SAND - sand less than 75 percent and equal to or greater  than 50 percent, clay is greater than silt, and silt less than 20 percent 

 SILT - silt equal to or greater than 75 percent 

 SANDY SILT - silt less than 75 percent and equal to or greater  than 50 percent, sand is greater than clay, and clay less than 20 percent 

 CLAYEY SILT - silt less than 75 percent and equal to or greater  than 50 percent, clay is greater than sand, and sand less than 20 percent 

 CLAY - clay equal to or greater than 75 percent 

 SANDY CLAY - clay less than 75 percent and equal to or greater  than 50 percent, sand is greater than silt, and silt less than 20 percent 

 SILTY CLAY - clay less than 75 percent and equal to or greater  than 50 percent, silt is greater than sand, and sand less than 20 percent 

 SAND SILT CLAY - all of these components greater than 20 percent 

 MEDIAN - Middle  point in the grain-size distribution, in phi units 

 MEAN - Average  value in the grain-size distribution, in phi units 

 STDDEV -  Standard deviation (root mean square of the deviations) of the grain-size  distribution, in phi units (that is, sorting) 

 SKEWNESS -  Deviation from symmetrical form of the grain-size distribution 

 KURTOSIS -  Degree of curvature near the mode of the grain-size distribution 

 PHI_11 - Weight  percent of the sample in the 11-phi fraction (nominal diameter of particles  greater than or equal to 0.0005 mm but less than 0.001 mm); fine clay 

 PHI_10 - Weight  percent of the sample in the 10-phi fraction (nominal diameter of particles  greater than or equal to 0.001 mm but less than 0.002 mm); medium clay 

 PHI_9 - Weight  percent of the sample in the 9-phi fraction (nominal diameter of particles  greater than or equal to 0.002 mm but less than 0.004 mm); coarse clay 

 PHI_8 - Weight  percent of the sample in the 8-phi fraction (nominal diameter of particles  greater than or equal to 0.004 mm but less than 0.008 mm); very fine silt 

 PHI_7 - Weight  percent of the sample in the 7-phi fraction (nominal diameter of particles  greater than or equal to 0.008 mm but less than 0.016 mm); fine silt 

 PHI_6 - Weight  percent of the sample in the 6-phi fraction (nominal diameter of particles  greater than or equal to 0.016 mm but less than 0.031 mm); medium silt 

 PHI_5 - Weight  percent of the sample in the 5-phi fraction (nominal diameter of particles  greater than or equal to 0.031 mm but less than 0.0625 mm); coarse silt 

 PHI_4 - Weight  percent of the sample in the 4-phi fraction (nominal diameter of particles  greater than or equal to 0.0625 mm but less than 0.125 mm); very fine sand 

 PHI_3 - Weight  percent of the sample in the 3-phi fraction (nominal diameter of particles  greater than or equal to 0.125 mm but less than 0.25 mm); fine sand 

 PHI_2 - Weight  percent of the sample in the 2-phi fraction (nominal diameter of particles  greater than or equal to 0.25 mm but less than 0.5 mm); medium sand 

 PHI_1 - Weight  percent of the sample in the 1-phi fraction (nominal diameter of particles  greater than or equal to 0.5 mm but less than 1 mm); coarse sand 

 PHI_0 - Weight  percent of the sample in the 0-phi fraction (nominal diameter of particles  greater than or equal to 1 mm but less than 2 mm); very coarse sand 

 PHIM1 - Weight  percent of the sample in the -1-phi fraction (nominal diameter of particles  greater than or equal to 2 mm but less than 4 mm); very fine pebbles (granules) 

 PHIM2 - Weight  percent of the sample in the -2-phi fraction (nominal diameter of particles  greater than or equal to 4 mm but less than 8 mm); fine pebbles 

 PHIM3 - Weight  percent of the sample in the -3-phi fraction (nominal diameter of particles  greater than or equal to 8 mm but less than 16 mm); medium pebbles 

 PHIM4 - Weight  percent of the sample in the -4-phi fraction (nominal diameter of particles  greater than or equal to 16 mm but less than 32 mm); coarse pebbles 

 PHIM5 - Weight  percent of the sample in the -5-phi fraction (nominal diameter of particles  greater than or equal to 32 mm); very coarse pebbles to boulders

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U.S. Department of the Interior |            U.S. Geological Survey                                                URL: http://pubs.usgs.gov/of/2014/1018/html/seds.html            Page Contact Information: GS Pubs Web Contact                        Page Last Modified: Friday, February 21, 2014, 12:29:03 PM |
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