Geology and geomorphology--Offshore Refugio Beach, California

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Title:
Geology and geomorphology--Offshore Refugio Beach, California
Abstract:
This part of SIM 3319 presents the geologic and geomorphic map (see sheets 10, SIM 3319) of Offshore Refugio Beach, California. The vector data file is included in "Geology_OffshoreRefugioBeach.zip," which is accessible from <https://pubs.usgs.gov/ds/781/OffshoreRefugioBeach/data_catalog_OffshoreRefugioBeach.html>.
The offshore Refugio Beach map area largely consists of a gently offshore-dipping (<1 degree) shelf (10 to ~ 90 m) underlain by sediments derived primarily from relatively small coastal watersheds draining the Santa Ynez Mountains. Nearshore and shelf deposits are primarily sand (Qms) at depths less than about 45 m and more fine-grained sediment - very fine sand, silt and clay (Qmsf), at depths greater than about 45 m. The boundary between Qms and Qmsf is based on observations and extrapolation from sediment sampling (for example, Reid and others, 2006) and camera groundtruthing. The Qms-Qmsf boundary is transitional and approximate, expected to shift based on seasonal to annual to decadal scale cycles in wave climate, sediment supply, and sediment transport. Fine-grained deposits similar to Qmsf also occur below the shelfbreak on the upper slope at water depths greater than 90 m, where they are broken out as a separate unit (Qmsl) based on their location and geomorphology.
More coarse-grained deposits recognized on the basis of high backscatter and in some cases moderate seafloor relief have two modes of occurrence. In the relative nearshore (10 to 30 m water depth), coarse-grained strata (Qmsc) underlie laterally coalescing and discontinuous bars at the mouths of steep coastal watersheds. Coarser-grained sediments also form several distinct lobes (Qmscl) in water depths of 25 to 70 m, about 600 to 3,000 m offshore. The lobes range in size from ~100,000 m2 to ~1.5 km2 and are mapped on the basis of high backscatter and subtle positive seafloor relief. These coarse-grained strata were clearly derived from fluvial point sources in the adjacent, steep Santa Ynez Mountains.
Bedrock exposures in the nearshore west of El Capitan are assigned to the Miocene Monterey Formation based on proximity to coastal outcrops mapped by Dibblee (1981a, b). Much of the outer shelf (water depths > 70 m) is also underlain by undifferentiated Tertiary bedrock (Tbu). Based on the regional cross sections constrained by deep seismic-reflection data and borehole logs (Heck, 1998; Tennyson and Kropp, 1998; Forman and Redin, 2005; Redin, 2005) and high-resolution seismic-reflection data coupled with proprietary oil industry dartcore data (Ashley, 1977), these outer-shelf outcrops consist of the Miocene Sisquoc Formation and the Pliocene Repetto and Pico Formations. These rocks have been uplifted in a large, warped, regional south-dipping homocline that formed above the blind, north-dipping North Channel fault. The fault tip is inferred at about 1.5 sec TWT (~2 km) about 6 to 7 km offshore, beneath the slope and just outside California's State Waters.
Bedrock that underlies some parts of the shelf is overlain by a thin (< 1 m?) sediment veneer, recognized based on high backscatter, flat relief, continuity with moderate to high relief bedrock outcrops, and (in some cases) high-resolution, seismic-reflection data (Qms/Qtbu. Qms/Tbu, Qms/Tm). These sediment layers are likely ephemeral - they may or may not be present based on storms, seasonal/annual patterns of sediment movement, or longer-term climate cycles.
This area has a long history of petroleum production (Barnum, 1998), and grouped to solitary pockmarks (Qmp) caused by gas seeps are common features in the offshore Refugio map area. Shell discovered the Molino gas field in 1962, 4 km offshore in the southwest part of the map area. Production, by onshore directional drilling of an anticlinal trap, has been underway since the 1960's (Galloway, 1998).
References cited:
Ashley, R.J., Berry, R.W., and Fischer, P.J., 1977, Offshore geology and sediment distribution of the El Capitan-Gaviota continental shelf, northern Santa Barbara Channel, California: Journal of Sedimentary Petrology, v. 47, no, 1, p. 199-208.
Barnum, H.P., 1998, Redevelopment of the western portion of the Rincon offshore oil field, Ventura, California, in Kunitomi, D.S., Hopps, T.E., and Galloway, J.M., eds., Structure and petroleum geology, Santa Barbara Channel, California: American Association of Petroleum Geologists, p. 201–215.
Dibblee, T.W., Jr., 1981a, Geologic map of the Tajiquas Quadrangle, California: U.S. Geological Survey Open-File Report 81-371, 1:24,000.
Dibblee, T.W., Jr., 1981b, Geologic map of the Gaviota Quadrangle, California: U.S. Geological Survey Open-File Report 81-374, 1:24,000.
Dibblee, T.W., Jr., 1981c, Geologic map of the Santa Ynez Quadrangle, California: U.S. Geological Survey Open-File Report 81-371, 1:24,000.
Dibblee, T.W., Jr., 1981d, Geologic map of the Solvang Quadrangle, California: U.S. Geological Survey Open-File Report 81-372, 1:24,000.
Forman, J., and Redin, T., 2005, Santa Barbara Channel structure and correlation sections, Correlation Section no 37, Arroyo Hondo, Gaviota Quadrangle, Santa Ynez Mts. To North West Santa Rosa Island: American Association of Petroleum Geologists, Pacific Section, Publication CS 37, 1 sheet.
Galloway, J.M., 1998, Chronology of petroleum exploration and development in the Santa Barbara channel area, offshore southern California, in Kunitomi, D.S., Hopps, T.E., and Galloway, J.M., eds., Structure and petroleum geology, Santa Barbara Channel, California: American Association of Petroleum Geologists, Pacific Section and Coast Geological Society, Miscellaneous Publication 46, p. 1–12, 1 sheet.
Heck, R.G., 1998, Santa Barbara Channel Regional Formline Map, Top Monterey Formation, in Kunitomi, D.S., Hopps, T.E., and Galloway, J.M., 1998, Structure and Petroleum Geology, Santa Barbara Channel, California: American Association of Petroleum Geologists, Pacific Section, Miscellaneous Publication 46, Plate 1.
Minor, S.A., Kellogg, K.S., Stanley, R.G., Gurrola, L.D., Keller, E.A., and Brandt, T.R., 2009, Geologic map of the Santa Barbara coastal plain area, Santa Barbara County, California: U.S. Geological Survey Scientific Investigations Map 3001, scale 1:25,000.
Redin, T., 2005, Santa Barbara Channel structure and correlation sections, Correlation Section no 36, N-S structure and correlation section, western Santa Ynez Mountains across the Santa Barbara channel to Santa Rosa Island: American Association of Petroleum Geologists, Pacific Section, Publication CS 35, 1 sheet.
Reid, J.A., Reid, J.M., Jenkins, C.J., Zimmerman, M., Williams, S.J., and Field, M.E., 2006,usSEABED:Pacific Coast (California Oregon, Washington) offshore surficial-sediment data release: U.S. Geological Survey Data Series 182, <https://pubs.usgs.gov/ds/2006/182/>.
Tennyson, M.E., and Kropp, A.P., 1998, Regional cross section across Santa Barbara channel from northwestern Santa Rosa Island to Canada de Molina, in Kunitomi, D.S., Hopps, T.E., and Galloway, J.M., eds., in Structure and petroleum geology, Santa Barbara Channel, California: American Association of Petroleum Geologists, Pacific Section and Coast Geological Society, Miscellaneous Publication 46, 1 plate.

Supplemental_Information:

Map political location: Santa Barbara County, California Compilation scale: 1:24,000 Base maps used are hillshades generated from IfSAR, LiDAR, and multibeam mapping both onshore and offshore (see sheet 2, SIM 3319 for more information).
  1. How should this data set be cited?

    Conrad, J.E., Ritchie, A.C., and Johnson, S.Y., 2015, Geology and geomorphology--Offshore Refugio Beach, California:.

    This is part of the following larger work.

    Johnson, Samuel Y., Dartnell, Peter, Cochrane, Guy R., Golden, Nadine E., Phillips, Eleyne L., Ritchie, Andrew C., Kvitek, Rikk G., Greene, H. Gary, Krigsman, Lisa M., Endris, Charles A., Clahan, Kevin B., Sliter, Ray W., Wong, Florence L., Yoklavich, Mary M., Normark, William R., and Conrad, James E., 2015, California State Waters Map Series--Offshore Refugio Beach, California: Scientific Investigations Map SIM 3319, U.S. Geological Survey, Reston, VA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -120.1877
    East_Bounding_Coordinate: -119.9988
    North_Bounding_Coordinate: 34.5439
    South_Bounding_Coordinate: 34.3782

  3. What does it look like?

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

    Calendar_Date: 2012
    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):

      • GT-polygon composed of chains (111)

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

      The map projection used is WGS 1984 UTM Zone 10N.

      Projection parameters:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -123.0
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000.0
      False_Northing: 0.0

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.0001
      Ordinates (y-coordinates) are specified to the nearest 0.0001
      Planar coordinates are specified in Meter

      The horizontal datum used is D WGS 1984.
      The ellipsoid used is WGS 1984.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.

  7. How does the data set describe geographic features?

    MapUnitPolys
    Polygons representing geologic / geomorphic map units (Source: This report)

    OBJECTID
    Internal feature number. (Source: ESRI)

    Sequential unique whole numbers that are automatically generated.

    Shape
    Feature geometry. (Source: ESRI)

    Coordinates defining the features.

    MapUnitAbbrev
    Map Unit abbreviation (Source: This report)

    ValueDefinition
    QmsMarine nearshore and shelf deposits
    QmscCoarse sand, gravel, and cobble
    Qmsc?Coarse sand, gravel, and cobble, questionable
    QmsfMostly mud, and muddy sand
    QmpMarine pockmarks
    QscMarine or nonmarine sediments
    QmsclMarine shelf sediments, lobate form
    Qmscl?Marine shelf sediments, lobate form, questionable
    QmslMarine slope deposits
    QTbuUndifferentiated bedrock
    Qms/QTbuSediment covered undifferentiated bedrock
    Qms/TbuSediment covered Tertiary Formation
    Qms/TmSediment covered Monterey Formation
    Qms/Tm?Sediment covered Monterey Formation, questionable
    TmMonterey Formation
    TbuTertiary bedrock
    TrRincon Formation

    MapUnit
    short description of map unit (Source: This report)

    text description of map unit

    Shape_Length
    Length of feature in internal units. (Source: ESRI)

    Positive real numbers that are automatically generated.

    Shape_Area
    Area of feature in internal units squared. (Source: ESRI)

    Positive real numbers that are automatically generated.

    RuleID
    Representation rule identifier (Source: This report)

    This field contains the representation rule in the ArcGIS file geodatabase which applies a solid color fill of a specified CMYK value to each polygon. Representation rules have the same name as the map unit abbreviation.

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?

    USGS Pacific Coastal & Marine Science Center
    Attn: Stephen Hartwell
    Geologist
    400 Natural Bridges Drive
    Santa Cruz, CA 95060
    USA

    (831) 460-7814 (voice)
    (831) 427-4748 (FAX)
    shartwell@usgs.gov

Why was the data set created?

To expand geologic mapping to the seafloor within California's State Waters, to update coastal geologic mapping, and to contribute to a uniform regional geologic database. Additionally, to provide a geologic map for the public and geoscience community to aid in assessments and mitigation of geologic hazards in the Santa Barbara coastal plain region and to provide sufficient geologic information for land-use and land-management decisions both onshore and offshore.

How was the data set created?

  1. From what previous works were the data drawn?

    SIM 3319 (sheet 1) (source 1 of 3)
    Dartnell, Peter, Phillips, Eleyne, Ritchie, Andy, Kvitek, Rikk, and Johnson, Samuel, 2012, Bathymetry--Offshore Refugio, California: Scientific Investigations Map SIM 3319 (sheet 1), U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    See metadata for sheet 1 ("Bathymetry_OffshoreRefugioBeach_metadata.txt") in SIM 3319 for source data and postprocessing/reprocessing information.
    Type_of_Source_Media: digital file of gridded bathymetry data (ArcInfo GRID)
    Source_Contribution: Gridded bathymetry data (2-meter resolution).

    SIM 3319 (sheet 3) (source 2 of 3)
    Dartnell, Peter, 2012, Acoustic backscatter--Offshore Refugio, California: Scientific Investigations Map SIM 3319 (sheet 3), U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    See metadata for sheet 3 ("BackscatterA_CSUMB_OffshoreRefugioBeach_metadata.txt" and "BackscatterB_USGS_OffshoreRefugioBeach_metadata.txt") in SIM 3319 for amplitude source data and postprocessing/reprocessing information.
    Type_of_Source_Media: digital file of gridded amplitude data (ArcInfo GRID)
    Source_Contribution: Gridded amplitude data (2-meter resolution).

    Sliter and others (2008) (source 3 of 3)
    Ray W. Sliter, Peter J. Triezenberg, Patrick E. Hart, Amy E. Draut, William R. Normark, and James E. Conrad, 2008, High-Resolution Chirp and Mini-Sparker Seismic-Reflection Data From the Southern California Continental Shelf--Gaviota to Mugu Canyon: U.S. Geological Survey Open-File Report 2008-1246, U.S. Geological Survey, Reston, VA.

    Online Links:

    Type_of_Source_Media:
    seismic data files (.sgy files) ASCII lat/long shotpoint files TIFF images of processed seismic lines
    Source_Contribution:
    Digital seismic data used to interpret subsurface geologic structure

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

    Date: 2010 (process 1 of 2)
    Map unit polygons were digitized over underlying 2-meter base layers developed from multibeam bathymetry and backscatter data. Derivatives such as slope and curvature were generated from source rasters. Interpreted rasters include amplitude, hillshaded bathymetry (using various illumination angles and vertical exaggeration), slope, and curvature. Curvature was decomposed into profile and plan curvature for analysis purposes.

    Date: 2011 (process 2 of 2)
    The mapped area was extended to the shoreline by generating a DEM using USACE NCMP lidar data collected in 2009 (USACE, unpub. data), with gaps filled by data from Barnard and Hoover (2010). These elevation data were then used to generate a shoreline at the NAVD88 +1.33 m contour, defined as the operational MHW shoreline by Weber and others (2005). The resulting boundary was transformed to WGS 84 UTM Zone 11 North in ArcGIS 10 using the NAD83 to WGS84 (ITRF00) transformation algorithm. This boundary was then used to extend and trim both onshore and offshore geology in the print and PDF product. The transformed boundary is contained within the WGS84 "contacts" feature class and identified as a shoreline in the associated representation rules.
    Only data for offshore map units are released digitally in this publication. For onshore geology (sheet 10) see Dibblee (1986a, 1986b, 1986c and 1986d), Tan and others, 2003a, 2003b, and Tan and Clahan (2003).
    References Cited:
    Barnard, P.L., and Hoover, D., 2010, A seamless, high-resolution coastal digital elevation model (DEM) for southern California: U.S. Geological Survey Data Series 487, 8 p., and database (<https://pubs.usgs.gov/ds/487/>).
    Clahan, K.B., 2003, Geologic map of the Oxnard 7.5' quadrangle, Ventura County, California--A digital database: California Geologic Survey Preliminary Geologic Map, accessed April 5, 2011, at <http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm>.
    Weber, K.M., List, J.H., Morgan, K.L., 2005, An operational Mean High Water datum for determination of shoreline position from topographic lidar data: U.S. Geological Survey Open-File Report 2005-1027 (<https://pubs.usgs.gov/of/2005/1027/>).

  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?

    Polygons were primarily mapped by one of the following methods: (1) interpretation of 2-meter-resolution hillshaded bathymetry data from bathymetric lidar and sonar surveys (see sheets 1 and 2, SIM 3319); (2) interpretation of 2-meter-resolution amplitude (backscatter) data from bathymetric sonar surveys (see sheet 3, SIM 3319); (3) interpretation of seismic-reflection-profile data (see sheet 8, SIM 3319).
    Map Unit contact locations were interpreted typically at a scale of between 1:1,000 and 1:2,000 using the above base data. Bathymetric sonar and LiDAR data have a horizontal accuracy greater than the resolution of the base data.
    Map unit contacts were digitized by heads-up screen digitization of line data on 2-meter-resolution DEMs described above. Horizontal accuracy is estimated to be between 2 and 5 meters depending on how clearly contacts can be resolved.
    Most digitized positions on the map are estimated to have better than 5 m horizontal accuracy. There is no elevation data in the database.

  3. How accurate are the heights or depths?

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

    Data are complete: no offshore features that could be accurately identified and represented at the compilation scale of 1:24,000 were eliminated or generalized. The smallest area represented is approximately 100 square meters. All geospatial database elements are attributed.

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

    Map elements were visually checked for overshoots, undershoots, duplicate features, polygon closure, and other errors by the lead authors and by the GIS technician(s) who created the digital database. Review drafts of the map were reviewed internally by at least two other geologists for consistency with basic geologic principles and general conformity to USGS mapping standards.

How can someone get a copy of the data set?

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

Access_Constraints:
If physical samples or materials are available, constraints on their on-site access are described in "WR CMG Sample Distribution Policy" at URL: <http://walrus.wr.usgs.gov/infobank/programs/html/main/sample-dist-policy.html>
Use_Constraints:
This information is not intended for navigational purposes.
Read and fully comprehend the metadata prior to data use. Uses of these data should not violate the spatial resolution of the data. Where these data are used in combination with other data of different resolution, the resolution of the combined output will be limited by the lowest resolution of all the data.
Acknowledge the U.S. Geological Survey in products derived from these data. Share data products developed using these data with the U.S. Geological Survey.
This database has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use.
Although this Federal Geographic Data Committee-compliant metadata file is intended to document these data in nonproprietary form, as well as in ArcInfo format, this metadata file may include some ArcInfo-specific terminology.

Who wrote the metadata?

Dates:
Last modified: 2012
Metadata author:
U.S. Geological Survey, Coastal and Marine Geology Program
Attn: Stephen R. Hartwell
400 Natural Bridges Drive
Santa Cruz, CA 95060-5792
US

831-460-7814 (voice)
831-427-4748 (FAX)
shartwell@usgs.gov

Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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