Geology and geomorphology--Offshore of Ventura, California

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Title: Geology and geomorphology--Offshore of Ventura, California
Abstract:
This part of SIM 3254 presents data for the geologic and geomorphic map (see sheet 10, SIM 3254) of the Offshore of Ventura map area, California. The vector data file is included in "Geology_OffshoreVentura.zip," which is accessible from <https://pubs.usgs.gov/ds/781/OffshoreVentura/data_catalog_OffshoreVentura.html>.
The offshore part of the map area largely consists of a relatively shallow (less than 40 m deep), gently offshore-dipping (less than 1 degree) shelf underlain by recent marine and deltaic deposits of the Santa Clara and Ventura Rivers. The mean annual sediment load of these two rivers exceeds 3.25 kt/yr (Warrick and Farnsworth, 2009a), and the area is largely part of an extensive Quaternary deltaic depocenter (Dahlen, 1992; Slater and others, 2002; Sommerfield and others, 2009). Shelf deposits are primarily sand (Qms) at depths less than about 25 m and, at depths greater than about 25 m, are more fine-grained sediment (very fine sand, silt and clay) (Qmsf). The boundary between Qms and Qmsf is based on observations and extrapolation from sediment sampling (for example, Reid and others, 2006) and camera ground-truth surveying (see sheet 6, SIM 3254). Given that this is an area of abundant sediment supply and active sediment transport (Barnard and others, 2009; Warrick and Farnsworth, 2009a), it is important to note that the boundary between Qms and Qmsf should be considered transitional and approximate and is expected to shift as a result of seasonal- to annual- to decadal-scale cycles in wave climate, sediment supply, and sediment transport. Offshore of the mouth of the Ventura River, at water depths of between 20 and 30 m, the sandy shelf (Qms) includes an area of irregular arcuate depressions floored by coarser sediment (coarse sand and possibly gravel; Qmss). Such features have been referred to as "rippled-scour depressions" (for example, Cacchione and others, 1984) or "sorted bedforms" (for example, Goff and others, 2005; Trembanis and Hume, 2011). Although the general area in which Qmss depressions are found is not likely to change substantially, the boundaries of the unit(s), as well as the locations of individual depressions and their intervening flat sand sheets, likely are ephemeral, changing during significant storm events. Coarser grained deposits (Qmsc), which are recognized on the basis of high backscatter (sheet 3, SIM 3254), camera observations (sheet 6, SIM 3254), and sampling (Reid and others, 2006; Barnard and others, 2009), are found locally in water depths less than about 15 m. These units are concentrated at the mouths of the Santa Clara and Ventura Rivers and a few smaller coastal watersheds to the northwest, and they are inferred to represent wave-winnowed lags of deltaic sediment. It is likely that these deposits are ephemeral and are commonly covered by finer grained sediment. However, a few outcrops of Qmsc between Ventura and Pitas Point are not obviously tied to coastal watersheds. One large area in particular is characterized by high backscatter and rugosity (sheets 3 and 5, SIM 3254, respectively); camera ground-truth aurveying (sheet 6, SIM 3254) reveals that this area consists of boulder, cobble, gravel, and sand. The area lies immediately offshore of steep slopes underlain by variably consolidated Pliocene and Pleistocene deposits (sand, gravel, cobbles) of the Pico, Santa Barbara, and Saugus Formations (onshore units Tp, QTsb, and Qs, respectively), which are highly susceptible to landsliding (Tan and others, 2003a,b); thus, this area mostly likely represents wave-winnowed landslide deposits. It is also possible that these high-backscatter areas are partly underlain by bedrock, as is inferred on sheet 7 (SIM 3254). The steep onshore slopes are immediately north of, and in the hanging wall of, the active Pitas Point Fault, a location that undoubtedly has contributed to slope instability.
The seafloor bedrock exposures south and west of Punta Gorda are inferred to consist of the Pico Formation (Tp) on the basis of their backscatter, rugosity, and relief, as well as adjacent exposures of Tp in coastal bluffs and platforms and their similar location along the axis of the Rincon-Ventura Avenue Anticline (Tan and others, 2003a,b). A few shallow (less than 10 m deep) areas offshore between Punta Gorda and Pitas Point are inferred to be underlain by a composite unit (Qms/Tp) consisting of the Pico Formation overlain by a thin (probably ephemeral) marine-sediment layer.
The Offshore of Ventura map area is in the Ventura Basin, in the southern part of the Western Transverse Ranges geologic province, which is north of the California Continental Borderland (Fisher and others, 2009). This province has undergone significant north-south compression since the Miocene, and recent GPS data suggest north-south shortening of about 6 to 10 mm/yr (Larson and Webb, 1992; Donnellan and others, 1993). The active, north-verging Oak Ridge Fault and the south-verging Pitas Point-Ventura Fault are two of the structures on which this shortening occurs (for example, Sorlien and others, 2000; Fisher and others, 2009). High-resolution seismic-reflection data (sheet 8, SIM 3254) reveal that neither fault ruptures the surface; instead the surface expression of each fault is a narrow, asymmetric fold that involves the uppermost Pleistocene and Holocene (less than 21 ka) sedimentary section. Both structures are inferred to be parts of long fault systems that extend for more than 100 km, representing important potential earthquake hazards (for example, Fisher and others, 2009). Shortening is also occurring on the Montalvo Fault and Anticline system along the southeast edge of the map area (part of the broader Oak Ridge Fault Zone; Yeats, 1998) and on the Rincon-Ventura Avenue Anticline (for example, Rockwell and others, 1988), which crosses the northwest edge of the map area.
References Cited
Barnard, P.L., Revell, D.L., Hoover, D., Warrick, J., Brocatus, J., Draut, A.E., Dartnell, P., Elias, E., Mustain, N., Hart, P.E., and Ryan, H.F., 2009, Coastal processes study of Santa Barbara and Ventura counties, California: U.S. Geological Survey Open-File Report 2009-1029, 926 p., available at <https://pubs.usgs.gov/of/2009/1029/>.
Cacchione, D.A., Drake, D.E., Grant, W.D., and Tate, G.B., 1984, Rippled scour depressions of the inner continental shelf off Central California: Journal of Sedimentary Petrology, v. 54, p. 1,280-1,291.
Dahlen, M.Z., 1992, Sequence stratigraphy, depositional history, and middle to late Quaternary sea levels of the Ventura shelf, California: Quaternary Research, v. 38, p. 234-245.
Donnellan, A., Hager, B.H., and King, R.W., 1993, Discrepancy between geologic and geodetic deformation rates in the Ventura basin: Nature, v. 346, p. 333-336.
Fisher, M.A., Sorlien, C.C., and Sliter, R.W., 2009, Potential earthquake faults offshore southern California from the eastern Santa Barbara channel to Dana Point, in Lee, H.J., and Normark, W.R., eds., Earth science in the urban ocean--The Southern California Continental Borderland: Geological Society of America Special Paper 454, p. 271-290.
Goff, J.A., Mayer, L.A., Traykovski, P., Buynevich, I., Wilkens, R., Raymond, R., Glang, G., Evans, R.L., Olson, H., and Jenkins, C., 2005, Detailed investigations of sorted bedforms or "rippled scour depressions," within the Marthas's Vineyard Coastal Observatory, Massachusetts: Continental Shelf Research, v. 25, p. 461-484.
Larson, K.M., and Webb, F.H., 1992, Deformation in the Santa Barbara Channel from GPS measurements 1987-1991: Geophysical News Letters, v. 19, p. 1,491-1,494.
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, available at <https://pubs.usgs.gov/ds/2006/182/>.
Rockwell, T.K., Keller, E.A., and Dembroff, G.R., 1988, Quaternary rate of folding of the Ventura Avenue anticline, western Transverse Ranges, southern California: Geological Society of America Bulletin, v. 100, p. 850-858.
Slater, R.A., Gorsline, D.S., Kolpack, R.L., and Shiller, G.I., 2002, Post-glacial sediments of the California shelf from Cape San Martin to the US-Mexico border: Quaternary International, v. 92, p. 45-61.
Sommerfield, C.R., Lee, H.J., and Normark, W.R., 2009, Postglacial sedimentary record of the southern California continental shelf and slope, Point Conception to Dana Point, in Lee, H.J., and Normark, W.R., eds., Earth science in the urban ocean--The Southern California Continental Borderland: Geological Society of America Special Paper 454, p. 89-116.
Sorlien, C.C., Gratier, J.P., Luyendyk, B.P., Hornafius, J.S., and Hopps, T.E, 2000, Map restoration of folded and faulted late Cenozoic strata across the Oak Ridge fault, onshore and offshore Ventura basin, California: Geological Society of America Bulletin, v. 112, p. 1,080-1,090.
Tan, S.S., Jones, T.A., and Clahan, K.B., 2003a, Geologic map of the Ventura 7.5' quadrangle, Ventura County, California--A digital database: California Geological Survey Preliminary Geologic Map, scale 1:24,000, available at <http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm>.
Tan, S.S., Jones, T.A., and Clahan, K.B., 2003b, Geologic map of the Pitas Point 7.5' quadrangle, Ventura County, California--A digital database: California Geological Survey Preliminary Geologic Map, scale 1:24,000, available at <http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm>.
Trembanis, A.C., and Hume, T.M., 2011, Sorted bedforms on the inner shelf off northeastern New Zealand--Spatiotemporal relationships and potential paleo-environmental implications: Geo-Marine Letters, v. 31, p. 203-214.
Warrick, J.A., and Farnsworth, K.L., 2009a, Sources of sediment to the coastal waters of the Southern California Bight, in Lee, H.J., and Normark, W.R., eds., Earth science in the urban ocean--The Southern California Continental Borderland: Geological Society of America Special Paper 454, p. 39-52.
Yeats, R.S., 1998, North-vergent thick-skinned or south-vergent thin-skinned Oak Ridge fault--A view from the coast, 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. 143-152.
Supplemental_Information:

Map political location: Ventura 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 3254, for more information).
  1. How should this data set be cited?

    Ritchie, A.C., and Johnson, S.Y., 2013, Geology and geomorphology--Offshore of Ventura, 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. , Seitz, Gordon G. , Gutierrez, Carlos I. , Sliter, Ray W. , Erdey, Mercedes D. , Wong, Florence L. , Yoklavich, Mary M. , Draut, Amy E. , Hart, Patrick E. , and Cochran, Susan A. , 2013, California State Waters Map Series--Offshore of Ventura, California: Scientific Investigations Map SIM 3254, U.S. Geological Survey, Reston, VA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -119.4481
    East_Bounding_Coordinate: -119.2494
    North_Bounding_Coordinate: 34.3761
    South_Bounding_Coordinate: 34.2187

  3. What does it look like?

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

    Calendar_Date: 2013
    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 (69)

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

      The map projection used is WGS 1984 UTM Zone 11N.

      Projection parameters:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -117.0
      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
    afArtificial fill
    pdPlatform debris
    QmsMarine nearshore and shelf deposits
    QmscCoarse-grained marine nearshore and shelf deposits
    QmsfFine-grained marine shelf deposits
    QmssMarine shelf scour depressions
    Qms/TpSediment-covered Pico Formation
    Qms/Tp?Sediment-covered Pico Formation, questionable
    TpPico 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 and Marine Science Center
    c/o 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 3254 (sheets 1, 2) (source 1 of 3)
    Kvitek, Rikk G. , Dartnell, Peter, Phillips, Eleyne L. , and Cochrane, Guy R. , 2013, Bathymetry--Offshore of Ventura, California: Scientific Investigations Map SIM 3254 (sheets 1, 2), U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    See metadata for sheets 1, 2 ("Bathymetry_OffshoreVentura_metadata.txt") in SIM 3254 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 3254 (sheet 3) (source 2 of 3)
    Dartnell, Peter, Kvitek, Rikk G. , Phillips, Eleyne L. , and Cochrane, Guy R. , 2013, Acoustic backscatter--Offshore of Ventura, California: Scientific Investigations Map SIM 3254 (sheet 3), U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    See metadata for sheet 3 ("BackscatterA_CSUMB_OffshoreVentura_metadata.txt" and "BackscatterB_USGS_OffshoreVentura_metadata.txt") in SIM 3254 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, 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 U.S. Army Corps of Engineers (USACE) National Coastal Mapping Program?s lidar data collected in 2009 (U.S. Army Corps of Engineers, 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, SIM 3254), see Dibblee (1986), Tan and others (2003a,b), and Tan and Clahan (2004).
    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, available at <https://pubs.usgs.gov/ds/487/>.
    Dibblee, T.W., Jr., 1986, Geologic map of the Carpinteria quadrangle, Santa Barbara County, California: Santa Barbara, Calif., Dibblee Geological Foundation Map DF-04, scale 1:24,000.
    Tan, S.S., and Clahan, K.B., 2004, Geologic map of the White Ledge Peak 7.5' quadrangle, Santa Barbara and Ventura Counties, California--A digital database: California Geological Survey Preliminary Geologic Map, scale 1:24,000, available at <http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm>.
    Tan, S.S., Jones, T.A., and Clahan, K.B., 2003a, Geologic map of the Ventura 7.5' quadrangle, Ventura County, California--A digital database: California Geological Survey Preliminary Geologic Map, scale 1:24,000, available at <http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm>.
    Tan, S.S., Jones, T.A., and Clahan, K.B., 2003b, Geologic map of the Pitas Point 7.5' quadrangle, Ventura County, California--A digital database: California Geological Survey Preliminary Geologic Map, scale 1:24,000, available at <http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm>.
    Weber, K.M., List, J.H., and 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, available at <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 3254); (2) interpretation of 2-meter-resolution amplitude (backscatter) data from bathymetric sonar surveys (see sheet 3, SIM 3254); (3) interpretation of 2-meter interpretation of seismic-reflection-profile data (see sheet 8, SIM 3254).
    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
c/o 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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