Marine geology of Tomales Bay, Central California

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Frequently-anticipated questions:

What does this data set describe?

Title: Marine geology of Tomales Bay, Central California
Abstract:
"Tomales Bay is a submerged rift valley lying along the axis of the northwest-trending, seismically active San Andreas fault zone. Protected bay sediments are being deposited in a narrow, elongated, structural depression, characterized by known strike-slip faulting in historic times. The primary objective of this investigation is to determine the relative effects of normal depositional processes and contemporaneous strike-slip faulting on the Recent sediment facies, thickness, distribution, and depositional history in Tomales Bay. The stratigraphic succession and major internal structure of the Recent sediments in the southern two-thirds of the bay were determined by combining an acoustic-reflection survey (Sonoprobe) with lithologic data obtained from cores and test borings. Lithologic variations of the Tomales Bay surface sediments are attributed to 1.) the location and character of the sediment sources and 2.) the dispersal of sediment by tidal currents. Sandy sediments, supplied to the bay entrance by southerly longshore currents, have been subsequently redistributed throughout the northern third of the bay by tidal currents. Within this area of sand deposition, further textural subdivisions can be made on the basis of size-sorting relationships and size-frequency distributions. A textural transition zone marks the boundary between the sandy sediments and the fine-grained homogeneous sediments of the remaining two-thirds of the bay. Large quantities of sediment fill have been deposited in historic times and are situated near the mouths of Walker and Lagunitas Creeks, which have supplied the fine-grained sediment to the bay. The subaerial rift valley, prior to the Late Wisconsin rise in sea level, contained features of fault morphology. A prominent, discontinuous, center rift ridge was present throughout the valley. When developed this ridge divided the valley into two topographically lower segments elongated parallel to the axis of the San Andreas fault zone. During the initial post-Wisconsin transgression, a basal transgressive facies was deposited locally over the pre-transgressive surface. Sand was transported southward from Bodega Bay and a constricting sand spit was formed southeast of Hog Island. South of this spit, muds were deposited and a mudflat and channel system developed. As sea level continued to rise, the entrance to Tomales Bay was gradually filled by sand. A new bay mouth spit (Sand Point) began to form. The formation of this feature at the bay entrance decreased the sand supplied to the southern bay. The southernmost sand spit was gradually transgressed and younger muds began to fill in the former tidal channels and cover the older mudflats. Small depressions, found along the bay margins south of Pelican Point, are the relicts of former tidal channels and are not related to seismic activity. Locations of several fault traces are inferred from vertical separations of the pre-transgressive surface. Net slip of the fault displacements was not determined since clear lines of displacement were not established. Factors of basin geometry, a rising sea level, and the rates of sediment supply and dispersal, have been more important than active strike-slip faulting in determining the stratigraphy and internal structure of the Tomales Bay Recent sediments."
Supplemental_Information:
Data digitized by the USGS for inclusion into usSEABED. (<http://walrus.wr.usgs.gov/usseabed>)
  1. How should this data set be cited?

    Calvin Crowell Daetwyler, Jr., 1965, Marine geology of Tomales Bay, Central California: University of California, San Diego, San Diego, CA.

    Other_Citation_Details:
    Funding from an American Chemical Society Donation Grant and National Science Foundation Grant 2550

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -122.9774
    East_Bounding_Coordinate: -122.8529
    North_Bounding_Coordinate: 38.2310
    South_Bounding_Coordinate: 38.1051

  3. What does it look like?

    Daetwyler_PhD_1965 (JPG)
    Screen grab of GIS-produced sample distribution, with bathymetry and land for reference.

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

    Calendar_Date: 1965
    Currentness_Reference: Publication date

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

    Geospatial_Data_Presentation_Form: Paper

  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):

      • Point (124)

    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 0.00014. Longitudes are given to the nearest 0.00014. Latitude and longitude values are specified in Decimal degrees.

  7. How does the data set describe geographic features?

    Point
    SDTS point (Source: Source report)

    Gravel
    Gravel (Source: Wentworth 1932)

    Range of values
    Minimum:0
    Maximum:29.9
    Units:Percent
    Resolution:0.1

    Sand
    Sand (Source: Wentworth 1932)

    Range of values
    Minimum:0.2
    Maximum:100
    Units:Percent
    Resolution:0.1

    Silt
    Silt (Source: Wentworth 1932)

    Range of values
    Minimum:0.5
    Maximum:68.4
    Units:Percent
    Resolution:0.1

    Clay
    Clay (Source: Wentworth 1932)

    Range of values
    Minimum:1.3
    Maximum:75.3
    Units:Percent
    Resolution:0.1

    Mud
    Mud (Source: Wentworth 1932)

    Range of values
    Minimum:0
    Maximum:11.8
    Units:Percent
    Resolution:0.1

    Mean
    Mean of grainsize distributions (Source: Inman, 1952)

    Range of values
    Minimum:1.6
    Maximum:7.28
    Units:Phi
    Resolution:0.01

    Dev.
    Standard deviation of grainsize distribution (sorting) (Source: Inman, 1952)

    Range of values
    Minimum:0.24
    Maximum:1.91
    Units:Phi
    Resolution:0.01

    Median
    Median grainsize (Source: Inman, 1952)

    Range of values
    Minimum:1.58
    Maximum:8.95
    Units:Phi
    Resolution:0.01

    Porosity
    Porosity of sample (Source: Source report)

    Range of values
    Minimum:63.7
    Maximum:76.
    Units:Phi
    Resolution:0.1

    Bulk density
    Wet bulk density (Source: Source report)

    Range of values
    Minimum:1.41
    Maximum:1.62
    Units:Gm/cc
    Resolution:0.01

    Text
    Descriptive text (Source: Source report)

    Descriptive text including color and Munsell code

    Shepard class
    Location of sample on the sand-silt-clay ternary (Source: Shepard 1954)

    Textural name representing position on sand-silt-clay ternary.

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?

    C. Daetwyler Jr. for collection and analysis of data. For inclusion into usSEABED, digitization: Jennifer Mendonca (USGS); Formatting corrections: Jane Reid (USGS) and Chris Jenkins (University of Colorado)

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

    Scripps Institute of Oceanography, University of California San Diego
    9500 Gilman Drive
    La Jolla, CA 92093 0223

    858 534 3624 (voice)

Why was the data set created?

"The primary objective of this investigation is to determine the effects of recurrent contemporaneous strike-slip faulting and normal depositional processes on the Recent sediment facies, thickness, distribution and depositional history in Tomales Bay. Specific objectives are: 1.) to explain the distribution and internal structure of the Recent sediments in terms of their immediate source, and the dominant processes controlling their dispersal and deposition, and 2.) to evaluate the effects of faulting on the Recent sediments being deposited in this seismically active structural setting."

How was the data set created?

  1. From what previous works were the data drawn?

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

    Date: Unknown (process 1 of 1)
    Split samples were treated with 10 per cent hydrogen peroxide to remove organic matter, dispersed in the presence of Ca2+ ions by 0.005 molal sodium oxalate and 0.062 molal sodium carbonate. Wet sieved on a 0.062 mm sieve. When necessary, the size fraction larger than 2.0 mm was also separated by wet sieving. A standard pipette analysis was made of the fine fractions. The sand fraction was reduced to a subsample of a few grams with an Otto microsplit. The size distribution was determined by a continuous-recording sedimentation balance developed at SIO (van Andel, 1964). For inclusion into usSEABED, gravel values > 0 for 14 grab samples were integrated and sand/silt/clay values recalculated. Mean and median grainsize values and standard deviations (sorting) for those samples are not used.

    Person who carried out this activity:

    Scripps Institute of Oceanography, University of California San Diego
    9500 Gilman Dr
    La Jolla, CA 92093 0223

    858 534 3624 (voice)

    Data sources used in this process:
    • Van Andel, 1964

    Data sources produced in this process:

    • Daetwyler_PhD_1965

  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?

    No estimate made for the accuracy of the data in the original report. Data digitized by the USGS and partners were visually compared to the source data, and corrected. Where appropriate, data were tested for completeness using MS Excel. Locations checked using GIS.

  2. How accurate are the geographic locations?

    Navigational technique not noted in report. Locations given to one-half seconds (degree, minute, second).

  3. How accurate are the heights or depths?

    Water depths not noted in report.

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

    For inclusion into usSEABED, appendix I (location of samples), Appendix II (grain size data), Appendix III (lithologic description of cores) and Appendix IV (Sound speed, density, porosity, and grain-size data, core 49 and 50) were completely digitized. Appendix V (Lithologic description of Merle Lawson water well No. 2 and Tomales Bay test borings) was not digitized.

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

    Data fall within normal ranges for sediment percents, statistics, and other sediment parameters.

How can someone get a copy of the data set?

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

Access_Constraints: Thesis available at the USGS library and other libraries
Use_Constraints:
Cite Calvin C. Daetwyler Jr. and the University of California San Diego as the originators of the data.

  1. Who distributes the data set? (Distributor 1 of 2)

    Scripps Institute of Oceanography, University of California San Diego
    9500 Gilman Drive
    La Jolla, CA 92093 0223

    858 534 3624 (voice)

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

    C.C. Daetwyler, Jr's PhD thesis, 1965

  3. What legal disclaimers am I supposed to read?

    Although this dataset has been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data. Users of the data should be aware of limitations of the data due to possible imprecision due to navigational inaccuracies and limitations of the statistical data.

  4. How can I download or order the data?

  1. Who distributes the data set? (Distributor 2 of 2)

    U.S. Geological Survey
    345 Middlefield Road
    Menlo Park, CA 94025

    650.329.5026 (voice)
    men_lib@usgs.gov

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

    Daetwyler PhD 1965

  3. What legal disclaimers am I supposed to read?

    Although this dataset has been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data. Users of the data should be aware of the limitations of the data due to possible imprecision due to navigational inaccuracies, statistical limitations, and digitizing errors.

  4. How can I download or order the data?

  5. What hardware or software do I need in order to use the data set?

    None

Who wrote the metadata?

Dates:
Last modified: 2005
Metadata author:
U.S. Geological Survey
c/o Jane A. Reid
Geologist
400 Natural Bridges Drive
Santa Cruz, CA 95060

831-427-4727 (voice)
jareid@usgs.gov

Contact_Instructions: Email preferred
Metadata standard:
CSDGM Version 2 (FGDC-STD-001-1998)

Generated by mp version 2.8.17 on Tue May 16 20:43:30 2006