Calvin Crowell Daetwyler, Jr.
1965
Marine geology of Tomales Bay, Central California
Paper
San Diego, CA
University of California, San Diego
Funding from an American Chemical Society Donation Grant and National Science Foundation Grant 2550
"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."
"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."
Data digitized by the USGS for inclusion into usSEABED. (http://walrus.wr.usgs.gov/usseabed)
1965
Publication date
None planned
-122.9774
-122.8529
38.2310
38.1051
None
University of California San Diego
Snapper grabs
Gravity cores
ISO 19115 Topic Category
Oceans and Estuaries
Location
GeoscientificInformation
NASA/Global Change Master Directory (GCMD) Earth Science Keyword. Version 5.3.3
Marine Sediments
Sediment Composition
Sedimentary Structures
Sedimentary Textures
Terrigenous Sediments
Geographic Names Information System (GNIS)
Tomales Bay
California, State of
Thesis available at the USGS library and other libraries
Cite Calvin C. Daetwyler Jr. and the University of California San Diego as the originators of the data.
Scripps Institute of Oceanography, University of California San Diego
Physical
9500 Gilman Drive
La Jolla
CA
92093 0223
858 534 3624
Daetwyler_PhD_1965
Screen grab of GIS-produced sample distribution, with bathymetry and land for reference.
JPG
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)
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.
Data fall within normal ranges for sediment percents, statistics, and other sediment parameters.
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.
Navigational technique not noted in report. Locations given to one-half seconds (degree, minute, second).
Water depths not noted in report.
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.
Van Andel, 1964
Unknown
Daetwyler_PhD_1965
Scripps Institute of Oceanography, University of California San Diego
Physical
9500 Gilman Dr
La Jolla
CA
92093 0223
858 534 3624
Vector
Point
124
0.00014
0.00014
Decimal degrees
Point
SDTS point
Source report
Gravel
Gravel
Wentworth 1932
0
29.9
Percent
0.1
Sand
Sand
Wentworth 1932
0.2
100
Percent
0.1
Silt
Silt
Wentworth 1932
0.5
68.4
Percent
0.1
Clay
Clay
Wentworth 1932
1.3
75.3
Percent
0.1
Mud
Mud
Wentworth 1932
0
11.8
Percent
0.1
Mean
Mean of grainsize distributions
Inman, 1952
1.6
7.28
Phi
0.01
Dev.
Standard deviation of grainsize distribution (sorting)
Inman, 1952
0.24
1.91
Phi
0.01
Median
Median grainsize
Inman, 1952
1.58
8.95
Phi
0.01
Porosity
Porosity of sample
Source report
63.7
76.
Phi
0.1
Bulk density
Wet bulk density
Source report
1.41
1.62
Gm/cc
0.01
Text
Descriptive text
Source report
Descriptive text including color and Munsell code
Shepard class
Location of sample on the sand-silt-clay ternary
Shepard 1954
Textural name representing position on sand-silt-clay ternary.
Scripps Institute of Oceanography, University of California San Diego
Physical
9500 Gilman Drive
La Jolla
CA
92093 0223
858 534 3624
C.C. Daetwyler, Jr's PhD thesis, 1965
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.
Report is available at some libraries.
None
U.S. Geological Survey
Mail and physical
345 Middlefield Road
Menlo Park
CA
94025
650.329.5026
men_lib@usgs.gov
Daetwyler PhD 1965
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.
Report is available for viewing or checkout at the USGS library, Menlo Park, and at other libraries.
None
None
1965
2005
U.S. Geological Survey
Jane A. Reid
Geologist
Physical and mail
400 Natural Bridges Drive
Santa Cruz
CA
95060
831-427-4727
jareid@usgs.gov
Email preferred
CSDGM Version 2
FGDC-STD-001-1998
None
Metadata was written by a user of the data. Any information contained in the physical report is authoritative and supercedes any information given here.