Dataset Identification:
Resource Abstract:
- description: This part of DS 781 presents data for the geologic and geomorphic map of the Offshore Pigeon Point map area,
California. The vector data file is included in "Geology_OffshorePigeonPoint.zip," which is accessible from http://dx.doi.org/10.5066/F7513W80
The continental shelf within California's State waters in the Pigeon Point map area is shallow (0 to ~55 m) and flat
with a very gentle (less than 0.5 degrees) offshore dip. Shelf morphology and evolution result from the interplay between
local tectonics and sedimentation as sea level rose about 125 to 130 m over the last ~ 21,000 years (Lambeck and Chappel,
2001). Shelf deposits are almost exclusively sand (unit Qms) at depths less than 60 m and transition to more fine grained,
muddy sediment (unit Qmsf) at greater depths in the southwestern most part of the map area. The boundary between units Qms
and Qmsf was determined based on seafloor sediment samples (Reid and others, 2006) and video observations from the Offshore
of Pigeon Point and adjacent map area. This boundary likely shifts seaward or landward based on seasonal to decadal changes
in sediment supply, sediment transport, and wave climate. More coarse-grained sands and gravels (units Qmss and Qmsc) are
primarily recognized on the basis of high backscatter. Unit Qmsc occurs as a nearshore, shore-parallel bar at typical water
depths between 5 and 10 meters. Unit Qmss forms erosional lags in rippled scour depressions (for example, Cacchione and others,
1984) at water depths of about 25 to 35 m, in contact with offshore bedrock uplifts and unit Qms. Although the general areas
in which unit Qmsc and unit Qmss occur are not likely to change substantially, the boundaries of the unit(s) are likely ephemeral,
changing seasonally and during significant storm events. Unit Qmss deposits are common along this stretch of the California
coast where offshore sandy sediment can be relatively thin (thus unable to fill the depressions) due to both lack of river
input and to significant sediment erosion and offshore sediment transport during large northwest winter swells. Areas where
shelf sediments form thin (< 2.5 m or less) veneers over low relief, undivided Cretaceous and (or) Tertiary bedrock are
mapped as units Qms/TKu and Qms/Tp. These areas are recognized based on the combination of flat relief, continuity with moderate
to high relief bedrock outcrops, high-resolution seismic-reflection data, and in some cases moderate backscatter. These units
are regarded as ephemeral and dynamic sediment layers that may or may not be present based on storms, seasonal/annual patterns
of sediment movement, or climate cycles. Tertiary deposits mapped in the offshore include two units of the Purisima Formation
(units Tp and Tpt). The Purisima units are characterized by high backscatter and distinct bedding recognized in multibeam
imagery and/or seismic-reflection data. These Tertiary rocks are underlain by or in fault contact with Upper Cretaceous basement
rocks, including sedimentary rocks of the Pigeon Point Formation (unit Kpp). The Pigeon Point Formation is mapped on the basis
of high backscatter, massive and (or) rugged texture on multibeam imagery, and reflection-free character on seismic-reflection
data. Offshore outcrops of the Pigeon Point Formation form the offshore Pigeon Point high, a major structural feature that
extends ~30 km to the northwest and represents the northeast boundary of the Outer Santa Cruz Basin (McCulloch, 1987). Areas
where bedrock is exposed on the seafloor but there is less certainty regarding age are mapped as Cretaceous and Tertiary,
undivided (unit TKu). Map unit polygons were digitized over underlying 2-meter base layers developed from multibeam bathymetry
and backscatter data (see "Bathymetry--Offshore of Pigeon Point Map Area, California" and "Backscatter--Offshore
of Pigeon Point Map Area, California"). The bathymetry and backscatter data were collected between 2006 and 2010. References
Cited 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. 1280-1291. Lambeck, K., and Chappell, J., 2001, Sea
level change through the last glacial cycle: Science, v. 292, p. 679-686. McCulloch, D.S., 1987, Regional geology and hydrocarbon
potential of offshore Central California, in Scholl, D.W., Grantz, A., and Vedder, J.G., eds., Geology and resource potential
of the continental margin of Western North America and adjacent ocean basins - Beaufort Sea to Baja California: Circum-Pacific
Council for Energy and Mineral Resources Earth Science Series, v. 6, p. 353-401. 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, http://pubs.usgs.gov/ds/2006/182/.; abstract: This part of DS 781 presents
data for the geologic and geomorphic map of the Offshore Pigeon Point map area, California. The vector data file is included
in "Geology_OffshorePigeonPoint.zip," which is accessible from http://dx.doi.org/10.5066/F7513W80 The continental
shelf within California's State waters in the Pigeon Point map area is shallow (0 to ~55 m) and flat with a very gentle
(less than 0.5 degrees) offshore dip. Shelf morphology and evolution result from the interplay between local tectonics and
sedimentation as sea level rose about 125 to 130 m over the last ~ 21,000 years (Lambeck and Chappel, 2001). Shelf deposits
are almost exclusively sand (unit Qms) at depths less than 60 m and transition to more fine grained, muddy sediment (unit
Qmsf) at greater depths in the southwestern most part of the map area. The boundary between units Qms and Qmsf was determined
based on seafloor sediment samples (Reid and others, 2006) and video observations from the Offshore of Pigeon Point and adjacent
map area. This boundary likely shifts seaward or landward based on seasonal to decadal changes in sediment supply, sediment
transport, and wave climate. More coarse-grained sands and gravels (units Qmss and Qmsc) are primarily recognized on the basis
of high backscatter. Unit Qmsc occurs as a nearshore, shore-parallel bar at typical water depths between 5 and 10 meters.
Unit Qmss forms erosional lags in rippled scour depressions (for example, Cacchione and others, 1984) at water depths of about
25 to 35 m, in contact with offshore bedrock uplifts and unit Qms. Although the general areas in which unit Qmsc and unit
Qmss occur are not likely to change substantially, the boundaries of the unit(s) are likely ephemeral, changing seasonally
and during significant storm events. Unit Qmss deposits are common along this stretch of the California coast where offshore
sandy sediment can be relatively thin (thus unable to fill the depressions) due to both lack of river input and to significant
sediment erosion and offshore sediment transport during large northwest winter swells. Areas where shelf sediments form thin
(< 2.5 m or less) veneers over low relief, undivided Cretaceous and (or) Tertiary bedrock are mapped as units Qms/TKu and
Qms/Tp. These areas are recognized based on the combination of flat relief, continuity with moderate to high relief bedrock
outcrops, high-resolution seismic-reflection data, and in some cases moderate backscatter. These units are regarded as ephemeral
and dynamic sediment layers that may or may not be present based on storms, seasonal/annual patterns of sediment movement,
or climate cycles. Tertiary deposits mapped in the offshore include two units of the Purisima Formation (units Tp and Tpt).
The Purisima units are characterized by high backscatter and distinct bedding recognized in multibeam imagery and/or seismic-reflection
data. These Tertiary rocks are underlain by or in fault contact with Upper Cretaceous basement rocks, including sedimentary
rocks of the Pigeon Point Formation (unit Kpp). The Pigeon Point Formation is mapped on the basis of high backscatter, massive
and (or) rugged texture on multibeam imagery, and reflection-free character on seismic-reflection data. Offshore outcrops
of the Pigeon Point Formation form the offshore Pigeon Point high, a major structural feature that extends ~30 km to the northwest
and represents the northeast boundary of the Outer Santa Cruz Basin (McCulloch, 1987). Areas where bedrock is exposed on the
seafloor but there is less certainty regarding age are mapped as Cretaceous and Tertiary, undivided (unit TKu). Map unit polygons
were digitized over underlying 2-meter base layers developed from multibeam bathymetry and backscatter data (see "Bathymetry--Offshore
of Pigeon Point Map Area, California" and "Backscatter--Offshore of Pigeon Point Map Area, California"). The
bathymetry and backscatter data were collected between 2006 and 2010. References Cited 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. 1280-1291. Lambeck, K., and Chappell, J., 2001, Sea level change through the last glacial cycle: Science,
v. 292, p. 679-686. McCulloch, D.S., 1987, Regional geology and hydrocarbon potential of offshore Central California, in Scholl,
D.W., Grantz, A., and Vedder, J.G., eds., Geology and resource potential of the continental margin of Western North America
and adjacent ocean basins - Beaufort Sea to Baja California: Circum-Pacific Council for Energy and Mineral Resources Earth
Science Series, v. 6, p. 353-401. 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, http://pubs.usgs.gov/ds/2006/182/.
Citation
- Title Geology and geomorphology--Offshore Pigeon Point, California.
-
- creation Date
2018-05-21T12:54:57.938670
Resource language:
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Metadata data stamp:
2018-08-06T23:53:41Z
Resource Maintenance Information
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- notes: This metadata record was generated by an xslt transformation from a dc metadata record; Transform by Stephen M. Richard, based
on a transform by Damian Ulbricht. Run on 2018-08-06T23:53:41Z
Metadata contact
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pointOfContact
- organisation Name
CINERGI Metadata catalog
-
- Contact information
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- Address
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- electronic Mail Address cinergi@sdsc.edu
Metadata language
eng
Metadata character set encoding:
utf8
Metadata standard for this record:
ISO 19139 Geographic Information - Metadata - Implementation Specification
standard version:
2007
Metadata record identifier:
urn:dciso:metadataabout:f75dfb1f-46c5-41a7-9830-8e285621bc67
Metadata record format is ISO19139 XML (MD_Metadata)