THE ORIGIN, EVOLUTION, AND CONTEMPORARY MORPHOLOGY OF
SOQUEL SUBMARINE CANYON, MONTEREY BAY, CALIFORNIA
A Thesis
Presented to San jose State UniYersity
and
!\loss Landing l\!arine Laboratories
In Partial Fulfillment
of the Requirements for the Degree
!\laster of Science
By
Deidre Ellen Sullivan
December, 199-1
© 1994
Deidre Ellen Sullivan
ALL RIGHTS RESERVED
ABSTRACT
THE ORIGIN, EVOLUTION, AND CONTEMPORARY MORPHOLOGY OF SOQUEL SUBMARINE CANYON, MONTEREY BAY, CALIFORNIA
by Deidre Ellen Sullivan
Soquel Canyon is the product of eustatic, tectonic, biological and
erosional processes. Soquel Canyon formed as the San Lorenzo River cut
across the emergent continental shelf during Pleistocene low stands of sea
level. At least three erosional episodes have taken place. Faulting and gas
discharge may have influenced the position of the canyon head. Extensive
mass wasting, in the past, is indicated by the large area covered by slumps
(40% of the 17 km2 surveyed). Presently, erosion in Soquel Canyon is less
vigorous and visible signs of erosion include biological modification, stress
release fracturing, water currents, and mass wasting on a small-scale.
ACKNOWLEDGMENTS
I would like to acknowledge the help and support of many people in
completing this thesis: Gary Greene for assuming the role of thesis advisor and
providing much needed e:,:pertise on the geology of !v!onterey Bay, l\1ik.e
Ledbetter my former advisor for his excellent presentation of the field of
marine geology, and Greg Cailliet for his thoughtful review of this
manuscript. I wish to give special thanks to Mary Yoklavich for her guidance
and support that made this study possible.
This study involved many people and many modes of transportation. I
thank. the captains and crew of the R/V jolly Roger, R/V ca,·afier, R/V McGaw,
Delta Oceanographics, and R/V Point Sur. The U.S. Geological Survey, Branch
of Pacific 1\!arine Geology provided navigational plots for each cruise, merged
data sets to produce bathymetric maps of Soquel Canyon, and reproduced
sonographs. I would like to thank. Clint Steele, Carolyn Degnan, Harry Lucky,
Tom Chase and Mike Boyle of the Survey for their assistance. Side scan sonar
data was e:>.:pertly gathered by David Caswell of Pelagos, San Diego. A special
thanks to Lynn McMasters for her help with figures. The help of fellow
students judy Mariant, Bob Barminski and Karen Press with data logging
during long cold nights on the geophysical cruises was much appreciated. I'd
like to thank Shelia Baldridge for finding obscure geology literature and not
forgetting the Geology Lab, or should I say me. I greatly appreciated the
organization and professionalism of the Moss Landing Marine Laboratories
administrative staff. Most of all I would like to thank my parents for their
support and encouragement in pursuing a graduate degree.
Research was supported by National Undersea Research Program, West
Coast Center, Fairbanks, Alaska (#CA 92-02, #CA 93-04). The Packard
Foundation provided a travel stipend to present my results at AGU Ocean
Sciences 1994, San Diego, CA.
\'
TABLE OF CONTENTS
ACKNOWLEDGMENTS .......................................................................................... v
UST OF FIGURES AND TABLES .................. :......................................................... vii
ABSTRACT ............................................................................................................. \'iii
INTRODUCTION .................................................................................................... 1
Geologic Setting ........................................................................................ 3
Stratigraphy .............................................................................................. 5
METHODS.............................................................................................................. 11
Bathymetric Mapping .............................................................................. 11
Side Scan Sonar Data ............................................................................... 13
Seismic Reflection Data ........................................................................... 15
Submersible Operations .......................................................................... 15
RESULTS................................................................................................................ 20
Geophysical Mapping .............................................................................. 20
Submersible Observations ....................................................................... 3 5
DISCUSSION .......................................................................................................... 45
Origin and Evolution of Soquel Canyon ................................................ 45
Small-Scale Geology from Submersible Operations .............................. 50
CONCLUSIONS ....................................................................................................... 54
REFERENCES .......................................................................................................... 56
APPENDICES.......................................................................................................... 61
vi
LIST OF FIGURES
Fig. 1. Location map of the study area ............................................................ 4
Fig. 2. Geologic structure map of Monterey Bay region ................................ 6
Fig. 3. Stratigraphy of Monterey Bay ............................................................... 7
Fig. 4. Purisima Formation exposed ................................................................. l 0
Fig. 5. Ship's track for the 3.5 kHz bathymetric survey................................ 12
Fig. 6. Ship's track for the side scan survey.................................................... 14
Fig. 7. Ship's track for the seismic reflection survey...................................... 17
Fig. 8. Submersible tracks for the Delta .......................................................... 18
Fig. 9. The Delta Submersible ............................................................................ 19
Fig. 10. Bathymetric chart generated from 3.5 kHz profiles........................... 21
Fig. 11. Computer generated physiographic diagram ...................................... 22
Fig. 12. Map showing various segments of Soquel Canyon .............................. 23
Fig. 13. A 3.5 kHz profiles of Soquel Canyon.................................................... 24
Fig. 14. l\lap showing location of slump deposits ............................................. 26
Fig. 15. A 3.5 kHz profile of a slump.................................................................. 27
Fig. 16. Line drawn interpretation of side scan sonographs ........................... 28
Fig. 17. Side scan sonographs of rocky ex-posures ............................................ 29
Fig. 18. Side scan sonographs of mass wasting ................................................. 31
Fig. 19. Seismic reflection profile shoreward of canyon head ......................... 32
Fig. 20. Correlation of faults or channel walls ................................................... 33
Fig. 21. Gas anomaly in the water column ......................................................... 34
Fig. 22. Float rock collected by the submersible ............................................... 36
Fig. 23. Diagram of Dive #2978 .......................................................................... 38
Fig. 24. Photographs from the submersible ....................................................... 40
Fig. 25. Sea-level curve of the Neogene .............................................................. 46
vii
ABSTRACT
Seventeen square kilometers of seafloor in Soquel Canyon, one of the
tributaries to the Monterey Canyon system off central Califon1ia, was
surveyed using 1) a 3.5 kHz depth recorder 2) a side scan sonar 3) a seismic
reflection profiler and 4) the Delta submersible in 1992 and 1993. Surveys
revealed a canyon of steep to gentle relief with close to 40% of the area
covered with well-defined slump deposits. Over one hundred linear outcrops
paralleling the canyon axis were detected. All rocky outcrops consis l of the
Pliocene Purisima Formation, a nearshore marine deposit.
The origin, evolution, and present morphology of Soquel Canyon are
the result of complex interactions of eustatic, tectonic, biological, and
erosional processes. Soquel Canyon fonned during the Pleistocene as a river,
probably the San Lorenzo, cut across the emergent continental shelf during a
low stand of sea level. Faulting and gas discharge may ha,·e influenced the
positioning of the head of Soquel Canyon. Based on sequence stratigraphy, at
least three major erosional episodes took place during Pleistocene low stands
of sea le\·el as the head of Soquel Canyon intercepted littoral and fluvial
sediments. Mass wasting and turbidity currents during these periods were
most important volumetrically in excavating and shaping the canyon.
Soquel Canyon, during the present high stand of sea level, is cut off
from coastal sediment supplies, resulting in a much less active canyon.
Presently, potential erosional processes modifying Soquel Canyon include
bioerosion and bioturbation, stress release fracturing, various water
currents, and mass wasting on a small-scale.
viii
INTRODUCTION
Soquel Canyon is one of the smallest and least studied of six canyons in
the Ascension-Monterey Canyon System, which includes Ascension, Ano
Nuevo, Cabrillo, Monterey, Soquel, and ~armel Canyons. The origin of Soquel
Canyon is uncertain. Previous studies have suggested subaerial erosion by the
San Lorenzo River flowing from the north across the shelf during the last low
stand of sea level (Martin, 1964; Greene, 1977), but there has been no direct
evidence to support this. This inference is not une>;pected because the
inception of many submarine canyons is generally thought to occur under
similar conditions (Shepard, 1952; Shepard, 1981; May eta!., 1983 ).
Other processes that have been proposed to influence submarine
canyon formation and modification include faulting, turbidity currents, water
currents, artesian spring sapping, fluid flow, biological modification,
tsunamis, and mass wasting (Shepard and Dill, 1966; Inman eta!., 1976; Greene,
1977; Shepard and Marshall, 1973; Shepard, 1981; May et al., 1983; Nagel et al.,
1986; Paull et al., 1990; Orange et al., 1993 ). The importance of each of these
processes varies regionally and over time. The effects of turbidity currents
and mass wasting generally dominate, but during high stands of sea level
canyon heads may be removed from sediment sources and become dormant
(!\-lay et al., 1983). During high stands of sea level, modification by biological
activity and water currents may be significant agents of canyon erosion
(Dillion and Zimmerman, 1970; Rowe et a!., 197 4; Warme eta!., 197 8; Valentine
et al., 1980; Hecker, 1982; Twichell et al., 1985 ).
Submarine canyons form a unique interface between the shallow
continental shelf and deep continental slope marine environments and
contain a variety of substrata, such as rock walls, ledges, talus slopes, and large
slumps, in close association. Surveying benthic canyon environments is
difficult and expensive, because of the steep and rugged relief. There is an
increasing need, however, to describe canyon geology and faunal associations
as more activities, such as fishing, dumping, and marine transport, target
these locations.
A study to assess deep-water rockfish populations and their habitat
associations in Soquel Submarine Canyon, Monterey Bay, central California,
was conducted in 1992 and 1993. The geology of the canyon was mapped and
described in detail to identify and quantify suitable rockfish habitat. The area
of primary interest was from 90 to 400 m in the canyon. The study was carried
out using data from 3. 5 kHz depth recorders, side scan sonar, seismic reflection
and a manned submersible. Synthesis of these data resulted in a more detailed
description of present morphology than in previous studies of Soquel Canyon
(lv!artin, 1964; Greene, 1977).
The geological portion of this multi disciplined study had three
objectives. The first was to provide direct evidence of the origin of Soquel
Canyon. The second was to describe the processes that may have contributed to
present canyon morphology. The third was to describe the canyon's geology
on a small spatial scale from submersible observations, and speculate on
processes that presently influence canyon erosion.
2
Geologic Setting
Monterey Canyon system, comprising Monterey, Soquel, and Carmel
Canyons, is located offshore of central California, and is the largest submarine
canyon system along the conterminous United States. The vertical relief of
the l\lonterey Canyon is comparable to that of the Grand Canyon of the
Colorado River (l\lartin, 1964; Shepard and Dill, 1966). The head of Monterey
Canyon begins less than 100m offshore of Moss Landing in the central region
of l\!onterey Bay, approximately 115 km south of San Francisco (Fig. 1 ). Soquel
Canyon is the shallowest canyon to intersect the Monterey Canyon 18 km west
of l\Ionterey Canyon's head at a depth of 915 m (Greene eta!., 1989). Carmel
Canyon joins Monterey Canyon 30 km southwest from the head of l\lonterey
Canyon at a depth of 1900 m. To the north, the Ascension Canyon system joins
the Monterey Fan-Valley system near the base of the continental slope at 3290
m.
The Monterey Submarine Canyon system along with the sou them
Coastal Ranges and valleys of west-central Califomia is located on an
allochthonous crustal block referred to as the Salinian terrane (Page, 1970).
The San Andreas fault, and the offshore Palo Colorado- San Gregorio and
onshore Sur-Nacimiento fault zones form the northeast and southwest
boundaries, respectively, of the block, which extends from the Transverse
Ranges northward to Cape l'v!endocino (Page, 1970). It is not clear how far the
Salinian block has been displaced from its point of origin, however, most
minimum estimates are in the range of 350 km (Graham, 1976; Page and
Engebretson, 1984 ).
Faults in the Monterey Bay region lie primarily within two north\l·est
trending converging fault zones, the Palo Colorado-San Gregorio and the
3
122' 55' 122' 50' 122' 45'
--------~
i i .. , o··,_
<;/.:, / 1': ·-, 36' 55' o,. ..
'/>--'•) . -- ..
36' 50'
36' 45'
36' 40'
S.F. =San Fransisco 0 1 2
Nautical Miles 0 5
Kilometers
Bathymetric base map taken !rom NOAA char! N365121W, N36122W
Depth contours in meters
Figure 1. Location map of the study area.
4
Monterey Bay (Greene, 1990) (Fig. 2). Soquel Canyon lies within the Monterey
Bay fault zone. Faults of the Monterey Bay zone have been identified from
high resolution seismic reflection profiles (Greene et al., 1973; Greene 1977;
Gardner-Taggart et al., 1993). This 10)5 km wide fault zone consists of
discontinuous en echelon faults trending N50°W. Gardner-Taggart (1991)
reports two types of faults in the southern part of the Monterey Bay fault zone,
normal or strike-slip and thrust. The primary NW-SE oriented faults appear as
right lateral-strike slip faults whereas the conjugate faults are thrust faults
and generally trend E-W (Gardner-Taggart, 1991). Most of these faults cut the
sea floor and displace Pliocene deposits.
Stratigraphy
The geology of the Monterey Bay region has been mapped extensively
onshore by Clark et al. (1974) and Clark (1981), and offshore by Ivlartin (1964)
and Greene (1977). The stratigraphy reflects a complicated late Cenozoic
tectonic history of uplift and depression that has produced a succession of
regressive and transgressive sedimentary units (Greene, 1977; Greene and
Clark, 1979). Greene (1977) correlated four distinct seismic stratigraphic
sequences with major onshore sequences: (1) Mesozoic basement rocks
overlain by sedimentary sequences of (2) middle Miocene, (3) upper Miocene
to Pliocene, and ( 4) upper Pliocene to Holocene ages (Fig. 3 ).
The Mesozoic basement consists of granodiorite and underlies all of
Monterey Bay. Greene (1977) refers to a basement called "Monterey High" that
extends northeastward from the city of Monterey to Aptos. This basement high
is bisected by the submarine Monterey Canyon. Greene (1977) suggests that
the Monterey High has undergone episodes of uplift from the early l\!iocene to
5
Figure 2. Geologic structure map of the Monterey Bay region showing locations of faults, folds and major physiographic features. Outline of submarine canyon shown in broad, gray lines; Monterey Canyon axis shown by broad, gray, dashed line. (from Greene, 1990).
6
w u z
AGE w 0 0 w •
> . " < 0 z ' " " w
" < 0 0 ' ';;~
:!:':: ~
" ~
1- ~
> j " < ~ . ' " w
" ~~ . f-0
0
i
' ' • ~ MESOZOIC
OR OLDER
AGE
CLOER
Figure 3.
NORTHERN MONTEREY BAY REGION
FORMAT !ON
Recent marine sedi..,ents
0 ' '"" 0 - Submarine 1 and - 0 !.~;~es and slump c 0 , 0 <>rill ~~
Canyon fl 11 / material
Aromas Sand
Deltaic material
Purlsi"'a F ormil t ion
" Santa Cruz Mudstone of Clark ( 1966b}
Sante Margarita(?)
~ Monterey Fon::Hlon
Granitic rocks (crystallin~ base:n~nt}
THICK-
LITHOLOGY NESS (mtltrl)
* 40
240
DESCRIPTION
Rec~ntl}' depo;i ted muine sand and mud.
Subrr.olrir.e landslide and slump ~1aterial
g 50 Gravel, sand, and mud; ~o,ue broHm <.:·"": consolidated materli!l.
.':·.:~;,; 300 \~ell sort~d. cross-bedded, ~uarnose sand~ '.::·_;~ nonmarine, eolian. fluvial 1oco11y at ba>~
§::2, \__'_'_f-'-'_"_'_'_"_'_"_"_'_'_"_''_'_'"_'_·_'_'_'_"_'_'_· _______ ~
~·== c~:~2 ~:.~':
670•
~:~·. 200+
~~---=--
X X X X X X X
X X X X X X X
X X X
370?
550
{;reenl sh-gray, semi -consol il!,n~~ to conoolid,J!ed sandston~. siltstone, and sMll'; marin~. generally fossiliferous.
Siliceous. organic mud;tone; m~rine
Bedded arkosic sandstone{?)
Li~ht olive-~r3y, rhythmically bedded, oroonic mudstone, diato~laceous df'ld ~ificeous st1ale MIC siltstone; r.:arine .
Probab 1 y rredo.Hi nantl y granod i ori te.
SOUTHERN MONTEREY BAY REGION
FORMATION
Monterey Formation
Granitic rocl:s (Crystalline basement)
DESCRIPTION
Light olive-gray, rhythmtu11y bedded, org<111ic mudstone, diatomac~OliS and siliceous shale and siltstone; marine
5a~e of unit locally contains coar~o-grained, 11hite, granitiC or ~rl.osic sandstone
Predominantly porphyritic biotite granodiorite
Stratigraphy of the Monterey Bay (from Greene, 1977).
7
Holocene based on progressiYely shallowing benthic micro-fossils in the
overlying sedimental}' units.
In northern Monterey Bay, the middle Miocene Santa Cruz Mudstone,
the late 1\liocene Santa Margarita Sandstone, and the Pliocene Purisima
Formation unconformably overlie the Monterey Formation and in some areas
the basement rocks. In southern Monterey Bay, the Purisima Formation
unconformably overlies the Monterey Formation. This change in
stratigraphy represents a time transgressive sequence with several facies
changes resulting from a general north to south transgression (Greene, 1977).
Rock exposures in the study area of Soquel Canyon are predominantly
from the Purisima Formation. The offshore thickness of the Purisima
Formation ranges from zero meters in the Monterey bight to 600 min the
northwestern part of the Bay (Greene, 1977). The Purisima Formation
mapped in the northern Santa Cruz Mountains consists of marine, fine-
grained sandstone, shale and conglomerate and has a maximum thickness of
1,722 m (Cummings eta!., 1962; Clark, 1981 ). The formation has been divided
into five major lithologic members (Cummings eta!., 1962). From dredge
samples collected in Soquel Canyon, Greene ( 1977) has identified the
presence of three of these Members: Tahana, Pomponio, and San Gregorio.
The Tahana Member forms the basal part of the Purisima Formation and
consists of medium to fine grained sandstone and siltstone with pebble
conglomerate beds at its base. The Pomponio Member consists of alternating
beds of silicified mudstone, siltstone and porcellanite. The San Gregorio
Member consists of fine to coarse grained massi\·e sandstone with
irregularly distributed pebbles of chert and volcanic rocks (Cummings et. a!,
1962). Megafossils are common throughout the Purisima.
8
The Purisima Formation is an important aquifer on land (Greene,
1970). Groundwater can be seen flowing from bedding contacts in the sea
cliffs at Capitola Beach, California (Fig. 4).
Holocene sediment unconformably m·erlies the Purisima Formation and
the Aromas Sands in northern Monterey Bay. These deposits extend as an
elongate body from the mouth of the Pajaro River westward for more than 25
km and attain a ma'>dmum thickness of nearly 40 m thick near the head of
Soquel Canyon (Greene, 1977).
9
Figure 4. Purisima Formation exposed along the sea cliffs in Capitola south of Santa Cruz. Groundwater can be seen flowing out from bedding contacts.
METHODS
Data for geological mapping in Soquel Canyon were collected using four
methodologies during four cruises. A bathymetric survey of Soquel Canyon
was conducted aboard the R/V Point Slfr. March 20-21, 1992. A side scan sonar
survey of Soquel Canyon was conducted aboard the 1\1/V jolly Roger, August
21-27, 1992. Ground truthing of sonographs also was conducted during this
cruise by in situ obsen·ations from the Delta submersible. During the third
cruise aboard the M/V McGaw seismic reflection data were collected in Soquel
Canyon, June 7-14, 1993. During the forth cruise, we continued detailed
observations of Soquel Canyon morphology aboard the M/V Cavalier using the
Delta submersible, October 5-15, 1993.
Bathymetric Mapping
High resolution bathymetric mapping of Soquel Canyon was
accomplished using a 3.5 kHz precision depth recorder to produce profiles of
the sea floor. A Trimble lOX Loran-GPS (Global Positioning System) with± 15m
accuracy was used to estimate position. Ship track lines were run at 80 m
intervals (Fig. 5; Appendix 1). The precision depth recorder penetrated 20-
50+ m beneath the ocean floor, and was used to distinguish hard from soft
bottom. All bathymetric profiles were digitized at the U.S. Geological Sun,ey
(USGS}, Branch of Pacific Marine Geology, and these data were merged with
navigational data to construct a detailed bathymetric chart of Soquel Canyon at
20m contour inten,als. Erroneous data points were identified visually then
removed if obviously incompatible with original bathymetric profiles.
Physiographical representations of the bathymetric data also were produced at
the USGS to aid in visualizing the canyon morphology.
11
122"01' 121 '57'
Figure 5. Ship's track during the 3.5 kHz bathymetric survey in Soquel Canyon.
12
Side Scan Sonar Data
The side scan sonar survey was conducted with EG&G sonar equipment
and technical personnel contracted from Pelagos Corporation, San Diego,
California. Navigation data were collected with a differential GPS (±. 1 m
accuracy) on loan from 1\lonterey Bay Aquarium Research Institute (MBARI),
using the differential-correction signal broadcast from Mt. Taro.
13
Side scan sonar produces images similar to low-angle, oblique, aerial
photography, except that the images are based on differences in the intensity
of reflected acoustical sound rather than reflected light (Belderson et al.,
1972). The images produced on the side scan sonographs largely are
determined by two factors, topography and fine scale texture of the ocean
bottom (Able eta!., 1987). Topographic features such as ledges, vertical walls,
and boulders produce dark and light images on the records depending upon
the orientation of the relief. A strong signal (dark) is received from the side
of the feature facing the transducer while a weak signal or shadow (light) is
received from the side sloping away from the transducer. Sediment size also
impacts the acoustic signal. For example, gravel produces a much stronger
return signal than mud because the many small facets facing the tranducers
appear as a darker gray while mud appears much lighter. These textural
differences can be distinguished from topographic differences because there
is no shadow associated with them.
A 1. 5 m long towfish that emitted a 100 kHz acoustic signal was towed
behind the ship at 3.5 knots. The acoustic signal produced a swath width of 600
m, 300m per side. One hundred and ten kilometers of track lines were
recorded (Fig 6; Appendix II). Because of steep relief, two hundred percent
overlap was necessary to produce a complete mosaic of the canyon. Records
36' 50'
122°01' 122'00' 121 °58'
Figure 6. Ship's track during the side scan survey in Soquel Canyon.
14
were microfilmed and photographically reproduced at the USGS to construct a
mosaic of Soquel Canyon.
Seismic Reflection Data
Seventy kilometers of seismic reflection data were collected on the
continental shelf north of Soquel Canyon (Fig. 7; Appendix III). Single
channel seismic reflection data were collected using a dual plate Geopulse
58 lOA sound source fired by a Geopulse 5-+20A power supply. A sweep of 112
second was used with a maximum power output of 900 joules. Recording
frequencies were from 500Hz to 1500Hz. A filter was attached to the
triggering device on the recorder to eliminate noise or erroneous signals. .L\n
EPC -+BOO recorder produced analog records and data were stored
simultaneously on a 16 bit digital optical disk at 8kHz. Stratigraphic resolution
of this system is about 2 meters. Sub-bottom penetration averaged about 80
meters.
Seismic reflection involves measuring the time required for a seismic
wave (or pulse) generated by a mechanical impact to return to the surface
after reflection from subsurface interfaces. An interface between two layers
may be detected if the acoustic impedance (product of acoutic velocity and
density) of the layers is different (Ewing and Ewing, 1970).
Submersible Operations
TVI·enty-nine submersible dives were made from August 21-27, 1992, and
22 dives were made from October 5-15, 1993, in Soquel Canyon using the Della
submersible (Fig 8). The Delta is a 4.7 m long two-person submersible that has
an operational depth to 380m (Fig. 9). A fusion track point system coupled
with the ship's navigation allowed for precision navigation of the
submersible. Of the 51 submersible dives, 8 dives specifically were devoted to
15
describing canyon geology on a small spatial scale (6 of the 8 are described in
the results). The primary objective of the other 43 dives was to survey fish
assemblages and associated habitat. All the dives were recorded
simultaneously by externally and internally mounted video (Hi-8) and still (35
mm) cameras. The video tapes include a voice overlay. The video tapes of the
fish surveys were reviewed to verify interpretations of remotely-sensed
images from 3.5 kHz bathymetric and side scan surveys. Rock samples were
taken with a manually operated remote arm from the submersible.
16
36' 59,.--------,\---------,------------------~-----------.
Santa Cruz
36' 55'
36' 50'
-122'
18
-121'55'
3
155 ls4 As
·121'50'
Moss Landing
Figure 7. Ship's track during the seismic reflection surYey in Monterey Bay, northeast of the head of Soquel Canyon.
17
36° 51'
36' 50'
36' 49'
122'01' 122'00' 121 '59' 121 '58'
Figure 8. Track lines of the Delta submersible in Soquel Canyon. Sites of dives dedicated to geologic characterization are indicated by the bold lines with corresponding dive number. The gray lines are fish suf\'ey dives.
18
19
f'igure 9. The Delta Submersible of Delta Oceanographics.
RESULTS
Geophysical Mapping
From the bathymetric chart constructed from 3.5 kHz bathymetric
profiles, Soquel Canyon is steeper and more rugged than previously
interpreted from NOAA Sea Beam bathymetric data (Fig. 10; Map 1). The steep
relief and gentle slopes of the canyon were vizualized easily from the
physiographic diagram (Fig. 11 ), to give an overall impression of canyon
morphology. Bathymetric data indicate that the head of Soquel Canyon begins
9 km south of Santa Cruz at a water depth of 90 m. From the canyon head the
axis trends 205° (S25°W) for 4.5 km then abruptly bends twice, first west then
south to continue along a new trend of 195'' (S15'W). The canyon continues
along this trend for 5 km at which point it joins the Monterey Canyon at a
20
depth just over 900 m. This study co\·ered the first 6.7 km of the canyon
(approximately 2/3 of the canyon) in the 90- 400 m depth range. At this point,
i.e., 6.7 km from the head, the canyon is 3.5 km wide and 650 m deep at the axis.
Seventeen square kilometers were surveyed. For reference, the canyon is
broken into four segments (with respective lengths): head (1.4 km), central
(1.8 km), bends (1.3 km), and lower segment (2.2 km) (Fig. 12). Each segment
has a west and east wall. The southen1most 4 km of the canyon were not
examined in this study.
The head of Soquel Canyon is U-shaped in profile with the exception of
the thal\\·eg, the deepest part of channel (Fig. 13a). The central segment
exhibits a steep V-shaped profile (Fig. 13b). Farther to the south the lower
segment of the canyon has aU-shaped profile and unconsolidated material has
accumulated in the axis (Fig. 13c). A thalweg breaches the eastern side of the
36°~----------------------------------------------~ 52'
36° 50'
36° 49'
121 '58
Figure 10. Bathymetric chart generated from 3.5 kHz bottom profile survey. Contours are at 20m intervals.
21
i
\
\ I
\
\ \
\ \ '
\
22
36' 52'
36' 51'
36'' 50'
36' 49'
'"""'
t..':l::J ~ /
/
/
c -a " "' E " Cl I <ll
rJl
iii c <ll
c E <ll Cl () <ll
rJl
c "' <ll -a E c <ll Cl
CD " rJl
:;; c <ll
:: E 0 Cl -' " rJl
122'01' 122'00' 121 '59' 121 '58' 121 '57'
Figure 12. Various segments of Soquel Canyon studied in this investigation. The lines and numbers correspond to figure numbers and locations.
23
24
Lmc 14 w
w ~Ill!:''' ,~.,._.,,.!,,_.,
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... , __ .._ ___ ,, __ _ .. ,.,...,._, ... _
""' """' "~
Lme wG
""'"- --'"'""-
f . ' ,. ... ·.,
Figure 13. (a) A 3.5 kHz profile across the head of Soquel Canyon showing Ushaped profile and thalweg. (b) A 3.5 kHz profile across the central region of Soquel Canyon showing V-shaped profile. (c) A 3.5 kHz profile across the lower region of Soquel Canyon showing U-shaped profile and recently eroded sediment pond on the right side of the canyon axis. (d) A 3.5 kHz profile showing extreme relief along a portion of the west wall of Soquel Canyon representative of the many small tributaries that cut canyon walls. See Fig. 12 for exact locations.
200 g
J50
ponded sediment in the lower segment profile. In some areas, such as the west
canyon wall in the central region, relief can vary greatly and the walls are
cut by small channels and gullies up to a 100m in depth (Fig. 13d ).
Close to 40% of the study area.was covered with 20m or more of slumped
material as indicated from the interpretations of 3.5 kHz profiles. These slump
deposits covered large parts of the canyon walls and portions of the canyon
axis (Fig. 14). In the bends segment of the canyon two extensive rock
exposures were identified on each canyon wall from the 3.5 kHz profiles; on
the west wall the rocky exposure is close to 1 km2 and on the east wall the
rocky area is half the size. Large slump deposits were found along both walls
of the central and lower segments of the canyon. Many of these deposits and
slump scarps exhibit youthful geomorphology indicated by sharp relief, little
or no sediment cover, the hummocky nature of the surface, and informal
stratigraphy of the deposits (Fig. 15).
The side scan sonographs indicate that Soquel Canyon has a series of
reflectors along the canyon walls that parallel the axis of the canyon (Fig. 16).
These reflectors were verified from submersible observations as exposures or
outcrops of the Purisima Formation composed of sandstone, mudstone and
coquina that form ledges running along the canyon walls. In the area of the
two large rocky exposures at the bends segment of the canyon, the side scan
sonographs revealed tens of closely spaced reflectors, or ledges, running
parallel to the canyon axis (Fig. 17a). Outside of the rocky exposures more
than fifty small groups and isolated individual reflectors (outcrops) were
identified from side scan sonograph throughout the canyon surrounded by
mud (Fig 17b). Some of these isolated reflectors were not detected in the 3.5
kHz profiles. Signs of past mass movement, such as block glides, and slump
36° 52'
36' 51'
/ I
/ /
/
..... -, /
122'01' 122'00' 121 '59' 121 °58' 12P57'
- - - - Inferred Scarps millJ Slump Deposits> 20m thick
Figure 14. Map showing location of slump deposits based on 3.5kHz profiles.
26
N
.,.,
Line wk
'•"'··""·""'· Lll!=-.,... .... JU:l..'JJ.AIIIIli..!J....lU llWrPI~
"'-~IUU 5e !lll.l..LntiP l'ftll--.--!!~~ fllllll IIPI_(b_ llH!OWlfU"_
-"-ltalf!l
--~----~
s
100
150 0 CD
"!l. :r
2003 ~ CD til
250 em
~ (/)
300 ill ~ ~
350
400
450
Figure 15. A 3.5 kHz profile of a slump deposit along the west wall of the lower segment in Soquel Canyon showing its hummocky nature. See Fig. 12 for exact location.
36° 52'
36° 51'
36' 50'
36° 49'
Figure 16.
c: "0 "' "' E "' "' I Ql
Ul
-C: !!' "' C: E Ql "' () "' Ul
"' c:
"0 " c: E " "' rn " Ul
'" c: " ;:: E
0 "' _J " Ul
Une drawn interpretation of side scan sonographs of Soquel Canyon; the dark lines are reflectors (outcrops).
28
120m Line 21
(a)
120m Line 24
',_', :
Figure 17. (a) Individual sonograph of the rocky exposure on the west wall of Soquel Canyon. (b) Individual sonograph of isolated outcrops found in the headward segment of Soquel Canyon. See Fig. 12 for exact locations.
29
scarps, were inferred from the side scan sonographs and verified by
submersible observations in many parts of the canyon (Fig. 18).
Horizontal bedding of the Purisima Formation that is overlain by recent
unconsolidated sediment from the shelf was determined from seismic
reflection profiles. Gas charged sediments (bright spots) along buried eroded
channel wails or faults and within folds were identified from two closely
spaced profiles running perpendicular to the axis just shoreward of the head
of Soquel Canyon. In addition, at least four buried channels can be identified
within these folds in the profiles (Fig. 19). Correlation of the buried channel
walls or faults from track line to track line indicate a trend of approximately
02S (or N25'E or S25"W; Fig. 20). The depth to which the buried channel walls
or faults extend could not be determined because of the loss of signal, however,
these features are truncated by an inferred erosional surface that is covered
by approximately 15 m of undisturbed flat lying sediment. Water column
anomalies on the 3.5 kHz profiles also suggest gas discharge along these faults
or channel walls (Fig. 21 ). This water column anomaly could also indicate an
aggregation of pelagic fishes, but the close alignment to the buried channel
walls or faults and the configuration of the plume in the overlying water
column suggest gas bubbles.
30
120m Line 26
+ + + + +
+
(a) ..
300m
Figure 18. (a) Side scan sonograph of a block glide found near the head of Soquel Canyon. (b) Side scan mosaic of slump scarps on the west wall of the central segment of Soquel Canyon. See Fig. 12 for exact locations.
31
(a)
(b)
Line 64
> :..:::: •• - ••
~0
\\ \~10 4030 20
Figure 19. Geopulse seismic reflection profile (line (J4) just shoreward of the head of Soquel Canyon. (a) uninterpreted seismic reflection profile (b) interpreted profile showing three faults or eroded channel walls and four buried channels. The bold lines show angular unconformities that are inferred erosional surfaces. The bright spots (light areas) are inferred gas charged sediments. See Fig. 2.0 for exact location.
0
32.
0 <P
"!/. 58 ::r
3 ~ <P iil
77 Ci" <P 0
" "' 95 2l ~ ~
113 ~ :J 0 0
132 ~ <n Eo
36' 59',---------,---------.------------------,------------,
36' 55'
36' 50'
Santa Cruz
-122'
Figure 20.
68
-121'55'
64
Moss Landing
Correlation of faults or channels walls from track line 64 to track line 68 showing trend of features. * Denotes the location of the gas anomaly in Figure 21.
33
34
Figure 21. Anomaly in the water column interpreted as discharge from a gas seep. See Fig. 20 for exact location.
Submersible Observations
Observations from the submersible were critical to interpretations of
remotely-collected data. The location, size, and substratum type of reflectors
(outcrops) that were identified on the side-scan songraphs were verified by in
situ obsen·ations from the submersible. Using differential GPS, the fusion
track point system, and depth of submersible, we also improved the
bathymetric data on a fine scale. We verified the lithology of the reflectors
with rock samples collected from the submersible.
The three samples were float rock composed of sandstone from the
Purisima Formation, as would be expected from previous investigations of the
area (Greene, 1977). The samples appeared to be derived from the outcrops
close to point of collection. Samples were not collected directly from the
outcrops because the submersible's mechanical arm was not appropriate. The
samples appeared to ha,·e been in place for some time because encrusting
organisms (e.g., solitary cup corals) were found on the top side of all the rocks.
Borings by invertebrates also were present in all the samples, however the
organisms responsible for the boring were not obsen•ed (Fig 22).
Six dives were dedicated to geologic obsen•ations and verification of
remotely collected data from Soquel Canyon. Relief, substratum type, size and
depth range of features, and signs of small-scale canyon modification were
described. See Figure 8 for dive locations.
On some dives bottom currents carrying suspended material decreased
visibility and made it difficult to maneuver the submersible. Current speeds
estimated from the submersible cruising speed and distance covered were close
to one knot.
35
Figure 22. Float rock collected by the submersible. Note the borings, solitary coral and the megafossils characteristic of the Purisima Formation.
36
37
Dive 7078 August 7S. 1002
Dive 297 8 traversed up the rocky exposure on the west wall of the bends
segment (Fig. 23 ). From bathymetric and side scan surveys, this segment was
characterized by steep relief and 30- 40 linear reflectors (interpreted as
outcrops paralleling the canyon axis). The dive commenced in 242 m on a 30'
mud slope scattered with boulders and cobbles. From 235m to 220m, the slope
alternated from massive friable mudstone with a 50- 90' slope to mud
interspersed with varying amounts of rubble composed of cobbles and
boulders on a slope of 20- 40'. The outcrops were heavily encrusted with
invertebrates. White sponges were a dominant taxa encrusting vertical
surfaces, and basket stars were common on many of the rocks. From 200m to
165 m, the slope steepened to 80 - 90' and outcrops began to show weak
horizontal bedding cut by fractures. The topography was convoluted and
rugged in three dimensions with small box gullies, up to 10 m across, cut into
the slope associated with fracture planes. At 165 m, distinct bedding planes
formed ledges, overhangs and caven1s created by alternating resistant and
friable sandstone, mudstone and coquina. Large rockfish (Sebastes spp.), some
close to a meter in length were found in and near these caverns (Fig. 24a).
Continuing upward the angle of slope decreased to 20' and the bottom was
covered with mud and cobbles. From 120m to 108 m crinoids covered the tops
of a few small ledges (0.2- 0.5 m). Dive 2978 terminated on a nearly horizontal
bottom at 108m, covered 0.3 km and had a bottom time of 58 minutes.
Dive 2984 August 7(), 1907
Dive 2984 traversed the northern side of the the west wall rocky
eJ<.'POsure of the bends segment. The submersible landed at 253m on a gently
lOOm
200m
300m
Ledges and caverns
Small ledges interspersed with mud and tal us slopes
Joints and fractures cutting across bedding planes
Distinct bedding planes of sandstone and mudstone
Massive mudstone, sandstone and coquina interspersed with unconsolidated muddy substrate
Boulders and loose debris on unconsolidated muddy substrate
KEY
(:? Boulders
Cobble
Indistinct Bedding
Distinct Bedding
~Ledges and Caverns
II Fractures and Joints
I Massive Rocky Outcrops
~ Basket Stars
q White Sponges
':f Crinoids
Figure 23. Diagram of the substrate and canyon wall stratigraphy encountered along submersible Dive #297 8 on the west rocky exposure in the bends segment of Soquel Can von.
Figure 2-1. Next page.
(a) Photograph of rockfish Sebasles chlorostictus occupying a cave.
(b) Photograph of a large rockfish disturbing soft sediment. (c) Photograph of crinoids on top of cobbles. (d) Photograph of a slump hea\·i!y bioturbated with a small
rockfish Sebastes diploproa near an indentation in the slope. Brittle star arms are protruding from the soft sediment.
39
40
sloping (20') mud bottom. From 227m to 156m, the substrata altemated
between massive friable mudstone and mud slope on a 30 - 50' slope. In a
number of areas, holes and indentations appeared to have been carved in the
soft friable rock. Rockfish, up to 0.5 m in length, occupied some of these
indentations. The fish at times were disturbed by the submersible and their
actions disturbed the bottom (Fig. 24b). Fish could modify the soft mudstone
by nestling, creating indentations in the slope; this could significantly alter
the appearance of the substrata. From 150m to 125 m, outcrops of varying
resistance formed ledges and overhangs interspersed with boulders, cobble,
and mud slopes. Invertebrate life was dense on the rock surfaces and fish
were found under a number of the ledges. Scours around some of the boulders
were occupied by large fish that presumably enhanced or created these
scours. The interspersed muddy slopes were covered with signs of faunal and
infaunal activity. From 124m to 115 m angular cobbles were scattered along
the mud slope. Crinoids were attached to a some of the cobbles and small
rockfish were associated with the cobbles and crinoids (Fig. 24c). Dive 2984
terminated at 115m, covered 0.4 km and had a bottom time of 47 minutes.
Dive 7989 August 7(), 1992
Dive 2989 traversed up a rocky exposure on the east wall of the bends
segment. From the bathymetric and side scan surveys, this segment was
characterized by steep relief and a series of linear reflectors (outcrops)
paralleling the axis, but not as extensive as those on the west wall. The
traverse over this section began at 288m on a 20' soft muddy slope. At 275m
the slope steepened to 30 - 40' and 50% of the area was covered with large
boulders, many of these were in the form of sharp-edged slabs on a mud
bottom. Continuing up slope, vertical faces of uniform rocky outcrops were
41
comprised of sandstone/mudstone. At 260m no distinct bedding was present
but vertical fracturing was moderate and open space between fractures was
minimal. Few fish were observed on these outcrops and white sponges were
42
the dominant invertebrate covering rock surfaces. From 250m to 200m the
bottom alternated amoung bedded vertical walls 1- 6 m in height, terraces
covered with mud, and talus slopes. All the bedding planes were nearly
horizontal. At 200m, ledges with caverns were prevalent and rockfish were
more abundant. From 178m to 165m the wrtical rock faces were highly
fractured. Continuing up slope from 145 m to 130 m, the height of the ledges
decreased to 0.3 m- 1 m and were a series of steps with broad terraces. Crinoids
and small rockfish were common on the tops of the ledges. Dive 2989 ended in
130m of water, covered 0.3 km and had a bottom time of 47 minutes.
Dive 79CJ1 August 77, 1997
The objective of di\·e 2991 was to examine the canyon axis and large
slump (0.3 km2) on the east wall of the central segment, and to look for signs
of recent instability such as glide planes and fresh scarp faces. These slumps
appeared fresh from 3.5 kHz bath) metric profile interpretations. This dive
commenced in a 11·ater depth of 245m and terminated at a depth of 112 m. The
entire dive was in mud with the exception of one rock with 4 Metridium spp.
The slope varied from <1 0- 20° and gently undulated with indentations and
mounds from recent fauna and infauna activity. Small rockfish were observed
in some of the indentations (Fig. 24d). No signs of scarps or glide planes were
present. It appeared that slumps that can look fresh from high resolution
bathymetric profiles could be covered with sediment cover whose thickness is
below the resolution of the bathymetric profiles. Dive 2991 covered 0.9 km and
had a bottom time of 98 minutes.
Dive 3104 October 6. l <J93
The purpose of dive 3104 was to examine the largest and most pronouced
reflector detected by the side scan survey in Soquel Canyon. This large black
reflector was interpreted as a massive vertical wall on the deepest portion of
the rocky exposure on the west wall of the bends segment. The submersible
reached a maximum depth of 376m at the base of a vertical wall. The
submersible traversed up this wall from south to north and reached the top of
the wall at 267m. The wall, over 100m in height, consisted of uniform massive
sandstone/mudstone with no bedding. !vlinor fracturing was present near the
top of the wall. o,·erall, invertebrate cover was low compared to other vertical
walls in the canyon and increased near the top. There were similar trends in
fish abundance. A blanket of detrital material covered available surfaces.
From the top of the wall to 230 m the slope varied from 30 to 90' and comprised
massive mudstone, taius blocks and mud. Fish and invertebrate abundances
were higher here than on the vertical wall below. Dive 3104 terminated at 230
m, covered 0.6 km and had a bottom time of 45 minutes.
Dive 3111 October 7 1 9<J3
The objectives of dive 3111 were to investigate the shallow portion of a
large slump (1 km2) and adjacent steep gully cut into the southern portion of
the lower segment's west wall. Side scan sonar only surveyed the shallow
portion of the canyon wall in this location, but a reflector over 0.5 km in
length ran along the shelf-edge of the canyon at 130m-110m. At 262m the
submersible landed on a mud bottom surrounded by a school of hake that
reacted to the submersible by di\'ing into the mud. The mud slope was close to
30' and the submersible sent small turbidity flm,·s down the slope upon
.:..1-3
landing. Benthic fauna and the traces of infauna mostly were absent.
Traversing to the south from 250 m to 160m rock outcrops a.ssociated with the
steep gully consisted of massive sand tone and mudstone. The slope had an
overall lumpy appearance and varied from 60- 90' in the rocky areas to 35+'
for the mud/sand areas. Chutes formed by fractures in the rock surface
transported sediment down the canyon wall. These chutes ranged from 1- 10
em across. A few sediment cones were associated with the chutes. Burrows
were abundant and gallethid crabs and hagfish occuppied some of the holes.
From 160m to 104m the slope altemated amoung ledges 0.5- 3m in height, to
talus slopes of cobble to boulder size slabs, to mud on a 20" slope. Dive 3111
terminated at 104m at the base of a 4 m vertical wall, covered 0.-l km and had a
bottom time of -16 minutes.
44
DISCUSSION
Origin and Evolution of Soquel Canyon
Seismic reflection profiles just north of the head of Soquel Canyon
suggest that the formation of the canyon. was controlled by eustatic processes.
Four shallow small buried channels were found between larger buried eroded
channel walls or faults, just shoreward of the head of Soquel Canyon. These
four buried channels are probably remnants of repeated episodes of subaerial
erosion during the Pleistocene. A stream or river, possibly the San Lorenzo
(lvlartin, 1964; Greene, 1977), eroded the continental shelf as it made its wav to
sea during low stands of sea level. The fill within these channels may be shelf
deposits from subsequent high stands. At least three transgressi\·e-regressive
sequences may be bounded by the unconformities in the seismic reflection
profiles. The most recent erosional surface truncates the buried channel walls
or faults and two of the smaller buried channels, and is covered by 15 m of
recent undisturbed sediment. This erosional surface may be the result of the
coastline transgressing across the continental shelf at the end of the last low
stand 18,000 years ago (Fig. 25; Vail and Hardenbol, 1979). The channels must
have been filled prior to this time because they are truncated by the erosional
surface. This may suggest that the upper two channels were created and filled
prior to the last low stand of sea le\·el.
Soquel Canyon lies within a tectonically active region bounded by two
large fault zones, the San Andreas to the east and the San Gregorio to the west
and within a smaller zone, the Monterey Bay fault zone (Greene, 1977).
Tectonic activity may have influenced the positioning of the headward region
of Soquel Canyon. The trend (N25oE) of the head of the canyon for four km
45
46
0 I z~w 0 0 w"' RELATIVE CHANGES OF SEA LEVEL a: 0 ~::;: 0~(!) . w a_ 1- Oa:<t a_ w zo
-10p m -50 m 0 50m 100m 150m ::::>u_ ' HOLOCENE 1- .018 >- w ,.-L a: I- .75 1-<( z
' z w -a: 0 M w 0 ~ 1- 1.75 - - - - .........
1- 1- -<( (f)
::::> w E -~ 0 ....J
a_ I- 2.8 - - - - - - -- \ w
z w \ 0 -0
\ ::i a_
5 -
- ~ t-- 6.6 - - - - - 1-w >- z -a: w <( 0 i= Q a: ::;: -w 1- w
\ 1-<( -....J
I- 9.8 -10-
w -w::Jz l-Ow
\ <COO ....J-0 -::;:-::;:
Figure 25. Sea-level curYe of the Neogene (after Vail and Hardenbol, 1979).
aligns with the buried eroded channel walls or faults mapped just shoreward
of the head. In the seismic profiles these boundaries appear to be faults, but
this is not conclusive. juxtaposition of differing lithologies or faulting and
gas discharge may have controlled the location and trend of the head and
central segments of Soquel Canyon. This is a reasonable inference as many
canyons originated as fault valleys that were greatly modified by marine
erosion (Shepard, 1981). If the gas-charged features bounding the buried
channels are fau! ts, their trend may indicate a conjugate relationship to the
northwest-southeast oriented faults of the l\lonterey Bay fault zone described
by Gardner-Taggart et a!. (1993). If faulting controlled canyon development,
then the faults ha\·e not been active since the last low stand because no offset
was detected in the top 15 m of recent sediment.
The inferred gas charged sediment zones and the presence of anomalies
in the water column along trends of the buried eroded channel walls or faults
suggest that gas is being released from the sedimentary channel fill, or
perhaps from greater depths into the overlying water column. Even though
gaseous hydrocarbons were not collected in this study, they have been
sampled 10 km to the west (Mullins and Nagel, 1982). Mullins and Nagel ( 1982)
found these hydrocarbons to be thermogenic in origin, but suggested that
some of the shelf edge anomalies may be biogenically produced within the
Quatemary sediment. Because the depth to which these faults or channel
walls extend is not clear from the seismic reflection data, it is not possible to
deduce whether these gases are thermogenic and from great depths or
biogenically produced within channel fill deposits. Therefore, it is not clear
whether these gases were present before the initial formation of Soquel
Canyon and may have facilitated early canyon formation. However, the
47
presence of gas charged sediments would have facilitated exhumation of later
buried channels.
The stability of most of the slumps and the absence of fresh scarps
suggest that Soquel Canyon presently is less active then it has been in the past.
The mass wasting, which dominates the canyon's morphology, probably took
place during the Pleistocene when sea level was lower. During low stands of
sea level, the head of Soquel Canyon intercepted the coastline and the canyon
became an active conduit transporting littoral and fluvial sediments to the
deep sea (Greene, 1977). Once coastal sediments were intercepted by the
canyon, they were deposited temporarily in the canyon axis near the head
until destabilized by some episodic event (e.g., storms and earthquakes) or
chronic activity such as tides (Inman eta!., 1976). Turbidity currents,
generated by destabilized sediments, would move the axis sediments farther
down canyon (Moore, 1965). Examination of modem canyon heads that are
accessible by scuba indicates that discreet flushing events occur on a yearly
basis and many times are associated with the first fall storm (Shepard and Dill,
1966; Shepard and l\larshall, 1973; Shepard, 1975; Okey, 1993).
A consequence of turbidity flows in submarine canyons is the
undercutting and oversteepening of canyon walls (Andrew and Hurley, 1978).
This makes the walls susceptible to mass wasting and the process begins again
(Martin, 196-1; Martin and Emery, 1967). The large amount of area covered by
slumps, close to -10% of Soquel Canyon, suggest that mass wasting was a
significant erosional process in the past.
The cross axis profile of Soquel Canyon changes from the head to the
lower segment. The U-shaped profile near the head of the canyon suggests
that little or no activity is presently occurring and that past mass wasting has
-18
piled up slump debris in the canyon axis. Farther to the south, the V-shaped
profile in the central and bends segments suggests that this region of the
canyon may have been cleared recently of accummulated sediment or has not
been subjected to extensive mass wasting. Continuing farther to the south the
profile in the lower segment is l.J-shaped with sediment in the axis, and
appears to have been breached recently because a thalweg cuts into the
sediment on the narrow flat canyon floor. This sediment may be a result of a
slump, as obserced on the lower west wall of the canyon, spilling into the
canyon axis or by sediment blocked by a large landslide that dammed the
canyon near it's mouth (H. G. Greene, 1994, pers. comm.).
49
50 Small-Scale Geology from Submersible Observations
General obserYations from the submersible verified that a large area of
Soquel Canyon is covered with mud. Even in the bends segment, where the
walls appeared to be dominated by rocky exposures from 3.5 kHz profiles and .
the side-scan sonographs, were interspersed with up to 50% mud. In many of
t: • ..:se areas within the rocky e:-;posures, the mud slopes were steeper than the
angle of repose (22- 2T for subaqueous grain flows, Lowe, 1976) suggesting
that hard substrate was not far below the surface.
Contemporarv Submarine Erosion
Evidence of mass wasting on a small scale was observed from the
submersible, including sediment mm·ing down slope via sediment chutes
located in fractures and turbidity-like flows initiated by the submersible
coming in contact with the slope on the west wall of the lower segment of the
canyon. Benthic fauna and signs of infaunal activity were much less here
than on other slopes. Lower density and diversity of fauna have been
documented in areas that are subject to disturbance (Trumble and McCamis,
1967; Stanley, 1971; VanBlaricom, 1978; Okey, 1993).
Gravity-induced rock fails along fractures are an inferred
contemporary erosional process that also was important during the
Pleistocene. Although rock falls were not observed directly, accumulation of
slabs and blocks of rock at the base of cliffs where fractured rock is exposed
suggests their occurrence. 1\lcHugh et al. ( 1993) suggest that stress release
fracturing can contribute to canyon growth as the unloading of rock from the
canyon wails leads to loss of support. The tectonically active region of
Monterey Bay also may contribute to fracturing in Soquel Canyon.
Biological activity has been identified as an important erosional
influence on canyon walls (Dillion and Zimmerman, 1970; Rowe et al., 197 4;
Warme et a!., 1978; Valentine et al., 1980; Hecker, 1982; Twichell et a!., 1985 ),
and this appears to be true in Soquel Canyon. Biologically induced erosion
includes bioturbation (i.e., the reworking and modification of unconsolidated
sediment by biological activity) and bioerosion (i.e., the breakdown of rock
outcrops by marine borers that range from small invertebrates to large fish;
Neumann, 1966; Warme et al., 1978; Hecker, 1982).
Most of the mud deposits in Soquel Canyon were covered with benthic
fauna and traces of infauna activity such as mounds, pits, and burrows. Both
fish and invertebrates appeared to be actively moving the sediment. On steep
slopes this would result in a net transport of unconsolidated sediment down
slope over time (Hecker, 1982).
The importance of biological activity on canyon erosion can vary
greatly with the type of substrate (Valentine eta!., 1980). In Soquel Canyon
this appears to be a function of the rock's resistance to erosion and degree of
surface complexity. Fish may be modif)ing semiconsolidated rock by creating
indentations in the friable mudstone for refuge. Bioerosion by tilefish
impacted semi-lithified silty clay of Hudson Canyon on the East Coast of the
United States (Grimes et al., 1986). Twichell eta!. (1985) has estimated the rate
of erosion by tilefish to be 13 em per 100 y as each generation of fish creates a
new burrow.
The surface complexity of the substrata influenced the size and
composition of associated fauna. At least two distinct assemblages of rockfishes
were present in Soquel Canyon. Large rockfish species (up to 1.0 min total
lenght) associated with rock ledges, cavems, and boulders of high relief, and
51
small rockfish species associated with mud and cobble of low relief (Yoklavich
eta!., 1992; 1993 ). The actions of fish enlarge the caverns they inhabit, or at
least prevent sedimentation (Palmer, 1976). Changes in fauna with depth also
could influence the degree of bioerosion on outcrops.
Boring by invertebrates was evident in all the rock samples and is
undoubtedly an important process in breaking down outcrops in the marine
environment (Warme and Marshall, 1969; Dillion and Zimmerman, 1970;
52
Warme eta!., 1971; Warme et al., 1978). Pholads can bore a foot or more into
rocks and occur at depths up to 1-lO m (Palmer, 1976). The degree of boring has
been associated with the grain size of the country rock, with the number of
borers decreasing with increasing grain size (Warme and Marshall, 1969). It
should be noted that some of these bored rock samples may be remnants of
Pleistocene activities when sea level was lower.
Bioerosion by macro borers, such as sponges, dominates all samples in
recent and fossil coral material from deep sea environments (Bromley and
D'Alessandro, 1990). The high frequency of occurrence of sponges on many of
the rock faces suggests that they are agents of bioerosion and should be
examined more closely in Soquel Canyon. little is known of the ecology of
Hexactinellida, the dominant sponge taxa in the canyon, but the erosive
capabilities of tropical sponges have not been described for this group
(]. Nybakken, 199-l, personal com.). Further investigations are necessary to
adequately address the importance of bioerosion to contemporary canyon
morphology.
Bottom currents work synergistically with biological acth·ities to
increase their effects on erosion (Rowe et al., 197-l; Stanley and Freeland,
1978). Canyon currents are generated by many forces including wind, surface
waves, intemal waves, tides, and spin-off eddies from large scale geostrophic
current systems (Inman et a!., 1976 ). Maximum bottom currents in Soquel
Canyon were estimated to be close to one knot (50 em s-1 ). Bottom current
speed up to 50 em s-1 also has ben estimated in one study in the head of
Monterey Canyon (Rosenfeld, 199-1 ). At times, especially in the shallow end of
the axis during falling tides, large amounts of suspended material indicated
these currents had the capability of removing sediment.
Submarine spring sapping can contribute substantially to canyon
erosion (Johnson 1939; Paull et a!. 1990). The Purisima Formation is an
important aquifer on land (Greene, 1970; Greene eta!., 1993), and groundwater
can be seen flowing from the cliffs composed of the Purisima Formation (Fig.
-1). Cold seep communities of chemos.ynthetic clams are associated with faults
and fluid flow within the Purisima Formation in Jvlonterey Bay (Greene et a!.,
1993; Barry et al., 1993). Groundwater discharge could directly cause grain by
grain erosion of strata and result in slumping of weaken substrata (Robb,
198-1). No signs of fluid flow, such as chemical stains or bacterial matts, were
seen during this study but spring sapping potentially can contribute to
growth of Soquel Canyon.
53
CONCLUSIONS
Eustatic, tectonic, biological and erosional processes contribute to the
origin, evolution and contemporary morphology of Soquel Canyon. During
the Pleistocene, when sea level was lower, the San Lorenzo Rh·er subaerially
cut a channel across the continental shelf south of Santa Cruz, CA. The river
cut through deposits of the Purisima Formation, a nearshore marine deposit of
Pliocene age. The placement of the newly created proto-Soquel Canyon may
have been fault controlled following a zone of weakness created by conjugate
faults of the Monterey Bay fault zone. Gas discharge along these faults also
may have contributed to canyon formation, hm,·ever, this remains unclear.
The coastline of Jvlonterey Bay fluctuated during the Pleistocene from
close to its present day position during high stands of sea level to over 100m
lower and near the shelf break during low stands. Once canyon formation
commenced on the emergent continental shelf several periods of erosion
followed during successive low stands of sea level. At least three erosional and
depositional events may have taken place to shape Soquel Canyon during the
Pleistocene. The periods of low stand were most important in excavating and
shaping the canyon. The head of Soquel Canyon was very near the ancient
low stand shoreline and acted as an active conduit transporting littoral and
fluvial sediment offshore. Mass wasting accompanied this transport of coastal
sediments as turbidity currents flushed sediment down the axis of the canyon.
Undercutting of canyon walls and down-cutting of the canyon axis are
consequences of turbidity currents that led to rapid periods of mass wasting
and canyon growth. Later transgressions planed the continental shelf and
subsequent high stands partially buried the shallow channels with shelf
54
deposits. Exhumation of buried channels resumed with low stands of sea level,
and was facilitated by gas discharge from the sediment.
Erosional processes during the present high stand of sea level result in
a much less active canyon, which is cut off from coastal sediment supplies.
Processes that currently modify Soquel Canyon include bioerosion, stress
release fracturing, water currents, and mass wasting on a small-scale.
55
56 REFERENCES
Able, K.W., Twichell, D.C., Grimes, C.B., and Jones, R.S., 1987. Sidescan sonar as a tool for detection of demersal fish habitats. Fishery Bulletin: 85: (4):725-736.
Andrews, J.E. and Hurley, R.J., 1978. Sedimentary processes in the formation of a submarine canyon. Mar. Geol., 26: M47-M50.
Barry, J.P .. Robison. B.H .. Greene. H.G., Baxter, C.H., Harrold, C .. Kochevar, R.E., Orange, D., Lisin, S., Whaling, P.J .. and Nybakken. J. 1993. Investigations of cold seep communities in Monterey Bay, California, using a remotely operated vehicle. Proceedings. Amer. Acad. Underwater Sci., 13th Annual Scientific Diving Symposium, Pacific Grove, Sept. 1993 p. 17-32.
Belderson, R.H., Kenyon, N.H .. Stride, A.B., and Stubbs A.R., 1972. Sonographs of the sea Floor. Elsevier Publishing Company New York, 185 p.
Bromley, R.G., D'AIIessandro, A. 1990. Comparative analysis of bioerosion in deep and shallow water, Pliocene to recent, Mediterranean Sea. Ichnos 1 :43-49.
Clark, J.C., 1981. Stratigraphy, paleontology, and geology of the central Santa Cruz Mountains, California Coast Ranges: U.S. Geological Survey Professional Paper 1168, 51 p.
Clark, J.C., Dibblee, T., Greene, H.G., and Bowen, O.E. Jr., 1974. Preliminary geologic map of the Monterey and Seaside 7 .5-minute quadrangles, Monterey County, California. U.S. Geol. Survey Misc. Field Studies Map MF-577, Scale 1:24,000.
Coleman. J.M. and Prior, D.B. 1988. Mass wasting on continental margins. Annual Review of Earth Planetary Sciences 16:101-119.
Cummings. J.C.. Touring, R.M., and Brabb, E.E., 1962. Geology of the northern Santa Cruz Mountains, California, in Bowen, O.E., Jr. (ed.), Geologic guide to the gas and oil fields of Northern California: California Div. Mines Bull. 181, p. 179-220.
Dillion, W.P. and Zimmerman H.B., 1970. Erosion by biological activity in two New England Submarine Canyons. J. Sed. Pet. 40(2):542-547.
Ewing, J. and Ewing. M., 1970. Seismic rel1ection. in The Sea, v. 1 p. 1-52, ed. A.E. Maxwell. New York: Wiley-lnterscience.
Gardner-Taggart, J.M .. 1991. Neogene folding and faulting in southern Monterey Bay. M.S. Thesis San Jose State University, 79 p.
57
Gardner-Taggart, J.M., Greene. H.G. and Ledbetler, M.T. 1993. Neogene folding and faulting in southern Monterey Bay, central California. USA. Marine Geology 113:163-177.
Graham, S.A. , 1976. Role system, California: 62:(11): 2214-2231.
of the Salinian block in evolution of San Andreas Fault American Association of Petroleum Geologists Bulletin,
Greene, H.G. 1970. Geology ground water basin and File Report 50pp.
of Southern Monterey Bay and its relationship to the salt water intrusion. U.S. Geological Survey Open
Greene, H.G., 1977. Geology of the Monterey Bay Region. U.S. Geological Survey Open File Report No. 77-718. 347 p.
Greene, H.G., 1990. Regional tectonics and structural evolution of the Monterey Bay region, central California. In: Geology and tectonics of the central California coastal region, San Francisco to Monterey. R.E. Garrison, H.G. Greene, K.R. Hicks, G.E. Weber, T.L. Wright, (Editors). Pacific section of the AAPG Guidebook, p. 31-56.
Greene, H.G .. Lee, W.H.K., McCulloch, D.S. and Brabb, E.E., earthquakes in the Monterey Bay region, California. Francisco Bay Region Environment and Resources Data contribution, 58: 1-14.
1973. Faults and U.S. Geol. Survey, San
Planning Study, Basic
Greene, H.G. and Clark, J.C .. 1979. Neogene paleogeography of the Monterey Bay area, California in Armentrout, J.M., Cole, M.R., and Terbest. H.Jr., eds., Pacific Coast paleogeography of the western United States: Society of Economic Paleontologists and Mineralogists Publication, Pacific Coast Paleogeography Symposium 3, p. 277-296.
Greene, H.G., McCulloch, D.S .. and Clark, J.C. 1989. Geology of the Monterey Submarine Canyon system and adjacent areas, offshore central California. U.S. Geol. Survey open-file report, 89-211: 1-33.
Greene, H.G., Gardener-Taggart, J.M., Ledbetter, M.T., Barminiski, R., Chase, T.E., Hicks, K., and Baxter, C. 1991. Offshore and onshore liquefaction at Moss Landing spit - result of the October 17. 1989, Loma Prieta earthquake. Geology 19: 945-949.
Greene, H.G., Stakes, D.S., Orange, D.L .. Barry, J.P., and Robison. B.H. 1993. Application of a remotely operated vehicle in geologic mapping of Monterey Bay, California, USA. Proceedings, Amer. Acad. Underwater Sci., 13th Annual Scientific Diving Symposium, Pacific Grove, Sept. 1993 p. 67-80.
Grimes, C.B., Able, K.W., and Jones, R.S., 1986. Tilefish, Lopho/atilus chamaeleonticeps, habitat, behavior and community structure in Mid-Atlantic and southern New England waters. 15(4): 273-292.
58
Hecker, B., 1982. Possible benthic fauna and slope instability relationships. In S. Saxov and J.K. Nieuwenhuis, editors. Marine Slides and Other Mass Movements. Plenum, New York, USA. p. 335-347.
Inman, D.L., Nordstrom, C.E. and Flick, R.E .. 1976. Currents in submarine canyons: an air-sea-land interaction. Ann. Rev. Fluid Mechanics 8: 275-310.
Johnson, D.W., 1939. The origin of submarine canyons. New York, Hafner Publishing Company, 126 p.
Lowe, D.R., 1976. Grain Flow and grain flow deposits. Jour. of Sed. Pet. 46(1): 188-199.
Malahoff, A., Embley. R.W., and Fornari, D.J. 1982. Geomorphology of Norfolk and Washington Canyons and the surrounding continental slope and upper rise as observed from DSRV Alvin. In The Ocean Floor ed. R.A. Scrutton and M. Talwani John Wiley & Sons Ltd. p. 97-111.
Martin, B.D., 1964. Monterey Submarine Canyon, California: genesis and relationship to continental geology (Ph.D. thesis): University of Southern California, Los Angeles, California. 249p.
Martin, B.D., and Emery, K.O .. 1967. Geology of Monterey Canyon, California. Bulletin of American Association of Petroleum Geologist, 51: 2281-2304.
May, J.A., Warme, J.E. and R.A. Slater. 1983. Role of Submarine Canyons on Shelf Break Erosion and Sedimentation: Modern and Ancient examples. Soc. Econ. Paleontologist Mineral.. Spec. Publication 33: 315-332.
McHugh, C.M., Ryan, W.B.F, and Schreiber, B.C., 1993. The role of diagenesis in exfoliation of submarine canyons. AAPG Bull. 77(2): 145-172.
Mulllins, H.T. and Nagel, D.K., 1982. Evidence for shallow hydrocarbons offshore Northern Santa Cruz County. California. AAPG Bull. 66(8): 1055-1075.
Nagel D.K .. H.T. Mullens and Greene, H.G., 1986. Ascension Submarine Canyon, California - Evolution of a Multi-head Canyon system along a Strike-slip Continental Margin. Marine Geology 73: 285-310.
Neumann, A.C., 1966. Observation on coastal erosion in Bermuda and measurements of the boring rate of the sponge, Cliona Lampa. Limnol. Oceanogr. 11: 92-108.
Okey, T.A., 1993. Natural disturbances and benthic communities in Monterey Canyon head. M.S. Thesis San Jose State University.
Orange, D.L., Geddes, D.S. and Moore, J.C. 1993. Structural and fluid evolution of a young accretionary complex: The Hoh rock assemblage of the western Olympic Peninsula, Washington. Geol. Soc. Am. Gull. 105: 1053-1075.
59 Page, B.M., 1970. Sur-Nacimiento fault zone of California: Continental margin
tectonics. Geol. Soc. Am. Bull., 81: 667-690.
Page, B.M., and Englebretson. D.C.. 1984. Correlation between the geologic record and computed plate motions for central California. Tectonics, 3: 133-155.
Palmer, A.E., 1976. Erosion of submarine outcrops, La Jolla submarine canyon. California. Geol. Soc. of Amer. Bull. 87: 427-432.
Paull. C.K., Spiess, F.N. Curray J.R. and Twichell D.C. 1990. Origin of Florida Canyon and the role of spring sapping on the formation of submarine box canyons. GSA Bull. 102:502-515.
Poulos, S.J., Castro, G., and France, J.W. 1985. Liquefaction evaluation procedure. J. Geotechnol. Eng. Div. ASCE, 111: 772-791.
Robb, J.M., 1984. Spring sapping on the lower continental slope, offshore New Jersey. Geology 12:278-282.
Rosenfeld, L.K., Noble, M.A., Pilskaln, C.H. and Schwing, F.B. 1994. Currents in Monterey Submarine Canyon. Abstract. 1994 Ocean Sciences Meeting: AGU & Lim. and Ocean. p. 204.
Rowe, G.T., Keller, G., Edgerton, H., Stareslinc, N. and Macllvaine, J., 1974. Timelapse photography of the biological reworking of sediments in Hudson Submarine Canyon. J. Sed. Pet. 44(2): 549-552.
Shepard, F.P., 1952. 60: 84-96.
Shepard, F.P., 1975. and high tides.
Composite origin of submarine canyons. Journal of Geology
Pulsating turbidity currents with relationship to high swell Nature 258: 704-706.
Shepard, F.P., 1981. Submarine canyons: Multiple causes and long-tine persistence. Bull. Am. Assoc. Pet. Geol., 65: 1062-1077.
Shepard, F.P. and Dill. F.R .. 1966. Submarine Canyons and other Sea Valleys, Rand McNally, Chicago, Ill., 381 p.
Shepard, F. P., and Marshall, N. F., 1973. Storm-generated current in La Jolla Submarine Canyon, California. Marine Geology 15:MI9-M24.
Stanley, D.J., 1971. Fish-produced markings on the outer continental margin east of the middle Atlantic states. J. Sediment. Petrol., 41(1): 159-170.
Stanley, D.J., and Freeland, G.L., 1978. The erosion-deposition boundary in the head of Hudson submarine canyon defined on the basis of sumersible observations. Mar. Geol .. 26: M37-46.
Trumble, V. A .. and McCamis. M. J., 1967. Geological exploration is an East Coast Submarine Canyon from a Research Submersible. Science 158: 370-372.
Twichell, D.C., Grimes, C.B., Jones. R.S., and Able, K.W., 1985. The role of erosion by fish in shaping topography around Hudson Submarine Canyon. J. Sed. Pet. 55(5): 712-719.
Vail, P.R. and Hardenbol, J., 1979. Sea-level changes during the Tertiary. Oceanus, 22: 71-79.
Valentine, P.C., Uzmann, J.R. and Cooper, R.P... 1980. Geology and Biology of Oceanogrpaher Submarine Canyon. Marine Geology 38: 283-312.
60
Van Blaricom, G.R., 1978. Disturbance, predation, and resource allocation in a high-envergy sub-littoral sand bottom ecosystem: experimental analyses of critical structuring processes for the infaunal community. Ph.D. Dissertation. Univertiy of California at San Diego, USA.
Warme, J.E., and Marshall, N.F., 1969. Marine Borers in Calcareous Terrigenous Rocks of the Pacific Coast. Am. Zoologist 9: 765-774.
Warmc. J.E., Slater, R.A. and Cooper, R.A., 1978. Bioerosion in submarine canyons. In: D.J. Stanley and G. Kelling (Editors), Sedimentations in Submarine Canyons, Fans. and Trenches. Dowden, Hutchinson and Ross, Stroudsburg, PA, p. 65-70.
Yoklavich, M.M., Greene, H.G., Moreno. G., Cailliet, G. M., Sullivan, D., Walters, D., and Love. R.M., 1992. The importance of small-scale refugia to deep water rockfishes (Scbastes spp.) - a pilot study in Soquel Canyon, Monterey Bay, CA. Jabs.]: EOS, Tranactions, American Geophys. Union, AGU 1992 Fall Meeting Program and Abstracts, 73(43): 318.
Yoklavich. M.M., Cailliet, G.M., and Moreno. G., 1993. Rock and Fishes: Submersible observations in a submarine canyon. Proceedings, Amer. Acad. Underwater Sci .. 13th Annual Scientific Diving Symposium, Pacific Grove, Sept. 1993 p. 173-181.
APPENDICES
The following appendices contain the nayigational starting and ending points for the track lines run on the geophysical cruises.
61
APPENDIX I 62
Ship track lines for the 3.5 kHz presicsion depth recorder survey. Lines are spaced at 80 m.
Line Start: Lat Start: Long End: Lat End: Long
eA 36 50.77 171 57.74 36 48.75 121 59.08
eB 36 50.77 121 57.68 36 48.66 12159.08
eC 36 50.77 121 57.62 36 48.57 121 59.08
eO 36 51.13 121 57.32 36 48.48 121 59.08
eE 36 51.13 121 57.26 36 48.39 121 59.08
eF 36 51.13 121 57.20 36 48.30 121 59.08 wG 36 48.63 122 01.06 36 51.64 121 57.09
eG 3651.13 121 57.14 36 48.21 121 59.08
wi-1 36 48.60 122 01.02 36 51.61 121 57.05
el-l 36 51.13 121 57.08 36 48.12 121 59.08
wi 36 48.57 172 00.98 36 51.58 121 57.01
e I 3651.13 171 5t.02 36 48.03 121 59.08
w.J 36 48.54 122 00.94 36 51.55 171 56.97
ej 36 51.13 171 56.96 36 47.94 121 59.08
wK 36 48.51 172 00.90 36 51.52 171 56.93
eK 36 51.13 121 56.90 36 47.90 171 59.03
wL 36 48.48 172 00.86 36 51.49 121 56.89
wM 36 48.45 177 00.87 36 51.46 171 56.85
wN 36 48.42 122 00.78 36 51.43 121 56.81
wO 36 48.39 122 00.74 3651.40 121 56.77
11 36 49.47 122 00.02 3651.06 121 58.46
12 3651.06 121 58.46 36 50.05 121 57.14
13 36 50.05 171 57.14 36 49.40 121 57.55
14 36 49.40 121 57.55 36 50.33 121 58.79
15 36 50.33 171 58.79 36 50.05 171 59.33
16 36 50.05 121 59.33 36 48.98 121 57.97
17 36 48.98 121 57.97 36 50.72 171 57.03
18 36 50.72 121 57.03 3651.98 121 58.77
19 36 52.00 121 57.79 36 51.97 121 54.99
20 3651.44 171 55.38 36 52.01 121 56.95
21 36 52.00 121 57.13 36 49.83 121 58.38 27 36 49.83 121 58.38 36 49.32 ]71 59.44
63 APPENDIX II
Ship track lines for the side scan sonar survey.
LINE North pt North pt South pt South pt
latitude longitude latitude longitude
16 36 52' .63 121 58' ,25 36 48' .00 121 59' .71
17 36 52' .63 121 58' .15 36 48' .00 121 59' .61
18 36 51' .63 121 58' .05 36 48' .00 121 59' .51
19 36 52' .63 121 57' .95 36 48' .00 121 59' .41
20 36 52' .63 121 57' .85 36 48' .00 121 59' .31
21 36 52' .63 121 57' .75 36 48' .00 121 59' .21 22 36 52' .63 121 57' .65 36 48' .00 12 I 59' .11
23 36 52' .63 121 57' .55 36 48' .00 121 59' .01
24 36 52' .63 121 57' .45 36 48' .00 121 58' .91 25 36 52' .63 121 57' .35 36 48' .87 121 58' .58
26 36 52' .63 121 57' .25 36 48' .87 121 58' .46
27 36 52' .63 121 57' .15 36 48' .87 121 58' .34 28 36 52' .63 121 57' .05 36 48' .87 121 58' .22
D 36 49.96 Pl 57.71 36 47.57 122 00.18
64
APPENDIX III
Ship track lines for seismic reflection surveys.
LINE Start: Lat Start: Long End: Lat End: Long
18 36 54.010 Pl 54.993 36 57.376 121 55.182 19 36 57.562 121 55.i66 36 51.316 121 58.881 20 3651.153 121 58.981 36 49.482 127 08.457 so 36 56.309 ]7] 58.378 36 57.704 121 55.578 51 36 57.736 121 55.516 36 55.017 121 56.543 52 36 54.649 171 56.799 36 57.146 171 54.577 53 36 57.364 121 54.333 36 55.549 121 54.169 54 36 55.336 121 54.171 36 56.363 121 53.523 55 36 56.575 ]71 53.372 36 55.370 121 53.254 56 36 54.882 121 53.233 3655.140 171 52.477 64 3651.426 121 54.775 36 52.641 121 58.444 68 36 57.475 171 58.773 36 51.156 ]71 55.051