Copyright Jefferson Vasconcellos · 2020. 12. 12. · deep-marine environments (Bloch, 1986)....
Transcript of Copyright Jefferson Vasconcellos · 2020. 12. 12. · deep-marine environments (Bloch, 1986)....
Copyright
By
Jefferson Vasconcellos
2016
ANALYSIS OF COMPETING HYPOTHESES FOR THE TECTONIC EVOLUTION OF THE
BAKERSFIELD ARCH
by
Jefferson Vasconcellos
A Thesis Submitted to the Department of Geology
California State University Bakersfield
In Partial Fulfillment for the Degree of
Masters of Petroleum Geology
Winter 2016
ANALYSIS OF COMPETING HYPOTHESES FOR THE TECTONIC EVOLUTION OF THE BAKERSFIELD ARCH
By Jefferson Vasconcellos
This thesis has been accepted on behalf of the Department of Geology by their supervisory committee:
' 'f: . uf~i::;e,~¥& Professor of Geology Committee Chair
Robert Negrini, PhD Professor of Geology
Dirk Baron, PhD Department Chair, Professor of Geology
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ABSTRACT
The widespread presence of Neogene and Quaternary units in the southeastern San
Joaquin Valley provide evidence for the tectonic evolution of the Bakersfield Arch, an area of
major oil production in California. The purpose of this study is to test two different age
hypotheses for the uplift of the Arch: middle Miocene and late Quaternary. Electric log
correlations of stratigraphic marker units were used to create isochore maps of sedimentary
packages of various ages across the Arch. These data indicate that changes in horizontal
distribution and thickness of stratigraphic units across the Arch are influenced by two distinct
uplift events in the area: 1) during middle to late Miocene time and 2) latest Miocene
(post-Etchegoin Formation deposition) to Pleistocene time. Future work incorporating more
detailed correlation of individual chert markers within the Monterey Formation would more
closely define the exact timing of the earlier episode of uplift in the area. Age diagnostic data are
insufficient to determine the time of onset of the later period of uplift.
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ACKNOWLEDGMENTS
I would like to express the deepest appreciation to my thesis advisor, Janice Gillespie,
who had the patience and the generosity to share her knowledge and expertise in this study. I
definitely learned a lot with every correction she made along the way. I would like to show my
special gratitude and thanks to my committee members Dirk Baron and Robert Negrini. Thanks
are also extended to Sue Holt and Elizabeth Powers for guiding and helping me in order to make
the study a well done achievement.
Special recognition to my friends that were always available to share and hang out
when I needed a study break.
My thanks and appreciations also go to my family for the moral and financial support
which helped me completing this study. I also would like to thank my beloved girlfriend Khanh
Lu for providing me with all love and companionship when I needed her the most during long
hours of study away from my family, country and culture.
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TABLE OF CONTENTS
Abstract………………………………………………………………………………….………..2
Acknowledgements………………………………………………………………………….…...3
Table of Contents…………………………………………………………………………….…..4
List of Figures……………………………………………………………………………….…....6
Introduction…………………………………………………………………………………..…..8
Geologic Setting……………………………………………………………………………….....9
Stratigraphy of the Bakersfield Arch Area……………………………………………………11
Vedder
Freeman-Jewett/Olcese
Bena
Round Mountain
Monterey
Stevens
Chanac
Santa Margarita
Fruitvale
Bellevue
Gosford
Coulter
Reef Ridge
Etchegoin/Macoma
San Joaquin
Tulare
Petroleum System………………………………………………………………………….……24
Importance
Maturation Timing
Traps and Seals
Previous Studies……………………………………………………………………...…………28
Middle Miocene Hypothesis
Late Quaternary Hypothesis
Data and Methods………………………………………………………………………………38
Results………………..……………………………………………………………….…………40
5
Top of Etchegoin to top of Macoma
Top of Macoma to top of Reef Ridge
Top of Reef Ridge to top of Monterey
Top of Monterey to top of Round Mountain
Top of Round Mountain to top of Freeman
Top of Freeman to top of Vedder
Discussion……………………………………………………………………………………….61
Conclusion………………………………………………………………………………………65
References…………………………………………………………………………….…………67
Appendix………………………………………………………………………………………...71
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LIST OF FIGURES
Figure 1 Location map of the Bakersfield Arch, Buttonwillow and Tejon depocenters.
Figure 2 Tectonic setting of the California borderland, from Oligocene to Miocene.
Figure 3 Stratigraphic column of the Bakersfield Arch area.
Figure 4 Diagrammatic cross section showing stratigraphic relations of Tertiary formations
south of the Bakersfield Arch.
Figure 5 Distribution of the Antelope and Fruitvale Formations
Figure 6 Stratigraphic column of the Bakersfield Arch area showing the Monterey turbidites.
Figure 7 Correlation chart of Tertiary formations in southeastern San Joaquin Valley.
Figure 8 Map of oil fields in the Bakersfield Arch area.
Figure 9 Seismic image and interpreted stacking of chert and sandstone beds.
Figure 10 Tectonic model of the Tehachapi block rotation.
Figure 11 Model of the kinematics involved in breaking the south San Joaquin Valley blocks
apart and the formation of basins in the Bakersfield Arch area.
Figure 12 Kinematic map of the westward deflection of the southern Sierra Nevada
Batholith.
Figure 13 Model of the Isabella anomaly and delamination of the mantle lithosphere.
Figure 14 Diagram showing the onset convergence and Coast Range uplift and sediment-
load subsidence.
Figure 15 Stratigraphic column of the Southern San Joaquin Valley and sedimentary
packages.
Figure 16 Etchegoin-Macoma isopach map.
Figure 17 Etchegoin-Macoma cross- section.
Figure 18 Macoma-Reef Ridge isopach map.
Figure 19 Macoma-Reef Ridge cross-section.
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Figure 20 Reef Ridge-Monterey. isopach map.
Figure 21 Reef Ridge-Monterey cross-section.
Figure 22 Monterey-Round Mountain isopach map.
Figure 23 Monterey-Round Mountain cross-section.
Figure 24 Round Mountain-Freeman isopach map.
Figure 25 Round Mountain-Freeman cross-section.
Figure 26 Freeman-Vedder isopach map.
Figure 27 Freeman-Vedder cross-section.
Figure 28 Late Miocene paleogeography of the San Joaquin basin area.
Figure 29 Present day topography of the Bakersfield Arch area.
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INTRODUCTION
The Bakersfield Arch is a major structural feature located in the southern end of the San
Joaquin Valley in California (Fig. 1). The city of Bakersfield is located along the axis of the Arch
and the city of Los Angeles lies about 100 miles to the southeast. The San Andreas Fault is to the
west and the Sierra Nevada to the northeast.
Fig. 1 – The Bakersfield Arch plunges to the southwest (delineated by the red lines). The
Buttonwillow depocenter to the north and Tejon depocenter to the south are shown in yellow.
The Arch plunges southwest from the city of Bakersfield toward the valley center. Oil
generated at the Tejon depocenter to the south and Buttonwillow depocenter to the north of the
Bakersfield Arch migrated into oil fields along the crest of the Arch. Timing of Arch uplift
Sierra Nevada
Bakersfield Arch
Los Angeles
Tejon
San Joaquin
Valley
Bakersfield
9
relative to deposition of organic-rich source rocks and reservoir sandstones affects the
distribution and thickness of the reservoirs, timing of oil migration, and the trapping
characteristics of the local oil fields.
A better understanding of the regional geology of the Bakersfield Arch oil fields is
hindered due to the lack of studies that extend beyond the individual oilfield-scale. Previous
works that discuss the tectonic evolution of the Bakersfield Arch area and geologic setting
include Bartow and McDougall (1984), Bloch (1991), Sheehan (1986), and Saleeby et al. (2013).
This study tests two hypotheses--one that the Arch was activated in middle Miocene time and the
other that the Arch did not form until late Quaternary--by presenting cross-sections, stratigraphic
columns and shale/chert thickness maps based on available log data in the area. The goal of this
study is to present data leading to an up-to-date and more complete interpretation of the broader
regional geology across the Bakersfield Arch.
GEOLOGIC SETTING
The San Joaquin basin is located east of the San Andreas Fault which forms the boundary
between the North American and Pacific plates. The margin was the site of a subduction zone
during Jurassic through early Miocene time at which time the San Joaquin basin was a forearc
basin. To the west, the Pacific plate was subducting beneath the North American plate, which led
to the formation of a continental volcanic arc represented by the Sierra Nevada Mountains to the
east of the San Joaquin Valley. Today the plutonic roots of the arc are exposed east of the Arch.
Sediments of the Great Valley Group filled the forearc basin north of the Arch during
Jurassic to Cretaceous time. In the southern part of the San Joaquin Valley, the Great Valley
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sequence thins, possibly due to uplift associated with the oroclinal bending of the southernmost
Sierra Nevada in the early Tertiary (Bartow, 1991). Saleeby et al. (2013), on the other hand,
attributed the lack of Cretaceous and Paleocene strata in the southern part of the basin along the
Arch to the collision and low-angle subduction of a seamount (correlated to the Shatsky Rise of
the modern NW Pacific Basin) in this area. This event caused late Cretaceous uplift and erosion
of the forearc basin and adjacent Sierran batholith across about 500 km of the batholith in the
southern California region (Saleeby et al., 2013).
A major tectonic change in the plate margin occurred during early to middle Miocene
time when the East Pacific spreading center encountered the trench, creating the Mendocino
triple junction (Fig. 2). This caused the plate boundary to change from subduction to dextral
strike slip. The current California segment of the western North American plate boundary is
complex and consists of a subduction zone to the north of the Cape Mendocino, and dextral
strike slip along the San Andreas Fault from there to Central Mexico (Bloch, 1991).
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Fig. 2 – Tectonic setting along the coast of California from Oligocene to present showing the
change from a convergent to a transform margin (Atwater, 1970).
STRATIGRAPHY OF THE BAKERSFIELD ARCH AREA
Vedder Formation
Figure 3 shows the stratigraphy, lithology and paleobathymetry of the units in the
Bakersfield Arch area. One of the oldest units is the Vedder Formation. Microfossils from
subsurface samples indicate a Zemorrian age for the Vedder Formation (33.5-22 Ma) (Oligocene
to earliest Miocene) (Bartow and McDougall, 1984; Bartow, 1991; Olson, et al., 2009). The
Vedder Formation is characterized by blue-gray, medium grained, well-sorted clean sand,
interbedded with brown organic siltstone layers (Fig. 3) (Albright et al., 1957) and its thickness
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may reach more than 300 m (984 ft) locally (Bartow and McDougall, 1984). It most often
comformably overlies the Walker Formation but, in places, is the lateral marine equivalent of the
upper part of the nonmarine Walker Formation (Bartow and McDougall, 1984). The silts and
sands of the Freeman and Jewett formations unconformably overlie the Vedder Formation along
the east margin of the basin, north of the Bakersfield Arch, but the contact may be conformable
south of the Bakersfield Arch and farther west (Bartow and McDougall, 1984). In some areas
the Vedder Formation is unconformably overlain by a 10 foot marker bed of Saucesian age
known as the “grit zone” (Albright et al., 1957), which consists of fine to coarse-grained sand
with black chert granules and quartz pebbles in a clay to silt matrix (Hackel and Krammes,
1958).
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Fig. 3: Stratigraphic column showing the formations in the Bakersfield Arch area. The average
thickness of the Vedder Formation is from Bartow and McDougall (1984), and the San Joaquin
and Tulare thicknesses are from Keller et al., (2000). The other average thicknesses are
calculated from well log curves: Freeman=258 m, Round Mountain=294 m, Monterey=516 m,
Reef Ridge=240 m, and Etchegoin=959 m.
300
600
900
1200
1500
1800
2100
2400
2700
3000
3300
3600
3900
4200
4500
4800
5100
5400
14
The Vedder Formation was deposited in a shallow marine environment (Ramseyer et al.,
1993). Subsurface mapping and analysis of well log data on the Bakersfield Arch suggests that
the Vedder Formation was deposited following a period of rapid subsidence (ca. 50 cm/1000
years) that lead to the formation of a ramp geometry with constant slope between nonmarine and
deep-marine environments (Bloch, 1986).
Freeman-Jewett/Olcese formations
Foraminiferal faunas indicate an upper Zemorrian and Saucesian age for the
Freeman Silt (Olson, et al., 2009). Therefore the age of the Freeman Silt is about 23-16.5 Ma
(early Miocene). It is characterized by grey-white, sandy to clayey, micaceous siltstones
containing fairly abundant early Miocene foraminifera (Fig. 3) (Olson, et al., 2009).
The upper Jewett Formation is a massive, concretionary, silty sandstone with megafossils,
sharkteeth and abundant marine mammal remains (Barnes, 1979). Its basal part consists of grey,
poorly sorted, coarse-grained sandstone containing sub-angular quartz grains and black chert
pebbles at the base of the Pyramid Hill Sand Member (also known as the grit zone) (Barnes,
1979).
The composite thickness of the Freeman Silt and Jewett Sand is about 300 m (984 ft) in
the Kern River area (Bartow and McDougall, 1984). The fossil assemblages indicate a deep
water environment for the deposition of the Freeman Silt, probably at lower middle bathyal
depths (1500-2000 m) (Bartow and McDougall, 1984; Olson, et al., 2009).The Freeman Silt
gradationally overlies and intertongues with the Jewett Sand and also intertongues with the
overlying Olcese Sand (Fig. 4). (Bartow and McDougall, 1984).
Bartow and McDougall (1984) indicate a Saucesian and Relizian age (early Miocene) for
the Olcese Formation. The Olcese Formation is a sandstone with some interbedded siltstone and
15
pebbly sandstone and conglomerate. It reaches a thickness of 300 to 360 m (984 to 1181 ft)
locally (Bartow and McDougall, 1984). This unit was deposited in a wide range of
paleoenvironments including nonmarine, estuarine and outer shelf depositional settings (Olson,
et al., 2009). In outcrop, the middle part is probably nonmarine, although the upper and lower
parts are marine and abundantly fossiliferous in some areas (Addicott, 1970). Farther basinward,
to the west, the Olcese is wholly marine (Bartow and McDougall, 1984).
The unit intertongues basinward with the underlying Freeman Silt and the overlying
Round Mountain Silt, and apparently pinches out completely within a few kilometers of the
outcrop at the south end of the basin (Bartow and McDougall, 1984). This unit was mapped
together with the Freeman-Jewett interval in this report.
Bena Gravel
Bartow and McDougall (1984) defined the age of the Bena Gravel to be late early
Miocene, middle Miocene, and late Miocene. This unit is restricted to the area south of the Kern
River where it can reach 750 m (2460 ft) thick (Bartow and McDougall, 1984). The Bena Gravel
is divided into an alluvial fan facies of sandstone and cobble conglomerate, and a paralic facies
containing plant material, fresh-water diatoms, foraminifers, rare oysters and marine mammal
bones (Bartow and McDougall, 1984). The Bena Gravel changes facies within a short distance
northward into the Olcese Sand and the Round Mountain Silt, and southwestward into the Edison
Shale of Kasline (Fig. 4) (Bartow and McDougall, 1984). The Edison Shale probably represents
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Fig. 4 – Diagrammatic cross section showing stratigraphic relationships of Tertiary formations
south of the Bakersfield Arch, especially the Bena Gravel (alluvial-fan and paralic facies) (blue)
grading southwestward into the Edison Shale of Kasline (green) during the late early and middle
Miocene. Location of the cross-section (blue line) and the axial trace of the Bakersfield Arch
(black thick solid line) are shown on the inset map (Modified from Bartow and McDougall,
1984).
a transitional facies between the Bena and the marine facies of the Round Mountain Silt and
Fruitvale Shale (Bartow and McDougall, 1984).
Round Mountain Silt
Foraminifera indicate the age of the Round Mountain Silt to be late Relizian to Luisian
(16.5-13.5 Ma—middle Miocene) (Beck, 1952). The Round Mountain Silt is a marine, greenish
grey, micaceous, clayey to sandy siltstone with abundant foraminifera representing upper middle
bathyal (1000-1500 m) depths (Fig. 3) (Olson, et al., 2009). The Round Mountain Silt reaches a
Bakersfield
Los Angeles
17
thickness of nearly 244 m (800 ft) in the vicinity of the Kern River (Albright et al., 1957). The
unit conformably overlies the Olcese Sand and is unconformably overlain by the Santa Margarita
or Chanac formations in the Kern River area (Bartow and McDougall, 1984). The depositional
environment of the Round Mountain Silt was offshore and deep marine (Pyenson et al., 2009).
Monterey Formation
The age of the Monterey Formation varies with location because the sedimentation
commenced and terminated at different times in separate depocenters. Behl (1999) notes the
typical duration of deposition to be from about Luisian to early Delmontian (16-6 Ma--middle to
late Miocene). Its thickness is up to 762 m (2500 ft) in some parts of the basin (Graham and
Williams, 1985). Interbedded rocks of different lithologies such as shale, mudstone, sandstone,
pyroclastics, and carbonates are present within the Monterey Formation (Fig. 3) (Bramlette,
1948). However, the strata is characterized by rocks with high silica content such as silica-
cemented rocks termed porcelanite and porcelanous shale, diatomaceous members, and large
amounts of hard and dense silica rocks classed as chert and cherty shale (Bramlette, 1948).
Scheirer and Magoon (2007) point out that the Antelope Shale is 10-6.5 Ma in age and the
Fruitvale is 13.5-6.5 Ma, and therefore their upper boundaries are considered the top of the
Monterey Formation. Further, both formations are shales, and their lithologies are considered to
be equivalent. However, Scheirer and Magoon (2007) also mentions that the well database
indicates that the Antelope is confined to the western margin of the San Joaquin Basin and
therefore should be considered separately from the Fruitvale Shale. As it can be seen in figure 5,
the Antelope Shale forms the upper part of the Monterey Formation on the west and the Fruitvale
Shale comprises the upper Monterey Formation on the east.
18
Fig. 5: Green represents the approximate area where the Antelope Formation is present, whereas
the Fruitvale Formation approximate location is represented by the blue area. Black line shows
the approximate location of the Bakersfield Arch crest. Polygons are oil fields and dots represent
the wells chosen for mapping in this project (DOGGR (Division of Oil, Gas, and Geothermal
Energy), 1998).
Sand-rich sediment sourced from the highlands to the west, south and east produced
submarine fans that prograded across the deep floor of the basin during deposition of the
Monterey Formation (MacPherson, 1978; Webb, 1981). Therefore, the Monterey Formation
serves as both source and reservoir for hydrocarbons. The Stevens sandstone occurs in the upper
part of the Monterey Formation and represents deep water turbidite deposition. Figure 6 shows
Antelope
Fruitvale
Bakersfield
0
18, 035 (5497 m)
FEET
19
Fig. 6 – Stratigraphy of the Bakersfield Arch area showing the most important sequences in the
Stevens sandstones. SB=sequence boundaries, LST=lowstand systems tracts, and black triangles
are condensed sections (Modified from Hewlett and Jordan., 1993).
that the Stevens sandstone in the southern San Joaquin Basin contains lowstand systems tracts of
the Rosedale, Coulter, Gosford, and Bellevue sequences in ascending order (Hewlett and Jordan,
1993). The three younger sequences were deposited during late Miocene and contain
progradational wedges (high stand and lowstand), incised valley fills, and retrogradational
systems (transgressive systems tracts) (Hewlett and Jordan, 1993). The lowermost lowstand
wedge is the Rosedale sequence, which was deposited during the middle Miocene.
Layers of siliceous shales and chert-rich rocks (N, O, and P cherts) are interbedded within
O Chert
P Chert
20
the Stevens sandstones. Recognizing these chert beds with the use of geophysical logs is the
primary method of subdividing the turbidite systems. The log signature of the chert beds is
suppressed SP and high resistivity.
The Santa Margarita and Chanac formations consist of coarse-grained sandstone and
conglomerate, with the Chanac Formation representing the eastern, non-marine facies and the
Santa Margarita Formation being the western shallow-marine equivalent. The Santa Margarita
and Chanac formations (Fig. 7) represent the shallow marine and non-marine lithostratigraphic
equivalent units of the deeper water Stevens sandstone (Hewlett and Jordan, 1993).
21
Fig. 7 - Correlation chart of Tertiary formations in southeastern San Joaquin Valley. The red box
emphasizes the variation within the Monterey Formation including the Santa Margarita and
Chanac (Modified from Bartow and McDougall, 1984)
Monterey Fm.
West East
22
Reef Ridge Formation
The Reef Ridge Formation was deposited during Delmontian time (10-5 Ma) (late
Miocene) and is defined as a soft, blue (brown weathering), shale with minor beds of sandy shale
(Fig. 3) (Barbat and Johnson, 1934). The average thickness of the unit in the Bakersfield Arch
area is 240 m (787 ft). The sandstone at the base of the Reef Ridge Shale south of the
Bakersfield Arch is interpreted to be deposited by a turbidity current (Bloch, 1991). This unit can
be distinguished from the underlying upper Monterey formation by the higher resistivity of the
latter (Bloch, 1991).
Etchegoin Formation/Macoma Claystone
Although age dating of the Etchegoin Formation is difficult due to the lack of age-
diagnostic microfauna and macrofauna, it appears that the formation is 5.5-4.5 Ma (Delmontian)
(late upper Miocene to early Pliocene) (Scheirer and Magoon, 2007). Its lithology consists of
bluish-gray to green shale, diatomaceous, micaceous claystones, and tan siltstones; lower in the
section, the sediments are dark-brown medium-grained, massive, and pebbly (Fig. 3) (Peirce,
1949). Its thickness varies from 305 to 1067 m (1000 to 3500 ft). This unit is considered to be
the basinward equivalent of the lower Kern River Formation, which Baron et al. (2008) dated as
6 Ma in age (latest Miocene) based on an ash bed found near the top of the Kern River
Formation. The Etchegoin Formation is known to pinch out approximately five miles northeast
of Bakersfield (Olson, et al., 2009). The Macoma Claystone, which occurs at the base of the
Etchegoin Formation, is mostly marine claystone and siltstone (Wagoner, 2009). This unit
provides a useful time-stratigraphic marker.
The Etchegoin Formation consists of interbedded shallow marine sandstone and offshore
shale. This boundary is time transgressive in places (Bloch, 1991). These deposits are interpreted
23
to be marine based on scattered occurrences of shelly fragments and bioturbation (Link et al.,
1990). The Etchegoin Formation was deposited during a minor transgression during Pliocene
time that resulted in deposition of shallow marine deposits, which separate the nonmarine
Chanac and Kern River Formations (Olson, et al., 2009).
Seismically, the Etchegoin Formation is distinguished from the Reef Ridge Shale by an
onlap surface separating the fairly discontinuous reflections of the former from the continuous
reflections of the latter (Bloch, 1991). This poor continuity of seismic reflections is probably due
to the fact that the Etchegoin Formation contains discontinuous sandstone bodies (Bloch, 1991).
San Joaquin Formation
Deposition of the San Joaquin Formation occurred between 4.5 and 2.5 Ma (Delmontian)
(late Pliocene) (Scheirer and Magoon, 2007). It consists of silt and clay beds alternating with
beds of sandstone and conglomerate and contains marine, brackish water and nonmarine fossils
(California Department of Water Resources, 2006), with a thickness of 100 to 1100 m (328 to
3609 ft) (Fig. 3) (Keller et al., 2000). This unit grades into the Kern River Formation to the east.
A brackish water depositional environment is indicated by the occurrence of mollusks of
Mya sp. (Loomis, 1990; MacGinitie, 1935). As the seaway connection between the Pacific
Ocean and the San Joaquin basin became more restricted, deposition of the San Joaquin
Formation sediments focused on the central region of the basin (Loomis, 1990). Fluvial and
deltaic environments prevailed in the north and south parts of the basin (Loomis, 1990).
Tulare Formation
The age of the Tulare Formation is 2.5-0.6 Ma (Pleistocene) (Scheirer and Magoon,
2007). This formation consists of lenticular deposits of poorly sorted clay, silt, and sand with
occasional interbeds of well-sorted fine-to-medium grained sand (Fig. 3) (California Department
24
of Water Resources, 2006). Its thickness can reach 2000 m (6562 ft) (Keller, et al., 2000). The
base of this unit is the First Mya Sand within the San Joaquin Formation, which separates fresh
water deposits of the Tulare Formation from brackish water deposits of the San Joaquin
Formation (Loomis, 1990). This marks a change from a predominantly marine environment to a
continental environment of lakes, swamps, and streams (Page, 1983).
Lakes of varying size occupied the valley throughout the deposition of this sequence and
caused the deposition of clay-rich sediments (Bloch, 1991). Coarser-grained fluvial and alluvial
sediments are also present (Bloch, 1991). Page (1983) notes that sediments have been derived
chiefly from the Sierra Nevada on the east and the Coast Ranges on the west and were deposited
as alluvial-fan, deltaic, flood-plain, lake and marsh deposits.
PETROLEUM SYSTEM
The Bakersfield Arch area contains many important oil fields. Since the 1930's, when the
first reservoirs were discovered in the Miocene Stevens sandstones of the southern San Joaquin
basin, about 472 MMBO and 1.3 TCF has been produced from 22 fields in the Bakersfield Arch
region (Hewlett and Jordan, 1993) (Fig. 8).
The importance of the Tejon and Buttonwillow depocenters as major areas for generation
of hydrocarbons and the related oil migration into the Bakersfield Arch is also highlighted by
Peters et al. (2012). Chemometric analyses of geochemical data for 165 crude oils were used to
identify oil families in the area, and their corresponding source rocks, migration pathways,
reservoirs, and filling histories. The results show that the source rocks for the oil families include
the (1) Eocene Kreyenhagen and Tumey formations, (2) Miocene Monterey Formation
25
Fig. 8 – Map showing oil fields in the Bakersfield Arch area. Oil and gas produced since the
1930's are shown as MMBO and BCF, respectively. Blue area is the East Gosford field, green is
the Canal oil field, orange the North Coles Levee and purple the South Coles Levee, as
mentioned in the text. The red line shows the location of the cross-section shown on Fig. 9
(Modified from Hewlett and Jordan, 1993).
26
(Buttonwillow depocenter), and (3) Miocene Monterey Formation (Tejon depocenter) (Peters et
al., 2012).
Maturation timing
Oils analyzed to date show that the source rocks near the Bakersfield Arch occur
predominantly within the middle and late Miocene-age Monterey Formation. This formation is
fine-grained and biosiliceous, with total organic carbon ranging from less than one to nearly six
percent (Gautier and Scheirer, 2008). The source rock feeding the reservoirs at the south part of
the Bakersfield Arch matured within the Tejon depocenter, whereas the Buttowillow depocenter
was the location of the source area for the north part of the Bakersfield Arch. Geochemical
analyses and petroleum systems modeling confirm that depths of about 4 to 4.6 kilometers (2.5
to 2.9 miles) are needed to produce oil from the Monterey Formation (Gautier and Scheirer,
2008). This depth constraint is important because the oldest members of the Monterey Formation
are currently at this depth on the Bakersfield Arch, and even the youngest strata of the Monterey
are in the oil window in the Tejon depocenter (Gautier and Scheirer, 2008).
Traps and seals
In addition to acting as source rocks, shales of the Monterey Formation also serve as seals
due to their low permeability and their ability to compartmentalize the sandstones bodies.
Siliceous shales and cherts, such as the N-, O-, and P-cherts, are important regional seals for
reservoirs (Fig. 9). The complex geology along the Bakersfield Arch provides a vast array of
traps for hydrocarbons, including updip sandstone pinch-outs, grain compaction decreasing the
permeability of rocks surrounding reservoirs, and structural traps created by anticlines and faults.
27
Fig. 9 – Seismic line and interpreted stacking of strata showing the chert condensed sections
(CS) (N, O and P cherts) and sequence boundaries (SB). The Coulter, upper Gosford, and lower
Bellevue of the Stevens sandstone sequence are shown here compartmentalized between the
chert marker beds. The approximate location of the cross-section is shown on Fig. 8 (red line)
(Hewlett and Jordan, 1993).
Almost every field on the Bakersfield Arch has at least one pool that is a combination
stratigraphic-structural trap, even though a few reservoirs occur in structurally dominated traps
(Hewlett and Jordan, 1993). Traps in the Coulter turbidite system are basically structural, with
faulting on post-depositional structures such as folds and within depositional (compactional)
28
anticlines. Compactional anticlines are formed by four-way closure developed by differential
compaction of channel/overbank complexes and/or turbidite lobes (Hewlett and Jordan, 1993).
Stratigraphic traps in the lower Gosford system are created by sandstone deposits
interbedded with low permeability shale such as those in the East Gosford oil field. The Gosford
turbidite lobes at the Canal oil field (Fig. 8) are trapped by compactional anticlines. Anticlines
also trap hydrocarbons in the upper Gosford turbidite wedge (i.e., Coles Levee oil field,)
(Hewlett and Jordan, 1993).
Pinch-out of strata across the top of anticlinal structures is the most common trap
mechanism for the lower Bellevue turbidite wedge. Up-dip pinch-out of confined turbidite and
channel fill sandstones along and across structural features and within slope gullies are the trap
mechanisms in the upper Bellevue sands (Hewlett and Jordan, 1993).
PREVIOUS STUDIES
Middle Miocene Hypothesis for growth of the Bakersfield Arch
Using a kinematic block model based on paleomagnetic data and faulting due to the
clockwise rotation of the Tehachapi block (Fig. 10), Bloch’s (1991) model indicates that the
extension in the southern San Joaquin basin is synchronously linked to the early Miocene
clockwise rotation of the Tehachapi block. However, the model does not explain pre-rotation
extension in the Edison area (prior to 22 Ma) that is responsible for faulting during late
Oligocene.
29
Fig. 10 – Model explaining the kinematics involved in the formation of the Tejon Embayment,
Edison area and Tehachapi Basin during clockwise rotation of the Tehachapi Block. The area is
subdivided into several small blocks in an attempt to capture the behavior at this complex
juncture between rotated and unrotated blocks (Bloch, 1991). The green rectangle represents the
approximate location of the Bakersfield Arch, right above the Tejon Embayment.
Bloch (1991) uses sequence stratigraphy techniques to investigate the tectonic activity in
the region during early Miocene time. His study employs seismic, borehole and outcrop data.
The tectonic activity started at 24-20 Ma with the passage of the Mendocino triple junction at the
latitude of the Southern San Joaquin basin, converting the adjacent plate interaction from
Edison Area
30
subduction to dextral slip (Bloch, 1991). Tectonic activity in the region south of the Bakersfield
Arch started during early Miocene and continued into the middle Miocene (Bloch, 1991).
Bloch (1991) notes that tectonic events in the San Joaquin basin are related to the plate tectonic
setting and the structural history of the basin should hold some record of the Mendocino triple
junction passage. Therefore, the change of the plate margin configuration might have introduced
compressional tectonic forces responsible for the rotation of the Tehachapi block during early
Miocene (Figs. 11a and 11b) and the subsequent uplift of the Bakersfield Arch during middle
Miocene. Bloch (1991) cites Bartow and McDougall (1984) who consider the formation of the
Arch to have occurred in middle Miocene time.
The lateral motion caused by the clockwise rotation of the Tehachapi block during the
period from 22 Ma to 16 Ma (early Miocene), along the south and east margin of the basin, is
inferred to have caused the crust beneath the basin to absorb the lateral motion caused by rotation
(Bloch, 1991). The San Joaquin basin could be subjected to extensional stress and/or deform in a
manner which allows movement of the Tehachapi block into space formerly occupied by the
basin (Bloch, 1991). Therefore, compressional forces probably caused the formation of folds as
the Tehachapi block rotated northward into the southern part of the San Joaquin basin. Post-early
Miocene shortening, mainly across the Temblor Range in the southwestern end of the San
Joaquin Basin, is not included in the model. The magnitude and orientation of extension
observed in the Mojave Desert equals that expected for the degree of rotation determined from
paleomagnetic studies (Bloch, 1991).
31
(a)
(b)
Figs. 11a and 11b – Early Miocene (22-16 Ma) kinematic model suggesting timing of
Bakersfield Arch formation. (a) Regional map showing blocks (red polygons) prior to clockwise
rotation of the Tehachapi block. (b) Regional map showing blocks (red polygons) after the
clockwise rotation of the Tehachapi block. Figure 11b suggests compressional forces imposed on
the basin as the Tehachapi block rotated. Green arrows represent direction of compression.
Approximate location of the Bakersfield Arch is represented by the green rectangle.
Paleomagnetic data are posted for comparison to the degree of rotation of sub-blocks (locations
of 7 ± 8 degrees, 21 ± 8 degrees and 24 ± 11 degrees rotations are shown). Blue arrows indicate
locations where paleomagnetic data were taken (Modified from Bloch, 1991).
7 ± 8
degrees
21 ± 8
degrees
24 ±11
degrees
32
Sheehan’s (1986) study also proposes a mechanism for Arch formation during middle
Miocene time. His study suggests that growth of the Arch probably began 16 Ma (early middle
Miocene) along with crustal extension in the Basin and Range Province. Left lateral movement
along the Garlock fault at about 16 Ma (early middle Miocene) and right lateral displacement
along the White Wolf fault caused clockwise rotation of the southern end of the Sierra Nevada
(Fig. 12). The rotation and extension eventually caused the Sierra Nevada block to break along
the Kern Canyon-Breckenridge-White Wolf fault system. The Tehachapi granitic block, which is
bounded by the Kern Canyon-Breckenridge-White Wolf fault on the north and the Garlock fault
on the south, was then moved southwestward across the south end of the San Joaquin Valley.
With the continued movement of the Tehachapi block and subsequent wedging of the Sierra
Nevada block westward into the San Joaquin Valley, the Bakersfield Arch was pushed up. This
tectonic explanation gives a mechanism responsible for uplifting the Arch. Also, it considers a
more regional event than the more localized clockwise rotation of the Tehachapi block referred
to by Bloch (1991).
33
Fig. 12 – Middle Miocene < 16 Ma model for Arch uplift. Geologic map of California showing
westward (clockwise) deflection of the southern Sierra Nevada Batholith. Figure suggests that
the southern San Joaquin Basin was pushed northward as compression was imposed from the
south by the rotation of the Tehachapi block. Deflection is shown by the blue arrow; Garlock
fault (brown); San Andreas fault (yellow); White Wolf fault (red); Breckenridge fault (green);
Kern Canyon fault (blue); BAR=Basin and Range Province; MD=Mojave Desert;
TM=Tehachapi Mountains; BA=Bakersfield Arch (purple area); SNB=Sierra Nevada Batholith
(silver area), and GCV=Great Central Valley (light orange area) (Modified from Sheehan, 1986).
Even though Bartow and McDougall’s (1984) study does not give an exact age and
mechanism for Arch formation, it provides evidence that the Arch was uplifted during the middle
MD
BAR BA
GCV
SNB
TM
34
Miocene, which supports Sheehan’s (1986) early middle Miocene age hypothesis. The evidence
used by Bartow and McDougall (1984) for dating the Arch uplift is the coarse clastic materials of
the Bena Gravel which originated from the uplift of the Sierra Nevada concurrent with faulting
and subsidence in the southern part of the basin. Alluvial-fan and paralic facies of the Bena
Gravel were deposited by a fan delta formed at the steep east margin of the basin in response to
the tectonic uplift in the Sierras to the east (Bartow and McDougall, 1984).
The 15-10 Ma Bena Gravel grades southwestward into the Edison Shale (Fig. 4), which
contrasts with the simple stratigraphy to the north of the Arch, where rapid facies changes are not
as apparent. This difference is evident by late early and middle Miocene, therefore, the
Bakersfield Arch became an important boundary between the far south end of the basin and a
relatively more stable shelf area to the north by this time period (Bartow and McDougall, 1984).
Late Quaternary Hypothesis
Saleeby et al. (2013), note that some of the structural features of the San Joaquin Basin,
such as the Bakersfield Arch, are the result of mid-Pleistocene orogeny. Saleeby et al. (2013)
describe the Bakersfield Arch as a compressional uplift created by the merging of a faulted uplift
northeast of Bakersfield, here described as the Kern Arch, and actively growing anticlines to the
west. Saleeby et al. (2013) identify the Kern Arch (Bakersfield Arch) as a structure formed by
ascending mantle lithosphere during late Quaternary. Saleeby et al. (2013) relate this structure to
the most recent phase of lower crustal lithosphere delamination below the Tulare Lake basin
area, known as the Isabella anomaly, and the consequent rise of asthenosphere material beneath
the area of the Kern Arch (Fig. 13).
35
Fig. 13 – Block diagram showing how the high-wave-speed body known as the Isabella anomaly
caused the uplift of the Arch. This anomaly occurs beneath the Tulare Lake basin and causes
delamination of the mantle lithosphere. The red line shows the location of the delamination
hinge, which is the place where the mantle lithosphere separates from the base of the crust.
Upwelling of mantle lithosphere into the area south and east of the delamination hinge is
interpreted to have caused uplift of the Bakersfield Arch, here depicted as the Kern Arch
(Saleeby et al., 2013).
Cecil et al. (2014) use thermomechanical models of mantle lithosphere removal from
beneath the southern Sierra Nevada to study vertical surface displacements in this area. This
study claims that the principal burial episode to be 2.5 Ma or later, and exhumation to 1 Ma or
later. Burial temperatures coupled with modern burial depths, and constraints on the geothermal
gradient indicate that the Kern Arch (Bakersfield Arch) strata underwent about 1000-2400 m
(3281-7874 ft) of Pliocene-early Quaternary subsidence (Cecil et al., 2014). Cecil et al. (2014)
estimates that about 1000-1800 m (3281-5906 ft) of Kern Arch strata were unroofed after 1 Ma
36
as a function of position on the Arch. The cause of such tectonic subsidence in the San Joaquin
Basin is attributed by the study to be the viscous coupling between the lower crust and a
downwelling mass in the delaminating slab, whereas the exhumation event is interpreted to be
the result from the northwestward peeling back of the slab and the associated replacement of
dense lithosphere with buoyant asthenosphere that drove rapid rock and surface uplift (Cecil et
al., 2014).
Another possible mechanism for post-Miocene uplift of the Arch is proposed by Miller
(1999). This study addresses the timing and causes of uplift of the Coast Ranges Provinces in
central California and connects this event with a forebulge structure at the Bakersfield Arch area.
Compression and shortening of the crust perpendicular to the San Andreas fault as a consequence
of oblique convergence of the Pacific and North American plates are thought to be the cause of
uplift in the Coast Ranges (Miller, 1999). This convergence and the resulting shortening
correspond to a clockwise rotation of 8 to 23 degrees of the Pacific plate motion (Miller, 1999).
The tectonic configuration change from strike slip with slightly oblique extension in central
California, to strike slip with oblique convergence angle along the San Andreas is thought to
have been caused by this event (Miller, 1999). Shortening perpendicular to the San Andreas fault
resulted from this event since the convergence angle after rotation has been about 5 degrees at
latitude 38 degrees (Miller, 1999). The onset of convergence created a foreland basin caused by
the basin flexing downward under the weight of north-vergent thrust sheets along the southern
margin of the San Joaquin Basin (figure 14). A small flexure called a forebulge forms along the
leading edge of the thrust belt-foreland basin pair and may have resulted in uplift of the area near
the Bakersfield Arch. Even though many other studies indicate age estimates for the uplift of the
Coast Ranges between 3 and 8 Ma, Miller (1999) uses reflection seismic, geohistory-subsidence
37
and lithologic data of the Miocene-Pliocene-Pleistocene sedimentary record to propose that the
foreland-style uplift began about 6 Ma and no later than 5.4 Ma (tectonic subsidence), with a
second event of subsidence at about 3.4 Ma (sediment-load subsidence driven by sea-level drop,
climate change, erosion and enhanced sediment flux into the basin) (Fig. 14).
Fig. 14: Diagram showing the onset of convergence and Coast Range uplift by 5.4 Ma (A) and
sediment-load subsidence by 3.4 Ma (B). The forebulge, which may have contributed to uplift of
the Bakersfield Arch area, is indicated by the blue arrow (Miller, 1999).
Forebulge
38
DATA AND METHODS
This study focuses on well data available from the California Division of Oil, Gas and
Geothermal Resources (DOGGR) and data published in other studies available in the literature.
Available well log data along the Bakersfield Arch are used to delineate the extent and
thicknesses of the Etchegoin, Macoma, Reef Ridge, Monterey, Round Mountain, Freeman, and
Vedder formations and determine the effect, if any, of the uplift of the Bakersfield Arch on the
thicknesses and distributions of these lithofacies across the Arch.
Consequently, cross-sections and stratigraphic thickness maps of shale units were created
based on well data across the crest of the Arch. Only shales are used as the tops for this study
rather than sandstones because the finer-grained clastic rocks have a more regional distribution
within the basin, whereas the distribution of sandy turbidites form local accumulations. Due to its
widespread presence in the Bakersfield Arch area, the only sand unit used for this study is the
Vedder Formation.
The stratigraphic interval this study focuses upon ranges from the top of the Etchegoin
Formation (latest Miocene or early Pliocene) to the top of the Vedder Formation (Oligocene).
The Macoma Claystone is used as a local marker within the Etchegoin Formation. Using the tops
defined for each unit and marker based on the log curves, thickness maps of six sedimentary
packages are presented (Table 1). Figure 15 shows these packages in a stratigraphic column.
39
From (top) To (top)
1. Etchegoin Macoma
2. Macoma Reef Ridge
3. Reef Ridge Monterey
4. Monterey Round
Mountain
5. Round
Mountain
Freeman
6. Freeman Vedder
Table 1: Tops used for mapping six sedimentary packages.
Fig. 15: Stratigraphic column of the Southern San Joaquin Valley and sedimentary packages
(Scheirer and Magoon, 2007).
Etchegoin-Macoma Macoma-Reef Ridge
Monterey-Round
Mountain
Round Mountain-
Freeman
Freeman-Vedder
Reef Ridge-Monterey
40
The thickness and distribution of the lithofacies across the Arch are used to determine the
timing of uplift of the Arch relative to the stratigraphy. Sedimentary packages will be thicker in
areas of subsidence and thinner over uplifts. For example, if strata pinches out or thins against
the flanks of and across the top of the Arch, uplift occurred before or during deposition of that
specific unit, unless there is an unconformity above the unit indicating that it thins by erosion
and the unit is non-marine in nature. If strata is continuous or thickens across the Arch,
deposition probably occurred before uplift of the Arch. The cross-sections show how the
thicknesses of the units change in the third dimension
By using the age of each unit, it is possible to set age constraints for the uplift event and
test the two competing hypotheses for the timing of uplift presented in this study, i.e., 1) the
middle Miocene hypothesis supported by Sheehan (1986), Bartow and McDougall (1984) and
Bloch (1991) and 2) the late Quaternary hypothesis by Saleeby et al. (2013). These methods
assume that the tops of the shale beds and chert layers approximate time horizons within the area
occupied by the Bakersfield Arch.
RESULTS
Mapping
Top of Etchegoin to top of Macoma
The contour lines of the Etchegoin-Macoma (Fig. 16) isopach map are perpendicular to
the crest of the Arch and the values show gradual thinning northeastward. Thickness reaches
4000 ft (1219 m) to the west, decreasing to less than 200 ft (610 m) to the east. The cross-section
shows no change in thickness across the axis of the Arch (Fig. 17).
41
Fig. 16: Top of Etchegoin to top of Macoma isopach map. Black line shows the approximate
location of the Bakersfield Arch crest. Contour lines show the Etchegoin Formation thinning to
the northeast but not across the crest of the Arch. Polygons are oil fields and dots the wells
chosen for this project. Contour interval = 100 feet (30.5 m).
Bakersfield
0
18, 035 (5497 m)
FEET
0
1000 (305 m)
2000 (610 m)
3000 (614 m)
4000 (1219 m)
N
42
(a)
A
A`
Bakersfield
N
;
l
;
l
;
l
;
l
;
l
0
18, 035 (5497 m)
FEET
43
(b)
Fig. 17: (a) Map showing the cross-section line (blue line), axis of the Arch (triangle), oil fields
(polygons), and wells (dots). (b) Cross-section showing that the Etchegoin-Macoma interval gets
thicker as the axis of the Arch is approached.
A
A’
0
101
50
(309
4 m)
FEET
29
18
54
0
0 20
0
(61
m)
FEET
Axis o
f
the A
rch
44
Top of Macoma to top of Reef Ridge
The Macoma-Reef-Ridge isopach map shows contour lines perpendicular to the crest of
the Arch and thickens to the southwest from the basin margin to the basin axis (Fig. 18).
Thickness is nearly 1800 ft (549 m) in the southwest and decreases to 200 ft (61 m) in the
northeast. The cross-section shows this interval thickening to the southeast into the Tejon sub-
basin (Fig. 19).
Fig. 18: Top of Macoma to top of Reef Ridge isopach map. Black line shows the approximate
location of the Bakersfield Arch crest. Contour lines show the Macoma Formation thinning to
the northeast. Polygons are oil fields and dots the wells chosen for this project. Contour interval
= 50 feet (15 m).
Bakersfield
1000 (305 m)
200 (61 m)
N
1900 (579 m)
0
18, 035 (5497 m)
FEET
45
(a)
A`
A
Bakersfield
N
0
18, 035 (5497 m)
FEET
46
(b)
Fig. 19: (a) Map showing the cross-section line (blue line), axis of the Arch (triangle), oil fields
(polygons), and wells (dots). (b) Cross-section showing the Macoma-Reef Ridge interval
thickening to the southeast into the Tejon sub-basin.
A
A’
0 20
0
(61
m)
FEET 0
101
50
(309
4 m)
FEET
Axis o
f
the A
rch
47
Top of Reef Ridge to top of Monterey
The Reef Ridge-Monterey (Fig. 20) isopach map shows gradual thinning across the crest
of the Arch. Thickness values reach about 1500 ft (457 m) on the flanks of the Arch, and 350 ft
(107 m) along the crest line of the Arch. The Reef Ridge-Monterey (Fig. 21) cross-section clearly
shows thinning as the over the crest of the Arch.
f
Fig. 20: Top of Reef Ridge to top of Monterey isopach map. Black line shows the approximate
location of the Bakersfield Arch crest. Contour lines show the Reef Ridge Formation gradually
thinning as the crest of the Arch is approached from the south and north. Polygons are oil fields
and dots the wells chosen for this project. Contour intervals = 25 feet (7.5 m).
Bakersfield
2000 (610 m)
1000 (305 m)
200 (61 m)
1400
1400
60
0
600
N
0
18, 035 (5497 m)
FEET
48
(a)
A
A`
Bakersfield
N
0
18, 035 (5497 m)
FEET
49
(b)
Fig. 21: (a) Map showing the cross-section line (blue line), axis of the Arch (triangle), oil fields
(polygons), and wells (dots). (b) Stratigraphic cross-section hung on a datum of the top of the
Reef Ridge Shale showing how the thickness of the Reef Ridge-Monterey interval changes
across the Arch--thinning across the crest of the Arch.
A
A’
0 20
0
(61
m)
FEET 0
10
150
(30
94 m
)
FEET
Axis o
f
the A
rch
50
Top of Monterey to top of Round Mountain
This interval from the top of the Monterey to the top of the Vedder Formation does not
show thinning across the crest of the Arch. The Monterey-Round Mountain isopach map
primarily presents northeast thinning from the basin axis onto the basin margin (Fig. 22). The
contour lines are roughly perpendicular to the crest of the Arch, and the values range from 4400
ft (1341 m) to the south and less than 200 ft (61 m) to the northeast. The Monterey-Round
Mountain cross-section shows thickening to the southeast (Fig. 23).
51
Fig. 22: Top of Monterey to top of Round Mountain isopach map. Black line shows the
approximate location of the Bakersfield Arch crest. Contour lines show the Monterey Formation
thinning to the northeast. Polygons are oil fields and dots the wells chosen for this project.
Contour intervals = 100 feet (30.5 m).
Bakersfield 0
1000 (309 m)
2000 (610 m)
3000 (914 m)
4000 (1219 m)
1000 1200
1600
2000
4000
4400
N
0
18, 035 (5497 m)
FEET
52
(a)
A
A`
Bakersfield
N
0
18, 035 (5497 m)
FEET
53
(b)
Fig. 23: (a) Map showing the cross-section line (blue line), axis of the Arch (triangle), oil fields
(polygons), and wells (dots). (b) Cross-section showing how the thickness of the Monterey-
Round Mountain interval increasing to the southeast.
A
A’
0 20
0
(61
m)
FEET 0
10
15
0
(30
94
m)
FEET
Axis o
f
the A
rch
54
Top of Round Mountain to top of Freeman
The Round Mountain-Freeman isopach map shows northeast thickening with values
ranging from 100 ft (30.5 m) to the southwest to about 2000 ft (610 m) to the northeast (Fig. 24).
The cross-section indicates roughly continuous thicknesses across the crest of the Arch (Fig. 25).
Fig. 24: Top of Round Mountain to top of Freeman isopach map. Black line shows the
approximate location of the Bakersfield Arch crest. Contour lines show the Round Mountain
Formation thinning to the southwest. Polygons are oil fields and dots the wells chosen for this
project. Contour interval = 40 feet (12 m).
Bakersfield
100 (30 m)
1000 (304 m)
2000 (610 m)
3000 (914 m) 940 700
1000
100
280
N
0
18, 035 (5497 m)
FEET
55
(a)
A
A`
Bakersfield
N
0
18, 035 (5497 m)
FEET
56
(b)
Fig. 25: (a) Map showing the cross-section line (blue line), axis of the Arch (triangle), oil fields
(polygons), and wells (dots). (b) Cross-section showing that the thickness of the Round
Mountain-Freeman interval (does not show any relevant thickness trend across the Arch
A
A’
0 20
0
(61
m)
FEET 0
10
15
0
(30
94
m)
FEET
29
06
07
7
Ro
un
d M
ou
ntain
Axis o
f
the A
rch
57
Top of Freeman to top of Vedder
The Freeman-Vedder isopach does not show any relevant trend (Fig. 26). Thicknesses
vary throughout the map without any distinguishable pattern, other than slightly thinning from
the basin axis onto the basin margin. If anything, the thickness appears to increase along the crest
of the Arch. Values range from less than 200 ft (61 m) to about 1600 ft (488 m) at different
locations of the map. The cross-sections show little change in thickness across the crest of the
Arch other than a slight thickening (Fig. 27).
58
Fig. 26: Top of Freeman to top of Vedder isopach map. Black line shows the approximate
location of the Bakersfield Arch crest. Contour lines do not show any relevant trend. Polygons
are oil fields and dots the wells chosen for this project. Contour intervals = 20 feet (6 m).
Bakersfield 200 (60 m)
1000 (305 m)
2000 (610 m)
1000
800
1000
N
0
18, 035 (5497 m)
FEET
59
(a)
A
A`
Bakersfield
N
0
18, 035 (5497 m)
FEET
60
(b)
Fig. 27: (a) Map showing the cross-section line (blue line), axis of the Arch (triangle), oil fields
(polygons), and wells (dots). (b) Cross-section showing that the thickness of the Freeman-Vedder
interval does not show any relevant trend across the Arch.
A
A’
0 2
00
(61
m)
FEET 0
101
50
(309
4 m)
FEET
Axis o
f
the A
rch
61
DISCUSSION
The maps and cross-sections suggest that the Arch was not a positive feature influencing
the sedimentation during the deposition of the Round Mountain (middle Miocene) and Freeman
(early Miocene) silts. However, the thinning of the Reef Ridge Shale (Fig. 20 and 21) over the
crest of the present-day location of the Arch does indicates that it was a positive feature during
late Miocene time.
If the Arch were a positive feature during middle Miocene time, as proposed by Bartow
and McDougall (1984) and Bloch (1991), or early middle Miocene (Sheehan,1986) , the
Monterey Formation might be expected to thin across the Arch since the Monterey is a middle to
late middle Miocene unit. However, figures 22 and 23 show the Monterey thinning
northeastward toward the basin margin, not over the crest of the Arch. This could be due to the
fact that the Arch is a southwest plunging structure; therefore, uplift might have started to the
northeast, affecting deposition of the Monterey in this area first, causing the Monterey to appear
thinner to the northeast. However, thinning to the northeast would be expected regardless as this
would represent greater proximity to the basin margin. The axis of the basin lies to the west of
the Bakersfield Arch. This area was the site of rapid subsidence and was occupied by a deep
marine environment whereas the northeast margin of the basin adjacent to the Sierra subsided
more slowly and was the site of a shallow shelf or non-marine depositional setting as can be seen
in figure 28. If the Monterey were mapped as individual units instead of mapping it as a single
package as in the case of this study, uplift of the Arch may have occurred during Monterey
deposition as well.
The irregular distribution of middle to late Miocene turbidites in the Monterey
Formation, such as the Stevens sands, suggest the presence of several smaller positive features
62
Fig. 28: Late Miocene (about 9-10 Ma) paleogeography of the San Joaquin basin area (Bartow,
1991).
such as the Coles Levee and Elk Hills anticlines on the seafloor in the area of the Arch by the
time of deposition of the uppermost Monterey. Hardoin (1962) and Dosch (1962) present cross-
sections along the North and South Coles Levee fields, respectively, indicating that the younger
turbidite sequences within the Monterey thin over or pinch out against the anticline structures,
whereas the older turbidites have continuous thicknesses over these structures. At the Elk Hills
63
field, the cross-sections presented by Lorshbough (1967) indicate that the Olig sand within the
upper part of the Reef Ridge Formation is truncated by an unconformity; the Reef Ridge thins
slightly and the thickness of the turbidites in the underlying Monterey is continuous over the
anticline structure.
The distribution of Monterey and Reef Ridge turbidite sands in the Coles Levee and Elk
Hills fields on the western end of the Bakersfield Arch suggest that these smaller anticlinal
structures had no appreciable seafloor topography until later when the uppermost Monterey
sands and the Reef Ridge Shale were deposited. The thinning of the uppermost Stevens sands
over the tops of the Elk Hills and Coles Levee structures indicate that these smaller anticlines
were rising during deposition of the uppermost part of the Monterey. These are smaller structures
superimposed upon the larger Bakersfield Arch structure and, as such, they do not reflect uplift
of the broader area of the Arch itself.
The uplift of the broader Arch primarily appears to have affected the thickness of the
Reef Ridge, since isopach maps and cross-sections indicate that this unit thins across the Arch.
The Etchegoin and Macoma intervals do not show evidence of thinning across the Arch,
suggesting that the seafloor topography created by the rising Arch during Reef Ridge deposition
was filled in prior to or during deposition of the upper Reef Ridge.
The present day topography seen in the study area (Fig. 29) consists of a topographic
high across the crest of the Arch. Sedimentary layers of the younger Etchegoin, San Joaquin,
Kern River and Tulare formations dip away from the crest indicating renewed uplift in the area
of the Arch after deposition of these younger formations. A geologic map presented by Bartow
(1984) shows the Kern River Formation (late Miocene to Pliocene) to the south of the Arch
dipping 5-15 degrees in the southeast direction, and to the north dipping 5-10 degrees in the
64
northwest direction.
Although the present topography and structural data suggest that a second uplift event
took place, an exact date for the start of this event is not possible to determine due to the lack of
good markers within post-Etchegoin units. Consequently, it was not possible to generate
thickness maps of post-Etchegoin units. The second uplift event, however, could have started at
any time after the deposition of the Etchegoin Formation, which is the youngest mapped
formation not showing evidence of thinning over the Arch. Since the exact age at which
Etchegoin deposition ended is not known, this second uplift event could have started during early
Pliocene or late Miocene. Also, the Kern River Formation, which is thought to be a late Miocene
formation and time equivalent to the upper Etchegoin, was not mapped due to the lack of a good
marker unit. Therefore, the Arch could have been reactivated in late Miocene time, when the
lower Kern River Formation was deposited.
Thickening of the Etchegoin Formation (Fig. 17) as the axis of the Arch is approached
from the south and north may be related to the Pliocene subsidence event described by Cecil et
al. (2014). This relationship can be drawn based on the ages of subsidence of the basin (2.5 Ma
or later) and deposition of the Etchegoin (5.5 to about 5 Ma). Although the exact age of the
Etchegoin Formation is not known, deposition of this formation is believed to have ceased
during late Miocene or early Pliocene time (around 5 Ma). The Pliocene subsidence event is
dated to 2.5 Ma or later according to Cecil et al. (2014). Therefore, the appreciable thickening
(about 61 m or 200 ft) of the Etchegoin observed on well 2918540 (Fig. 17) might be related to
the Pliocene subsidence episode mentioned by Cecil et al. (2014).
65
Fig. 29: Google Earth satellite photo showing the present day Bakersfield Arch area. The graph
below shows the topopraphic profile along the red line in the photo. The black line represents
the approximate location of the Arch crest.
CONCLUSION
The maps and cross-sections created in this study suggest that two periods of uplift took
place across the broader Bakersfield Arch area: 1) during middle to late Miocene time and 2)
during latest Miocene (post-Etchegoin Formation deposition) to Pleistocene time. The evidence
for the former is based on the thinning of the interval between the top of the Reef Ridge to the
top of the Monterey across the present day location of the axis of the Bakersfield Arch. The
formations older and younger than this interval do not thin across the crest of the Arch.
Uplift of the Arch may have started as early as middle Miocene as proposed by previous
studies however, in this study, sub-units within the Monterey Formation were not mapped
5 km (3mi) 15 km (9mi) 25 km (15mi)
110m (361ft)
105 m (344ft)
100 m (328ft)
Min., Avg., Max. Elevation: 334, 361, 379ft. Total Distance: 18.6 mi. Imagery Date: 3/26/2015
66
separately. Future detailed thickness mapping using chert marker beds within the Monterey
Formation may provide better resolution of the timing of uplift.
Finally, the present day topography in the area shows a positive feature across the crest of
the Arch which suggests reactivation of the feature since deposition of the Etchegoin Formation.
The dip of post-Reef Ridge strata away from the crest of the Arch and the fact that the Etchegoin
is the youngest mapped unit that does not thin over the Arch suggest that uplift was reactivated
on or after latest Miocene to Pleistocene time.
67
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71
APPENDIX: wells and tops (measured depths) used in the study
API Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Maco-
ma
Reef
Ridge Monterey
Round
Mountain Freeman Vedder
2963863 35 27S
23E 17500 5630 10200 14395 14830
2909478 25 27S
23E 14770 4370 7500 9112 14252
2949212 3 27S
23E 15880 12700
2946452 12 27S
23E 16505 8500 9698 11282 12280 13194
2941957 35 27S
24E 15476 4620 7490 7720 11960 12560
2909489 17 27S
24E 13716 4300 7860 12800
2937135 8 27S
24E 13253 7400 8960 12720
2937131 7 27S
24E 13453 7880 8980 12700
2948583 6 27S
24E 15435 4750 8400 9720 12950 13510
2930723 36 27S
26E 6050 2780 2990 5420 5946
2942852 25 27S
26E 5765 2830 3190 5450
2950284 27 27S
26E 7355 3670 4260 5810 6915
2930721 15 27S
26E 7737 3280 3000 4970 5828
2930728 16 27S
26E 7549 4070 5630 6489
2930718 12 27S
26E 7213 2450 4350 5005
2930722 2 27S
26E 6703 2530 4310 4975
2930727 4 27S
26E 7486 3570 5350 6125
2916088 32 27S
27E 3546 2280 2490
2916183 34 27S
27E 4220 3300 3918
2916564 36 27S
27E 3098 2190 3045
2916187 36 27S
27E 3187 1380 2325 3057
2916138 26 27S
27E 3747 1620 2600 3268
2914928 27 27S
27E 3700 1910 2900 3585
2914931 28 27S
27E 4178 1520 1680 3250 3850
2916503 24 27S
27E 4517 1250 2150
72
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin
Macoma Reef
Ridge Monterey
Round
Mountain Freeman Vedder
2916056
20 27S
27E 4219 2150 2280
2916125 13 27S
27E 2935 2190 2850
2914787 15 27S
27E 5540 1360 3150 3780
2914930 17 27S
27E 2364 1880 2010
2952963 12 27S
27E 2713 1150 2010 2685
2914779 10 27S
27E 1429 1295 1429
2916157 7 27S
27E 3046 2170 2500
2914786 9 27S
27E 2513 1500 1855 2400
2914932 1 27S
27E 2876 2105 2665
2916100 2 27S
27E 4656 1020 1700 2500 3160
2916105 4 27S
27E 5205 2100 2960 3540
2914763 4 27S
27E 5084 1770 2100 2950 3515
2914728 6 27S
27E 2808 1900 2210
2912296 31 27S
28E 2765 1780 2508
2912377 32 27S
28E 2201 870 1700 2175
2912378 33 27S
28E 2127 740 1710 2121
2912251 34 27S
28E 2053 400 1450
2912248 35 27S
28E 1403 750 1380
2900006 28 27S
28E 2144 410 1182
3004666 30 27S
28E 3600 870 1720 2437
2912275 22 27S
28E 1539 885 1462
2914070 20 27S
28E 2341 1670 2280
2912479 19 27S
28E 2768 980 1810 2456
2912667 15 27S
28E 1307 780 1285
2954754 15 27S
28E 1878 1210 1706
2914057 18 27S
28E 2565 1150 1880 2468
2912395 11 27S
28E 1183 588 1137
73
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Macoma Reef
Ridge Monterey
Round
Mountain Freeman Vedder
2954441 10 27S
28E 1808 1180 1690
2957343 9 27S
28E 1977 1020 1876
2912084 8 27S
28E 2337 870 1650 2296
2912013 7 27S
28E 1987 1185 1900
2912225 3 27S
28E 1564 135 900 1327
2912458 4 27S
28E 1954 640 1230 1638
2954644 5 27S
28E 2345 855 1615 2262
2912492 6 27S
28E 1989 1130 1820
2903173 5 28S
23E 13614 4863 10670 12120
2964052 30 28S
23E 16285
3048481 4 28S
23E 12709 5600 11595
2919848 8 28S
23E 12900 10705
2975353 14 28S
23E 13700 5860 9490
2947380 10 28S
23E 20753 5652 10500
2921230 35 28S
24E 11988 4955
2919890 36 28S
24E 10987
2936449 23 28S
24E 7502 3809 6441 8138 10917 12390
2916643 33 28S
R25 11510 7638 8432 9820 10503
2916657 34 28S
25E 11700 7472 8156 10245 11280
2916682 35 28S
25E 11500 8273 9410 10242
2971552 25 28S
25E 11830 7885 10229 11227
2965091 26 28S
25E 12092 9675 10401 11390
2916579 27 28S
25E 11695 8078 9458 10149 11275
2930750 21 28S
25E 11754 6539 10575 11738
2930749 20 28S
25E 12404 4830 6759 11130
2960414 19 28S
25E 13170 9907
2955045 16 28S
25E 13963 5670 9819 10660 11552
74
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Macoma Reef
Ridge Monterey
Round
Mountain Freeman Vedder
2930755 17 28S
25E 15068 4720 6470 9950 10725
2910932 18 28S
25E 12563 3812 6610 6909 10052 10771
2910930 7 28S
25E 12628 6829 9440 10004 10699
3001226 34 28S
25E 8100 5190 6630
2947999 32 28S
26E 8200 3336 5566
3014351 33 28S
26E 11130 7885 8688 9689
2979500 26 28S
26E 10184 4025 4460 7800 8520
2930769 27 28S
26E 7543 4403 4930
3033663 28 28S
26E 7846 4755 7690
2930760 20 28S
26E 7001 3284 5567
2930761 15 28S
26E 8515 3086 4206 6315 7299
2930768 16 28S
26E 9100 2967 4664 6572 7505 8618
2930773 11 28S
26E 4300 3376 3680
2930764 13 28S
26E 9498 3386 3683 6318 7513
2985041 31 28S
27E 4900 3512 3787
3037484 25 28S
27E 2593 1696 1880
2910282 26 28S
27E 2415 1857 2050
2910611 27 28S
27E 2590 1954 2161
2910453 28 28S
27E 2899 2483 2755
3049469 24 28S
27E 2085 1626 1809
3037795 23 28S
27E 2252 1685 1873
3037480 23 28S
27E 2820 1785 1975
2916575 20 28S
27E 3492 2750 2990
2930787 19 28S
27E 3964 3210 3580
2916486 16 28S
27E 2950 2250 2505 4590 5650
2970225 17 28S
27E 3600 2650 2940
2916411 18 28S
27E 3756 2980 3255
75
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Maco-
ma
Reef
Ridge Monterey
Round
Mountain Freeman Vedder
2946156 12 28S
27E 4505 2190 3240 4310
2959847 8 28S
27E 3225 2560 2770
2916275 7 28S
27E 3597 2700 2906
2930844 35 28S
28E 3141 310 1840 3034
2983701 36 28S
28E 4043 180 1740 2885
2930836 25 28S
28E 3168 310 1770 2900
2930815 26 28S
28E 4231 270 1870 3040
2924047 27 28S
28E 3463 900 1160 2510 3126
2928038 30 28S
28E 5998 2060 2300 3460 4605
2918193 24 28S
28E 2250 1210 2208
2916913 23 28S
28E 2891 670 1850 2845
2918463 22 28S
28E 3270 1063 2196 3204
2918169 13 28S
28E 2287 1230 2253
2918276 14 28S
28E 2721 645 1780 2688
2918149 15 28S
28E 2794 800 1960 2775
2930824 16 28S
28E 3385 1440 2380 3314
2926738 17 28S
28E 3762 1700 2800 3750
2918445 15 28S
28E 2928 930 2043 2912
2930871 31 28S
29E 4462 1320
2916876 32 28S
29E 2250 1220 2225
2930879 33 28S
29E 2634 1440 2435
2940467 35 28S
29E 3386 2475 3240
2930859 27 28S
29E 3170 2050 3140
2942653 28 28S
29E 2250 920 1817
2930881 21 28S
29E 2250 1100 1922
2969120 20 28S
29E 2875 1520 2325
2972088 16 28S
29E 2020 990 1602
76
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Macoma Reef
Ridge Monterey
Round
Mountain Freeman Vedder
2918375 17 28S
29E 2117 1490 2055
2953853 18 28S
29E 2235 1140 2038
2918313 7 28S
29E 1655 1120 1955
2911407 32 29S
23E 15006 11569
2952494 30 29S
23E 16005 11450
2901176 25 29S
24E 11948 4718 8850
3022259 23 29S
24E 11498 4600 9200 10400
2965169 16 29S
24E 11495
2901177 9 29S
24E 15396 13890 14490
2939158 7 29S
24E 12989 4570 9950
2930904 32 29S
25E 9766 7750 8500
2947429 35 29S
25E 10025 3188 6407 8801
2942011 36 29S
25E 12723 6470 7400 10970
2930892 25 29S
25E 10300 6490 7380
2930889 26 29S
25E 10265 6580 7580
7960,
9530
(lower)
2930894 27 29S
25E 10267 7680 8250
2930890 28 29S
25E 13768 8600
2930903 29 29S
25E 10194 4540 8900 9490
3033912 24 29S
25E 13850 5800 6850 7860 10250 11900
2904265 23 29S
25E 12733 6400 7300
8410,
9570
(lower)
12010 12635
2930895 21 29S
25E 10648 8850
2930883 20 29S
25E 10235 4570 8930 9550
2908597 13 29S
25E 11741 6420 7290 8290 9200 10934 11584
2946490 14 29S
25E 12600 6650 7600 12010 12575
2930887 17 29S
25E 10595 4610 9170 9700
2930899 18 29S
25E 14011 9650 13320 13690
77
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Macoma Reef
Ridge Monterey
Round
Mountain Freeman Vedder
2908578 12 29S
25E 11488 6590 7470 8370 9970 11540
2930906 8 29S
25E 10843 9500 10160
2908572 1 29S
25E 11492 6730 7550 8450 9950 11460
2916708 2 29S
25E 11589
2968934 3 29S
25E 12000 4580 7500 8600 9994 10830 11630
2969336 4 29S
25E 12166 4680 8910
2930935 31 29S
26E 12130 6370 7307 10414 11028 11975
2966322 32 29S
26E 13084 6080 6925 7203 10565 11029 12000
2904248 33 29S
26E 9671 5706 6498 6842
2965543 34 29S
26E 11632 5625 6295 6642 10941
2966599 35 29S
26E 11182 4824 5292 5430 9950
2985636 36 29S
26E 12070 4315 4792 5091 9360 10291
2930927 26 29S
26E 8700 5353 5880 6330
3000334 27 29S
26E 9406 5675 6460 6750
2930939 28 29S
26E 11638 6300 6600 9750 10340
2930915 29 29S
26E 9384 6130 6960 7310
2972285 30 29S
26E 11970 7280 7520 9850 10457 11880
2916773 23 29S
26E 10617 4415 4895 9210 9700
2930918 22 29S
26E 11470 5382 6040 6380 9600 10080
2908564 21 29S
26E 11756 6045 6800 7025 10140 11591
2908639 20 29S
26E 11536 6150 6980 7270 9370 9950 11473
2908635 19 29S
26E 11785 7140 7650 9200
2916723 14 29S
26E 10761 4595 5025 8940 9470
2916740 15 29S
26E 7321 5050 5482
2908542 16 29S
26E 8253 6062 6783 7060
2908611 17 29S
26E 11610 6370 7200 7630 9380 10640
2908617 18 29S
26E 11510 6420 7300 7670 9180 10030
78
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Macoma Reef
Ridge Monterey
Round
Moun-tain Freeman Vedder
2916777 12 29S
26E 9200 3840 7790
2930912 11 29S
26E 9788 4210 4660 8080 8900
2940003 10 29S
26E 12705 3050 5240 5740 9700 10495
2930936 9 29S
26E 8620 5605
2900728 7 29S
26E 11510 6370 7158 8063 9102 9900 11285
2940837 5 29S
26E 11725 6125 7084 8748 9368 11056
2942802 4 29S
26E 8250 5374 5947 8096
2916850 2 29S
26E 5020 3897
2916839 1 29S
26E 4810 3694
2908312 34 29S
27E 11570 7800 8750
2930950 30 29S
27E 10866 3960 4350 7250 9920
2961380 21 29S
27E 4623 2870
2908493 20 29S
27E 4959 3500
2906729 19 29S
27E 9772 3640 8660 9594
2930978 13 29S
27E 8252 1750 2670 6925
2963414 14 29S
27E 3592 2380
2908438 11 29S
27E 7719 2847 5850 6870
2954448 10 29S
27E 8082 2896 5950
2930968 7 29S
27E 7133 7140
2930973 1 29S
27E 7014 5820
2944869 3 29S
27E 8350 5620 2860 6725
2930952 4 29S
27E 8670 3165 5900 7170
2930979 5 29S
27E 4500
2916782 6 29S
27E 8522 3620 4110 7330
2932002 34 29S
28E 6717 3930
2932020 35 29S
28E 7890 3790 6450 7620
2930983 36 29S
28E 6444 3210 5080 6208
79
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Macoma Reef
Ridge Monterey
Round
Mountain Freeman Vedder
2932005 26 29S
28E 7009
2932021 24 29S
28E 6163
2932009 15 29S
28E 7124 2256 5710
2977088 1 29S
28E 5300 4360
2971358 3 29S
28E 5140 3079
2956263 5 29S
28E 1375 120
2932104 31 29S
29E 5986 4550 5565
2904581 32 29S
29E 5375 3040 4000
2904605 33 29S
29E 4950 2460 4090 4906
2906109 34 29S
29E 4798 1283 3950 4770
2932118 35 29S
29E 5200 1250 2605
2942882 25 29S
29E 4752 2045 3767 4510
2906290 26 29S
29E 4704 739 4430 4682
2906382 27 29S
29E 4682 990 2270 3910 4750
2900812 29 29S
29E 5889 1668 4000 4920
2932133 24 29S
29E 3510 1100 2720 3410
2932055 23 29S
29E 4005 740 3060 3734
2904005 22 29S
29E 4031 2990 3940
2932116 21 29S
29E 5004 1101 3355
2932054 20 29S
29E 5689 4250 5210
2932098 14 29S
29E 4439 3210 4135
2900967 15 29S
29E 4582 536 4005
2904014 16 29S
29E 4408 280 3252
2932092 12 29S
29E 3578 650 2450 3250
2932070 11 29S
29E 3600 800 2610
2949694 10 29S
29E 4472 3040 4050
2932040 9 29S
29E 4747 2488
80
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Macoma Reef
Ridge Monterey
Round
Mountain Freeman Vedder
2947863 8 29S
29E 3911 2060 3245
2956058 7 29S
29E 5650 780 2480 3742
2944053 1 29S
29E 3167 1782 2730
2932062 2 29S
29E 3060 300 2175 2800
2932130 3 29S
29E 3100 2050 2965
2932132 4 29S
29E 3859 2745 3109
2978271 6 29S
29E 4200 2500 3727
2980083 24 30S
24E 12650 9300 9700
2973421 25 30S
24E 10100 6767 8450 8920
2915246 31 30S
25E 9160 5800 7420 7780
2915275 32 30S
25E 9148 6630
2915306 33 30S
25E 9350 5870 7740 8150
2901452 34 30S
25E 9609 6650 8400 8700
2915342 35 30S
25E 9827 7030 8720 9030
2940087 25 30S
25E 10455 3750 7000
2901064 26 30S
25E 13930 8550 8842
2915161 27 30S
25E 9385 7012 8530 8850
2915180 28 30S
25E 9728 6612 7950 8250
2915210 29 30S
25E 9370 5950 7720 7980
2915230 30 30S
25E 9230 7950 8200
2900655 24 30S
25E 9785 3750 7250
2920537 23 30S
25E 9904 3730 7290
2900103 13 30S
25E 9983 3940 6010 7200 7690
2904310 14 30S
25E 13400 6070 7200
2918566 12 30S
25E 12425 6120 7250 8067 11400 12350
2932167 11 30S
25E 10323 6380 7680
3002902 10 30S
25E 13413 6330 7400 8100 11830 13160
81
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Macoma Reef
Ridge Monterey
Round
Mountain Freeman Vedder
2932163 9 30S
25E 10655 6513 7900 8310
2932168 8 30S
25E 9511 8400 8900
2900120 1 30S
25E 10240 6350 7300
2918604 2 30S
25E 12665 3900 7014 11250 11600 12570
2932165 3 30S
25E 10310 4000 6520 7510 8410
2932161 4 30S
25E 13957 7500 12130 12560
2932166 5 30S
25E 9600 6130 7350
2920673 31 30S
26E 8196 3830 7130 7700
2920535 32 30S
26E 10645 7120 7882
2932820 33 30S
26E 10800 6430 7590
2900004 34 30S
26E 16322 6500 7410 12820
2910924 35 30S
26E 11011 6570 7510
2904346 36 30S
26E 10868 6290 7250 7588
2904393 25 30S
26E 10656 6040 6990 7331
2904407 26 30S
26E 10606 6210 7115 7500
2904519 27 30S
26E 10734 6290 7366 7681
2953125 28 30S
26E 10510 3800 7010
2948167 29 30S
26E 9534 3840 6760 7520
2900275 30 30S
26E 14000 3650 6850 7600
2904518 24 30S
26E 10262 5780 6600 6960
2904507 23 30S
26E 10300 5920 6900
2904488 22 30S
26E 10024 6020 6890 7331
2900398 21 30S
26E 10774 6220 7220 7654
2920688 19 30S
26E 9940 3800 7000 7910
3003281 13 30S
26E 10450 6305 6640
2904460 14 30S
26E 10400 6480 6917
2979970 15 30S
26E 10546 7030 7383
82
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Macoma Reef
Ridge
Monte-
rey
Round
Mountain Freeman Vedder
2904450 15 30S
26E 10190 6700 7123
2900760 16 30S
26E 10300 6420 7350 7830
2944205 18 30S
26E 13626 6070 7100 7920 11000 11310 12350
2956684 10 30S
26E 10317 5960 6790 7259
2918589 9 30S
26E 10373 6220 7150 7642
2918557 8 30S
26E 10152 7270 7830
2918540 7 30S
26E 9596 3860 6040 7090
2918578 6 30S
26E 9650 5960 7070 8068
3006412 5 30S
26E 9935 6160 7000 7450
2972460 3 30S
26E 11600 5670 6420 6800 10000 10650
2932204 33 30S
27E 12355 5266 7330 11045
2977284 36 30S
27E 12853 7045 7471 12406
2932203 25 30S
27E 11031 7050 7510 8580
2932198 30 30S
27E 10765 6010 6671 7365
2974451 23 30S
27E 11880 6226 6590 7502 10203
2970086 22 30S
27E 11743 5984 6590 7255 10484
2976546 21 30S
27E 11941 5630 6154 7075 10725
2973855 20 30S
27E 12015 5873 6395 7351 11276
2904087 19 30S
27E 10300 5859 6500 6905
2932197 13 30S
27E 7800 5081 5330
2972368 14 30S
27E 13350 5026 5666 6672 9974
2932199 15 30S
27E 13690 5561 6052 6895 9989 12495
2932202 17 30S
27E 10305 5495 5965 6972
2932205 7 30S
27E 8008 5180 5730 5995
2932194 5 30S
27E 12222 4581 4925 5442 11196
2980759 6 30S
27E 11095 4707 5352 6206 10480
2963355 25 30S
28E 12404 9992 10875
83
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Macoma Reef
Ridge
Monte-
rey
Round
Mountain Freeman Vedder
2989352 27 30S
28E 11041 6951 9220
2982030 22 30S
28E 10500 6361 8290
2932234 28 30S
28E 10874 7227 9940
2932231 24 30S
28E 10509 7554 10439
2979382 11 30S
28E 9758 4289 7386
2932247 9 30S
28E 9645 5050 7532
2932227 8 30S
28E 8604 5579 5210
2906002 1 30S
28E 6700 3220
2906367 2 30S
28E 6037 3771
2914346 32 30S
29E 8688 5200 6640 7410 8215
2914639 30 30S
29E 10510 6080 7700
2906447 21 30S
29E 5509 3500 5153
2914451 20 30S
29E 8107 4790 6060 6903
2906314 16 30S
29E 5378 3374 4500
2906183 18 30S
29E 7450 4270 5960 5810 7250
2973115 9 30S
29E 7000 2000 3300 4270 5163
2904652 8 30S
29E 5942 4840 5775
2932260 2 30S
29E 5810 1133 4200
2906131 3 30S
29E 4699 1510 2900 4070
2906077 4 30S
29E 5278 3560 4090 5025
2963490 36 31S
25E 14890 5605 8980 10258 14890
2915786 25 31S
25E 11084 5800 9320 10350
2950170 26 31S
25E 16455 5900 9436 10467 15032
2959597 21 31S
25E 13780 9250
2945524 20 31S
25E 13600 11103 11650
2911297 13 31S
25E 11043 9450 10100
2929411 12 31S
25E 12823 7801 9030 9530
84
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Macoma Reef
Ridge
Monte-
rey
Round
Mountain Freeman Vedder
2929396 11 31S
25E 10192 7430 8800 9300
2956928 10 31S
25E 9750 4430 7970 8470
2929373 9 31S
25E 9958 7920 8480
2939272 8 31S
25E 9359 6945 7950
2939291 2 31S
25E 10050 8910 9250
2929346 3 31S
25E 9889 4860 7250 8670 8950
3001480 4 31S
25E 11213 7700 8270
2903276 5 31S
25E 16176 6650 8210 8640
2921672 32 31S
26E 10558 5780 8150 9060
2921677 33 31S
26E 10833 8410 9330
2921656 28 31S
26E 11441 9090 9850
2921665 29 31S
26E 11110 6150 8520
2921667 30 31S
26E 10811 5850 8270 9330
2903687 23 31S
26E 14945 9180 9950 10410
2939857 20 31S
26E 11713 8500
2961295 14 31S
26E 10551 8340 9050 9550
2932355 16 31S
26E 11500 8830 9600
2973377 9 31S
26E 10400 7680 8812 9252
2932356 1 31S
26E 10499 6807 7720
2932350 2 31S
26E 9484 7300 8300 8650
2910925 3 31S
26E 12517 7170 8360
2981162 26 31S
27E 15399 9000 10260
2979059 20 31S
28E 16025 5710 8100 9130
2914251 34 31S
29E 11711 10540 10810
2914464 27 31S
29E 9526 8160 9260
2987345 8 31S
29E 13800 10700 11400 12400
2921643 12 32S
26E 11213 6890 9600 10130
85
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Macoma Reef
Ridge
Monte-
rey
Round
Mountain Freeman Vedder
2929558 11 32S
26E 12507 6360 8960 9600
2962062 10 32S
26E 12500 5900 8200 8930
2935506 9 32S
26E 11467 6270 8800 9480
2973154 2 32S
26E 12790 6280 8737 9200
2971260 3 32S
26E 12273 5920 8530 8980
2921731 4 32S
26E 21482 5940 8250 8950
2921181 6 32S
26E 12700 6690 9890 10620
2932422 17 32S
27E 13515 12630
2921650 7 32S
27E 11858 10800
2962666 32 32S
28E 17191 12250
2959267 33 32S
28E 17199 8900 12500
2932458 26 32S
29E 3270 2000 2320
2932436 23 32S
29E 2056 800 1120
2959180 32 12N
22W 14678 8170 10580
2959519 33 12N
22W 13778 8750 11160
2959090 34 12N
22W 13816 8700 11180 11970
2984174 36 12 N
22W 13185 9050 11680 12833
2952487 34 12N
21W 14439 12350 13660
29611210 35 12N
21W 14952 10420 12650 13880
2955327 26 12N
21W 16548 10850 13130 14500
2956431 28 12N
21W 14775 10210 12550 13850
2900086 35 12N
19W 12894 10040 11940
2935297 10 11N
22W 12446 8400 10050 11330
2954331 12 11N
22W 12200 8600 10820 11422
2983574 24 11N
22W 12642 11700 12400
2909408 32 11N
22W 10017 800 1030 3002
2986161 6 11N
22W 11600 7392 9750 10700
86
API
Location TD
(ft)
Top of Units or Stratigraphic Markers (ft)
Etchegoin Macoma Reef
Ridge
Monte-
rey
Round
Mountain Freeman Vedder
2954464 4 11N
22W 16300 8700 9955 10980
2979723 7 11N
22W 10350 7700 8750 9920
2985023 20 11N
21W 14325 12500 14200
2915820 15 11N
21W 14471 10030 12170 13500
2915793 5 11N
21W 13960 11700 12750
2915789 3 11N
21W 12899 9890 12250
2915806 9 11N
21W 12645 9170 11270 12612
2986323 12 11N
21W 16050 11200 13445 15012
2978673 30 11N
21W 12650 9400 11460
2913706 29 11N
21W 13600 10250 12120
2932768 15 11N
20W 16421 4280 5580 6625 7310 8330
2979722 32 11N
20W 11150 9410
2976062 34 11N
20W 13249 8770 9290
2932776 35 11N
20W 12750 3100 6000
2920448 25 11N
20W 9089
2973640 21 11N
19W 7900 3000 6800 7850
2920515 29 11N
19W 8820 6330 7430
2932751 27 11N
19W 7650 2950 5610 6380
2920507 20 11N
19EW 12470 3150 7820
2932732 15 11N
19W 9550 7690