The Cozy Dell was first described in 1928 as the middle member of the Tejon Formation. However, Dibblee (1966) reclassified it as a formation, along with the underlying Matilija Sandstone and overlying Coldwater Sandstone. He also named the formation after its type locality at Cozy Dell Canyon, which is located on the south side of Nordhoff Ridge, just north of Ojai in Ventura County.[3]
The Cozy Dell crops out continuously in the mountains to the north and east of Ojai, where it is exposed along much of the south slope of the Topatopa Mountains in Ventura County, and continues westward along the south slope of Santa Ynez Mountains into Santa Barbara County. Here, it is overlain by younger rocks at San Marcos Pass, on the crest of the Santa Ynez Range, cropping out west of the pass and forming much of the crest north of Goleta. It disappears north of the Santa Ynez Mountains beneath younger formations, and is removed, for the most part, by erosion north of the Santa Ynez River, where it appears at only a few localities. It grades into and is overlain by the Sacate Formation in the western part of its outcrop belt, and dips south beneath the modern California coastal plain in the southern part.[3] Continuing south into the offshore region beneath the Santa Barbara Channel, the Cozy Dell is found in oil wells at Molino field some 13,000 feet (3,962m) feet below the sea floor.[4]
The thickness of the formation increases, more or less, from east to west and averages about 1,700 feet (518m) in the Santa Ynez Mountains. However, thicknesses vary widely, ranging from a maximum of 4,000 feet (1,219m) west of San Marcos Pass,[3] to 50 feet (15m) thick in the subsurface of the offshore Hondo Oil Field,[5] and only 350 feet (107m) thick in the offshore Molino Gas Field, which is located west of Hondo.[4]
Description
The Cozy Dell is a gray to dark gray argillaceous to silty shale that weathers to brown and olive. It contains minor sandstone beds at some localities, and some conglomerate at others, most significantly west of San Marcos Pass.[3][6] When exposed to surface conditions, it breaks down quickly to form a clay-rich soil that supports dense chaparral growth. Because the Cozy Dell is layered between the highly resistant Matilija and Coldwater sandstones, and turned up on end through most of its extent, it erodes to create passes and saddles between peaks and ridges of the adjacent units.
Paleontology, age and depositional environments
Microfauna in the Cozy Dell, primarily planktonic (i.e., floating) foraminifera, place it in the upper part of the Lutetianstage (middle Eocene) of the geologic timescale - the Lutetian correlating, more or less, to the middle part of a local Californian stage named the Narizian that is based largely on benthic (i.e., bottom-dwelling) foraminifera. Although the formation is rich in microfossils, especially ones indicating deep-marine deposition, no significant larger fossils have been found in southwestern Santa Barbara County.[7] However, some larger fossils have been found in a few localities in the Topatopa Mountains to the east in Ventura County, particularly in the upper Sespe Creek area near Ojai, which contains an unusual shallow-marine assemblage of molluscs, starfish and brittle stars, as well as plant imprints that indicate close proximity to an ancient shoreline.[8]
The Cozy Dell represents a time when the Eocene sea covering the California border land region reached its widest extent and maximum water depths. Thus, only the finest-grained sediments, principally a micaceous mud, reached the ocean bottom. A fairly high organic content of up to 3% or more of Total Organic Carbon (TOC) in these sediments indicate that microorganisms flourished and that there were anoxic conditions on the ocean floor conducive to the preservation of organic matter. These observations, together with the fossil evidence, indicate that the Cozy Dell was deposited in an ocean basin with a shoreline on what today would be the east and north side of the basin and gradually deepening to the west to water depths of possibly a thousand feet or more.[3]
Magnetostratigraphy
Recent magnetostratigraphic dating demonstrates that the Cozy Dell at its type locality was deposited during the chron 20 geomagnetic reversal through the chron 19 reversal - approximately 46 to 42 Ma (million years ago), which is consistent with deposition during Lutetian time. The paleomagnetic data also show that the tectonic block on which the Cozy Dell was deposited with other Eocene formations has rotated clockwise about 100 degrees since the onset of deposition. Thus, modern-day east-west trends indicated within the formation would originally have been oriented north-south.[2][9]
Economic importance
The Cozy Dell is grouped with underlying and overlying sandstones as a potential hydrocarbon resource. Where this shale is found in the subsurface of oil and gas fields on the California coast, and offshore in the Santa Barbara Channel, it tends to be impermeable to fluid flow, as with most shales, and represents a cap rock that can trap hydrocarbons in underlying sandstone reservoirs.[5] However, a few offshore oil fields contain sections of Cozy Dell with sufficient porosity to act as petroleum reservoirs, and sufficient permeability to produce hydrocarbons at economic rates. One example is the now-abandoned Cuarta field, located about six miles offshore from Gaviota, where the Cozy Dell is mainly shale but contains minor sandstone interbeds that previously produced oil from 7,000 feet (2,134m) feet below the ocean floor.[10][11] Although there is no onshore oil or gas production from the Cozy Dell, its organic content is high enough that some geologists believe it may be a potential source rock for petroleum found in other units.[12]
References and notes
↑ Kerr, P.F.; Schenk, H.G. (1929). "Significance of the Matilija overturn". Geological Society of America Bulletin. 39 (4): 1087–1102. doi:10.1130/gsab-39-1087.
1 2 3 4 5 6 Dibblee, Thomas (1966). Geology of the central Santa Ynez Mountains, Santa Barbara County, California. San Francisco: California Division of Mines and Geology. Bulletin 186, p. 28–30.
1 2 Miles, Gregory A.; Rigsby, Catherine A. (1990). "Lithostratigraphy and Depositional Environments of the Vaqueros and Upper Sespe/Alegria Formations, Hondo Field, Santa Barbara Channel, California". SEPM Core Workshop No. 14, San Francisco, June 3, 1990. p.43. ISBN0-918985-84-6.
1 2 Hinman, Nancy W.; Schwartz, Daniel E. (1990). "Lithologic and Diagenetic Sequences of the Monterey Formation, Molino Field, Offshore Santa Barbara, California". SEPM Core Workshop No. 14, San Francisco, June 3, 1990. p.274. ISBN0-918985-84-6.
↑ Squires, Richard L. (1994). "Macropaleontology of Eocene marine rocks, upper Sespe Creek area, Ventura County, Southern California". In Fritsche, A.E. (ed.). Sedimentology and paleontology of Eocene rocks in the Sespe Creek area, Ventura County, California. Pacific Section SEPM. Book 74, p. 39–56.
↑ Harden, Deborah R. (1997). California Geology. Prentice Hall. p.433. ISBN0-02-350042-5.
↑ California Division of Oil, Gas, and Geothermal Resources (1992). "Cuarta Offshore Oil Field (ABD)". California Oil and Gas Fields. California Dept. of Conservation. vol. II, p. 652–653.{{cite book}}: CS1 maint: multiple names: authors list (link) PDF file available on CD from www.consrv.ca.gov.
↑ Cordova, Simon (1972). "Cuarta offshore oil field". Summary of Operations. California Div. of Oil and Gas. v. 58, no. 1, p. 5–14.
The Santa Ynez Mountains are a portion of the Transverse Ranges, part of the Pacific Coast Ranges of the west coast of North America. It is the westernmost range in the Transverse Ranges.
The Topatopa Mountains are a mountain range in Ventura County, California, north of Ojai, Santa Paula, and Fillmore. They are part of the Transverse Ranges of Southern California.
The Dick Smith Wilderness is a wilderness area in the mountains of eastern Santa Barbara County, California, United States, with a portion in Ventura County. It is completely contained within the Los Padres National Forest, and is northeast of the city of Santa Barbara and north of the city of Ojai. It is most easily accessible from two trailheads off State Route 33, which runs north from Ojai. It is adjacent to the large San Rafael Wilderness on the west and the Matilija Wilderness on the south. Across Highway 33 to the east, and also in the Los Padres National Forest, is the large Sespe Wilderness.
Pine Mountain Ridge is a massif of the Transverse Ranges located in northern Ventura County, and entirely within the Los Padres National Forest. The ridge is a large block of Matilija Sandstone, and reaches some of the highest elevations in the southern Transverse Ranges. The north slope of the ridge is part of the Sespe Wilderness.
Simi Valley is a synclinal valley in Southern California in the United States. It is an enclosed or hidden valley surrounded by mountains and hills. It is connected to the San Fernando Valley to the east by the Santa Susana Pass and the 118 freeway, and in the west the narrows of the Arroyo Simi and the Reagan Freeway connection to Moorpark. The relatively flat bottom of the valley contains soils formed from shales, sandstones, and conglomerates eroded from the surrounding hills of the Santa Susana Mountains to the north, which separate Simi Valley from the Santa Clara River Valley, and the Simi Hills.
The Vaqueros Formation is a sedimentary geologic unit primarily of Upper Oligocene and Lower Miocene age, which is widespread on the California coast and coastal ranges in approximately the southern half of the state. It is predominantly a medium-grained sandstone unit, deposited in a shallow marine environment. Because of its high porosity and nearness to petroleum source rocks, in many places it is an oil-bearing unit, wherever it has been configured into structural or stratigraphic traps by folding and faulting. Being resistant to erosion, it forms dramatic outcrops in the coastal mountains. Its color ranges from grayish-green to light gray when freshly broken, and it weathers to a light brown or buff color.
The Mesa Oil Field is an abandoned oil field entirely within the city limits of Santa Barbara, California, in the United States. Discovered in 1929, it was quickly developed and quickly declined, as it proved to be but a relatively small accumulation of oil in a single geologic formation. While the field was active in the 1930s, residential development in most of the Mesa neighborhood of Santa Barbara came to a halt. The field included two major productive areas with a total surface extent of only 210 acres (0.85 km2), and produced 3,700,000 barrels (590,000 m3) of oil during its brief lifetime.
The Sespe Formation is a widespread fossiliferous sedimentary geologic unit in southern and south central California in the United States. It is of nonmarine origin, consisting predominantly of sandstones and conglomerates laid down in a riverine, shoreline, and floodplain environment between the upper Eocene Epoch through the lower Miocene. It is often distinctive in appearance, with its sandstones weathering to reddish-brown, maroon, pinkish-gray, tan, and green. Since many of its sandstones are more resistant to erosion than many other regional sedimentary units it often forms dramatic outcrops and ridgelines in many local mountain ranges.
The Sisquoc Formation is a sedimentary geologic unit widespread in Southern California, both on the coast and in mountains near the coast. Overlying the Monterey Formation, it is of upper Miocene and lower Pliocene age. The formation consists of claystone, mudstone, siltstone, shale, diatomite, and conglomerates, with considerable regional variation, and was deposited in a moderately deep marine environment at a depth of approximately 500–5,000 feet (150–1,520 m). Since some of its diatomites, along with those of the underlying Monterey Formation, are of unusual purity and extent, they can be mined as diatomaceous earth. France-based Imerys operates a mine in the Sisquoc and Monterey Formations in the hills south of Lompoc, California, the largest such operation in the world.
The Rincon Formation is a sedimentary geologic unit of Lower Miocene age, abundant in the coastal portions of southern Santa Barbara County, California eastward into Ventura County. Consisting of massive to poorly bedded shale, mudstone, and siltstone, it weathers readily to a rounded hilly topography with clayey, loamy soils in which landslides and slumps are frequent. It is recognizable on the south slopes of the Santa Ynez Mountains as the band at the base of the mountains which supports grasses rather than chaparral. Outcrops of the unit are infrequent, with the best exposures on the coastal bluffs near Naples, in the San Marcos Foothills, at the Tajiguas Landfill, and in road cuts. The geologic unit is notorious as a source of radon gas related to its high uranium content, released by radioactive decay.
The Coldwater Sandstone is a sedimentary geologic unit of Eocene age found in Southern California, primarily in and south of the Santa Ynez Mountains of Santa Barbara County, and east into Ventura County. It consists primarily of massive arkosic sandstone with some siltstone and shale. Being exceptionally resistant to erosion, outcrops of the Coldwater form some of the most dramatic terrain on the south slope of the Santa Ynez Mountains, with immense white sculpted slabs forming peaks, hogback ridges, and sheer cliff faces.
The Matilija Sandstone is a sedimentary geologic unit of Eocene epoch in the Paleogene Period, found in Santa Barbara and Ventura Counties in Southern California.
The Juncal Formation is a prominent sedimentary geologic unit of Eocene age found in and north of the Santa Ynez Mountain range in southern and central Santa Barbara County and central Ventura County, California. An enormously thick series of sediments deposited over millions of years in environments ranging from nearshore to deep water, it makes up much of the crest of the Santa Ynez range north of Montecito, as well as portions of the San Rafael Mountains in the interior of the county. Its softer shales weather to saddles and swales, supporting a dense growth of brush, and its sandstones form prominent outcrops.
The Jalama Formation is a sedimentary rock formation widespread in southern Santa Barbara County and northern Ventura County, southern California. Of the Late Cretaceous epoch, the unit consists predominantly of clay shale with some beds of sandstone.
The Espada Formation is a sedimentary rock formation widespread in Santa Barbara County, California. Of late Jurassic to Cretaceous age, the unit consists primarily of shale with some interbedded thin layers of sandstone, conglomerate, and limestone.
Little Pine Mountain is a mountain in Santa Barbara County, California, in the Los Padres National Forest at the southern edge of the San Rafael Mountains. It separates the drainages of Oso Creek, which flows into the upper Santa Ynez River, from the drainage of Santa Cruz Creek, which flows into the middle section of the river via Lake Cachuma. The mountain is named for a thin grove of Coulter pines located on the summit.
The La Goleta Gas Field is a natural gas field in unincorporated Santa Barbara County, California, adjacent to the city of Goleta. Discovered in 1929, and first put into production in 1932, it has been in continuous use ever since, producing approximately 12 billion cubic feet of gas. With production declining, the field was converted into a gas storage reservoir in 1941. As of 2016 it remains one of the four gas storage facilities maintained by Southern California Gas Company (SoCalGas), a division of Sempra Energy, with the others being Aliso Canyon, Honor Rancho and Playa del Rey. It is the oldest storage facility of the four and the third largest, with a maximum capacity of 21.5 billion cubic feet. The storage facilities are necessary to balance load for the over ten million customers of SoCalGas: during summer months, when gas usage is at a minimum, gas is pumped into the reservoirs; and in the winter when usage is high, gas is withdrawn. The La Goleta field serves the northern portion of SoCalGas's geographic range.
Wheeler Springs is an unincorporated community that grew around a set of sulphurated hot springs in Ventura County, California. It is located 6 miles north of the Ojai Valley, within Los Padres National Forest. It is named for Wheeler Blumberg, who founded the town in 1891, and the many natural hot springs.
The Matilija Wilderness is a 29,207-acre (11,820 ha) wilderness area in Ventura and Santa Barbara Counties, Southern California. It is managed by the U.S. Forest Service, being situated within the Ojai Ranger District of the Los Padres National Forest. It is located adjacent to the Dick Smith Wilderness to the northwest and the Sespe Wilderness to the northeast, although it is much smaller than either one. The Matilija Wilderness was established in 1992 in part to protect California condor habitat.
The geology of California is highly complex, with numerous mountain ranges, substantial faulting and tectonic activity, rich natural resources and a history of both ancient and comparatively recent intense geological activity. The area formed as a series of small island arcs, deep-ocean sediments and mafic oceanic crust accreted to the western edge of North America, producing a series of deep basins and high mountain ranges.
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