Matilija Sandstone
Encyclopedia
The Matilija Sandstone is a sedimentary geologic unit of Eocene
age, found in Santa Barbara
and Ventura
Counties in Southern California. It consists of thick layers of sandstone
, made up of grains of feldspar
and quartz
from a granitic source rock, interbedded with thin layers of siltstone
and shale
. Hard, massive, and exceptionally resistant to weathering, it forms the high rocky summits of the Santa Ynez Mountain
range north of Santa Barbara, California, eastward into Ventura County.
of the unit is at Matilija Hot Springs, along the Ventura River
about ten miles (16 km) northwest of Ojai
, near to California State Route 33
. At its type locality it is around 2500 feet (762 m) thick, and consists of both marine and non-marine sandstones with occasional thin beds of micaceous shale separating massive sandstone layers. The sandstone layers are made up of well-sorted grains of quartz and feldspar. The unit can be found along the crest of the Santa Ynez range all the way from the western extremity of the mountains near Point Arguello
, to its type locality north of Ojai, and east and northeast into the Ventura County backcountry, where Piru
and Sespe
creeks cross through the formation. It accounts for the highest peaks in the Santa Ynez range, dipping underneath the younger Coldwater Sandstone
, Cozy Dell Shale
, and Sespe Formation
near San Marcos Pass in the center of the range.
Thickness of the unit is widely variable, generally decreasing to the west. In its type locality it is around 2500 feet (762 m) thick; in the vicinity of La Cumbre Peak it is 2000 feet (609.6 m) thick; and while it thins to only 500 feet (152.4 m) thick underneath San Marcos Pass, it thickens again to around 2000 feet (609.6 m) at the high summits of Santa Ynez and Broadcast Peaks. It thins westward from there, being only 500 feet (152.4 m) thick at Refugio Pass, and less than 300 in the Santa Rosa Hills and west to Point Conception.
Along with the younger Coldwater Formation, the Matilija is the source of the enormous sandstone boulders which are found abundantly along the creeks and shoreline of Santa Barbara and Goleta. Additionally, boulders are strewn on hillsides in the upper Riviera, and elsewhere on hillsides and floodplains. These boulders, none of which can be moved even in the most intense modern-day flood events, tumbled down the mountains during Pleistocene-age storms and mudflows of unimaginable intensity.
The Matilija Sandstone produces little soil when it weathers, and generally supports only hard chaparral
on slopes that are not bare rock. North-facing slopes have some stands of pine and fir in the higher elevations.
The formation appears in boreholes drilled into oil fields offshore, indicating the formation dips steeply underneath the Santa Barbara Channel. At the Point Conception Oil Field, the Matilija is at least 2000 feet (609.6 m) thick, and first appears approximately 4300 feet (1,310.6 m) below ground surface. In the Molino Offshore Gas Field, southeast of Gaviota
about two miles (3 km) offshore, the formation is at an average of 10500 feet (3,200.4 m) below the sea floor, and a well drilled to 12589 feet (3,837.1 m) had not reached the bottom of the formation.
After reaching its current position along the coast, the entire Santa Ynez range was uplifted, mostly during the Quaternary
period and late Pliocene
, by crustal shortening and compression from tectonic forces at the boundary of the Pacific
and North American Plate
s. The Matilija Sandstone and other units, formerly submerged, rose over 4000 feet (1,219.2 m) from their original positions. In some places the forces causing this uplift were so abrupt that sedimentary layers deposited as recently as the Pleistocene
are now angled 60 degrees from horizontal.
Since this deep-lying play is incompletely explored, with many boreholes not even reaching the Matilija, the estimates for hydrocarbon resources are speculative, with the United States Bureau of Ocean Energy Management, Regulation and Enforcement giving a range of 117 Moilbbl of oil recoverable using current technology for the entire Santa Barbara-Ventura Basin Province. In general in the eastern and central parts of the basin, the sandstone would be too deeply buried to have reservoir potential; however, the area potentially containing oil and gas is large, including approximately 1500 square miles (3,885 km²) within the Federal Outer Continental Shelf
. The largest single hydrocarbon accumulation yet identified in the Matilija Sandstone is in the Molino Offshore Gas Field, discovered in 1983, and contains approximately 39 Moilbbl of oil equivalent.
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
age, found in Santa Barbara
Santa Barbara County, California
Santa Barbara County is a county located in the southern portion of the U.S. state of California, on the Pacific coast. As of 2010 the county had a population of 423,895. The county seat is Santa Barbara and the largest city is Santa Maria.-History:...
and Ventura
Ventura County, California
Ventura County is a county in the southern part of the U.S. state of California. It is located on California's Pacific coast. It is often referred to as the Gold Coast, and has a reputation of being one of the safest populated places and one of the most affluent places in the country...
Counties in Southern California. It consists of thick layers of sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
, made up of grains of feldspar
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
and quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
from a granitic source rock, interbedded with thin layers of siltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
and shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
. Hard, massive, and exceptionally resistant to weathering, it forms the high rocky summits of the Santa Ynez Mountain
Santa Ynez Mountains
The Santa Ynez Mountains are a portion of the Transverse Ranges, part of the Pacific Coast Ranges of the west coast of North America, and are one of the northernmost mountain ranges in Southern California.-Geography:...
range north of Santa Barbara, California, eastward into Ventura County.
Type locality, description, and distribution
The type localityType locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....
of the unit is at Matilija Hot Springs, along the Ventura River
Ventura River
The Ventura River is a river in Ventura County, California. The river forms at the confluence of Matilija Creek and North Fork Matilija Creek, upstream from the Pacific Ocean...
about ten miles (16 km) northwest of Ojai
Ojai, California
Ojai is a city in Ventura County, California, USA. It is situated in the Ojai Valley , surrounded by hills and mountains. The population was 7,461 at the 2010 census, down from 7,862 at the 2000 census.-History:Chumash Indians were the early inhabitants of the valley...
, near to California State Route 33
California State Route 33
State Route 33 is a north–south state highway in the U.S. state of California. SR 33 replaced part of U.S. Route 399 in 1964 during the "great renumbering" of routes. In the unincorporated sections of Kern County it is known as the West Side Highway...
. At its type locality it is around 2500 feet (762 m) thick, and consists of both marine and non-marine sandstones with occasional thin beds of micaceous shale separating massive sandstone layers. The sandstone layers are made up of well-sorted grains of quartz and feldspar. The unit can be found along the crest of the Santa Ynez range all the way from the western extremity of the mountains near Point Arguello
Point Arguello
Point Arguello is a headland used as a launch site by the United States Navy. Point Arguello was first used in 1959 for the launch of military and sounding rockets. It was transferred to the United States Air Force in 1964, at which time it became part of Vandenberg Air Force Base.There were 6...
, to its type locality north of Ojai, and east and northeast into the Ventura County backcountry, where Piru
Piru Creek
Piru Creek is a large stream in northern Los Angeles County and eastern Ventura County, California. It is a tributary of the Santa Clara River, the largest stream system in Southern California that is still relatively natural. It drains an area of about and is about long. The creek is the Santa...
and Sespe
Sespe Creek
Sespe Creek is a stream, some long, in Ventura County, California, in the United States. The creek starts at Potrero Seco in the Sierra Madre Mountains, and is formed by more than thirty tributary streams before it empties into the Santa Clara River in Fillmore. Thirty-one miles of Sespe Creek are...
creeks cross through the formation. It accounts for the highest peaks in the Santa Ynez range, dipping underneath the younger Coldwater Sandstone
Coldwater Sandstone
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...
, Cozy Dell Shale
Cozy Dell Shale
The Cozy Dell Shale is a sedimentary geologic unit of late Eocene age found principally in the Santa Ynez Mountain range north of Santa Barbara, California, from near Point Arguello in the west to central Ventura County in the east...
, and Sespe Formation
Sespe Formation
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...
near San Marcos Pass in the center of the range.
Thickness of the unit is widely variable, generally decreasing to the west. In its type locality it is around 2500 feet (762 m) thick; in the vicinity of La Cumbre Peak it is 2000 feet (609.6 m) thick; and while it thins to only 500 feet (152.4 m) thick underneath San Marcos Pass, it thickens again to around 2000 feet (609.6 m) at the high summits of Santa Ynez and Broadcast Peaks. It thins westward from there, being only 500 feet (152.4 m) thick at Refugio Pass, and less than 300 in the Santa Rosa Hills and west to Point Conception.
Along with the younger Coldwater Formation, the Matilija is the source of the enormous sandstone boulders which are found abundantly along the creeks and shoreline of Santa Barbara and Goleta. Additionally, boulders are strewn on hillsides in the upper Riviera, and elsewhere on hillsides and floodplains. These boulders, none of which can be moved even in the most intense modern-day flood events, tumbled down the mountains during Pleistocene-age storms and mudflows of unimaginable intensity.
The Matilija Sandstone produces little soil when it weathers, and generally supports only hard chaparral
Chaparral
Chaparral is a shrubland or heathland plant community found primarily in the U.S. state of California and in the northern portion of the Baja California peninsula, Mexico...
on slopes that are not bare rock. North-facing slopes have some stands of pine and fir in the higher elevations.
The formation appears in boreholes drilled into oil fields offshore, indicating the formation dips steeply underneath the Santa Barbara Channel. At the Point Conception Oil Field, the Matilija is at least 2000 feet (609.6 m) thick, and first appears approximately 4300 feet (1,310.6 m) below ground surface. In the Molino Offshore Gas Field, southeast of Gaviota
Gaviota, California
Gaviota is an unincorporated town in Santa Barbara County, California located about west of Santa Barbara and south of Buellton. Approximately 35 people live in and near Gaviota. The ZIP Code is 93117, and the community is inside area code 805....
about two miles (3 km) offshore, the formation is at an average of 10500 feet (3,200.4 m) below the sea floor, and a well drilled to 12589 feet (3,837.1 m) had not reached the bottom of the formation.
Deposition environment and tectonic history
Sometime in the early Eocene, around 50 million years ago, the land mass containing present-day Santa Barbara County submerged, allowing sediment deposition offshore. During this time the sea alternately deepened and became shallow again, with the deposition environment supporting either sandstones or shales corresponding to shallow or deep conditions. The Matilija Sandstone dates from the earliest sustained shallow-water episode during this time, the period from 48.5 to 46 million years ago. Additionally, the piece of the crustal block on which the sandstone was deposited has rotated approximately 90 degrees clockwise since time of deposition, moving from a location approximately adjacent to present-day San Diego to the region it occupies in the present day.After reaching its current position along the coast, the entire Santa Ynez range was uplifted, mostly during the Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
period and late Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
, by crustal shortening and compression from tectonic forces at the boundary of the Pacific
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
and North American Plate
North American Plate
The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...
s. The Matilija Sandstone and other units, formerly submerged, rose over 4000 feet (1,219.2 m) from their original positions. In some places the forces causing this uplift were so abrupt that sedimentary layers deposited as recently as the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
are now angled 60 degrees from horizontal.
Paleontology
While the formation is rich in microfossils, it is considered to be of low paleontologic sensitivity, i.e. larger fossils are unlikely to be encountered. In the Santa Rosa Hills, the unit has yielded numerous shells of molluscs, including bivalves and gastropods.Economic importance
As a potential reservoir for oil and gas deposits, the Matilija Sandstone is grouped with the above-lying Cozy Dell Shale and Coldwater Sandstone as the Gaviota-Sacate-Matilija Sandstone Play. The likely source rocks for any petroleum accumulation in the Gaviota-Sacate-Matilija Play are the lower-lying organic-rich shale units, such as the Juncal-Anita Formations.Since this deep-lying play is incompletely explored, with many boreholes not even reaching the Matilija, the estimates for hydrocarbon resources are speculative, with the United States Bureau of Ocean Energy Management, Regulation and Enforcement giving a range of 117 Moilbbl of oil recoverable using current technology for the entire Santa Barbara-Ventura Basin Province. In general in the eastern and central parts of the basin, the sandstone would be too deeply buried to have reservoir potential; however, the area potentially containing oil and gas is large, including approximately 1500 square miles (3,885 km²) within the Federal Outer Continental Shelf
Outer Continental Shelf
The Outer Continental Shelf is a peculiarity of the political geography of the United States and is the part of the internationally recognized continental shelf of the United States which does not fall under the jurisdictions of the individual U.S...
. The largest single hydrocarbon accumulation yet identified in the Matilija Sandstone is in the Molino Offshore Gas Field, discovered in 1983, and contains approximately 39 Moilbbl of oil equivalent.