Coldwater Sandstone
Encyclopedia
The Coldwater Sandstone (or Coldwater Formation) 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.
for the Coldwater Sandstone is in Coldwater Canyon, a western branch of the Sespe River
a few miles north of Fillmore. The unit is typically around half a mile thick, ranging from 2,500 to 3,200 feet through most of its extent, although it thins westward to around 1,000 feet thick in the hills north of El Capitan State Beach
. From there going west to Gaviota
, the unit gradually grades into the Sacate Formation, a similar but shalier and more siltstone-rich unit which is also conformably overlain on the Cozy Dell Formation. The Coldwater and Sacate Formations are sometimes considered as a single unit, particularly underneath the Santa Barbara Channel where they appear in drill cores. The Gaviota Formation is deposited conformably on top of the Coldwater-Sacate in the western part of the dual unit's extent, and the Sespe Formation
appears conformably on top of it elsewhere.
The Coldwater outcrops predominantly on the south slope of the Santa Ynez Range, and on the crest of the range at San Marcos Pass
. Cathedral Peak, the 3,333-foot prominence directly north of Santa Barbara, is within the Coldwater unit. Because the sandstone beds are resistant to erosion, wherever they dip steeply, they form distinctive hogback ridges and dip-slopes, a topography particularly characteristic of the ridge north of Goleta, where the Coldwater accounts for almost all of the terrain above approximately 1,000 feet. While the unit is exposed prominently throughout the Santa Ynez Mountains, it dips steeply to the south and vanishes underneath the coastal plain and then the Santa Barbara Channel
. Well bores in the numerous oil and gas fields in the Channel show the Gaviota Formation overlying the Cozy Dell directly, with no intervening Coldwater, excepting the offshore portion of the Capitan Oil Field, in which the Coldwater Formation is present as a natural-gas-bearing unit, underlying the Gaviota.
As a potential hydrocarbon resource, the unit is considered to be equivalent to the Sacate, and is grouped with the lower-lying Cozy Dell Shale and Matilija Sandstone as the Gaviota-Sacate-Matilija Sandstone Play. The likely source rocks for any petroleum accumulation in the Coldwater-Sacate are the lower-lying organic-rich shale units, such as the Cozy Dell and the Juncal-Anita Formations
. Since this deep-lying play is incompletely explored, the estimates for hydrocarbon resources are speculative, with the United States Bureau of Ocean Energy Management, Regulation and Enforcement giving a range of 117 to 127 million barrels of oil recoverable using current technology for the entire Santa Barbara-Ventura Basin Province. Some onshore oil fields produce from the Coldwater, including the Ojai Oil Field north of Santa Paula
and Sespe oil field north of Fillmore, not far from the type locality for the formation.
age, being deposited in a shallow marine environment, during a time in which the sea was receding and becoming more shallow. Since the process was not uniform, with periods of shallow-water deposition alternating with deeper water conditions, the predominantly sandstone unit is interbedded with siltstones and shales, with the siltstone and shale making up around 20% of the total composition. Late in the period of deposition, large oyster beds appear in the stratigraphic record, indicating a brackish-water nearshore environment. The source rock for the sediment making up the Coldwater was mostly granitic, and pebbles or cobbles of granite and quartzite appear in some of the nearshore sandstones near the top of the unit. At its top the unit grades into the redbeds and conglomerates of the Sespe Formation, which was deposited in a floodplain, riverine, and estuarine environment onshore.
A 1996 study by Donald R. Prothero and Robert J. Emry determined the age of the unit using magnetostratigraphy
, and gave its period of deposition as from 39.5 Ma (million years ago) to 42.5 Ma. Additionally, studies of the correlation of the underlying Cozy Dell and Matilija Sandstone
with similar units in the California Central Valley, along with paleomagnetic data, show that the tectonic block on which the Coldwater and its surrounding formations were deposited – including the western part of the Transverse Ranges – has rotated clockwise almost 90 degrees since the time of deposition, also moving north-northwest from its original location. Uplift along the Santa Ynez Fault during the Quaternary
period – the last 2.5 million years – has brought the Coldwater and the other formations up from their deposition environments to their present prominent locations in the Santa Ynez Range. In the area north and northeast of Santa Barbara, on the south slope of the Santa Ynez Mountains eastward to near Ojai, the compression and folding associated with tectonic movements have been sufficiently intense to overturn the rock units so that the older ones are on top. This stretch of overturned rock formations is known as the "Montecito Overturn".
are rich locations for finding remnants of these sea-snails. Elsewhere near the top contact with the Sespe, the remnants of oyster beds can be found.
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
geologic unit of Eocene
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 Southern California, primarily in and south of the Santa Ynez Mountains
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:...
of Santa Barbara County
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 east into Ventura County. It consists primarily of massive arkosic 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,...
with some 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...
. 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.
Type locality, description, and occurrence
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....
for the Coldwater Sandstone is in Coldwater Canyon, a western branch of the Sespe River
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...
a few miles north of Fillmore. The unit is typically around half a mile thick, ranging from 2,500 to 3,200 feet through most of its extent, although it thins westward to around 1,000 feet thick in the hills north of El Capitan State Beach
El Capitán State Beach
El Capitán State Beach is a protected beach in southern California, United States, located about 20 miles west of downtown Santa Barbara. El Capitan has a day use beach as well as a campground with 131 sites, 6 of which are RV only, and 5 group sites...
. From there going west to 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....
, the unit gradually grades into the Sacate Formation, a similar but shalier and more siltstone-rich unit which is also conformably overlain on the Cozy Dell Formation. The Coldwater and Sacate Formations are sometimes considered as a single unit, particularly underneath the Santa Barbara Channel where they appear in drill cores. The Gaviota Formation is deposited conformably on top of the Coldwater-Sacate in the western part of the dual unit's extent, and the 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...
appears conformably on top of it elsewhere.
The Coldwater outcrops predominantly on the south slope of the Santa Ynez Range, and on the crest of the range at San Marcos Pass
San Marcos Pass
San Marcos Pass is a mountain pass in the Santa Ynez Mountains in California.It is traversed by State Route 154. The pass connects Los Olivos and the Santa Ynez Valley with Santa Barbara, California...
. Cathedral Peak, the 3,333-foot prominence directly north of Santa Barbara, is within the Coldwater unit. Because the sandstone beds are resistant to erosion, wherever they dip steeply, they form distinctive hogback ridges and dip-slopes, a topography particularly characteristic of the ridge north of Goleta, where the Coldwater accounts for almost all of the terrain above approximately 1,000 feet. While the unit is exposed prominently throughout the Santa Ynez Mountains, it dips steeply to the south and vanishes underneath the coastal plain and then the Santa Barbara Channel
Santa Barbara Channel
The Santa Barbara Channel is a portion of the Pacific Ocean which separates the mainland of California from the northern Channel Islands. It is generally south of the city of Santa Barbara, and west of the city of Ventura....
. Well bores in the numerous oil and gas fields in the Channel show the Gaviota Formation overlying the Cozy Dell directly, with no intervening Coldwater, excepting the offshore portion of the Capitan Oil Field, in which the Coldwater Formation is present as a natural-gas-bearing unit, underlying the Gaviota.
As a potential hydrocarbon resource, the unit is considered to be equivalent to the Sacate, and is grouped with the lower-lying Cozy Dell Shale and Matilija Sandstone as the Gaviota-Sacate-Matilija Sandstone Play. The likely source rocks for any petroleum accumulation in the Coldwater-Sacate are the lower-lying organic-rich shale units, such as the Cozy Dell and the Juncal-Anita Formations
Juncal Formation
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...
. Since this deep-lying play is incompletely explored, the estimates for hydrocarbon resources are speculative, with the United States Bureau of Ocean Energy Management, Regulation and Enforcement giving a range of 117 to 127 million barrels of oil recoverable using current technology for the entire Santa Barbara-Ventura Basin Province. Some onshore oil fields produce from the Coldwater, including the Ojai Oil Field north of Santa Paula
Santa Paula, California
Santa Paula is a city within Ventura County, California, United States. The population was 29,321 at the 2010 census, up from 28,598 at the 2000 census...
and Sespe oil field north of Fillmore, not far from the type locality for the formation.
Deposition environment and tectonic history
The unit is of middle to upper EoceneEocene
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, being deposited in a shallow marine environment, during a time in which the sea was receding and becoming more shallow. Since the process was not uniform, with periods of shallow-water deposition alternating with deeper water conditions, the predominantly sandstone unit is interbedded with siltstones and shales, with the siltstone and shale making up around 20% of the total composition. Late in the period of deposition, large oyster beds appear in the stratigraphic record, indicating a brackish-water nearshore environment. The source rock for the sediment making up the Coldwater was mostly granitic, and pebbles or cobbles of granite and quartzite appear in some of the nearshore sandstones near the top of the unit. At its top the unit grades into the redbeds and conglomerates of the Sespe Formation, which was deposited in a floodplain, riverine, and estuarine environment onshore.
A 1996 study by Donald R. Prothero and Robert J. Emry determined the age of the unit using magnetostratigraphy
Magnetostratigraphy
Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their characteristic remanent magnetization , that is, the...
, and gave its period of deposition as from 39.5 Ma (million years ago) to 42.5 Ma. Additionally, studies of the correlation of the underlying Cozy Dell and Matilija Sandstone
Matilija Sandstone
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...
with similar units in the California Central Valley, along with paleomagnetic data, show that the tectonic block on which the Coldwater and its surrounding formations were deposited – including the western part of the Transverse Ranges – has rotated clockwise almost 90 degrees since the time of deposition, also moving north-northwest from its original location. Uplift along the Santa Ynez Fault 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 – the last 2.5 million years – has brought the Coldwater and the other formations up from their deposition environments to their present prominent locations in the Santa Ynez Range. In the area north and northeast of Santa Barbara, on the south slope of the Santa Ynez Mountains eastward to near Ojai, the compression and folding associated with tectonic movements have been sufficiently intense to overturn the rock units so that the older ones are on top. This stretch of overturned rock formations is known as the "Montecito Overturn".
Paleontology
Fossils of numerous mullusks, including many species of the genus turritella can be found in the Coldwater, particularly near the top of the formation where the water at time of deposition was shallowest. Outcrops along Old San Marcos Pass Road near the contact with the Sespe FormationSespe 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...
are rich locations for finding remnants of these sea-snails. Elsewhere near the top contact with the Sespe, the remnants of oyster beds can be found.