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46-554: 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. The Cozy Dell crops out continuously in

92-427: A stratigraphic section depends on the rate of deposition and the age of the section. In sedimentary layers, the preferred lithologies are mudstones , claystones , and very fine-grained siltstones because the magnetic grains are finer and more likely to orient with the ambient field during deposition. Samples are first analyzed in their natural state to obtain their natural remanent magnetization (NRM). The NRM

138-454: A thermoremanent magnetization and sediments acquire a depositional remanent magnetization , both of which reflect the direction of the Earth's field at the time of formation. This technique is typically used to date sequences that generally lack fossils or interbedded igneous rock. It is particularly useful in high-resolution correlation of deep marine stratigraphy where it allowed the validation of

184-407: A certain time period in geologic history where the Earth's magnetic field was in predominantly a "normal" or "reversed" position. Chrons are numbered in order starting from today and increasing in number into the past. As well as a number, each chron is divided into two parts, labelled "n" and "r", thereby showing the position of the field's polarity. Chrons are also referred by a capital letter of

230-460: 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. Microfauna in the Cozy Dell, primarily planktonic (i.e., floating) foraminifera , place it in the upper part of

276-459: A duration between 10 and 10 years, Superchron for a duration between 10 and 10 years and Crytochron for a duration less than 3×10 years. The nomenclature for the succession of polarity intervals, especially when changes are of short durations, or not universal (the earth's magnetic field is complex) is challenging, as each new discovery has to be inserted (or if not validated, removed). The two standardised marine magnetic anomalies sequences are

322-628: 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. 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

368-629: 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 period and late Pliocene , by crustal shortening and compression from tectonic forces at the boundary of the Pacific and North American Plates . The Matilija Sandstone and other units, formerly submerged, rose over 4,000 feet (1,200 m) from their original positions. In some places

414-606: A polarity to a biostratigraphic event that has been correlated elsewhere with isotopic ages. With the aid of the independent isotopic age or ages, the local magnetostratigraphic column is correlated with the Global Magnetic Polarity Time Scale (GMPTS). Because the age of each reversal shown on the GMPTS is relatively well known, the correlation establishes numerous time lines through the stratigraphic section. These ages provide relatively precise dates for features in

460-589: 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. 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

506-663: 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

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552-417: A reference sequence such as "C". A chron is the time equivalent to a chronozone or a polarity zone. It was called a "polarity subchron" when the interval is less than 200,000 years long, although the term was redefined in 2020 to an approximate duration between 10,000 to 100,000 years and polarity chron for an approximate duration between 100,000 years and a million years. Other terms used are Megachron for

598-418: 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 (ChRM), that is, the polarity of Earth's magnetic field at the time a stratum was deposited. This is possible because volcanic flows acquire

644-596: Is a sedimentary geologic unit of Eocene epoch in the Paleogene Period , 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

690-432: 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. The Cozy Dell is grouped with underlying and overlying sandstones as

736-578: 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 to 127 million barrels (18,600,000 to 20,200,000 m ) of oil recoverable using current technology for the entire Santa Barbara-Ventura Basin Province. In general, in

782-410: Is named C1n-1. Certain terms in the literature such as M-1r to describe a postulated brief reversal at about 118 Ma are provisional. Oriented paleomagnetic samples are collected in the field using a rock core drill, or as hand samples (chunks broken off the rock face). To average out sampling errors, a minimum of three samples is taken from each sample site. Spacing of the sample sites within

828-545: 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 (2,134 m) feet below the ocean floor. 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. Matilija Sandstone The Matilija Sandstone ( / m ə ˈ t ɪ l ə h ə / )

874-424: Is then stripped away in a stepwise manner using thermal or alternating field demagnetization techniques to reveal the stable magnetic component. Magnetic orientations of all samples from a site are then compared and their average magnetic polarity is determined with directional statistics , most commonly Fisher statistics or bootstrapping . The statistical significance of each average is evaluated. The latitudes of

920-599: The Geographic North Pole ) the strata retains a normal polarity. If the data indicates that the North Magnetic Pole was near the Geographic South Pole , the strata exhibits reversed polarity. A polarity chron , or in context chron , is the time interval between polarity reversals of Earth's magnetic field . It is the time interval represented by a magnetostratigraphic polarity unit. It represents

966-632: The Lutetian stage (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. However, some larger fossils have been found in

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1012-557: The Santa Barbara Channel , the Cozy Dell is found in oil wells at Molino field some 13,000 feet (3,962 m) feet below the sea floor. The thickness of the formation increases, more or less, from east to west and averages about 1,700 feet (518 m) in the Santa Ynez Mountains. However, thicknesses vary widely, ranging from a maximum of 4,000 feet (1,219 m) west of San Marcos Pass, to 50 feet (15 m) thick in

1058-695: The Santa Ynez Mountain range north of Santa Barbara, eastward into Ventura County. The type locality 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 2,500 feet (760 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

1104-619: The Santonian geologic age. The M series is defined from M0, with full label M0r, at 121.400 Ma, which is the beginning of the Aptian to M44n.2r which is before 171.533 Ma in the Aalenian . Subdivisions in the sequencies also have specific nomenclature so C8n.2n is the second oldest normal polarity subchron comprising normal-polarity Chron C8n and the youngest cryptochron, the Emperor cryptochron,

1150-478: The Vine–Matthews–Morley hypothesis related to the theory of plate tectonics . When measurable magnetic properties of rocks vary stratigraphically they may be the basis for related but different kinds of stratigraphic units known collectively as magnetostratigraphic units (magnetozones) . The magnetic property most useful in stratigraphic work is the change in the direction of the remanent magnetization of

1196-605: The source rock passed through the generation window and hydrocarbon migration began. Because the ages of cross-cutting trapping structures can usually be determined from magnetostratigraphic data, a comparison of these ages will assist reservoir geologists in their determination of whether or not a play is likely in a given trap. Changes in sedimentation rate revealed by magnetostratigraphy are often related to either climatic factors or to tectonic developments in nearby or distant mountain ranges. Evidence to strengthen this interpretation can often be found by looking for subtle changes in

1242-700: The "C-sequence" and "M-sequence" and cover from the Middle Jurassic to date. Accordingly the main C polarity chrons series extend backwards from the current C1n, commonly termed Brunhes, with the most recent transition at C1r, commonly termed Matuyama, at 0.773  Ma which is the Brunhes–Matuyama reversal . The C (for Cenozoic) sequence ends in the Cretaceous Normal Superchron termed C34n which on age calibration occurred at 120.964 Ma and lasted to Chron C33r at 83.650  Ma that defined

1288-449: 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. 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

1334-472: 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

1380-518: 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. Continuing south into the offshore region beneath

1426-478: The Virtual Geomagnetic Poles from those sites determined to be statistically significant are plotted against the stratigraphic level at which they were collected. These data are then abstracted to the standard black and white magnetostratigraphic columns in which black indicates normal polarity and white is reversed polarity. Because the polarity of a stratum can only be normal or reversed, variations in

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1472-539: The center of the range. The thickness of the unit is widely variable, generally decreasing to the west. In its type locality it is around 2,500 feet (760 m) thick; in the vicinity of La Cumbre Peak it is 2,000 feet (610 m) thick; and while it thins to only 500 feet (150 m) thick underneath San Marcos Pass, it thickens again to around 2,000 feet (610 m) at the high summits of Santa Ynez and Broadcast Peaks. It thins westward from there, being only 500 feet (150 m) thick at Refugio Pass, and less than 300 in

1518-502: 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

1564-426: 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 the time of deposition, moving from

1610-708: 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 1,500 square miles (3,900 km ) 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 million barrels (6,200,000 m ) of oil equivalent. Magnetostratigraphy Magnetostratigraphy

1656-401: 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

1702-491: The forces causing this uplift were so abrupt that sedimentary layers deposited as recently as the Pleistocene are now angled 60 degrees from horizontal. 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 . As

1748-428: The formation is at an average of 10,500 feet (3,200 m) below the seafloor, and a well drilled to 12,589 feet (3,837 m) had not reached the bottom of the formation. Sometime in the early Eocene, around 50 million years ago, the landmass containing present-day Santa Barbara County became submerged, allowing sediment deposition offshore. During this time the sea alternately deepened and became shallow again, with

1794-578: 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 2,000 feet (610 m) thick, and first appears approximately 4,300 feet (1,300 m) below ground surface. In the Molino Offshore Gas Field, southeast of Gaviota about two miles (3.2 km) offshore,

1840-498: The most intense modern-day flood events, tumbled down the mountains during Pleistocene-age storms and mudflows of unimaginable intensity. Boulders of the Matilija were included in the mud and debris flows in the January 2018 Montecito mudflows . 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

1886-492: 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

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1932-420: The rate at which the sediment accumulated can cause the thickness of a given polarity zone to vary from one area to another. This presents the problem of how to correlate zones of like polarities between different stratigraphic sections. To avoid confusion at least one isotopic age needs to be collected from each section. In sediments, this is often obtained from layers of volcanic ash . Failing that, one can tie

1978-419: The rocks such as fossils , changes in sedimentary rock composition, changes in depositional environment, etc. They also constrain the ages of cross-cutting features such as faults , dikes , and unconformities . Perhaps the most powerful application of these data is to determine the rate at which the sediment accumulated. This is accomplished by plotting the age of each reversal (in millions of years ago) vs.

2024-449: The rocks, caused by reversals in the polarity of the Earth's magnetic field . The direction of the remnant magnetic polarity recorded in the stratigraphic sequence can be used as the basis for the subdivision of the sequence into units characterized by their magnetic polarity. Such units are called "magnetostratigraphic polarity units" or chrons. If the ancient magnetic field was oriented similar to today's field ( North Magnetic Pole near

2070-415: The stratigraphic level at which the reversal is found (in meters). This provides the rate in meters per million years which is usually rewritten in terms of millimeters per year (which is the same as kilometers per million years). These data are also used to model basin subsidence rates . Knowing the depth of a hydrocarbon source rock beneath the basin-filling strata allows calculation of the age at which

2116-455: The subsurface of the offshore Hondo Oil Field , and only 350 feet (107 m) thick in the offshore Molino Gas Field, which is located west of Hondo. 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. When exposed to surface conditions, it breaks down quickly to form

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