Dark shale beds of the Jalama Formation on the Santa Ynez Mountain crest north of Montecito, California. These beds are overturned; "up" is down and to the left.
The type locality of the Jalama Formation is in southwestern Santa Barbara County on the low ridgeline between Santa Anita and Bulito Canyons, within Hollister Ranch, near the crest of the Santa Ynez Mountains, and near the headwaters of Jalama Creek. The formation is found from this area eastward along the Santa Ynez Range in periodic outcrops, underlying either the Anita Shale (in the western portion of its range) or the Juncal Formation Shale (in the east). The largest outcrop in the Santa Ynez Range is along the north slope of the mountains near Santa Ynez Peak, where it is exposed for approximately six miles.[2][4] Other outcrops occur north of the Santa Ynez Fault, in the San Rafael Mountains along the Little Pine Syncline and along the Hildreth Fault.[5]
Characteristic shale beds within the Jalama are dark gray to black, micaceous, and often carbonaceous. Sandstones interbedded with the shales are arkosic, light gray to tan, and sometimes massive, as at the base of the type section on Hollister Ranch.[2][5] Another interbedded unit occasionally encountered is a cobbly conglomerate, which outcrops on the north slope of the Santa Ynez Mountains south of Gibraltar Reservoir. The cobbles in this unit are detritus from a granitic source rock in a gray to brown matrix.[6] The overall Jalama Formation varies in thickness from around 2,000 feet near the Romero Saddle north of Carpinteria, to about 4,000 feet at the type location more than forty miles to the west.[2][4]
Deposition environment and geologic history
Sandstone unit within the Jalama Formation.
The region of present-day Santa Barbara and Ventura County during the Late Cretaceous was submerged, and the depositional environment was one of a narrow shelf and submarine fans. The previously exposed Espada Formation, after a period of erosion, was now underwater, and began to receive layers of sediment which would become the Jalama Formation. Periodic episodes of deeper and shallower water resulted in finer and coarser sediments, respectively – shales versus sandstones.[7] The crustal block on which the Jalama formation was deposited has been inferred to have rotated approximately 90 degrees clockwise and moved northward along the coast from its former position nearer San Diego. This motion took place beginning in the early Miocene, during a period of deformation along the boundaries of the Pacific and North American Plates, a boundary represented today by the San Andreas Fault.[7]
The unit lies unconformably on the Espada Formation, also of Cretaceous age, and in places on the older Franciscan Formation, which is probably of Jurassic age.[8][9] In one location, in Nojoqui Canyon near the Nojoqui Falls, the Jalama is in conformable contact with the underlying Espada, indicating one area that remained submerged through the era.[2]
The Jalama formation is separated by overlying sedimentary layers by an unconformity most everywhere it has been found, as the Paleocene is unrepresented in the fossil record in southern Santa Barbara County, and the stratigraphic sequence goes directly from the Cretaceous Jalama to Eocene units, including the Anita and Juncal Formations.[10] In his 1966 book on the geology of the central Santa Ynez Mountains, Dibblee finds the Cretaceous Jalama Formation to be in conformable contact with the Eocene Juncal in the eastern part of the Santa Ynez range, without mentioning the intervening Paleocene; in this portion of the unit there are no fossils to provide clues as to date.[4]
Paleontology
While the eastern part of the Jalama Formation is almost without fossils, some localities in the western part are richly fossiliferous, with Campanian age foraminifer and molluscan assemblages.[11]
At least one species – Lysis jalamaca, from an extinct genus of shallow-marine gastropod – has been named for the unit. Lysus jalamaca has been dated to between 70-75 million years before present, in the late Cretaceous.[12] Other fossils found in the Jalama Formation, listed in Dibblee's 1950 book include six species of bivalves and one species each of gastropod and cephalopod. All of these are described as "abundant", with numerous others not listed; all are indicative of upper Cretaceous.[13]
↑ Dibblee, Thomas. Geology of the central Santa Ynez Mountains, Santa Barbara County, California. Bulletin 186, California Division of Mines and Geology. San Francisco, 1966. 21
1 2 3 4 5 6 7 Dibblee, Thomas. Geology of Southwestern Santa Barbara County, California. Bulletin 150, California Division of Mines and Geology. San Francisco, 1950. 23
1 2 Thomas M. Dibblee, 1986. Geologic Map of the Little Pine Mountain Quadrangle, Santa Barbara County, California. California Department of Conservation, Division of Mines and Geology. Dibblee Foundation Map DF#05.
↑ Thomas M. Dibblee, 1986. Geologic Map of the Santa Barbara Quadrangle, Santa Barbara County, California. California Department of Conservation, Division of Mines and Geology. Dibblee Foundation Map DF#06.
1 2 Marilyn E. Tennyson and Caroline M. Isaacs, "Geologic setting and petroleum geology of Santa Maria and Santa Barbara Basins, Coastal California." In: Isaacs, Caroline M. and Rullkötter, Jürgen. The Monterey Formation: From Rocks to Molecules. Columbia University Press, 2001. ISBN0-231-10585-1 p. 219.
↑ Norris, Robert M. (2003). The geology and landscape of Santa Barbara County, California. Santa Barbara, California: Santa Barbara Museum of Natural History. pp.77–80. ISBN0-936494-35-2.
↑ Saul L. R. & Richard L. Squires R. L. (2008). "Cretaceous trichotropid gastropods from the Pacific slope of North America: Possible pathways to calyptraeid morphology". The Nautilus122(3): 115–142, 2008. PDF.
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 exposed geology of the Capitol Reef area presents a record of mostly Mesozoic-aged sedimentation in an area of North America in and around Capitol Reef National Park, on the Colorado Plateau in southeastern Utah.
The San Juan Basin is a geologic structural basin located near the Four Corners region of the Southwestern United States. The basin covers 7,500 square miles and resides in northwestern New Mexico, southwestern Colorado, and parts of Utah and Arizona. Specifically, the basin occupies space in the San Juan, Rio Arriba, Sandoval, and McKinley counties in New Mexico, and La Plata and Archuleta counties in Colorado. The basin extends roughly 100 miles (160 km) N-S and 90 miles (140 km) E-W.
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 Foremost Formation is a stratigraphic unit of Late Cretaceous (Campanian) age that underlies much of southern Alberta, Canada. It was named for outcrops in Chin Coulee near the town of Foremost and is known primarily for its dinosaur remains and other fossils.
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 Mist Mountain Formation is a geologic formation of latest Jurassic to earliest Cretaceous age in the Western Canada Sedimentary Basin that is present in the southern and central Canadian Rockies. It was named for outcrops along the western spur of Mist Mountain in Alberta by D.W. Gibson in 1979. The Mist Mountain Formation contains economically important coal seams that have been mined in southeastern British Columbia and southwestern Alberta.
The Mancos Shale or Mancos Group is a Late Cretaceous geologic formation of the Western United States.
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 Cozy Dell Shale is a geologic formation of middle Eocene age that crops out in the Santa Ynez Mountains and Topatopa Mountains of California, extending from north of Fillmore in Ventura County westward to near Point Arguello, north of Santa Barbara. Because the Cozy Dell easily weathers to a clay-rich soil, it crops out infrequently and generally forms dense stands of chaparral in saddles between peaks and ridges of the more resistant Matilija and Coldwater formations.
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 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.
The Elk Formation is a stratigraphic unit of the Western Canada Sedimentary Basin that is present in southeastern British Columbia and southwestern Alberta. It is probably of Early Cretaceous age, but in some areas its strata could be as old as Late Jurassic. It includes minor thin coal beds and was named for outcrops near the now-abandoned Elk River coal mine east of Fernie, British Columbia.
The Del Norte Formation is a geologic formation in Mexico, New Mexico and Texas near the city of El Paso. It preserves fossils dating back to the early Cretaceous period.
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 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.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
