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42-425: The Raven Ridge and the adjacent parallel Squaw Ridge are northwest striking rock exposures which provide an opportunity to understand this part of Earth's history. This section through a sequence of rock layers that were deposited between ~53-49 million years ago, has become exposed because of its later tectonic history. The outcrops span the geological time interval that includes the early and middle portions of

84-613: A doubly plunging anticline , and may be formed from multiple deformations, or superposition of two sets of folds. It may also be related to the geometry of the underlying detachment fault and the varying amount of displacement along the surface of that detachment fault. An anticlinorium is a large anticline in which a series of minor anticlinal folds are superimposed. Examples include the Late Jurassic to Early Cretaceous Purcell Anticlinorium in British Columbia and

126-425: A feature with a dip of 45° and a dip direction of 75°, the strike and dip can be written as 345/45 NE, 165/45 NE, or 075,45. The compass quadrant direction for the strike can also be used in place of the azimuth, written as S15E or N15W. Strike and dip are measured in the field using a compass and with a clinometer . A compass is used to measure the azimuth of the strike, and the clinometer measures inclination of

168-412: A few conventions geologists use when measuring a feature's azimuth. When using the strike, two directions can be measured at 180° apart, at either clockwise or counterclockwise of north. One common convention is to use the "right-hand rule" (RHR) where the plane dips down towards the right when facing the strike direction, or that the dip direction should be 90° clockwise of the strike direction. However, in

210-479: A high rate of compression and seismic activity due to the converging San Andreas Fault. As a result, the Ventura anticline rises at a rate of 5 mm/year with the adjacent Ventura Basin converging at a rate of about 7–10 mm/year. The anticline is composed of a series of sandstone rock beds and an impermeable rock cap under which vast reserves of oil and gas are trapped. Eight different oil bearing zones along

252-470: A number (between 0° and 90°) indicating the angle in degrees below horizontal. It can be accompanied with the rough direction of dip (N, SE, etc) to avoid ambiguity. The direction can sometimes be omitted, as long as the convention used (such as right-hand rule) is known. A feature that is completely flat will have the same dip value over the entire surface. The dip of a curved feature, such as an anticline or syncline , will change at different points along

294-423: A single three-digit number in terms of the angle from true north (for example, N25°E would simply become 025 or 025°). A feature's orientation can also be represented by its dip direction. Rather than the azimuth of a horizontal line on the plane, the azimuth of the steepest line on the plane is used. The direction of dip can be visualized as the direction water would flow if poured onto a plane. While true dip

336-434: A type of anticlines that have a well-defined, but curved hinge line and are doubly plunging and thus elongate domes . Folds in which the limbs dip toward the hinge and display a more U-like shape are called synclines . They usually flank the sides of anticlines and display opposite characteristics. A syncline's oldest rock strata are in its outer limbs; the rocks become progressively younger toward its hinge. A monocline

378-455: Is a dome . Domes may be created via diapirism from underlying magmatic intrusions or upwardly mobile, mechanically ductile material such as rock salt ( salt dome ) and shale (shale diapir) that cause deformations and uplift in the surface rock. The Richat Structure of the Sahara is considered a dome that has been laid bare by erosion. An anticline which plunges at both ends is termed

420-431: Is a bend in the strata resulting in a local steepening in only one direction of dip. Monoclines have the shape of a carpet draped over a stairstep. An anticline that has been more deeply eroded in the center is called a breached or scalped anticline . Breached anticlines can become incised by stream erosion, forming an anticlinal valley. A structure that plunges in all directions to form a circular or elongate structure

462-462: Is a type of fold that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex up in which the hinge or crest is the location where the curvature is greatest, and the limbs are the sides of the fold that dip away from the hinge. Anticlines can be recognized and differentiated from antiforms by a sequence of rock layers that become progressively older toward

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504-401: Is cylindrical has a well-defined axial surface, whereas non-cylindrical anticlines are too complex to have a single axial plane. An overturned anticline is an asymmetrical anticline with a limb that has been tilted beyond perpendicular , so that the beds in that limb have basically flipped over and may dip in the same direction on both sides of the axial plane. If the angle between the limbs

546-547: Is large (70–120 degrees), then the fold is an "open" fold , but if the angle between the limbs is small (30 degrees or less), then the fold is a "tight" fold . If an anticline plunges (i.e., the anticline crest is inclined to the Earth's surface), it will form V s on a geologic map view that point in the direction of plunge . A plunging anticline has a hinge that is not parallel to the earth's surface. All anticlines and synclines have some degree of plunge. Periclinal folds are

588-815: Is measured perpendicular to the strike, apparent dip refers to an observed dip which is not perpendicular to the strike line. This can be seen in outcroppings or cross-sections which do not run parallel to the dip direction. Apparent dip is always shallower than the true dip. If the strike is known, the apparent dip or true dip can be calculated using trigonometry: α = arctan ⁡ ( sin ⁡ β × tan ⁡ δ ) {\displaystyle \alpha =\arctan(\sin \beta \times \tan \delta )} δ = arctan ⁡ ( tan ⁡ α ÷ sin ⁡ β ) {\displaystyle \delta =\arctan(\tan \alpha \div \sin \beta )} where δ

630-521: Is no mechanical contrast between layers in this type of fold. Passive-flow folds are extremely dependent on the rock composition of the stratum and can typically occur in areas with high temperatures. Anticlines, structural domes, fault zones and stratigraphic traps are very favorable locations for oil and natural gas drilling. About 80 percent of the world's petroleum has been found in anticlinal traps. The low density of petroleum causes oil to buoyantly migrate out of its source rock and upward toward

672-606: Is the El Dorado anticline in Kansas. The anticline was first tapped into for its petroleum in 1918. Soon after the site became a very prosperous area for entrepreneurs following World War I and the rapid popularization of motor vehicles . By 1995 the El Dorado oil fields had produced 300 million barrels of oil. The central Kansas uplift is an antiform composed of several small anticlines that have collectively produced more than 2.5 million barrels of oil. Another notable anticline

714-548: Is the Tierra Amarilla anticline in San Ysidro, New Mexico. This is a popular hiking and biking site because of the great biodiversity, geologic beauty and paleontological resources. This plunging anticline is made up of Petrified Forest mudstones and sandstone and its caprock is made of Pleistocene and Holocene travertine. The anticline contains springs that deposit carbon dioxide travertine that help to contribute to

756-420: Is the area on the limbs where the curvature changes direction. The axial surface is an imaginary plane connecting the hinge of each layer of rock stratum through the cross section of an anticline. If the axial surface is vertical and the angles on each side of the fold are equivalent, then the anticline is symmetrical. If the axial plane is tilted or offset, then the anticline is asymmetrical. An anticline that

798-443: Is the relative ages of the rock strata that distinguish anticlines from antiforms. The hinge of an anticline refers to the location where the curvature is greatest, also called the crest . The hinge is also the highest point on a stratum along the top of the fold. The culmination also refers to the highest point along any geologic structure. The limbs are the sides of the fold that display less curvature. The inflection point

840-401: Is the true dip, α is the apparent dip, and β is the angle between the strike direction and the apparent dip direction, all in degrees. The measurement of a linear feature's orientation is similar to strike and dip, though the terminology differs because "strike" and "dip" are reserved for planes. Linear features use trend and plunge instead. Plunge, or angle of plunge, is the inclination of

882-424: Is to bend a deck of cards and to imagine each card as a layer of rock stratum. The amount of slip on each side of the anticline increases from the hinge to the inflection point. Passive-flow folds form when the rock is so soft that it behaves like weak plastic and slowly flows. In this process different parts of the rock body move at different rates causing shear stress to gradually shift from layer to layer. There

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924-653: The Blue Ridge anticlinorium of northern Virginia and Maryland in the Appalachians, or the Nittany Valley in central Pennsylvania. Anticlines are usually developed above thrust faults, so any small compression and motion within the inner crust can have large effects on the upper rock stratum. Stresses developed during mountain building or during other tectonic processes can similarly warp or bend bedding and foliation (or other planar features). The more

966-529: The Eocene Epoch . During this time, ancestral horses, primates, and rodents, among many other mammal groups, were common at Raven Ridge. At the southern edge of Raven Ridge are found the only available surface coal beds in the area. The rocks of Raven Ridge were originally deposited on or near a shore line as horizontal sedimentary layers within the Uinta Basin . Uplift and folding associated with

1008-571: The GPS functionality of such devices, this allows readings to be recorded and later downloaded onto a map. When studying subsurface features, a dipmeter can be used. A dipmeter is a tool that is lowered into a borehole , and has arms radially attached which can detect the microresistivity of the rock. By recording the times at which the rock's properties change across each of the sensors, the strike and dip of subsurface features can be worked out. Anticline In structural geology , an anticline

1050-401: The azimuth of an imagined horizontal line across the plane, and its dip is the angle of inclination (or depression angle ) measured downward from horizontal. They are used together to measure and document a structure's characteristics for study or for use on a geologic map . A feature's orientation can also be represented by dip and dip direction , using the azimuth of the dip rather than

1092-463: The structural trap for the largest conventional oil field in the world. The Weald–Artois Anticline is a major anticline which outcrops in southeast England and northern France. It was formed from the late Oligocene to middle Miocene , during the Alpine orogeny . Anticlines can have a major effect on the local geomorphology and economy of the regions in which they occur. One example of this

1134-562: The UK, the right-hand rule has sometimes been specified so that the dip direction is instead counterclockwise from the strike. Some geologists prefer to use whichever strike direction is less than 180°. Others prefer to use the "dip-direction, dip" (DDD) convention instead of using the strike direction. Strike and dip are generally written as 'strike/dip' or 'dip direction,dip', with the degree symbol typically omitted. The general alphabetical dip direction (N, SE, etc) can be added to reduce ambiguity. For

1176-407: The attitude of an inclined feature, two quantities are needed. The angle the slope descends, or dip, and the direction of descent, which can be represented by strike or dip direction. Dip is the inclination of a given feature, and is measured from the steepest angle of descent of a tilted bed or feature relative to a horizontal plane. True dip is always perpendicular to the strike. It is written as

1218-429: The center of the fold. Therefore, if age relationships between various rock strata are unknown, the term antiform should be used. The progressing age of the rock strata towards the core and uplifted center, are the trademark indications for evidence of anticlines on a geologic map . These formations occur because anticlinal ridges typically develop above thrust faults during crustal deformations. The uplifted core of

1260-407: The dip line on both sides of the strike, and horizontal bedding is denoted by a cross within a circle. Interpretation of strike and dip is a part of creating a cross-section of an area. Strike and dip information recorded on a map can be used to reconstruct various structures, determine the orientation of subsurface features, or detect the presence of anticline or syncline folds. There are

1302-549: The dip. Dr. E. Clar first described the modern compass-clinometer in 1954, and some continue to be referred to as Clar compasses. Compasses in use today include the Brunton compass and the Silva compass . Smartphone apps which can make strike and dip measurements are also available, including apps such as GeoTools . These apps can make use of the phone's internal accelerometer to provide orientation measurements. Combined with

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1344-422: The feature and be flat on any fold axis . Strike is a representation of the orientation of a tilted feature. The strike line of a bed , fault, or other planar feature, is a line representing the intersection of that feature with a horizontal plane. The strike of the feature is the azimuth (compass direction) of the strike line. This can be represented by either a quadrant compass bearing (such as N25°E), or as

1386-407: The feature measured downward relative to horizontal. Trend is the feature's azimuth, measured in the direction of plunge. A horizontal line would have a plunge of 0°, and a vertical line would have a plunge of 90°. A linear feature which lies within a plane can also be measured by its rake (or pitch). Unlike plunge, which is the feature's azimuth, the rake is the angle measured within the plane from

1428-399: The fold causes compression of strata that preferentially erodes to a deeper stratigraphic level relative to the topographically lower flanks. Motion along the fault including both shortening and extension of tectonic plates, usually also deforms strata near the fault. This can result in an asymmetrical or overturned fold. An antiform can be used to describe any fold that is convex up. It

1470-643: The later stages of the Laramide Orogeny subsequently tilted them into a nearly vertical position. Raven Ridge is the habitat for eight endemic rare plant species: Penstemon grahamii (Graham's beardtongue), Penstemon albifluvis (White River beardtongue), Astragalus lutosus (Dragon milkvetch), Aquilegia barnebyi (Mancos columbine), Cryptantha rollinsii (Rollins's catseye), Parthenium ligulata (Colorado feverfew), Eriogonum ephedroides (ephedra buckwheat), and Phacelia incana (hoary phacelia). Numerous other plants are found there as well. Found at

1512-628: The rich diversity of microorganisms. This area also contains remains of fossils and ancient plants from the Jurassic period that are sometimes exposed through geological erosion. The Ventura Anticline is a geologic structure that is part of the Ventura oil fields , the seventh largest oil field in California that was discovered in the 1860s. The anticline runs east to west for 16 miles, dipping steeply 30–60 degrees at both ends. Ventura County has

1554-540: The strike line. On geologic maps , strike and dip can be represented by a T symbol with a number next to it. The longer line represents strike, and is in the same orientation as the strike angle. Dip is represented by the shorter line, which is perpendicular to the strike line in the downhill direction. The number gives the dip angle, in degrees, below horizontal, and often does not have the degree symbol. Vertical and horizontal features are not marked with numbers, and instead use their own symbols. Beds dipping vertically have

1596-418: The strike value. Linear features are similarly measured with trend and plunge , where "trend" is analogous to dip direction and "plunge" is the dip angle. Strike and dip are measured using a compass and a clinometer . A compass is used to measure the feature's strike by holding the compass horizontally against the feature. A clinometer measures the feature's dip by recording the inclination perpendicular to

1638-520: The strike. These can be done separately, or together using a tool such as a Brunton transit or a Silva compass . Any planar feature can be described by strike and dip, including sedimentary bedding , fractures , faults , joints , cuestas , igneous dikes and sills , metamorphic foliation and fabric , etc. Observations about a structure's orientation can lead to inferences about certain parts of an area's history, such as movement, deformation, or tectonic activity . When measuring or describing

1680-399: The summit of the ridge are a multitude of perfectly preserved fossil gastropods . 40°11′22″N 109°03′53″W  /  40.18944°N 109.06472°W  / 40.18944; -109.06472 Strike and dip In geology , strike and dip is a measurement convention used to describe the plane orientation or attitude of a planar geologic feature . A feature's strike is

1722-786: The surface until it is trapped and stored in reservoir rock such as sandstone or porous limestone. The oil becomes trapped along with water and natural gas by a caprock that is made up of impermeable barrier such as an impermeable stratum or fault zone. Examples of low-permeability seals that contain the hydrocarbons, oil and gas, in the ground include shale , limestone , sandstone , and rock salt. The actual type of stratum does not matter as long as it has low permeability. Water, minerals and specific rock strata such as limestone found inside anticlines are also extracted and commercialized. Lastly, ancient fossils are often found in anticlines and are used for paleontological research or harvested into products to be sold. Ghawar Anticline, Saudi Arabia,

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1764-435: The underlying fault is tectonically uplifted, the more the strata will be deformed and must adapt to new shapes. The shape formed will also be very dependent on the properties and cohesion of the different types of rock within each layer. During the formation of flexural-slip folds, the different rock layers form parallel-slip folds to accommodate for buckling . A good way to visualize how the multiple layers are manipulated,

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