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Lowe Sequence
The Lowe sequence describes a set of sedimentary structures in turbidite sandstone beds that are deposited by high-density turbidity currents. It is intended to complement, not replace, the better known Bouma sequence, which applies primarily to turbidites deposited by low-density (i.e., low-sand concentration) turbidity currents. Description The Lowe sequence adds three layers labelled S1 through S3 to Bouma's terminology, with S1 being at the bottom and S3 at the top of a sandy turbidite bed. As with the Bouma sequence, each layer has a specific set of sedimentary structures and lithology. And like the Bouma sequence, the layers become finer grained from bottom to top. The layers are described as follows. * S3 - Massive to graded, fine- to coarse-grained sandstones that overlie the S2 layer represent deposition from a turbulent suspension. Sometimes dish structures and dewatering pipes are present. This layer is essentially the same as the Bouma A layer. * S2 - Inverse (revers ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sedimentary Structure
Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition. Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment, with different particle sizes are deposited on top of each other. These beds range from millimeters to centimeters thick and can even go to meters or multiple meters thick. Sedimentary structures such as cross-bedding, graded bedding, and ripple marks are utilized in stratigraphic studies to indicate original position of strata in geologically complex terrains and understand the depositional environment of the sediment. Flow structures There are two kinds of flow structures: bidirectional (multiple directions, back-and-forth) and unidirectional. Flow regimes in single-direction (typically fluvial) flow, which at varying speeds and velocities produce different structures, are called bedforms. In the ''lower flow regime'', the natural progression is from a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Turbidite
A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites were first properly described by Arnold H. Bouma (1962), who studied deepwater sediments and recognized particular "fining-up intervals" within deep water, fine-grained shales, which were anomalous because they started at pebble conglomerates and terminated in shales. This was anomalous because within the deep ocean it had historically been assumed that there was no mechanism by which tractional flow could carry and deposit coarse-grained sediments into the abyssal depths. Bouma cycles begin with an erosional contact of a coarse lower bed of pebble to granule conglomerate in a sandy matrix, and grade up through coarse then medium plane parallel sandstone; through cross-bedded sandstone; rippled cross-bedded sand/silty sand, and finally la ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) because they are the most resistant minerals to weathering processes at the Earth's surface. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions. Rock formations that are primarily composed of sandstone usually allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Quartz-bearing sandstone can be changed into quartzite through metamorphism, usually relate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Turbidity Current
A turbidity current is most typically an underwater current of usually rapidly moving, sediment-laden water moving down a slope; although current research (2018) indicates that water-saturated sediment may be the primary actor in the process. Turbidity currents can also occur in other fluids besides water. Researchers from the Monterey Bay Aquarium Research Institute found that a layer of water-saturated sediment moved rapidly over the seafloor and mobilized the upper few meters of the preexisting seafloor. Plumes of sediment-laden water were observed during turbidity current events but they believe that these were secondary to the pulse of the seafloor sediment moving during the events. The belief of the researchers is that the water flow is the tail-end of the process that starts at the seafloor. In the most typical case of oceanic turbidity currents, sediment laden waters situated over sloping ground will flow down-hill because they have a higher density than the adjacent ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bouma Sequence
300px, thumbnail, Turbidite from the Devonian-age Becke-Oese Sandstone">Devonian.html" ;"title="Turbidite from the Devonian">Turbidite from the Devonian-age Becke-Oese Sandstone, Germany showing a complete Bouma sequence. The Bouma Sequence (after Arnold H. Bouma, 1932–2011) describes a classic set of sedimentary structures in turbidite beds deposited by turbidity currents at the bottoms of lakes, oceans and rivers. Description The Bouma sequence specifically describes the ideal vertical succession of structures deposited by low-density (i.e., low sand concentration, fine-grained) turbidity currents. An alternate classification scheme that is generally called the Lowe sequence exists for the ideal vertical sequence of structures deposited by high-density flows. The Bouma sequence is divided into 5 distinct layers labelled A through E, with A being at the bottom and E being at the top. Each layer described by Bouma has a specific set of sedimentary structures and a specific l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sedimentary Structures
Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition. Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment, with different particle sizes are deposited on top of each other. These beds range from millimeters to centimeters thick and can even go to meters or multiple meters thick. Sedimentary structures such as cross-bedding, graded bedding, and ripple marks are utilized in stratigraphic studies to indicate original position of strata in geologically complex terrains and understand the depositional environment of the sediment. Flow structures There are two kinds of flow structures: bidirectional (multiple directions, back-and-forth) and unidirectional. Flow regimes in single-direction (typically fluvial) flow, which at varying speeds and velocities produce different structures, are called bedforms. In the ''lower flow regime'', the natural progression is from a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lithology
The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lithology may refer to either a detailed description of these characteristics, or a summary of the gross physical character of a rock. Examples of lithologies in the second sense include sandstone, slate, basalt, or limestone. Lithology is the basis of subdividing rock sequences into individual lithostratigraphic units for the purposes of mapping and correlation between areas. In certain applications, such as site investigations, lithology is described using a standard terminology such as in the European geotechnical standard Eurocode 7. Rock type The naming of a lithology is based on the rock type. The three major rock types are igneous, sedimentary, and metamorphic. Igneous rocks are formed directly from magma, which is a mixture ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Traction (geology)
Traction is the geologic Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other E ... process whereby a current transports larger, heavier rocks by rolling or sliding them along the bottom. Thus, the grains and clasts interact with the substratum during transport. By contrast, saltation, a related sediment transport process, moves grains across the bottom by bouncing or hopping. The actual current carries the sediment load in traction and saltation flows, whereas downslope movement under the force of gravity carries the sediment in gravity flows. These processes contrast with suspension settling, in which there is no current.Ritter, M.E. (2006), The Physical Environment: an Introduction to Physical Geography: The Geologic Work of Streams,'' online textbook. accessed 25 June 2013. Traction is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cozy Dell Formation
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. Type locality and extent 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 the mountains to the north and east of Ojai, where it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
California
California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the most populated subnational entity in North America and the 34th most populous in the world. The Greater Los Angeles area and the San Francisco Bay Area are the nation's second and fifth most populous urban regions respectively, with the former having more than 18.7million residents and the latter having over 9.6million. Sacramento is the state's capital, while Los Angeles is the most populous city in the state and the second most populous city in the country. San Francisco is the second most densely populated major city in the country. Los Angeles County is the country's most populous, while San Bernardino County is the largest county by area in the country. California borders Oregon to the north, Nevada and Arizona to the east, t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Turbidites
A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites were first properly described by Arnold H. Bouma (1962), who studied deepwater sediments and recognized particular "fining-up intervals" within deep water, fine-grained shales, which were anomalous because they started at pebble conglomerates and terminated in shales. This was anomalous because within the deep ocean it had historically been assumed that there was no mechanism by which tractional flow could carry and deposit coarse-grained sediments into the abyssal depths. Bouma cycles begin with an erosional contact of a coarse lower bed of pebble to granule conglomerate in a sandy matrix, and grade up through coarse then medium plane parallel sandstone; through cross-bedded sandstone; rippled cross-bedded sand/silty sand, and finally lamina ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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