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Absaroka Sequence
The Absaroka sequence was a cratonic sequence that extended from the end of the Mississippian through the Permian periods. It is the unconformity between this sequence and the preceding Kaskaskia that divides the Carboniferous into the Mississippian and Pennsylvanian periods in North America. Like the Kaskaskia sequence, Absaroka sedimentary deposits were dominated by detrital or siliclastic rocks. The first sediments were deposited near the continental margins, particularly near the Ouachita and Appalachian highlands. Characteristic of the strata from this time are cyclothems: alternating marine and non-marine strata indicative of changes in sea-level, probably due to cyclic glaciation in the Southern Hemisphere. In North America, the waters of the Absaroka sequence regressed westward as the highlands to the east steadily eroded. Restricted oceanic circulation in the west led to extensive evaporite formation. By the end of the period, the regression was complete, and t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cratonic Sequence
A cratonic sequence in geology is a very large-scale lithostratigraphic sequence in the rock record that represents a complete cycle of marine transgression and regression on a craton (block of continental crust) over geologic time. Cratonic sequences are also known as "megasequences", "stratigraphic sequences", "Sloss sequences", "supersequences" or simply "sequences". They are geologic evidence of relative sea level rising and then falling (transgressing and regressing), thereby depositing varying layers of sediment onto the craton, now expressed as sedimentary rock. Places such as the Grand Canyon are a good visual example of this process, demonstrating the changes between layers deposited over time as the ancient environment changed. Cratonic sequences were first proposed by Laurence L. Sloss in 1963. Each one represents a time when inland seas deposited sediments across the craton. The top and bottom edges of a sequence are each bounded by craton-wide unconformities (time ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyclothems
In geology, cyclothems are alternating stratigraphy, stratigraphic sequences of Marine (ocean), marine and non-marine sediments, sometimes interbedded with coal seams. Historically, the term was defined by the European coal geologists who worked in coal basins formed during the Carboniferous and earliest Permian periods. The cyclothems consist of repeated sequences, each typically several meters thick, of sandstone resting upon an unconformity, erosional surface, passing upwards to pelites (finer-grained than sandstone) and topped by coal. Depositional sequences have been thoroughly studied by oil geologists using geophysical profiles of continental and marine basins. A general theory of basin-scale deposition has been formalized under the name of sequence stratigraphy. Some cyclothems might have formed as a result of marine regressions and Transgression (geology), transgressions related to growth and decay of ice sheets, respectively, as the Carboniferous was a time of widespre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Historical Geology
Historical geology or palaeogeology is a discipline that uses the principles and methods of geology to reconstruct the geological history of Earth. Historical geology examines the vastness of geologic time, measured in billions of years, and investigates changes in the Earth, gradual and sudden, over this deep time. It focuses on geological processes, such as plate tectonics, that have changed the Earth's surface and subsurface over time and the use of methods including stratigraphy, structural geology, paleontology, and sedimentology to tell the sequence of these events. It also focuses on the evolution of life during different time periods in the geologic time scale. Historical development During the 17th century, Nicolas Steno was the first to observe and propose a number of basic principles of historical geology, including three key stratigraphic principles: the law of superposition, the principle of original horizontality, and the principle of lateral continuity. 18th-cent ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geology Of The United States
The richly textured landscape of the United States is a product of the dueling forces of plate tectonics, weathering and erosion. Over the 4.5 billion-year history of our Earth, tectonic upheavals and colliding plates have raised great mountain ranges while the forces of erosion and weathering worked to tear them down. Even after many millions of years, records of Earth's great upheavals remain imprinted as textural variations and surface patterns that define distinctive landscapes or provinces. The diversity of the landscapes of the United States can be easily seen on the shaded relief image to the right. The stark contrast between the ‘rough' texture of the western US and the ‘smooth' central and eastern regions is immediately apparent. Differences in roughness (topographic relief) result from a variety of processes acting on the underlying rock. The plate tectonic history of a region strongly influences the rock type and structure exposed at the surface, but differing rat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrocarbon Exploration
Hydrocarbon exploration (or oil and gas exploration) is the search by petroleum geologists and geophysicists for deposits of hydrocarbons, particularly petroleum and natural gas, in the Earth using petroleum geology. Exploration methods Visible surface features such as oil seeps, natural gas seeps, pockmarks (underwater craters caused by escaping gas) provide basic evidence of hydrocarbon generation (be it shallow or deep in the Earth). However, most exploration depends on highly sophisticated technology to detect and determine the extent of these deposits using exploration geophysics. Areas thought to contain hydrocarbons are initially subjected to a gravity survey, magnetic survey, passive seismic or regional seismic reflection surveys to detect large-scale features of the sub-surface geology. Features of interest (known as ''leads'') are subjected to more detailed seismic surveys which work on the principle of the time it takes for reflected sound waves to travel thro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sea Level
Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised geodetic datumthat is used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and, consequently, aircraft flight levels. A common and relatively straightforward mean sea-level standard is instead the midpoint between a mean low and mean high tide at a particular location. Sea levels can be affected by many factors and are known to have varied greatly over geological time scales. Current sea level rise is mainly caused by human-induced climate change. When temperatures rise, mountain glaciers and the polar ice caps melt, increasing the amount of water in water bodies. Because most of human settlement and in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Red Bed
Red beds (or redbeds) are sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain thin beds of conglomerate, marl, limestone, or some combination of these sedimentary rocks. The ferric oxides, which are responsible for the red color of red beds, typically occur as a coating on the grains of sediments comprising red beds. Classic examples of red beds are the Permian and Triassic strata of the western United States and the Devonian Old Red Sandstone facies of Europe. Primary red beds Primary red beds may be formed by the erosion and redeposition of red soils or older red beds, but a fundamental problem with this hypothesis is the relative scarcity of red-colored source sediments of suitable age close to an area of red-bed sediments in Cheshire, England. Primary red beds may also form by in situ (early diagenetic) redd ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Evaporite
An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocean deposits, and non-marine, which are found in standing bodies of water such as lakes. Evaporites are considered sedimentary rocks and are formed by chemical sediments. Formation of evaporite rocks Although all water bodies on the surface and in aquifers contain dissolved salts, the water must evaporate into the atmosphere for the minerals to precipitate. For this to happen, the water body must enter a restricted environment where water input into this environment remains below the net rate of evaporation. This is usually an arid environment with a small basin fed by a limited input of water. When evaporation occurs, the remaining water is enriched in salts, and they precipitate when the water becomes supersaturated. Evaporite depositio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Marine (ocean)
The ocean (also the sea or the world ocean) is the body of Saline water, salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Water distribution on Earth, Earth's water. An ocean can also refer to any of the large bodies of water into which the world ocean is conventionally divided."Ocean." ''Merriam-Webster.com Dictionary'', Merriam-Webster, [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Appalachian Mountains
The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They once reached elevations similar to those of the Alps and the Rocky Mountains before experiencing natural erosion. The Appalachian chain is a barrier to east–west travel, as it forms a series of alternating ridgelines and valleys oriented in opposition to most highways and railroads running east–west. Definitions vary on the precise boundaries of the Appalachians. The United States Geological Survey (USGS) defines the ''Appalachian Highlands'' physiographic division as consisting of 13 provinces: the Atlantic Coast Uplands, Eastern Newfoundland Atlantic, Maritime Acadian Highlands, Maritime Plain, Notre Dame and Mégantic Mountains, Western Newfoundland Mountains, Piedmont, Blue Ridge, Valley and Ridge, St. Lawrence Valley, A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mississippian Age
The Mississippian ( , also known as Lower Carboniferous or Early Carboniferous) is a subperiod in the geologic timescale or a subsystem of the geologic record. It is the earlier of two subperiods of the Carboniferous period lasting from roughly 358.9 to 323.2 million years ago. As with most other geochronologic units, the rock beds that define the Mississippian are well identified, but the exact start and end dates are uncertain by a few million years. The Mississippian is so named because rocks with this age are exposed in the Mississippi Valley. The Mississippian was a period of marine transgression in the Northern Hemisphere: the sea level was so high that only the Fennoscandian Shield and the Laurentian Shield were dry land. The cratons were surrounded by extensive delta systems and lagoons, and carbonate sedimentation on the surrounding continental platforms, covered by shallow seas. In North America, where the interval consists primarily of marine limestones, it is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
