层序地层学的名词英语解释.doc

层序地层学的名词英语解释0 Glossary Accommodation. Another term for relative sea-level. Can be thought of as the space in which sediments can fill, defined at its base by the top of the lithosphere and at its top by the ocean surface. Basinward Shift in Facies. When viewed in cross-section, a shifting of all facies towards the center of a basin. Note that this is a lateral shift in facies, such that in vertical succession, a basinward shift in facies is characterized by a shift to shallow facies (and not a vertical shift to more basinward or deeper-water facies). Bed. Layer of sedimentary rocks or sediments bounded above and below by bedding surfaces. Bedding surfaces are produced during periods of nondeposition or abrupt changes in depositional conditions, including erosion. Bedding surfaces are synchronous when traced laterally; therefore, beds are time-stratigraphic units. See Campbell, 1967 (Sedimentology 8:7-26) for more information. Bedset. Two or more superposed beds characterized by the same composition, texture, and sedimentary structures. Thus, a bedset forms the record of deposition in an environment characterized by a certain set of depositional processes. In this way, bedsets are what define sedimentary facies. Equivalent to McKee and Weir's coset, as applied to cross-stratification. See Campbell, 1967 (Sedimentology 8:7-26) for more information. Condensation. Slow net rates of sediment accumulation. Stratigraphic condensation can occur not only through a cessation in the supply of sediment at the site of accumulation, but also in cases where the supply of sediment to a site is balanced by the rate of removal of sediment from that site. Where net sediment accumulation rates are slow, a variety of unusual sedimentologic features may form, including burrowed horizons, accumulations of shells, authigenic minerals (such as phosphate, pyrite, siderite, glauconite, etc.), early cementation and hardgrounds, and enrichment in normally rare sedimentary components, such as volcanic ash and micrometeorites. Conformity. Bedding surface separating younger from older strata, along which there is no evidence of subaerial or submarine erosion or nondeposition and along which there is no evidence of a significant hiatus. Unconformities (sequence boundaries) and flooding surfaces (parasequence boundary) will pass laterally into correlative conformities, most commonly in deeper marine sediments. Eustatic Sea Level. Global sea level, which changes in response to changes in the volume of ocean water and the volume of ocean basins. Flooding Surface. Shortened term for a marine flooding surface. Highstand Systems Tract. Systems tract overlying a maximum flooding surface, overlain by a sequence boundary, and characterized by an aggradational to progradational parasequence set. High-Frequency Cycle. A term applied to a cycle of fourth order or higher, that is, having a period of less than 1 million years. Parasequences and sequences can each be considered high-frequency cycles when their period is less than 1 million years. Isostatic Subsidence. Vertical movements of the lithosphere as a result of increased weight on the lithosphere from sediments, water, or ice. Isostatic subsidence is a fraction of the thickness of accumulated material. For example, 100 meters of sediment will drive about 33 meters of subsidence (or less, depending on the rigidity of the lithosphere). Lowstand Systems Tract. Systems tract overlying a type 1 sequence boundary, overlain by a transgressive surface, and characterized by a progradational to aggradational parasequence set. Marine Flooding Surface. Surface separating younger from older strata, across which there is evidence of an abrupt increase in water depth. Surface may also display evidence of minor submarine erosion. Forms in response to an increase in water depth. Maximum Flooding Surface. Marine flooding surface separating the underlying transgressive systems tract from the overlying highstand systems tract. This surface also marks the deepest water facies within a sequence. This flooding surface lies at the turnaround from retrogradational to progradational parasequence stacking, although this turnaround may be gradational and characterized by aggradational stacking. In this case, a single surface defining the point of maximum flooding may not be identifiable, and a maximum flooding zone is recognized instead. The maximum flooding surface commonly, but not always, displays evidence of condensation or slow deposition, such as burrowing, hardgrounds, mineralization, and fossil accumulations. Because other flooding surfaces can have evidence of condensation (in some cases, more than the maximum flooding surface), condensation alone should not be used to define the maximum flooding surface. Meter-Scale Cycle. A term applied to a cycle with a thickness of a couple of meters or less. Parasequences and sequences can each be considered meter-scale cycles when they are thinner than a c。