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In geology, a bed is a layer of sediment, sedimentary rock, or volcanic rock "bounded above and below by more or less well-defined bedding surfaces". [1] A bedding surface or bedding plane is respectively a curved surface or plane that visibly separates each successive bed (of the same or different lithology ) from the preceding or following bed.
Also, sedimentary beds may pinch out along strike, implying that slight angles existed during their deposition. Thus the principle of original horizontality is widely, but not universally, applicable in the study of sedimentology, stratigraphy, and structural geology.
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. They help indicate the original position of strata in geologically complex terrains.
In geology, rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another. Prior to the discovery of radiometric dating in the early 20th century, which provided a means of absolute dating , archaeologists and geologists used relative dating to determine ages of materials.
In geology, a graded bed is a bed characterized by a systematic change in grain or clast size from bottom to top of the bed. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones. Such a bed is also described as fining upward. [1]
In order for originally horizontal beds to form the allochthonous salts, they must first break free of their geological restraints. The first base structure can be formed in a combination of six ways: [1] Reactive piercement – a normal fault synrift relieves pressure above the salt layer. This causes the salt to flow into the area of lower ...
Cross-beds are layers of sediment that are inclined relative to the base and top of the bed they are associated with. Cross-beds can tell modern geologists many things about ancient environments such as- depositional environment, the direction of sediment transport (paleocurrent) and even environmental conditions at the time of deposition.
The new edition that was published in 2009, contains a 1:75,000 geology map of the island, 6 maps (1:25,000) containing topography, street directory and geology, a sheet of cross section and a locality map. The difference found between the 1976 Geology of Singapore report include numerous formations found in literature between 1976 and 2009.