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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.
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 the dip line on both sides of the strike, and horizontal bedding is denoted by a cross within a circle. [2] [9]
Graded bedding is a sorting of particles according to clast size and shape on a lithified horizontal plane. The term is an explanation as to how a geologic profile was formed. Stratification on a lateral plane is the physical result of active depositing of different size materials.
Cross-bedding Cross-bedding is the layering of beds deposited by wind or water inclined at an angle as much as 35° from the horizontal. [1] Cross-beds form when sediment particles are deposited on steeper slopes of sand dunes on land or of sandbars in rivers and on the seafloor. [1]
Tabular cross-bedding, or planar bedding consists of cross-bedded units that are extensive horizontally relative to the set thickness and that have essentially planar bounding surfaces. [3] Trough cross-bedding, on the other hand, consists of cross-bedded units in which the bounding surfaces are curved, and hence limited in horizontal extent. [3]
A geologic map or geological map is a special-purpose map made to show various geological features. Rock units or geologic strata are shown by color or symbols. Bedding planes and structural features such as faults, folds, are shown with strike and dip or trend and plunge symbols which give three-dimensional orientations features.
Horizontal joints in the sedimentary rocks of the foreground and a more varied set of joints in the granitic rocks in the background. Image from the Kazakh Uplands in Balkhash District, Kazakhstan. Orthogonal joint sets on a bedding plane in flagstones, Caithness, Scotland Joints in the Almo Pluton, City of Rocks National Reserve, Idaho.
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.