Oblique stratification
Diagonally layering ( engl . Cross-bedding ) is a term of Sedimentology and refers to the deposition of granular sediment (usually sand or gravel ) in oblique incident layers . This type of deposit is found on the leeward side of dunes and of current and wave ripples in waters. The oblique stratification in superimposed layers can be oriented differently or in opposite directions due to changing flow conditions during the deposition ( cross stratification ).
Emergence
Oblique stratification can be caused by both flowing water and wind. Their formation can be observed in deserts, rivers, lakes and seas and is found in geologically young unconsolidated rocks and solidified sedimentary rocks , e.g. B. sandstone , widely preserved. It occurs when grains of sand are poured and deposited in the lee of sandbanks or bumps. Sloping stratification is also found on the leeward side of gravel banks, where the pebbles are regulated like roof tiles.
Oblique stratification also occurs when loose sediment is transported up the windward side of a ripple wave in a river or in the sea as well as a dune, usually as spring freight ( saltation ), passes the ripple ridge and then slides down the lee side ( grain flow ) or falls. The leeward side is always steeper than the windward side. The crests of the corrugated nipples can be worn away by erosion processes , so that only the lower areas of the sloping bodies remain.
Oblique stratification occurs in different dimensions, depending on the height of the inclined stratification, from micro-inclined stratification (height up to 2 cm) through small (2 to 20 cm) and medium-dimensional (20 - 200 cm) to large-dimensional diagonal stratification (2 to 20 m and more) ) pass. The dimension reflects the flow speed of the respective transport medium.
The angle of incidence of the oblique stratification depends on the cohesion of the transported material and is around 30 ° due to the frequent static charging of the sand grains in dunes and around 15 ° in water because of the lower cohesion due to the transport medium.
The orientation of the pre-fill can be used to determine the direction of the causative flow and plays a role in the reconstruction of surface form and deposition processes of past ages.
Tabular and trough-shaped oblique stratification
A distinction is made between planar (or tabular) diagonal stratification (English tabular cross-bedding) and trough-shaped diagonal stratification (English trough cross bedding) as the morphological end links . The contact surfaces of the individual inclined stratification bodies are flat in the oblique stratification, and curved in the trough-shaped. The former arise with straight combs, the latter with wavy, curved combs.
Picture gallery
Trough-shaped inclined layering.
Planar oblique stratification in the red sandstone at the foot of the Teufelstisch / Pfalz
swell
- ↑ Hohl, p. 129f.
literature
- Hans Füchtbauer : Sediments and sedimentary rocks . 4th revised edition. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart 1988, 1141 pp. ISBN 978-3-510-65138-2
- Rudolf Hohl (ed.): The history of the development of the earth . 6th edition, Werner Dausien Verlag, Hanau 1985, 703 pp. ISBN 978-3-768-46526-7
- Tom McCann, Mario Valdivia Manchego: Geology in the field: The outdoor manual. Springer-Verlag, Berlin Heidelberg 2015.