Transgression (geology)
A transgression (from latin transgredior ,, transgress exceed '; almost invariably short for marine transgression ) denotes the landward rise to a coastline and the thereby induced change in the Sedimentationsdynamik the affected sedimentary basin . This can result from the tectonic subsidence of a land mass or a rise in global ( eustatic ) sea levels, e.g. B. be due to the climatic release of water from continental ice sheets .
In contrast, there is the regression , in which the coastline moves seaward.
Concept history
The corresponding German verb is called transgressieren and the adjective is called transgressive . The term was used by Eduard Suess in 1875, but its origin is much older. So said Abraham Gottlob Werner in 1800 from cross-Storage in discordant resting söhliger layers on several formations of the basement at the same time what he interpreted correctly than younger "wet formations" in formerly dry lying country (though mainly in respect of its Neptunian error that basalt , a marine sedimentary rock be). The cross was later transgressive Latinized and used by some authors and non-marine deposits, so Suess in 1888 distinguished between limnic and marine transgression. Hans Stille spoke of extension in the non-marine fall in 1924 .
features
A transgression manifests itself in the sediment sequence by a reversal of the sedimentation from z. B. a more terrestrial deposition environment to a more marine deposition environment. Insofar as the flooded area was previously characterized by erosion , the transgressive deposits form a so-called discordance with the rocks below the erosion surface . Due to the erosive effect of the sea surf , a so-called transgressive conglomerate is often formed at the base of a transgressive sequence .
Examples
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The formation of today's North Sea and thus the youngest sediments in the North Sea basin can be traced back to the Flanders Transgression after the inland ice masses in the northern hemisphere finally melted about 10,000 years ago. The Littorina transgression in the Baltic Sea region around 8500 years ago is closely related to these processes .
Another example of a geologically very recent marine transgression is the flooding of the Black Sea basin about 9000 years ago due to the influx of salt water from the Mediterranean via the Strait of the Bosphorus . So far there has been speculation as to whether this slump was catastrophic and whether it was the template for the biblical legend of the Flood .
Examples of somewhat older marine transgressions in Central Europe are the collapse of the Muschelkalk Sea around 240 million years ago and the collapse of the Zechstein Sea around 255 million years ago.
One of the most important global detectable transgressions recent Earth is called the Upper Cretaceous or Cenomanian -Transgression before about 90 million years ago. As a result, massive limestone deposits (“ chalk ”) formed on the flooded continents around the world .
See also
literature
- Hans Murawski: Geological Dictionary . 8th edition. Enke Verlag, Stuttgart 1983, ISBN 978-3-432-84108-3 , p. 226 .
- Dieter Richter: General Geology . 3. Edition. de Gruyter Verlag, Berlin - New York 1985, ISBN 3-11-010416-4 , pp. 191 .
Individual evidence
- ↑ Abraham Gottlob Werner, Franz Reichetzer: Instructions for geognosy, especially for mountain science . Second revised edition. JG Heubner, Vienna 1821, doi: 10.3931 / e-rara-73153 , p. 40 , 192 f.
- ↑ Héron de Villefosse: About the mineral wealth. German edited by Carl Hartmann. Second volume. Bernhard Friedrich Vogt, Sondershausen 1822, doi: 10.3931 / e-rara-11650 , p. 18
- ↑ Entire paragraph, unless otherwise quoted, based on: Hans Murawski, Wilhelm Meyer: Geological Dictionary. 12th edition. Spektrum Akademischer Verlag, Heidelberg 2010, ISBN 978-3-8274-1810-4 , p. 172