Progress

from Wikipedia, the free encyclopedia
Satellite image of the northernmost lobe of the Danube Delta (Chilia lobe). Over the past thousand years, the Danube has shifted the coastline further and further east by unloading its sediment load. Where there was once the sea, marshland stretches today.

As Progradieren or progradation ( lat. : Per = before; gradus = step; progress ) is in the Sedimentology growth or advancing a Sedimentationskörpers , for example a river deltas or alluvial alluvial , toward the center of the corresponding sedimentary basin designated. This growth is reflected in the displacement of the facies belt (see FIG. Depositional environment ) of such sedimentary body in the direction of the center of the sedimentary basin. The main cause is a high intake or in-situ production of sediments.

As a result of progression or shifting of the facies belts, deposits of sandy grain size ( psammites ) are often introduced into the previous sedimentation space of finer, pelitic deposits. Within the vertical sequence , a progressive system is therefore often characterized by the increase in grain size from the lying (below) to the hanging wall (above), the coarsening upward . It is not uncommon for this to be accompanied by a change from marine to terrestrial or more terrestrially influenced sedimentation. Progradation in ocean basins ( Schelfen ) thus always synonymous with regression , and at a "normal regression" (English. Normal regression ) only the high deposit rates for the progradation are crucial, while "forced regression" (English. Forced regression ) a There is also a slow eustatic drop in sea level and, in addition to progression, so-called downstepping , i.e. H. there is a reduction in the overall thickness of the sediment body.

The identification of sedimentary cycles that indicate progression and the underlying causes is carried out in sequence stratigraphy for the reconstruction of the sedimentation process and the paleogeographical development as well as the parallelization of geological profiles in a sedimentary basin. The techniques required for this were developed in connection with the commercial exploration of fossil hydrocarbons .

In contrast, there is retrograding , in which the facies belts shift inland.

literature

  • Lexicon of Geosciences. Spectrum - Akademischer Verlag, Heidelberg et al. 2002, ISBN 3-8274-0427-4 (6 CDs).
  • Andreas Schäfer: Clastic Sediments. Facies and sequence stratigraphy. Spectrum - Akademischer Verlag, Munich 2005, ISBN 3-8274-1351-6 .
  • Steven M. Stanley: Historical Geology. 2nd, German edition. Spectrum - Akademischer Verlag, Heidelberg et al. 2001, ISBN 3-8274-0569-6 .