Sequence stratigraphy

The sequence stratigraphy is a geoscientific method of stratigraphic correlation of sedimentary rocks. Based on the correlation are cyclical swings in the Sedimentationsdynamik within the sedimentary sequences compared that are the result of cyclical changes in the relative sea-level (also called the Accommodation Space) are in the course of geologic time. These reversals are controlled by both global sea level cycles as well as by regional tectonics ( " Uplift " and subsidence ). Although express changes in the relative sea level, among others, by the change of lithological characteristics, but they are in sequence stratigraphy, in contrast to the lithostratigraphy, rocks do not correlate with the same lithological characteristics with each other, but only those which during the same phase of a cycle of relative sea level likely to deposit arrived. This permitted a correlation also of sedimentary rocks, the relatively very different depositional environment come from (eg neritic and pelagic sediments ).

Since the sequence stratigraphy was developed by North American geologists, it has an English-language terminology that is also used in German-speaking broadly.

Principle

Traditionally considered the sequence stratigraphy mainly passive continental margins and Epikontinentalmeere. With a rise in the relative sea level ( transgression ) is such a deposition system altered in a way that sediments with the same facies characteristics (eg, grain size, sedimentary structures, fossil leadership - the depositional environment reflected reflect ) further inland (ie closer to the origin or deposited the edge of the sedimentary basin ) than before. With a drop in relative sea level ( regression) sediments of the same facies are further seaward (ie, closer to the center of the sedimentary basin ) deposited as previously and previously deposited sediments landwärtiger be removed.

Since sediments and sedimentary facies certain that co- occur at a specific time ( in lateral series ), on geological time scales well above the other ( vertical sequence ) occur ( Walther'sche Faziesregel ), can in any vertical profile Sedimentationstrends or the movements the relative sea levels ( regressive or transgressive ) determined in the geological past. These trends point to cyclical patterns that form the basic framework of sequence stratigraphy.

The smallest unit of sequence stratigraphy is the parasequence. It corresponds to a small regressive cycle ( a so-called cycle 4th or 5th order ), represented by a stack of layers with regressive tendency. A parasequence is bounded by so-called Flooding Surfaces. A flooding surface is defined as the surface layer above which always are deposits that a seewärtigeren ( deposited in deeper water ) facies correspond to the deposits as below, where the Walther'sche Faziesregel can not be applied, ie the deposits above and below the Flooding Surface originate not immediately laterally adjacent depositional environment.

Sequences of parasequences form parasequence sets. The latter have a particular Stapelungsmuster ( " stacking pattern "), whereby progradation ( corresponding to a regressive trend), retrogradation ( corresponding to a transgressive trend) and aggradation ( corresponding to a constant relative sea level) can be distinguished.

A sequence, the eponymous unit of Sequenzstratigrapie corresponds to a larger cycle ( a so-called cycle 3rd order ) and consists of a sequence of parasequence sets that account for up to four so-called system Tracts, each consisting of at least one parasequence set and for each of which a particular Stapelungsmuster is characteristic. The system Tracts are limited by particularly striking Flooding Surfaces. The sequence itself is limited by so-called Sequence boundarys.

The affiliation of parasequence sets to one of the four system Tracts depends on their Stapelungsmuster from which both the Sedimentationstrend ( vs. transgressive. Regressive ) and also reflects the rate of change of relative sea-level during its deposition. Both factors have a direct influence on the Sedimentationsdynamik and are therefore of particular importance for sequence stratigraphy. The four system tacts, which are differentiated within a sequence ( to ), are characterized as follows:

  • High stand systems tract (HST) represents a generally high, but only slowly rising or stagnant relative sea
  • Stapelungsmuster: aggradational - progradational
  • Corresponding deposits occur beck far
  • Hangendgrenze is the Sequence Boundary, which is formed partly as a conspicuous hiatus, partly as a distinct facies changes towards a seewärtigeren facies
  • Falling Stage Systems Tract ( FSST ) represents a falling sea level
  • Stapelungsmuster: progradational ( " stepping down " )
  • Corresponding deposits occur exclusively in beckenwärtigen areas on or may be entirely absent
  • Lowstand systems tract ( LST) represents a generally low but slowly rising relative sea
  • Stapelungsmuster: progradational - aggradational
  • Corresponding deposits occur mainly in areas beckenwärtigen
  • Hangendgrenze is the transgressive surface, characterized by the supports retrogradationaler parasequence sets
  • Transgressive systems tract (TST ) represents a rapidly rising relative sea
  • Stapelungsmuster: retrogradational
  • Corresponding deposits occur beck far
  • Hangendgrenze is the maximum flooding surface, a surface layer marked by the effects of Mangelsedimentation

All Flooding Surfaces are called isochronous surfaces, ie they are created at the same time and therefore being able to stratigraphic correlation are used, even if their associated sediments differ from sequence to sequence from each other.

Continental shelf Marine regression
723252
de