Post on 23-Aug-2019
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HvE / Fazies- und Beckenanalyse
Beckenanalyse → 1. Subsidenz
ρwhw + ρshs + ρchc + ρmhm + ρaha = c
Hohe Sediment-Akkumulation und die Bildung Sedimentärer Becken sind nicht möglich ohneentsprechenden Subsidenz. Subsidenz beschreibt die Senkung der Erdoberfläche (Landober-fläche oder Meeresboden) bzw. der Basis des Sedimentbeckens relativ zum Erdmittelpunkt (bzw. eines Bezugniveaus konstanten Drucks in der viskosen Asthenossphäre, s.u.).
Subsidenz ist eng verknüpft mit dem Prinzip der Isostasie: die Hebung (oder Senkung) derErdoberfläche ist eine Funktion der Dichte ρ und Dicke h der unterschiedlichen Lagen (Schalen). Vereinfacht sind dies: Meerwasser (w), Sediment (s), konsolidierte Kruste (c), lithosphärischer Mantel (m) und astenossphärischer Mantel (a). Die Masse über einem Bezugniveau konstanten Drucks in der viskosen Asthenossphäre
Ein Beispiel zur Größenordnung (unter stark vereinfachten Bedingungen, ohne thermische Relaxation): Eine durch Extension bedingte Verdünnung der Kruste auf 15 km (statt normalen ca. 30 km) führt zu einer Subsidenz von Meeresspiegelniveau auf 3,5 km Wassertiefe.
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Initiale (tektonische) vs thermische Subsidenz
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Flexural response of thelithosphere due to crustalor sediment loading
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HvE / Fazies- und Beckenanalyse
Leeder1999
Fig. 27.7 Cartoon to show how shortening across a deep thrust fault causes a regional load, which must flexure the whole brittle lithosphere and cause deeper compensatory viscoplastic flow (from Felemings & Jordan 1990).
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HvE / Fazies- und BeckenanalyseEinsele 2000
Backstripping → 1. Dekompaktion
HvE / Fazies- und BeckenanalyseEinsele 2000
2. sediment load – isostasy
(3. paleo-bathymetry & sea-level change)
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Young rift zones
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Pro
fil d
urch
den
Atla
ntik
-Sch
elf v
or B
altim
ore,
US
A
passive margin subsidence models
nach Bouma et al. (1982)
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cm/ka
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Grand Banks area(off Newfoundland)
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Grand Banks area(off Newfoundland)
a, b
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fore
land
bas
ins
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HvE / Fazies- und Beckenanalyse
Beckenanalyse → 2. Genetische stratigraphische Konzepte
Ein
sele
200
0
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Ein
sele
200
0
CYCLIC BEDDING
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Das Konzept der Sequenzstratigraphie beruht auf dem Zusammenspiel von Sedimentzufuhr und Akkomodationsraum, letzterer wird gesteu-ert über eustatische Meeresspiegelschwankun-gen und Subsidenz bzw. Hebung (Raten!).
Coe et al. 2003
Sequenzstratigraphie
HvE / Fazies- und Beckenanalyse
sedimentary response to perturbations of the equilibrium profile caused by uplift / subsidence and/or sea level change
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HvE / Fazies- und Beckenanalyse Coe et al. 2003
The parasequence forms the smallest and simplest unit in the framework of sequence stratigraphy. It results from a small-amplitude, short-term oszillation in the balance between sediment supply and accomodation space.
Example: coastal environment:
The simplest way to understand sequence stratigraphy is to consider the interface area between coastal and shallow-marine siliciclastic depositional environments where changes in relative sea level are easiest to interpret.
HvE / Fazies- und Beckenanalyse
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Parasequence Sets
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Parasequence Sets
forced regression
HvE / Fazies- und Beckenanalyse
Sequences and System Tracts
A sequence or depositional sequence is composed of a succession of parasequence sets. Each sequence represents one cycle of change in the balance between accomodation space and sediment supply. Sequences generally range in thickness from a few meter to tens or even hundreds of m, and they are the next larger (or longer duration) cycles above parasequences.
Similar to parasequences, sequences are the result of changes in eustatic sea-level and/or subsidence/uplift resulting in a changing relative sea-level ( → accomodation space, see below), and/or changes in sediment supply.
eustatic sea level + subsidence → relative sea-level
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Every sequence is composed of up to four systems tracts, each of which represents a specific part in the cyclic change in the balance between accomodation space and sediment supply. Each systems tract is made up of at least one parasequence set. Different conditions may result in one or more of the systems tracts not being developed or preserved.
The four systems tracts are:- Highstand Systems Tract (HST)- Falling Stage Systems Tract (FSST) - Lowstand Systems Tract (LST) - Transgressive Systems Tract (TST)
The high number of different factors involved in any one geological situation (such as climate, eustatic sea-level change, subsidence rate, sediment supply, lithology, ...) means that the resultant sequences are highly variable. However, every sequence has similar genetic components related to changes in the rate of accomodation space creation and sediment supply.
Fig. 4.8b: blue curve taken from Fig. 4.8a; purple curve combines blue curve with short-term changes in accomodation space associated with the development of parasequences.
relative sea-level curves
HvE / Fazies- und Beckenanalyse
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shelf-break margin
ramp margin
Because the geometry of the basin floor is crucial to the evolution of depositional sequences and systems tracts, we will consider in the following to principal types of depositional profiles from the land to the sea:
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The Highstand Systems Tract (HST)
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(c)
shelf-break margin
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ramp margin(d)
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→ Sequence Boundary (SB)
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ramp margin
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HvE / Fazies- und BeckenanalyseCoe et al. 2003
The Falling Stage Systems Tract (FSST)
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(c)
shelf-break marginC
oe e
t al.
2003
submarine fans deposited at base of continental slope
ramp margin(d)
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old young
increasing rate of relative sea-level fallor (and)decreasing rate of sediment supply
Different geometries of Falling Stage Systems Tracts on ramp type margins
HvE / Fazies- und BeckenanalyseCoe et al. 2003
A + B
C + D<<
B
D
Loss of accomodation space caused by relative sea-level fall
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HvE / Fazies- und BeckenanalyseCoe et al. 2003
The Lowstand Systems Tract (LST)
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ramp margin
(d)
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shelf-break margin(c)
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→ TransgressiveSurface (TS)
HvE / Fazies- und BeckenanalyseCoe et al. 2003
The Transgressive Systems Tract (TST)
(a)
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shelf-break margin
(c)
ramp margin(d)
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03→ Maximum FloodingSurface (MFS)
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