Beckenanalyse 2. Genetische stratigraphische Konzepte

Transcription

1 Beckenanalyse 2. Genetische stratigraphische Konzepte Einsele 2000 CYCLIC BEDDING Einsele

2 Sequenzstratigraphie Das Konzept der Sequenzstratigraphie beruht auf dem Zusammenspiel von Sedimentzufuhr und Akkomodationsraum, letzterer wird gesteuert über eustatische Meeresspiegelschwankungen und Subsidenz bzw. Hebung (Raten!). sedimentary response to perturbations of the equilibrium profile caused by uplift / subsidence and/or sea level change 2

3 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. 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: 3

4 4

5 Parasequence Sets 5

6 Parasequence Sets forced regression 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 6

7 relative sea-level curves 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. 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. 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: shelf-break margin ramp margin 7

8 The Highstand Systems Tract (HST) shelf-break margin (c) (d) ramp margin 8

9 Sequence Boundary (SB) Coe et al ramp margin 9

10 The Falling Stage Systems Tract (FSST) shelf-break margin (c) submarine fans deposited at base of continental slope (d) ramp margin 10

11 Different geometries of Falling Stage Systems Tracts on ramp type margins increasing rate of relative sea-level fall or (and) decreasing rate of sediment supply old young Loss of accomodation space caused by relative sea-level fall A + B << B C + D D 11

12 The Lowstand Systems Tract (LST) ramp margin (d) (c) shelf-break margin 12

13 Transgressive Surface (TS) The Transgressive Systems Tract (TST) (a) 13

14 shelf-break margin (c) (d) ramp margin Maximum FloodingSurface (MFS) 14

15 15

16 Beckenanalyse 3. Meeresspiegelschwankungen global vs. local / regional Einsele

17 Mesozoic sea-level change Reading 1996 Chronostratigraphic chart and sea-level curve for the Jurassic (Haq et al. 1988) Reading

18 Chronostratigraphic chart and sea-level curve for the Cretaceous (Haq et al. 1988) Reading 1996 Different estimates of long-term Mesozoic sea-level changes Leeder

19 How to measure sea-level change? coastal maps coastal sediments tidal gauge oxygen isotopes 19

20 Late Pliocene to Recent oxygen isotopic cycles Holocene (b) Leeder 1999 LGM 20

21 The hierarchy of stratigraphical cycles next slide The hierarchy of stratigraphical cycles 21

22 Bahlburg & Breitkreuz 1998 Processes controlling relative sea-level and sediment supply 22

23 Processes controlling eustatic sea-level change Reading 1996 Bahlburg & Breitkreuz 1998 Leeder

24 Break-up of Pangea and associated increase in sea-floor spreading Einsele 2000 The three orbital parameters that cause orbital cyclicity ( Milankovich Cycles ) 24

25 Fig (a) Orbital parameters of the sun-moon-earth system and their temporal variation during the last 800 ka. (b) sum of the signals shown in (a) in terms of energy received by the outer atmosphere. Einsele 2000 time [Ma] greenhouse vs. icehouse 25

26 Multiple order sea-level fluctuations 26

27 27

28 Principal factors influencing sequence development (from Galloway 1989) Beckenanalyse 4. Sediment Supply / Sediment Budget Denudation: average amount of lowering of the land surface in a certain region due to weathering and erosion Fig c General trends in climaticallycontrolled production of clastic sediments and the input of dissolved constituents into sedimentary basins. Ca Einsele

29 Einsele 2000 Chemical denudation vs rock type Einsele

30 Denudation vs Exhumation Leeder 1999 (a) (b) Leeder

31 sediment yield vs drainage area specific sediment yield SY (t/km 2 /a) Einsele 2000 Einsele

32 modern vs long-term denudation rates Einsele 2000 Basin Fill the filling of sedimentary basins and the architecture and facies associations of their sediments are generally controlled by the interaction between several more or less independent factors: (1) size and denudation characteristics of land areas delivering terrigenous sediments (specific sediment yield) (2) areal extent and geometry of the corresponding basin receiving sediment (3) biogenic sediment production in the basin itself (4) tectonic and total subsidence of basin floor as well as compaction of sediments (5) distribution of the sediment in relation to the hydraulic regime of the water-filled basin, or, on land, of the river system crossing and feeding the basin with sediments. (6) relative sea-level or base level changes and their frequencies and amplitudes. (Einsele 2000) 32

33 Sediment budget denudation rate vs sedimentation rate Fig a Qualitative model showing the influence of size and relief of denudation area on sediment fill of neighbouring basins. Einsele 2000 sedimentation rate (sediment thickness per unit time [m/ma]) Fig Overview of sedimentation rates in various depositional environments which are dominated either by allochthonous, siliciclastic sediments, or autochthonous, biogenic materials Einsele

34 long-term vs short-term sedimentation rates Einsele 2000 suspended dissolved loads solids Einsele

35 F D VS VS Einsele 2000 Einsele

36 Einsele