What is Seqeuence Stratigraphy Introduction
- 1. A framework of genetically related stratigraphic facies geometries and their bounding surfaces used to determine depositional setting. or Sequence stratigraphy is 'the sub- division of sedimentary basin fills into genetic packages bounded by unconformities and their correlative conformities'. Upper Middle Lower GeoHikingClub-2020
- 2. What is a sequence? ”A sequence is a succession of genetically related strata that can be delineated chronologically and spatially, and which possesses some characteristic property that defines the sequence as a particular product of the total geological history, with respect to events and processes”. Nystuen 1998, p. 33 GeoHikingClub-2020
- 3. Sequence Stratigraphy Applications Academic applications: Genesis and internal architecture of sedimentary basin fills Age estimation: First approximation from the Cycle Chart. Global Correlations: First-order comparisons Facies Distribution: Prediction of horizontal and vertical migration of sedimentary facies. Industry applications: Exploration for hydrocarbons, coal, and mineral resources A tool for interpretation of dynamics of basin sediment infill A tool for predicting sedimentary facies, source rocks and reservoir rocks Applies for all types of sedimentary basins Optimal use presupposes knowledge of geological processes in time and space. Shale Gas and Tight Gas. GeoHikingClub-2020
- 4. Stratigraphy - Outcrop mapping and definition of sequences as ‘assemblages of strata and formations bounded by prominent interregional unconformities’ (Sloss, Krumbein & Dapples 1949). Very large scale, the succession of rocks bound by unconformities spans c.60- 100Ma, now termed a Megasequence. Seismic Stratigraphy - 1960’s/70’s saw the development of seismic acquisition . Allowed imaging of the sub-surface and sequence recognition based on unconformities at seismic scale. A ‘seismic sequence’ was defined by Mitchum et al. 1977). Various controls on sequence development were emphasised, from eustatic sea- level change (Vail et al. 1977) to tectonic (Hubbard et al. 1985). Relative sea-level change is referred to when the causal mechanism of the change is not constrained. Brief Historical Review GeoHikingClub-2020
- 5. The meaning of a stratigraphic ‘sequence’ has been subsequently expanded to include any ‘relatively conformable succession of genetically related strata’ (Mitchum, 1977), irrespective of temporal and spatial scales. In parallel with the development of the ‘sequence’ concept in a stratigraphic context, sedimentologists in the 1960s and 1970s have redefined the meaning of the term ‘sequence’ to include a vertical succession of facies that are ‘organized in a coherent and predictable way’ (Pettijohn, 1975), reflecting the natural evolution of a depositional environment. The development of seismic and sequence stratigraphy in the late 1970s and 1980s revitalized the use of the term ‘sequence’ in a stratigraphic context, which remained the dominant approach to date. The unconformity-bounded sequences promoted by Sloss (1963). The concept of ‘unconformity-bounded unit’ (i.e., Sloss’ ‘sequence’) was formalized by the European ‘International Stratigraphic Guide’ in 1994. Brief Historical Review GeoHikingClub-2020
- 6. The introduction of ‘correlative conformities,’ which are extensions towards the basin center of basin margin unconformities, marked the birth of modern seismic and sequence stratigraphy (Fig. 1.3 & 1.4) (Mitchum, 1977). The advantage of the modern sequence, bounded by a composite surface that may include a conformable portion, lies in its basin-wide extent - hence, the number of sequences mapped at the basin margin equals the number of sequences that are found in the basin center. Brief Historical Review GeoHikingClub-2020
- 7. Haq et al.’s Cycle Chart based on global data. A beak through in the history of the global sequence stratigraphy. GeoHikingClub-2020
- 8. Relative sea level = (f) Eustasy + Tectonic subsidence or uplift + Compaction + Isostasy Figure 1.5 Showing basic concept of the eustatic sea level changes relative sea level changes. GeoHikingClub-2020
- 9. First order cycle A sea-level cycle with a duration on the order of hundred of millions of years. During Phanerozoic time (post – Precambrian), there were two such cycles, A 300 m.y cycle from the Precambrian to the Triassic, and A 225 m.y. cycle from Triassic to the present (Fig. 1.6). Second order cycle A sea-level cycle generally with duration on the order of 9-10 million years (Fig. 1.6). Several such cycles are superimposed upon the Phanerozoic first- order cycles shown in Figure 1.5 A. Third order cycle A sea level cycle generally with a duration on the order of 1-5 million years (Figs. 1.6 and 1.9). Fourth order cycle A sea-level cycle with a duration generally on the order of 100,000-250,000 years (Fig. 1.6 and 1.9). Several such cycles are superimposed upon the third order cycles (Fig. 1.9). Fifth order cycle A sea-level cycle generally on the order of tens of thousands of years duration (Fig.1.6). Sixth order cycle A sea-level cycle with a duration generally on the order of thousands of years (Fig.1.6). GeoHikingClub-2020
- 12. Stacking Patterns Transgression Regression Progradation (regression) Retrogradation (transgression) Aggradation (Stillstand) GeoHikingClub-2020
- 13. Sediment Supply > Accommodation = Progradation Facies migrate basin wards Regression of shoreline Sediment Supply = Accommodation = Aggradation Facies stack vertically Sediment Supply < Accommodation = Retrogradation Facies migrate landward Transgression of shoreline GeoHikingClub-2020
- 14. Basic Units of Sequence Stratigraphy (Vail at.al., 1991) 0.5-5 Ma 0.2-1.0 Ma 0.01-0.5 Ma GeoHikingClub-2020
- 15. The Classic Slug Exxon Model SB – sequence boundary LST – lowstand systems tract TST – transgressive systems tract HST – highstand systems tract SMW – shelf-margin wedge Mfs – maximum flooding surface Lsw – lowstand wedge Sf – slope fan Bf – basin-floor fan GeoHikingClub-2020