Introduction to Sequence Stratigraphy Flashcards
What is sequence stratigraphy?
study of genetically related facies within a framework of chronostratigraphy significant surfaces
What does sequence stratigraphy focus on?
- correlation
- discontinuity surfaces
- relative sea level changes
- hierarchy of stratal units
Walter’s Law
processes/env that occur laterally adjacent to each other has facies that gradually change in a vertical column
Parasequence
succession of related beds/bedsets bounded by marine flooding surfaces. IT SHALLOWS UPWARD
Parasequence set
stacking pattern of parasequences bounded by major marine-flooding
shallowing marine, wave-dominated parasequence
-coarsening upward from offshore-marine sediments to alluvial and coastal plain sedimens
Progradation of parasequences
- sea-level rise
- high sediment flux (causing a regression).
- A progradational stacking pattern of parasequences=facies at the top of each parasequence becomes progressively more proximal
- flooding can occur
- Progradational parasequence set
- retrogradational parasequence set
- aggradational parasequence set
- rate of dep>rate of accommodation so coastal plain sandstones/mudstones grow towards shelf mudstones (basin). This results in a coarsening upwards. sea level falls
- coastal plain sandstones/mudstones recede landward as the rise in sea level rises and shelf mudstones grow towards coastal plain. fining upward
- equal stacking pattern of the sediments that coarsen upwards
What is regression and transgression?
Regression
- progradation of coastal plane.
- rate of sediment supply>rate of accommodation so coastal sediments grow and sea level falls. Erosion may occur on forces regression.
Transgression
- retrogradation of coastal plain
- rate of sed supply
How are bounding unconformities produced?
-made by a relative fall in sea level because erosion occurs
what are hierarchy of stratal units composed of?
- a succession of system tracts:
1. Falling stage systems tract
2. lowstand systems tract
3. transgressive systems tract
4. highstand systems tract
what are the deposition processes and products of falling stage systems tract during forced regression
Forced regression: initially the falling leg of base-level cycle there is reduced accommodation and shoreline regresses despite sedimentation rate.
Early Forced Regression Processes:
- delta plain erodes
- delta front progrades
- there is erosion in lower shoreface
- there is instability in outer shelf (storm reworking)
- debris flows
- sea level falls
- slumps arae pressent
- detached overlapping lobes
What processes happen in late forced regression?
- valleys and tributaries
- paleosols
- deep water sands are present
- frontal splays
- levee channels
- delta front progradation and offlap
- high density turbidites
What processes happen in lowstand systems tract during normal regression?
- backfilled incised valleys
- braidedplains
- open shorelines
- prograding shoreface/delta front
- entrenched channels and levee channels
- channel fills from fluvial aggradation
- Gilbert type deltas
- low density turbidites
- sea level slowly rises
What processes happen in early transgression tract
- crevasse splays
- floodplains
- estuaries
- backstepping beaches/barrier islands
- entrenched channels
- levee channels
- instability in shelf edge
- low density turbidites
- wave ravinement
- sea level begins to rise
