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Tom Wilson, Department of Geology and GeographyTom Wilson, Department of Geology and Geography
Objectives for the Day
• General review seismic stratigraphy exercises• Lithic surfaces versus reflection events• Edge enhancement and detection • Some additional conceptual diagrams illustrating deposition under cycles of eustatic sea level rise and fall• The Woodbine play• Synthetic tie• Identifying the sequence and internal reflection patterns associated with the Woodbine• The influence of processing• Construction the chronostratigraphic chart
Tom Wilson, Department of Geology and Geography
Island Platform, Deep Water, Southern Bahamas
Tom Wilson, Department of Geology and Geography
In the preceding section, the platform lies to the left. The prominent seismic sequence to the right appears as a simple wedge of sediments dipping down to the right which is in turn onlapped by flatter lying sediments.
Closer inspection reveals several distinct intervals of onlap belonging to at least three different sequences.
The section reveals an earlier prograding sequence that was extensively eroded and itself followed by additional onlap against the escarpment to the left.
Subtle downlap and onlap mark locations of smaller sequences within the latest package that extends to the water bottom.
The pattern suggests presence of an earlier high stand system followed by significant sea level drop and then by gradual and relatively steady sea level rise
Tom Wilson, Department of Geology and Geography
Baltimore Canyon, East Coast, US
Erosional Truncation
A combination of prograding clinoforms followed by sealevel drop and coastal onlap (3 and above) overlie a thick sequence
characterized by predominantly parallel reflection events with some local onlap (1) above a deeper erosional inconformity
Prograding clinoforms/oblique
Tom Wilson, Department of Geology and Geography
National Petroleum Reserve, Alaska
Sigmoid clinoforms
Tom Wilson, Department of Geology and Geography
National Petroleum Reserve, Alaska
Sigmoid clinoforms
Some questions to contemplate:
1) What was the bathymetric relief between the top and base of the prograding wedge?
2) Was the wedge building upward, outward, or a combination of the two?
3) What caused the reflectors on the left (4) to become hump shaped?
Tom Wilson, Department of Geology and Geography
Central Atlantic Shelf, near the Baltimore Canyon
Prograding clastic wedge
The reflectors to the right of 1) build both out and up. The internal configuration is oblique (left) to sigmoid (near 1) and then oblique
again. The environment is prograding shelf margin.
Tom Wilson, Department of Geology and Geography
Splay, Floodplain, & Channel Environments
Flattened on the F37 reflection event
F37 Event
Manual pick of the F37 Lithic surface
Tom Wilson, Department of Geology and Geography
Splay, Floodplain, & Channel Environments
Hardage et al. (1994)The F37 “stratal” time surface
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
Enhancing Discontinuities to Resolve Depositional and Structural Features
Bahorich and Farmer, 1995
Results from an analysis of coherency between events in the seismic data set
Tom Wilson, Department of Geology and Geography
Schlumberger’s Ant Tracking Process
Tom Wilson, Department of Geology and Geography
General background on the Woodbine
Upper Cretaceous shoreline deposits USGS Fact Sheet
Tom Wilson, Department of Geology and Geography
Sea Level Rise and Fall
Posamentier and Vail, 1985
Tom Wilson, Department of Geology and Geography
Identifying the Woodbine reflection events using a synthetic seismic tie
Dynamite source
Tom Wilson, Department of Geology and Geography
Synthetic Seismogram
The Ogletree #1
sonic impedanceReflection coefficient train
No +-
composite
Austin ChalkEagleford Shale
Top of the Woodbine
Buda Limestone
Tom Wilson, Department of Geology and Geography
Seismic Response of the Woodbine
AustinEagle Fd.Woodbine
Buda
Ogletree #1
Stricklin, 2007
Tom Wilson, Department of Geology and Geography
Identifying the Woodbine Sequence
Tom Wilson, Department of Geology and Geography
The Woodbine Seismic Sequence
Where do intervals 1 through 5 fall on the relative depositional time scale?
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
http://homepage.ufp.pt/biblioteca/GlossarySaltTectonics/Pages/PageD.html
Tom Wilson, Department of Geology and Geography
Seis Strat Exercise
Tom Wilson, Department of Geology and Geography
Seis Strat Exercise
Start working on the Woodbine sequence and hand in next Wednesday
Tom Wilson, Department of Geology and Geography
Older 1970s processing
Newer processing flow. Better or worse?
The influence of processing on the interpretation. 1970s versus 1997 – which is better?
Tom Wilson, Department of Geology and Geography
Migration before or after
Migration after stacking
Migration before stacking provides a slightly better
view of internal prograding intervals
Tom Wilson, Department of Geology and Geography
Basic lesson is that processing flow can
influence what you see in your section and thus
your geologic interpretation
Tom Wilson, Department of Geology and Geography
Seismic Stratigraphy Exercise
Identify internal subdivisions. Use lapout and truncation relationships to establish subdivisions.
Consider the relationship between sediment supply and sea level rise during deposition of these sediment packages.
Tom Wilson, Department of Geology and Geography
Seis Strat Exercise
89 Mya
91 Mya
93 Mya
95 Mya
87 Mya
97 Mya
Chronostratigraphic Section
Global sea level curves from Vail and Mitchum
Tom Wilson, Department of Geology and GeographyTom Wilson, Department of Geology and Geography
To do
• Hand in the initial seismic sequence interpretations.• Complete the construction of the chronostratigraphic chart and hand in ….. •
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