tom wilson, department of geology and geography objectives for the day general review seismic...

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 ….. •