Biology 224 Instructor: Tom Peavy Oct 11, 2010 Gene Structure & Genomes.
Detailed Architecture of the Sub-Coastal Plain South Georgia Basin as Revealed by Geophysical Data...
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Transcript of Detailed Architecture of the Sub-Coastal Plain South Georgia Basin as Revealed by Geophysical Data...
Detailed Architecture of theSub-Coastal Plain
South Georgia Basin as Revealed by Geophysical Data
Samuel T. PeavyDepartment of Geology and Physics
Georgia Southwestern State UniversityAmericus, Georgia
A Plan for Today’s Talk:
1. Data and Approach2. Results of Potential Field Analyses3. Tectonic Tie-in
Data and Approach: Data Sets
• Gravity Data (from USGS)• COCORP Georgia/Florida Seismic Lines• Pre-Cretaceous Well Data (Chowns & Williams, 1983)
100000 200000 300000 400000 500000
3350000
3450000
3550000
3650000
1
1 111 1
11
1 1
1 1
1
11 11
1
1
111 1
2
2
2
22
22
2
2
22
3
3
3
3
3
3
33
3
3
44
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444
55
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55
55
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7
8 8 8 -60
-50
-40
-30
-20
-10
0
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Data and Approach: Data Sets – Gravity
18,968 data points
100000 200000 300000 400000 500000
3350000
3450000
3550000
3650000
-60
-50
-40
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-20
-10
0
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Data and Approach: Data Sets – Gravity
Data were gridded and contouredusing “Surfer” program
100000 200000 300000 400000 500000
3350000
3450000
3550000
3650000
-60
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-10
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Data and Approach: Data Sets – Gravity
The data were sub-divided into Western, Central, Northeast and Southeast regions.
100000 200000 300000 400000 500000
3350000
3450000
3550000
3650000
-60
-50
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-20
-10
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West
North Central Northeast
SoutheastSouth Central
Data and Approach: Data Sets – Gravity
Each region was analyzed separately and then combined to provide the best overall result.
100000 200000 300000 400000 500000
3350000
3450000
3550000
3650000
-60
-50
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-20
-10
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West
North Central Northeast
SoutheastSouth Central
Data and Approach: Data Sets – Seismic
COCORP SEGY files were used to aid in the interpretation of the data.
Data and Approach: Data Sets – Deep Wells
Lithologic information from Chowns & Willams (1983) were used to guide interpretation
Data and Approach: Data Sets – Deep Wells
100000 200000 300000 400000 500000
3350000
3450000
3550000
3650000
1
1 111 1
11
1 1
1 1
1
11 11
1
1
111 1
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2
2
22
22
2
2
22
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8 8 8 -60
-50
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-20
-10
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Well Information Overlain on Gravity Data
Potential Field Attribute Analysis (PFA) Consists of 3 analysis methods:
•Analytic Signal (Nabighian, 1972; 1984)•Tilt Angle (Miller and Singh, 1994)•Local Wavenumber (Peavy, 1997)
Data and Approach: Potential Field Attributes
Analytic Signal
A x,y H x,y 2 Z x,y 2
Data and Approach: Potential Field Attributes
Tilt Angle
x, y tan -1 Z x,y H x,y
Local Wavenumber
x, y x,y
x
2
x,y
y
2
Data and Approach: Potential Field Attributes
Data and Approach: Potential Field Attributes
What to look for in the maps:
1.Analytic Signal and Local Wavenumber will detect the edges of bodies, although the latter is more sensitive.
2.Tilt Angle will find the central location where the density contrast is locally greatest.
100000 140000 1800003350000
3390000
3430000
3470000
3510000
3550000
3590000
11 1
2
2
4
44
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5
5
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Results: West Georgia – Gravity Data with Wells and COCORP Lines
1 Metamorphic2 Felsic/Inter. Igneous3 Rhyolite/Tuff4 Triassic Red Beds5 Triassic/Diabase6 Diabase7 ?/Diabase8 Pz/Tr/Diabase
-45
-35
-25
-15
-5
5
15
25
35
13
11
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Results: West Georgia – Analytic Signal
80000.00 120000.00 160000.00 200000.003350000.00
3400000.00
3450000.00
3500000.00
3550000.00
0
1
2
3
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Not much to see…
Results: West Georgia – Tilt Angle
1 Metamorphic2 Felsic/Inter. Igneous3 Rhyolite/Tuff4 Triassic Red Beds5 Triassic/Diabase6 Diabase7 ?/Diabase8 Pz/Tr/Diabase
80000 120000 160000 2000003350000
3390000
3430000
3470000
3510000
3550000
11 1
2
2
4
44
5
5
5
5
55
5
8 8
-90
-70
-50
-30
-10
10
30
50
70
13
11
12
Interesting Results!Lows seem to correlate with Triassic Materials.
Results: West Georgia – Wavenumber
0
2
4
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10
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14
16
18
20
80000 105000 130000 155000 180000 205000
3360000
3400000
3440000
3480000
3520000
3560000
13
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Complex trends may establish the locations of border faults.
Results: West GeorgiaTilt Angle and Wavenumber seem to reveal some interesting features. Let’s compare them to some seismic data from the same area…
80000 120000 160000 2000003350000
3390000
3430000
3470000
3510000
3550000
11 1
2
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80000 105000 130000 155000 180000 205000
3360000
3400000
3440000
3480000
3520000
3560000
13
11
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3,430,000
-80
-60
-40
-20
0
20
40
60
3430000 3450000 3470000 3490000 3510000
3,500,000
3499880
Results: Tilt Angle vs. GA-11
Results: Tilt Angle vs. GA-12
-80
-60
-40
-20
0
20
40
60
80
3410000 3420000 3430000 3440000 3450000 3460000
3,415,000 3,452,000
Results: Wavenumber vs. GA-11
0
2
4
6
8
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14
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3475000 3485000 3495000 3505000
3,430,000 3,500,000
Results: Wavenumber vs. GA-12
0
2
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3410000 3420000 3430000 3440000 3450000 3460000
3,415,000 3,452,000
Results: West GeorgiaIn general, lower regions on the Tilt Angle correlates with basin depocenters, while Wavenumber indicates boundaries.
80000 120000 160000 2000003350000
3390000
3430000
3470000
3510000
3550000
11 1
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80000 105000 130000 155000 180000 205000
3360000
3400000
3440000
3480000
3520000
3560000
13
11
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Since the goal is to get an idea of overall basin geometry, let’s focus on the Tilt Angle maps from the rest of southern Georgia.
80000 120000 160000 2000003350000
3390000
3430000
3470000
3510000
3550000
11 1
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Results: West Georgia
Results: North Central Georgia – Tilt Angle
200000 240000 280000 320000 3600003500000
3540000
3580000
3620000
3660000
25
4
4
54
4 7
5511 1
17
5
541 5
1
1 11
1 Metamorphic2 Felsic/Inter. Igneous3 Rhyolite/Tuff4 Triassic Red Beds5 Triassic/Diabase6 Diabase7 ?/Diabase8 Pz/Tr/Diabase
Results: South Central Georgia – Tilt Angle
1 Metamorphic2 Felsic/Inter. Igneous3 Rhyolite/Tuff4 Triassic Red Beds5 Triassic/Diabase6 Diabase7 ?/Diabase8 Pz/Tr/Diabase
200000 240000 280000 320000 360000
3360000
3400000
3440000
3480000
3520000
8 8
3
5 4 554
5
65
3
24
2
3
25
46
4
Results: Northeast Georgia – Tilt Angle
1 Metamorphic2 Felsic/Inter. Igneous3 Rhyolite/Tuff4 Triassic Red Beds5 Triassic/Diabase6 Diabase7 ?/Diabase8 Pz/Tr/Diabase
360000 400000 440000 480000 5200003500000
3540000
3580000
3620000
3660000
3
6
4
7
11
1
414
1 411
2 1 11 1
Results: Southeast Georgia – Tilt Angle
1 Metamorphic2 Felsic/Inter. Igneous3 Rhyolite/Tuff4 Triassic Red Beds5 Triassic/Diabase6 Diabase7 ?/Diabase8 Pz/Tr/Diabase
360000 400000 440000 480000 520000
3360000
3400000
3440000
3480000
3520000
3
3
2
2 332
33 3
3
6
Merged Tilt Angle Map
Cross Strike Trends?
Generalized Basin GeometryUsing Tilt Angle, Well and Seismic Information
“Tifton”
From Costain and Çoruh (1989)
Results: Tectonic Tie-In
Exposed Mesozoic basins along the Applachians follow a pattern that seems to reflect preexisting structures.
(after Thomas, 1983)
Results: Tectonic Tie-InThe basins closely follow the trend established by rifting of the Laurentian Margin.
Suture?
(after Thomas, 1983)
Results: Tectonic Tie-InRifting during the Mesozoic was oblique to the trend of structures in southern Georgia
Results: Tectonic Tie-InResults of physical model experiments, such as those by McClay and White below, show that oblique rifting leads to complex fault systems with complex basin geometries such as seen here.
From McClay and White (1995)
Results: Tectonic Tie-In
Another possibility is that there may have been two-phase rifting, with initial orthogonal rifting followed by oblique extension.
From Keep and McClay (1997)
“Tifton”
Results: Tectonic Tie-InThe combination of apparent cross-strike structures and complex, synthe tic and antithetic fault geometries could be the result of rifting oblique to major structures in south Georgia, or perhaps two phases of rifting (orthogonal followed by oblique).
Conclusions:1.Analysis of potential field, well and seismic
information reveal the complexities of the structure of the South Georgia Basin.
2.Tilt Angle proves particularly useful in combination with seismic and well data in establishing basin locations.
3.The complex geometry of the Basin was established by either oblique or two-phase rifting during the Mesozoic.