Comparison of Salt Withdrawn Basin on the Louisiana
Continental Shelf, Northern Gulf of Mexico
Introduction
The continental margin off the coast of
Louisiana is a part of the passive margin in the
Gulf of Mexico. The geomorphology of the area is
dominated by salt diapirs (or salt domes) and salt
withdrawal depocenters termed mini basins or salt
withdrawn basins (Sumner et al., 1991). These
basins are small in size and grow and form as salt
is withdrawn from denser sediments moving
downward and less dense salt moving upward
(Hamiter et al., 1997; Peel, 2014). Sedimentation
of these basins includes gravity-driven high energy
turbidity currents (Hamiter et al., 1997).
This study compares the effect of depth to the
basin’s geometry and hardness of the bottom of
several identified basins. Within this study area are
basins ranging in depth from 820 meters to 1472
meters.
Megan Jackson and Dr. Leslie Sautter
College of Charleston, Charleston, SC USA
Abstract
Multibeam sonar data of submarine basins were analyzed along the continental shelf in the Northern Gulf of
Mexico, an area known for its numerous salt domes (diapirs). The sonar data were collected in 2014 using a
Kongsberg EM302 abroad the NOAA Ship Okeanos Explorer. Three areas of the region off the Louisiana coast
were studied and consisted of diapirs and several small basins, referred to as salt withdrawn basins. Depths of
these basins were measured along with each basin’s short and long axes. A comparison of the axis ratios to basin
depths showed depth does not affect the basin shape. Several of the basins measured were nearly perfect circles
with varying depths. Backscatter intensity analysis was performed on three basins of varying depths and showed
no relationship between basin bottom hardness and basin depth.
NOAA Ship Okeanos Explorer
Methods
• Data for this research were
collected aboard the NOAA Ship
Okeanos Explorer on Cruises
Ex1402L1 and Ex140L2.
• Multibeam data were downloaded
from the NOAA NGDC website
and post processed in CARIS HIPS
8.1
• X,Y,Z measurements were made
from cross-sectional profiles.
• Backscatter mosaics were created
using CARIS HIPS & SIPS 8.1.
Figure 1. 5m Swath Angle Base
surface of study site
Location
of Study
Site
Figure 3. 3D view of BASE surface (VE=10x).
Figure 2. Google
Earth image
showing study site
in the Gulf of
Mexico
Figure 4. 3D
view
of Area 1
(VE=10x).
D
Backscatter
Figure 7 Backscatter Mosaics
C
Figure 5.
3D view of
Area 2
(VE=10x).
E
B
G
H
Backscatter of
Basin E
I
Backscatter of
Basin D
Backscatter of
Basin B
A
Backscatter intensity of 14.205 dB at deepest point
Figure 6. 3D
view of Area 3
(VE=10x).
A
B
J
Backscatter intensity of 19.081 dB at deepest point
B
’
A
B’
A’
Backscatter intensity of 28.762 dB at deepest point
B
A
A
’
B’
B
A’
K
1,050
L
B
1,050
1,150
Basin B
Basin B
1,150
B’
1,250
A’
A
1,250
1,350
Results
Short Axis vs Long Axis
20000
18000
y = 0.8823x - 2426.6
R² = 0.86264
12000
16000
Short Axis (m)
14000
10000
8000
6000
4000
2000
0
8000
10000
12000
14000
16000
18000
20000
22000
24000
26000
Long Axis (m)
Graph 1. Relationship between the short and long axis
of each basin. See Table 1.
Short: Long vs Depth
1.4
1.2
Short : Long
1
0 1,000
y = -0.0006x + 1.4073
R² = 0.22745
0.8
700
0.6
Table 1. Observed measurements of basins
0.2
0
800
900
1000
1100
1200
1300
1400
1500
1600
Basin Short Axis
(m)
Depth (m)
Long
Deepest
Axis (m) Depth
(m)
Graph 2. Relationship between depth and axes ratios (Table 1).
Work Cited
Diegel,F.,Schuster, D.,Karlo, J.,Shoup,R.,&Tauvers,P.(1995). Cenozoic
Structural Evolution and Tectono-Stratirahic Framework of the Northern Gulf
Coast Continental Margin. Salt Tectonics :A
Global Perspective 109-151
Hamiter, R., Lowrie, A., MacKenzie, M.,& Guderian, E.(1997). Origin of SaltWithdrawal Mini-Basins, Proven Produces Along Present and Paleo-Louisiana
Slope. Gulf Coast Association of
Geological Societies Transactions, 47, 185-191
Peel, F. (2014). How do salt withdrawal minibasins form? Insights from
forward modelling, and implications for hydrocarbon migration.
Tectonophysics, 630, 222-235. Retrieved from Science
Direct.
Pell, A(2007) Evolution of an Allochthonous Salt System, Southern Mars-URSA
Basin,
Northern Gulf of Mexico
References
Sumner,H.(Director)(1991,April 7).Mophology
and Evolution of Salt/Mini-Basin
Systems:Lowere Shelf and Upper Slope, Central Offshore Louisiana. AAPG Annual
Convention. Lecture conducted from AAPG, Dallas
Twichell,D., Nelson,H., $ Damuth, J.(2000). Late-Stage Development of the Byrant
canyon
Turbidite Pathway on the Louisiana Continental Slope. 1032-1044
Acknowledgements
Thank you to the College of
Charleston BEAMS Program. To
CARIS for teaching and
HighlandGeo for software license
support. To the CofC Dept. of
Geology and Environmental
Geosciences. And finally, to the
crew of the Okeonos Explorer.
Short
Axis:
Long
Axis
A
11,539.76 16969.91 1292.37
0.68
B
12,373.21 16568.32 1472.03
0.75
C
17,056.28 23257.63 1043.03
0.73
D
11,922.11 13,897.63
826.81
0.86
E
13,323.10 15,343.40 1241.47
0.87
F
G
4,936.83
9506.19 1271.81
11,529.70 14789.73
5,000
7,000
9,000
11,000 13,000
0.52
990.60
1.28
H
9,176.61 12430.92 1294.08
0.74
I
7,323.24 12317.87 1294.01
0.60
J
6,941.22 12479.13 1134.66
0.56
K
6,633.05 10484.94 1292.48
0.63
1,350
1,450
Distance (m)
• The short and long axis of the basins were identified
visually and measured.
• Basins in Area A (Fig. 1) all had similar short/long
axis ratios close to 1 indicating a circular shape.
• Basins in Area 3 (Fig. 1) had the smallest short/long
ratios closer to 0.5 indicating a noncircular shape.
• Graph 1 shows a high positive correlation between
the basins in all three areas.
• Graph 2 shows a low negative correlation between
the depth of the basin and its ratio.
• Backscatter mosaics showed no relationship
between depth and hardness of the basin’s bottom.
0.4
3,000
0 1,000
3,000
5,000
7,000
9,000
11,000
13,000 15,000 17,000
A’
A
Basin E
900
700
B
B’
Basin E
900
1,100
1,100
1,300
0 1,000
3,000
5,000
7,000
9,000
11,000
13,000
1,300
A
650
0 1,000
3,000
5,000
7,000
9,000 11,000 13,000 15,000
Basin D
675
700
A’
750
B
725
B’
Basin D
775
800
0
1,500
3,500
5,500
7,500
9,500
11,000
825
0
1,500
3,500
5,500
7,500
9,500
11,500
Discussion
Three areas of submarine basin were analyzed in the Northern Gulf of Mexico along the
Louisiana coast (Fig. 1). The depths of these basins range from 826 to 1472 m. The basins were
identified as salt withdrawn basins. When salt is withdrawn it creates a basin, which then fills with
sediments. In map view (Fig. 1) these basins are circular in shape and are composed of thick
sequences of sediment (Sumner et al. 1991). Collapse of the basin is the result of gravity spread once
the salt below is depleted (Pell, 2007). Further study is needed to determine if these basins are still
spreading and expanding in size. Within the Northern Gulf of Mexico, there is much variation in
geomorphology, however sediment-filled mini basins represent the dominant structural style (Diegel
et al. 1995), just as they dominate this study area. This type of sea floor morphology is the result of
the exchange between sediment loading and salt movement (Twichell et al. 2000).
This study showed that there is weak negative correlation (Graph 2) between the depths of
the basins and the ratio of their size, meaning that with changing depth the ratio of the size of the
basin changes only slightly. However the smaller more circular basins did have greater depths than
the much larger basins. The backscatter analysis (Fig. 7) on three basins of varying depths revealed
that the hardness of the basin bottom is not affect by depth, and that increasing depth does not result
in a harder bottom. Further backscatter analysis is required to make a stronger evaluation of the
correlation between depth and hardness.