attribute expression of mass transport deposits in an intraslope basin- a case study. supratik...
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Attribute Expression of Mass Transport Deposits in an Intraslope Basin- A Case Study.
Supratik Sarkar*, Kurt J. Marfurt, Belinda Ferrero Hodgson, Roger M. SlattConocoPhillips School of Geology & Geophysics, University of Oklahoma
Mass transport deposits (MTDs) are common features along most continental margins that help us reconstruct the depositional environment in complex deepwater systems. MTDs are associated
with genetically related turbidites and fans through the sequence stratigraphy of the basin. Alternatively called slumps, slides, mass flow units, or debrites, MTDs constitute large volumes of
sediments in deepwater settings. Unlike turbidite sands that form in the same environment, MTDs only rarely form hydrocarbon reservoirs. While MTDs can compartmentalize pre-existing fans
deposits, they can also form a good seal. Near the water bottom, recent MTDs can indicate the risk of future slumping hazards to submarine platform legs, drill stems, pipelines, and communication
cables. MTDs commonly exhibit an overall chaotic seismic pattern; several other associated features help to differentiate MTDs from other kinds of deposits in deep water depositional environments.
MTDs have similar characteristics in intraslope basins (also called salt minibasins) but vary as a function of restricted transport direction for sediment input, limited accommodation space, and
syndepositional salt movement. By coupling principles of geomorphology with seismic attributes and a depositional model, we analyze the characteristics of an MTD within an offshore Gulf of Mexico
study area to determine how it differs from other deepwater architectural elements and how it affects the overlying and underlying sediments.
Summary
Schematic Figure illustrating different facies present In MTD ( After Weimer and Slatt, 2006)
Mass Transport deposits within a sequence stratigraphic framework
Location and Geologic Setting
The area of study is within the tabular salt-minibasin tectono-stratigraphic province, which is structurally characterized by the presence of allochthonous salt tongues or tabular salt within sediment-filled minibasins that are formed by salt withdrawal (Diegel et al.,1995).
Sequences identified on the basis of seismic characters, well logs and Biostratigraphy.
Inline 5155
Depth Slice at 13500 ftDepth Slice at 17000 ft
Demarcating Salts
The final geometric configuration of the minibasin is a function of the interaction of the continuously-deposited sediment load on top of the allochthonous salt, giving rise to temporally-varying lateral changes in subsea topography
Objectives
‘Chaotic’ MTDs have a distinct seismic geomorphological expression that can be easily recognized but not easily picked. The objective of the current study is to analyze the seismic attribute
expression of a MTD in an intraslope basin salt minibasin in the deep water Gulf of Mexico, with the goal understanding the seismic geomorphologic significance of different elements and its
impact on the underlying and overlying sequences and the basin configuration as a whole.
Methodology• Use conventional interpretation pattern recognition skills to identify MTDs on vertical seismic slices.
• Demarcate bounding surfaces for the mass transport deposit using the seismic texture, well logs, and paleontological data (to validate the markers).
• Study the attribute expressions of the mass transport deposit including: RMS amplitudeCoherent Energy (the square of the RMS amplitude of the coherent component of the data)Eigenstructure coherenceGeneralized Sobel filter edge detectorsAmplitude gradientsMost-positive and most-negative curvatureVariance
• Proportionally slice amplitude and attribute volumes between the two bounding horizons, generating a suite of stratal slices. Although attributes such as RMS amplitude, coherence, and curvature are mathematically independent, they are often coupled through the underlying geology. For this reason, some the features can be identified on all the attributes while others are illuminated by only one or two attributes. Using this approach, characterize different components of the mass transport deposit within a seismic geomorphology framework
• Evaluate the control of MTDs by topography and lithology of underlying packages, erosion by MTDs of underlying packages, and control (primarily through changes in accomodation space and differential compaction) on overlying packages.
BA
Seismic lines (a) AA’ and (b) BB’ showing a mass transport deposit (MTD) imaged by our 3D seismic survey. The MTD unit is comprised of two discrete flow events forming two discrete layers having different seismic characteristics. The attribute expression of the two units are also quite different. We denote the two flows as Flow A and Flow B.
The Upper packages (Flow B) exhibits wavy, undulating and chaotic seismic character.
The Lower flow unit (Flow A) is less undulating and chaotic, has lower reflectivity, and exhibits some stratification.
Note how Flow B of the MTD cuts down through and erodes Flow A . Erosion is maximum along the flow axis, where the flow magnitude is maximum and decreases gradually away from the axis.
(Okuma et al., 2000)
B’
A’
SSE
B’
NNW
B
Mass TransportDeposit
Basin Floor fan;Levees
Begin backfill of leveed-channels
Incised valleys backfill;Mud deposited in basin
Transgressive sands;Condensed section; MFSall on shelf.
Deltaic/Interdeltaicdeposits
A singlerelativesea levelcycle
Slatt, 2006
Lowstand systemstract (LST)
Transgressive systemstract (TST)
Highstand systems tract (HST)
Mass TransportDeposit
NW SE
UC1
Salt
UC2
Sequence 1: GephyrocapsaL
Sequence 2: MFS102
Sequence 3: LacunosaVar
Sequence 4: TrimA
Sequence 6: LacunosaA
Sequence 5: Truncatulinoides
Sequence 7: Flexuosa
De
pth
(K
ft)
2.5
10
7.5
5
De
pth
(K
ft)
7
6
5
9
8
1 Km
Seabed
MTD2
Studied Mass Transport Complex Interval
Top of Mass Transport Deposit
Base of Mass Transport Deposit
NNW SSE
Flow B
Flow A
Salt Body in South
Salt Body in West 1.6 Km
A A’
De
pth
(K
ft)
2.5
10
7.5
5
17.5
15
12.5
20
Flow
axi
s of
Flo
wB
Eroded remnant of FlowA
Post Flow
Pre Flow
Flow
axi
s of
Flo
wB
HA
R
HA
R
Top of Mass Transport Deposit
Base of Mass Transport Deposit
Flow B
Flow A
Pre Flow
Debris Flows
Glide blocks
Thrust blocks
Escarpment
Rotated blocks
Outrunner blocks
SeismicMax
Min
0
SeismicMax
Min
0SeismicMax
Min
0
SeismicMax
Min
0