Attribute Expression of Mass Transport Deposits in an Intraslope Basin- A Case Study. Supratik Sarkar*, Kurt J. Marfurt, Belinda Ferrero Hodgson, Roger M. Slatt ConocoPhillips School of Geology & Geophysics, University of Oklahoma Summary A single relative sea level cycle Slatt, 2006 Lowstand systems tract (LST) Transgressive systems tract (TST) Highstand systems tract (HST) Mass Transport Deposit 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. Schematic Figure illustrating different facies present In MTD ( After Weimer and Slatt, 2006) Debris Flows Glide blocks Thrust blocks Escarpment Rotated blocks Outrunner blocks Mass Transport deposits within a sequence stratigraphic framework Mass Transport Deposit Basin Floor fan; Levees Begin backfill of leveed-channels Incised valleys backfill; Mud deposited in basin Transgressive sands; Condensed section; MFS all on shelf. Deltaic/Interdeltaic deposits 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. Demarcating Salts Methodology Location and Geologic Setting 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 amplitude Coherent Energy (the square of the RMS amplitude of the coherent component of the data) Eigenstructure coherence Generalized Sobel filter edge detectors Amplitude gradients Most-positive and most-negative curvature Variance 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. 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 Seismic Max Min Depth Slice at 17000 ft Depth Slice at 13500 ft (Okuma et al., 2000) 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). Inline 5155 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’ Depth (Kft) 2.5 10 7.5 5 17.5 15 12.5 20 Flow axis of FlowB Eroded remnant of FlowA Post Flow Pre Flow B Sequences identified on the basis of seismic characters, well logs and Biostratigraphy. A NNW SSE 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. 5 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 B B’ B’ HAR HAR 2.5 6 Seismic Max Min Top of Mass Transport Deposit A’ Flow B Depth (Kft) 5 Flow axis of FlowB 7 Depth (Kft) Seismic Max Min Flow A 8 7.5 Seismic Max Min Pre Flow Base of Mass Transport Deposit 9 10 1 Km