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PSHigh-Resolution Spatial Models of a High Rising Carbonate Platform Slope
(Early Jurassic, Djebel Bou Dahar, High Atlas, Morocco)*
By
Klaas Verwer1, Oscar Merino-Tomé2, Jeroen A. M. Kenter3, Giovanna Della Porta2, Erwin Adams4, and Paul (Mitch) Harris5
Search and Discovery Article #40301 (2008)
Posted September 3, 2008
*Adapted from poster presentation at AAPG Annual Convention, San Antonio, Texas, April 20-23, 2008
Click to view list of articles adapted from presentations by P.M. (Mitch) Harris or by his co-workers and him at AAPG meetings from 2000 to 2008.
1 Faculty of Earth and Life Sciences, Vrije Universiteit, Amsterdam, The Netherlands
2 School of Earth, Ocean and Planetary Sciences, Cardiff University, Cardiff, UK ([email protected])
3 Chevron Energy and Technology Company, Voorburg, The Netherlands, [email protected]
4 Shell International E&P, Rijswijk, The Netherlands
5 Chevron Energy and Technology Company, San Ramon, CA ([email protected])
Seismic-scale continuous exposures of a Lower Jurassic (Hettangien–Pliensbachien) carbonate platform (High Atlas, Morocco) provide detailed information on lithofacies and stratal geometries in a slope setting strongly affected by synsedimentary extensional tectonics. Aggradational, backstepping, and progradational platform-to-slope transects were characterized by distinct lithological features and stratal patterns and were integrated in a digital outcrop model through digital field technologies (RTK GPS and lidar).
The first stage corresponds to a low-relief carbonate platform, which was affected by block faulting. The second platform stage developed as a retrograding platform and built considerable relief (height-above-basin of > 420 m). Small listric “subsurface” faults affected sedimentation patterns in the middle and lower slope. The third stage involved a major change in focus of sediment deposition and a time during which the slope was sediment starved. During stage four, following a major backstep, 70-meter high clinoforms prograded across the platform top until reaching the relict shelf edge. Deposition re-established in the slope environment, and a coral-sponge-microbial boundstone-dominated margin formed. The platform was not able to fill the available accommodation space in the basin, and the prograding clinoforms steepened up to dips of 23o, with a total relief of 460 m. Within the slope environment, deposits from stage four are present in the form of channelized olistolith bodies and coarse sheet-like beds, which are interbedded in thick wedges of fine-grained background sediments and calciturbidites.
The spatial information on sedimentary bodies and stratal anatomy will be used to populate 3D depositional models of a retrograding and prograding margin. A number of deterministic and stochastic realizations of rock type population will be presented.
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Three-dimensional depositional anatomy of a high-relief steeply-inclined lower Jurassic carbonate platform slope has been reconstructed making use of digital field technologies. Stratal patterns and lithofacies characteristics reveal trends specific to aggradational, retrogradational and progradational platform geometries. The dominant control of platform-slope architecture development at the Djebel Bou Dahar was active syndepositional tectonics within an intracratonic rift basin. The study illustrates how style of slope architecture and slope evolution is strongly influenced by active syndepositional tectonics, and how nature of the produced sediment and depositional processes are responsible for the geometry of sedimentary bodies in such carbonate slope settings. This outcrop example could be an excellent analog for many ancient outcrop as well as subsurface carbonate platform slopes in extensional basins, with active synsedimentary tectonics, or for other high-relief carbonate slope systems in which similar sedimentation mechanisms might act.
Adams, E.W., and W. Schlager, 2000, Basic types of submarine slope curvature: Journal of Sedimentary Research, v. 70, p. 814-828. Merino-Tome, Oscar, Giovanna Della Porta, Jeroen A. M. Kenter, Klaas Verwer, Mitch Harris, Erwin Adams, Diego Corrochano, and Noel Canto Toimil, 2007, Evolution of stratal anatomy and depositional patterns in a Lower Jurassic isolated carbonate platform captured by GIS (Djebel Bou Dahar, Southern High Atlas, Morocco) (abstract, First MAPG International Conference, Marrakech, Morocco, October 28-31, 2007): Search and Discovery Article #90074 (2007).
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