Facies Distribution and Stratigraphic Architecture along Growing Basin Margins, Eocene Deepwater Morillo Depositional System, Ainsa Basin, Spain
Deepwater depositional systems associated with actively growing basins are important targets for hydrocarbon exploration and production. Seismic data of deepwater basin-fills often reveal the occurrence of low amplitude/chaotic non-reservoir seismic facies located close to basin margins. These strata separate the basin margins from high amplitude/good continuity reservoir facies located in the axis of the basins. Outcrop studies often focus on the nature of reservoir facies in the axial part of the basin, but little is known about sedimentological and stratigraphic characteristics of basin margin strata. This study describes and quantifies sedimentary facies and architectural elements of basin margin strata using measured sections, paleocurrent data, photopanel interpretation, petrographic analysis, and key-surfaces mapping.
The Morillo depositional system consists of axially restricted siliciclastic turbidite channels and channel complexes deposited coevally to carbonate-dominated basin margin strata. Morillo deposits are delivered through four main delivery systems: (1) an eastern siliciclastic dominated slope, (2) a southeastern mixed carbonate-clastic submarine canyon, (3) a southwestern stable carbonate platform, and (4) a western MTC and debris flow-dominated carbonate system. Nine facies associations are identified and represent the entire spectrum of sediment gravity flow processes ranging from slides, slumps, debris flows to turbidity currents. Six types of architectural elements (canyon, channel, levee, slump/slide, mudstone sheets, and lobes) are identified and mapped within the basin.
Cross sections built along the basin margins reveals relationships between basin margin geometry and stratal characteristics. First, slides, slumps and debris flows are empirically related to steep basin margins. Second, the angle of basin margin at the time of deposition is related to the width of non-reservoir quality strata that physically separates reservoir facies from the margin. Third, steepest basin margins have the narrowest zone of non-reservoir strata between the axis and margin. Those relationships are quantified using outcrop data and can be used to predict facies and architectural elements in subsurface data using stratigraphic and angular information.
It is possible to use the results of this study in other similar geological settings to reduce uncertainty in the determination of the minimum distance between basin margin and reservoir facies.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009