Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Stratigraphic Stacking of Outcropping Slope Channels, Tres Pasos Formation, Chile: Insights into Turbidite Reservoir Delineation
(1) University of Calgary, Calgary, AB, Canada.
Deep-water slope channel deposits have been proven to hold substantial hydrocarbon reserves making them attractive targets for exploration along continental margins. Advances in seismic imaging has resulted in vivid 3D perspectives of deep-water sedimentary systems in the subsurface. Despite these advances, sedimentological detail irresolvable in seismic data is crucial for understanding the connectivity within, and amongst, reservoir scale sedimentary bodies. An outcrop belt 130 m high and 2.5 km long from the Cretaceous Tres Pasos Formation, Chile, represents an important means for acquiring this sedimentological data, allowing turbidite channel development to be analyzed from the bed- to channel body-scale. This study attempts to capture the stratigraphic complexities of slope channel strata, with a focus on internal channel fill architecture and channel stacking behavior.
The Tres Pasos Formation consists primarily of mudstone- and siltstone-dominated strata associated with a progradational, graded slope system characterized by > 800 m of relief. Architectural analysis was completed on coarse clastic lower- to base-of- slope deposits. Numerous gullies cross-cut the outcrop at high angles and provide excellent 2D and 3D exposures of channel geometries. The data collected consists of >1600 m of measured section, hundreds of paleoflow measurements, numerous photomosaics, and thousands of GPS waypoints used to map channel strata in 3D. At least three channel complexes characterize the stratigraphy, demarcated by bounding siltstone-dominated deposits, and significant shifts in channel stacking patterns. Channel complexes are composite features comprised of stacked channels, each of which are 6-15 m thick. The margins of channels are characterized by thinly interbedded sandstone and siltstone that was deposited within the confines of the conduit. Channel axes consist of sedimentation units 0.2-3 m thick, attributed to collapsing high-concentration turbidity currents.
Eighteen channel elements stack vertically, or slightly offset of one another, in the 130 m thick section. The overall aggradational stacking pattern is likely associated with confinement of the channel system; however a mechanism for this confinement is speculative because channel complex-scale outer levees have yet to be recognized in the outcrop belt. It is also plausible that structural confinement in the narrow Magallanes Basin foredeep influenced the architecture of slope channels.