Shelf to Lower Slope Deposits of an Over-Steepened High-Relief Slope Clinoform, Chilean Patagonia
High-relief slope clinoforms are rarely observed in outcrop. The ability to recognize and study these extensive depositional systems in detail offers an opportunity to understand their fine-scale stratigraphic architecture and formative sedimentary processes. The Tres Pasos and Dorotea formations of the Magallanes basin, Chile, represent shelf, slope and basin floor deposits of an overall graded, high-relief (>850 m) clinoform system with punctuated over-steepened intervals. High-relief clinoform work to date has focused on the relationship of shelf-edge trajectories and the accumulation of Deepwater reservoir quality sandstone. The objective of this study is to outline the facies distribution, stratigraphic architecture and context of a shelf through lower slope transect along the over-steepened high-relief “Puma” clinoform.
Parts of at least four clinothems are documented over a 100 km2 area along a depositional dip oriented outcrop belt characterized by ~3500 m of stratigraphy. The dataset consists of high-resolution satellite imagery, extensive measured section and photo mosaics. The Puma Clinoform is >30 km long (shelf-edge to lower slope) and characterized by 950 m relief. In the overall evolution of the high-relief slope system, the surface is part of a flat shelf-edge trajectory sequence that was associated with delivery of significant coarse detritus to the deep basin. The shelf topset of the Puma clinoform is comprised of river-dominated deltaic deposits. At the shelf-edge, both abundant MTDs and slump scars with up to 50 m relief are prevalent and reflect shelf-edge instability. Progradation of deltaic sediments to the shelf-edge coupled with extensive mass wasting enhance the overall efficiency of sediment delivery to the deep basin. ~5 km basinward of the shelf-edge, the upper slope consists of fine-grained sandstone and siltstone with local incision surfaces overlain by similar facies, coarse-grained detritus largely bypassed the setting. ~22 km from the shelf-edge, the lower slope surface consists of conglomerate- and sandstone- filled channel bodies >12 m thick and 200 m wide. These units are dominated by traction structures indicating significant sediment bypass. Further downslope, conglomerate is absent and channelform sedimentary bodies dominated by thick-bedded sandstone fill are present. These facies observations enable realistic interpretations for analogous hydrocarbon-prone clinoform systems (e.g., Alaska North Slope).
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California