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Longitudinal Channel Architecture and Facies Variability Along an Eight Kilometer Long Down-Slope Transect of a High-Relief Clinoform, Tres Pasos Formation, Chile

Abstract

Deep-water slope channel deposits, which represent important reservoir targets on numerous continental margins, are highly variable along the length of a continental slope. While current high-resolution 3-D seismic surveys yield insight into large-scale variability of channel stacking patterns along the slope profile, they are rarely able to resolve variability below the scale of individual channels (8-15 m thick, 150-300 m wide). We employ an outcrop study, which comprises 300 m of strata over an 8 km-long depositional-dip-oriented transect in the Tres Pasos Formation of southern Chile, to provide perspectives of internal channel architecture and stacking pattern variability, at seismic to sub-seismic scale. At least 24 individual slope channels are present in the outcrop trend. Channel strata were documented with 18 measured sections (550 m), which were captured at the dm-scale. Measured section locations, as well as channel tops, bases, and other important intra-channel surfaces were surveyed with differential GPS. These data provide the basis for digital architectural model construction of the 8-km outcrop, from which calculations of channel width, thickness, and offsets can be calculated. At the intra-channel scale, deposits are divided into three main facies associations, representing processes of erosion, sediment bypass, and deposition, in channel axis, off-axis, and margin settings. Along the 8 km long downslope transect, two key variations in the stratigraphic architecture are observed. Fundamental slope channels, or channel elements, are characterized by intra-channel fill showing significant changes downslope from more bypass-dominated (i.e. lag and bypass drape deposits with limited sandstone fill in some instances) to channels filled with heterolithic deposits, including amalgamated sandstone from channel base to top in axes. Channel stacking patterns change from north to south; although overall eastward channel stacking is evident, the width of the composite channel complex narrows from 1800 m to 1100 m along the length of the outcrop. Systematic changes within the channel strata along the unprecedented depositional-dip-oriented outcrop exposure stand to improve our understanding of longitudinal variation in processes of sediment transfer (i.e. erosion, bypass and deposition), and provide an opportunity to consider variation in large-scale channel stacking patterns that we commonly only observe in subsurface datasets.