Multi-phase submarine channel-fill history recorded by stratigraphic architectures in outcropping slope-channel deposits, Tres Pasos Formation, southern Chile

Abstract:

The relationship between sediment transport processes, deposits, and channel morphology is well established for subaerial channel systems. Linking channel-fill patterns with planform morphology in submarine systems, however, is less constrained because of the difficulty in direct observation of sediment transport processes, including deposition of coarse-grained turbidites. Ever-increasing resolution of 3-D seismic-reflection and integrated bathymetry-sonar tools have led to significant improvement, but resolution issues still hinder effective analysis. For example, are inclined reflectors observed in seismic cross sections of channels associated with sinuous planforms indicative of turbidity-current-scale morphodynamics or are they composite surfaces that record larger-scale/longer-term evolution? Documenting the nature and variability of intra-channel fill architecture in outcropping submarine channel deposits provides insight into linking depositional processes and channel morphologies.

The Late Cretaceous retroarc foreland Magallanes Basin in southern Chile formed during uplift of the Andean Cordillera. Deep-water slope strata of the Tres Pasos Formation are exposed along a depositional-dip-oriented outcrop belt up to 2000 m thick and at least 100 km long. These strata provide an excellent natural laboratory for comparison of slope channel architectures from different positions on the slope and stages of basin infilling. We consider channelized architectural element dimensions and internal stratigraphic surface characteristics from multiple exposures along the outcrop belt. We also document varying stacking patterns of channel elements over time, from both laterally to vertically offset end-members. Results suggest that for both lateral and vertical channel stacking patterns, phases of accommodation generation (e.g., incision or sediment bypass) and migration of the channel are temporally distinct from phases of channel infilling (e.g., turbidity current collapse), which is an important difference compared to conceptual stratigraphic models of subaerial channel systems.