DEEP-WATER SEDIMENT TRANSFER VIA SLOPE CHANNELS AS REFLECTED IN OUTCROPPING CRETACEOUS STRATA OF THE ANDEAN CORDILLERA, SOUTHERN CHILE

Coarse-grained sediment transfer across continental slopes cannot be directly monitored and therefore, deducing processes from sedimentary rocks provides critical insight into both ancient and present-day seascapes. Late Cretaceous deep-water slope strata of the Magallanes retroarc foreland basin are exposed along a depositional-dip-oriented outcrop belt up to 2000 m thick and nearly 100 km long, providing an exceptional natural laboratory for the consideration of off-shelf sediment transfer. More than 50 distinct channel fills have been analyzed, many in various positions along continuously exposed paleo-depositional profiles. The variability in fill composition, facies distribution, expression of basal erosion surfaces, as well as internal stratigraphic surfaces, provides a record of punctuated erosional events, coarse-grained sediment bypass, and deposition. Systematic downslope shifts in facies proportions, and erosional surface relief and frequency, record variation in dominant processes.

A prolonged history of sediment transfer is apparent from patterns of stacked channel fills, which are also variable amongst the outcrops studied. Both laterally offset and vertically aggraded channel patterns are developed, presumably linked to the magnitude of: (1) fine-grained sediment overspill into channel-overbank areas, and/or (2) channel base incision. The caliber of dominant sediment grain-size in channel fills ranges from conglomerate to mudstone, associated with significant differences in the shape and fill of channelform sedimentary bodies, as well as channel stacking patterns. All of these factors are controlled, in part, by fluctuations in sediment supply and position on paleoslope.