ARCHITECTURE OF A CRETACEOUS CHANNEL-LEVEE COMPLEX, CERRO TORO FORMATION, MAGALLANES BASIN, CHILE

The Upper Cretaceous Cerro Toro Formation exposed around the Silla Syncline in Parque Nacional Torres del Paine, southern Chile, includes at least three 50 to 100 meter thick intervals of sandstone and conglomerate in an otherwise mud-dominated deep-water section that reaches at least 1000 meters in thickness. The coarse-grained intervals commonly consist of a lower section of medium bedded turbidite sands and muds overlain by interbedded debris flow deposits and thick, inversely-to-normally graded pebble to cobble conglomerate. The best studied conglomerate and sand unit is replaced by mudstone in both directions when traced laterally. To the north this facies change is accomplished through a series of stacked channel forms within which conglomerate passes laterally into sandstone that laps out against south-dipping erosional surfaces developed on mudstone and fine-grained sandstone. To the south the conglomerate and sandstone abut against a steeply dipping surface interpreted to represent a single major incised submarine valley wall. The distribution of coarse-grained deep-water deposits in the Silla Syncline indicates the existence of a long-lived but migrating submarine depositional fairway during the middle to late Cretaceous. Paleocurrent evidence suggests transport of coarse sediment primarily to the southeast. Major conglomerate outcrops east of the Silla Syncline imply the presence of a much more extensive coarse-grained transport fairway and depositional system along the axis of the Magallanes basin. The Silla Syncline section may represent a large lateral feeder to this axial system. Ongoing research is aimed at further understanding the lithofacies distribution within the Silla Syncline and ultimately developing three-dimensional geometric models to serve as a basis for synthetic seismic and reservoir modeling.