The stratigraphic expression of decreasing confinement along a deep water sediment routing system: Outcrop example from southern Chile
The products of sediment laden turbidity currents that traverse areas of decreasing confinement on submarine slopes include erosional and depositional features that record the inception and propagation of deep sea channels. The cumulative stratigraphic expression and deposits of such transitions, however, are poorly constrained relative to depositional settings dominated by end member confined (i.e. submarine channel fill) and unconfined (i.e. lobe) deposits. Upper Cretaceous strata of the Magallanes foreland basin in southern Chile are characterized by a variety of stratigraphic architectural elements in close juxtaposition both laterally and vertically, including: (1) low aspect ratio channelform bodies attributed to slope channel fills; (2) high aspect ratio channelform bodies interpreted as the deposits of weakly confined submarine channels; (3) lenticular sedimentary bodies considered to represent the infill of laterally coalesced scours; (4) discontinuous channelform bodies representing isolated scour fills; and (5) a cross stratified, positive relief sedimentary body, which is interpreted to record an upslope migrating depositional bedform. These elements are interpreted to have formed at a submarine sediment routing system segment characterized by a break in slope, and an accompanying decrease in confinement. The various architectural elements examined are interpreted to record a unique stratigraphic perspective of turbidite channels at various stages of development, from early stage discontinuous and isolated scour fills to low aspect ratio channel units.