The results of coring on the Amazon submarine fan in 1994 challenge previous ideas about facies architecture and genesis of fan deposits. A shingled set of latest Pleistocene, upward-fining channel-levee units is underlain by, and locally interleaved with, equally voluminous sand-rich deposits. The sands occur as 5-25 m-thick packets, locally rich in semi-consolidated mud clasts. Each sand-rich unit is inferred to have been partly derived from an upfan avulsion site, landward of which entrenchment of the preexisting channel floor occurred. Sands were distributed into the adjacent interchannel low, where lack of confinement allowed spreading of turbidity currents to form sheet-like sand-rich bodies. Subsequently the advance of a new leveed channel over the sheet sands focussed sand transport along the channel axis, with simultaneous accumulation of muddy overbank deposits in the levees. Ancient channel-levee systems atop sheet sands, including those in some oilfields, may have similarly formed during single lowstands of sea level and as a result of repeated cycles of levee progradation and upfan avulsion.
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