TIMING OF TURBIDITE SEDIMENTATION ON THE MISSISSIPPI FAN

Sandy turbidite sedimentation on the Mississippi Fan, initiated during the falling and maximum relative lowstand stages of sea level during the last glacio-eustatic cycle, was significant well into the mid to l ate sea level rise until the Holocene, 12,000-11,000 yr B.P. or slight ly thereafter. Several factors suggest this late continuation of sandy turbidite sedimentation: (1) landward extension of the Mississippi Ca nyon into the mid-shelf water depths as sea level rose, (2) a major in crease in glacial melt-water discharge and sediment loads (pebble to c lay size) delivered directly to the head of the canyon by the Mississi ppi River during the rising sea level, (3) probable persistent interce ption of longshore drift by the canyon as it eroded landward, (4) stee p gradients at the head of the canyon that favored slumping of depocen ters and formation of turbidity currents, and (5) absence of expected coarse-grained lithologies and deltaic stratal patterns within the can yon, indicating sediment bypass through the canyon into deep water.The late sand-prone turbidite sedimentation inferred herein for the Missi ssippi Fan is compatible with the occurrence of sandy turbidites in th e middle Amazon Fan subsequent to 13,285 +/- 650 yr B.P. and significa nt deposition of turbidites and clastics until the Holocene elsewhere in the deep ocean. Sand-prone turbidite sedimentation into the middle/ late rise of sea level is in contrast to the common perception of sequ ence-stratigraphic models. This perception assumes that turbidite and fan sedimentation occurs mainly during falling, maximum lowstand, and early rise of sea level. Late continuation of significant sandy turbid ite sedimentation will impact concepts of subsurface stratigraphic cal ibration, inferences of depositional systems, and reservoir prediction s.