FLEXURAL RESPONSE OF PASSIVE MARGINS TO DEEP-SEA EROSION AND SLOPE RETREAT - IMPLICATIONS FOR RELATIVE SEA-LEVEL CHANGE

We suggest that the magnitude of the early-late Oligocene eustatic fai l, as predicted from sequence stratigraphy, has been overestimated bec ause of flexural rebound along margins that was induced by late Eocene to early Oligocene erosional unloading. The unloading of sediments fr om a continental margin during periods of deep-sea erosion and slope r etreat will be accompanied by some form of flexural rebound. The magni tude and form of this rebound are controlled by (1) the amount of sedi ment removed from the margin and (2) the strength of the lithosphere a t the time of sediment removal. Along margins with narrow continental shelves, this rebound witt induce a relative sea-level fall resulting in a basinward shift in the shoreline, and the predicted systems tract s will be similar to those expected for a eustatic fall. In contrast, rebound along wide continental shelves will not alter the position of the shoreline, even though a relative sea-level fall may be recorded a cross the outer shelf. Deep-sea drifting and seismic reflection data f rom many margins support the interpretation of a late Eocene to early Oligocene (approximately 38-34 Ma) deep-sea erosional event best devel oped along the continental slope and rise. Seismic reflection and dril ling data also document a prominent canyon-cutting event across the sh elf during the early-late Oligocene (approximately 32-29 Ma). This eve nt has been interpreted in terms of a large eustatic fall (>150 m). Ne vertheless, there appears to be a correlation between late Eocene to e arly Oligocene deep-sea erosion and the development, or at least enhan cement, of unconformities across the shelf during the early-late Oligo cene.