ODP Drilling on the Amazon Fan: Initial Results on Growth Pattern and Timing of Fan Sedimentation

R. D. Flood and D. J. W. Piper

The study of turbidite sediment patterns on modern submarine fans can provide insights into the allocyclic and autocyclic factors important in turbidite systems. Over 4000 m of core from 17 sites (and wire-line logs) provide important evidence for the character and timing of sediment deposits on Amazon Fan where a series of surface and subsurface channel-levee systems have been identified on high-resolution seismic profiles. Many of these channels have been formed through bifurcation from active channels, and are underlain by flat-lying reflections on seismic profiles (HARPs). Groups of levee systems are separated from one another by debris flows of large regional extent. One of the objectives of drilling on the Amazon Fan was to determine the absolute ages of the different channel-levee system through micropaleontologic, paleomagnetic, and AMS ¹⁴C dating. Initial results suggest that at least the six most recent levee systems were formed during the maximum glacial lowstand from about 12-40 kybp, with fewer channels formed earlier in the last glacial period. More deeply buried levees were active during earlier glacial lowstands (to ~400 kybp). The large debris flows have eroded the tops of some levees, appear to have sources on the upper continental slope, and may have occurred shortly after the deposition of carbonate layers during sea-level high stands. A site on the flank of Amazon Fan shows that low-stand turbidite sedimentation was limited to within about 150 km of the canyon along the margin, but a record of turbidite sedimentation from 8-125 ky preserved with increased turbidite flux during minor sea-level falls.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California