20. AMAZON FAN MASS-TRANSPORT DEPOSITS AND UNDERLYING INTERGLACIAL DEPOSITS: AGE ESTIMATES AND FAN DYNAMICS¹

Mark Maslin² and Naja Mikkelsen³

ABSTRACT

The Amazon Fan complex comprises two conspicuous features, huge mass-transport deposits (MTDs) and relatively thin interglacial deposits. There are two sets of MTDs: the near-surface MTDs and the deep MTDs. The near-surface MTDs are divided into the Eastern and Western Debris Flows and are capped by Holocene sediments. The deep debris flows are divided into the Unit R MTD in the western Amazon Fan complex, and the deep Eastern MTD (EMTD) in the eastern Amazon Fan complex. Characteristic of the MTDs is the inclusion of reworked glacial and interglacial materials from both the continental slope and the surrounding fan. The relatively thin interglacial deposits below the MTDs are from nannozones CN14b and CN15a, and are thus younger than 475 ka. Bio-, seismic-, and magnetostratigraphy and sedimentation-rate constraints have been used to date the top of both the near-surface and the deep MTDs. The deep EMTD was last active at 33 ka, whereas the Unit R MTD was last active at about 45 ka. It is inferred that the interglacial deposits below the MTDs were formed during oxygen isotope Stages 7, 9, and possibly 11. It is further suggested that the initiation of the MTDs was triggered by climatically induced changes in sea level that may have caused degassing of gas hydrates underlying the MTDs. Moreover, it is speculated that the interglacial deposits underlying the MTDs acted as slip planes for the MTDs.

¹Flood, R.D., Piper, D.J.W., Klaus, A., and Peterson, L.C. (Eds.), 1997. Proc. ODP, Sci. Results, 155: College Station, TX (Ocean Drilling Program).
²Environmental Change Research Centre, Department of Geography, University College London, 26 Bedford Way, London WC1H 0AP, United Kingdom. mmaslin@geog.ucl.ac.uk
³Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen NV, Denmark.