5. FINE-GRAINED TURBIDITES OF THE AMAZON FAN: FACIES CHARACTERIZATION AND INTERPRETATION¹

David J.W. Piper² and Mark Deptuck²

ABSTRACT

Much of the sediment thickness found on Amazon Fan levees is attributed to mud with silt laminae. The distribution of sharp-based graded beds and the distribution of bioturbation, diagenetic fronts, and nannofossils demonstrates that many of the beds were deposited rapidly and episodically. The total thickness of mud decreases sharply away from active channels. These observations suggest that most of the levees are built of fine-grained turbidites. Twelve facies of fine-grained turbidites are distinguished from visual core description, X-radiography, and grain-size analysis. Some facies appear diagnostic of particular fan settings. Modal grain size of both muds and thin silt laminae decreases downfan. Facies distribution is consistent with the progressive spillover of a turbidity current as it moves down the channel system.

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).
²Atlantic Geoscience Centre, Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, N.S., B2Y 4A2 Canada. piper@agc.bio.ns.ca