Patrick M. Goldstrand 2


At two of the seven sites drilled during Leg 157, located south of the Canary Islands (Sites 955 and 956), more than 1000 thinly bedded to finely laminated volcaniclastic and nonvolcaniclastic silt and sand turbidite units interbedded within thick sequences of hemipelagic mud were recovered. The sediments range in age from Pleistocene to middle Miocene. Turbidite deposits composed mostly of volcaniclastic detritus are related to known periods of volcanism in the Canary Islands. The non-volcaniclastic turbidites include various mixtures of quartz and foraminifer sand and silt derived from the continental margin of northwestern Africa. Shallow marine bioclastic deposits are thicker at Site 956 than at Site 955, suggesting that these sediments were derived from the southern Canary Islands.

Although age constraints cannot be precisely defined at these sites, the general trend of sedimentation is consistent with sea-level variations being responsible for transport of the continentally derived turbidites. Quartz-rich turbidite deposits composed of well-rounded, very fine-grained sand were derived from Saharan eolian sands that migrated onto the subaerially exposed continental shelf and were shed into the deep marine environment during falls in sea level. Shallow marine bioclastic and foraminifer- rich turbidites also correspond to periods of sea-level fluctuations. However, the presence of volcaniclastic material within several bioclastic deposits indicates volcanic activity may have been responsible for some of their deposition.

Large-scale submarine slumping appears to be more active during periods of intensified bottom currents and upwelling. Additionally, slumping was more frequent at Site 956 on the lower flank of Gran Canaria. Slump block ages are only slightly older than those of the surrounding sediment, and mass movement may have resulted from increased sedimentation and/or earthquakes associated with Canary Islands volcanism.

1 Weaver, P.P.E., Schmincke, H.-U., Firth, J.V., and Duffield, W. (Eds.), 1998. Proc. ODP, Sci. Results, 157: College Station, TX (Ocean Drilling Program).
2 Geological Sciences, University of Nevada, Reno, NV 89557, U.S.A. patrick@cs.unr.edu (Present address: Midas Joint Venture, Star Route Midas, via Gol-conda, NV 89414, U.S.A.).