Abstract: Lateral Infill as Major Factor in Submarine-Canyon and Fan-Valley Sedimentation

Daniel Jean Stanley, Harold D. Palmer, Robert F. Dill

Submarine-valley studies emphasize entrapment in canyon heads and down-axis transport to channel systems on submarine fans at the base of the slope, but generally neglect the role of lateral-infill processes. Furthermore, the interrelation of canyon-wall facies to adjacent slope and canyon-axis sequences is a poorly defined aspect in modern canyon studies. We formulate a submarine-valley sedimentation model, based on ancient and modern examples, which involves lateral infill. A comparison is made of the well-exposed Tertiary canyon deposits at the Annot, Contes, and Menton localities in the French Maritime Alps with the La Jolla, San Lucas, Los Frailes, and some U.S. East Coast canyons. Ancient fan-channel deposits in the Lac d'Allos and Peira-Cava regions, in turn, are c mpared to channels in the La Jolla and San Jose del Cabo fans.

The major characteristics of valley-wall deposits are: (1) notable lithologic variability in time and space; (2) poor stratification and impossibility of tracing sedimentation units laterally; (3) a marked diversity of transport mechanisms: chaotic slumps and debris-flow deposits predominate but sandflows and turbidites are somewhat less important than in the axial fill; (4) structures record variable transport directions. The geometry, assemblage of trace fossils, and relative proportion of wall-rock debris are three of the factors used to distinguish canyon-wall from fan-valley-wall facies. A complex of subaqueous gravity processes active on steep canyon-wall slopes (which facilitates failure of metastable sediments) results in rapid sedimentation. Lateral infill is an important tri ger for subsequent downslope transfer of material in both canyon and fan-channel axes.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA