Variation of Mass-Transport and Turbidite Deposits in Different Continental Margin Settings and Time Periods
C. Hans Nelson1, Carlota Escutia2, D.C. Twichell3, and John E. Damuth4
1 CSIC University of Granada, Granada, Spain
2 Department of Oceanography, Texas A & M University, College Station, TX
3 U.S. Geological Survey, Woods Hole, MA
4 University of Texas at Arlington, Arlington, TX
The volume of mass-transport (MTD) and turbidite deposits vary on different continental margins depending on local and global controls. In the Bering Sea, MTDs from giant, gullied canyons dominate the margin and prevent the development of turbidite systems. In contrast, on the Cascadia and San Andreas margins off North America, MTDs are minor compared to turbidite deposits. Other margins, like the Ebro in Spain, have some segments with only turbidite systems and others with only aprons of MTDs. Some large delta-fed passive margins like Mississippi and Amazon exhibit MTDs and turbidites that are intermixed at large and small scales. Both the Mississippi Fan and intraslope mini-basins in the northern Gulf of Mexico contain MTD sheets derived from large-scale slope failures; these sheets, tens of meters thick cover major portions of the fan turbidites and blanket ponded turbidites of mini-basin floors. Multiple failures of Mississippi canyons and mini-basin walls have deposited (a) MTD lobes that underlie many fan channel-levee complexes and (b) MTD wedges that intrude into mini-basin channel and ponded turbidite units. Small-scale failures in canyon and mini-basin walls result in thin (cm-scale) MTD beds that can be funneled through channels as much as 600 km to deposit in the distal Mississippi Fan. Amounts of MTDs also vary with time, such as epochs of apparent polythermal ice streaming when massive MTDs dominate in some Antarctic margins, compared to the mixed MTDs and turbidites of other glacial times. In temperate regions, MTD processes increase during lower sea levels as shown by the age of modern seafloor MTDs and by MTDs that are found mainly in mini-basin lowstand deposits.