Completed Study
Stratigraphic Record of Translation Down Ramps in a Passive-Margin Detachment:
Kwanza Basin, Angola
Michael R. Hudec and Martin P. A. Jackson
Translation of strata down a monoclinal ramp in a passive-margin detachment is stratigraphically recorded by synkinematic sediments. A ramp basin forms an isopach thick on the seaward side of the monocline. This basin is then moved seaward down and then off the monocline, as if on a conveyor belt. This shift creates accommodation space for a new isopach thick to form just landward of the older one. Repetition of this cycle creates a shingled series of isopach thicks within the ramp basin. Bathymetric scarps can create spectacular seaward-dipping onlap surfaces more than 30 km long downdip.
Kinematic forward models and restored cross sections from the Kwanza Basin, Angola, show that the stratigraphic pattern of ramp basins is most influenced by (1) the relative rates of translation and aggradation, and (2) the presence or absence of salt structures. Salt structures are commonly shortened at the top of the ramp, especially where the ramp coincides with the base of the continental slope. Diapir shortening acts like a compressed buffer to absorb translation from its landward side and impede translation on its seaward side. Ramp basins record the incremental translation history and translation rates of units transported over the ramp.
For more information, please contact Michael Hudec. Telephone 512-471-1428. E-mail
August 2003