The Composite Salt Glacier: Extension of the Salt Glacier Model to Post-Burial Conditions
M. R. Hudec, R. C. Fletcher, I. A. Watson
Fluid dynamics modeling suggests that during emplacement, salt glaciers maintain a relief of hundreds of meters, and are thus unlikely to be buried. Most salt sheets are not buried until salt supply up the feeder stock slows or is cut off entirely, leading to relaxation of the dynamically supported topography of the sheet and progradation of sediments across its updip end.
The onset of sedimentation on top of a salt sheet does little to alter the
mechanics controlling salt deformation. There is still relief on the
sediment-water contact, driving downdip flow of the salt and sedimentary
carapace. The salt itself may no longer be extrusive, but the system as a whole,
which we term a composite salt-sediment glacier, is still governed by the
mechanics of gravity spreading. Instead of being fed entirely by salt supply
from below, a composite glacier is fed by sedimentation, especially in
extensional minibasins near its updip end (Figure 1). The extension in the updip
minibasins is compensated at the toe
of the glacier either by extrusion of salt
(if the
toe
remains uncovered) or by contractional folds and thrust faults (if
the
toe
is buried, Figure 2). A com osite glacier will remain active as long as
the relief on its upper surface is sufficient to overcome the forces resisting
its lateral motion. Many composite glaciers stop moving shortly after the
toe
is
buried. Once density inversion is achieved in the minibasins, buoyancy forces
begin to compete with lateral spreading as a control on the style of salt
tectonism, and a point will eventually be reached where it is no longer useful
to consider the system as a glacier.
AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995