ABSTRACT: Physical Modeling of the Growth of Extensional and Contractional Salt Tongues on Continental Slopes
B. C. Vendeville, M. P. A. Jackson
Salt tongues are allochthonous sheets of salt emplaced above younger strata. They are typically wedge shaped with lengths greater than 10 times the thickness. Using models composed of layered sand (brittle overburden) and viscous silicone polymer ("salt"), we simulated two categories of tongues: extensional and contractional. Extensional tongues formed as extrusions or shallow intrusions spreading asymmetrically from a diapiric stock or wall. During coeval sedimentation the distal (basinward) leading edge of the tongue climbed section, cutting off underlying strata at a low angle proportional to the ratio of the rates of aggradation and tongue spreading. Little or no sediment accumulated above the tongue; the resulting missing stratigraphic section had a thickness equal t that of the tongue. The proximal (landward) edge of the tongue was progressively buried under a prograding depotrough that squeezed salt downslope, deflating the proximal part of the tongue and inflating the distal part. After the feeder stem pinched off, complete evacuation of the proximal part of the salt tongue would weld suprasalt and infrasalt strata. Extensional tongues had discordant stems and were underlain by noninverted younger strata. Contractional tongues formed ahead of the toe of a prograding slope above a salt basin. Unlike extensional tongues, contractional tongues rose from asymmetric anticlines and were associated with significant shortening. Rising from concordant stems leaning basinward, these tongues overlie inverted, folded, younger strata.
AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990