Invited Speakers

Mark received a B.S. in biology from CalTech in 1976, an M.S. in geology from Berkeley in 1982, and a Ph.D. in structural geology from the University of Colorado at Boulder in 1991. He spent 3 years at Sohio Petroleum Co. in Denver (1982 to 1985), four years at Geo-Logic Systems in Boulder (1985-1989), and three years at Alastair Beach Associates in Glasgow, Scotland (1989-1992). He then returned to the University of Colorado, and in 1996 he was appointed a Research Assistant Professor and headed up a large industrial research consortium investigating Gulf of Mexico salt tectonics. Mark left this position in 1998 and founded his own company, where he consults and teaches for the petroleum industry and conducts research sponsored by industry.
Although Mark’s background includes many types of tectonic environments, his recent research and consulting interests are focused on the styles and processes of salt tectonics, salt-sediment interaction, the geometry and kinematics of fold-and-thrust belts, and the applications to petroleum exploration. He is the author or coauthor of over 60 papers and 120 abstracts, is the regular instructor for AAPG’s Salt Tectonics school, and has been an AAPG Distinguished Lecturer.

ABSTRACT

SLOPES, BASIN FLOORS, DIAPIRS, AND CANOPIES: REGIONAL-SCALE SALT-SEDIMENT INTERACTION IN THE NORTHERN GULF OF MEXICO AND THE SCOTIAN OFFSHORE

Rowan, Mark G.- Rowan Consulting, Inc. 850 8th St., Boulder, CO, 80302, United States

Salt diapirs and allochthonous canopies are well known from the northern Gulf of Mexico and the Nova Scotian offshore. Canopies can be divided into two end-member styles: salt-stock canopies, in which the canopy is linked to the autochthonous salt layer by vertical feeder diapirs and intervening minibasins are characterized by turtle structures; and salt-tongue systems, where the canopies are connected to the deep layer by counterregional welds that have basinward-dipping expulsion-rollover structures in their hanging walls.

The fundamental difference between the two styles is the degree of asymmetry. In salt-stock canopies, diapirs grow vertically and spread radially before amalgamating, and sub-canopy withdrawal geometries tend to be symmetrical. In salt-tongue canopies, diapirs grow up and basinward and extrude basinward, and the withdrawal basins are correspondingly asymmetric. Because both diapirs and allochthonous bodies grow passively at the sea floor, the simplest explanation for the difference is the slope of the sea floor. If it is horizontal, there will be no preferred direction of growth and extrusion, resulting in vertical diapirs and salt-stock canopies. If the sea floor slopes, diapirs will lean basinward and extrude salt tongues basinward. Thus, the structural style is largely determined by the evolving bathymetric profile of the passive margin, which in turn is controlled by the history of sediment progradation.

In the northern Gulf of Mexico, a regional boundary between more proximal salt-tongue canopies and more distal salt-stock canopies roughly parallels the margin and probably represents a long-lived base of slope initially established during Paleogene Wilcox deposition. In the Scotian deepwater, a similar boundary is oriented highly oblique to the margin, with vertical diapirs to the southwest (Shelburne Subbasin) and salt-tongue canopies to the northeast (Sable Subbasin). The structural boundary is located along the southwestern edge of the Upper Jurassic to Lower Cretaceous Mic Mac and Missisauga progradational system, and thus represents a lateral boundary to a broad slope to the northeast, with a basin floor along strike to the southwest. One of the key applications of this model is that it can be used to estimate the paleo-toe of slope and thus regional turbidite facies distribution, with channelized slope facies dominant in areas of salt-tongue canopies and ponded basinal facies more likely in areas with vertical diapirs and salt-stock canopies.