Regional Motions along the Northern Gulf of Mexico Passive Continental Margin Indicate Lateral Basinward Tectonics

Allen Lowrie¹, Juan Lorenzo², and Nancye Dawers^3
1Consultant, Picayune, MS
²Louisiana State University, Baton Rouge, LA
³Tulane University, New Orleans, LA

Basic structure review of passive continental margins, especially of the northern Gulf of Mexico, suggests that on a margin-wide basis the general movement along the margin is downslope and basinward. In the northern Gulf, the continental margin extends from the fall line, classically depicted at Little Rock, Arkansas, to the Gulf's abyssal plain. This margin represents a dip-oriented distance of circa 10 degrees of latitude, circa 1200 km. The descent is from continental elevations of some 500 m to submarine depths of 2.5- 3 km. As the rifting basin evolves during the tectonic subsidence phase, the rifted basement blocks subside and rotate basinward,at subsidence rates from seafloor spreading/plate tectonics. Tectonic motions within the overlying sediment are extensional as represented by listric faulting. Localized compression occurs at the foot of the listric faulting. The principal migration of shale/salt serves as a 'tectonic escape' moving basinward, the overall motion being downslope. This myriad of motions from margin-spanning regional/local/minute- occur at highly irregular intervals from instantaneous to geologically leisurely. The second order sedimentary units determined from sequence and seismic stratigraphy record deposition at the then-depths prescribed by basin evolution. Sediments record their depths of deposition and as sampled well past deposition, the sediments occur at greater sub-surface depths with that area now at deeper water depths. The family of motions and the concomitant geo-physical changes in heat/fluid collection/mobilization with their associated migration routes may be termed as "margin tectonics", a general term to depict continental margin evolution.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece