The structure and evolution of sutures in allochthonous salt Tim P. Dooley, Michael R. Hudec, and Martin P. A. Jackson ABSTRACT Salt canopies, formed by the coalescence of salt sheets, are an integral part of the slope and deep-water areas of many passive margin salt basins. A suture separates the two coalesced salt sheets (allosuture) or two lobes from a single salt sheet (auto- suture), including any trapped sediments. Autosutures can form in two ways. An overriding auto- suture is produced when part of a salt sheet overrides its neighbor in the direction of salt movement. The overridden roof sub- sides into the salt sheet, and these trapped sediments appear as intrasalt reflections on seismic data. An encircling autosuture forms when two lobes of a salt sheet separate to bypass an ob- stacle and then rejoin on the downstream side of the obstacle. Encircling autosutures tend to be short and parallel to the dom- inant salt-flow direction. Allosutures separate sheets sourced from two different feeders. If neither salt sheet overrides the other, the resulting suture is symmetric, forming an upright zone of roof sediments trapped between the two sheets. More typically, one salt sheet is more vigorous (generally the larger sheet or the one whose feeder is farther updip) and overrides the other. Sediments trapped in an asymmetric allosuture are mostly from the roof of the overridden sheet. The overriding sheet shears and ex- tends the roof of the overridden sheet, detaching it from the base of the canopy and obscuring its origin. We present diagnostic criteria to distinguish between su- ture types and provide physical-model examples of each. This distinction between suture types is important because auto- sutures and allosutures have very different implications for can- opy dynamics and evolution. AUTHORS Tim P. Dooley  Bureau of Economic Geology, Jackson School of Geosciences, Uni- versity of Texas at Austin, University Station, Box X, Austin, Texas 78713-8924; tim.dooley@beg.utexas.edu Tim P. Dooley received his Ph.D. from the Uni- versity of London in 1994. After 9 yr of post- doctoral research, he joined the Bureau of Economic Geology in 2003. Since then, his focus has been on a variety of aspects of salt tectonics using innovative physical modeling and analytical and graphical techniques. He received the AAPG Jules Braunstein Memorial Award in 2009. Michael R. Hudec  Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin, University Station, Box X, Austin, Texas 78713-8924; michael.hudec@beg.utexas.edu Michael R. Hudec received his Ph.D. from the University of Wyoming in 1990. He worked for Exxon Production Research and taught at Baylor University. He joined the Bureau of Economic Geology in 2000, where he codirects the Applied Geodynamics Laboratory. His current research interests include salt-sheet emplacement mech- anisms and minibasin initiation. He is a co- recipient of the AAPG Jules Braunstein Memorial Award. Martin P. A. Jackson  Bureau of Eco- nomic Geology, Jackson School of Geosciences, University of Texas at Austin, University Sta- tion, Box X, Austin, Texas 78713-8924; martin.jackson@beg.utexas.edu Martin P. A. Jackson received his Ph.D. from the University of Cape Town in 1976. After teaching, he joined the Bureau of Economic Geology in 1980 and founded the Applied Geodynamics Laboratory in 1988. He has re- ceived several AAPG awards: the Sproule Award, the Matson Award, the Dott Award, and the Berg Outstanding Research Award for his re- search on salt tectonics. ACKNOWLEDGEMENTS We thank Bill Hart, Russ Propes and colleagues at BP for suggesting the concept and term “autosuture.” We thank Mark Rowan, Joseph Copyright ©2012. The American Association of Petroleum Geologists. All rights reserved. Manuscript received March 7, 2011; provisional acceptance July 1, 2011; revised manuscript received September 9, 2011; final acceptance September 23, 2011. DOI:10.1306/09231111036 AAPG Bulletin, v. 96, no. 6 (June 2012), pp. 1045 – 1070 1045