Salt Tectonics Topics w Salt Deposition w Salt Movement w Diapir Structures w Imaging w Link to faulting Composition of Salt Domes Salt Deposition Restricted marine basins w Mostly halite w Also gypsum or anhydrite w Often interbedded and folded Bonneville Salt Flats, Utah Gypsum, Ca(SO ).2H 0 4 2 Halite, NaCl Density, kg/m3 Unusual Properties of Salt Density vs compared to Clastic rocks burial curve •Salt density= 2 g/ cm3 •Salt undergoes no compaction •Mechanically weak - viscous •Shale Density Depth, m •Initial Density = 1.8 g/ cm3 ( 40% water) •Final Density = 2.4 g/ cm3 (after water is expelled) Relative Strength of Salt and Rock Lab model of the rise of a diaper driven by buoyancy Salt Salt at the Surface Salt Structures -Iran Salt Glacier - Iran Gulf of Mexico – US platforms in 2012 Gulf of Mexico Gulf of Variety of Salt Structures Mexico Salt Jackson and Talbot, 1991 3D Seismic Interpretation of Salt Internal flow of salt Structures Jackson et al. 1990 6 Mechanisms for Salt Movement (halokinesis) Internal structure of diapirs from centrifuge experiments Detection of Salt Domes Main Classes of Diapirs Active rise of salt w Gravity surveys • Find gravity lows • Low density Passive: Salt keeps up with sedimentation w Seismic Imaging Reactive: Response to extension Reactive: Response to thrusting Fossen, 2010 Gravity GM-SYS™ Profile model of salt structure integrating seismic reflection, FTG gravity, and Geosoft GmsYs-3D model of a salt body embedded in a 3D magnetic data (EarthExplorer, 2009). density volume (Earth Explorer, 2009)_ Seismic Image of a Salt Dome Salt edges are hard to see Rootless Salt- Gulf of Mexico AAPG Explorer, 2013 Diapir movement and extension Sandbox Experiment Relationship between salt dome and normal faulting http://www.beg.utexas.edu/indassoc/agl/animations/AGL95-MM-001/index.html GUGLIELMO, G., Jr., , B. C. VENDEVILLE, D. D. SCHULTZ-ELA, and M. P. A. JACKSON Bureau of Economic Geology, The University of Texas at Austin, Sand box model of Cypress Creek Field Normal fault- a diaper in an diapir extensional setting relationship Gulf Coast Hughes, 1968 Diapir in a contractional setting Ekofisk Formation Extension Above Salt Diapir W E Late Cretaceous . Shallow Sea . Continued regional subsidence . Rising sea level . Active phytoplankton growth Late Cretaceous: Ekofisk Formation Salt Domes Pierce the Strata Time Danish North Sea CI = 30ms 8km Fractures around Salt Domes Salt moves up, sediment moves down Ant-Tracking displaying radial fracture pattern around salt domes 8km Once the salt is gone, unusual Salt movement affects sediment thickness structures remain Salt Traps Salt is the best seal w Examples of Petroleum Salt Provinces • Gulf of Mexico • North Sea • Middle East Zagros Mts., Iran La Popa Basin, Mexico Salt Structures vs. Tectonic Structures •Caused by movement of salt, not by plate boundary stresses •Often linked to sedimentation •Often localized by tectonic structures •Both upwards movement of salt and salt withdrawal cause deformation.