Salt Tectonics Topics
Total Page：16
File Type：pdf, Size：1020Kb
Salt Tectonics Topics Salt Deposition Salt Movement Diapir Structures Imaging Link to faulting Composition of Salt Domes Salt Deposition Restricted marine basins Mostly halite Minor traces of gypsum or anhydrite Often the two are interbedded and folded Bonneville Salt Flats, Utah Gypsum, Ca(SO ).2H 0 4 2 Halite, NaCl Salt moves driven by buoyancy Sequential Stages of a Salt Diapir •Salt density= 2 g/ cm3 •Salt undergoes no compaction •Mechanically weak - viscous •Shale Density is initially 40% water •Initial Density = 1.8 g/ cm3 •Water expelled during compaction • Final Density = 2.4 g/ cm3 Salt at the Surface Salt Structures -Iran Salt Glacier - Iran Gulf of Gulf of Mexico Mexico Salt Variety of Salt Structures Internal flow of salt Jackson et al. 1990 Detection of Salt Domes Gravity Gravity surveys • Find gravity lows • Low density Seismic Imaging GM-SYS™ Profile model of salt structure integrating seismic reflection, FTG gravity, and magnetic data (EarthExplorer, 2009). Seismic Image of a Salt Dome Geosoft GmsYs-3D model of a salt body embedded in a 3D density volume (Earth Explorer, 2009)_ 3D Seismic Interpretation of Salt Sandbox Experiment Relationship between salt dome and normal faulting Structures 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, Extension Above Salt Diapir 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 Salt movement affects sediment thickness Salt in the North Sea Salt Traps Salt is the best seal Examples of Petroleum Salt Provinces • Gulf of Mexico • North Sea • Middle East Zagros Mts., Iran La Popa Basin, Mexico Ekofisk Field Ekofisk Formation analog W E Late Cretaceous Shallow Sea Continued regional subsidence Rising sea level Active phytoplankton growth Van der Bark & Thomas, 1980 Late Cretaceous: Ekofisk Formation Salt Domes Pierce the Strata Time Danish North Sea CI = 30ms 8km Crestal Deformation Fractures around Salt Domes Ant-Tracking displaying radial fracture pattern around salt domes 8km Fossen, 2010 Salt in Compressional Province Salt in Extensional province Gulf of Mexico Salt is an excellent detachment surface.