Publication Date:
2012-02-13
Description:
SALT: AN INTRODUCTION Salt is a crystalline aggregate of the mineral halite, which forms in restricted environments where the hydrodynamic balance is dominated by evaporation. The term is used non-descriptively to incorporate all evaporitic deposits that are mobile in the subsurface. It is the mobility of salt that makes it such an interesting and complex material to study. As a rock, salt is almost unique in that it can deform rapidly under geological conditions, reacting on slopes =0.5° dip and behaving much like a viscous fluid. Salt has a negligible yield strength and so is easy to deform, principally by differential sedimentary or tectonic loading. Significant differences in rheology and behavioural characteristics exist between the individual evaporitic deposits. Wet salt deforms largely by diffusion creep, especially under low strain rates and when differential stresses are low. Basins that contain salt therefore evolve and deform more complexly than basins where salt is absent. The addition of halokinetic processes to the geodynamic history of a basin can lead to a plethora of architectures and geometries. The rich variety of resultant morphologies have considerable economic as well as academic interest. Historically, salt has played an important role in petroleum exploration since the Spindletop Dome discovery in Beaumont, Texas in 1906. Today, much of the prime interest in salt tectonics still derives from the petroleum industry because many of the world's largest hydrocarbon provinces reside in salt-related sedimentary basins (e.g. Gulf of Mexico, North Sea, Campos Basin, Lower Congo Basin, Santos Basin and Zagros). An understanding of salt and how it influences tectonics and sedimentation is therefore critical to effective and efficient petroleum exploration. Within rift basins in particular, salt is seen to orchestrate the petroleum system. Through halokinesis it creates structural traps, counter-regional dips on continental margins, and it can carry or entrain adjacent lithologies via...
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