GEOL 5903 Seminar: Jesse Demaries-Smith
GEOL 5903 Seminar: Jesse Demaries-Smith
Title: Models for the formation of saline giants: take them with a grain of salt
Location & Time: Huggins Science Hall, Room 336, 4:00 p.m.
Abstract:
The present being the key to the past is a fundamental concept for our understanding of past geological events and the conditions in which they occurred. However, an issue arises where no modern analogues exist to explain geological phenomenon, as seen in “saline giants” found around the world. Large salt and evaporite deposits occur in sedimentary basins with tectonic settings including intracratonic basins, synrift basins, postrift passive margins, continental collision zones, and foreland basins. The processes of precipitation and emplacement of these salt deposits, specifically saline giants, remain controversial. Modern salt bodies are precipitated from hypersaline brines with restricted inflow of water, but this model fails to demonstrate how massive saline giants such as the Messinian in the Mediterranean or the Aptian in the South Atlantic formed. For example, a 1200 m-thick package of halite would require evaporation of a 100 km thick column of seawater. Some argue that salt giants were formed by the same processes as the much smaller deposits that form today. Most current evaporite packages develop through solar evaporation of marine-fed seawater in shallow and deep basins, such as in the Salar de Uyuni in the Bolivian Andes. Others argue that saline giants form from brines that exceed threshold pressure and temperature parameters. The brines flash into a mixture of water and salt particles which are then precipitated, a process called shock crystallization. Lastly, some argue for oceanic basins that saline giant formation is a result of sea-water-driven serpentinization in abyssal serpentinite systems. Sea-water-driven serpentinization occurs where hydration of ultramafic rocks consumes water and rejects most solutes, creating a hypersaline brine that precipitates into salt. Since sea-water-driven serpentinization is not applicable to continental basins, it is not viable as a universal solution to saline giant precipitation. Ultimately, the controversy remains as no widely accepted cause for the formation of saline giants has yet been proposed.