Evaporite Diagenesis Driven by Synsedimentary Evolution of Brines

Susan D. Hovorka

Back-reaction of brines has modified cyclic shallow water carbonate-sulfate-halite sequences (Permian) in the Palo Duro basin, Texas Panhandle. Successive parts of regressive evaporite cycles were deposited from progressively more highly evaporated seawater. The reaction of the brine with sediments deposited during earlier parts of each cycle was the major force driving diagenetic reactions and determining the final mineralogy. Normal marine limestones at the base of cycles were dolomitized in the shallow subsurface environments by brines that precipitated brine-pool evaporites in the upper parts of cycles. Gypsum dehydrated to anhydrite at burial depths of 1-2 m beneath the brine-pool floor as brine salinity increased toward halite saturation. Diagenetic limpid dolomite nd anhydrite replacing halite were probably derived from mixed meteoric and evaporated-marine brines squeezed from mudstone beds during compaction in the shallow subsurface. Anhydrite and halite pervasively cemented and partly replaced carbonates and gypsum. The resulting low permeability limited later diagenetic alteration, so that the early diagenetic textures and mineralogy were preserved in the burial environment. Reduction in permeability occurred before the transgression initiating the next cycle; the only major result of the introduction of seawater into the evaporite environment was dissolution of the last-deposited few meters of halite.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.