Role of Halite in the Evolution of Sandstone Porosity, Upper Jurassic Norphlet Formation, Mississippi Salt Basin

Abstract

ABSTRACT Analysis of petrographic point-count data, cement paragenesis, and SEM examination of pores has shown that poikilitic halite cement in sandstones of the Norphlet Formation in a core from Wayne County, Mississippi, formed following cementation by quartz, feldspar, dolomite, and anhydrite. Intergranular volume ranges from 26 to 42%, averaging 35%, indicating that an average of 10% of the rock volume has been lost to compaction, and a further 10 to 15% was lost to cementation prior to halite cementation, assuming a depositional porosity of about 45%. Most halite occurs as intergranular cement, but some halite is present as intragranular cement within framework feldspars and lithic fragments. Halite is easily removed from a sandstone during coring, slabbing, and thin-section preparation techniques that do not use oil-based fluids and muds, so the amount of porosity in these samples that is a product of artificial removal of halite is unknown. Although the present and former distribution of halite cement is poorly known in the Norphlet, natural halite dissolution could have produced about 20% secondary porosity in the Norphlet Formation in this part of the Mississippi Salt Basin.