DIAGENESIS OF THE SALT MOUNTAIN LIMESTONE, CLARKE COUNTY, ALABAMA

The Tertiary (Paleocene) Salt Mountain Limestone is a predominantly subsurface startigraphic unit in Alabama; however, limited surface exposure occurs along the up-thrown side of the Jackson Fault in Clarke County. The thickest continuous section is less than 10 m, but additional sections can be assembled from sporadic outcrop that occurs across the tree-lined hilltop. Salt Mountain Limestone is predominantly white to cream-colored fossiliferous floatstone and framestone, with intervals of wackestone and skeletal grainstone/packstone. Fossil content is diverse. It includes corals, coralline algae, molluscs, sponges and numerous other less abundant invertebrates. The amount of cementation and porosity is variable. Some parts of the outcrop are friable and recessive due to limited cementation or extensive secondary dissolution. Microkarst features are common across the outcrop. Other parts of the outcrop are highly indurated resulting in laterally continuous scarps. Our study is attempting to identify and quantify cement phases in relation to other diagenetic events in the Salt Mountain Limestone. With the help of a Total Station GPS system, we are also mapping the distribution of carbonate cements in the formation relative to topography. To date, we have identified several meteoric phases of calcite cement. Most are intergranular drusy non-ferroan spars. Latter phases of pore-filling calcite within corals and other porous skeletal allochems may also be zoned and/or more ferroan. This suggests that minor changes in pore water chemistry were occurring during diagenesis.