Ooid Mineralogy and Diagenesis of the Pitkin Formation, North-Central Arkansas: Chapter 13

The Pitkin Formation is a Late Mississippian (Chesterian) high-energy marine oolitic-bioclastic limestone. The original mineralogy of Pitkin ooids varied across the Pitkin carbonate shelf. In the eastern part of the study area, originally aragonite ooids deposited in shoal and shoreface environments. These ooids are presently replaced by calcite and exhibit high Sr and low Mg concentrations. Originally calcite ooids in overlying lagoonal facies are composed of well-preserved, radial fabric. These ooids contain low Sr and high Mg values. Similar characteristics indicate that ooids in the central and western part of the study area were all originally calcite. An early marine nonferroan low-Mg calcite cement occurs as fibrous-to-bladed circumgranular crust, equant mosaic pore fill, and syntaxial overgrowth on echinoderm bioclasts. An extensive early dissolution event related to meteoric diagenesis dissolved aragonite and high- and low-Mg calcite components and created moldic and vuggy porosity. A late burial ferroan calcite occurs as mosaic and poikilotopic cements filling intergranular and moldic pores. Early marine and late burial calcite cementation eliminated virtually all porosity within Pitkin grainstones. End_Page 175------------------------