Diagenesis and dolomitization of Swope Formation (upper Pennsylvania), southeast Kansas

Abstract

ABSTRACT In the Pennsylvanian Swope Formation of southeastern Kansas, diagenetic replacement phenomena involving pyrite, sphalerite, calcite, dolomite, silica, kaolinite and dickite took place in the same sequence within different carbonate facies. Two stages of dolomitization are evident in the Swope Formation: 1) The earlier stage of dolomitization selectively replaces micrite in the basal portion of the formation; 2) Later ferroan dolomite selectively replaces grains, chiefly algal blades and ooids, and fills primary voids and fractures in the middle and upper parts of the formation. Neither stage of dolomitization can be unequivocally demonstrated to result from capillary concentration of saline waters in evaporite lagoons or reflux of hypersaline waters from such lagoons. Therefore dolomi ization in the Swope Formation may possibly be due to diagenetic alteration by nonevaporitic, metasomatic processes. Pyrite was the first diagenetic mineral to form within the limestone. It continued to form through the stage of precipitation of drusy calcite cement. Trace amounts of sphalerite formed after initial pyritization. Calcite spar cementation apparently followed the first stage dolomitization and preceded the second stage dolomitization. The youngest calcite spar contains iron rich zones. Silicification followed the second stage of dolomitization. Later kaolinite and dickite formation is believed to be related to hydrothermal events associated with Tertiary intrusions in southeastern Kansas. Calcitization of dolomite is interpreted to be a late, possibly Holocene event.