HISTORY OF DIAGENETIC FLUIDS IN A DISTANT FORELAND AREA, MIDDLE AND UPPER PENNSYLVANIAN, CHEROKEE BASIN, KANSAS, USA - FLUID INCLUSION EVIDENCE

Analysis of fluid inclusion data in diagenetic cements from Pennsylvan ian limestones and sandstones of the Cherokee basin in southeastern Ka nsas reveals the succession of diagenetic fluids in a distant foreland of the Arkoma-Ouachita system. This succession includes early low-sal inity (0.0-2.4 wt% NaCl eq.) fluids of meteoric affinity (Fluid I) fol lowed by low-temperature Na-Ca-Cl brines (Fluid II with salinities bet ween 8.4 and 24.1 wt% NaCl eq.). Fluids I and II were present in the s ystem during precipitation of early-stage calcite cements at temperatu res less than about 50-degrees-C. Another Na-Ca-Cl brine (Fluid III wi th salinity up to 25 wt% NaCl eq.) was present in the system later, at temperatures of maximum burial (at least 80-85-degrees-C) and higher. Fluid Ill is followed by a Na-Cl brine (Fluid IV, with salinities abo ut 19-21 wt% NaCl eq.) characterized by temperatures distinctly higher than maximum burial, up to 150-degrees-C. Fluid III and Fluid IV were entrapped during precipitation of late-stage baroque dolomite and Fe- dolomite in Pennsylvanian limestones, and late-stage Fe-dolomite and a nkerite in Pennsylvanian sandstones. The record of progression from Fl uid III to Fluid IV may have been partially obscured by thermal re-equ ilibriation of some inclusions during migration of Fluid IV. Fluids wi th Na-Ca-Cl chemistry (Fluid II and III) were either indigenous subsur face fluids of the Cherokee and Arkoma basins, or might have originate d as reflux fluids in a Permian evaporitic basin of Central Kansas. La ter Na-Cl brine (Fluid IV) originated in deeper parts of the Arkoma-Ou achita system and might have acquired their salinity by dissolution of hypothetical salts buried beneath the Ouachitas. Temperatures recorde d by fluid inclusions in late-diagenetic carbonates are 20-60-degrees- C higher than those calculated for the maximum burial of the studied s ection. This thermal anomaly suggests an advective heat transfer from the Arkoma-Ouachita system onto the shelf of the Cherokee basin relate d to the invasion of late-diagenetic fluids.