Ordovician, Mississippian, and Pennsylvanian strata in Kansas all show fracturing, megaquartz, silica dissolution, carbonate dissolution, baroque dolomite, MVT minerals, and calcite after stylolitization. CL petrography, fluid inclusions, ⁸⁷Sr/⁸⁶Sr, and d¹⁸O indicate hydrothermal fluid flow affected Ordovician-through-Pennsylvanian stratigraphic units.

The history is simplified into three phases of hydrothermal fluid flow (86-144°C). All show evidence of thermal pulses, suggesting tectonic valving. Phase I was from brines near seawater salinity, interpreted as connate fluids migrating out of the Anadarko basin, likely during the Pennsylvanian or early Permian. Fluids were associated with gas, and precipitated megaquartz.

Phase II led to precipitation of baroque dolomite. Fluid inclusion data indicate high salinities (20 wt. %) and ⁸⁷Sr/⁸⁶Sr indicate advective fluid flow across long distances. d¹⁸O data indicate the Ordovician-Mississippian section acted as an aquifer in vertical communication, leading to warmer fluids and preferred flow towards the top of the Mississippian. The shale-rich Pennsylvanian section acted as a leaky confining unit. This phase of fluid flow was associated with oil migration and likely occurred late in the Permian or after.

The first two phases of hydrothermal fluid flow are associated with fracturing, silica dissolution and carbonate dissolution. Much of the porosity, typically assumed to originate from subaerial weathering, may have been generated by these late hydrothermal fluids. The fluids followed fracture systems and were concentrated along the tops of hydrothermal aquifers by stratigraphic discontinuities and temperature-controlled density differences. This model for hydrothermal porosity formation helps to explain the spatial variation in reservoir quality in the Mississippian and leads to an enhanced model for locating the best producers.

Phase III of hydrothermal fluid flow was complex, and is recorded by calcite cements. Spatial variation of d¹⁸O and ⁸⁷Sr/⁸⁶Sr indicate cessation of advective fluid flow and initiation of localized vertical fluid flow, possibly directly from basement. A driver could be localized faulting and fracturing associated with Laramide or other deformation. Comparison of fluid inclusion temperature and salinity data to modern reservoir conditions indicate that this phase clearly predates the current fluid flow and thermal regime, but played a part in evolution of the reservoir system.