STRUCTURAL ANALYSIS OF MISSISSIPPIAN (KINDERHOOKIAN- OSAGEAN) CARBONATES IN NORTHEASTERN OKLAHOMA

Carbonate rocks are known for acting as complex fluid conduits due to their heterogeneous nature in terms of origin, evolution, and geometry. For decades, it has been recognized that characterizing structures in carbonate rocks is crucial for the subsurface study of hydrocarbons and the characterization of water flow in aquifers. Despite this, the fracture network in Mississippian-aged limestone facies and other lithologies in northeastern Oklahoma have not been completely understood. In this study, we examine structures such as bedding planes, dissolution surfaces, joints, and faults within the lithologies of the well-exposed Mississippian outcrops in Mayes County, Oklahoma, as pathways for fluid.

We conducted photogrammetric surveys from an uncrewed aerial vehicle to create digital elevation models and orthomosaics from high-resolution topographic data. These were used in a GIS as base maps for the mapping of the geology and structures of the study areas. We collected geological and structural data from outcrops during fieldwork.

The Keokuk and Reeds Spring formations outcrop in the study area. Within the Reeds Spring Fm., we find segmented and systematic joint sets that cut through limestone and chert beds, non-systematic joints perpendicular to the bedding surface in chert, dissolution features in limestone, calcite veins, and joints along the bedding planes. On average, large joints are 22 m long with an aperture of 0.13 m, while smaller joints are 1.14 m long. Both strike NE-SW, and dip NW. The small joints spacing ranges from 3.1— 4.7 joints per m. The same types of structures are found in the Keokuk Fm. but are not as widespread throughout. The joints found in the Keokuk Fm. strike N— S and dip west. Normal faults, thrust faults, and joints related to the Seneca Fault also cut the Keokuk and Reeds Spring formations. Normal faults 12— 60 m in length in the Keokuk Fm. strike NE—SW and dip NW in places, while they also strike NW— SE and dip S—SW in others. The dissolution surfaces occur along bedding planes and are up to 2 m wide. We hypothesize that the joints along the bedding planes, the fractured chert beds, the systematic joint sets, and the dissolution surfaces contribute the most to the permeability of the rocks. These structures intersect at high angles to form a fracture network that allows for fluid passage.