Effect of the Post-Tippecanoe Unconformity on Regional Fluid Movement and Geomorphology in Ohio
Regional unconformities can serve as pervasive fluid movement routes, with importance for groundwater movement and petroleum reservoir filling. As part of a project to understand the Bellevue-Castalia Karst Plain in north-central Ohio, we examined the literature, performed extensive GIS analysis, looked at water chemistries, and examined present day geomorphology.
The karstifiable strata here consist of Late Silurian and Middle Devonian limestones, dolomites, shales, and evaporites (gypsum/anhydrite). Spatial analysis indicates that karst features occur almost exclusively in the Columbus Limestone (Middle Devonian) where it is atop the regional unconformity (post-Tippecanoe/pre-Kaskaskia) developed on the Bass Islands Dolomite and Salina Group (Late Silurian). A high density of karst features has developed along a dissolution front of Salina anhydrite and gypsum beds where the latter are exposed to undersaturated waters entering through suffosion dolines. Collapsed blocks of limestone and dolomite sometimes core these sinkholes. Regional water flow is deep and diffuse, and most emerges from Vauclusian springs near Lake Erie. Although expression of these features is mostly post-Quaternary, the karstic evolution of these rocks is lengthy, and continues to this day. Other spatial data suggest that intrastratal dissolution of gypsum/anhydrite in the Salina G unit and lower evaporite beds below the regional unconformity is a controlling factor on sinkhole development here. High hydraulic gradients in the aquifer concentrate sinkhole development on the Karst Plain above a potentiometric low that may mark the active dissolution front of Salina Gypsum/Anhydrite. Evidence of mechanical breakdown into subsurface voids is found throughout the Karst Plain. Karst springs emerging at or below the regional unconformity to the north show obvious fluid connections across the basal Kaskaskia erosional surface. Indications are that sinkhole development on the Bellevue Castalia Karst Plain is more intimately related to the regional Siluro-Devonian unconformity than previously recognized. Conversely, the importance of this, and other, regional unconformtities for fluid migration should not be underestimated. These paleosurfaces cannot be considered static features, because continued evolution of their nature and permeability will occur. In this case, such changes may have been ongoing for over 400 million years.
AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012