OBSERVED KARST FROM SOURCE TO SURFACE-BURKE COUNTY, GEORGIA

Excellent exposures of middle and upper Eocene deposits at two recent, large, industrial excavations in the Upper Coastal Plain of Burke County, Georgia aid in understanding the relationship between subsurface solution features and irregular surface depressions. The base of the excavations is in the middle middle Eocene Blue Bluff Marl, which is indurated calcareous siltstone. The Utley “limestone” unit of late middle Eocene age (submitted separately from this abstract), in general, unconformably overlies the relatively insoluble Blue Bluff Marl and unconformably underlies thin limestone of the Griffins Landing Member or the quartzose Irwinton Sand member, both of the upper Eocene Dry Branch Formation. Limestone in the Utley is glauconitic, fossiliferous packstone and is largely moldic. Common small solution tunnels to caves large enough for human ingress occurred at the north end of the two parallel excavations and trended approximately N25^oW. Speleothems (stalactites, stalagmites) and loose or cemented, fallen cave debris and fluvial cave fill were observed in some of the solution cavities. Also, several collapse structures were noted where the Utley locally thinned. Pre-excavation topography shows coincidence of irregular surface depressions with Utley solution features and advanced solution to collapse features in the excavations. The coincidence of positions indicates a causal relationship between subsurface solution and irregular surface depressions. The excavations have allowed a rare opportunity to demonstrate this relationship.