The Development of Karren Karst Forms on the Newala Limestone in Dry Valley, Shelby County, Alabama
The main objective of this study is to identify karrenforms and to evaluate factors affecting their development inan area representative of folded limestones of the Valleyand Ridge physiographic province in the southern Appalachians.In Dry Valley, Shelby County, Alabama, karren are abundantand highly diversified on outcrops of the Newala Limestoneof Ordovician age. They occur on bedrock surfaces below athin soil cover and on pinnacles protruding above the soil.Karren range from simple, isolated forms, to complex groups.One form may grade into another as cover conditions vary, orthey may be superimposed because of a complete change in environment.Karren have been identified and classified usingAlfred B5gli's genetic classification. B6gli's three principalcategories of free karren, semi-free karren, and coveredkarren are represented in the area. Covered karren, characterizedby rundkarren, are the most abundant; semi-freekarren are the next most abundant; and free karren are theleast abundant yet the most diversified of karren forms. Freekarren development has been restricted to a few isolated pinnaclesand outcrops by a nearly continuous soil cover overthe valley floor. Factors controlling karren development in Dry Valley include: geologic structure, lithology of thelimestone, stratigraphy, the presence or absence of a soilcover, climate, and local hydrologic conditions. These factorsdetermine the nature of the chemical reaction involvingthe limestone, carbon dioxide, and water; the solution rates;and the nature of the water flow over the limestone surfaces.These physical and chemical parameters are directly responsiblefor fashioning the various karren forms. Geologic structurehas had a pronounced effect on the distribution andorientation of karren forms and local hydrologic conditionsthroughout Dry Valley. Faulting has had little direct effecton karren development with the exception of low angle thrustfaulting that has produced a wide and highly permeable fracturezone. One such thrust fault located in the Vulcan Materialsquarry has created a bedrock low and a thicker soilzone that limits karren to covered forms. Folding, faultingand subsequent weathering of· limestone beds have resulted inlimestone surface slopes that range from 90° to nearly horizontalwithin the valley; consequently, a full range of karrenforms are possible. The Newala Limestone has many ofthe most favorable lithologic characteristics necessary toproduce karren including: fine-grained size, high density,strength, massive bedding and chemical purity. Local hydrologyhas played an important role in karren development inthe valley. Conditions may vary from poorly drained, swampy,permanently wet areas with a very shallow water table to well drained areas with a deep water table. Karren in the permanentlywet areas are characterized by highly developedrundkarren and wide shallow kluftkarren. Karren in the welldrained areas are generally more diversified and kluftkarrenmay achieve maximum development.