DEFORMED ROCKS

     All rock types described in this book, as well as coal and bone, have been found in deformed attitudes in the Southern Appalachian Coal Fields. In some cases, layers are folded, rolled (e.g. 87L) or steeply inclined (e.g. 89L); in others, the rock has been ground into a pulpy mass of mud and fragments. In many cases, deformation has occurred shortly after the sediments have been deposited and involves movement of soft mud or wet sand. In others, solid rocks have been deformed and, in some examples, very large masses (cubic miles) have been folded or displaced. Differentiating soft sediment and hard rock deformation in a single core is often difficult and results from adjoining core holes and investigation of the general geological setting is required.

Examples of deformed rocks are from localities where the origin is known. The most common type of deformed rocks are the mudflows, which are produced by the sliding of soft sediment and occur in well defined zones up to five feet thick. Two types are illustrated–Sandy Shale Mudflow (e.g. 87R) and Sandstone Mudflow (e.g. 87L). Another type of soft sediment deformation is slumping and an example, a Sandy Shale Slump is shown on 89L. Such deposits are characterized by steeply inclined beds bounded by and cut by slickenside surfaces. These deposits, which form by fracture displacement of soft sediment (as in channel bank collapse), occur in zones up to 50 feet thick. Where slumped rocks overlie minable coal seams, they produce serious roof problems and in some cases even displace the seam itself.

An example of deformation produced by movement of solid rock is shown on 89R. Examination of this picture compared to 87L, 87R, 88L, 88R and 89L illustrate the difficulty in distinguishing the products of soft sediment and hard rock deformation. If deformed rocks similar to those shown on these pages are found in zones greater than five feet in thickness, efforts should be made to determine the type and extent of deformation as rocks of this type are known to cause serious difficulties in underground mining.