SAPROLITE FABRIC IN WEATHERED SHALE IN EAST TENNESSEE WITH COMPARISON TO PENNSYLVANIA AND PUERTO RICO

Saprolite fabric, which results from the isovolumetric weathering of bedrock, is ubiquitous in weathered shale in east Tennessee but is not as common in other areas within the eastern United States. This study summarizes the distribution and characteristics of saprolite in east Tennessee and compares it to weathered shale in Pennsylvania and Puerto Rico. Soil profiles developed from weathered shale in east Tennessee typically consist of thin A and B horizons (10-30 cm) overlying 1-6 m (or more) of un-cemented saprolite. The saprolite can be broken up by hand but still retains the same fabric as the parent bedrock, including tectonic fractures, sedimentary layers, and bedding plane fractures. Fracture preservation in the saprolite allows for easy transport of water, pedogenic clays and bacteria into the subsurface. By comparison, at the Susquehanna Shale Hills Critical Zone Observatory (SSHO CZO) in Pennsylvania, there is no saprolite zone overlying unweathered bedrock. In Puerto Rico, saprolite fabric overlying unweathered shale is potentially obscured in many areas due to the greater extent of weathering and deeper root penetration. Shale weathering in these three regions is expected to be controlled primarily by climate, but the periglacial history in PA and differences in shale cements may also contribute to the presence or absence of saprolite fabric overlying shale bedrock.