TUFA DEPOSITS IN WESTERN PENNSYLVANIA

Active calcium carbonate precipitation and accretion around springs and other groundwater seepages, related to the degassing of carbon dioxide, results in formations variably referred to as tufa or travertine. Such deposits in eastern North America are especially well-known in the karst region of western Virginia, often associated with the discharge of thermal spring waters, but reports of tufa formations outside of this region are scanty. Here we report on our preliminary observations on the occurrence of tufa in western Pennsylvania associated with springs and seeps adjacent to limestone units. The Upper Pennsylvanian Monongahela Group Benwood Limestone and the Middle Pennsylvanian Allegheny Group Vanport Limestone provide the likely source of calcium for the carbonate minerals that make up the deposits. Most tufa occurrences in the study area can be classified as perched springline tufas that are lobate, convex to flat-surfaced deposits, thickening away from a spring mouth. Many of the discovered sites are associated with human disturbances of natural terrain during the past 150 years that resulted in steep elevational drops in discharged water and enhanced carbon dioxide release – these include such activities as highway and railroad construction and the strip mining of bituminous coal. Preliminary data illustrating the general chemical, geological and biological characteristics of these tufa sites and their corresponding waters are presented. Future multidisciplinary scientific studies of these sites will incorporate geology, geochemistry, microbiology, isotopic analysis, hydrology and ecology.