GEOLOGY OF WESTERN PENNSYLVANIA IN THE CLASSROOM AND IN THE FIELD

Diversity of geologic phenomena of Pennsylvania (PA) can be addressed to illustrate almost any geological concepts in the classroom. One may start with Pennsylvanian period to introduce the concept of geologic time and its subdivisions. Proceed with fossil assemblages such as trunk and branches of Calamites, bark imprints of Sigillaria, leaves of tropical ferns that are well preserved in sandstones and shales of Pennsylvanian cyclotherms. These rocks were deposited in various depositional environments: alluvial-plain, delta, swamp, and lacustrine environments and stacked one upon the other because repeated transgression and regressions shifted facies and stacked sedimentary rocks in cyclic sequences. In coastal wetlands and swamps adjacent to the rivers, vast quantities of peat accumulated, that later turned into coal seams. Why tropical? Concept of Plate Tectonics explains geographic location of Pennsylvania about 5-10° south of the equator. Most structures in the rocks of Pennsylvania are related to plate-tectonic activity; rifting and convergence resulted in three orogenies. Folds, normal and thrust faults rise through stratigraphic sequences of Allegheny Mountains and Valley and Ridge province. Pleistocene ice sheets advanced into NW Pennsylvania from Erie sculptured the landscape forming erosional and depositional features, changed the drainage pattern of major streams, and established periglacial conditions south to the glacial edge. Coastal process shaped the Lake Erie shoreline in Holocene. This brief geologic history of Western PA along with numerous environmental concerns related to floods, slope failures, coal mining, oil and gas industry, coastal erosion, water pollution, waste management could be discussed in many geology courses, tied into a week long field course, or one day field trips to supplement geology curricula.