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Reconstructing Paleoflow of Glacial Fluvial Systems in Crawford County Background 11,700 years ago the Wisconsonian glacier receded out of North America leading to the end of the Pleistocene epoch. Methods Results • The gravel pits were located initially on maps found on www.usgwarchives.net/maps/pa/county/crawfo/usgs/ then later confirmed on google earth. • Once at a gravel pit there were observations needing to be made. The 2 most important observations pertaining to this research; Bedding and strike/dip directions. • Among the field sites where imbrication was collected, there is consistent south-directed paleoflow • These data reveal that present-day southward drainage is inherited from the Pleisticene systems. • Due to the lack of sites with visible/ measurable clast imbrications, an accurate map of the paleoflow in Crawford County cannot be made. Thomas Hunter ‘17 Professor Ron Cole Geology Department • As glaciers transgress, rocks that come in contact with the glacier are scraped up and moved along with the glacier. • As glaciers regress, the ice melts and forms meltwater streams. • All rocks suspended in the glacier would be deposited. • The meltwater streams that occurred in Northwest Pennsylvania were braided river systems. A braided river in New Zeland (left) http://braidedchannels.wikispaces.com/ Glaciers should be thought of as “a river of ice” Bucher glacier Alaska (below) http://pubs.usgs.gov/ • The rocks deposited by the glacier will then be moved by the meltwater streams. • The rocks under a constant current will eventually become oriented by the current in the way that the current flows over them easily (Rust, 1972b). • The current orients most of the rocks in the same way, this is known as clast imbrication. 2D Diagram of how clast imbrication occurs in a river bed. all-geo.org • After many years the river bed is buried under other sediments, with the clast imbrications preserved • The modern day gravel industry can flourish in Crawford County because of these deposits. • In order to reach the gravel, excavation is required, the areas where there is excavation are known as gravel pits. • Gravel pits give geologists a unique opportunity to see a cross section of glacial and fluvial (river) deposits. Clast imbrications can be seen at this gravel pit in Bloomfield Township (Hunter- Miller) Field Observation Checklist (left) Lenticular bedding can be seen at the Hunter- Miller pit near Union City (right) • The bedding can help signify what kind of depositional environment the rocks were deposited. • Braided rivers leave behind lenticular beds. • Strike/ dip is a measurement of a rocks orientation while still in formation (undisturbed in the ground). • A Brunton compass is the tool that is used for this measurement. • In order for this measurement to work the clasts must be flat (not rounded). • Once the strike/ dip data was taken, it had to be analyzed. • The paleoflow direction would be exactly 180 degrees from the dip direction. • All of the paleoflow data would then be used to generate a rose diagram using the program on http://www.yongtechnology.com/yong-lab/online-rose-diagram/. • A rose diagram will show the paleoflow vectors for a site • A rose diagram was made for each site where imbrication data is found. An Unexpected Problem There are 35 mines in Crawford County, though this sounds great for the research, the problem wasn’t how many mines there were. The problem was that most mines didn’t have lenticular beds or clast imbrications. The reasons for a site not having good data includes; reclaimed, bedrock mine, till/ sand, rounded clasts, no permission to enter the site. Overall there ended up only being 5 gravel pits that gave conclusive data for this research. A reclaimed gravel pit in Richmond Township (Gravel Run Road)(Left) A Bedrock Mine in Oil Creek Township near Hydetown (Donovan)(top) Abstract: Constructing a map of the paleoflow of glacial fluvial systems will help in the estimation of where new economically beneficial resources such as sand, gravel, and potential aquifers may be. The paleoflow direction will be determined by inverting the dip direction of imbricated clasts of pebble to cobble sized gravel (as discussed in [Rust,1972a]). A Brunton compass (top), a level (bottom left), and a GPS (bottom right) were tools used to make field observations. • This rose diagram shows the paleoflow vectors at the Hunter- Miller pit • The average paleoflow vector at this site was 206 degrees from North • The chart shows the average paleoflow direction for all of the pits Pit Average Paleoflow Vector General Com passDirection Hunter 205SW Hunter-Miller 206SW Infield 198.5SW Centerville-Miller 152SE Hillside 198.5SW Acknowledgments Funding: •Allegheny College •Christine Scott Nelson Faculty Support Fund Technical support: •Professor O’Brien Field sites: •R. Hunter Inc. •Glover Sand and Gravel •Hillside Stone •Centerville Sand and Gravel •Lakeland Construction •Hasbrook Sand and Gravel •Kosurick Construction References •Dahms, D.E., 2002, Glacial stratigraphy of Stough Creek Basin, Wind River Range, Wyoming: Geomorphology, v. 42, p. 59-83, doi: 10.1016/S0169-555X(01)00073-3. •DeCelles, P., Langford, R., and Schwarz, R., Two New Methods of Paleocurrent Determination from Trough Cross-Stratification: , 629-643 p. •Rust, 1972a, Pebble Orientation in Fluvial Sediments: Journal of Sedimentary Petrology, v. 42, p. 384-388. •Rust, 1972b, Structure and Process in a Braided River: Sedimentology, v. 23, p. 213-234. •van Rensbergen, P., de Batist, M., Beck, C., and Chapron, E., 1999, High-resolution seismic stratigraphy of glacial to interglacial fill of a deep glacigenic lake: Lake Le Bourget, Northwestern Alps, France: Sedimentary Geology, v. 128, p. 99-129, doi: 10.1016/S0037-0738(99)00064-0. •Glacial Facies. (1984). In R. Walker (Ed.), Facies Models, Second Edition (2nd ed., Vol. 1, pp. 19-26). Hamilton, Ontario: Geological Association of Canada. •Compton, R. (1985). Chapters 9 & 10. In Geology in the Field (1st ed., Vol. 1, pp. 169-176, 203-206). New York, New York: John Wiley & Sons. •Schiner, G., & Gallaher, J. (1979). Groundwater. In Geology and Groundwater Resources of Western Crawford County, Pennsylvania (1st ed., Vol. 1, pp. 8-11). Harrisburg, Pennsylvania: United States Geological
