| Autor: |
KURAK, E., PAZZAGLIA, F. J., LI, C. X., PATCHING, A., SHAULIS, J., CORBETT, L., BIERMAN, P., NELSON, M., RITTENOUR, T. |
| Předmět: |
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| Zdroj: |
Guidebook for the Annual Field Conference of Pennsylvania Geologists; 2021, Issue 85, Special section p51-73, 23p |
| Abstrakt: |
New surficial mapping and dating of alluvial deposits along the Youghiogheny River in southwestern Pennsylvania has generated a new terrace stratigraphic model linking well-known deposits of the Carmichaels Formation with terraces further upstream through Ohiopyle State Park. Flights of four to six terraces are found in three distinct zones with gradients that are subparallel to the channel, including a steep convex reach of the river. Numeric ages obtained from 25 terrestrial cosmogenic nuclide (TCN) samples and one optically stimulated luminescence (OSL) sample constrains the timing of terrace genesis on the Youghiogheny River, over the past 1.2 Ma, with terrace deposition coinciding with glacial climates. TCN burial and isochron ages of ~610 ka and ~300-350 ka are used to construct long-term incision rates ranging from ~20 m/Myrs upstream of Ohiopyle where the channel gradient and subparallel terrace profiles are gentle to ~50 m/Myrs downstream of Ohiopyle where the river profile is steeper in a broad convex knickzone. There were at least two base level falls totaling ~81 m conflated in the knickzone between Ohiopyle and Connellsville, the top of which includes Ohiopyle Falls and is retreating at a rate of ~1 cm/yr. Of the total base level fall, ~45 m is likely attributed to the draining of Glacial Lake Monongahela and formation of the Ohio River now dated at ~1.8 Ma by TCN burial ages on type-Carmichaels lacustrine facies exposed along the river in the Pittsburgh low plateau. The other ~36 m is attributed to non-uniform uplift of the Laurel Highlands, with a hinge more or less at Connellsville, which may be ongoing. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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