2000 GSA Annual Meeting -- Reno, Nevada

Abstract 50281

CLASTIC SEDIMENTS IN A LONG-TERM KARST TRAP, VALLEY AND RIDGE, CENTRAL PENNSYVLANIA

Presented by Kempthorne, Rebecca A.
Authors:
      Sasowsky, Ira D.,
      Crowell, Bryan,
      Walko, Selena M.,
      LaRock, Edward J.,
      Harbert, William.

Key words: karst, sediments, Pennsylvania, geomorphology, Kooken-Cave

In Session 9     Quaternary Geology and Geomorphology (Posters) Monday, November 13, 2000 AM in Room: Hall C at 08:00 AM for .

Abstract: Clastic sediments deposited within karst voids (caves) have the potential to record useful geomorphic and paleohydraulic information, particularly at timescales between 0 and 4 Ma. Long-term, uninterrupted deposits are the most desirable. Kooken Cave is located in the Appalachian Mountains near the western margin of the Valley and Ridge physiographic province, and contains the thickest sediment deposits of any cave in the region. To understand their significance, we examined the hydrology, stratigraphy, and magnetostratigraphy of the cave.

Influent waters from nearby surface streams enter the cave via swallets. At high stage, the karst groundwater system is unable to accommodate all of the flow, and the cave floods and stagnates. This causes the deposition of stream-borne sediments within the cave, further occluding the drainage. Water eventually drains through the cave to the Little Juniata River. Fifteen meters of sediments were measured and examined in the cave. The lower 2 m of sediments found in the cave are cobbles, sand, and clay. The remainder of the section is clay. The lower sediments resulted from initial invasion of surface waters into the cave. The subsequent sediments result from annual-scale flooding. Twenty-four paleomagnetic samples were collected from the column. All samples showed normal polarity, indicating deposition within the present chron (<780 ka). Declinations were generally eastward of the present-day field, and represent paleosecular variation. Inclinations show compactional shallowing. Based on rough calculations of sediment accumulation, the entire column could have accumulated in as few as 1,440 years. However, geomorphic considerations suggest that the trap may have been active for 100's of ka or more, and that it contains a long-term record of erosional history.

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