Tectonic implications of fluvial deposits associated with flood basalt volcanism, the Neoproterozoic Catoctin Formation, central Applachians, U.S.A.

DILLIARD, K. A.

The Catoctin Formation infills a Neoproterozoic rift basin associated with the development of the Laurentian continental margin, one of the many similar basins that are distributed along the length of the southern and central Appalachians. Stratigraphically, the Catoctin Formation records changes in greenstone volumes and characteristics of associated fluvial deposits which reflect variations in effusive and subsidence rates.

Two distinct facies associations, channel sheet types are recognized in the Catoctin Formation. The channel facies association (CFA) is restricted to the lower Catoctin Formation and is characterized by single channel geometries incised into basaltic flows and infilled with finning-upward sedimentary sequences. Facies in the CFA are indicative of tractional transport with conglomerates of local derivation. The younger sheet-sandstone facies association (SSFA) consists primarily of massive sandstone with diffuse horizontal stratification and subordinate trough cross and horizontal stratification. The massive sandstones are interpreted to be the product of hyperconcentrated flows, whereas trough and horizontal stratification reflect normal stream flow processes.

In the lower Catoctin Formation, the CFA sandstone are intercalated within numerous basalt flows, whereas the upper Catoctin Formation is primarily sheet sandstones (SSFA) with subordinate basalts. This stratigraphy reflects a change from high to low subsidence and effusive rates. The uppermost Catoctin Formation consists of basalts with minor sediment interbeds, which represents a return to high subsidence and effusive rates. This relatively complex infill pattern indicates varied subsidence and effusive rates during deposition, and suggests a complicated extensional history.

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D.J. Moore
Oct. 2002
Last modified Sept. 2004
moore@kutztown.edu

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