FLUVIAL SEDIMENTOLOGY AND ARCHITECTURE OF THE CATSKILL AND HUNTLEY MOUNTAIN FORMATIONS, NORTH-CENTRAL PENNSYLVANIA, USA

Thick successions of Upper Devonian fluvial strata accumulated in the Appalachian foreland basin during the Acadian Orogeny, but the internal and external controls on the morphology of the rivers and basin infilling remain unclear. This study assesses upsection changes in the sedimentology, channel geometry, and stratigraphic architecture of the upper Catskill Formation and the lower Huntley Mountain Formation near Blossburg, Pennsylvania, using field-based lithofacies observations, high-resolution panoramic photographs, and terrestrial lidar scanning.

Low in the transition stratigraphy, floodplain deposits contain red mudrock with abundant desiccation cracks, pedogenic features (rootlets, slickensides, and caliche nodules), and crevasse splay deposits. Pedogenic features and crevasse splay deposits are less abundant higher in the stratigraphy. Sandstone bodies transition upsection from 1-3 m thick, very fine- to fine-grained, single-story lenses to 6-26 m thick, fine- to medium-grained, multi-story lenses. Evidence for significant upsection changes in channel morphology is lacking; channel depths measured from bar clinoform heights range from 0.9-2.6 m and dune heights range from 0.15-1.05 m throughout the section. However, subtle upsection increases in grain size, horizontal stratification, and mudstone rip-up layers indicate higher flow velocities consistent with a gradually steepening paleoslope. Moreover, upsection increases in channel stacking suggest a change in avulsion frequency or avulsion pattern, possibly in response to a decrease in basin accommodation and the effects of regional glaciation documented previously in coeval proximal strata. Finally, the upsection decrease in paleosol development and splay deposition suggests that the avulsion style changed from a crevasse-prone system that avulsed progradationally through levee breaches to a system prone to avulsing via floodplain incision. The observed upsection changes may help explain a distinct upsection decrease in the abundance and diversity of fish fossils in the stratigraphy. Collectively, these results document a gradational change in fluvial processes during latest Devonian basin infilling.