Sedimentological, Architectural, and Paleoenvironmental Analysis of the Fluvial Upper Devonian Catskill Formation, North-Central Pennsylvania, USA

During the Late Devonian time period, sediments eroded from the Acadian mountains were transported westward and deposited in fluvial environments, but the morphology of the rivers, avulsion style, and controls on basin infilling remain unclear. This study assesses the sedimentology, channel geometry, stratigraphic architecture, and avulsion style of the paleochannels and floodplains of the uppermost 80 meters of the Catskill Formation near Blossburg, Pennsylvania, using field-based lithofacies observations, high-resolution panoramic photographs, and terrestrial lidar scanning. Upper Catskill Formation strata at Blossburg Middle consist of sandy channel and muddy floodplain deposits. Floodplain deposits were categorized into either proximal floodplain deposits or distal floodplain deposits. Proximal floodplain deposits consist of interbedded mudstone and very fine-grained sandstone interpreted as crevasse splay and levee deposits. Distal floodplain deposits consist of red mudstone with desiccation cracks, rootlets, pedogenic slickensides, and caliche nodules. Floodplain scours are abundant within the distal floodplain deposits and indicate channelization on the floodplain. In the Blossburg Middle outcrop, single-story sand bodies (71% of channel bodies) are very fine- to medium-grained and cross-stratified. Multistory sand bodies occur high in the section and consist of similar sandstones that are separated by scours between individual stories. Paleochannel depths measured from bar clinoform heights range from 0.6 m to 3.5 m with median grain sizes from 59.93 μm to 204.58 μm (silt to fine sand). Paleoslope values range from 6.10 x 10-6 to 6.41 x 10-4, across the sampled interval, which is similar to very low slope modern rivers. Additionally, five of the channel bodies (71%) are consistent with progradational avulsion, while two of the channel bodies (29%) are consistent with incisional avulsion. These results suggest a mixed avulsion style system of these Late Devonian paleorivers. The well-preserved lenticular and ribbon channel bodies, sandy bedforms, abundant pedogenic features, and a crevasse splay deposits suggest that the upper Catskill Formation at Blossburg Middle represents a fine-grained meandering river system. There is no evidence for significant temporal changes in flow depth or paleoslope within the sampled stratigraphic interval. Integration of these results with those from a companion study (Filion, 2020) of the stratigraphically younger lower Huntley Mountain Formation at Blossburg South and Blossburg West document an upsection increase in channel depth and grain size