IDENTIFYING BASE LEVEL CHANGES OF THE UPPER ORDOVICIAN JUNIATA FORMATION THROUGH STACKING PATTERN ANALYSIS

The Upper Ordovician Juniata Formation consists of interbedded grayish red sandstone and mudstone. Observed sedimentary structures such as cross-bedding, convolute bedding, and flaser bedding have been previously interpreted as marginal marine features, while potential pedogenic features within the mudstones are indicative of soil formation and have been previously interpreted as terrestrial. The apparent ambiguity in depositional setting poses a challenge to placing interpreted well-preserved clay-filled burrows into a paleoenvironmental context. This study uses an exposure of the Juniata Formation along Rt. 322 in Potters Mills, PA to propose a transitional depositional environment with fluctuations in sea level resulting in shifting marine-to-terrestrial influences. Given the conformable nature of this succession, we apply here a Fluvial Aggradation Cycle (FAC) methodology to evaluate changes in accommodation and base level. Given the marginal marine/terrestrial transitional nature of the depositional environment, we infer any changes in accommodation as related to base-level and thus sea level. The studied roadcut is over 500 meters in length, exposing upwards of 20 meters of vertical succession. We have identified 16 potential FACs representing floodplain aggradation and 3 FAC sets that are indicative of fluvial stability through detailed measurements of bedding thickness and grain size analysis. Stacking pattern analysis reveals a cyclicity within these FAC sets that represents a potential alluvial sequence boundary. An understanding of base level changes is compared with not only sedimentary structures but also the identified trace fossils for a more holistic interpretation of the depositional environment at this location. Additionally, an understanding of this stacking pattern of FACs and FAC sets will allow future correlation across different Juniata Formation sites.