42-7 An Integrated Sedimentological-Ichnological-Paleontological Study Reconstructs Coastal Depositional Systems of the Late Devonian Lock Haven Formation, West Burlington, North-Central Pennsylvania

Session: Paleozoic Events and Processes: Sedimentary Geology, Paleontology, and Geochemistry (Posters)

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Abstract:

The Lock Haven Formation (LHF) in north-central Pennsylvania preserves abundant sedimentary features, palynomorphs, trace fossils, and body fossils, including fishes, making this region ideal for reconstructing paleoenvironments that hosted the fin-to-limb transition and initial arborescence. However, integrated sedimentological-ichnological-paleontological studies on the LHF are rare. A recently exposed 46 m thick quarry succession in West Burlington, Pennsylvania, reveals three lithofacies associations yielding middle to early late Famennian palynomorph-acritarch assemblages. Lithofacies association I consists of heterolithic grey mudstone, sandstone, shale, and shelly sandstone with flaser-wavy-lenticular bedding, symmetrical-asymmetrical-interference ripples, cross-stratification with mud drapes, mud-chip clasts, microbial mats, acritarchs, transported terrestrial plant fragments, abraded brachiopod and arthrodire placoderm body fossils, and diverse aquatic trace fossils, including Archaeonassa, Beaconites, Bergaueria, Conichnus, Cruziana, Cylindrichum, Didymaulichnus, Dimorphichnus, Diplichnites, Gordia, Ichnocumulus, Imbrichnus, Kouphichnium, Limulichubichnus, Lockeia, Lophoctenium, Merostomichnites, Monomorphichnus, Nereites, Olivellites, Paleomeandron, Palaeophycus, Parataenidium, Planolites, Protovirgularia, Rhizocorallium, Rusophycus, Sagittichnus, Scolicia, Taenidium, Teichichnus, Thalassinoides, Treptichnus, and Undichna. Lenticular packages, 1 to 22 m wide and 1.5 to 2.5 m tall with concave basal bounding surfaces overlain by sigmoidal clinoforms. Fully preserved bar deposits exhibit clinoform sets with bar-top rollover whereas partially preserved bar deposits lack bar-top rollover and may be truncated by a scour surface. This association records bidirectional tidal currents, slackwater, and minor wave influence in subtidal to intertidal flats, bars, and channels. Lithofacies association II consists of heterolithic olive-grey mudstone and red-grey sandstone with planar laminae, hummocky-swaley bedding, acritarchs, Teichichnus, Fucusopsis, and abraded brachiopod, crinoid, and arthrodire body fossils. This association records tidal and wave processes in subtidal bar environments. Lithofacies association III consists of red sandstone, shale, and mudstone with rhizohaloes, rhizoliths, cross-stratification, Lockeia, Scoyenia, and body fossils of Lingula, Holoptychius lobe-finned fish, and Bothriolepis placoderms. This association records suspension settling, unidirectional currents, and soil development in partly vegetated coastal plain environments. Rhizoliths include large-diameter (≤ 10 cm), vertical, primary and secondary taproots that extend to depths of 2 m and crosscut both fluvial and tidal deposits; deeply vertically penetrating roots are extremely rare in Devonian strata. Overall, deposition was in a tide-dominated coastal plain environment. This is also supported by palynology assemblages containing a minor marine component in a relatively locally derived low-diversity terrestrial miospore assemblage with one or two dominant species. Additionally, kerogen types are all terrestrial.

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