42-9 EXCEPTIONALLY DEEP, VERTICAL RHIZOLITHS IN COASTAL PLAIN PALEOSOLS, LATE FAMENNIAN LOCK HAVEN FORMATION, WEST BURLINGTON, NORTHCENTRAL PENNSYLVANIA: IMPLICATIONS FOR ATMOSPHERIC CO2, WEATHERING, AND THE EVOLUTION OF SOIL ECOSYSTEMS

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

Presenting Author:

Authors:

Abstract:

We report on 2-m-deep, vertically penetrating rhizoliths in deposits recently exposed in a 46-m-thick quarry exposure of the Upper Devonian Lock Haven Formation (Fm) in West Burlington, Pennsylvania (PA). These rhizoliths occur in pedogenically modified, interbedded ripple cross-stratified, red sandstone, mudstone, and shale; they include trace fossils Lockeia and Scoyenia, invertebrate fossil Lingula, and fish fossils of Holoptychius and Bothriolepis. Palynomorphs are dominated by a terrestrial miospore assemblage with a minor marine component. Together, these record a vegetated coastal plain environment in the transitional zone between continental and marine settings.

            Rhizoliths up to 10 cm in diameter exhibit a taproot morphology with a central, relatively straight, conical root that tapers downward to at least 2-m deep where they terminate. Secondary roots arcuately branch laterally greater than 1 m from the primary root, from a diameter of < 5 cm, tapering along their length. Tertiary roots branch from secondary roots and become fibrous in appearance. The root systems crosscut the fluvial and underlying interbedded fluvial and tidal deposits of the paleosol profile. The number of secondary roots decrease along the taproot; the number of tertiary roots increases away from the taproot. This depth is likely a minimum because the upper part was truncated by deposition of overlying strata and no associated surface or nearsurface, laterally extensive rhizoliths were observed.

            These rhizoliths are the deepest vertically penetrating recorded to date anywhere in the world during the Devonian. Previously reported deep Devonian rhizoliths include: 1) up to 1.5 m deep roots in fluvial strata of the Upper Devonian Catskill Fm, Trout Run, PA; 2) ~1.2–1.6 m deep roots in coastal plain strata of the Middle Devonian Plattekill Fm, Cairo, NY; and 3) ~90 cm deep roots in fluvial strata of the Lower Devonian Battery Point Fm, Canada.

            This discovery is significant because deep rooting further accelerated weathering of the soil profile––composed of rock and mineral fragments and secondary clay minerals––and enhanced the removal of atmospheric CO₂, which may have contributed to latest Famennian global cooling and glaciation. Deep rooting and increased abundance of secondary and tertiary roots created higher surface area to breakdown sediment and release nutrients. It also enhanced carbon sequestration and facilitated the evolution of soil ecosystems and the detritivore-nutrient cycling system.

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.