ICHNOLOGY RELATED TO PALEOPEDOLOGY AND ECOLOGICAL SUCCESSION IN THE UPPER DEVONIAN CATSKILL FORMATION (FAMENNIAN–FRASNIAN) OF NORTH-CENTRAL PENNSYLVANIA, USA: DEVONIAN SOIL ORGANISMS AND INITIATION OF SOIL ECOSYSTEM ENGINEERING

The Catskill Formation (CF) of northcentral Pennsylvania comprises a thick succession of alluvial deposits pedogenically modified to varying degrees. Mudstones are finely laminated, weakly laminated to weakly blocky, massive, or thoroughly churned with angular blocky or prismatic peds, abundant caliche, and small- to large-scale pedogenic slickensides with a variety of trace-fossil associations (TFA). Channel deposits are low-angle to trough crossbedded and contain various TFA, depending on degree of pedogenesis. TFA are characterized by small backfilled burrows, Beaconites, lungfish burrows, Diplichnites, 1–30-mm-diameter rhizoliths and rare in situ tree stump casts. Finely laminated mudstones contain abundant 1–3-mm-diameter rhizoliths, rare small backfilled burrows, and Beaconites. Weakly laminated mudstones contain abundant 1–5-mm-diameter rhizoliths, small backfilled burrows, Beaconites, and lungfish burrows. Thoroughly churned mudstones contain rare backfilled burrows and lungfish burrows, and abundant 1–10-mm-hematitic rhizoliths, carbonate rhizoliths, and 10–30-mm-diameter gleyed, sediment-filled rhizoliths. Differences in trace-fossil abundances based on paleosol development indicate environmental tolerances of soil organisms and stages of ecological succession within channel–overbank deposits. The greater abundance of burrows, the greater the degree of pedogenesis when comparing well-laminated to structureless mudstone. Rarity of burrows in well-developed paleosols resulted from destruction by bioturbation and abiotic pedoturbation. CF traces represent behaviors that facilitated ecological succession by contributing to aeration, mixing, nutrient availability, and improved drainage of soils. The intimate relationship between TFA and paleopedogenesis represents the initiation of ecosystem engineering of alluvial settings by soil biota. Ecosystem engineering—beneficial modification of the physicochemical environment by organisms—has long been recognized as a driving force of ecological succession in continental ecosystems. Fossil evidence of ecosystem engineering has been recognized in Mesozoic and Cenozoic paleosols of North America; however, it has not been proposed for middle Paleozoic deposits until now.