Ichnology and stratigraphy of the Crescent Valley Mine: evidence for a Carboniferous megatracksite in Walker County, Alabama

Early Pennsylvanian trace fossil-bearing deposits from the Crescent Valley Mine of Walker County in Alabama are correlated with those from the nearby Minkin Paleozoic Footprint Site. These represent end- members of a megatracksite that spans an environmental gradient from the inland, freshwater part of a deltaic
system at the Minkin site to more near shore environments at Crescent Valley, where variable salinity conditions and tidal processes prevailed. This is reflected by preservation of a depauperate ichnofauna at the Crescent Valley
mine. Recorded trace fossils are identified and interpreted as amniote trackways (Attenosaurus subulensis and Cincosaurus cobbi), apterygote insect trackways (Stiaria) and jumping traces (Tonganoxichnus), myriapod trackways (Diplichnites
-Diplopodichnus), invertebrate burrows (Arenicolites and Treptichnus), and bivalve resting traces (Lockeia). A continuum of trail morphologies from chevronate, to feather-stitch and leveéd forms is also observed. These are interpreted as recording the activities of juvenile xiphosurans and possibly bivalves in a shallow-water tidal environment. Arborichnus, present in deeper-water facies, is interpreted as recording the combined resting and swimming activities of adult xiphosurans. In contrast to the Minkin site,
Kouphichnium is absent. The spatial and environmental separation of these different trace fossils attributed to xiphosurans reflects that of different phases in their life cycles. The environmental distinction from the Minkin site may explain the apparent absence of temnospondyl amphibians. The fish-fin trace
Undichna is common at the Minkin site but absent from the Crescent Valley mine, which may be due to interrelated environmental and preservational conditions.