Ichnology of the Upper Mississippian Hartselle Sandstone of Alabama, with notes on other Carboniferous formations

The Hartselle Sandstone of northern Alabama contains a diverse suite of trace fossils, comprising 23 ichnospecies. This report focuses on their description, distribution, and environmental significance. Four additional species from the subjacent Pride Mountain Formation are described. New ichnotaxa include Lockeia cordata n. isp., Rusophycus hartselleanus n. isp., Cymataulus undulatus n. igen. n. isp., Hartsellea sursumramosa n. igen. n. isp., and Uchirites implexus n. isp. The sandstone was deposited as a strandplain complex that was later reworked as sealevel rose. The lower part consists mainly of thickly bedded beach to shoreface sandstone and is virtually unbioturbated. The upper part consists largely of wavy-bedded back-barrier to shelf sandstone with four trace-fossil assemblages representing different paleoenvironments. Back-barrier tidal flat and lagoon deposits have trace-fossil assemblages dominated by bivalve traces that represent marine to brackish environments. Marginal-marine sandstone contains chiefly monospecific assemblages and is reworked by bivalves and unknown organisms; Lockeia, Uchirites, and Rosselia are dominant at different sites. The Lockeia assemblage includes bedding surfaces with crowded bivalve resting traces. The abundance, density, and small size of monospecific burrows suggests estuarine conditions with high food supply and rapid larval colonization. The Uchirites assemblage is characterized by bivalve trails, representing probably brackish substrates with a high sedimentation rate. Shelf sandstone and shale include bivalve resting traces and trails (Lockeia ispp., Uchirites implexus, Walcottia rugosa, and W. imbricata), asteroid and ophiuroid resting traces (Asteriacites stelliforme and Pentichnus pratti), trilobite resting traces and trackways (Rusophycus hartselleanus and Petalichnus isp.), and dwelling burrows, feeding burrows, trails, and trackways of unknown organisms (Cymataulus undulatus, Hartsellea sursumramosa, Phycodes isp., Haplotichnus isp., Rosselia isp., Planolites montanus, Nereites missouriensis, Tasmanadia twelvetreesi, and Petromonile benstedii).