Ichnology of transgressive-regressive surfaces in mixed carbonate-siliciclastic sequences, Early Permian Chase Group, Oklahoma

Early Permian rocks of the Chase Group in north-central Oklahoma consist of repeated couplets of carbonates and clastics. The carbonates and clastics correlate to major transgressive and regressive events, respectively. Regressive parts of the depositional couplets consist of thicker (10–40 m [33–131 ft]), more clastic-rich marginalmarine and/or continental facies dominantly composed of red and green mudstones and/or shales locally capped by exposure surfaces and paleosols. Transgressive parts of the couplets consist of thinner (1–20 m [3–66 ft]), more carbonate-rich marine and marginal-marine facies dominantly composed of shallowing-upward units of coatedgrain, fossiliferous wackestones, packstones, and grainstones. The sole of the lowest (first) transgressive carbonate bed of each depositional couplet is covered with ubiquitous horizontal boxworks of the trace fossil Thalassinoides isp. These burrow systems were constructed as excavations into the underlying regressive mudstones and occur at a discontinuity surface at the culmination of a major regressive event and the initial onset of a major transgressive event. Horizontal forms of the trace fossil Rhizocorallium isp. characterize the top bedding-plane surface of the highest (last) carbonate unit of each couplet, and mark the discontinuity surface at the culmination of a major transgression and the initial onset of a major regression. These trace-fossil associations are assigned to the substrate-controlled Glossifungites ichnofacies. In the Early Permian Chase Group of north-central Oklahoma, this ichnofacies is dominated by the ichnogenera Thalassinoides and Rhizocorallium in association with Diplocraterion, Arenicolites, Chondrites, Teichichnus, and Planolites. The Glossifungites ichnofacies, at least in this particular geographic and stratigraphic setting, characterizes discontinuity surfaces that correlate to hiatuses in deposition, typically concomitant with shallow-water erosion associated with transgressiveregressive events.