PALAIOS, 2011, v. 26, p. 639–657 Research Article DOI: 10.2110/palo.2010.p10-121r FISHES AND TETRAPODS IN THE UPPER PENNSYLVANIAN (KASIMOVIAN) COHN COAL MEMBER OF THE MATTOON FORMATION OF ILLINOIS, UNITED STATES: SYSTEMATICS, PALEOECOLOGY, AND PALEOENVIRONMENTS DAVID CARPENTER,1 HOWARD J. FALCON-LANG,2* MICHAEL J. BENTON,1 and W. JOHN NELSON 3 1Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK, [email protected], [email protected]; 2Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK, [email protected]; 3Illinois State Geological Survey, Champaign, Illinois 61820, USA, [email protected] ABSTRACT sedimentation are dominant in Pennsylvanian successions in Euramer- ica (Wanless and Weller, 1932), reflecting coupled fluctuations in A newly discovered vertebrate assemblage is reported from the Upper climate and sea level (Tandon and Gibling, 1994) linked to Gondwanan Pennsylvanian (mid- to upper Kasimovian) Cohn Coal Member of the glacial–interglacial cycles (Fielding et al., 2008a, 2008b; Falcon-Lang et Mattoon Formation of southeast Illinois, United States. Teeth, scales, al., 2009). With paleoenvironments rapidly oscillating between fresh, and spines of xenacanth (Dicentrodus, Orthacanthus, Triodus, Xena- brackish, and marine conditions in space and time (e.g., Hampson et canthus) and euselachian (Sphenacanthus) sharks dominate the assem- al., 1999; Falcon-Lang, 2004, 2005), unusually precise geologic control blage. Less common are the teeth, scales, and centra of holocephalan of assemblages is required to determine habitat salinity. Notable (Helodus) and actinopterygian fishes, together with rare tetrapod (mainly examples of such analyses include the classic studies on faunal pelycosaur) phalanges and centra. The assemblage occurs within a broad, distribution in vertical profiles through British marine bands (Calver, shallow channel incised into a prominent Vertisol. The channel is 1968), or the identification of a salinity gradient from brackish interpreted as having been cut during a seasonally dry glacial phase nearshore to marine offshore assemblages in the Mazon Creek estuary when sea level was low, but filled during a subsequent transgression (Baird, 1997a, 1997b, 1997c). triggered by deglaciation. We interpret this as a brackish water In this paper, a new assemblage of Pennsylvanian fishes, together (estuarine) assemblage, based on the co-occurrence of the vertebrate with some rare tetrapods, is reported from the Friendsville Mine of material with spirorbids (putative microconchids) and paleoecological Illinois, United States (Fig. 1). In addition to describing vertebrate inferences gleaned from a critical analysis of the literature dealing with systematics, an analysis of the facies context, sequence stratigraphy, Pennsylvanian fish ecology. This interpretation is broadly consistent with taphonomy, and 87Sr/86Sr isotope geochemistry of the vertebrate 87 86 taphonomic data and the results of Sr/ Sr isotope analysis of shark assemblage is presented. These data, combined with a critical review material. The pelycosaur material may have been reworked from the of the literature concerning the geological context of Pennsylvanian lowstand Vertisol, however, and these animals occupied dryland niches fishes, allow assessment of paleoenvironments and paleosalinity, in that developed during glacial phases. particular, and provide a firm basis for interpretation of fish paleobiology and paleoecology. INTRODUCTION Fish assemblages have been widely reported from the Pennsylvanian GEOLOGICAL SETTING of Euramerica (e.g., Agassiz, 1837–1843; Traquair, 1881; Fitsch, 1889; The vertebrate fossil assemblage from the Friendsville Mine comes Woodward, 1891; Zidek, 1978; Zangerl, 1981; Schultze, 1985; Soler- from an incised channel below the Cohn Coal, a member of the middle Gijo´n, 1997; Calder, 1998; Hampe, 2003; Johnson and Thayer, 2009), Missourian to Virgilian Mattoon Formation (Nance and Treworgy, but in many cases relatively little attention has been given to their 1981). In earlier reports, this coal was termed the McCleary’s Bluff Coal paleoenvironmental context and paleoecology (see Zangerl and (Kosanke et al., 1960). Regional correlation based on borehole cores, Richardson, 1963; Baird et al., 1985a, 1985b for notable exceptions). however, shows that it is equivalent to the type Cohn Coal in Clark Traditionally, Pennsylvanian fishes have been classified either as marine County, Illinois, 110 km north of the Friendsville Mine (W.J. Nelson, or nonmarine (Calder, 1998), the latter often taken to mean freshwater unpublished data, 2009). Although the two coals are no longer (Dick, 1998). In very many cases, the mere absence of an associated continuous following erosion across the La Salle Anticlinorium, stenohaline fauna and the co-occurrence of plant fossils have been cited correlation is beyond reasonable doubt because the prominent as sure evidence for a freshwater habitat (Hook and Baird, 1988; Hook Livingston Limestone and Eudora Shale bracket the coals in both and Ferm, 1988; Sander, 1989). Many such analyses, however, overlook areas (Heckel, 2008). As the name Cohn Coal (Newton and Weller, the importance and widespread distribution of Pennsylvanian brackish 1937) has priority over McCleary’s Bluff Coal (Kosanke et al., 1960) we water settings, e.g., commonly encountered in estuaries, interdistribu- use the former stratigraphic term. tary bays, and even certain epicontinental seas (Buatois et al., 1998; The Cohn Coal can be tied precisely to global Carboniferous Schultze, 1998; Falcon-Lang, 2005). Advances in the understanding of stratigraphy, based on the biostratigraphy of bracketing marine units tidal deposits (Kvale et al., 1989), invertebrate salinity tolerances (Fig. 2; Gradstein et al., 2004; Heckel, 2008; Davydov et al., 2010; (Calver, 1968; Bennett, 2008), and ichnology (Archer et al., 1995; Falcon-Lang et al., 2011). As noted above, the Cohn Coal occurs just Buatois et al., 2005) now permit recognition of such brackish facies in above the widespread marine transgressive unit termed the Livingston the rock record (Schultze, 2009). Limestone (Willman et al., 1975). This unit is positioned two major Nonetheless, determining paleosalinity for Pennsylvanian fish 400 ka cyclothem groups (Iola Group) below the top of the Missourian assemblages is particularly challenging. Cyclothemic patterns of regional stage in North America (Heckel, 2008). The Livingston Limestone and its lateral equivalents can be correlated, based on * Corresponding author. conodont biostratigraphy, throughout the Midcontinent, Illinois, and Copyright G 2011, SEPM (Society for Sedimentary Geology) 0883-1351/11/0026-0639/$3.00 640 CARPENTER ET AL. PALAIOS overlying Cohn Coal interval is of mid- to upper Kasimovian age (,304 Ma) and may be broadly time-equivalent to the mid-Stephanian (Barruelian) of western Europe. GEOLOGY OF FRIENDSVILLE MINE, ILLINOIS The Friendsville Mine is located 9 km west northwest of Mount Carmel in Wabash County, southeast Illinois, United States (Latitude 38u269280N; Longitude 87u519470W; Section 9, T1S, R13W, Wabash County, Mount Carmel 7.59 quadrangle map). Operated by the Vigo Coal Company, it comprises a 1.8-km-long highwall oriented N–S and advancing to the east. We studied the geology in the course of three visits on 14 June 2005, 19 August 2008, and 26 January 2009. In the course of the latter visit the vertebrate remains were discovered. Sedimentary Facies In the Friendsville Mine, a 19.5-m-thick succession is accessible in multiple benches and comprises part of the lower Mattoon Formation. Five main depositional units were recognizable during our site visits (Fig. 3). Unit 1: The lowermost unit currently exposed is the 0.7–1.1-m-thick Friendsville Coal, a low pyrite, dull-banded, semibituminous coal with a stigmarian seat earth. This comprises the Vigo Coal Company’s main target coal and forms the floor of the strip mine. FIGURE 1—Location of Friendsville Mine in United States (inset map) and Wabash Unit 2: Sharply overlying the Friendsville Coal is a complex body of County, southeast Illinois, near the border with Kentucky and Indiana, United States laterally variable facies about 9 m thick. This succession is dominated (modified from Falcon-Lang et al., 2009). The outcrop belt of Pennsylvanian rock is over much of the length of the highwall by medium- to dark-gray, shown (gray). heterolithic, rhythmically laminated shale, which coarsens upward. Features include flaser lamination, symmetrical ripples, siderite Appalachian basins of North America (Heckel, 2008) and into the nodules, and a rich ichnofauna of Cochlichnus, Arenicolites, and Moscow and Donets basins of eastern Europe (Falcon-Lang et al., Lockeia. Along strike, especially within scoured surfaces, however, 2011), where the global stratotypes are defined (Davydov et al., 2010). sediments may grade up into very fine to fine-grained, thinly bedded, This correlation suggests that the Livingston Limestone and the sandstone showing cross ripple lamination, soft-sediment deformation, FIGURE 2—Stratigraphic position of the Missourian (mid- to upper Kasimovian) Cohn Coal in relation to regional and global stratigraphy (after Heckel et al., 2007; Heckel, 2008; Davydov et al., 2010; Falcon-Lang et al., 2011). Dotted boundaries between European units reflect that these are dominantly terrestrial (t) sections that cannot be correlated, with certainty, to the marine global stratotypes