Geological Society of America 3300 Penrose Place P.O. Box 9140 Boulder, CO 80301 (303) 357-1000 • fax 303-357-1073 www.geosociety.org Chapter 16: “Appalachian sedimentary cycles during the Pennsylvanian: Changing influences of sea level, climate, and tectonics” (Greb et al.), in Fielding, C.R., Frank, T.D., and Isbell, J.L., eds., Resolving the Late Paleozoic Ice Age in Time and Space: Geological Society of America Special Paper 441. This PDF file is subject to the following conditions and restrictions: Copyright © 2008, The Geological Society of America, Inc. (GSA). All rights reserved. Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. Individual scientists are hereby granted permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in other subsequent works and to make unlimited copies for noncommercial use in classrooms to further education and science. For any other use, contact Copyright Permissions, GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA, fax 303-357-1073, [email protected]. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. This file may not be posted on the Internet. The Geological Society of America Special Paper 441 2008 Appalachian sedimentary cycles during the Pennsylvanian: Changing infl uences of sea level, climate, and tectonics Stephen F. Greb Kentucky Geological Survey, University of Kentucky, Lexington, Kentucky 40506, USA Jack C. Pashin Geologic Survey of Alabama, Alabama State Oil and Gas Board, Tuscaloosa, Alabama 35486, USA Ronald L. Martino Department of Geology, Marshall University, Huntington, West Virginia 25755, USA Cortland F. Eble Kentucky Geological Survey, 228 MMRB, University of Kentucky, Lexington, Kentucky 40506, USA ABSTRACT Various orders of marine fl ooding surface–bounded depositional sequences are recognized in coal-bearing, Pennsylvanian-age strata of the greater Appa- lachian Basin. The best preserved of these from the Lower Pennsylvanian are in the southern and central Appalachians; Middle Pennsylvanian cyclothemic sequences are best preserved in the central Appalachians; and Upper Pennsylvanian cyclo- themic sequences are best preserved in the northern Appalachians. Palynological and litho strati graphic correlations to global time scales have been used to infer eustatic controls on accumulation of cyclothem-scale sequences in each of these areas, albeit with signifi cant tectonic and climatic overprints. New U-Pb absolute age dates from upper Lower Pennsylvanian and Middle Pennsylvanian tonsteins in the central basin can be used to infer an average maximum duration of 0.1 m.y. for minor transgressive-regressive depositional cycles, which supports the possibility of short eccentricity-driven eustatic infl uences on sedimentation. Although glacial eustasy infl uenced Pennsylvanian sedimentation throughout the basin, the thick- ness, lateral continuity, and constituent facies of high-frequency depositional cycles were strongly infl uenced by changing rates of tectonic accommodation in at least three depocenters, sediment fl ux, and changing paleoclimate. Keywords: Carboniferous, cyclothem, sequence, coal, eustasy. Greb, S.F., Pashin, J.C., Martino, R.L., and Eble, C.F., 2008, Appalachian sedimentary cycles during the Pennsylvanian: Changing infl uences of sea level, climate, and tectonics, in Fielding, C.R., Frank, T.D., and Isbell, J.L., eds., Resolving the Late Paleozoic Ice Age in Time and Space: Geological Society of America Special Paper 441, p. 235–248, doi: 10.1130/2008.2441(16). For permission to copy, contact [email protected]. ©2008 The Geological Society of America. All rights reserved. 235 236 Greb et al. INTRODUCTION The Appalachian Basin is one of the largest coal-producing regions in the world, with annual production of more than 390 million short tons. The vast coal resources and long history of mining have made this region a major focus of Carboniferous studies. One area of research that has received considerable attention through the years is the cyclothem concept and the idea that repetitive sedimentation patterns in the Appalachian Basin resulted from Gondwanan glaciation (e.g., Wanless and Shepard, 1936). Several orders of cycles have been reported in different parts of the basin (Busch and Rollins, 1984; Donaldson and Eble, 1991; Chesnut, 1992, 1994), and these have variously been inter- preted as resulting from glacial eustasy (e.g., Busch and Rollins, 1984), delta-lobe switching (e.g., Ferm, 1974), climatic changes (e.g., Cecil et al., 1985), and tectonic controls (e.g., Klein and Willard, 1989). In more recent years, sequence and genetic strati- graphic techniques have been used to defi ne and subdivide depo- sitional successions into lowstand, highstand, and transgressive sequences similar in scale to the allocycles of earlier workers (Aitken and Flint, 1994, 1995; Chesnut, 1994; Gastaldo et al., 1993; Martino, 1996; Pashin, 1998; Greb et al., 2004; Martino, 2004). The mechanism responsible for formation of these minor, cyclothem-scale depositional sequences, either in response to high-magnitude sea-level changes in the Milankovitch orbital eccentricity band (e.g., Heckel, 1994) or in response to the inter- action of eustasy and rapid tectonic accommodation (e.g., Pashin, 2004), may have depended on the age and position of the strata relative to basin depocenters. Widespread, fl ooding surface–bounded depositional units were best developed at different times across the Appalachian trend. Examples of Pennsylvanian strata from the Appalachians are described and compared in order to examine the relative infl u- ence of glacial eustasy, climate, and tectonics on sedimentation in different parts of the basin at different times in the Pennsyl- vanian. Estimates of cyclothem-scale duration based on new age dates in the central Appalachian Basin fall within the fi fth-order short eccentricity range, supporting glacial-eustatic infl uences analogous to those that have been active for the past two million years for some of these sequences. Tectonics and Depocenters The Appalachian foreland basin developed in response to thrust and sediment loading on the convergent margin of the Laurentian craton during the Acadian, Taconic, and Alleghanian-Variscan orogenies (Thomas, 1976, 1995; Tankard , 1986; Chesnut, 1991). Discrete depocenters developed along Figure 1. Isopach map (A) of Pennsylvanian strata in the greater Appa- lachian Basin (modifi ed from Wanless, 1975) and (B) generalized the Appalachian trend (Fig. 1A) cratonward of promontories cross sections across the basin (A–A′ modifi ed from Wanless, 1975; on the continental margin in the middle to late Mississippian B–B′ and C–C′ modifi ed from Chesnut, 1992; D–D′ and E–E′ from (Thomas, 1976, 1995; Quinlan and Beaumont, 1984). The Edmunds et al., 1999, and Wanless, 1975). greatest preserved thickness of Pennsylvanian strata, more than 2438 m (8000 ft), accumulated in the Cahaba coalfi eld of the greater Black Warrior Basin (Figs. 1A and 1B) in response to Appalachian sedimentary cycles during the Pennsylvanian 237 converging thrust and sediment loads in the Alabama recess Torispora secures–Vestispora fenestrate (SF) microfl oral zone of (Pashin et al., 1995; Pashin, 1997). Discrete coalfi elds in the Peppers (1996), and a 310–311 Ma age corresponds relatively greater Black Warrior Basin are in large synclinoria separated by well with the stratigraphic position of the coal based on palyno- thin-skinned folds and thrust faults. Although the Black Warrior morphs in recent time scales (Fig. 2). Recent U-Pb analyses Basin is largely a Ouachita foreland basin (e.g., Thomas, 1976, of zircons from the tonstein have yielded a slightly older date, 1995), a signifi cant fl exural depocenter formed adjacent to 314.6 ± 0.9 Ma (Lyons et al., 2006). The older age for the the Appalachian orogen during the early Pennsylvanian (e.g., same bed may indicate a discrepancy between dating methods Pashin, 1994a, 2004), and the coalfi elds of the greater Black that needs to be investigated. A 314 Ma age would make the Warrior Basin are typically considered to be Appalachian by the coal Langsettian, which is older than would be inferred from mining industry and in coal resource studies. palynomorphs (Fig. 2). The other bed that has been dated is the In the central Appalachian basin, more than 1000 m (4000 ft) Upper Banner coal, Norton Formation, of Virginia (Fig. 2). of Pennsylvanian strata are preserved in southeastern Kentucky The Upper Banner is in the Schulzospora rara –Laevigatosporites and southwestern Virginia (Figs. 1A and 1B). The central area desmoinensis (SR) microfl oral zone of Peppers (1996). U-Pb extends northward to the northern margin of the Rome Trough, analyses indicates a 316.1 ± 0.8 Ma date (Lyons et al., 1997; which is a late Proterozoic–Early Cambrian graben that formed Outerbridge and Lyons, 2006), which is toward the base of the during Iapetan rifting. The northern margin of the Rome Trough Langsettian and close to or older than ages that would be based acted as a hinge line throughout much of the Pennsylvanian, and on palynofl ora depending on the time scale used (Fig. 2). Pennsylvanian strata thicken southward into the central Appa- lachian depocenter (Donaldson