Lower–Middle Pennsylvanian Strata in the North American Midcontinent Record the Interplay Between Erosional Unroofing of the A

Home , Carbondale Formation, Caseyville Formation, Petersburg Formation, Shelburn Formation, Tradewater Formation

Research Paper

GEOSPHERE Lower–Middle Pennsylvanian strata in the North American midcontinent record the interplay between erosional unroofing of GEOSPHERE; v. 14, no. 1, p. XXX–XXX the Appalachians and eustatic sea-level rise doi:10.1130/GES01512.1 J.K. Kissock1, E.S. Finzel1, D.H. Malone2, and J.P. Craddock3 9 figures; 2 tables; 1 supplemental file 1Earth & Environmental Sciences, University of Iowa, 115 Trowbridge Hall, Iowa City, Iowa 52242, USA 2Department of Geography-Geology, Illinois State University, Normal, Illinois 61790-4400, USA 3Geology Department, Macalester College, St. Paul, Minnesota 55105, USA CORRESPONDENCE: [email protected]

CITATION: Kissock, J.K., Finzel, E.S., Malone, D.H., and Craddock, J.P., 2018, Lower–Middle Pennsyl- vanian strata in the North American midcontinent ABSTRACT INTRODUCTION record the interplay between erosional unroofing of the Appalachians and eustatic sea-level rise: Morrowan, Atokan, and Desmoinesian (Lower–Middle Pennsylvanian) Paleogeographic reconstructions of the Carboniferous North American Geosphere, v. 14, no. 1, p. 141–161, doi:10.1130/ GES01512.1. clastic strata in the Forest City (Iowa, northwest Missouri, eastern Nebraska, midcontinent have focused on Upper Pennsylvanian mixed carbonate-clastic and Kansas) and Illinois Basins on the North American midcontinent re- strata that record sea-level highstands at the expense of the underlying Lower–

Science Editor: Raymond M. Russo cord the interaction between fluctuations in eustatic sea-level and major Middle Pennsylvanian clastic-rich strata deposited during sea-level lowstand Associate Editor: Nancy Riggs tectonic events. One of three major Paleozoic eustatic sea-level lows oc- and transgression (e.g., Heckel, 1977, 1986, 2008, 2013; Boardman and Heckel, curred near the Mississippian/Pennsylvanian boundary and was followed 1989; Klein and Willard, 1989; Hatch and Leventhal, 1992; Cruse and Lyons, Received 8 February 2017 by a eustatic rise that continued into Late Pennsylvanian time. Alleghenian 2004; Mazzullo et al., 2007; Tabor et al., 2008). The depositional context of Revision received 31 July 2017 mountain building that is linked to the creation of the Pangean supercon- Lower–Middle Pennsylvanian strata is significant, however, because these Accepted 18 September 2017 Published online 22 November 2017 tinent also began during latest Mississippian time and continued until lat- rocks record deposition of almost exclusively clastic sediment into intracra- est Pennsylvanian or earliest Permian time. Detrital-zircon geochronology tonic basins, including the Illinois and Forest City Basins (Fig. 1A), after a pro- and stratigraphic descriptions allow reconstruction of sediment dispersal longed depositional period of carbonate-clastic cycles followed by a deposi- patterns associated with these events. Our detrital-zircon signatures from tional hiatus during the Early Pennsylvanian. This rejuvenation of dominantly Morrowan–lower Desmoinesian strata in the Illinois Basin are interpreted clastic deposition to the midcontinent was concurrent with both Alleghenian to reflect a change from regional drainages that reworked underlying Mis- orogenesis (Hatcher, 1972, 2002) and eustatic sea-level rise (Haq and Schutter, sissippian strata to extensive extrabasinal fluvial systems that supplied de- 2008). Previous studies have speculated about the individual influence each of tritus shed from southeastern New England. By middle Desmoinesian time, these events had on midcontinent Pennsylvanian depositional systems (e.g., detrital-zircon signatures in the Illinois Basin are more similar to those from Archer and Greb, 1995); however, the interplay between the two and a link to coeval units in the central Appalachian Basin, indicating a southward shift variations in sediment provenance have not been sufficiently explored. in the provenance of the fluvial systems. In the Forest City Basin, Morrowan For example, in the Illinois Basin, it was originally postulated that the Ca- OLD G strata are absent and our detrital-zircon data indicate that Atokan–early Des- nadian Shield and highlands east of the Appalachian Basin were the primary moinesian sedimentation was dominated by regional fluvial systems that sediment sources for Early Pennsylvanian quartz arenites (Potter and Siever, recycled underlying strata. The introduction of extrabasinal fluvial systems 1956a, 1956b; Siever and Potter, 1956). In the adjacent Forest City Basin, the with New England headwaters in the middle Desmoinesian coincided with Canadian Shield also was evoked as the dominant source for Early Pennsyl- OPEN ACCESS the overtopping of the Mississippi River Arch and depositional linking of the vanian sediment (Lemish et al., 1981). Compositional variations, including the Forest City and Illinois Basins. The Forest City and Illinois Basins collectively increasing preponderance of mica in Middle Pennsylvanian strata, however, contain an Early–Middle Pennsylvanian sedimentary record in the backbulge have been cited as evidence for a more distal allochthonous unroofing se- depozone of the Alleghenian foreland basin system that reflects overtopping quence that strengthened support for the Appalachian orogen as playing a ma- of the forebulge located along the Cincinnati Arch and the effects of eustatic jor role in midcontinent provenance (Fitzgerald, 1977; Quinlan and Beaumont, sea-level rise. These results lend credence to the previously proposed trans- 1984; Scal, 1990; Archer and Greb, 1995; Patchett et al., 1999). More recently, This paper is published under the terms of the continental fluvial systems during late Paleozoic time and help to better con- detrital-zircon U-Pb data from Mississippian strata in the Grand Canyon were CC‑BY-NC license. strain their courses. interpreted to reflect primary sediment input from plutonic assemblages on

- 96° - 94° - 92° - 90° - 88° - 86°

B A n Iowa Basement terranes 330–490 Ma FCB-D3 Illinois 42 ° 530–750 Ma FCB-D4 FCB-A1 IB-M2 Appalachia 45° 980–1300 Ma Mountains FCB-D1 IB-D1 IB-M1 IB-D3 N FCB-D2 IB-D2 1300–1750 Ma IB-D4 Maritimes FCB-A2 IB-AD 1800–2000 Ma basin 40 ° Forest FCB-AD City >2500 Ma basin Illinois basin -60°

38 ° 40°

Boston and Cherokee Superior n Narragansett platform Missouri basins Arkansas n 36 Desmoinesian i ° u q Atokan n -65° Arkoma o Morrowan g Appalachia basin l Mountains MCR A Michigan C. 35°

Pennsylvanian outcrop W F

Penokean basin F

is i

34 ° i n Upper Pennsylvanian co n 0100 km ns d in l Lower Pennsylvanian K a anka y kee

M C

Forest City i s i basin n s -70° basin c Appalachian . i R Illinois n

i n 30°

a v a

e basin

t t

i r i

Nemaha Ozark on - urb Bo Appalachian Mountains S. Ouachita Mountains 25°

a 0 250 km N Cub -120° -115° -110° -105° -100° -95° -90° -85° -80° 20°

Figure 1. (A) Regional index map of eastern North America including the modern extent of basement terranes (Whitmeyer and Karlstrom, 2007), sedimentary cover (shown in white; Reed et al., 2005), major sedimentary basins (Coleman and Cahan, 2012), and major igneous belts along the eastern margin (Reed et al., 2005). Stippled patterns show locations of sedimentary basins discussed in the text. Red arrows indicate generalized paleoflow directions for Pennsylvanian strata. (B) Generalized geologic map of the study area showing modern surface extent of Pennsylvanian strata (Reed et al., 2005) and sample locations. MCR—Midcontinental Rift; GC—Grand Canyon.

the Appalachian margin to the southwestern United States by early Carbonif- The FCB and IB are regarded as intracratonic basins that are separated erous time, requiring the presence of a Pennsylvanian transcontinental fluvial from the Appalachian foreland region by a series of basement-cored arch system (Gehrels et al., 2011). The position of the Forest City and Illinois Basins complexes (Fig. 1A; Quinlan and Beaumont, 1984; Root and Onasch, 1999; between the Grand Canyon and former late Paleozoic Appalachian highlands Craddock et al., 2017). Deformation that defined the boundaries of the FCB was means that the provenance record in those basins will test the transcontinental initiated in the Early Ordovician and continued sporadically into the Carbon- connection (e.g., Thomas, 2011). iferous (Anderson and Wells, 1968; Mason, 1980; Root and Onasch, 1999). To In this paper, we present 3051 new U-Pb ages from detrital zircons collected the west of the basin in eastern Kansas and Nebraska, uplift during the Late from Early–Middle Pennsylvanian strata in the Forest City and Illinois Basins. Mississippian exposed the Precambrian basement to over 120 m above the ba- Integration of these data with current paleogeographic models permits an im- sin floor, forming the Nemaha Ridge (Bunker et al., 1988). This structural high provement to our understanding of sediment transport across the North Amer- separated the FCB from the Salina Basin during Early–Middle Pennsylvanian ican midcontinent during Early–Middle Pennsylvanian time. Furthermore, our time but was overtopped by sediments during the Late Pennsylvanian. The provenance interpretations are placed within the context of tectonic events Bourbon Arch and Ozark Uplift (Fig. 1A) separate the FCB from the Cherokee along the Appalachian margin and eustatic sea-level variations affecting the Platform to the south, whereas the Mississippi River Arch denotes the eastern midcontinent and demonstrate that provenance analysis may permit differen- margin of the basin. By middle–late Middle Pennsylvanian time, episodes of tiation between the relative roles of each in a cratonic fluvial system. marine deposition had become continuous across the Mississippi River Arch, depositionally linking the FCB with the IB to the east (Nelson et al., 2013). The modern IB is delineated structurally by a system of regional arches that BACKGROUND emerged in the early Paleozoic and defined the margins of the basin by the end of the Ordovician (Potter, 1963; Root and Onasch, 1999). The basin is bound by Regional Geology the Cincinnati, Findlay, and Algonquin arches to the south and east, and the Kankakee Arch separates the IB from the Michigan Basin to the north. The Cin- During the Carboniferous, the eastern and southern margins of Lauren- cinnati and related arches are considered to have acted as a forebulge for the tia were dominated tectonically by the collision of Gondwana with Laurentia, Appalachian foreland basin during the Pennsylvanian–Permian Alleghenian which combined with other landmasses to form the supercontinent Pangea orogeny, and the Kankakee arch is interpreted as a secondary feature related to (e.g., Cocks and Torsvik, 2011). Collision of the two landmasses created the subsidence of the Illinois and Michigan Basins (Quinlan and Beaumont, 1984; Ouachita orogeny along the southern margin of Laurentia and the Alleghe- Root and Onasch, 1999). Despite these potential topographic barriers, models nian orogeny on the eastern margin. Denudation of the exhumed orogens by Quinlan and Beaumont (1988) suggest that both the Cincinnati and Kanka- dispersed sediments into proximal foreland basins that were periodically kee arches were ultimately overtopped by sediments from the unroofing of the overfilled, allowing orogen-sourced fluvial systems to distribute clastic sed- Appalachians by at least Late Pennsylvanian time, if not earlier, depositionally iment across the cratonic interior of Laurentia (Tankard, 1986; Dickinson and linking the intracratonic basins with the Appalachian foreland. Gehrels, 2003; Thomas et al., 2004). Late Paleozoic cratonic sedimentation is largely encompassed by the Absaroka megasequence (Sloss, 1963), which began during the Late Mississippian. The basal unconformity of this package is a Regional Stratigraphic Summary major disconformity present in all Laurentian cratonic basins and is most often characterized by a system of pre-Pennsylvanian incised valleys, such as those The stratigraphic positions of the samples analyzed in this study were found in the Forest City and Illinois Basins, the fills of which preserve a record collected in the context of key marker beds within each basin. Therefore, we of sedimentation during Early Pennsylvanian and later base-level rise (Archer summarize below the existing sedimentology and stratigraphy for these strata et al., 1994; Feldman et al., 1995). with an emphasis on those key marker beds. Schematic stratigraphic columns The Forest City Basin (FCB) encompasses ~65,000 km2 of Iowa, Missouri, with key marker beds and sample localities for the northeastern FCB and IB are Kansas, and Nebraska (Fig. 1A). The thickness of Cambrian to Late Pennsylva- shown in Figure 2. Detailed sample location information is provided in Table 1. nian strata exceeds 1.5 km in the deepest parts of the basin (Derynck, 1980; Bun- ker et al., 1988). Pennsylvanian strata thicken toward the southern and western margins, attaining a maximum thickness of ~600 m in northwestern Missouri. Forest City Basin The Illinois Basin (IB) lies to the east of the FCB, trends northwest-southeast encompassing Illinois and southwestern Indiana, and extends marginally into The Kilbourn Formation extends from its unconformable basal contact western Kentucky and eastern Iowa. It contains up to 4.5 km of Paleozoic strata, with the pre-Pennsylvanian paleosurface to the bottom of the Blackoak Coal including up to 900 m of Pennsylvanian strata (Nelson et al., 2013). (Fig. 2; Ravn et al., 1984). Dominant lithologies include fine-grained sandstone,

GEOSPHERE | Volume 14 | Number 1 Kissock et al. | Lower–Middle Pennsylvanian strata in the North American midcontinent Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/14/1/141/4035197/141.pdf 143 by guest on 26 September 2021 on 26 September 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/14/1/141/4035197/141.pdf Research Paper 323 322 321 320 319 318 317 316 315 314 313 312 310 309 308 307 306 31 al. (2016) and North American (NA) stages from Heckel and Clayton (2006). SS — sandstone. positions of samples, key marker beds, and the long- short-term eustatic sea-level curves (Haq and Schutter, 2008). Standard chronostratigraphy from Ogg et Figure 2. Schematic stratigraphic columns for the Forest City (Anderson and Fields, and Illinois (Jacobson, 2007) Basins in the study area 2002) with stratigraphic 1 Age (Ma)

Early Pennsylvanian Middle Pennsylvanian Late Pn. Epoch Morrowan Stage Atokan Stage Desmoinesian Stage NA Stage

Verdigris &

Mississippian Kilbourn Fm. Kalo Fm. Floris Fm.MSwede Hollow Fm. armaton Group carbonate Forest City Basin Blackoak Coal Laddsdale Coals Whitebreast Coal Oakley Shale Ardmore Limestone Mulky Coal FCB-D1 FCB-D2 FCB-D3 FCB-D4 FCB-A2 FCB-A1 FCB-AD LITHOSTRATIGRAPHY

Caseyville Fm. Tradewater Fm. Carbondale Fm. Shelburn Fm. Mississippian

carbonate

Illinois

n Basi

Brush Coal Brush

Providence Limestone Providence Colchester Coal #2 Coal Colchester Seelyville or Davis Coal Davis or Seelyville

Pope Creek Coal Creek Pope

Bernadotte Sandstone Bernadotte

Vermillionville SS Vermillionville Copperas Creek SS Creek Copperas IB-D1 IB-M1 IB-M2 IB-AD IB-D3 IB-D4 IB-D2 EUSTATIC SEA LEVEL 100 (m above present day) Long-term sea level Short-term sea level 0

GEOSPHERE | Volume 14 | Number 1 Kissock et al. | Lower–Middle Pennsylvanian strata in the North American midcontinent 144 Research Paper

TABLE 1. DETAILED SAMPLE LOCATION INFORMATION Sample Latitude Longitude Location description location (°N) (°W) (sampled interval) Geologic unit References FCB-A1 41.67723 91.53146 Outcrop south of Mayﬂ ower dormitory in Iowa City, Iowa Pennsylvanian Kissock, 2016 FCB-A2 40.613315 92.627301 Core sample from Iowa Geological Survey (IGS) #CP-09 (507ʹ–511ʹ)Kilbourn Formation Ravn et al., 1984; Ravn, 1986 FCB-AD 40.613315 92.627301 Core sample from IGS #CP-09 (389ʹ–390ʹ, 406ʹ–409ʹ, 412ʹ–415ʹ)Kalo Formation Ravn et al., 1984; Ravn, 1986 FCB-D1 41.36681 92.98911 Measured section near Red Rock Dam, Iowa (~6.5 m) Floris Formation Pope, 2012; Kissock, 2016 FCB-D2 41.389268 93.03411 Measured section in White Breast Recreation Area, Iowa (~8.2 m) Floris Formation Pope, 2012; Kissock, 2016 FCB-D3 42.392883 94.0808 Measured section in Dolliver State Park, Iowa (~4.0 m) Floris Formation Pope, 2012; Kissock, 2016 FCB-D4 41.98279 93.8933 Outcrop in Ledges State Park, Iowa Floris Formation Pope, 2012; Kissock, 2016 IB-M1 41.43458 90.94035 Measured section at Wyoming Hill road cut, Iowa (~0.8 m) Caseyville Formation Ravn et al., 1984; Kissock, 2016 IB-M2 41.46379 90.57081 Outcrop in Blackhawk State Park, Illinois Caseyville Formation Anderson et al., 1999; Nelson et al., 2013 IB-AD 40.49139 90.36767 Outcrop along tributary to Spoon River, Illinois Tradewater Formation Reinertsen et al., 1993 IB-D1 41.43458 90.94201 Outcrop at Wyoming Hill road cut, Iowa Tradewater Formation Fitzgerald, 1977 IB-D2 41.46856 90.0808 Outcrop in Wildcat Den State Park, Iowa Tradewater Formation Fitzgerald, 1977 IB-D3 41.19389 88.90296 Outcrop at Sandy Ford Nature Preserve, Illinois Carbondale Formation Nelson et al., 1996 IB-D4 40.63748 89.65417 Outcrop along Pfeiffer Road, Bartonville, Illinois Shelburn Formation Frankie et al., 1995 Abbreviations: FCB—Forest City Basin; IB—Illinois Basin.

shale, coal, and mudstone. Sandstones are generally texturally and composi- interpreted to represent high-energy fluvial depositional systems with minor tionally mature quartz arenites (Fig. 3; Scal, 1990). The paleotopography of the influence by marginal marine processes. In addition, sandstone in this unit pre-Pennsylvanian erosional surface is interpreted to have confined deposition contains more mica and feldspar than the underlying units, and the grains are of the generally thin and discontinuous beds of the Kilbourn Formation to a more angular (Fig. 3; Isbell, 1985; Scal, 1990). southwest-trending system of incised paleovalleys (Ravn et al., 1984). The Kalo Formation extends from the Blackoak Coal to the base of the Laddsdale coal (Pope, 2012). Palynological assemblages in the coals from Illinois Basin within this formation are consistent with the Kalo Formation straddling the Atokan–Desmoinesian stage boundary (Fig. 2). Lithologies are mud domi- The Caseyville Formation extends from its unconformable basal contact nated, and marine layers are scarce (Gregory, 1982). Coals are more common with the pre-Pennsylvanian unconformity to the base of the Tradewater Forma- relative to the underlying Kilbourn Formation, whereas channel-fill sandstone tion (Fig. 2; Nelson et al., 2013). The Caseyville-Tradewater contact is defined as is less common. The sandstone is largely quartz arenite, but the proportions of the uppermost limit of locally occurring quartz-pebble–bearing conglomerates mica and feldspar begin to increase above the Desmoinesian stage boundary (Potter, 1963; Fitzgerald, 1977; Nelson et al., 2013). This boundary is interpreted (Fig. 3; Scal, 1990). Clastics in both the Kilbourn and Kalo Formations are in- to coincide with the top of the Morrowan stage based on palynology (Pep- terpreted to be derived from Mississippian and older strata (Ravn et al., 1984). pers, 1996). In the western IB, the Caseyville Formation consists of thin-bedded The Floris Formation extends from the Laddsdale Coal to the base of the sandstone, siltstone, shale, and thin coal. Caseyville Formation sandstone is Oakley Shale (Pope, 2012). While it typically overlies the Kalo Formation, texturally mature quartz arenite (Fig. 3) and is petrologically similar to the un- channelized sandstone in the Floris Formation in some subsurface cores have derlying Upper Mississippian sandstones (Potter and Glass, 1958). Similar to deeply incised into the older Pennsylvanian strata and locally extend to the the Kilbourn Formation in the FCB, pre-Pennsylvanian paleotopography likely pre-Pennsylvanian erosional surface. Based on conodonts, palynology, and influenced Caseyville Formation fluvial systems, which are interpreted to have fern fossils, the Laddsdale and Whitebreast coals of the Floris Formation cor- supplied reworked pre-Pennsylvanian detritus to the basin (Potter and Glass, relate with the Brush and Colchester coals of western Illinois, respectively 1958; Fitzgerald, 1977). Paleocurrent trends are dominantly southwest directed, (Peppers, 1970; Hopkins and Simon, 1975). Palynological assemblages in the but in the northwest part of the basin are locally northwest and northeast di- coals of the Floris Formation are consistent with deposition during the Des- rected likely due to deflection by the Mississippi River Arch (Isbell, 1985). moinesian stage. Minor cyclothems occur in the upper part of this formation, The Tradewater Formation extends from the Caseyville Formation to the indicating increased marine influence relative to underlying formations (Mar- Seelyville or Davis Coal Member of the Carbondale Formation (Nelson et al., 2013). shall, 2010). The Floris Formation is characterized by channelized sandstone Sandstone petrography of the informal lower member records a compositional

Q erates become increasingly common upsection. Paleoflow trends in the upper Qa member demonstrate dominantly south-southwest flow directions (Potter and 10 10 Glass, 1958). The transition away from variable flow directions in the underlying Caseyville Formation has been interpreted to reflect inundation of the Mississippi Forest City River Arch and leveling of the depositional plain (Isbell, 1985). basin The Carbondale Formation extends from the top of the Tradewater Forma- tion to the base of the Providence or Brereton Limestone Member of the Shel- Sa Sl burn Formation. The top of the Shelburn Formation is marked by the Scottville Limestone or Trivoli Sandstone of the Patoka Formation (Nelson et al., 2013).

25 Feldspathic litharenite 25 Both formations contain abundant marine cyclothems that record sea-level highstands, in addition to thick channelized sandstone bodies that are inter- Lithic arkose preted to reflect lowstand conditions (Rusnak, 1957; Hopkins, 1958; Potter and Arkose Simon, 1961; Eggert and Adams, 1979; Utgaard, 1979; Eggert, 1981). Argilla-

Lithic arkose ceous sandstone in the Carbondale and Shelburn Formations generally occurs Desmoinesian in thick, fining-upward channel sequences similar to the upper Tradewater For- Atokan mation. The sandstone also has petrological characteristics that are similar to the upper Tradewater Formation. Paleoflow measurements in these formations F50 L50 have south-southwest trends. However, the vector means of cross-bedding ex- Q hibit a subtle change from S39°W in the Pennsylvanian strata below the lowest portion of the Carbondale Formation to S47°W over the interval between the Qa lowest Carbondale to just above the top of the Shelburn Formation (Potter and Glass, 1958). This westward transition continues upward in Missourian strata Sa Sl above the Shelburn Formation, where the vector mean is S52°W.

Illinois

basin Feldspathic litharenite Potential Sediment Sources

Lithic arkose Based on previous provenance work, several regions have been identified as potential sources of sediment for the Pennsylvanian FCB and IB strata.

Arkose Prospective crystalline sources include (Fig. 1A): (1) plutonic assemblages

Lithic arkose associated with the Alleghenian (270–330 Ma), Acadian (350–420 Ma), and Taconic (440–490 Ma) orogenies along the eastern margin of North America, Desmoinesian collectively referred to in this study as an Appalachian source; (2) Pan-African Atokan Morrowan terranes that are generally situated within and outboard of the Appalachian igneous belts along the eastern seaboard, or Iapetan synrift rocks along the F100 L100 eastern Laurentian margin that produce Neoproterozoic ages (530–750 Ma); (3) the Grenville igneous belt in the Appalachian region (980–1300 Ma) and Figure 3. QFL ternary diagrams illustrating the data for the Lower the Midcontinent Rift belt in the northern midcontinent (1080–1120 Ma); (4) the Pennsylvanian sandstones across the Forest City (Scal, 1990) and in the northwestern Illinois (Isbell, 1985) Basins. Q—total quartz; F— Granite-Rhyolite belt (1300–1550 Ma) and Yavapai and Mazatzal terranes (1653– feldspar; L—lithics. 1750 Ma) that extend from northeastern Canada (Mazatzal ages are associated with the Labradorian Province in the Quebec Region) to the southwestern United States and are collectively referred to in this study as midcontinent transition from quartz arenite of the Caseyville Formation to lithic arenite of the terranes; (5) the Trans-Hudson (1800–1900 Ma) and Penokean (1800–1900 Ma) informal upper Tradewater Formation (Fig. 3; Potter, 1963). The upper part con- provinces located in northern and central Canada, and Wisconsin and northern tains very fine to coarse-grained sandstone comprising ~5%–10% mica, feldspar, Michigan, respectively; and (6) the Superior Province (>2500 Ma) in central lithic grains (mainly chlorite schist), and argillaceous matrix (Potter and Glass, Canada. Some of the potential source terranes listed above, including large 1958). Multi-story sandstone channels that fine upward from basal conglom- tracts of the Midcontinent Rift belt, Granite-Rhyolite belt, and Yavapai and

Mazatzal terranes, are beneath pre-Pennsylvanian strata today and so are not defined by palynological studies of coals in the core by the Iowa Coal Project considered to be a primary source for the Pennsylvanian sandstones. (Ravn et al., 1984; Ravn, 1986). There is also the potential for the erosion and recycling of Neoproterozoic– early Paleozoic clastic units in the midcontinent region, which were exposed north of the Illinois and Forest City Basins during the Pennsylvanian. Malone Atokan to Desmoinesian Strata et al. (2016) in their study of the Neoproterozoic Jacobsville Sandstone, which was deposited during tectonic inversion of the Midcontinent Rift, reported zir- FCB-AD is a composite sample that was collected from several ~1–2-m-thick, cons of Grenville, Granite-Rhyolite, Penokean, and Archean ages. Konstanti- fine-grained quartz arenites in the IGS core #CP-09 from southeastern Iowa nou et al. (2014) provided an analysis of the detrital-zircon age distribution of (Fig. 1B) at the 389–390′, 406–409′, and 412–415′ intervals. These intervals fall Cambrian and Ordovician quartz arenites in Minnesota, Wisconsin, Illinois, and within the upper part of the Kalo Formation as defined by palynological studies Missouri. They determined that these rocks were dominated by Archean and of the Iowa Coal Project (Ravn et al., 1984; Ravn, 1986). Grenville-age zircons. Pennsylvanian strata across most of the FCB and IB overlie Mississippian– Devonian strata that are composed of both carbonate and clastic intervals. Desmoinesian Strata These strata are exposed today on the arches that bound the basins and thus could have been recycled into the basins in the past. To the east, recycling of FCB-D1 was collected from a <1-m-thick, thin-bedded sandstone that is pre-Pennsylvanian sandstone from the Appalachian fold-and-thrust belt is also interbedded with mudstone and coal in southcentral Iowa (Figs. 1B and 4D). possible; however, the foreland basin fill in that region is still largely intact and The strata at the FCB-D1 sample site are inferred to belong to the Floris For- was likely not a significant contributor. Uplift in the Ozark region to the south mation due to their similar stratigraphic position as the strata at the nearby was not renewed until the Late Pennsylvanian (Branson, 1962) and the abun- FCB-D2 site that is discussed below. FCB-D2 was collected from the base of an dance of southwest directed paleoflow indicators in Pennsylvanian strata of the ~8-m-thick outcrop of thin-bedded sandstone that is interbedded with mud- FCB and IB generally preclude the potential for southern or westerly sources. stone and coal in southcentral Iowa (Fig. 1B). These strata have been identified as the Floris Formation (Pope, 2012). FCB-D3 was collected from an ~10-m-thick outcrop of medium- to thick- METHODS bedded (10–100 cm) sandstone with scarce mudstone interbeds in northcentral Iowa (Figs. 1B and 4E). Pope (2012) identified the strata at this locality as the Seven sandstone samples were collected for detrital-zircon analyses from Floris Formation. Because the strata are essentially flat lying along deposi- Atokan and Desmoinesian strata in the FCB, as well as seven sandstone sam- tional strike (northwest to southeast), we infer the stratigraphic position of the ples from Morrowan through Desmoinesian strata in the IB (Figs. 1B and 2). FCB-D3 sandstone to be above FCB-D1 and FCB-D2 based on the differences in elevation between the outcrops. FCB-D4 was collected from an ~10-m-thick outcrop of thick- to very Forest City Basin thick-bedded (~1 m or greater), fine- to coarse-grained micaceous litharenite in central Iowa (Figs. 1B and 5A). Osolin (1983) considered this outcrop to be part Atokan Strata of the Swede Hollow Formation (middle–upper Desmoinesian stage) based on its position above the Whitebreast Coal and Ardmore Limestone that had been FCB-A1 was collected from an ~2-m-thick, thin-bedded (3–10 cm) quartz tentatively identified in nearby cores. More recently, however, this outcrop was arenite in eastern Iowa (Figs. 1B and 4A–4C). Strata in this outcrop are con- identified as the Floris Formation (Pope, 2012). We infer it to be near the same sidered Pennsylvanian (P.H. Heckel, 2015, personal commun.), but the precise stratigraphic position as FCB-D3 based on the elevation of the sample site. stratigraphic position is uncertain. We consider these strata to be basal Penn- sylvanian, probably Atokan, because they lie directly on the sub-Pennsylvanian unconformity. This interpretation is supported by the widespread occurrence of Illinois Basin Atokan stage strata above the basal Pennsylvanian unconformity and a demon- strable lack of spatially continuous Morrowan strata in the FCB (Pope, 2012). Morrowan Strata FCB-A2 was collected from an ~1-m-thick, fine-grained quartz arenite from the Iowa Geological Survey (IGS) core #CP-09 (Fig. 1B) at the 507–511′ interval. IB-M1 was collected from an ~2-m-thick, thin-bedded, fine-grained quartz A detailed core description can be found on the IGS Web site (https://www arenite in the upper part of the Caseyville Formation in eastern Iowa (Figs. .iihr.uiowa.edu/igs). The sample interval falls within the Kilbourn Formation as 1B and 4G). Ravn et al. (1984) constrained the stratigraphic position of this

GEOSPHERE | Volume 14 | Number 1 Kissock et al. | Lower–Middle Pennsylvanian strata in the North American midcontinent Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/14/1/141/4035197/141.pdf 147 by guest on 26 September 2021 on 26 September 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/14/1/141/4035197/141.pdf Research Paper sandstone at IB-AD. FCB-D3 (note hammer for scale). Illinois Basin: (F) tidal rhythmites at IB-M1; (G) two fine-grained sandstone bodies separated by a coal horizon at IB-M1; and (H) thin-bedded rythmites at FCB-A1; (C) bioturbated tidal rhythmites at FCB-A1; (D) thin-bedded sandstone overlying coal and siltstone at FCB-D1; (E) planar tangential cross-bedding at Figure 4. Outcrop photographs of Type 1 sandstone localities. Forest City Basin: (A) Thin-bedded sandstone overlying mudstone at FCB-A1 (note hammer for scale); (B) tidal A G D ~1m E B H ~1 m F C

GEOSPHERE | Volume 14 | Number 1 Kissock et al. | Lower–Middle Pennsylvanian strata in the North American midcontinent 148 on 26 September 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/14/1/141/4035197/141.pdf Research Paper sure at IB-D2; (F) thick-bedded sandstone exposure at IB-D3; and (G) thin-bedded sandstone exposure at IB-D4. (B) thick-bedded sandstone exposure at IB-M2; (C) thick-bedded sandstone exposure at IB-D1; (D) planar tangential cross-bedding at IB-D1; (E) thick-bedded sandstone expo - Figure 5. Outcrop photographs of Type 2 (A–E) and Type 3 (F–G) sandstone localities. Forest City Basin: (A) Thick, cross-bedded sandstone exposure at FCB-D4. Illinois Basin: A F D ~1 m ~1 m G E C B ~1 m

GEOSPHERE | Volume 14 | Number 1 Kissock et al. | Lower–Middle Pennsylvanian strata in the North American midcontinent 149 Research Paper

outcrop using palynomorphs from coals that have characteristic Morrowan RESULTS assemblages. IB-M2 was collected from an ~5-m-thick outcrop of thick- to very thick-bedded fine- to medium-grained quartz arenite in the Caseyville For- Detrital-Zircon U-Pb Type Signatures mation (Anderson et al., 1999; Nelson et al., 2013) in northwest Illinois (Figs. 1B and 5B). Grenville-age zircons (980–1300 Ma) make up the dominant population of 13 of the 14 samples in both basins. However, Grenville igneous rocks are notoriously zircon-fertile (Moecher and Samson, 2006) and were deposited in Atokan to Early Desmoinesian Strata older strata across the North American continent, limiting their utility in provenance interpretation (e.g., Gehrels et al., 2011; Rainbird et al., 2012). Therefore, IB-AD was collected from a ~2-m-thick, thin-bedded, fine-grained, quartz we define three type signatures based on the presence (>10% of total distri- arenite from the Bernadotte member of the lower Tradewater Formation (Rein- bution) and relative abundance of the other age populations present. Type 1 ertsen et al., 1993) in western Illinois (Figs. 1B and 4H). signatures are characterized by the dominance of a Midcontinent population (1300–1750 Ma) with a minimal Neoproterozoic (530–750 Ma) population. Su- perior (>2500 Ma) and Appalachian (270–490 Ma) populations may or may Middle to Late Desmoinesian Strata not be present as well. Type 2 signatures are dominated by Appalachian and Neoproterozoic populations that are present in relatively even proportions, IB-D1 was collected from an ~15-m-thick, thick- to very thick-bedded, fine- with lesser amounts of all other populations. Type 3 signatures have a large to coarse-grained micaceous litharenite in the upper Tradewater Formation Appalachian population, a minimal Neoproterozoic population, and no grains (Fitzgerald, 1977) in eastern Iowa (Figs. 1B, 5C, and 5D). IB-D2 was collected with ages older than the Granite-Rhyolite province (>1550 Ma). On a cumula- from an ~10-m-thick, thick- to very thick-bedded, fine- to coarse-grained mica- tive probability density plot (Fig. 6), the major difference between Type 2 and ceous litharenite in the upper Tradewater Formation (Fitzgerald, 1977) in east- the others, however, is in the Neoproterozoic age range (530–750 Ma). There, ern Iowa (Figs. 1B and 5E). IB-D3 was collected from an ~3-m-thick outcrop of the Type 1 and Type 3 curves remain relatively flat, reflecting an absence of thin- to medium-bedded, fine- to medium-grained micaceous litharenite in the this population in their distributions. The Type 2 signatures, in contrast, have Vermilionville member of the Carbondale Formation (Nelson et al., 1996) in a steeper slope that records the presence of a Neoproterozoic population in northcentral Illinois (Figs. 1B and 5F). The Vermilionville Sandstone can be up those samples.

Table S1. Detrital zircon U-Pb data FCB-A1 to 24 m thick (Wanless, 1956). IB-D4 was collected from an ~2-m-thick outcrop Sample location: 41.67723° -91.53146°n=294 AnalysisU206PbU/Th206Pb*±207Pb* ±206Pb*±error 206Pb* ± 207Pb* ± 206Pb* ±Best age± Conc (ppm)204Pb 207Pb* (%)235U* (%)238U(%) corr. 238U*(Ma) 235U (Ma) 207Pb* (Ma) (Ma) (Ma) (%) FCB-A1-Spot 15 12039279 1.218.0254 3.60.5112 4.00.06681.8 0.46 417 7 419 14 431 79 417 7 100.5 of thin- to medium-bedded, fine- to medium-grained micaceous litharenite in FCB-A1-Spot 11 5591271451.4 17.72531.5 0.5214 1.90.06701.1 0.57 418 4 426 7 469 34 418 4 101.9 FCB-A1-Spot 176610 1293700.6 17.90761.3 0.5172 1.70.06721.1 0.66 419 5 423 6 446 29 419 5 101.0 FCB-A1-Spot 26912281303221.0 18.19360.9 0.5096 1.60.06721.3 0.82 420 5 418 6411 21 420 5 99.7 FCB-A1-Spot 175239 551441.4 17.33872.3 0.5594 2.80.07031.6 0.56 438 7 451 10 517 51 438 7 102.9 the Copperas Creek member of the Shelburn Formation (Frankie et al., 1995) in Forest City Basin FCB-A1-Spot 100659 481051.1 17.71501.2 0.5591 1.70.07181.2 0.72 447 5 451 6 470 26 447 5 100.8 FCB-A1-Spot 146168 433643.8 17.27912.6 0.5941 3.10.07451.6 0.52 463 7 473 12 525 58 463 7 102.3 FCB-A1-Spot 226106 330202.5 16.34202.2 0.7474 2.80.08861.7 0.61 547 9 567 12 646 47 547 9 103.6 FCB-A1-Spot 107147 428680.6 15.94632.1 0.8417 2.60.09731.5 0.57 599 8 620 12 698 45 599 8 103.5 central Illinois (Figs. 1B and 5G). The Copperas Creek Sandstone can be up to FCB-A1-Spot 101254 299281.8 15.83141.9 0.8745 2.40.10041.6 0.64 617 9 638 12 714 39 617 9 103.4 FCB-A1-Spot 200251 337152.3 14.34681.2 1.4940 1.60.15541.0 0.63 931 9 928 10 920 25 920 25 101.3 FCB-A1-Spot 134211 833838.8 14.20891.5 1.4960 1.90.15421.2 0.64 924 11 929 12 939 31 939 31 98.4 FCB-A1-Spot 30 16831168 3.014.0871 1.41.56892.0 0.1603 1.4 0.70 958 12 958 12 957 29 957 29 100.1 9 m thick (Wanless, 1957). All but one of the samples from the Forest City Basin have Type 1 signa- FCB-A1-Spot 163578 1696855.1 14.02740.8 1.5997 1.30.16271.0 0.76 972 9 970 8 966 17 966 17 100.6 FCB-A1-Spot 56 21158410 5.413.9658 0.91.66081.8 0.1682 1.5 0.85 1002 14 994 11 975 19 975 19 102.8 FCB-A1-Spot 75 40 385882.4 13.94883.0 1.5829 3.50.16011.7 0.50 958 15 964 22 977 61 977 61 98.0 FCB-A1-Spot 159131 459924.2 13.94211.7 1.5904 2.30.16081.6 0.67 961 14 966 15 978 36 978 36 98.3 FCB-A1-Spot 170275 270591.3 13.93581.5 1.6861 2.20.17041.6 0.73 1014 15 1003 14 979 31 979 31 103.6 tures. FCB-A1 (n = 294) has prominent age groups representing the Midcon- FCB-A1-Spot 34 59 270131.9 13.89192.6 1.5835 3.10.15951.7 0.55 954 15 964 20 985 53 985 53 96.8 FCB-A1-Spot 201278 569832.6 13.88031.1 1.6367 1.80.16481.3 0.76 983 12 984 11 987 23 987 23 99.6 FCB-A1-Spot 234548 1286621.4 13.81950.9 1.6658 1.50.16701.2 0.80 995 11 996 10 996 19 996 19 99.9 FCB-A1-Spot 136255 397763.4 13.81231.5 1.6486 2.00.16511.3 0.66 985 12 989 13 997 31 997 31 98.8 tinent terranes (21%) and Superior grains (16%) (Fig. 7). FCB-A2 (n = 267) is FCB-A1-Spot 294255 1196931.6 13.81161.2 1.6537 1.50.16570.9 0.58 988 8 991 10 997 25 997 25 99.1 FCB-A1-Spot 85 14231919 7.313.7891 1.71.70112.0 0.1701 1.0 0.51 1013 10 1009 13 1001 35 1001 35 101.2 FCB-A1-Spot 275354 1077632.1 13.77581.5 1.6632 2.00.16621.3 0.65 991 12 995 12 1003 30 1003 30 98.8 FCB-A1-Spot 21 81 458041.9 13.77192.9 1.6726 3.20.16711.3 0.42 996 12 998 20 1003 58 1003 58 99.3 U-Pb Geochronology characterized by Appalachian (10%) and Midcontinent (32%) populations. FCB-A1-Spot 229296 1783511.0 13.77191.3 1.6165 1.80.16151.3 0.69 965 11 977 12 1003 27 1003 27 96.2 FCB-A1-Spot 3019134871 1.313.7460 2.41.69762.8 0.1692 1.3 0.48 1008 12 1008 18 1007 50 1007 50 100.1 FCB-A1-Spot 25 54998376 2.813.7141 1.31.64711.8 0.1638 1.3 0.70 978 11 988 11 1012 26 1012 26 96.7 FCB-A1-Spot 160205 977005.0 13.71001.4 1.6791 2.00.16701.5 0.71 995 13 1001 13 1012 29 1012 29 98.3 FCB-AD (n = 259) contains 12% Appalachian grains and 30% Midcontinent FCB-A1-Spot 60 14564735 3.813.6943 1.51.63341.9 0.1622 1.2 0.63 969 11 983 12 1015 30 1015 30 95.5 FCB-A1-Spot 40 45 226003.6 13.69362.2 1.6853 2.70.16741.5 0.56 998 14 1003 17 1015 45 1015 45 98.3 FCB-A1-Spot 83 20290559 1.713.6796 1.61.70202.0 0.1689 1.2 0.62 1006 12 1009 13 1017 32 1017 32 98.9 FCB-A1-Spot 79 10733108 3.613.6719 1.91.60982.3 0.1596 1.3 0.57 955 11 974 14 1018 38 1018 38 93.8 FCB-A1-Spot 189138 565530.7 13.66231.5 1.6782 1.80.16630.9 0.52 992 9 1000 11 1019 31 1019 31 97.3 Zircons were separated via crushing, milling, water table, sieving, and grains. FCB-D1 (n = 296) has a signature with 15% Midcontinent ages and neg- FCB-A1-Spot 92 32276873 4.913.6545 1.21.61511.8 0.1599 1.4 0.74 956 12 976 12 1020 25 1020 25 93.7 FCB-A1-Spot 96 59 143483.3 13.64991.9 1.7079 2.10.16911.0 0.48 1007 10 1012 14 1021 38 1021 38 98.6 FCB-A1-Spot 205160 388961.2 13.62961.3 1.6828 1.80.16631.2 0.67 992 11 1002 11 1024 27 1024 27 96.9 FCB-A1-Spot 2744239281 2.213.6289 2.41.52103.1 0.1503 1.9 0.63 903 16 939 19 1024 49 1024 49 88.2 magnetic and heavy liquid separations. Analysis of individual grains was per- ligible proportions of the other non-Grenville populations. FCB-D2 (n = 285) FCB-A1-Spot 2197723367 5.213.6096 2.11.54242.7 0.1522 1.7 0.62 914 14 947 17 1027 43 1027 43 88.9 FCB-A1-Spot 216921735871.4 13.59461.9 1.7138 2.40.16901.5 0.61 1006 14 1014 15 1029 38 1029 38 97.8 FCB-A1-Spot 292357 381738.6 13.59031.3 1.7039 1.70.16801.1 0.64 1001 10 1010 11 1030 26 1030 26 97.2 FCB-A1-Spot 279250 608591.9 13.58621.1 1.7622 1.50.17361.0 0.66 1032 10 1032 10 1031 23 1031 23 100.1 formed at the Arizona LaserChron Center. U-Pb analyses were conducted by has ~34% of grains that are Midcontinent age. FCB-D3 (n = 279) contains 14% FCB-A1-Spot 306189 406132.8 13.58271.4 1.7323 1.90.17061.3 0.67 1016 12 1021 12 1031 29 1031 29 98.5 FCB-A1-Spot 3144840966 1.113.5793 2.91.69293.5 0.1667 1.9 0.54 994 17 1006 22 1032 59 1032 59 96.4 FCB-A1-Spot 262202 397212.0 13.56491.6 1.6649 2.30.16381.6 0.69 978 14 995 14 1034 33 1034 33 94.6 FCB-A1-Spot 313131 1361552.7 13.55651.4 1.7023 1.90.16741.3 0.68 998 12 1009 12 1035 28 1035 28 96.4 laser ablation–multi-collector inductively coupled plasma mass spectrometry Appalachian and 17% Midcontinent grains. Only FCB-D4 (n = 263) has a Type FCB-A1-Spot 238289 661715.8 13.55081.4 1.7479 2.20.17181.7 0.76 1022 16 1026 14 1036 29 1036 29 98.7 FCB-A1-Spot 270270 1671932.3 13.54071.3 1.7421 2.00.17111.5 0.75 1018 14 1024 13 1037 27 1037 27 98.1 FCB-A1-Spot 68 14334020 1.113.5309 1.81.71202.1 0.1680 1.2 0.56 1001 11 1013 14 1039 36 1039 36 96.4 FCB-A1-Spot 249294 721191.2 13.52271.4 1.6833 1.80.16511.1 0.59 985 10 1002 11 1040 29 1040 29 94.7 FCB-A1-Spot 288349 371031.5 13.52101.0 1.8095 1.70.17741.4 0.81 1053 14 1049 11 1040 21 1040 21 101.2 (LA-MC-ICPMS) following the methods described by Gehrels and Pecha (2014). 2 signature that contains significant Appalachian (23%) and Neoproterozoic FCB-A1-Spot 183125 346845.1 13.51311.5 1.7785 2.20.17431.6 0.74 1036 16 1038 14 1042 30 1042 30 99.4 FCB-A1-Spot 19 20545767 7.313.5019 1.41.78932.0 0.1752 1.4 0.71 1041 14 1042 13 1043 28 1043 28 99.8 FCB-A1-Spot 145120 274800.8 13.49171.9 1.8235 2.40.17841.5 0.61 1058 14 1054 16 1045 38 1045 38 101.3 FCB-A1-Spot 178191 111958 1.513.4905 1.11.74221.6 0.1705 1.2 0.74 1015 11 1024 10 1045 22 1045 22 97.1 Final age data have been filtered using a cut-off of >20% for discordance and (33%) populations. FCB-A1-Spot 98 75 497210.8 13.48672.1 1.8533 2.50.18131.4 0.55 1074 13 1065 16 1045 41 1045 41 102.7 FCB-A1-Spot 129192 258662.8 13.48121.2 1.8453 2.00.18041.6 0.78 1069 15 1062 13 1046 25 1046 25 102.2 FCB-A1-Spot 227114 370871.8 13.48091.9 1.7042 2.50.16661.6 0.65 993 15 1010 16 1046 38 1046 38 94.9 FCB-A1-Spot 59 1012030162.0 13.48052.0 1.7339 2.40.16951.3 0.53 1010 12 1021 15 1046 41 1046 41 96.5 >5% for reverse discordance. For grains younger than 900 Ma, discordance FCB-A1-Spot 180233 534781.4 13.48001.7 1.8000 2.00.17601.1 0.55 1045 11 1045 13 1046 34 1046 34 99.9 FCB-A1-Spot 168134 1146953.0 13.47711.7 1.7786 2.20.17381.3 0.60 1033 12 1038 14 1047 35 1047 35 98.7 FCB-A1-Spot 80 43 177830.9 13.47183.4 1.7571 3.80.17171.7 0.45 1021 16 1030 24 1048 68 1048 68 97.5 207 235 206 238 FCB-A1-Spot 120181 270873.5 13.46951.4 1.7113 2.00.16721.4 0.72 997 13 1013 13 1048 28 1048 28 95.1 was calculated by comparing the Pb/ U age to the Pb/ U age, and the FCB-A1-Spot 128147 1927252.5 13.46521.7 1.6532 2.30.16141.5 0.66 965 14 991 15 1049 35 1049 35 92.0 FCB-A1-Spot 88 16534467 3.413.4599 1.51.72532.1 0.1684 1.4 0.68 1003 13 1018 13 1049 31 1049 31 95.6 FCB-A1-Spot 203179 362051.9 13.45971.3 1.7851 1.80.17431.3 0.69 1036 12 1040 12 1050 27 1050 27 98.7 206 238 FCB-A1-Spot 192652 807891.9 13.45920.9 1.8127 1.70.17691.4 0.83 1050 14 1050 11 1050 19 1050 19 100.1 Pb/ U ages are reported. For grains older than 900 Ma, discordance was FCB-A1-Spot 122296 1002102.4 13.45231.4 1.7396 1.70.16971.0 0.59 1011 9 1023 11 1051 28 1051 28 96.2 Illinois Basin FCB-A1-Spot 99 45 582472.1 13.44802.7 1.7290 3.00.16861.2 0.42 1005 12 1019 19 1051 55 1051 55 95.6 calculated by comparing the 206Pb/238U age to the 206Pb/207Pb age, and the 206 207 1Supplemental Table S1. Detrital-zircon data. Please Pb/ Pb ages are reported. A common lead correction is applied to all grains All three type signatures are represented in the Illinois Basin. Type 1 sig- visit http://doi.org/10.1130/GES01512.S1 or the full- following the method of Gehrels (2014). The analytical data are reported in natures are found in the Morrowan and Atokan strata. For example, IB-M1 text article on www.gsapubs.org to view Table S1. Supplemental Table S11. (n = 280) contains approximately equal proportions of Appalachian (15%)

1 Type 3 samples do not have ages >ca. 1550 Ma 0.9

Type 2: higher proportions 0.8 of Appalachian (270-490 Ma) y 0.7 and Neoproterozoic TYPE 1 TYPE 2 0.6 (530-750 Ma) FCB-A1 IB-M2 FCB-A2 FCB-D4 FCB-AD IB-D1 0.5 Figure 6. Cumulative probability plot of detrital-zircon data. FCB-D1 IB-D2 Gray box denotes the age range where Type 2 signatures are FCB-D2 most distinguishable from other types of signatures. 0.4 FCB-D3 TYPE 3

Cumulative Probabilit IB-M1 IB-D3 0.3 IB-AD IB-D4

0.2 Type 1 samples have generally lower proportions of 0.1 Appalachian (270-490 Ma) and Neoproterozoic (530-750 Ma)

0 400600 80010001200140016001800200022002400260028003000 Age (Ma)

and Superior (11%) populations, with a dominant Midcontinent cluster (31%). ulations (Fig. 8). Cambrian and older strata from the upper midcontinent and IB-M2 (n = 69) has approximately equal proportions of Appalachian (14%), Midcontinent Rift, which contain substantial Paleoproterozoic and Archean Neoproterozoic (19%), and Midcontinent (12%) populations. IB-AD (n = 81) is detrital-zircon populations (e.g., Craddock et al., 2013; Lovell and Bowen, 2013), dominated by a Midcontinent population (24%) and a subsidiary Appalachian are likely not primary contributors to sandstones with Type 1 signatures. Un- population (10%). derlying Mississippian strata from the midcontinent region, however, contain Desmoinesian strata in the Illinois Basin have both Type 2 and Type 3 signa- nearly identical zircon populations as the Type 1 signature (Fig. 8). Therefore, tures. IB-D1 (n = 258) has a Type 2 signature that is dominated by Appalachian we infer that remobilization of Mississippian sandstone in the IB and FCB by (16%) and Neoproterozoic (23%) populations. IB-D2 (n = 264) also has a Type 2 fluvial incision resulted in the detrital-zircon signature exemplified by Type 1 signature with approximately equal proportions of Appalachian (16%) and Neo- sandstones. This interpretation is supported by the lithological observations proterozoic (~15%) populations. IB-D3 (n = 91) has a Type 3 signature with 26% by Potter (1963), Potter and Pryor (1961), and Isbell (1985) in the IB and by Appalachian grains, 10% Midcontinent grains, and is devoid of grains older than Gregory (1982) and Scal (1990) in the FCB that sandstones identified as Type 1 1481 ± 23 Ma. IB-D4 (n = 65) has approximately equal proportions of Appalachian are often more compositionally similar to Mississippian sandstone than their (15%) and Midcontinent (17%) populations and no grains older than 1484 ± 48 Ma. overlying Pennsylvanian counterparts. Furthermore, Mississippian strata were likely exposed on topographic highs (i.e., the Mississippi River and Transcon- tinental Arches) adjacent to the IB and FCB (Potter and Siever, 1956a, 1956b; PROVENANCE INTERPRETATIONS Siever and Potter, 1956; Potter and Pryor, 1961) and could have been a significant source of sediment during Early and Middle Pennsylvanian time. Type 1 Signature

A composite Type 1 detrital-zircon signature is characterized by the domi- Type 2 Signature nance of a Midcontinent population (1300–1750 Ma; 15%–35%), a minimal Neo- proterozoic (530–750 Ma; <4%) population, and minor to moderate amounts of A composite Type 2 detrital-zircon signature is characterized by the Superior (>2500 Ma; 6%–17%) and Appalachian (270–490 Ma; 5%–16%) pop- dominance of Appalachian (15%–24%) and late Neoproterozoic (15%–36%)

Forest City Basin Illinois Basin

Appalachian Midcontinent terranes: Granite- Rhyolite belt and Yavapai-Mazatzal Neoproterozoic Trans-Hudson and Penokean Shelburn Fm. IB-D4 Grenville and Midcontinent Rift Superior province n=65

Carbondale Fm. IB-D3 n=91 Floris Fm. FCB-D4 n=263 Floris Fm. FCB-D3 Desmoinesian n=279 Floris Fm. Tradewater Fm. FCB-D2 IB-D2 n=285 n=264

Floris Fm. Tradewater Fm. FCB-D1 IB-D1 n=296 n=258

Kalo Fm. Tradewater Fm. FCB-AD IB-AD n=259 n=81 Kilbourn Fm. an FCB-A2 n=267 Atok

FCB-A1 n=294

Caseyville Fm. IB-M2

owan n=69

Morr Caseyville Fm. IB-M1 n=280 0 400 800 1200 1600 2000 2400 2800 3200 3600 0 400 800 1200 1600 2000 2400 2800 3200 3600 Age (Ma) Age (Ma)

Figure 7. Normalized relative age probability diagrams of detrital-zircon data. Colored rectangles illustrate age ranges of potential source terranes, and colors coordinate with basement terranes and magmatic belts shown on Figure 1A. n—number of grains.

as a potential source area. However, they are relatively common in Cambrian– Ordovician sediments in Newfoundland (Pollock et al., 2007), New Brunswick Type 1 composite (Fyfee et al., 2009), and New York (McLennan et al., 2001), where they sit on n=2041 peri-Gondwanan basement. The Gander and Avalonia peri-Gondwanan terranes that originated on Midcontinent Dev.-Miss. strata n=965 the margin of Amazonia (Gondwana) docked on the Laurentian margin either during Silurian and Devonian time (Fyffe et al., 2009) or during Carboniferous time (Wintsch et al., 2014). The Gander terrane comprises Archean through Neoproterozoic basement covered by Cambrian and Ordovician strata, while Type 2 composite the Avalonia terrane is composed of Neoproterozoic (ca. 760 Ma) volcanic and n=854 plutonic rocks and Neoproterozoic to Cambrian (545–630 Ma) volcanic, sedimentary, and plutonic assemblages. Today, these terranes are exposed from southeastern New England to Newfoundland (Fig. 1A). Appalachian Penn. strata n=493 Exposures of the Gander and Avalonia terranes in eastern Canada can be ruled out as potential sources for the Neoproterozoic grains because abundant paleocurrent information from the Maritimes Basin in eastern Canada support the presence of a complex of internally drained sedimentary basins with dom- Type 3 composite inant sediment transport toward the north-northeast (Fig. 1A; Gibling et al., n=156 1992; van de Poll et al., 1995; Gibling et al., 2008). Therefore, we favor a head- 0 400 800 1200 1600 2000 2400 2800 3200 3600 water position in southeastern New England for rivers that deposited Type 2 Age (Ma) sandstones in the FCB and IB. If accretion of the Gander and Avalonia terranes

Figure 8. Normalized relative age probability diagrams of detrital-zircon data from did occur during Carboniferous time (Wintsch et al., 2014), deformation as- this study (composites of Type signatures 1, 2, and 3), midcontinent Mississippian sociated with accretion could have exhumed parts of these peri-Gondwanan strata (D.H. Malone, 2016, personal commun.), and Pennsylvanian strata from the terranes and provided a new sediment source to the intracratonic basins. How- Appalachian foreland basin (Eriksson et al., 2004; Thomas et al., 2004; Becker et ever, even if accretion took place much earlier (e.g., Silurian–Devonian), defor- al., 2005, 2006). mation associated with the Alleghenian orogeny could have exhumed these potential source rocks.

populations, with minor to moderate Midcontinent grains (5%–13%; Fig. 8). Type 3 Signature Detrital-zircon signatures from older strata in the midcontinent (Lovell and Bowen, 2013; Konstantinou et al., 2014), as well as Laurentian midcontinent A composite Type 3 detrital-zircon signature has prominent Appalachian basement rocks, are virtually devoid of Neoproterozoic ages. Potential known (15%–26%) and Midcontinent (10%–17%) populations but lacks pre-Granite sources of Neoproterozoic-age zircons include the Iapetan synrift ca. 520– Rhyolite grains (>1550 Ma; Fig. 8), which suggests that recycling of the un- 620 Ma dikes and rhyolites that range from Newfoundland to the southern derlying Type 1 or Type 2 sandstones or older strata was minimal. The di- Oklahoma fault system (e.g., Thompson et al., 1996; Hogan and Gilbert, 1998; minished amount of Neoproterozoic ages also suggests abandonment of the Cawood and Nemchin, 2001), the ca. 750 Ma Mt. Rogers volcanics in western northeastern provenance that was characteristic of Type 2 signatures. Type 3 North Carolina (e.g., Su et al., 1994), and Pan-African metasedimentary ter- signatures most closely resemble the signatures of coeval strata in the central ranes that underlie present-day New England and Newfoundland, as well as Appalachian foreland basin (Fig. 8; Eriksson et al., 2004; Becker et al., 2005; Maritime Canada and the southeastern United States (Fig. 1A; Zartman et al., Becker et al., 2006); these strata also contain very few Neoproterozoic grains 1988; Heatherington et al., 1999; Wortman et al., 2000; Hibbard et al., 2002; and are dominated by Appalachian and Midcontinent ages. Therefore, we in- Pollock et al., 2007; Fyffe et al., 2009). fer that the Type 3 sandstones represent sediment derivation from the distal Several lines of evidence suggest that the Pan-African terranes underlying central Appalachian orogen. This interpretation is supported by numerical southeastern New England may be the most likely source for these popula- models that suggest that the Cincinnati Arch was covered by sediments from tions in Type 2 sandstones. Neoproterozoic ages are largely absent in Paleo- the unroofing of the Appalachians by at least Late Pennsylvanian time, if not zoic strata adjacent to the central and southern portions of the Appalachian earlier, depositionally linking the IB with the Appalachian foreland (Quinlan Basin (Fig. 8; Thomas et al., 2004; Becker et al., 2005), precluding those regions and Beaumont, 1984).

DISCUSSION 1956, 1957; Kosanke et al., 1960; Fitzgerald, 1977; Lemish et al., 1981; Gregory, 1982; Ravn et al., 1984). In general, in both basins, Lower–Middle Pennsylva- Early–Middle Pennsylvanian Paleogeography nian strata that have a Type 1 signature have been interpreted as fluvial deposits in regional-scale depositional systems with relatively small watersheds Morrowan Time and spatially limited provenance located on adjacent structural highs or the Canadian Shield (Fitzgerald, 1977; Lemish et al., 1981; Gregory, 1982). Although mudstone-dominated Morrowan strata occur as small, isolated Type 2 sandstones, in contrast, share different key characteristics with the paleokarst fills in eastern Iowa and western Illinois, between the FCB and IB, in- longitudinal and trunk systems described above, including (1) being multi-story, tact stratigraphic sections of Morrowan strata have not been identified within >10-m-thick sandstone bodies; (2) 1–1.5-m-thick cross-bedding and moderate- the FCB (Pope, 2012). In the IB, two samples from the Caseyville Formation to high-relief erosional bases (Fig. 5); (3) litharenite sandstone compositions suggest variable provenance during Morrowan time. IB-M1 from eastern Iowa with an increase in the relative proportion of mica (Fig. 3); and (4) a general has a Type 1 signature that suggests a regional-scale fluvial system that was paucity of fine-grained interbeds (Table 2; Fitzgerald, 1977; Osolin, 1983; An- reworking locally derived and underlying strata, whereas IB-M2 from northern derson et al., 1999). Strata at Type 2 localities have generally been interpreted Illinois has a Type 2 signature indicative of a more distal provenance in the as channel deposits from larger fluvial systems, indicating that the watershed New England region. regions were larger compared to those for Type 1 sandstones (Fitzgerald, 1977; Grimm et al. (2013) documented Lower Pennsylvanian transverse and Osolin, 1983; Isbell, 1985). Furthermore, analyses by Siever and Potter (1956), longitudinal fluvial systems in the Pocahantas subbasin of the Appalachian Fitzgerald (1977), Osolin (1983), and Scal (1990) classify Type 2 sandstones as foreland basin in southern West Virginia, Virginia, and eastern Kentucky. less compositionally mature than typical Type 1 sandstones, and thus more There, the deposits of transverse systems are characterized by channelized, likely to have been derived at least in part from a crystalline source. interbedded sandstone and mudstone bodies 5–25 m thick with mostly trough Our model for Morrowan axial rivers in the western IB is similar to the cross-bedded cosets from 0.1 to 2 m thick. Longitudinal systems, however, previously proposed Early Pennsylvanian sediment dispersal models in the have 10–50-m-thick multi-story sandstone bodies, with individual cross-bed eastern IB (Bristol and Howard, 1971; Rice and Schwietering, 1988; Droste and sets that are 0.5–1.5 m thick. Combined, these strata are interpreted to repre- Keller, 1989; Archer and Greb, 1995). In the model by Archer and Greb (1995), sent a S- to SW-flowing, continental-scale axial fluvial system in the Appala- rivers with headwaters as far north as southeastern Canada drained into the chian Basin during Lower Pennsylvanian time (Fig. 9A). eastern IB on the western side of the southwest-trending Cincinnati Arch (Fig. In the eastern IB, lithological variations in the Morrowan Caseyville Forma- 9A). Our data suggest that another far-traveled fluvial system with headwaters tion have also been attributed to the interplay between trunk (i.e., longitudinal) in the New England area brought sediment to the western IB during Morrowan and tributary (i.e., transverse) rivers as well (Kvale and Archer, 2007). Trunk time (Fig. 9B). systems are dominated by purely fluvial deposits consisting of medium- to Combined uplift and erosion of source areas to the north and east of the IB coarse-grained sandstone and conglomerate. In contrast, tributary systems and FCB that was initiated by Alleghenian crustal loading, along with a lower have mudstone with thin, interbedded sandstone, as well as tidal rhythmites, base level and marine basin in the Ouachita region during Mississippian time traces fossils, and macro- and microfauna that provide evidence for marine (Beaumont et al., 1988), resulted in a continental-scale, southwest-inclined pa- influence far inboard from the paleoshoreline. Evoking the modern Amazon leoslope that facilitated transcontinental sediment dispersal prior to and during Basin as an example, where marine influences are observed ~800 km inland Morrowan time (Potter and Pryor, 1961). Paleoflow indicators and petrological from the shoreline, those authors postulated that sandy trunk rivers, similar to observations in the northern part of the IB indicate Morrowan rivers reworked our Type 2 deposits, had the capability to efficiently dampen marine processes pre-Pennsylvanian sedimentary strata exposed to the west and northeast of from the distant shoreline as well as supply extrabasinal detritus. In contrast, the basin (Fitzgerald, 1977). The Mississippi River Arch, situated between the muddy tributary rivers, similar to our Type 1 deposits, were more strongly in- FCB and the IB, served as a topographic high and possible sediment source fluenced by long tidal ranges and consisted of more locally derived sediments. during this time (Isbell, 1985). Type 1 sandstones in this study share several key characteristics with the The role of the northern portion of the Cincinnati Arch in Ohio and southern transverse and tributary deposits described above, including (1) being very Canada in preventing east-to-west sediment transport during the Carbonifer- fine to fine-grained, thin- to medium-bedded, quartz-rich sandstone (Fig. 3) in ous, however, is still poorly understood due to the absence of Mississippian single- or multi-story bodies generally <5 m thick; (2) dm-scale cross-bedding and Pennsylvanian sediments on the arch (Root and Onasch, 1999). Nonethe- and low-relief erosional or sharp bases; (3) abundant and thick fine-grained in- less, in Kentucky, stratigraphic relationships indicate that the arch was a prom- terbeds; (4) evidence for marine influence (Figs. 4C, 4D, and 4F). Furthermore, inent topographic feature until Middle Pennsylvanian time (Tankard, 1986; Rice Type 1 sandstones are stratigraphically positioned in the lower parts of both and Schwietering, 1988). In contrast, our results suggest that the Kankakee and basins, often near the basal Pennsylvanian unconformity (Table 2; Wanless, Wisconsin arches between the Michigan and Illinois Basins were structural

A. Previous interpretations B. Morrowan Bristol and Howard, 1971 IB: Type 1 and Type 2 Rice and Schwietering, 1988 FCB: no Morrowan strata Droste and Keller, 1989 Archer and Greb, 1995

in in u u q q n n o o g AB g l l A A MB MB F F AB i i n n

d d W l W l is a is a con y con y sin Kankakee sin Kankakee C C i i n n

M c M c i i n n i IB i IB s n s n s s a a Figure 9. Schematic paleogeographic . . t t R i R i reconstructions showing previously in- iv iv terpreted as well as our inferred paleo- e e r r geographic evolution of eastern North FCB FCB America during Early–Middle Pennsylva- N N nian time. These diagrams illustrate the 0 250 0 250 general sediment dispersal patterns for km km each time period shown. Details of each C. Atokan to early Desmoinesian D. Early-middle Desmoinesian illustration are discussed in the text. Po- sitions of structural basement arch com- IB: Type 1 and Type 2 IB: Type 3 plexes that are inferred to have a topo- FCB: Type 1 FCB: Type 2 graphic expression are shown in red, and those inferred to not influence sediment dispersal patterns for each time period are shown in gray. n n i i u u

q q

n n

o o

g g l l

A A AB MB MB F AB F i i n n

d d W l W l is a is a co y con y nsin Kankakee sin Kankakee C C i i n n c c M i i n M IB n i n n s i IB a s a s t s t . i i . R R iv i e v r FCB er FCB N N 0 250 0 250 km km

TABLE 2. SEDIMENTOLOGIC CHARACTERISTICS OF TYPE SANDSTONES Type signature Sedimentologic characteristicsSandstone composition Stratigraphic position Type 1Very fi ne to fi ne-grained, thin-bedded (<~1 m), <~5 dm-thick cross beds when Quartz-arenite with minor mica and Lower parts of both basins, often present, evidence for tidal infl uence, low-relief erosional or sharp bases, carbonate lithics near the basal Pennsylvanian abundant and thick fi ne-grained interbeds unconformity Type 2 Fine- to coarse-grained, multi-story, multi-meter-thick sandstone, <~1.5-m-thick Dominantly subarkose or sublithic to Throughout the Illinois Basin and in cross beds, moderate- to high-relief erosional bases, general lack of fi ne- lithic arkose or feldspathic litharenite, the upper part of the Forest City grained interbeds ~5%–10% mica, feldspar, lithic grains Basin Type 3 Fine- to coarse-grained, multi-story, multi-meter-thick sandstone with moderate- Dominantly subarkose or sublithic to Stratigraphically highest samples to high-relief erosional bases, general lack of fi ne-grained interbeds lithic arkose or feldspathic litharenite, in the Illinois Basin; not found in ~5%–10% mica, feldspar, lithic grains Forest City Basin Note: Each type has a distinct detrital-zircon signature as well as unique sedimentologic characteristics.

arches but not topographic highs that presented a southward-directed sedi- in the central and southern Alleghenian orogeny (Tankard, 1986; Rice and ment dispersal pattern across the two basins. Furthermore, numerical models Schwietering, 1988). by Beaumont et al. (1988) infer that the Kankakee Arch was a region of nondeposition, but not erosion, during Early Pennsylvanian time. Middle Desmoinesian Time

Atokan to Early Desmoinesian Time In the FCB, our stratigraphically highest sample (IB-D4) has a Type 2 detrital-zircon signature and sedimentological characteristics consistent with In the FCB, Atokan and early Desmoinesian strata exhibit Type 1 detrital- the continued westward migration of a large-scale fluvial system with head- zircon signatures and sedimentological characteristics consistent with waters in southeastern New England into central Iowa (Fig. 9D). This inference, regional-scale fluvial systems and local sediment reworking. These strata rep- as well as stratigraphic data and correlations between the IB and FCB (Isbell, resent the oldest widespread evidence for establishment of post-Mississippian 1985; Nelson et al., 2013), indicate that the Mississippi River Arch was over- depositional systems in the FCB. Our results suggest that regional-scale fluvial topped by sediment during middle Desmoinesian time, and that the basins systems dominated during this time and that Mississippian strata were eroded became depositionally linked. from adjacent topographic highs and deposited into the basin (Fig. 9C). In the IB, however, middle Desmoinesian strata have Type 3 detrital-zircon In the IB, three samples from the Tradewater Formation suggest the per- signatures. Type 3 sandstones in this study share several key characteristics, sistence of variable provenance into Atokan and early Desmoinesian time. including (1) being multi-story, multimeter-thick sandstone with moderate- to IB-AD from west-central Illinois has a Type 1 detrital-zircon signature and sed- high-relief erosional bases (Figs. 5F and 5G); (2) having litharenite sandstone imentological characteristics that are consistent with smaller-scale fluvial sys- compositions with high proportions of mica; and (3) being the stratigraphically tems and regional provenance. IB-D1 and IB-D2 from eastern Iowa, however, highest samples in the IB (Table 2). Strata at our Type 3 localities have previ- have Type 2 detrital-zircon signature and sedimentological characteristics that ously been interpreted as deposits of continent-scale fluvial systems (Wanless we infer to represent a larger network of fluvial systems that supplied detri- et al., 1963). tus from southeastern New England to the basin. This pattern demonstrates a Earlier workers had inferred that by the end of the Middle Pennsylvanian, slight westward shift of the extrabasinal fluvial systems from northern Illinois filling of the Appalachian Basin and overtopping of the Cincinnati Arch likely in Morrowan time to eastern Iowa by early Desmoinesian time. leveled the depositional plain between the Alleghenian orogen and the Lauren- We infer that the topographic configuration of the basin-bounding arches tian midcontinent (Nelson et al., 2013). Type 3 signatures in the IB indicate that persisted from Morrowan time into Atokan and early Desmoinesian time transverse, orogen-perpendicular drainage systems extended into the basin (Fig. 9C). The Mississippi River Arch likely served as a barrier to the large- during Middle Pennsylvanian time, replacing axial systems and shifting prov- scale fluvial system head-watered in southeastern New England that was enance to central or southern Appalachian sources (Fig. 9D). The overtopping migrating to the west in the IB. The Kankakee Arch appears to have contin- of the Cincinnati and related arches would have removed the barrier to trans- ued to be a region of nondeposition or sediment bypass for this extrabasinal verse flow and enabled the westward propagation of these fluvial systems. A fluvial system. Furthermore, the Cincinnati and related arches continued to subtle transition from southwest (~220°) to west-southwest (~252°) paleoflow separate the IB from the Appalachian Basin and sediment sources located directions in Missourian strata just above our Type 3 sandstones (Potter and

Pryor, 1961) may reflect this inferred shift in drainage style, from rivers with Tornqvist, 2000; van Heijst and Potsma, 2001). In the FCB, we infer that fluvial catchment areas in the New England area to more westward-flowing systems systems responded to eustatic rise by aggrading and accumulating sediments with headwaters in the central Appalachians. that comprise the Kalo and Kilbourn Formations. Schumm (1993) proposed that sea-level rise would result in “backfilling” of incised valleys, the deposits of which should thicken downstream and fine up- Interplay between Sedimentation, Sea-Level Rise, and Tectonics ward. Although the overall thickness of the Kalo and Kilbourn Formations in- creases in a general down-dip direction in the FCB, the thickness of these units During late Paleozoic time, variations in eustatic sea level and significant in individual paleovalleys has not been explored. However, there is an overall changes in the global tectonic configuration of landmasses affected the North upsection decrease in grain size from the Kilbourn to the Kalo Formation and American continent. One of three major Paleozoic eustatic sea-level lows oc- lower parts of the Floris Formation, suggesting “backfilling” in response to curred near the Mississippian/Pennsylvanian boundary and was followed by eustatic sea-level rise as a potential mechanism for these units. Furthermore, a eustatic rise that continued into Late Pennsylvanian time (Haq and Schutter, because our data preclude a significant extrabasinal sediment source during 2008). Alleghenian mountain building that is linked to the creation of the Pan- this time, we infer that the Kilbourn and Kalo river systems recycled older, gean supercontinent also began in latest Mississippian time and continued underlying sedimentary strata in order to aggrade their beds. until latest Pennsylvanian or Permian time (Hatcher, 1989). Lower to Middle In the IB, sedimentation continued during Atokan to early Desmoinesian Pennsylvanian strata deposited in the IB and FCB record the interplay between time with deposition of the Tradewater Formation. The Tradewater Formation these two pivotal events. is interpreted to represent dominantly nonmarine environments; however, cy- During Morrowan time, eustatic sea level was falling and reached its ul- clothems are better developed and more prominent in the upper parts of the timate low position at the Morrowan/Atokan boundary (Fig. 2). There are no Tradewater Formation during latest Atokan and earliest Desmoinesian time intact Morrowan strata preserved in the FCB, but the Caseyville Formation (Nelson et al., 2013). This increase in marine influence earlier in the IB relative was deposited and preserved in the IB. Although accommodation for sedi- to the FCB may be related to both the south-directed depositional slope and ment accumulation was likely limited by eustatic fall, the IB is located in a greater amount of subsidence produced by Alleghenian crustal loading and, as more proximal position to the advancing thrust loads located in the Ouachita a result, seaways that impinged in the IB before the FCB. and Appalachian regions than the FCB. Therefore, it may have experienced Eustatic sea level continued to rise during Desmoinesian time (Fig. 2). As a more profound flexural depression that permitted accumulation of sediments result in the FCB, the first appearance of poorly developed cyclothems occurs in the basin. in the upper part of the Floris Formation, with the first well-developed cyclo- Beaumont et al. (1988) predicted ~240 m of tectonic subsidence at the cen- thems in the overlying Verdigris Formation (Pope, 2012). Lowstand conditions, ter of the IB during Early Pennsylvanian time. In the classic model of tectonic however, continued to afford episodic fluvial deposition in both the IB and FCB. subsidence of foreland basins (e.g., DeCelles and Giles, 1996), the degree of Alleghenian deformation continued along the eastern margin of the con- subsidence induced by thrust loading decreases dramatically inboard from the tinent including the southern and central Appalachians (Hatcher, 1989). Exhu- forebulge. The IB sits adjacent to the Alleghenian forebulge (Cincinnati Arch) mation of those regions likely increased the sediment flux to the Appalachian and therefore was affected by tectonically driven subsidence; whereas the FCB foreland basin, which became overfilled during Middle Pennsylvanian time is situated ~400 km farther inboard and thus was not affected by Alleghenian and allowed sediments derived from the southern and central Appalachians thrust loading (e.g., Beaumont et al., 1988). to reach the IB. The low-amplitude, long-wavelength foreland subsidence in A significant provenance region for some of the Morrowan Caseyville For- the Appalachian Basin also promoted rapid overfilling of the basin (Thomas et mation strata in the IB is inferred to be southeast New England. That region ex- al., 2004). This westward migration of depositional systems is mimicked in the perienced intense deformation with the Acadian orogeny during Middle Devo- FCB by the arrival of the large fluvial system with a New England provenance. nian to Early Mississippian time (Hatcher, 1989). Relict highlands in that region, Farther west, late Paleozoic strata in the Grand Canyon have detrital-zircon combined with flexural loading along the southwest margin of the continent age populations that are interpreted to reflect sediment flux from the southern during Late Mississippian to Early Pennsylvanian time (Beaumont et al., 1988) and central Appalachians (Gehrels et al., 2011). Mississippian and Pennsylva- produced an overall southward slope to the continental surface (Siever and nian strata there have signatures that are similar to our Type 1 in that they con- Potter, 1956) that likely contributed to the New England provenance signature. tain abundant Appalachian (270–490 Ma) and Grenville (980–1300 Ma) ages, Beginning in Atokan time, eustatic sea level began to rise (Fig. 2). Although with smaller proportions of Superior ages (>2500 Ma) but essentially lack any the controls on fluvial aggradation are complicated and can include climate, Neoproterozoic ages (530–750 Ma). By Early Permian time, however, strata in sediment supply, and stream power, it is generally agreed that during eustatic the Grand Canyon record the influx of Neoproterozoic age populations, more sea-level rise there is a downstream decrease in sediment transport rate and similar to our Type 2 signature. We infer this trend to represent the continued increase in the rate of channel-bed aggradation (Schumm, 1993; Blum and westward migration of the transcontinental fluvial system with headwaters in

southeastern New England across the North American continent from the Il- provenance that is typically associated with the distal portions of a foreland linois Basin during Early Pennsylvanian time, to the Forest City Basin during basin system. late Middle Pennsylvanian time, to the southwestern United States by Early Permian time. CONCLUSIONS

Implications for Foreland Basin Systems New detrital-zircon geochronologic data from Early to Middle Pennsylvanian strata in the Illinois and Forest City Basins provide additional constraints on the The Cincinnati Arch is considered to have acted as a forebulge during the paleogeography and sediment dispersal patterns on the North American mid- Alleghenian orogeny, placing the IB in a backbulge position in the Appalachian continent. Morrowan–middle Desmoinesian strata in the Illinois and Forest City foreland basin system during Pennsylvanian time (Quinlan and Beaumont, Basins have detrital-zircon signatures and sedimentologic characteristics that 1984; Root and Onasch, 1999). Sediment preservation in the backbulge region are interpreted to reflect the presence of both regional-scale fluvial systems that of collisional foreland basin systems is relatively uncommon (DeCelles, 2012). recycled underlying sedimentary strata and large-scale fluvial systems that sup- Nevertheless, several factors, including gradual weakening of the lithosphere, plied detritus shed from southeastern New England. By Early Permian time, the availability and efficiency of sediment transport, and prevalence of accom- fluvial systems with headwaters in New England may have been delivering sedi- modation, all play a role in determining whether backbulge deposits are pre- ment to the Grand Canyon area in the southwestern United States. In the midcon- served in the stratigraphic record (Jordan, 1995). tinent, these depositional systems were ultimately replaced by transverse fluvial Deposition in the Appalachian backbulge region during Early to Middle systems that supplied sediment from the southern and central Appalachians to Pennsylvanian time was likely enabled by a number of factors. The midconti- the intracratonic basins. Increased subsidence in the intracratonic Illinois Basin, nent was situated within tropical to equatorial latitudes on or near the equator due to its backbulge position, in combination with high sediment flux from the during the Early Pennsylvanian (Witzke, 1990). The climate transitioned from Alleghenian orogeny, climatic conditions conducive to high rates of erosion, and semi-arid during Late Mississippian time to tropical and monsoonal equatorial accommodation created by rising eustatic sea level may have resulted in the during Early Pennsylvanian time (Cecil et al., 1985). These subtropical climatic greater thickness of Pennsylvanian strata in that basin. In a broader sense, our conditions are conducive to high rates of erosion. This circumstance, in combi- results suggest that aggradation of sediments in cratonic depositional systems nation with the axial fluvial systems with larger watersheds, may have resulted that are responding to eustatic sea-level rise should result in a provenance signa- in higher rates of sediment flux than are normally found in the backbulge depo- ture that reflects recycling of readily available, underlying strata. When tectonics zone. In addition, accommodation on the craton continued to increase during plays a dominant role in compelling sedimentation, however, the provenance Pennsylvanian time as a result of eustatic sea-level rise (Haq and Schutter, signature would be characterized by extrabasinal sediment sources. 2008), as well as potentially from reactivation of basement structures beneath the basins (Anderson and Wells, 1968; Mason, 1980; Root and Onasch, 1999). While continental-scale drainages in cratonic settings may exist inde- ACKNOWLEDGMENTS pendently of orogenic-related exhumation, the progradation of transverse This work was the result of an M.S. project completed by Kyle Kissock (2016). EF and KK are grate- rivers across the continent, even during a time of overall sea-level rise, was ful to Phil Heckel and Bill McClelland for advising Kyle and providing valuable feedback on the thesis. Financial support for this project was provided by a Geological Society of America Gradu- likely the result of a massive erosional response to the formation of Pangea. ate Student Research Grant and the Earth and Environmental Sciences at the University of Iowa. The flooding of cratons with orogen-derived sediments is a documented by- We thank Iowa graduate student Will Ward, University of Iowa undergraduates Dan Alberts and product of supercontinent cycles (Veevers, 2004; Cawood et al., 2007). For Zach Miller, and Illinois State University undergraduate Justin Calhoun for their assistance with mineral separation and analyses, and the Iowa Geological Survey for access to the core. Student example, the Grenville orogen was a major late Mesoproterozoic mountain- support to travel to the Arizona LaserChron Center was provided by National Science Foundation building event that included the amalgamation of continents to form the Rod- grant EAR-1338583. Bill Thomas, Mike Blum, and Greg Ludvigson kindly provided very helpful inian supercontinent (Rainbird et al., 2012; Konstantinou et al., 2014; Spencer comments on an early version of this manuscript. Paul Umhoefer, Bill Hein, and Associate Editor et al., 2014; Malone et al., 2016). The exhumation and denudation of the Gren- Nancy Riggs provided valuable feedback that helped to improve this manuscript. ville orogen is recorded in sedimentary basins on all margins of Laurentia, as far away as the Amundsen Basin in northwest Canada, several thousands of REFERENCES CITED kilometers from the sediment source (Rainbird et al., 2012). Transcontinental sediment dispersal related to mountain building during amalgamation of a su- Anderson, K.H., and Wells, J.S., 1968, Forest City basin of Missouri, Kansas, Nebraska, and Iowa: percontinent is a typical response for coeval depositional systems preserved in American Association of Petroleum Geologists Bulletin, v. 52, no. 2, p. 264–281. 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