Part I. Characterization of Paleosol Types and Interpretation of Pedogenic Processes

Home , Bond Formation, Patoka Formation, Shelburn Formation

Journal of Sedimentary Research, 2013, v. 83, 606–636 Research Article DOI: 10.2110/jsr.2013.50

POLYGENETIC HISTORY OF PALEOSOLS IN MIDDLE–UPPER PENNSYLVANIAN CYCLOTHEMS OF THE ILLINOIS BASIN, U.S.A.: PART I. CHARACTERIZATION OF PALEOSOL TYPES AND INTERPRETATION OF PEDOGENIC PROCESSES

1 1 2 2 NICHOLAS A. ROSENAU, NEIL J. TABOR, SCOTT D. ELRICK, AND W. JOHN NELSON 1Roy M. Huffington Department of Earth Sciences, Southern Methodist University, 3225 Daniel Avenue, Dallas, Texas 75275-0395, U.S.A. 2Illinois State Geological Survey, 615 East Peabody, Champaign, Illinois 61820, U.S.A. e-mail: [email protected]

ABSTRACT: The morphology, mineralogy, and stratigraphic and lateral distribution of paleosols in Pennsylvanian (Moscovian–Gzhelian; Atokan–Virgilian) mixed marine and terrestrial coal-bearing strata (i.e., cyclothems) in the Illinois basin (IB) are presented in order to determine the dominant pedogenic processes within a cyclic sedimentary depositional framework. Paleosol morphologies range from weakly developed horizons with evidence of rooting and little to no pedogenic structure, to horizons with well-developed pedogenic slickensides, angular blocky structure, and carbonate nodules and tubules. The majority of paleosols in strata from the basin interior preserve (1) low chroma (gley) colors, (2) identifiable fossil plant organic matter that increases in abundance upward in the profiles toward the interpreted paleo-surface, and (3) calcite, sphaerosiderite, and pyrite cements and nodules. In contrast, paleosols in strata from the northern margin of the basin display high chroma colors and calcite cements and less fossil organic matter, sphaerosiderite, and pyrite cements. These observations indicate that paleosols from the basin interior underwent a multi-phase pedogenic and shallow burial history characterized by an initial better-drained, oxygenated stage under seasonal precipitation, followed by a poorly drained, reducing stage, while paleosols from the northern margin of the basin experienced overall more oxygenated conditions throughout their pedogenic development. X-ray diffraction analysis of the , 2 mm size fraction of paleosol matrix in IB paleosols indicates a mineralogical composition dominated by kaolinite, randomly interstratified (R0) and ordered (R1) illite–smectite (I/S), and subordinate amounts of chlorite. These combined observational and mineralogical datasets indicate that significant changes in paleohydrology were largely responsible for the development of Pennsylvanian soil profiles in the IB.

INTRODUCTION petrology of Pennsylvanian paleosols in the IB and utilized their morphologies as general indicators of paleoenvironmental conditions The objective of this paper is to provide detailed descriptions and (e.g., Weller 1930; Archer and Greb 1995; de Wet et al. 1997; Cecil et al. interpretations of pedogenically modified horizons in middle–upper Penn- sylvanian cyclic strata (cyclothems) in the Illinois basin (IB). The economic 2003; DiMichele et al. 2010; Falcon-Lang and DiMichele 2010). and paleoenvironmental significance of Pennsylvanian cyclothemic coal- However, until now, a detailed documentation of their stratigraphic bearing strata in the Illinois basin has long been recognized, resulting in an distribution and spatial variability across the basin as well as a thorough extensive collection of paleobotanical (e.g., Winslow 1959; Peppers 1964, discussion of the genesis of paleosol profiles in the IB have not been 1970, 1996; Phillips et al. 1974, 1985; Pfefferkorn and Thomson 1982; undertaken. This study is the first detailed and stratigraphically complete DiMichele and Phillips 1985; DiMichele and Aronson 1992), sedimentolog- presentation of the morphological and mineralogical content of paleosol ical (e.g., Siever 1957; Smith and O’Brien 1965; Keller 1968, 1979; Kvale et al. profiles preserved in Pennsylvanian (Atokan–Virgilian; Westphalian– 1994; Archer and Greb 1995; Archer et al. 1995), and stratigraphic studies Stephanian) strata of the IB. Widespread exposures and the ability to (e.g., Wanless 1931; Wanless and Weller 1932; Siever 1951), the results of define age-equivalent deposits across the basin based on laterally which have provided a richer understanding of the geologic, paleoecologic, extensive coal seams and distinct lithostratigraphic units makes the IB and paleoclimatic history of the Pennsylvanian tropics of North America. an ideal area to examine the pedogenic history and spatial variability of Fine-grained, non-bedded strata (i.e., underclays) commonly underlie paleosols developed in cyclothemic strata. This paper focuses on detailed Pennsylvanian Euramerican coal beds in cyclothems and constitute a field-based observations of paleosol morphology, as well as the significant stratigraphic component of Pennsylvanian strata in the IB. distribution and occurrence of redox-sensitive minerals in conjunction Various interpretations have been developed regarding the origin of these with complementary petrographic and mineralogical analyses, in order to units (Potonie 1910; Grim 1935; Grim and Allen 1938; Schultz 1958; characterize the pedogenic processes that dominated in soil profiles across Baker 1962; Duff and Walton 1962; Parham 1966 and references therein); Pennsylvanian-age paleolandscapes in the IB. A companion paper to this however, it is now widely recognized that these strata are principally fossil contribution (Part II; Rosenau et al. 2013) discusses the basinal, regional, soils (paleosols) that developed on paleolandscapes during periods of and global controls responsible for the spatial and temporal distribution relative stability. Previous workers have documented the occurrence and of paleosol types preserved in IB cyclothems.

Published Online: July 2013 Copyright E 2013, SEPM (Society for Sedimentary Geology) 1527-1404/13/083-606/$03.00 JSR PENNSYLVANIAN PALEOSOLS OF THE ILLINOIS BASIN: PART I 607

FIG. 1.—Map illustrating extent of the Illinois basin in Illinois, Indiana, and Kentucky, as defined by the distribution of Pennsylvanian rocks in outcrop and subcrop. Circles illustrate paleosol-bearing stratigraphic sections in cores and outcrops. Encircled numbers illustrate locations of paleosol-bearing stratigraphic sections discussed in detail in this study. Cinc. Arch 5 Cincinnati Arch. See Table 1 for details on cores and outcrops.

GEOLOGIC BACKGROUND vanian strata in the IB is , 2400 m. However, temperature estimates Tectonics and Basin History based on fluid inclusions from diagenetic sphalerites (Damberger 1971, 1974, 1991; Cobb 1981; Coveney et al. 1987), vitrinite reflectance (Comer The IB is an oval-shaped cratonic basin that began accommodation of et al. 1994; Barrows and Cluff 1984), smectite to illite transformations sedimentary strata in the late Precambrian to Early Cambrian in response (Gharrabi and Velde 1995; Grathoff et al. 2001; Rowan et al. 2002), and to extension in the Reelfoot rift and Rough Creek graben in the eastern stable-isotope analysis of quartz cements (Chen et al. 2001; Pollington et midcontinent of the United States (Kolata and Nelson 1991, 1997). The al. 2011) suggest that most Pennsylvanian strata in the IB did not likely IB covers approximately 155,000 km2 in parts of Illinois, Indiana, and exceed a burial depth of , 1500 m (equivalent to eroded post- Kentucky, and contains approximately 450,000 km3 of Cambrian– Carboniferous strata), and except for perhaps a brief duration, in deeper, Pennsylvanian sedimentary strata that noncomformably overlie Precam- southern portions of the basin, most strata did not experience burial brian granites (Fig. 1; Buschbach and Kolata 1991). Major bounding temperatures . 100uC (Harris 1979; Elliott and Aronson 1993; Grathoff structures, which separate the IB from adjacent provinces, are the et al. 2001). Kankakee Arch to the northeast, the Wisconsin Arch to the north, the The IB remained between 0 and 5u N throughout this interval, though Ozark Dome to the southwest, and the Cincinnati Arch to the east northward drift persisted through the late Pennsylvanian to Early (Fig. 1; Willman et al. 1975). Permian (Fig. 3A, B; Scotese et al. 1999; Blakey 2007). The North Pennsylvanian strata constitute a significant stratigraphic component American Midcontinent Sea (NAMS) covered much of the current of the IB (Hopkins and Simon 1975; Buschbach and Kolata 1991). The United States from the Appalachian Basin westward during times of sea- greatest degree of Pennsylvanian subsidence and sediment accumulation level highstand, opening westward and northward into the Panthalassa occurred in the southeastern part of the IB, resulting in a maximum Ocean (Fig. 3B; Algeo et al. 2004; Algeo and Heckel 2008). The dominant thickness of nearly 760 meters (Fig. 2; Willman et al. 1975). Many of the Pennsylvanian depositional environments in the IB were fluvial and lower Pennsylvanian stratigraphic units, including the Caseyville, Trade- estuarine incised valleys and deltaic systems, as well as clastic- and water, and Carbondale formations, pinch out to the north and northwest carbonate-dominated shallow marine systems (Wanless et al. 1963). (Hopkins and Simon 1975). The upper surface of the Pennsylvanian rocks During sea-level lowstands, the dominant fluvial transport direction in is an eroded post-Pennsylvanian surface (Willman et al. 1975) where it is the basin was from north-northeast to south-southwest (Willman et al. estimated that up to 1600 m of Permian to Lower Cretaceous strata were 1975). Pennsylvanian biostratigraphic zones in the IB are based on eroded (Damberger 1971; Zimmerman 1986; Buschbach and Kolata fusulinids (Dunbar and Henbest 1942; Douglass 1987), ostracods 1991). Therefore, a potential maximum burial depth for basal Pennsyl- (Thompson et al. 1959; Thompson and Shaver 1964), spores (Winslow 608 N.A. ROSENAU ET AL. JSR

1959; Peppers 1964, 1970, 1996), and conodonts (Heckel and Baesemann 1975; Swade 1985; Heckel 1991; Heckel and Weibel 1991) that facilitate regional and global correlations to Moscovian–Gzhelian strata in contemporaneous basins (Ritter et al. 2002; Barrick et al. 2004; Heckel et al. 2007; Falcon-Lang et al. 2011).

Stacking Patterns of Pennsylvanian Strata Pennsylvanian strata of the IB are characterized by abundant (. 500) and commonly abrupt vertical changes in lithology that may include underclay (i.e., paleosols), coal, shale, limestone, siltstone, and sandstone (Fig. 2; Kosanke et al. 1960; Willman et al. 1975; Nelson et al. 2011). Approximately 90–95% of the Pennsylvanian strata consist of clastic rocks (Willman et al. 1975). Sixty percent of the lower Pennsylvanian (Morrowan; Caseyville–lower Tradewater formations) is composed of quartz sandstone, followed by siltstone, shale, and , 1% limestone and coal, whereas only , 25% of the middle and upper Pennsylvanian strata (Atokan–lower Desmoinesian; upper Tradewater Formation) are composed of sandstone, while shale, claystone, and paleosols make up 65– 70% of these strata (Siever 1957; Hopkins and Simon 1975). Upper Desmoinesian–Virgilian strata in the IB are characterized by a series of repeated successions of terrestrial, deltaic, and marine deposits that are called cyclothems (Udden 1912; Wanless and Weller 1932). These stratigraphic sections contain numerous pedogenically modified horizons with a broad range of morphologies (Hopkins and Simon 1975; Greb et al. 1992; Mastalerz and Shaffer 2000). Heckel (2008) recognized patterns of minor, intermediate, and major sea-level fluctuations in the Mid- continent basin and postulated that each major cyclothem grouping has an average duration of approximately 400 kyr. Independent evidence from U-Pb zircon ages obtained from tuffs and tonsteins in Carbonif- erous cyclothemic strata from the Donets basin of eastern Europe (Davydov et al. 2010) indicate that individual high-frequency, intermediate Pennsylvanian cyclothems and stratigraphic ‘‘bundles’’ of cyclothems (major cyclothems) are a consequence of different eustatic and climatic responses to Milankovitch-forced (, 100 kyr and 400 kyr) orbital eccentricity. Considering the similarities in sedimentology and stacking patterns between biostratigraphically correlated cyclothems in the Donets basin and those in the North American Midcontinent basin (Heckel 2002; Heckel et al. 2007), it has been suggested that the Donets basin cyclothem model provides a reasonable explanation of cyclothem formation in North America (Davydov et al. 2010; Schmitz and Davydov 2012).

METHODS Field Pennsylvanian (Morrowan–Virgilian) paleosols of the IB were analyzed from five long, continuous drill cores housed at the Illinois State Geological Survey (Fig. 1, Table 1). These include the ISGS #1 Monterey Coal Company (MAC), the ISGS #1 Elysium Energy

FIG. 2.—Generalized stratigraphic column of the Pennsylvanian sub-system in Illinois. Select members are displayed for points of reference. The larger, detailed stratigraphic column shows units that are discussed in this contribution (i.e., upper Tradewater–lower Mattoon formations). The smaller, less-detailed stratigraphic column shows all of the Pennsylvanian formations present in the Illinois basin. Global stage-boundary date and North American series dates are based on North American cyclothem calibration of Heckel (2008) in conjunction with radiometric (U-Pb) dates of zircons from the Donets Basin of Eastern Europe (Davydov et al. 2010). Figure modified from Willman et al. (1975) and Nelson et al. (2011). JSR PENNSYLVANIAN PALEOSOLS OF THE ILLINOIS BASIN: PART I 609

FIG. 3.—Late Pennsylvanian paleogeography. A) Molleweide projection of paleogeography during the Moscovian (, 300 Ma) showing the location of the Illinois basin (black star), Central Pangaean Mountain range (CPM), and Tethys and Panthalassa oceans. Figure from Blakey (2007). B) Late Pennsylvanian paleogeographic reconstruction of North America showing the extent of the North American Midcontinent Sea (NAMS) during interglacial highstands (dotted line with white fill). Gray areas represent land that was not submerged during inundation of the craton. The Illinois basin (IB) is shaded dark gray. The positions of several other basins are shown for reference. Figure modified from Heckel (1977, 1991) and Algeo et al. (2004). Wisc. Arch 5 Wisconsin Arch; Kan. Arch 5 Kankakee Arch; Cinc. Arch 5 Cincinnati Arch.

(ELY), the Lone Star Cement Company #TH-1 (LSC), the ISGS #H-1 , 2 mm(n5 79) equivalent spherical diameter (e.s.d) size fraction was COGEOMAP (SAL), and the ISGS U.S. Fish & Wildlife Service #1 isolated from the paleosol matrix by centrifugation. A subset (n 5 19) of (FWL). Also included in this study are 13 outcrop sites in southern , 2 mm size fraction samples were processed further to isolate the Illinois and Indiana (Fig. 1, Table 1). Paleosols from drill cores (n 5 66) , 0.2 mm size fraction, which has been shown to contain dominantly and outcrop (n 5 31) were identified and described in detail following pedogenic, rather than detrital, clay minerals (Stern et al. 1997; Tabor et established criteria (Retallack 1988, 1991; Kraus 1999; Tabor and al. 2002; Vitali et al. 2002). A set of chemical and heat treatments were Montan˜ez 2004; Tabor et al. 2006). Outcrops were sampled from performed upon different aliquots of the size fractions that included (1) picked-back stratigraphic sections exposed at coal mines and roadcuts. K+ saturation at room temperature, (2) Mg2+ saturation at room Paleosol profile bases were delineated at the lowest position of unaltered temperature, (3) Mg2+ saturation and glycerol solvation at room parent material as deduced from sedimentary structure and/or changes in temperature, and (4) K+ saturation and heating at 500uC for at least grain size. Paleosol horizons were assigned to each profile on the basis of 2 hours. Each aliquot was prepared on filter membranes and transferred observed changes in color, pedogenic or sedimentary structure, pedogenic to glass slides as oriented aggregates. Estimates of the relative abundance minerals, and grain size. Colors were described from dry hand samples of clay minerals in the , 2 mm size fraction were determined using the using a Munsell color chart (Munsell Color 1975). The descriptive terms area of the 001 peak on X-ray diffraction (XRD) patterns of Mg2+- and paleosol classification scheme applied herein follow the system of saturated samples with the background removed. To facilitate character- Mack et al. (1993). ization of mixed-layer phases (e.g., illite–smectite; I/S) and permit an estimate of the proportion of each phase in the mixed-layer minerals, Laboratory representative samples prepared as oriented aggregates were solvated in a vapor of ethylene glycol (EG) at 60uC for at least 8 hours. Step-scan Clay Mineralogy.—A total of 319 bulk paleosol matrix samples were analyses of each treatment were performed on a Rigaku Ultima III X-ray collected at 10–15 cm intervals within each paleosol profile for diffractometer using Cu-Ka radiation over a range of 2 to 30 u2h, a step mineralogical, petrological, and geochemical analysis. Sample aliquots size of 0.04 u2h, and 1 s count time per step. Mineralogical identification were disaggregated by ultrasonic agitation in deionized water and the from XRD spectra follows the procedures outlined in Moore and 610 N.A. ROSENAU ET AL. JSR

TABLE 1.—Locations of cores and outcrops.

Core or Field Site Location Core ISGS #1 Monterey Coal Company (MAC): County #23993 Macoupin County, IL., Sec. 7, T9N, R6W ISGS #1 Elysium Energy (ELY): County #25922 Richland County, IL., Sec. 27, T4N, R9E Lone Star Cement Company #TH-1 (LSC): County #25988 La Salle County, IL., Sec. 31, T33N, R2E ISGS #H-1 COGEOMAP (SAL): County #25522 Saline County, IL., Sec. 20, T10S, R6E ISGS #1 U.S. Fish and Wildlife Service #1 (FWL): County #28962 Williamson County, IL., Sec. 18, T9S, R1E Field Site 1 Knight Hawk Coal, Creek Paum Mine; Jackson County, IL., Sec. 14, T7S, R3W 2 Peabody Energy, Wildcat Hills Mine, Cottage Grove Pit; Saline County, IL., Sec. 1, T9S, R7E 3 Vigo Coal Operating Company, Inc., Friendsville Mine; Wabash County, IL., Sec. 16, T1S, R13W 4 Triad Mining, Inc, South Augusta Mine; Pike County, IN., Sec. 20, T2S, R7W 5, 6 Peabody Coal Co., LLC, Francisco Mine; Gibson County, IN., Sec. 13, T2S, R10W 7 Peabody Energy (United Minerals Co., LLC), West 61 Mine; Warrick County, IN., Sec. 21, T4S, R8W 8 Peabody Energy (Black Beauty Coal Co.), Viking Mine, Corning Pit; Daviess County, IN., Sec. 24, T2N, R6W 9 I-24 Roadcut; Johnson County, IL., Secs. 8, 9, 16, and 17, T12S, R3E

Reynolds (1997). The proportions of each phase in mixed-layer minerals Taxonomy system (Soil Survey Staff 2010). Distinctive field-based were estimated from EG-solvated samples using differential 2h measure- relationships, including paleosol morphological development, thickness, ments (uD2h;S´rodon´ 1980; Moore and Reynolds 1997), where uD2h is a and relationships to adjacent strata, in conjunction with clay mineralogy, measure of the difference between the positions of the reflections of the provide the impetus for organizing all paleosols amongst the IB strata composite illite 001/smectite 002 and illite 002/smectite 003 peaks near 9 into seven general profiles, or pedotypes (Table 2). The number of to 10.3 u2h and 16 to 17 u2h space, respectively. paleosol profiles in the IB that reside within each pedotype as well as the distribution in each core and outcrop exposure is presented in Table 3. Micromorphology.—Petrographic thin sections from siderite-bearing Paleosols assigned to each pedotype are interpreted as being the product horizons as well as representative paleosol horizons and profiles were of similar soil-forming processes (Retallack 1990, 1994; Bestland et al. commercially prepared. Paleosol matrix samples were epoxy impregnated 1997; Tabor and Montan˜ez 2004; Tabor et al. 2006). We emphasize that and described using the micromorphological terminology of Brewer we classify pedotypes based upon the preservation of features that are (1976) and Stoops (2003). Siderite-bearing layers were examined and interpreted to have formed during active pedogenesis. Features interpret- described under plane-polarized and cross-polarized light from thin ed to be post-pedogenic (e.g., diagenetic gley overprinting of paleosol sections that were cut perpendicular to bedding in order to evaluate profiles and accumulations of pyrite) are not used to differentiate textures, crosscutting relations of carbonate cements, and to distinguish pedotypes. The features of the pedotypes, as observed in the field, are between primary pedogenic and secondary (burial) carbonate phases. In described in the following sections, with emphasis on pedogenic features particular, samples containing well-preserved sphaerosiderite, as indicat- most representative of all paleosols assigned to a given pedotype. The ed by smooth margins and radial-concentric crystalline microstructures morphological and mineralogical range of variation within a pedotype is (Ludvigson et al. 1998), are considered to be pedogenic. Imaging and summarized in Table 2. determination of bulk elemental composition of the sphaerosiderite crystals and surrounding paleosol or sedimentary rock matrix was made Justification of Paleosol Classification Scheme from representative thin sections from each sphaerosiderite-bearing In this study we adopt the paleosol-specific classification scheme of horizon using a Leo-Zeiss 1450VPSE electron microscope equipped with Mack et al. (1993). This classification system is largely descriptive, relying an EDAX Genesis 4000 XMS SYSTEM 60 energy-dispersive spectrom- upon morphological and mineralogic features that have a high eter. The mineralogy of the siderite-bearing layers was determined by preservation potential and can be easily recognized in the field and by XRD of random powder mounts of the , 125 mm size fraction. Step-scan petrographic inspection. We have chosen this system instead of modern analyses were performed on a Rigaku Ultima III X-ray diffractometer soil classification systems for the following reasons: (1) many of the using Cu-Ka radiation over a range of 2 to 70 u2h, a step size of 0.05 u2h, original features and characteristics that are necessary for classification of and 1 s count time per step. modern soils, such as texture, color, organic-matter content, presence of particular minerals, cation exchange capacity, pH, and bulk density are RESULTS rarely preserved in paleosols, or have been modified, as a result of Description of Paleosols diagenesis and compaction (Retallack 1981, 1990), and (2) classification of paleosols using modern soil taxonomy (e.g., Soil Survey Staff 1975) Diagnostic field-scale indicators of weathering profiles and pedogenesis would require detailed knowledge of climatic conditions under which the in Pennsylvanian mixed terrestrial–marine–deltaic strata of the IB include soil originally formed, such as the original soil moisture and temperature color, pedogenic mottling, rhizoliths, ped structure, redoximorphic regimes. Such information is difficult, if not impossible, to obtain for features, clay films on peds, carbonate nodules, and shrink–swell (vertic) ancient systems. We understand there is disagreement in the scientific structures. Profiles were divided into horizons based on changes in community regarding which classification system to apply to paleosols structure (sedimentary and pedogenic), grain size, color, macromorphol- (Retallack 1993); however, our intent here is to effectively communicate ogy, clay mineralogy, redoximorphic features, and fossil organic-matter the suite of properties observed in IB paleosols and, when possible, link accumulation. Subordinate descriptors (e.g., w, k, g, ss) and master these properties to modern soil analogs in order to provide insight into horizons (e.g., A, B, BC, R) follow the definitions in the USDA Soil the pedogenic history of IB paleosols. JSR

TABLE 2.—Macromorphology, micromorphology, mineralogy, and stratigraphic and lateral distribution of representative profiles of the differenttypes. paleosol

Pedotype Section and Horizon , 2 mm Clay Variations of Stratigraphic Intrabasinal Pedotype Depth (m)a Depth (cm) Macromorphology Micromorphology BoundaryMineralogyb Type Profile Distribution Distribution Classificationc Found Histosol - Abrupt, - Across the basin, coal Tradewater Fm., A(n 5 68) FWL core Oa (40 to 70) Coal with laminae of black throughout smooth thickness varies from Carbondale (61.3 m) (G1 2.5/N) to dark gray the basin (G1 4/N) organic-rich , 1 cm to 230 cm. Fm., Shelburn mudstone. Fm., Patoka Fm., Bond Fm., - Abrupt, - Mattoon Fm. Histosol Ag (30 to 40) Very dark gray (G1 3/N) to smooth black (G1 2.5/N), massive to laminated, fossil I PART BASIN: ILLINOIS THE OF PALEOSOLS PENNSYLVANIAN organic-matter-rich, noncalcareous mudstone. Many fine, vertical to subvertical root traces, some of which are coalified. Rare coal pieces in matrix. Cg (0 to 30) Gray (G1 6/5G) to dark - Clear, l, K, Ch Histosol gray (G1 4/N), massive, smooth Found gleyed silty, fossil organic- Tradewater Fm., Protosol matter-rich, calcareous throughout Abrupt, I, K, Ch Extent of redoximorphic Carbondale mudstone. Laminated, Fm., Shelburn the basin smooth features varies depending B(n 5 31) MAC core ABw (50 to 62) Very dark gray (G1 3/N) abundant Fm., Patoka on paleolandscape position carbonized root Fm., Bond Fm., (140.7 m) wavy laminated, micaceous, within the basin. Paleosols calcareous mudstone with traces and fossil Mattoon Fm. plant matter. from the northern margin weak, fine to medium display high chroma (red) angular blocky structure. hues and abundant fine to Few, distinct, fine to coarse yellow, red, and medium, massive olive bluish-gray mottles, while yellow (5Y 6/6) mottles. those of the interior of the Dense bifurcating network basin are dominantly drab of vertically oriented root (gley) color, with rare, traces. Rare, fine to fine to medium, high- medium mud filled tubules chroma mottles as well as and wispy carbonate Clear, I, K, Ch abundant sphaerosiderite gleyed cements. Laminated, and pyrite. BCk (30 to 50) Very dark gray (G1 3/N) common smooth Protosol weakly laminated to wavy carbonized root laminated micaceous traces. calcareous mudstone. Few wispy carbonate cements. Vertically to subvertically oriented calcareous tubules, rhizoliths and bifurcating network of root traces. Few, prominent, fine, massive yellow (5Y 7/3) mottles. 611 612 TABLE 2.—Continued.

Pedotype Section and Horizon , 2 mm Clay Variations of Stratigraphic Intrabasinal Pedotype Depth (m)a Depth (cm) Macromorphology MicromorphologyAbrupt, wavy BoundaryMineralogy -b Type Profile Distribution Distribution Classification gleyedc Laminated, rare Protosol BCg (0 to 30) Dark gray (G1 4/N) laminated,fossil plant micaceous, calcareous siltstone.matter, Rare fossil organic-matter. abundant Common fine to medium micritic siderite massive pale yellow (5Y 7/3) andcement, and rare dark olive gray (5Y 3/2) mottles.sphaerosiderite. gleyed Vertisol Dense, bifurcating network of Tradewater Fm.,Found micritic siderite cements. Carbondale Fm.,throughout Stigmariain upper 6 cm of Abrupt, I, I/S K, Ch Extent of redoximorphic Parallel striated Shelburn Fm., the basin horizon. smooth features varies depending on C(n 5 31) ELY core Bssg1 (184 to Greenish gray (G1 5/10GY) b-fabric, paleolandscape position withinPatoka Fm., (83.3 m) 202) noncalcareous mudstone withabundant fossil the basin. Paleosols from the Bond Fm., fine to medium wedge-shapedplant matter and northern margin display high Mattoon Fm. aggregate structure defined bycarbonized root chroma (red) hues and well-developed slickensides traces. Many abundant fine to coarse yellow, and secondary fine to mediumroot traces red, and bluish-gray mottles, angular blocky structure. replaced by while those of the interior of the Common, distinct, olive (5Ypyrite. basin are dominantly drab 5/4) root mottling. Abundant (gley) color, with rare, fine to

fossil vascular plant matter. Gradual, K,Ch, I, I/S medium, high-chroma mottles gleyed Vertisol AL. ET ROSENAU N.A. Common pyrite. Dense Parallel striated smooth as well as abundant network of bifurcating root b-fabric, rare sphaerosiderite and pyrite. Bssg2 (121 to Greenishtraces. gray (G1 5/10GY) 184) noncalcareous mudstone with sub-angular fine to medium sub-angular blocky blocky structure. Well-definedmicrostructure, slickensides with manganese common oxide coatings on some slickenvertically to sub- planes. Bifurcating network ofvertically root traces with olive (5Y 4/3)oriented root mottling. Rare pyrite. carbonized root Common, distinct, medium traces. Some vermicular to massive, pale root traces olive (5Y 6/3) mottles. replaced by Common, vertically orientedCrystalliticpyrite. b- Clear, I, Ch, K, I/S gleyed Vertisol Cg (0 to 121) Greenishcoalified rooting gray (G1 structures. 5/10GY) fabric, abundant smooth massive, micaceous, calcareousmicritic siderite mudstone. Common cements and rare bifurcating micritic siderite andpyrite. sphaerosiderite cements. Rare pyrite. Few root traces with yellow (5Y 7/8) mottling. Common, distinct, medium to coarse massive olive yellow (5Y 6/6) mottles. JSR JSR TABLE 2.—Continued.

Pedotype Section and Horizon , 2 mm Clay Variations of Stratigraphic Intrabasinal Pedotype Depth (m)a Depth (cm) Macromorphology Micromorphology BoundaryMineralogyb Type Profile Distribution Distribution Classificationc gleyed calcic - Abrupt, - Tradewater Fm.,Restricted to D(n 5 13) ELY core Ag (311 to Dark greenish gray (G1 4/ Vertisol smooth Carbondale interior of (312.5 m) 363) 10GY) massive, basin noncalcareous mudstone. Fm., Shelburn Abundant fossil vascular Fm., Patoka plant matter. Fm., Bond Fm., Gradual, I/S, I, K Mattoon Fm. gleyed calcic Random striated smooth Vertisol Bwg1 (207 to Greenish gray (G1 5/5GY) b-fabric, 311) massive, noncalcareous common root mudstone. Few (1-2% by traces replaced I PART BASIN: ILLINOIS THE OF PALEOSOLS PENNSYLVANIAN volume) sphaerosiderite- by replaced rhizoliths and sphaerosiderite disorthic sphaerosiderite and pyrite. Rare concentrations. Abundant Gradual, I/S, I, K gleyed calcic sphaerosiderite smooth Vertisol fossil root traces. Randomnodules. striated Bkg (174 to Greenish gray (G1 5/10Y) b-fabric, few 207) sandy, noncalcareous disorthic, mixed mudstone with fine to micrite and medium angular blocky sparite calcareous structure. Common (5–10% nodules and by volume) fine to medium, aggregates of stage II calcareous nodules. nodules. Rare Bifurcating network of angular blocky micritic siderite and microstructure. sphaerosiderite nodules. Common Common carbonized fossil sphaerosiderite root traces in upper 10 cm. nodules and micritic siderite cements. Abundant Abrupt, I/S, I, K gleyed calcic carbonized root Paralleltraces. striated smooth Vertisol Bkssg (65 to Very dark gray (G1 3/N) b-fabric, rare 174) massive, calcareous linear clay mudstone. Well-developed, concentrations, propagating slickensides. and abundant Fine to medium subangular disorthic mixed blocky structure. Abundant micrite and (, 20% by volume) disorthic sparite calcareous medium to coarse stage II nodules, many of calcareous nodules. Nodules which are coated are sometimes concentrated with pyrite. along slicken planes. Common, medium-coarse, distinct, massive greenish gray (G1 5/10Y) mottles. Rare micritic siderite cements. 613 614

TABLE 2.—Continued.

Pedotype Section and Horizon , 2 mm Clay Variations of Stratigraphic Intrabasinal Pedotype Depth (m)a Depth (cm) Macromorphology Micromorphology BoundaryMineralogyb Type Profile Distribution Distribution Classificationc Abrupt, K, I/S, I gleyed calcic Bwg2 (47 to 65) Very dark gray (G1 3/N) Granostriated smooth Vertisol noncalcareous mudstone. and crystallitic Fine to medium subangular b-fabrics. Few blocky structure. fossil plant Abrupt, I, I/S, K, Ch, gleyed calcic Laminated,fragments. smooth Vertisol Cg (0 to 47) Dark gray (G1 4/N) abundant laminated, noncalcareous micritic siderite mudstone. Common, and calcite distinct, medium to coarse, cements, and massive greenish gray (G1 6/common 10Y) mottles associated withsphaerosiderite a bifurcating network of nodules. micritic siderite and calcite Common Tradewater Fm., gleyed vertic cements. Rare fossil carbonized root Carbondale Fm., Calcisol vascular plant matter traces and fossilAbrupt, I/S, I, K Extent of redoximorphic Shelburn Fm., dispersed throughout Parallelplant matter. striated smooth features varies depending onPatoka Fm., E(n 5 11) MAC core Bkssg1 (169 to Greenishhorizon. gray (G1 5/10GY) b-fabric, paleolandscape position Bond Fm., (87.2 m) 195) noncalcareous mudstone common within the basin. Paleosols Mattoon Fm. with medium wedge-shaped disorthic, from the northern margin AL. ET ROSENAU N.A. aggregate structure defined calcareous, display high chroma (red) by well-developed mixed micrite hues and abundant fine to slickensides. Few (1–3% by and sparite coarse yellow, red, and bluish- volume), disorthic, fine nodules, gray mottles, while those of calcareous nodules. Commonabundant the interior of the basin are fossil vascular plant matter. carbonized root dominantly drab (gley) color, traces and pyrite- with rare fine to medium, replaced root high-chroma mottles and traces. abundant sphaerosiderite and pyrite. Some Type E paleosols exhibit carbonate-filled slicken planes. Matrix does Abrupt, I/S, I, K not always display wedge- gleyed vertic Cross striated b- smooth shaped aggregate structure. Calcisol Bkssg2 (97 to Dark gray (5Y 5/4) weakly fabric, few 169) calcareous mudstone. Fine disorthic to medium wedge-shaped calcareous, aggregates defined by well- mixed micrite developed slickensides. and sparite Common (3–5% by volume) nodules, some of fine to medium disorthic stagewhich are coated II calcareous nodules. Many,with pyrite. Rare fine calcareous nodules and carbonized root cements throughout. traces. JSR JSR TABLE 2.—Continued.

Pedotype Section and Horizon , 2 mm Clay Variations of Stratigraphic Intrabasinal Abrupt, I/S, K, I, Ch gleyed vertic Pedotype Depth (m)a Depth (cm) Macromorphology Micromorphology BoundaryMineralogyb Type Profile Distribution Distribution Classificationc Parallel striated smooth Calcisol Bkssg3 (77 to Brown (7.5YR 4/2) b-fabric, rare 97) noncalcareous mudstone. angular blocky Fine to medium wedge-shapedmicrostructure, aggregate structure defined bycommon slickensides. Common (3–5% disorthic by volume) fine to medium calcareous mixed disorthic stage II calcareous micrite and nodules that are concentrated sparite nodules.

along slicken planes. Common, I PART BASIN: ILLINOIS THE OF PALEOSOLS PENNSYLVANIAN prominent, medium to coarse greenish gray (G1 6/5GY) Clear, I/S, I, Ch, K gleyed vertic mottles. Random striated Bkssg4 (12 to Gray (G1 6/N) massive, smooth Calcisol 77) weakly calcareous mudstoneb-fabric, rare with well-developed disorthic micritic slickensides. Common calcareous (, 10% by volume), fine to nodules, many of which are coated medium disorthic stage II with iron-oxides. calcareous nodules. C (0 to 12) Greenish gray (G1 6/10GY), -Abrupt, Abrupt, -I, K Patoka Fm.,Restricted gleyed Calcisolvertic rubbly marine limestone. Crystallitic b- smooth Bond Fm. to interior Calcisol F(n 5 3) ELY core Bkg1 (87 to Dark greenish gray (G1 4/ fabric, abundant of basin (173.7 m) 148) 10GY) noncalcareous carbonized root mudstone. Fine to medium traces and angular blocky structure. rhizoliths Common (3–5% by volume),replaced by fine, disorthic calcareous sphaerosiderite. nodules. Abundant, Few, disorthic horizontally oriented fossil micrite and root traces. Common sparite rhizoliths with yellow (5Y 7/3)calcareous Abrupt, I, K gleyed Calcisol root mottling. Crystalliticnodules. b- smooth Bkg2 (54 to Greenish gray (G1 5/10GY) fabric with few 87) noncalcareous, silty disorthic, mixed mudstone. Massive, to weaklymicrite and developed, fine to medium sparite angular blocky structure. Fewcalcareous (1–3% by volume), fine to nodules and medium siderite-coated aggregates of calcareous nodules. Rare nodules. Rare fossil vascular plant matter. siderite cements and sphaerosiderite nodules. Rare carbonized root traces. 615 616 TABLE 2.—Continued.

Pedotype Section and Horizon , 2 mm Clay Variations of Stratigraphic Intrabasinal a b c Pedotype Depth (m) Depth (cm) Macromorphology MicromorphologyAbrupt, BoundaryK,Mineralogy I, ChType Profile Distribution Distribution Classification gleyed Calcisol Cg (0 to 54) Greenish gray (G1 6/10GY),Granostriated wavy massive, calcareous, micaceousb-fabric, sandstone. Dense, bifurcating abundant network of vertically to sub- micritic siderite vertically oriented micritic cement and common siderite and sphaerosiderite. calcic Vertisol sphaerosiderite Abrupt, I/S, I, K Degree of carbonate Restricted to nodules. Parallel striated smooth development varies. Some northern G(n 5 7) LSC core Bkss1 (240 to Dark reddish gray (10R 4/1) b-fabric, few paleosols belonging to this margin of (34.7 m) 299) and gray (G1 6/5G) massive, disorthic mixed pedotype display indurated basin variegated, calcareous micrite and stage III carbonate mudstone. Well-developed sparite development. slickensides. Few (1–3% by calcareous volume) fine, stage II calcareousnodules, and nodules. Few, fine, prominent,linear Clear, I/S, K, I upper Shelburn- calcic Vertisol greenish gray (G2 6/10G) concentrations Cross striated smooth Patoka fms. vermicular mottles. of clay. Bkss2 (142 to Dark reddish gray (7.5R 3/1) b-fabric, linear 240) massive, calcareous mudstone.concentrations

Well-developed slickensides of clay, many AL. ET ROSENAU N.A. with manganese oxide coatingsdisorthic mixed on some slicken planes. micrite and Common, ( 5% by volume), sparite fine to medium stage II calcareous calcareous nodules. Common,nodules. Mottled fine to medium, distinct, matrix with vermicular to massive, weak redabundant iron- (5R 4/4) and gray (G1 6/N) oxide staining mottles. and iron-oxide nodules.- Abrupt, I/S, K, I calcic Vertisol Bss1 (107 Variegated light olive brown smooth to 142) (2.5Y 5/6) and dusky red (2.5YR 3/2) weakly-calcareous mudstone. Weakly developed fine angular blocky structure. Well-developed slickensides. Few, fine, distinct, greenish gray (G1 6/10G) vermicular and Abrupt, I/S, I, K, calcic Vertisol diffuse mottles. Parallel striated wavy Bss2 (89 Variegated dark reddish gray b-fabric, linear to 107) (5R 3/1) and light olive concentrations brown (2.5Y 5/6) noncalcareousof clay, mottled mudstone. Weak, medium, matrix with angular blocky structure. abundant iron- Well-developed slickensides. oxide staining Abundant medium to coarse and iron-oxide vermicular and massive nodules. greenish gray (G1 6/5G) mottles. JSR JSR PENNSYLVANIAN PALEOSOLS OF THE ILLINOIS BASIN: PART I 617

c Type A Paleosols

Description.—Pedotype A is a 70-cm-thick profile with three horizons: (1) a lower 30-cm-thick massive to laminated gray (G1 6/5G) to dark gray (G1 4/N) siltstone with abundant fossil vascular plant debris, some of which is coalified (Cg), (2) a massive to laminated 10-cm-thick very dark gray (G1 3/N) to black (G1 2.5/N) siltstone with abundant fossil plant debris (Ag) and (3) a 30-cm-thick black (G1 2.5/N) to very dark gray (G1 Intrabasinal Distribution Classification 4/N) organic layer of degraded, to weakly degraded, coalified plant material (Oa; Fig. 4, Table 2). The organic-rich upper horizon (Oa) is the most obvious feature of this pedotype and is a coal (Fig. 5A). Low- chroma matrix colors (Vepraskas 1994) characterize the massive and laminated siltstone horizons of Pedotype A. The pedotype displays a chlorite. Distribution Stratigraphic gradual lower boundary with a massive, to ripple cross-laminated, fine 5 sandstone and an abrupt upper contact with a laminated mudstone with abundant fossil vascular plant matter. Type A paleosols are the most abundant paleosol type in the IB and they are closely associated with, and often overlie, other paleosols (Fig. 6). Type A paleosols are often abruptly overlain by fissile, black, marine shales or gray, laminated

illite-smectite; Ch siltstones containing abundant fossilized plant material (Fig. 6). In some

5 places, Type A paleosols are truncated by large fluvial sandstone channels Type Profile Variations of (Fig. 2, e.g., the Galatia, and Crown Mine sandstones; Allgaier and Hopkins 1975; Nelson 1983). illite, I/S 5

b Stratigraphic and Lateral Distribution.—The thickness of the upper organic layer in Type A paleosols (i.e., coal) varies from , 1to, 230 cm - calcic Vertisol m Clay

m across the basin. Maximum thicknesses of the coals occur in the central 2

kaolinite; I and southern portions of the basin, and they typically become thinner to Mineralogy , 5 I, K, I/S, Chthe east calcic Vertisol and north (e.g., the Herrin Coal; Mastalerz and Shaffer 2000). Type A paleosols are found throughout the Pennsylvanian strata in the

Continued. IB; however, they are concentrated in the lower Desmoinesian–upper Missourian strata (upper Tradewater–lower Mattoon formations; Fig. 2). 2.— smooth smooth Gradual, Abrupt, Pedotype A Classification.—Type A paleosols are dominated by coal, ABLE

T and are therefore classified as Histosols (Table 2; Mack et al. 1993).

Type B Paleosols fabric. Mottled matrix with common iron- oxide staining and few iron oxide nodules. b-fabric, angular blocky microstructure, and linear concentrations of clay. Mottled matrix with common iron- oxide nodules and iron-oxide staining. Crystallitic b- Random striated Description.—Pedotype B is 62 cm thick and consists of three weakly laminated to wavy-laminated siltstone horizons exhibiting very weak horizonation (Figs. 4, 5B, Table 2). All horizons of Pedotype B exhibit drab, dark gray (G1 4/N) to very dark gray (G1 3/N) matrix colors and fine to medium, massive, olive yellow (5Y 6/6) and yellow (5Y 7/3) mottles. The upper two horizons (ABw and BCk) preserve bifurcating 0m. networks of vertically oriented mud- and carbonate-filled tubules, 5 abundant disseminated, carbonized, fossil vascular plant matter that increases in abundance upward, and wispy carbonate cements. The siltstone. Medium angular blocky structure. Common, prominent, medium to coarse, dark reddish brown (5YR 3/2) vermicular mottles in upper 18 cm of horizon. calcareous mudstone. Medium to coarse angular blocky structure that becomes better developed upward in the horizon. Well-developed slickensides. Few, fine, faint gray (G1 5/N) vermicular and massive mottles. Rare manganese oxide deposits. uppermost horizon (ABw) exhibits weak, fine to medium angular blocky structure, while the lowermost horizon (BCg) preserves a dense bifurcating network of micritic siderite cements. The pedotype displays an abrupt upper contact with a coal and a clear lower contact with a Horizon Depth (cm) Macromorphology Micromorphology Boundary m size fraction of paleosol matrix organized in relativelaminated order of abundance; K mudstone rich in fossil vascular plant matter. Type B paleosols m BCw (0 to 32) Greenish gray (G1 6/5G) Bss3 (32 to 89) Dark brown (7.5YR 3/3) 2 are typically developed in peritidal (sensu Kvale et al. 1994) interlami- , a nated siltstones and sandstones dominated by branching, micritic siderite and sphaerosiderite cements (Fig. 6). However, Type B paleosols also occur in a range of other lithologies including sandstones, marine Pedotype Depth (m) Section and limestones, marine shales, and upon coals (Fig. 6). Type B paleosols are often overlain by Type A paleosols (Fig. 6).

Stratigraphic and Lateral Distribution.—Type B paleosols occur in each Clay mineralogy of the Depth refers to top of paleosol profile. Top of core Classification follows Mack et al. (1993). Pennsylvanian formation in the IB (Fig. 2), although they are more Pedotype a b c common in lower Pennsylvanian strata (lower–middle Tradewater 618 N.A. ROSENAU ET AL. JSR

TABLE 3.—Stratigraphic distribution of paleosols described and sampled TABLE 3.—Continued. from core and outcrop. Core or Number of Formation Pedotype Field site Occurences Total Core or Number of Formation Pedotype Field site Occurences Total Bond E - 0 0 Bond F ELY 2 2 Tradewater A SAL 5 Bond G LSC 2 2 Tradewater A FWL 6 Mattoon A ELY 5 Tradewater A MAC 1 Mattoon A Site 3 4 9 Tradewater A LSC 3 Mattoon B ELY 2 2 Tradewater A Site 1 1 Mattoon C ELY 2 2 Tradewater A Site 8 3 19 Mattoon D ELY 1 Tradewater B SAL 7 Mattoon D Site 3a 1 2 Tradewater B FWL 4 Mattoon E ELY 2 Tradewater B MAC 2 Mattoon E Site 3b 1 3 Tradewater B LSC 2 Mattoon F - 0 0 Tradewater B Site 1 1 16 Mattoon G - 0 0 Tradewater C - 0 0 Tradewater D - 0 0 Tradewater E - 0 0 Formation; Fig. 2). Type B paleosols are present in the interior of the Tradewater F - 0 0 Tradewater G - 0 0 basin and along the northern and southern margins (Fig. 1). However, Carbondale A FWL 2 Type B paleosols from the northern margin (LSC core) of the IB are Carbondale A MAC 6 characterized by high-chroma (red hues) coloration and redoximorphic Carbondale A ELY 5 features, including common, fine to coarse, red (2.5YR 5/8), bluish gray Carbondale A LSC 3 (G2 5/5PB), yellow (2.5Y 7/6), and pale yellow (5Y 7/4) mottling Carbondale A Site 4 2 (Table 2). Carbondale A Site 6 1 19 Carbondale B MAC 3 Carbondale B LSC 2 Pedotype B Classification.—The lack of well-developed soil structure, Carbondale B Site 4 1 6 weak horizonation, gley colors, common mottling, accumulation of Carbondale C MAC 2 siderite cements and common laminated bedding associated with Type B Carbondale C ELY 2 paleosols indicate that these profiles are gleyed Protosols (Table 2; Mack Carbondale C LSC 1 Carbondale C Site 4 1 et al. 1993). Carbondale C Site 6 1 7 Carbondale D MAC 1 Type C Paleosols Carbondale D ELY 2 3 Carbondale E LSC 3 3 Description.—Pedotype C is developed in gray to greenish-gray Carbondale F - 0 0 Carbondale G - 0 0 mudstones and siltstones and displays three moderately distinctive Shelburn A MAC 1 greenish-gray (G1 5/10GY) mudstone horizons that define a 202-cm- Shelburn A ELY 5 thick paleosol profile (Figs. 4, 5C, Table 2). Fine to medium wedge- Shelburn A LSC 1 shaped and angular blocky ped structures, as well as propagating Shelburn A Site 2 2 slickensides, occur in each horizon (Cg, Bssg2 and Bssg1). Manganese- Shelburn A Site 5 1 oxide coatings occur along slicken planes in the Bssg2 horizon. All Shelburn A Site 7 2 12 Shelburn B MAC 1 horizons in the type profile preserve fossil vascular plant matter, Shelburn B ELY 2 bifurcating root traces with redox concentrations, including olive (5Y 5/ Shelburn B LSC 1 4 4; 5Y 4/3) root mottling, as well as distinct redoximorphic features, Shelburn C MAC 2 including abundant medium to coarse, pale olive (5Y 6/3) and olive Shelburn C Site 2 2 yellow (5Y 5/6) mottling, millimeter-scale sphaerosiderite nodules, pyrite Shelburn C Site 5 1 framboids, and drab, low-chroma matrix colors (G1 5/10GY). The Shelburn C Site 7 1 6 Shelburn D Mac 1 concentration of vascular plant matter increases upward in the profile. Shelburn D ELY 1 Pedotype C exhibits a gradual lower boundary with a fossil organic Shelburn D Site 7 1 3 matter-rich massive siltstone and an abrupt upper contact with a coal. Shelburn E MAC 3 3 Type C paleosols are commonly abruptly overlain by thin, laminated Shelburn F - 0 0 (, 5 cm) organic-rich, kaolinitic clay layers that contain pieces of coal. Shelburn G MAC 1 Type C paleosols are often stratigraphically associated with siderite-rich Shelburn G LSC 2 3 Patoka A MAC 2 peritidal interlaminated siltstone–mudstone deposits (Fig. 6); however, Patoka A ELY 3 5 they are also associated with massive sandstones, marine limestones, Patoka B ELY 1 1 freshwater limestones, coals, and shales (Fig. 6). Patoka C - 0 0 Patoka D MAC 2 2 Stratigraphic and Lateral Distribution.—Type C paleosols commonly Patoka E ELY 1 1 occur as thick (100–300 cm) composite and compound (Fig. 6, MAC Patoka F ELY 1 1 Patoka G LSC 2 2 core at 78.5 m) paleosols (sensu Marriott and Wright 1993; Kraus 1999) Bond A ELY 4 4 in the lower Desmoinesian–lower Virgilian stratigraphy of the IB (upper Bond B - 0 0 Tradewater–lower Mattoon formations), coincident with the strati- Bond C ELY 1 1 graphic range of Type A and B paleosols (Fig. 2). Notable differences Bond D ELY 2 2 between paleosols belonging to this pedotype include development in JSR PENNSYLVANIAN PALEOSOLS OF THE ILLINOIS BASIN: PART I 619

FIG. 4.—Key to symbols and measured sections with field observations, paleosol horizon designation, and Munsell colors, representing the seven different pedotypes in the Illinois basin. Vertical scales next to each pedotype are in increments of centimeters. A) Pedotype A from the middle Pennsylvanian, Tradewater Formation (FWL core; Fig. 1, Table 2). B) Pedotype B from the middle Pennsylvanian, Tradewater Formation (MAC core; Fig. 1, Table 2). C) Pedotype C from the upper Pennsylvanian, Mattoon Formation (ELY core; Fig. 1, Table 2). D) Pedotype D from the middle Pennsylvanian, Shelburn Formation (ELY core; Fig. 1, Table 2). E) Pedotype E from the middle Pennsylvanian, Shelburn Formation (MAC core; Fig. 1, Table 2). F) Pedotype F from the upper Pennsylvanian, Bond Formation (ELY core; Fig, 1, Table 2). G) Pedotype G from the middle Pennsylvanian Shelburn Formation (LSC core; Fig. 1, Table 2). Note that coal layers (Oa horizons) associated with Pedotypes B, C, D, E, and F are not included as part of these pedotypes; rather, the Oa horizons presented in Pedotypes B, C, D, E, and F are included in the figure simply to illustrate that each of these pedotypes is overlain by a coal. 620 N.A. ROSENAU ET AL. JSR

FIG. 5.—Field photos showing macromorphologies of Illinois basin paleosols. A) Example of a Type A paleosol (Baker coal) from the Desmoinesian, Shelburn Formation at site 7. B) Type B paleosol from the Desmoinesian, Shelburn Formation at site 5. Organic rich, dark upper layer in photo is the Danville Coal. Top of pick handle demarcates Ag–Cg horizon contact. C) Type C paleosol (Baker coal) from Desmoinesian, Shelburn Formation, from a dugout pit below mine floor showing pedogenic slickensides (intersecting white curves) in cross section at site 7. D) Type D paleosol beneath Cohn coal, lower Mattoon Formation at Site 3a. Arrows demarcate siderite stained calcite nodules (cc). Inset shows close up of siderite-stained calcite nodules in Bkssg2 horizon. E) Type E paleosol beneath Cohn Coal, lower Mattoon Formation at Site 3b. Nodular features that stand out in relief from the paleosol profile are pedogenic carbonate nodules (cc) in B horizons. Hammer is lying on R horizon. F) Picture of LSC core at , 57 m from top of core showing Type G paleosol (variegated red and gray crumbly deposit). different lithologies, extent of mottling in different profiles stratigraphi- Pedotype C Classification.—Based on the occurrence of well-developed cally and laterally across the basin, and thickness of the paleosol profile shrink–swell features, including pedogenic slickensides and wedge-shaped (Table 2). These differences correlate with paleolandscape position. aggregate structure, in conjunction with gley matrix colors and abundant Specifically, Type C paleosols from the northern margin (LSC core) redoximorphic features, Type C paleosols are classified as gleyed Vertisols display high-chroma (red) hues and abundant medium to coarse light (Table 2; Mack et al. 1993). olive brown (2.5Y 5/6), dark reddish brown (2.5YR 2.5/3) red (7.5R 3/6), and bluish gray (G2 5/10B) mottles, while those from the interior of the Type D Paleosols basin are dominated by drab, gley (G1 5/10GY; G1 5/10GY) colors, with rare, fine to medium, high-chroma light red (2.5YR 6/6) and yellowish- Description.—Pedotype D is a 363-cm-thick very dark gray (G1 3/N) to red (5YR 5/6) mottles and abundant sphaerosiderite nodules and greenish-gray (G1 5/5GY) mudstone that is divided into six well- concretions. developed horizons (Fig. 4, Table 2). The lowermost Cg horizon is JSR PENNSYLVANIAN PALEOSOLS OF THE ILLINOIS BASIN: PART I 621

laminated, contains abundant micritic siderite and calcite cements, and exhibits common, distinct, medium to coarse, massive greenish gray (G1 6/10Y) mottles. The middle two horizons (Bkssg and Bkg) exhibit fine to medium angular to subangular blocky structure, common to many (5– 20% by volume) discrete, fine to medium, stage II calcareous nodules (Machette 1985) and rare (, 3% by volume) to abundant (. 20% by volume) millimeter-scale sphaerosiderite nodules, as well as abundant (. 20% by volume) branching sphaerosiderite tubules and micritic siderite cements (Fig. 5D). Some slicken planes in the Bkssg horizon contain sheared, lenticular calcareous nodules. Fine to medium, distinct and prominent mottling (G1 5/10Y) is present in the middle Bkssg horizon and lowermost Cg horizon of Pedotype D. The upper B horizon (Bwg1) of the profile exhibits massive structure, an increased abundance of fossil organic matter, preserved as carbonized roots or vascular plant debris, and few (1–2% by volume) sphaerosiderite nodules and sphaerosiderite-replaced rhizoliths. The uppermost Ag horizon exhibits massive structure and preserves abundant fossil vascular plant matter and carbonized roots. The pedotype (Fig. 4) displays a clear lower boundary with a nonmarine limestone and an abrupt upper contact with the Danville Coal (Shelburn Formation). As with other paleosol types in the basin, Type D paleosols may be associated with several different lithologies, including sandstones, siderite-cemented peritidal siltstones and sandstones, as well as marine limestones (Fig. 6). Paleosols representative of this pedotype are commonly abruptly overlain by a thin (, 5 cm), laminated organic-rich kaolinitic claystone that includes coalified plant organic matter.

Stratigraphic and Lateral Distribution.—Type D paleosols are found only in the interior of the basin. They are found throughout middle Desmoinesian–lower Virgilian strata (lower Carbondale–lower Mattoon formations), coincident with the stratigraphic range of Type A, B, and C paleosols (Fig. 2) and may occur as composite (Fig. 6, MAC core at 118 m) and compound (sensu Marriott and Wright 1993) profiles.

Pedotype D Classification.—The occurrence of well-developed shrink– swell features in conjunction with accumulations of calcite nodules, mottling, gley matrix colors, and sphaerosiderite in Type D profiles indicates these paleosols are gleyed calcic Vertisols (Table 2; Mack et al. 1993).

Type E Paleosols

Description.—Pedotype E is a 195-cm-thick unit composed of greenish- gray (G1 5/5GY), dark gray (5Y 5/4), gray (G1 6/N), and brown (7.5R 4/ 2) mudstone layers that is divided into four well-developed horizons (Fig. 4, Table 2). The three upper horizons (Bkssg1, Bkssg2, and Bkssg3) of the type profile preserve fine to medium, wedge-shaped structural aggregates defined by well-developed slickensides (Fig. 5E). Common (3– 10% by volume) stage II calcareous nodules (Machette 1985) are present in the middle and lower horizons (Bkssg2, Bkssg3, and Bkssg4). Common, prominent, medium to coarse greenish gray (G1 6/5GY) mottles are present in the Bkssg3 horizon. The upper horizon of the

FIG. 6.—Representative stratigraphic section from the Desmoinesian–Missour- ian (Carbondale–Patoka formations) interval in the MAC core showing lithology, paleosol types, and sedimentary structures. Measurements depicted on core graphic log are in meters (bold text) and feet (italicized text) as measured from the top of the core. Secondary scale (black and white bar scale) is in increments of 10 feet. Capital letters mark the positions of paleosol types in the stratigraphy, whereas encircled capital letters refer to pedotypes discussed in the text. 622 N.A. ROSENAU ET AL. JSR profile exhibits medium, wedge-shaped aggregate structure, a decrease in shale, and (3) the pedotype (Fig. 4), a greenish gray (G1 5/10GY; G1 6/ the size and abundance of carbonate nodules, and an increase in 10GY) and dark greenish gray (G1 4/10GY) profile in the lower Bond abundance of fossil organic matter preserved as carbonized roots or Formation developed upon sandstone. detrital vascular plant debris. Type E paleosols preserve morphological characteristics similar to those observed in Type D paleosols. Differen- Pedotype F Classification.—The abundance of pedogenic carbonate tiation of the two pedotypes is based on evaluation of the relative nodules, well-developed angular blocky structure, gley matrix colors, and prominence of pedogenic features. Specifically, the concentration of common sphaerosiderite in Type F paleosols indicates these paleosols are nodular and tubular carbonate in Type E paleosol profiles is more gleyed Calcisols (Table 2; Mack et al. 1993). extensive throughout the profile, while the most distinguishing characteristic of Type D paleosols is the preservation of vertic features. Type E Type G Paleosols paleosols occur in association with many different lithologies but occur most commonly with interlaminated siltstones and sandstones. The Description.—Pedotype G is a 299-cm-thick bluish gray and red pedotype displays an abrupt lower contact with a marine limestone variegated (5R 3/1, G2 5/5PB, and 7.5R 3/3) mudstone composed of five (Bankston Fork Limestone, Shelburn Formation) and is abruptly well-developed horizons overlying a greenish-gray (G1 6/5G) siltstone overlain by the Danville Coal (Fig. 6, MAC core at 89.5 m). (Fig. 4, Table 2). The lower four horizons (Bss1, Bss2, Bss3, and BCw) exhibit fine to coarse angular blocky structure, well-developed slicken- Stratigraphic and Lateral Distribution.—Type E paleosols commonly sides with manganese oxides on some slicken planes, and common fine, occur as compound (sensu Marriott and Wright 1993) profiles throughout distinct to prominent, gray (G1 5/N) and greenish gray (G1 6/5G) the middle Desmoinesian–lower Virgilian (lower Carbondale–lower vermicular mottles. The upper two horizons (Bkss1 and Bkss2) display an Mattoon formations), coincident with the stratigraphic range of increase in abundance of diffuse and vermicular light olive brown (2.5Y 5/ Pedotypes A–F (Fig. 2). Similar to Type C paleosols, Type E paleosols 6) and weak red (5R 4/4) mottles, well-developed slickensides with display a distinct distribution of morphological characteristics across the manganese-oxide deposits on some slicken planes, and few to common basin. Type E paleosols from the northern margin of the basin (LSC) (1–5% by volume), fine to medium stage II calcareous nodules (Fig. 5F; display redoximorphic features such as extensive medium to coarse Machette 1985). The pedotype displays a clear upper boundary with a mottling that includes variegated hues of dark reddish brown (5YR 3/2), Type B paleosol and a gradual lower boundary with a laminated, to ripple light bluish gray (G2 7/5B), light olive brown (2.5Y 5/6), and olive (5Y 5/ cross-laminated, siderite-cemented fine sandstone. Variants of the 6). Paleosols belonging to this pedotype from the interior and southern pedotype are underlain by massive claystones and marine limestones. margins of the basin are dominated by drab, gley, colors of greenish-gray (G1 5/5GY) and gray (G1 6/N; G1 5/N), with few fine to medium, high- Stratigraphic and Lateral Distribution.—Type G paleosols occur as chroma mottles of light red (2.5YR 7/6) and reddish yellow (7.6YR 6/6), compound and composite (sensu Marriott and Wright 1993) profiles and abundant (. 20% by volume) micritic siderite and sphaerosiderite restricted to upper Desmoinesian–lower Virgilian (upper Shelburn–Bond (Fig. 1, Table 2). formations; Fig. 2) strata, and its morphological development is unique among the paleosols of the IB. Type G paleosols are restricted (with one Pedotype E Classification.—The prominence of carbonate nodules in exception in the MAC core, Fig. 6 at 78.2 m) to the northern margin of Type E paleosols in conjunction with shrink–swell features, color the basin (Fig. 1; LSC core) and it is the only pedotype in the basin that mottling, gley matrix colors, and sphaerosiderite corresponds to gleyed exhibits high-chroma matrix colors. vertic Calcisols (Table 2; Mack et al. 1993). Pedotype G Classification.—The occurrence of well-developed shrink– Type F Paleosols swell features, high-chroma relict hues, common pedogenic calcite nodules, and common drab mottling in Type G paleosols indicates that Description.—Pedotype F is a 148-cm-thick unit composed of greenish- these paleosols are calcic Vertisols (Table 2; Mack et al. 1993). gray (G1 6/10GY) sandstone in the lower 54 cm that is overlain by greenish-gray (G1 5/10GY) to dark greenish-gray (G1 4/10GY) Distribution of Phyllosilicate Minerals in Illinois Basin Paleosols mudstone layers (Fig. 4, Table 2). The lowermost horizon (Cg) of the X-ray diffraction (XRD) spectra from oriented aggregates of the profile preserves millimeter-scale sphaerosiderite nodules, and common to , 2 mm size fraction in each of the paleosol types display a peak at 3.3 A˚ , abundant (10–30% by volume) micritic, vertically to subvertically indicating the presence of quartz, as well as a sharp peak at 7.2 A˚ , after oriented bifurcating siderite cements. The upper two horizons (Bkg1 K+ saturation at 25uC, that collapses after heating at 500uC for 2 hrs, and Bkg2) of the profile preserve fine to medium angular blocky structure indicating the presence of kaolinite (Fig. 7). Peaks also occur at , 10 A˚ , and common (3–5% by volume) fine to medium stage II calcareous regardless of treatment, in each paleosol type (Fig. 7). This corresponds nodules (Machette 1985). The uppermost horizon contains abundant to the d(001) diffraction peak of illite. Intensities of the 7.2 A˚ peak are carbonized root traces, and yellow (5Y 7/3) root mottling which increases typically diminished in the upper horizons of a pedotype, suggesting in abundance towards the interpreted paleosurface. A 15-cm-thick coal higher concentrations and coarser crystallinities of kaolinite at depth abruptly overlies the pedotype, while the lower horizon gradually changes (Fig. 8A). A peak at , 14.2 A˚ after K+ saturation, Mg2+-saturation, and to a siderite-rich shale. Mg+-saturation glycerol solvation, which shifts to , 13.7–13.9 A˚ after heating for 2 hr at 500uC in the , 2 mm size fraction of Types A–D and F Stratigraphic and Lateral Distribution.—Type F paleosols occur only in paleosols indicates the presence of chlorite in these profiles (Fig. 7). In the interior of the basin (ELY core) and are limited to three examples in most paleosols, the chlorite peak becomes less intense and broader in the the Missourian strata (Patoka–Bond formations): (1) a drab, dark upper horizons of paleosol profiles (Fig. 8A). Chlorite is not present in greenish gray (G1 4/10Y) and greenish gray (G1 6/10GY) profile in the the , 0.2 mm fraction of most paleosols profiles (Fig. 8B). With Mg2+- lower Patoka Formation developed upon interlaminated siltstone and saturation, and Mg2+-saturation glycerol solvation treatments, XRD sandstone, (2) a dark gray (G1 4/N) and dark greenish gray (G1 4/5GY) spectra of the , 2 mm and , 0.2 mm size fractions of Types C–E composite profile in the upper Bond Formation developed upon marine paleosols display the following: (1) an asymmetrical illite d(001) peak that JSR PENNSYLVANIAN PALEOSOLS OF THE ILLINOIS BASIN: PART I 623

FIG. 7.—Comparison of X-ray diffraction spectra of oriented aggregate mounts of the , 2 mm size fraction from B horizons (Pedo- types B–G) and C horizon (Pedotype A) in Illinois basin Type paleosols. Spectra belonging to each pedotype are denoted by encircled capital letters. All spectra correspond to Mg2+- saturated, glycerol-solvated samples. Chl 5 chlorite; I 5 illite; K 5 kaolinite; I/S 5 illite–smectite; Q 5 quartz. broadens in the low angle direction, (2) broad peak expansion in the tions) paleosols is composed of , 35–80% kaolinite, with the greatest , 10.5–14.5 A˚ range, and (3) peak expansion in the 34–36 A˚ range amount of kaolinite occurring in the upper Tradewater–lower Shelburn (Fig. 7). Collectively, this behavior indicates the presence of interstratified formations. The remainder of the clay-mineral assemblage is made up of illite-rich illite–smectite (I/S; Grim 1935; Moore and Reynolds 1997; varying amounts of I/S and illite. In the lowermost Missourian (lower Velde et al. 2003). Differential 2h (uD2h) values determined from XRD Patoka–Bond formations), there is a significant decrease in the relative spectra of representative EG-solvated samples from the , 2 mm size abundance of kaolinite coincident with an increase in the relative fraction in Pedotypes C–E confirm the interstratified I/S is illite-rich abundance of I/S. In the lower Patoka–Bond formations, kaolinite makes (, 20–40% smectite) and indicate ordered (R1) mixed-layering (Table 4; up , 10% of the total clay fraction, while I/S makes up the greater part of Reynolds and Hower 1970; Schultz 1978; Moore and Reynolds 1997). the remaining clay fraction (, 30–95%). In the LSC core, the relative The , 2 mm and , 0.2 mm size fractions of Type G paleosols exhibit abundance of illite is not significantly different between Desmoinesian an , 12 A˚ peak with K+ saturation at 25uC that collapses to , 10 A˚ and Missourian paleosols. after heating to 500uC for 2 hours, broad expansion in the , 10.3–14.5 A˚ Similar stratigraphic trends in clay–mineral abundances are present in 2+ 2+ range with Mg -saturation and , 14.5 A˚ peak with Mg -saturation the MAC core, although the differences in relative abundances of that expands to 17.8 A˚ upon glycerol solvation (Fig. 8C). With EG kaolinite, I/S, and illite are not as pronounced (Fig. 9). Regardless of solvation, the X-ray diffraction spectra of Type G paleosols displays a stratigraphic position, paleosols in the MAC core are composed primarily high-angle shoulder on the 17.8 A˚ peak at , 14.5 A˚ , as well as broad, of I/S, with varying amounts of illite. The relative abundance of I/S in higher-order reflections at , 9A˚ , 4.7 A˚ , and 3.5 A˚ . Unlike Types A–D these paleosols is typically . 50%, while kaolinite typically makes up and F paleosols, Type G paleosols do not display low-angle (32–36 A˚ ) , 40% of the total clay fraction. Similar to the trend observed in the LSC peak expansion. Collectively, this behavior indicates the presence of core, beginning in the upper Desmoinesian (upper Shelburn Formation) randomly interstratified (R0) smectite-rich (70–80% smectite) I/S and continuing through the Patoka Formation (lower Missourian), there (Table 4; Reynolds and Hower 1970; Moore and Reynolds 1997). is a decrease in the relative abundance of kaolinite and a slight increase in ˚ Furthermore, 7.2 A peak heights in both size fractions indicate lower the relative abundance of I/S. concentration or crystallinity of kaolinite in Pedotype G than in other pedotypes in the IB. Micromorphology The , 2 mm clay-mineral assemblage of IB paleosols in the MAC and LSC cores exhibit distinct stratigraphic trends in the relative abundance The predominant birefringent fabrics (b-fabric) in IB paleosols are of kaolinite, I/S, and illite (Fig. 9). In the LSC core, the clay-mineral crystallitic, parallel striated, and random striated (Bullock et al. 1985; assemblage of Desmoinesian (upper Tradewater–lower Patoka forma- Stoops 2003). Granostriated b-fabrics are less common. Crystallitic b- 624 N.A. ROSENAU ET AL. JSR

fabrics are characterized by the occurrence of small birefringent mineral grains (e.g., fine-grained mica or calcite). This type of fabric is common in lower horizons of Types C–G paleosols (Fig. 10A). Alternatively, the upper horizons of most paleosol types exhibit parallel and random striated fabrics (Fig. 10B, C). Continuous elongated zones of oriented clay particles that occur in parallel sets or as an irregular pattern of streaks characterize these striated b-fabrics. These types of fabrics are associated with paleosols that exhibit field-scale shrink–swell features (e.g., Paleosol types C–E and G). Microstructures are not commonly observed in IB paleosols; however, some of the upper horizons of paleosol Types C–E and G exhibit subangular to blocky peds (Fig. 10D). B-fabrics and microstructure of individual paleosols types are similar across the basin (i.e., basin interior to margin). Clay coatings are relatively rare in IB paleosols. However, linear concentrations of clay, which may represent either former clay coatings or channels filled with illuvial clay, are observed in paleosol Types D, E, and G (Fig. 10E). These linear concentrations of clay are yellow to orange in color and may display laminations. Paleosol Types A–F contain abundant fossil organic matter preserved as root traces, rhizocretions, and fossil plant material. Fossil organic matter is found throughout IB paleosols but is most abundant in the upper 10–30 cm of the profiles. Fossil plant material occurs as opaque fragments and commonly exhibits preserved cellular structure (Fig. 10F,G). Root traces are commonly preserved as carbonized films with fine root hairs extending from them (Fig. 10H). Many root traces and rhizocretions are replaced by pyrite (Fig. 10I) and/or sphaerosiderite (Fig. 10J), while some root traces have a hollow interior that has been filled with silt-size mineral grains or calcite (Fig. 10K). Most root traces are , 1 mm wide and up to several centimeters long, oriented vertically to sub-vertically in the paleosol profiles. Pedogenic calcium carbonate nodules are present in B horizons of paleosol Types D–G. Individual calcite nodules are commonly composed of mixtures of micrite and microspar (Fig. 10L, M). Nodules occur as disorthic (Fig. 10L) and aggregated masses (Fig. 10M) and exhibit rounded to sub-angular shapes and sharp boundaries with the surrounding matrix. The nodules sometimes envelop mineral grains, and the outer surfaces of the nodules are commonly coated with iron oxides and/or pyrite (Fig. 10L, M).

Redox-Sensitive Mineral Accumulations.—Redox-sensitive mineral accumulations include pyrite, siderite, iron-oxide concentrations, and mottling. Pyrite is found in gleyed paleosol horizons of Pedotypes A–E and is more abundant in paleosol profiles from the interior of the IB (i.e., MAC, ELY, SAL, FWL cores). For example, 14% of the paleosols in the MAC core and 22% of the paleosols in the ELY core contain pyrite, whereas only 5% of the paleosols from the basin margin (LSC core) contain pyrite. Iron-oxide concentrations and staining are prominent features of Type G paleosols from the basin margin (LSC core), resulting in extensive mottling of the matrix (Fig. 10N, O). These features are recognized in thin section as adjacent zones of oxidized and reduced matrix.

FIG. 8.—X-ray diffraction (XRD) spectra of oriented aggregate mounts of the , 2 mm and , 0.2 mm size fractions from representative paleosol matrix samples. A) Profile-scale XRD pattern of oriented aggregate mounts of the , 2 mm size fraction in Pedotype D. All spectra represent Mg2+-saturated sample aliquots. B) Comparison of XRD spectra of the , 2 mm and , 0.2 mm size fractions from B horizons in Pedotypes C, D, and G. C) X-ray diffraction spectra of oriented aggregate mounts of the , 2 mm size fraction from the Bss1 horizon of Pedotype G. K (500uC) 5 K+-saturated sample analyzed after heating at 500 uCfor2h;K (r.t.) 5 K+-saturated sample analyzed at room temperature; Mg 5 Mg2+- saturated sample; Mg-Gly 5 Mg2+-saturated, glycerol-solvated sample. Chl 5 chlorite; I 5 illite; K 5 kaolinite; I/S 5 illite–smectite; Q 5 quartz. JSR PENNSYLVANIAN PALEOSOLS OF THE ILLINOIS BASIN: PART I 625

TABLE 4.—The positions of the reflections of the composite illite 001/smectite 002 and illite 002/smectite 003 peaks of representative ethylene glycol (EG)- solvated samples used to estimate the percentage of smectite interlayers in interstratified illite/smectite (Moore and Reynolds, 1997).

Paleosol Type u2h (001/002) u2h (002/003) uD2h % Smectite C 9.46 16.89 7.43 30–40 D 9.30 16.65 7.35 30–35 E 9.54 17.30 7.76 20–30 G 10.10 15.99 5.90 70–80

Rare, subrounded iron-rich nodules displaying sharp boundaries with the nodules in paleosol horizons (Fig. 5D). Sphaerosiderite is more com- surrounding matrix are present in Type G paleosols (Fig. 10N, O). monly associated with morphologically mature gleyed B horizons of Siderite-bearing horizons exhibit two different cement textures: (1) paleosol profiles among Pedotypes B–D but is also observed in micritic nodules of various size and shape and (2) millimeter-scale interlaminated calcareous siltstones and sandstones. spherules composed of radial-fibrous crystals (sphaerosiderite; Ludvigson Micritic siderite is typically admixed with micritic to coarsely et al. 1998). The micritic form of siderite most commonly occurs in thinly crystalline calcite cements that often define bifurcating tubular networks interlaminated calcareous siltstones and sandstones underlying paleosols that partially deformed sedimentary bedding (Fig. 11A–E). Petrographic (Fig. 11A–C) but also occurs rarely as thin coatings on calcium carbonate analyses of carbonate nodules delineate multiple generations of mineral

FIG. 9.—Relative abundance of clay minerals in the , 2 mm size fraction in paleosols from the basin margin (LSC core) and basin interior (MAC core). Note that in both cores the relative abundance of kaolinite decreases near the Desmoinesian–Missourian (Shelburn–Patoka) boundary. 626 N.A. ROSENAU ET AL. JSR JSR PENNSYLVANIAN PALEOSOLS OF THE ILLINOIS BASIN: PART I 627 growth including initial micritic calcite nodules (Fig. 11F) and microspar (Fig. 8B). This assemblage of clay minerals is similar to that reported in nodules (Fig. 11G–I) that were fractured and subsequently filled with previous studies of Pennsylvanian underclays (Grim 1935; Schultz 1958; secondary veins of sparry calcite cement and siderite. In the interlami- Parham 1966; Rimmer and Eberl 1982) and coals (Gluskoter 1967) in the nated siltstones and sandstones underlying paleosols, micritic siderite IB. Discrete illite is defined herein as a 100% nonexpanding 1:1 mica-like cement, and occasionally sphaerosiderite, are typically found crosscutting mineral (sensu S´rodon´ 1984) that displays a basal (001) 10 A˚ reflection on the sparry calcite veins or coating the exteriors of the initial micritic X-ray-diffraction spectra. Chlorite and discrete illite are not typically calcite nodules (Fig. 11F–I). These observations suggest that siderite produced in soil-forming environments (Schaetzl and Anderson 2005) formed after micritic calcite and sparry calcite crystallization, but before and are likely inherited from the parent material of the paleosol profiles compaction and cementation of the surrounding soil matrix and as detrital minerals (Southard and Miller 1966; Yemane et al. 1996). sediments. Kaolinite occurs in every paleosol type in the IB. Kaolinite is typically Sphaerosiderite cements occur as radial crystals organized into discrete formed by weathering of aluminosilicates under acidic, warm, humid spherules up to 0.5 mm in diameter and as intergrown aggregates, or conditions in well-drained and highly weathered soils characterized by clusters, of spherules (Fig. 11J–L). Discrete spherules are rounded but in long periods of leaching (Schwertmann 1985; Folkoff and Meentemeyer rare cases appear sheared along one axis (Fig. 11J–L). Sphaerosiderites 1987; Dixon 1989; Dixon and Skinner 1992; Wilson 1999). The distinct are commonly concentrically zoned, and display alternating zones of stratigraphic distribution of the relative abundance of kaolinite in IB siderite and calcite, suggesting multiple periods of crystal growth under paleosols (Fig. 9) suggests that Desmoinesian (Carbondale–Shelburn fluctuating reducing-oxidizing states. Most sphaerosiderite samples show formation) paleosols formed under warmer, more humid, and better- oxidation within the crystallites or along the outer rims (Fig. 11J–L). drained conditions than Missourian (Patoka–Bond formation) paleosols. Sphaerosiderites typically display small cores darkened by ferric (Fe3+) However, most paleosols in the IB exhibit gley colors, preserve oxides and larger anhedral crystals of siderite on exteriors. The cores redoximorphic minerals, and are associated with coals and fossils floras contain inclusions of opaque material that may be framboidal pyrite and/ indicative of at least intermittent poor drainage and wetland settings or pyritized organic matter (Fig. 11J, K). X-ray-diffraction analysis of (DiMichele et al. 2009). Considering the controls on clay mineralogy concentrated aliquots of sphaerosiderites indicate a mineral assemblage determined from observations of recent peat swamps, it is possible that dominated by quartz and siderite, with varying amounts of calcite and leaching of acidic fluids from overlying peats could have created kaolinite, and occasionally ankerite, dolomite, pyrite, and illite hydrolytic reactions favorable for the formation of kaolinite-rich soils (Fig. 12A). The elemental composition of sphaerosiderite is organized underlying coal beds in the IB in an early burial environment (Staub and into three concentric zones, as determined by SEMS-EDAX: (1) an Cohen 1978). Yet, coal thickness and clay-mineral composition in the IB , 15 mm Fe-rich (siderite) core, (2) an , 3 mm Fe-poor zone (calcite) do not share a parametric correlation (Parham 1966). Furthermore, surrounding the core, and (3) a thicker (, 30–40 mm) Fe-rich (siderite) underclays and paleosols associated with coals exhibit 7.2 A˚ kaolinite zone on the exterior (Fig. 12B). peaks with depth in the profile (Parham 1966; this work) that indicates a Similar to the pattern of pyrite distribution in the IB, both forms of greater relative abundance of kaolinite at depth (i.e., away from the siderite are more abundant in interior portions of the basin (Fig. 1; ELY, overlying coal deposits; Fig. 8A). This observation is inconsistent with MAC, FWL, SAL cores and field sites). In the study interval, previously reported pedogenic trends in modern environments that sphaerosiderite was documented in morphologically mature horizons (B document greater leaching (and a greater relative abundance of kaolinite) horizons) of six paleosol profiles in the MAC core and three profiles in toward the soil surface (Rolfe 1954; Wilson 1999; Tabor et al. 2002), and the ELY core (Carbondale–Patoka formations). No occurrences of instead, may indicate periods of leaching of acidic fluids to substantial sphaerosiderite were recognized in the LSC core, which is from the depths through IB soils. However, other profile trends in clay mineralogy northern margin of the IB (Fig. 1). in IB paleosols are analogous to modern soil weathering profiles, including an increase in the abundance and crystallinity of chlorite and DISCUSSION discrete illite at depth and higher concentrations of quartz in lower horizons of IB paleosol profiles. Finally, in contrast to previous work on Interpretation of Paleosol Clay Mineralogy the clay mineralogy of Pennsylvanian paleosols (Parham 1966), this work The , 2 mm size fraction of Pennsylvanian paleosols in the IB are shows a clear decrease in the relative abundance of kaolinite in paleosols composed primarily of illite, I/S, kaolinite, and varying amounts of from the northern margin compared to paleosols from the interior of the chlorite (Fig. 7). The , 0.2 mm size fraction, which consists predomi- IB (Fig. 8A, C). This pattern may be attributable to more substantial nantly of pedogenic clay minerals in paleosol profiles described in other periods of leaching as a result of generally thicker overlying peat studies (Stern et al. 1997; Tabor et al. 2002; Vitali et al. 2002), is accumulations in the basin-interior environments. composed of a clay-mineral assemblage similar to the , 2 mm fraction, Interstratified I/S is a common constituent of Types C–E and G although chlorite is absent and illite peaks are broader and less intense paleosols of the IB and is absent in Types A and F paleosols (Fig. 7). r

FIG. 10.—Thin-section photomicrographs of Illinois basin paleosols. All photos were taken under crossed-polarized light. A) Crystallitic birefringent-fabric (b-fabric) in Cg horizon of Type D paleosol. B) Parallel striated b-fabric in Bkss horizon of Type G paleosol. C) Random striated b-fabric in Bss horizon of Type G paleosol. D) Subangular blocky microstructure in Bkssg horizon of Type E paleosols. E) Linear concentration of clay (cl) and root traces replaced by pyrite (p) in Bkssg horizon of Type D paleosol. F) Fossil plant material with preserved cellular structure in uppermost Bssg horizon of Type C paleosol. G) Well-preserved fossil plant material showing cellular structure in Ag horizon of Type D paleosol. H) Carbonized root traces in uppermost Bssg horizon of Type C paleosol. I) Root traces replaced by pyrite in Bkssg horizon of Type E paleosol. J) Organic matter and root traces replaced by sphaerosiderite (s) in upper Bssg horizon of Type C paleosols. K) Root trace filled with silt-size mineral grains in BC horizon of Type B paleosol. L) Disorthic, mixed micrite and sparite, calcium carbonate nodule coated with pyrite (p) in Bkssg horizon of Type E paleosol. M) Aggregate of rounded to subangular mixed micrite and sparite calcium carbonate nodules coated with secondary iron oxides (ox) in Bkg horizon of Type F paleosols. N) Mottled paleosols matrix due to iron-oxide depletions and concentrations in Bss horizon of Type G paleosol. O) Oxidized paleosol matrix and iron-oxide nodule in Bss horizon of Type G paleosol. 628 N.A. ROSENAU ET AL. JSR

FIG. 11.—Photographs and photomicrographs of micritic siderite- and calcite-bearing horizons illustrating bifurcating nature of siderite cements and nodules, deformation of sedimentary bedding, and crosscutting relationships (A–I) and photomicrographs showing the two primary occurrences of sphaerosiderite in paleosol horizons as distinct crystals and intergrown aggregates of clusters (J–L). All photomicrographs were taken under crossed-polarized light. A) Photograph of ELY Core at , 90.5 m illustrating bifurcating network of siderite (s) cement extending through sedimentary bedding. B) Photograph of ELY core at , 22 m showing deformation of sedimentary structure by calcite (c) and siderite (s) cements. C) Field photograph from Site 3 showing bifurcating network of siderite (s) in siltstone below Type D paleosol. Pen is , 14 cm long. D) Photomicrograph of siderite- and calcite-bearing horizon below Type E paleosol in the MAC core at , 79.5 m showing micritic calcite (m) and siderite (s) deforming sedimentary bedding (db) and multiple generations of carbonate precipitation including micrite (m), sparry calcite (sp), and siderite (s). JSR PENNSYLVANIAN PALEOSOLS OF THE ILLINOIS BASIN: PART I 629

FIG. 12.—Sphaerosiderite mineralogy and elemental composition. A) X-ray diffraction (XRD) spectra of powder mounts (, 125 mm size fraction) of various sphaerosiderite-bearing horizons (ELY1-4: Mattoon Formation; ELY1- 90: Carbondale Formation; MAC1-18: Patoka Formation; MAC1-22: Shelburn Formation; MAC1-27: Shelburn Formation) showing a mineral assemblage dominated by quartz, calcite, and siderite, represented by diagnostic first-order XRD peaks at 3.34 A˚ ,3.04A˚ , and 2.8 A˚ , respectively. I 5 illite; K 5 kaolinite; Q 5 quartz; C 5 calcite; D 5 dolomite; A 5 ankerite; S 5 siderite; P 5 pyrite. B) Backscattered secondary electron microscope (SEM) image and elemental composition of a representative sphaerosiderite crystal from the upper Desmoinesian Shelburn Formation (MAC core). Elemental composition is expressed as cation mole fractions as determined by energy- dispersive spectrometry. Notice concentric zon- ing of sphaerosiderites composed of (1) an Fe- rich core, (2) a thin Fe-poor zone surrounding the core, and (3) a thicker Fe-rich exterior zone.

Pennsylvanian rocks of the IB, in particular shales, siltstones, and product of pre-existing detrital minerals, where, specifically, there was an mudstones underlying many paleosols, are characterized by an abun- initial transformation of discrete illite (Jackson 1964; Wilson 1999) or dance of discrete illite and chlorite and lesser amounts of mixed-layer detrital chlorite (Barnhisel and Bertsch 1989) to smectite, followed by clays (e.g., I/S) with respect to overlying paleosols (Grim et al. 1957; low-temperature illitization of smectite to I/S in the pedogenic environ- Schultz 1958). Illite–smectite is interpreted to represent a weathering ment via the mechanism discussed below; although inheritance of I/S r

Note that siderite coats calcite crystal surfaces and infills secondary fractures in the calcite. E) Photomicrograph of a siderite-bearing siltstone horizon below Type E paleosol in the MAC core at 80.5 m showing micritic calcite cement (m), sparry calcite (sp), clusters of siderite crystals (s), and calcite deforming sedimentary bedding (db). F–I) Photomicrographs of siderite-bearing horizons below a Type D paleosol in the ELY core at 194 m (F), below a Type D paleosol in the MAC core at 27.5 m (G) and in a Cg horizon of a Type D paleosols in the ELY core at 177.5 m (H, I) illustrating multiple generations of calcite precipitation including micrite (m) and sparry calcite (sp). Sphaerosiderite (s) is shown forming along calcite surfaces (F–H), and in fractures in a microspar nodule (I) indicating that the siderite formed post micritic and microspar calcite crystallization. J–L) Photomicrographs showing the two primary occurrences of sphaerosiderite in paleosol horizons as distinct crystals and intergrown aggregates of clusters. (J, K) Type D paleosols in the ELY core at 177 m. L) Type E paleosol in the ELY core at 123 m. Notice dark, opaque inclusions of pyrite (p) around which sphaerosiderite sometimes nucleate (J, K) as well as cores and exterior surfaces of sphaerosiderite darkened by ferric oxide (ox; J–L). 630 N.A. ROSENAU ET AL. JSR JSR PENNSYLVANIAN PALEOSOLS OF THE ILLINOIS BASIN: PART I 631 from the preexisting parent rock cannot be completely ruled out, the paleosols (Types C, D, and E paleosols), while the occurrence of smectite- abundance of I/S in the , 0.2 mm size fraction (Fig. 8B) and its restricted rich (70–80% smectite) I/S is restricted to Type G paleosols (calcic occurrence in paleosols that exhibit field-scale vertic features (Fig. 7) Vertisols) (Figs. 7, 8B, C, Table 2). Types C–E paleosols exhibit a suggest that I/S most likely formed in the ancient soil weathering polygenetic development history as evidenced by features related to environment under seasonally wet conditions. development in an environment with seasonal wetting and drying The illitization of smectite, through random interstratification into followed by saturation of the profiles and subsequent gleying and peat ordered mixed layering, is normally attributed to increasing temperature, accumulation during flooding (Fig. 13). Alternatively, Type G paleosols as burial diagenesis proceeds (Burst 1959; Perry and Hower 1970; Hower preserve features that suggest formation under generally more well- et al. 1976). However, I/S exhibiting a range of expansibilities (# 5% to drained, oxidizing conditions, and mostly lack evidence of post-pedogenic . 90% smectite) and mixed-layer stacking patterns (randomly interstrat- profile saturation and gleying (Fig. 13). While the effects of burial ified (R0) to R1 ordered) has been reported from rocks, soils, and diagenesis cannot be completely ruled out, we interpret the more illitic paleosols that have never been subjected to deep burial or elevated (less expandable) composition of I/S in Types C–E paleosols with respect temperatures (Schultz 1978; Rimmer and Eberl 1982; Deconinck et al. to Type G paleosols to be the result of (1) initial transformation of 1988; Turner and Fishman 1991; Kirsima¨e et al. 1999; Gilg et al. 2003; smectite to illite during pedogenesis as a result of repeated wetting and Moore 2003; Huggett and Cuadros 2003; Velde et al. 2003). Indeed, the drying cycles, followed by (2) additional post-pedogenic alteration of occurrence of I/S in soils and paleosols is very common, more so than the authigenic (soil-formed) smectite in the presence of brackish to marine + 2+ occurrence of either discrete illite or discrete smectite (Grim 1935; water (Fig. 13). In acidic waters, K and Mg are easily removed from Barnhisel 1977; Wilson 1987; Moore and Reynolds 1997). clays, but under the alkaline environment of seawater they are readily The mechanism inferred for the illitization of smectite in the pedogenic substituted into the interlayers of phyllosilicate minerals (e.g., smectite) as environment is that of fluctuating redox conditions as a result of seasonal exchange ions in illite and chlorite, respectively, resulting in partial to wetting and drying cycles (Watts 1980; Robinson and Wright 1987; complete collapse of the swelling layers (Bradley 1953; Parham 1966; Deconinck et al. 1988; Gilg et al. 2003; Huggett and Cuadros 2003). This Schultz 1978; Deconinck et al. 1988). ‘‘surface-temperature’’ pedogenic illitization mechanism is supported by experimental studies which have shown that, when subjected to periods of Redox-Sensitive Mineral Accumulations and Paleosol Micromorphology as wetting and drying in the presence of K+, smectite can undergo partial Paleoenvironmental Indicators layer collapse, resulting in the transformation of smectite to randomly Mineral suites and micromorphological features in IB paleosols suggest interstratified I/S and occasionally, R1 ordered I/S (Mamy and Gaultier that soil development proceeded through periods of both well-drained ´ 1975; Srodon´ and Eberl 1984; Eberl et al. 1986; Shen and Stucki 1994; (chemically oxidizing) and poorly drained (chemically reducing) condi- Stucki 1997). Huggett and Cuadros (2003) provided persuasive mineral- tions (Fig. 13). Moderately well-drained oxygenated conditions, as ogical evidence that the driving mechanism behind the transformation of suggested by the presence of red and yellow mottling, pedogenic smectite to illite in soil-forming environments is bacterially mediated 3+ 2+ slickensides, calcium carbonate accumulation, and, more rarely, linear reduction of Fe to Fe during water-saturated periods, whereby the clay concentrations, are found in paleosols both interior to the basin and 3+ reduction of Fe serves to increase the interlayer charge necessary for along the northern margin, suggesting that common processes responsible + fixation of K and promotes generation of illite layers without atom for their formation were acting across the basin (Table 2, Fig. 13). substitution in the octahedral or tetrahedral layers of the original smectite Alternatively, the occurrence of ferrous (Fe2+) iron minerals, pyrite, and crystal structure. siderite in Types C, D and E paleosols are indicators of sustained periods Modern soils that exhibit wedge-shaped features and slickensides of poorly drained, reducing conditions in the IB coastal plain and typically form by shrinking and swelling of expandable 2:1 phyllosilicate floodplain, while Fe3+-rich nodules as well as Fe3+-rich coatings on peds minerals (e.g., smectite) during cycles of wetting and drying in climates (Fig. 5D) and calcium carbonate nodules (Fig. 4) are evidence of that experience seasonal precipitation and/or changes in water-table fluctuating redox cycles during paleosol development (Fig. 13). position (Yaalon and Kalmar 1978; Wilding and Tessier 1988; Buol et al. Pyrite is typically found in marine sediments (Berner 1984) but also 2003). Given (1) the widespread occurrence of I/S in IB paleosol types occurs in poorly drained soils forming in coastal, deltaic, or estuarine 2+ 22 that preserve shrink–swell features (Fig. 4; Types C–E and G paleosols), settings with high concentrations of dissolved Fe and sulfate (SO4 ) (2) the absence of I/S in paleosol types that lack shrink–swell features and abundant organic matter (van Breemen 1973; Miedema et al. 1974; 22 (Fig. 4; Types A, B, and F paleosols), (3) inferred IB burial temperatures Pons et al. 1982; Rabenhorst and Haering 1989). Addition of SO4 -rich of , 100uC, and (4) no apparent relationship between the degree of fluids to anoxic, organic-matter-rich soil profiles leads to bacterially 22 22 ordering of I/S, the percentage of illite in I/S, or the relative concentration mediated reduction of SO4 to sulfide (S ), which readily reacts with of I/S in paleosols profiles, with respect to stratigraphic position, we Fe2+ in the system to crystallize pyrite (Berner 1984; Curtis et al. 1986; suggest that an original smectite component in Types C–E and G Kraus 1997, 1998). The occurrence of pyrite in IB paleosols suggests that paleosols underwent transformation to I/S via the low-temperature pore spaces in many of these profiles were periodically inundated by 22 pedogenic illitization process discussed above, which requires repeated SO4 -rich waters, such as marine or mixed marine–freshwater (brackish) wetting and drying of the profile. fluids, which eventually became anoxic (Fig. 13). It is important to note, however, that there is a distinct distribution in Siderite precipitation is typical of wetland soils (Curtis et al. 1986; the relative amount of expandable component (% smectite) preserved in I/ Moore et al. 1992; Ludvigson et al. 1998; Driese and Ober 2005), where it S in the , 2 mm size fraction with respect to paleosol types in the IB. For forms by geomicrobiological processes in conditions of very low pO2, very example, illite-rich (, 20–40% smectite) I/S is associated with gleyed high pCO2, slightly acidic environments with high concentrations of r

FIG. 13.—Schematic diagrams illustrating the development of each paleosol type (pedotype) across the Illinois basin. The ‘‘interior’’ pathway illustrates the development of paleosols found in the ELY, MAC, FWL, and SAL cores, and field sites, while the ‘‘margin’’ pathways show the development of paleosols found in the LSC core (Fig. 1). 632 N.A. ROSENAU ET AL. JSR

2+ 22 dissolved Fe , and low SO4 concentrations (Ohmoto et al. 2004). Types C, D, and E paleosols (Figs. 4, 5C, D, E, 13) all have Therefore, in conjunction with associated abundant redoximorphic morphological properties similar to modern Vertisols, including wedge- features in paleosol profiles, siderite cements and nodules are further shaped aggregate paleosol structure and slickensides, and therefore an evidence for periods of soil formation and/or drowning under reducing important characteristic of their formation included shrink–swell conditions in the IB (Fig. 13). Furthermore, siderite is observed to processes. Such processes in modern soils are typically associated with crosscut and form along the edges of ped structures and carbonate expandable 2:1 phyllosilicate minerals (e.g., smectite) in climates that nodules in the paleosol matrix, and in some cases appears to have experience seasonal precipitation and/or episodic changes in water-table nucleated around pyrite, indicating that siderite formed at a later stage in position (Yaalon and Kalmar 1978; Wilding and Tessier 1988; Buol et al. the pedogenic process or during drowning of the soil profile (Fig. 11F, 2003). Comparative geochemical studies of ancient and modern Vertisols 22 K). Variations in SO4 concentration are considered to be the principal suggest that paleosol profiles of Vertisols may behave as approximately factor leading to crystallization of either siderite or pyrite in poorly closed systems because of their low permeability and high clay content drained soil profiles because the presence of S22 inhibits siderite and (Driese et al. 2000, 2003, 2005). Accordingly, studies of ancient Vertisols favors pyrite crystallization (Berner 1984; Heese 1990; Ufnar et al. 2001). may provide reliable information about pedogenic processes and The inclusion of pyrite in the cortex of some sphaerosiderite spherules paleoclimate. In this regard, it is important to note that Type C, D, 22 (Fig. 11J, K) suggests SO4 -rich fluids were present, at least intermit- and E paleosols differ from modern Vertisols in that they lack smectite in tently, in some of the IB soil profiles prior to siderite precipitation. Most the , 2 mm clay-mineral fraction. Rather, the preservation of illite-rich I/ 22 likely, the SO4 -rich waters were derived from the mixing of marine and S in these paleosols is interpreted to be the result of (1) initial freshwater fluids in coastal plains and floodplains of the IB; however, transformation of smectite to illite during pedogenesis as a result of 22 high concentrations of dissolved SO4 have also been observed in repeated wetting and drying cycles followed by (2) additional post- modern freshwater swamp soils (Farrell 1987; Jakobsen 1988; Rabenhorst pedogenic illitization of authigenic smectite (or I/S) in the presence of and Haering 1989; Moore et al. 1992; Aslan and Autin 1996, 1998). brackish to marine waters (Fig. 13; Bradley 1953; Deconinck et al. 1988; 22 Regardless of the precise source of the dissolved SO4 , it is clear that in Huggett and Cuadros 2003). many instances when siderite and pyrite occur together in a paleosol Furthermore, Types C, D, and E paleosols contain siderite and pyrite, profile, pyrite precipitation preceded sphaerosiderite precipitation. features indicative of poorly drained, reducing conditions (Driese et al. Specifically, sphaerosiderite precipitation did not begin until the source 1995; Ludvigson et al. 1998). Nevertheless, the well-developed shrink–swell 22 of the SO4 was removed and/or depleted. In other instances, however, features and preservation of I/S associated with Types C, D, and E pyrite is found in paleosols devoid of sphaerosiderite. This would seem to paleosols indicate that at one point these soils likely contained smectite and 22 indicate consistently higher SO4 concentrations in soil pore spaces, such there were sufficient periods of drying to allow shrink–swell processes to that sphaerosiderite precipitation was inhibited. The higher concentration dominate (Fig. 13; Duchaufour 1982; Retallack 1990). The laminated, 22 of SO4 in soil profiles could be the result of either more frequent influx organic-rich, kaolinitic layer directly beneath coal layers and overlying of marine to mixed marine–freshwater fluids during waterlogging and some of these paleosols, represents the cessation of pedogenesis and is 22 pedogenesis and/or post-burial interaction with SO4 rich groundwater interpreted to indicate deposition in a calm, swampy, lagoonal environ- and seawater during marine transgressions (Fig. 13). ment, just prior to the onset of peat accumulation. The presence of this thin As mentioned, while pyrite and siderite can be found throughout the sedimentary layer that separates the underlying paleosol profile from the IB, they are most concentrated in paleosols from the basin interior overlying coal has been observed in Pennsylvanian strata before (Wanless (Figs. 1, 13). This basin-scale trend in the distribution of redox indicators 1950, 1955), where it was interpreted as evidence that the paleosol and suggests that soils forming in the interior of the basin experienced overlying coal beds formed at separate times under different environmental substantially greater periods of hydromorphy, episodes of anoxia, and conditions. When present the contact between the laminated layer and intensity of redox reactions during pedogenesis and early burial than soils overlying coal is sharp, suggesting that erosion was insignificant. that developed upon the northern basin-margin landscapes (Fig. 13). Paleosol Types D, E, and F contain accumulations of pedogenic calcite (Figs. 4, 13). In modern soils, pedogenic calcite precipitation results from 2+ Paleoenvironmental Interpretation of Paleosol Types the translocation of Ca ions through the soil profile by downward- percolating water (Machette 1985; Birkeland 1999) in subhumid to Type A paleosols are Histosols. The majority of modern Histosols form semiarid climates (Buol et al. 2003; Schaetzl and Anderson 2005). in low-lying, humid, ever-wet environments characterized by a high water Accordingly, we interpret the occurrence of discrete pedogenic calcite in table where precipitation is usually greater than 1000 mm/year and paleosol Types D, E, and F to indicate that at one time these profiles were precipitation exceeds evapotranspiration for 10–11 months of the year well-drained (Fig. 13). While pedogenic calcite accumulation in most soil (Cecil et al. 1985, 2003; Ziegler et al. 1987; Le´zine and Chateauneuf 1991) orders indicates pedogenesis in climates that experience relatively low that leads to the development of anoxic pore water, which promotes amounts of rainfall (, 800 mm/ year; Jenny 1941; Arkley 1963; Royer preservation of in-situ organic-matter. Gley matrix colors, and preserva- 1999), modern Vertisols have been shown to retain calcite in the profile tion of organic root traces in the mineral horizons underlying the coal under significantly greater amounts of mean annual rainfall (up to layers that is observed in many Type A paleosols (Fig. 4), suggest , 1500 mm/year; Nordt et al. 2006) than other types of soils. Following prolonged saturation of these soil profiles (Simonson and Boersma 1972; this relatively well-drained period in which shrink–swell and calcite Wilding et al. 1983). As evidenced by their laterally extensive nature, accumulation processes prevailed, the profiles became saturated, leading stratigraphic thickness, and common occurrence throughout the IB to anoxia, reduction of Fe3+-oxide minerals, and formation of aqueous Pennsylvanian stratigraphy, Histosols are interpreted to have formed in Fe2+, which was either transported out of the soil or crystallized as Fe2+- large, poorly drained, sediment-starved, interfluvial coastal swamps. bearing minerals such as pyrite or siderite, which is also present in many Type B paleosols are Protosols characterized by weakly developed of these profiles (Fig. 13). These processes resulted in gleyed matrix horizonation (Figs. 4, 5B). These profiles are interpreted to have formed colors, well-preserved organic-matter, and common sphaerosiderite and on unstable landscapes, such as upper-tidal sand flats and mud flats on pyrite in the paleosol profiles. Given the long durations typically required the lower coastal plain to deltaic plain, which resulted in intermittent and to form calcic horizons in modern soils (, 1000–10,000 years; Gile et al. rapid input of sediments and prolonged to episodic saturation of the 1981), pedotypes D, E, and F likely correspond to prolonged intervals of profile (Marriott and Wright 1993; Buol et al. 2003). landscape stability and nondeposition across the IB prior to onset of poor JSR PENNSYLVANIAN PALEOSOLS OF THE ILLINOIS BASIN: PART I 633 drainage and drowning of the profiles. The duration is unknown, but ALLGAIER,G.J.,AND M.E. HOPKINS, 1975, Reserves of the Herrin (No. 6) Coal in the Fairfield Basin in southeastern Illinois: Illinois Geological Survey, Circular 489, 31 p. siderite accumulation in these soils during the subsequent, post-calcite ARCHER, A.W., AND GREB, S.F., 1995, An Amazon-scale drainage system in the Early accumulation phases indicates complex, or polygenetic (sensu Chadwick et Pennsylvanian of North America: Journal of Geology, v. 103, p. 611–628. al. 1995), soil-forming conditions for Types D, E, and F paleosols (Fig. 13). ARCHER, A.W., KUECHER, G.J., AND KVALE, E.P., 1995, The role of tidal-velocity asymmetries in the deposition of silty tidal rhythmites (Carboniferous, Eastern Analogous to paleosol Types D, E, and F, the occurrence of pedogenic Interior Coal Basin, U.S.A.): Journal of Sedimentary Research, v. 65, p. 408–416. calcite in Type G paleosols (Figs. 4, 5F, 13) suggests that these profiles ARKLEY, R.J., 1963, Calculation of carbonate and water movement in soil from climatic formed on well-drained, stable portions of the IB landscape under data: Soil Science, v. 96, p. 239–248. subhumid to semiarid climates (Soil Survey Staff 1975; Machete 1985; ASLAN,A.,AND AUTIN, W.J., 1996, Depositional and pedogenic influences on the environmental geology of Holocene Mississippi River floodplain deposits near Buol et al. 2003; Schaetzl and Anderson 2005). Type G paleosols are the Ferriday, Louisiana: Engineering Geology, v. 45, p. 417–432. only paleosols in the basin that contain smectite-rich I/S in the clay-mineral ASLAN A, AND AUTIN, W.J., 1998, Holocene flood-plain soil formation in the southern (, 2 mm) fraction (Fig. 8C) and display high-chroma matrix colors lower Mississippi Valley: implications for interpreting alluvial paleosols: Geological (Fig. 5F). These characteristics suggest that Type G paleosols developed Society of America, Bulletin, v. 110, p. 433–449. BAKER, D.R., 1962, Organic geochemistry of Cherokee Group in southeastern Kansas during episodic wetting-drying cycles under oxygenated conditions that and northeastern Oklahoma: American Association of Petroleum Geologists, favored preservation of Fe-oxides throughout their formation and burial Bulletin, v. 46, p. 1621–1642. history (Fig. 13). However, the presence of drab mottles indicates that at BARNHISEL, R.I., 1977, Chlorites and hydroxyl interlayered vermiculite and smectite, in Dixon, J.B., and Weed, S.B., eds., Minerals in Soil Environments: Soil Science Society least for brief periods of time the profiles were water-saturated and of America, Madison, Wisconsin, p. 331–356. 2+ reducing conditions led to the mobilization of Fe (Fig. 13). BARNHISEL, R.I., AND BERTSCH, P.M., 1989, Chlorites and hydroxy-interlayered vermiculite and smectite, in Dixon, J.B., and Weed, S.B., eds., Minerals in Soil Environments, Second Edition: Soil Science Society of America, Book Series, v. 1, CONCLUSIONS p. 729–788. BARRICK, J.E., LAMBERT, L.L., HECKEL, P.H., AND BOARDMAN, D.R., 2004, Pennsylva- The results of this study offer the first detailed and stratigraphically nian conodont zonation for Midcontinent North America: Revista Espan˜ola de complete analysis of the macromorphological, micromorphological, and Micropaleontologia, v. 36, p. 231–250. BARROWS, M.H., AND CLUFF, R.M., 1984, New Albany Shale Group, (Devonian– mineralogic content of paleosol profiles preserved in Pennsylvanian Mississippian) source rocks and hydrocarbon generation in the Illinois basin, in (Atokan–Virgilian; Westphalian–Stephanian) strata of the Illinois basin. Demaison, G., and Murris, R.J., eds., Petroleum Geochemistry and Basin Evaluation: Based on field observations, including morphological development, American Association of Petroleum Geologists, Memoir 35, p. 111–138. thickness, and relationships to adjacent strata, as well as clay mineralogy BERNER, R.A., 1984, Sedimentary pyrite formation: an update: Geochimica et Cosmochimica Acta, v. 48, p. 605–615. and micromorphology, middle–upper Pennsylvanian paleosols preserved in BESTLAND, E.A., RETALLACK, G.J., AND SWISHER, III, C.C., 1997, Stepwise climate mixed marine and terrestrial coal-bearing strata (cyclothems) in the Illinois change recorded in Eocene–Oligocene paleosol sequences from central Oregon: basin can be organized into seven general profile types, or pedotypes. The Journal of Geology, v. 105, p. 153–172. BIRKELAND, P.W., 1999, Soils and Geomorphology, Third edition: New York, Oxford features preserved in the pedotypes represent formation under variable University Press, 430 p. degrees of soil drainage, ranging from poorly drained Histosols (Type A BLAKEY, R.C., 2007, Carboniferous–Permian paleogeography of the assembly of paleosols) to well-drained calcic Vertisols (Type G paleosols). 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CECIL, C.B., STANTON, R.W., NEUZIL, S.G., DULONG, F.T., RUPPERT, L.F., AND PIERCE, The authors would like to thank Phil Ames of Peabody Energy, Barry B.J., 1985, Paleoclimate controls on late Paleozoic sedimentation and peat formation Sargeant of Knight Hawk Coal, Vigo Coal Operating Company, and Triad in the central Appalachian Basin: International Journal of Coal Geology, v. 5, p. 195– Mining, Inc. for providing access to their mines and permitting collection of 230. samples, as well as the Illinois State Geological Survey for providing access to CECIL, C.B., DULONG, F.T., WEST, R.R., STAMM, R., WARDLAW,B.,AND EDGAR,N.T., cores, core descriptions, and core samples. We thank Drs. Paul McCarthy, 2003, Climate controls on the stratigraphy of a middle Pennsylvanian cyclothem in Julia Kahmann-Robinson, Peter Flaig, and Cindy Stiles for constructive North America, in Cecil, C.B., and Edgar, N.T., eds., Climate Controls on reviews that considerably improved the quality of the manuscript. 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