Middle and Late Pennsylvanian Cyclothems, American Midcontinent
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C. R. Geoscience 346 (2014) 159–168 Contents lists available at ScienceDirect Comptes Rendus Geoscience ww w.sciencedirect.com External Geophysics, Climate Middle and Late Pennsylvanian cyclothems, American Midcontinent: Ice-age environmental changes and terrestrial biotic dynamics a,b b, c C. Blaine Cecil , William A. DiMichele *, Scott D. Elrick a U.S. Geological Survey, 425 Brownsburg Turnpike, Rockbridge Baths, VA 20743, United States b Department of Paleobiology MRC-121, NMNH Smithsonian Institution, Washington, DC 20560, United States c Illinois State Geological Survey, University of Illinois, Champaign, IL 61820, United States A R T I C L E I N F O A B S T R A C T Article history: The Pennsylvanian portion of the Late Paleozoic Ice Age was characterized by stratigraphic Received 13 January 2014 repetition of chemical and siliciclastic rocks in the equatorial regions of the Pangean Accepted after revision 13 March 2014 5 interior. Known as ‘‘cyclothems’’, these stratigraphic successions are a 10 yr-record of Available online 10 August 2014 6 glacial waxing and waning, superimposed on longer term, 10 yr intervals of global warming and cooling and a still longer term trend of increasing equatorial aridity. During Keywords: periods of maximum ice–minimum sea level, the interior craton was widely exposed. Climate Epicontinental landscapes were initially subjected to dry subhumid climate when first Coal exposed, as sea level fell, but transitioned to humid climates and widespread wetlands Cyclothem during maximum lowstands. During interglacials (ice-minima) seasonally dry vegetation Paleoecology Pennsylvanian predominated. The wetland and seasonally dry biomes were compositionally distinct and had different ecological and evolutionary dynamics. Published by Elsevier Masson SAS on behalf of Acade´mie des sciences. 7 1. Introduction drying and warming (10 yr) (Tabor and Poulsen, 2008). Regularity of climate and sea-level changes at the glacial- The Pennsylvanian portion of the Late Paleozoic Ice Age stage scale has permitted correlation across North America (approx. 323–299 Ma) was characterized by regular (Cecil et al., 2003a) and even across the Euramerican waxing and waning of Southern Hemisphere continental portions of Pangea in deposits of paralic (marine influ- glaciers (Fielding et al., 2008; Isbell et al., 2003a). In order enced) basins from the American Midcontinent to the to provide a precise definition of time scales for Earth’s Donets Basin (Eros et al., 2012; Heckel et al., 2007). warming and cooling events, we use terminology as Patterns of equatorial sea-level change strongly correlate outlined in Cecil (2013). Glacial stage (shortest scale of a 5 with inferred polar ice volume on both stage and epoch single glacial–interglacial cycle, 10 yr) pacing may have temporal scales (Rygel et al., 2008). been on the rhythm of Milankovich-band orbital frequen- Equatorial climate changed in concert with ice volume cies (Heckel, 2008). These individual glacial–interglacial and sea level, most notably the patterns, durations and cycles were superimposed on glacial epoch scale (longer- 6 amounts of equatorial rainfall (Fig. 1B). These changes term, 10 yr) intervals of global warming and cooling occurred on all time scales from glacial–interglacial stages (Birgenheier et al., 2009, Joeckel, 1999), further super- (Cecil et al., 2003a; Horton et al., 2012), to epoch-scale imposed on a period-scale trend of long-term equatorial intervals of global warming and cooling (e.g., Cecil, 1990; Rygel et al., 2008), to a period-scale, long-term trend of warming and drying (Cecil, 1990; Montan˜ez and Poulsen, * Corresponding author. E-mail address: [email protected] (W.A. DiMichele). 2013, Tabor and Poulsen, 2008). Climate change has been http://dx.doi.org/10.1016/j.crte.2014.03.008 1631-0713/Published by Elsevier Masson SAS on behalf of Acade´mie des sciences. 160 C. Blaine Cecil et al. / C. R. Geoscience 346 (2014) 159–168 Fig. 1. (Color online.) Interior Pangean cyclothem. A. Stratigraphic architecture of a complete glacial–interglacial, stage-scale cycle. 1-paleosol; 2-coal; 3- esturaine gray-shale wedge; 4-ravinement surface; 5-marine black shale; 6-marine limestone; 7-deltaic and nearshore siliciclastics. B. Patterns of change in ice volume, sea level, equatorial climate. C. Equatorial floristic changes, tracking climate change. D. Pennsylvanian Pangea. E. Climate-Siliciclastic sediment yield relationship. F. Climate-Sediment type relationship. integrated into the broader understanding of sedimentary scales (DiMichele et al., 2009, 2010; Falcon-Lang and and biological dynamics of the Late Paleozoic Ice Age DiMichele, 2010; Oplusˇtil et al., 2013). Thus, many (LPIA). Climate has a strong, direct effect on lithofacies paleontological patterns, including evolutionary dynamics, patterns in both limnic (non-marine) and paralic basins. are direct reflections of regional climatic patterns, con- Lithologies such as coal (formerly peat–a Histosol) and trolled by global-scale factors. Here we review the mineral paleosols directly record climatic conditions. lithological signature and biological effects of LPIA There are strong climatic effects on siliciclastic sediment glacial–interglacial cyclicity on landscapes of the vast, availability and transport (Cecil et al., 2003b) (Fig. 1E), the flat, central-western portions of the Pangean superconti- extent to which environments of deposition are mixed and nent, between the Central Pangean Mountains and oxygenated, and the chemical conditions. Where silici- Ancestral Rockies (Fig. 1D). These patterns are expressed clastic input is absent or minimal, and where necessary primarily during the late Middle and Late Pennsylvanian in chemical and physical conditions are met, climate the Western Interior (Midcontinent) and Eastern Interior becomes an important control on carbonate formation (Illinois) basins, USA, more so than in the Appalachian (Fig. 1F) (Cecil and Dulong, 2003; Cecil et al., 2003b). basin. It is there that the ‘‘cyclothem’’ concept developed Pangean plants and animals also strongly reflected and (see Cecil et al., 2003a; Heckel, 1990; Langenheim and tracked environments (Fig. 1C), at all spatio-temporal Nelson, 1992; Weller, 1931). This region is well suited for C. Blaine Cecil et al. / C. R. Geoscience 346 (2014) 159–168 161 revealing ice-age climate and sea level dynamics in surface may be overlain by a relatively thin ‘‘transgressive’’ equatorial latitudes: Paralic character and low elevations marine limestone (Heckel, 2008), which is more common permitted far reaching sea-level fluctuations. Great dis- in Western Interior cycles than in the Eastern Interior or tance from mountain ranges in the eastern and western Appalachians. Variably developed, the transgressive lime- interior areas greatly reduced habitat variation and effects stone is often absent or represented only by shell hash. of uplands on climate and biological patterns. Great Where limestone is absent, the ravinement surface may be flatness of the cratonic surface created widespread marked by local accumulations of phosphatic nodules or environmental spatio-temporal uniformity. pyrite-permineralized plant remains. A marine, black, generally fissile shale typically lies in sharp, erosional contact with the underlying strata, immediately above the 2. Record and dynamic drivers of glacial–interglacial ravinement surface (Fig. 1A-4) and may be extremely cycles widespread (e.g., Cecil et al., 2003a; James and Baker, 1972). In the Western and Eastern Interior basins, black 2.1. The Cyclothem shale is overlain by open-marine limestone in conformable contact (Fig. 1A-5). The black shale and overlying lime- Glacial–interglacial cyclicity has a distinctive, if geo- stone are generally the most widespread marine beds. graphically and environmentally variable, lithological In many successions, coarsening upward, gray-shale signature. Such successions can be entirely marine (e.g., overlies the open-marine limestone, (Fig. 1A-6). These Elrick and Scott, 2010), entirely terrestrial (e.g., Eble et al., deposits are likely of fluvial-deltaic origin. It is on this 2006), or mixed (e.g., Heckel, 2008), and subject to local heterogeneous surface, following exposure during sea tectonic, and climatic overprints. We focus on mixed level regression and early lowstand, that the terrestrial terrestrial-marine cyclothems, as found in cratonic set- part of the next cycle, the paleosol, is developed. tings, particularly of the Eastern Interior basin USA, located between the more marine influenced Western Interior and 2.1.1. The flat craton and water depth more terrestrial Appalachian basins. Over time, the high During the late Middle and Late Pennsylvanian, the relief, eroded surface of the Mid-Carboniferous unconfor- Pangean interior was a low relief surface with a gradient mity (Bristol and Howard, 1974) was in-filled across the possibly < 1 m/km, with a few areas, e.g. the Ozark Dome American Midcontinent. This lowered the relief of the in Missouri, of tectonically created higher relief (McKee cratonic platform over which glacial–interglacial cycles and Crosby, 1975). As a consequence of flat topography, were expressed (e.g. McKee and Crosby, 1975; Watney small sea-level changes likely had large effects on coverage et al., 1989), resulting in alternation of marine and of the craton by marine waters. Low gradient and lack of terrestrial environments in the Western and Eastern significant topography would have allowed unimpeded Interior regions of Pangea during