Research Paper GEOSPHERE Revealing the hidden Milankovitch record from Pennsylvanian cyclothem successions and implications regarding late Paleozoic GEOSPHERE; v. 11, no. 4 chronology and terrestrial-carbon (coal) storage doi:10.1130/GES01177.1 Frank J.G. van den Belt1, Thomas B. van Hoof2, and Henk J.M. Pagnier3 1Department of Earth Sciences, University of Utrecht, P.O. Box 80021, 3508 TA Utrecht, Netherlands 9 figures 2TNO Geo-Energy Division, P.O. Box 80015, 3508 TA Utrecht, Netherlands 3TNO/Geological Survey of the Netherlands, P.O. Box 80015, 3508 TA Utrecht, Netherlands CORRESPONDENCE: [email protected] CITATION: van den Belt, F.J.G., van Hoof, T.B., ABSTRACT An analysis of cumulative coal-bed thickness further indicates that terres- and Pagnier, H.J.M., 2015, Revealing the hidden Milankovitch record from Pennsylvanian cyclothem trial-carbon (coal) storage patterns are comparable in the two remote areas: successions and implications regarding late Paleo- The widely held view that Pennsylvanian cyclothems formed in response in the Netherlands ~5 m coal per m.y. during the Langsettian (Westphalian zoic chronology and terrestrial-carbon (coal) stor- to Milankovitch-controlled, glacio-eustatic, sea-level oscillations lacks unam- A) and increasing abruptly to ~20 m/m.y. at the start of the Duckmantian age: Geosphere, v. 11, no. 4, p. 1062–1076, doi:10 .1130 /GES01177.1. biguous quantitative support and is challenged by models that are based on substage (Westphalian B). In Kentucky, storage rates were lower, but when climate-controlled precipitation-driven changes in depositional style. This standardized to Dutch subsidence, the pattern is identical. This suggests that Received 13 February 2015 study shows that cyclothem successions do in fact contain a clear record of burial of terrestrial carbon during the Late Paleozoic Ice Age was globally con- Revision received 7 April 2015 Milankovitch-controlled oscillating sea level, but that it is prerequisite that trolled and possibly very predictable. Accepted 20 May 2015 besides cyclothem thickness, cyclothem composition is taken into account. Published online 1 July 2015 A simple subdivision of cyclothems into subaqueous and subaerial facies is sufficient to reveal the signal, provided that sufficiently long and complete INTRODUCTION successions are studied. Two Duckmantian–Bolsovian (Westphalian B–C) successions were stud- Pennsylvanian cyclothems, deposited in paleoequatorial Euramerican ba- ied—one from a high-accommodation setting in the Netherlands and another sins during the late Paleozoic ice-house period, are a classic example of sedi- from a medium-accommodation setting in Kentucky in the United States. The men ta tion controlled by glacio-eustasy, with sea-level fluctuations driven by Dutch record comprises an exceptional, 1728-m-long, continuously cored in- the waxing and waning of Southern Hemisphere ice caps (Veevers and Powell, terval, and it shows a distinct twofold cyclicity in the subaerial-facies ratio of 1987). The concept of sea-level control emerged in the first half of the twentieth subsequent cyclothems at wavelengths of ~256 m and ~59 m, which is con- century in publications by Udden (1912), Weller (1930), and in particular Wanless firmed by power-spectral analysis. The signal is not present in the Kentucky and Shepard (1936), who linked the cyclic character of coal-bearing Pennsyl- succession due to subsidence-controlled low preservation of only one out of vanian deposits with growing evidence for widespread late Paleozoic glaciation. three to four cyclothems, and that explains why many cyclothem studies have The case was strengthened during the latter part of the twentieth century with a yielded inconclusive results. large body of studies dealing with various aspects of the cyclothem formation, Recent U/Pb ages indicate that the 256 m cycle represents ~395 k.y., including possible Milankovitch control (Busch and Rollins, 1984; Heckel, 1986; which matches with long eccentricity (413 k.y.). This then gives a 95 k.y. du- Veevers and Powell, 1987; Klein and Willard, 1989; Davies et al., 1992; Maynard ration for the 59 m cycle (short eccentricity). Individual cyclothems in the and Leeder, 1992; Aitken and Flint, 1995; Greb et al., 2008; Heckel, 2008). high-accommodation Dutch succession are mostly between 5 and 35 m Although the influence of glacio-eustatic sea-level fluctuations on depo- thick, which points to a sub-eccentricity duration (mean 21 k.y.). The highly sition during the Pennsylvanian became accepted in the general sense, skep- variable thickness may be due to interference of precession-, obliquity-, and ticism has remained, not in the least because the resolution of data sets and eccen tricity-driven sea-level fluctuations or alternatively to autocyclic or the precision of the absolute time scale have proven insufficient to unambig- climate-controlled variations in sediment supply. Integration of the results uously demonstrate a causal and temporal link (Algeo and Wilkinson, 1988; with U/Pb calibrated radiometric ages for “tonstein” ash layers from North Klein, 1990; Wilkinson et al., 2003). An alternative mechanism was proposed America and Europe allowed refinements of the chronology of the main West- by Cecil (1990), who argued that—in sync with eccentricity-driven sea-level For permission to copy, contact Copyright phalian (Moskovian–Bashkirian) coal interval; these refinements are consis- fluctuations—the formation of Pennsylvanian cyclothems was primarily con- Permissions, GSA, or [email protected]. tent across Euramerica. trolled by paleoclimate, with precipitation cycles triggering the alternation of © 2015 Geological Society of America GEOSPHERE | Volume 11 | Number 4 van den Belt et al. | Revealing the hidden Milankovitch record from Pennsylvanian cyclothem successions Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/4/1062/3333634/1062.pdf 1062 by guest on 26 September 2021 Research Paper coal and clastics. This model has gained popularity recently (Cecil et al., 2003; relatively thin (~100s m to ~1 km). In high-subsidence areas such as Nova Eros et al. 2012; Rosenau et al., 2013; Cecil et al., 2014; DiMichele, 2014). It ex- Scotia, continental Europe, as well as a number depocenters in the southern plains the formation of cyclothems still within the framework of glacio-eustasy and central parts of the Appalachian Basin, Mid-Pennsylvanian successions and sequence stratigraphy (Cecil et al., 2014; Eros et al., 2012), but the model are many kilometers thick (Drozdzewski, 1993; Falcon-Lang, 2004; Greb et al., differs in the mechanism by which the glacio-eustatic signal is translated to the 2008), and cyclothems are so numerous that they must represent shorter time sedimentary system (driven by sediment supply rather than accommodation) intervals to be consistent with age data. Hence, the interpreted dominance of and in the timing of deposition of the different facies (e.g., peat accumulation eccentricity cycles in low to medium subsidence areas, where successions are during lowstand of sea level rather than transgression). This study focuses much thinner, could well be preservation driven. Chesnut (1997) noted that on the role of glacio-eustasy in cyclothem formation, and we test whether the cyclothems with a ~100 k.y. duration in the central Appalachian Basin grade typical “cyclothemic” alternation of marine and non-marine sediments can be into cyclothems with a 400 k.y. duration toward areas of lower subsidence, unambiguously explained in terms of Milankovitch control. indicating that multiple depositional hiatuses and/or erosion surfaces may Sea-level fluctuations are also believed to have triggered the accumula- characterize areas of low accommodation. tion of peat layers (coal) over vast areas during early transgression (Heckel, In this study, a Langsettian–Bolsovian (Westphalian A–C) cyclothem suc- 1990; Flint et al., 1995; Bohacs and Sutter, 1997) or under conditions of high cession was analyzed from a high subsidence area in the Netherlands, which is precipitation during sea-level lowstand (Cecil et al., 2014; DiMichele, 2014). ~1728 m thick and covers ~145 cyclothems. The interval was cored completely, Pennsylvanian coal beds constitute the largest reservoir of terrestrial carbon allowing analysis of the gradual compositional variation of cyclothems over on the globe (Berner, 2003). Hence, when linked with volcanic-ash dates, thick time. This resulted in a much higher resolution cyclicity interpretation than cyclothem successions may not only hold the key to detailed reconstruction of based on cyclothem thickness alone. The succession was compared with an sea-level fluctuations during a major ice-house period and to the fine-tuning overlapping cyclothem succession from a medium-accommodation setting in of late Paleozoic chronology but also to accurate estimates of global carbon Kentucky (USA) to see how subsidence rate affected deposition and the pres- fixation rates in coal swamps. ervation of cyclothems. The results were used to refine Middle Pennsylvanian Although estimated cyclothem periods are in the Milankovitch range chronology and to determine coal thickness per unit time for coal basins. (Heckel, 1986; Maynard and Leeder, 1992) and cyclothem bundling patterns match Milankovitch-cycle ratios (Busch and Rollins, 1984; Heckel, 1986), or- bital control has not been demonstrated unambiguously and lacks a strong PERIODICITY IN CYCLOTHEM RECORDS quantitative support (Algeo and Wilkinson,