Research Paper

GEOSPHERE Revealing the hidden Milankovitch record from cyclothem successions and implications regarding late 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 ( 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 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 menta­ 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 eccen­tricity-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–) 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

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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 (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, 1988; Wilkinson et al., 2003; Meyers et al., 2008). Difficulties in matching data with the Milankovitch model include Thickness and average cycle length have been the primary data source in poor time control (Klein, 1990), incomplete successions (De Boer, 1991; Hinnov, cyclothem analysis. Thus far this has not yielded conclusive evidence in terms 2013), nonlinear time-sediment relations (Algeo and Wilkinson, 1988; Hinnov, of cycle periods. This may be related to the above-mentioned problems, such 2013), and the interference of cycles (De Boer, 1991). Therefore, the extraction as poor time control, but may be intrinsic to the method as well. Counterintui­ ­ of accurate sea-level records, which could contribute to the understanding of tively, cyclothem boundaries are not typically created at sea-level highstand ice-sheet dynamics, terrestrial carbon storage, and other aspects of paleo­ or lowstand. For example, it may take many thousands of before rising climate, remains a challenge. sea level causes flooding of the land and before deposition of marine shales In older studies, Pennsylvanian cycle periods are variably linked with pre- on top of a previous cycle starts. This is illustrated by the example in Figure 1, cession (17 k.y.), obliquity (35 k.y.), and short and long eccentricity (95–413 k.y.) which is based on the simple, theoretical depositional model of Jervey (1988). (Heckel, 1986; Klein, 1990; De Boer, 1991; Maynard and Leeder, 1992; Goldham- It assumes that subaqueous facies are deposited when base level is above the mer et al., 1994), but the low resolution of the Pennsylvanian time scale has land surface, followed by non-deposition (or local erosion) when it falls be- hampered detailed cycle determinations (Klein, 1990). Various recent studies, low the land surface, followed by subaerial deposition when rising base level however, have indicated that cyclothem deposition during the Pennsylvanian meets the land surface again and as long as it is balanced by sediment supply. was primarily forced by short eccentricity (Greb et al., 2008; Eros et al., 2012; The synthetic sea-level curve in Figure 1 combines precession (17 k.y.), Waters and Condon, 2012). However, this alleged Pennsylvanian dominance obliquity (35 k.y.), and eccentricity (95 and 413 k.y.) cycles (Pennsylvanian cycle of short eccentricity is not in line with insolation models. These periods after Berger and Loutre, 1994) with relative amplitudes of 0.5, 1, 1, predict alternating eccentricity and obliquity control, as well as some influence and 0.5. The predicted cyclothem succession displayed in the figure shows the of precession (Ruddiman, 2006), which is reflected inδ 18O records for much of thickness as well as the composition of the cyclothems in terms of subaqueous the Quaternary (Hays et al., 1976; Raymo et al., 1990). and subaerial facies. Most cyclothem studies have been performed in low to medium sub­ The individual cyclothems have a predicted duration between 9 and 82 k.y. sidence areas in the USA and the UK, where Pennsylvanian successions are (Fig. 1B). None of the basic input cycles stands out, but with ~50% of the cycles

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Sed. supply

Cyclothems 42 37 ooding sf. 21 43 34 ooding sf. 69 Subsidence 33 75 30 ooding sf. 36 50 Facies 16 72 Subaerial 76 nondeposition/erosion 24 82 Subaqueous Figure 1. (A) Calculated cyclothem succession 29 41 based on the deposition model of Jervey (1988). 42 Cyclothem duration (in k.y.) 34 31 Sea-level curve based on superimposed precession Time (k.y.) 39 (17 k.y.), obliquity (35 k.y.), and short and long ec- 30 0 100 200 300 400 500 600700 800900 1000 centricity (95 k.y. and 413 k.y.) with relative ampli- tudes of 0.5, 1, 1, and 0.5. (B) Comparison of the thickness of stacked cyclothems with the input ec- B centricity signal. (C) Comparison of the percentage 100 ++ of subaqueous sediment in subsequent cyclothems (“subaqueous ratio”) with the input eccentricity 80 + signal, showing a much better relation than cyclo- ness (m ) 60 them thickness. 0 40 – cle thick 20 Cy

–– Sea level (eccentricity) 0 1000 Time (ky) 2000 3000 C 100 ++

80 + 60 0 40 – 20

–– Sea level (eccentricity) Subaqueous ratio (%) 0 1000 Time (ky) 2000 3000

in the 29 to 39 k.y. range, the record suggests obliquity dominance; although that input sea level can be more accurately reconstructed on the basis of the fluc- the input sea-level amplitudes for obliquity and short eccentricity were equal. tuation of the percentage of subaqueous facies in subsequent cyclothems (Fig. Short eccentricity is represented as trimmed cycles shorter than 82 k.y., and long 1C), which is referred to here as the “subaqueous-facies ratio.” In that signal, eccentricity is faintly present as a long-term fluctuation of cyclothem thickness. both the 95 k.y. and the 413 k.y. stand out prominently, and a comparison with A comparison with the eccentricity components of the input sea-level signal input sea level shows that peaks line up well with the eccentricity signal (Fig. 1C). shows that the cyclothem thickness fluctuations are locally in phase with sea- The above model may explain why cyclothem-thickness records so far have level change but frequently are out of phase (Fig. 1B). From the model, it appears not yielded conclusive evidence of Milankovitch control, and it indicates that

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results may be better if the composition of cyclothems is taken into account. an up to 1.5-km-thick Pennsylvanian interval that rapidly thins westward. Both In addition to the subaqueous-facies ratio, the fluctuation of the percentage of basins were located near the paleoequator and were ~3000 km apart during coal within the subaerial parts of cyclothems was analyzed. the Late (Blakey, 2014). In both areas, the coal-bearing successions span the Langsettian to Bolso- vian substages (Westphalian A–C; Fig. 3) and consist of stacked cyclothems, THE PENNSYLVANIAN OF EURAMERICA mostly 10–25 m thick, of alternating (marginal) marine shales and coal-bearing lower and upper delta-plain deposits. The lower ~2 km of the Dutch interval is The Dutch wells are from the Northwest European thermal-sag basin lo- shale dominated; 10–20-m-thick fluvial sandstone bodies only become prom- cated to the north of the Variscan orogenic chain (Fig. 2). It contains an up inent in the Upper Bolsovian. In Kentucky, such sandstone bodies are present to 3–4-km-thick Pennsylvanian succession with only gradual thickness varia- throughout the succession and constitute the basal parts of cyclothems as de- tions over relatively great distances throughout most of the basin (Drozdzew­ fined by, for example, Weller (1930), Klein and Willard (1989), and Aitken and ski, 1993). The studied Kentucky interval is from the central Appalachian Basin, Flint (1995). These commonly overlie regionally extensive erosion surfaces that which during the Pennsylvanian was an E/W-aligned, elongate foreland basin. cut down into underlying strata. It was at times separated from the larger Late Pennsylvanian Midcontinent In both basins, fossiliferous marine shales are present at the base of the Sea that lay to its north (Algeo and Heckel, 2008) by the subdued highs of the Duckmantian (Vanderbeckei/Betsie) and Bolsovian (Aegiranum/Magoffin), and Cincinnati-Findlay-Algonquin arch system (Tankard, 1986). The basin contains at ~40% below the top of the Duckmantian (Maltby/Kendrick) (Fig. 3). These


10°N Variscan foreland Appalachian Basin

Equato N r Appalachian - Variscan orogenic chain

B EASTERN KENTUCKY (USA) WILLIAMSON (WA) C NETHERLANDS Figure 2. Maps of the two study areas. (A) Paleo­ geographic reconstruction of paleoequatorial Road cut coal-basins of Euramerica, with the Netherlands and Kentucky (United States) indicated in black locations (Blakey, 2014). (B) Location of road cuts along SIDNEY North Sea US 119 between Pikeville and Sidney, eastern Kentucky. (C) Well locations in the Netherlands.

To BELFRY Gray shaded area in Germany is the study area of Pr US-119 Achterhoek Drozdzewski (1993) mentioned in the text. estonsbur coal district META Germany

g ZEBULON N US-119 5 km (3 mi) Belgium Limburg US-23 (Road cut Fig. 4) 100 km (60 mi) coal district

Well KPK-1 (Kemperkoul-1) PIKE- Well JOP-1 (Joppe-1) VILLE Well RLO-1 (Ruurlo-1) N To Jenkins Well HGV-1 (Hengevelde-1)

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is only 320 m thick due to a more limited stratigraphic coverage and a lower

enn. REGIONAL (SUB)STAGES MARINE BANDS STRATIGRAPHY subsidence rate (~35%). Europe Kentucky Cyclothem successions were recorded as alternations of subaqueous de- TIME (Ma)

Late P (USA) posits (laminated and/or bioturbated shales and mouthbar sands), and subaerial 307 deposits (coals, rooted shales, and fluvial sands) and cyclothem boundaries were placed at the base of the subaqueous interval (cf. Galloway, 1989). The 308 D Asturian Dutch succession is little affected by fluvial incision, possibly as a result of much higher subsidence rates. In the few cases where the presence of thick

anian Kilgore Flint fluvial sandstone bodies is associated with unconventionally thick cyclothems 309 (e.g., top half of road cut in Fig. 4), this was interpreted as the result of erosion of the subaqueous part of a cyclothem due to fluvial processes during low-

ennsylv C Bolsovian Stoney Fork stand (cf. Davies et al., 1992; Aitken and Flint, 1995). In such cases, a cyclothem­ Aegiranum 311 (Aegir) Magoffin boundary was placed at the midpoint of the composite cycle. In the Kentucky

iddle P succession, thick fluvial sandstones are so numerous that this was not consid- M Maltby (Domina) Kendrick stphalian ered feasible, and fluvial sands were included in the subaerial part of cyclo- 312 B Duckmantian

We Vanderbeckei thems resulting in a less accurate record. (Catharina) Betsie . The Dutch wells were merged into a composite succession based on palynology­ by Van de Laar and Fermont (1989), and the correlation was fine- tuned using the cyclothem data. The Kentucky section was matched with the 313 nnsylv A Langsettian

Pe Dutch composite using the marine bands at the base of the Duckmantian and Subcrenatum Bolsovian as anchor points for correlation (Riley and Turner, 1995). For each

Early cyclothem, the subaqueous-facies ratio and the percentage of coal in its sub- aerial part were calculated. Figure 3. Pennsylvanian stratigraphy in the study areas. Time after Gradstein The presence of cyclic signatures in the records was evaluated using Black- et al. (2004). Regional stratigraphy based on marine bands, which are cor- relatable between basins (Riley and Turner, 1995). man-Tukey spectral analysis, making use of AnalySeries 1.1. software (Paillard et al., 1996). This was followed by a visual inspection at the detected frequen- cies using simple sine waves. Calculation of cycle periods was based on an integration of Ar/Ar and U/Pb radiometric dates. “marine bands” are attributed to highstands of global sea level and can be correlated between the basins (Riley and Turner, 1995). A facies example from a road cut along highway US 119 in eastern Ken- RESULTS tucky is presented in Figure 4, which shows a fluvial-sandstone–dominated section in its upper part and a marine shale at the base (Kendrick Shale, Euro- Results for the Dutch wells are presented in Figure 5A. Note that the sub- pean equivalent: Maltby/Domina M.B.). aqueous-facies ratio is plotted in mirror image, i.e., as a subaerial-facies ratio, giving a better visual representation. The original correlation based on palynol­ ogy by Van de Laar and Fermont (1989) is confirmed by the data presented ANALYSIS here and needed only a minor adjustment. Wells HGV-1 and JOP-1 overlap with KPK-1, and after thickness adjustments of 85% (JOP-1) and 95% (HGV-1) cor- More than 2.5 km of continuous core from the Pennsylvanian in wells recting for differential subsidence, a good match was achieved, in particular RLO-1, HGV-1, JOP-1, and KPK-1 from the Netherlands was studied (Fig. 2). A for the coal percentage (Fig. 5A, third graph). A thickness adjustment to 90% 1728-m-long composite section was built spanning the Late Langsettian–Late (average of the nearby wells HGV-1 and JOP-1) was applied to well RLO-1 to Bolsovian (Van de Laar and Fermont, 1989). Well KPK-1 was drilled ~140 km correct for slightly higher subsidence compared to the more southerly well south of the other wells, but regional thickness differences are small (Van de KPK-1. From RLO-1 and KPK-1 an Upper Langsettian to Upper Bolsovian com- Laar and Fermont, 1989). posite of 145 cyclothems was constructed (Figs. 5B and 5C). For comparison, a composite sedimentary section was recorded from The Dutch succession was matched with the more condensed succes- large, fresh road cuts along highway US 119 in eastern Kentucky (example sion from Kentucky according to the interbasinal correlations of the marine shown in Fig. 4). The section spans the Duckmantian (Westphalian B), which bands at the base and top of the Duckmantian proposed by Riley and Turner

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NE SW Composite logged section cp 80 fc sb cp 70 fc sb 60 cp Fire Clay coal bed (datum*)

fc 50 sb

cp 40

Fire Clay coal bed sb bf 30 fs fc 20 sb

Kendrick shale (marine band) mb 10 Kendrick Shale (marine band*) mfs mfsMaximum ooding surface Facies types Basal uvial erosion surface Appr. trajectory fs Flooding surface (minor) fc uvial channel mb marine basin/prodelta fc Marine Band (Kendrick Shale) logged section 0 sb Sequence boundary cp coastal plain/coal bf bayll/minor delta SaSi Cl

Figure 4. Example facies panel and sequence stratigraphic interpretation for a road cut along US 119 (see Fig. 2 for exact location), Kentucky (USA). Section on the right is part of the Kentucky composite cyclothem succession presented in Figure 5C.

(1995). These correlations are based on comparable , ammonoid, and Cyclothem thickness in the Dutch interval varies strongly, with cycles dis- palynological­ content. Matching required a 2.8 stretching factor. The overlap- tributed evenly between 5 and 20 m, and occasional cycles between 20 and ping Duckmantian interval, which consists of 62 cycles in the Netherlands, is 36 m. The average cycle is 12.5 m thick. The Kentucky cycles are evenly distrib- represented by only 16 cycles in Kentucky. Visual comparison of the two suc- uted between 3 and 27 m with occasional cycles up to 44 m and an average of cessions shows only moderate correlation, which is probably partly due to the 17.3 m. This greater mean thickness of the Kentucky cycles is attributed to less different number of cycles and the stretching correction. The cycle thickness compaction due to a much higher sandstone percentage and to the undetected patterns do not show an obvious match (Fig. 5C, first graph). The subaerial-­ merging of some of the cycles due to fluvial erosion and the formation of con- facies ratio data (second graph), however, match well; the number of measure- densed paleosol intervals during lowstands (Aitken and Flint, 1995). ments is obviously lower, but the general trends are comparable. Trends in the coal-percentage record are not a perfect match but still show a fair degree­ of correlation (third graph). It is further noted that the major coal peaks line up CYCLICITY INTERPRETATION well. The fact that the composition of the cyclothems, in particular the sub­ aerial-facies ratio, shows a much better match is in line with the model pre- Blackman-Tukey power spectra were calculated for the subaerial-facies dictions presented earlier (Fig. 1). Although the results do not prove the am- ­ratio and the coal-percentage data sets for the extensive Dutch data set (Fig. 6). monoid, conodont, and palynology-based interbasinal correlations proposed The spectrum for the subaerial-facies ratio shows two pronounced cycles with by Riley and Turner (1995), the similarity in trends for the subaerial-facies ratio wavelengths of 256 m and 59 m and a subordinate, more subdued peak with and the coal percentage do indeed support it. a wavelength of 146 m. The 256 m cycle observed in the subaerial-facies ratio

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Coal in subaerial Subaerial facies Cycle C Coal in subaerial Subaerial facies Cycle B Coal in subaerial Subaerial facies Cycle A

facies per cycle (%) per cycle (%)100 thickness (m) facies per cycle (%) per cycle (%)100 thickness (m) facies per cycle (%) per cycle (%)100 thickness (m) 20 40 60 20 40 60 20 40 60 80 10 20 30 40 10 20 30 40 10 20 30 40 20 40 60 80 20 40 60 80 20 40 60 80 NETHERL KENTUCKY (USA) NETHERL 0 0 0 0 0 0 0 0 0 0 0 0 0 06 0 01 Ke W ell KPK-1 ntuck 00 Depth below top KPK-1 (m) Bolso ANDS/KENTUCKY C ANDS y 200 200 200 200 200 200 vian 30 0 (W estphalian C) 400 400 400 400 400

Original datasets stretched to 284% thcikness 60 08 60 08 60 08 60 08 60 08 00 ORREL 05 05 marine band A Depth below top KPK-1 (m Aegiranum/ Magoffin egir anum/ Magoffin A 01 01 80 01 80 01 800 800 TED 00 00 00 00 00 Duckmantian We Depth belo ll JOP- 00 00 Depth belo (stretched to 280%) Ke 1000 100 01 100 01 100 01 100 01 100 01 100 01 1W 00 01 00 01 ntucky sequence w top of 15 02 150 (W W estphalian B) ell HGV-1 ) w top of 200 Ke 1200 00 20 0 20 0 20 0 20 0 20 0 20 0 20 0 20 0 ntuc Ke ky sequenc ntucky sequen 25 03 25 03 14 14 14 14 14 14 14 14 14 Betsie marine band Va 00 00 00 00 00 00 00 Vanderbeckei 00 00

nderbeck Langsettian Langsettian 00 00 e (m ) Betsie ell RL ce 16 16 16 16 16 16 16 16 16 ei/ O- 1 (m ) 35 0 35 0 00 00 00

00 00 00 00 00 00

(W est. A) 18 18 18 18 18 18 18 18 18 00 00 00 00 00 00 00 00 00 10 0 10 20 30 0 10 20 30 0 20 40 60 80 10 0 0 20 30 40 50 -

GEOSPHERE | Volume 11 | Number 4 van den Belt et al. | Revealing the hidden Milankovitch record from Pennsylvanian cyclothem successions 1068 Research Paper

The 256 m cycle has a consistent, strong visual presence in the subaerial-­ A 120 Subaerial-facies facies ratio as a gradual increase from ~10% to ~80% subaerial-facies per cycle 254 m ratio and a gradual decrease back to ~10% over ~4–5 higher-frequency cycles in the 100 subaerial-facies ratio (Fig. 7A, top graph). In the coal-percentage record, it is not well developed; although in parts of the data set, peaks line up moderately

r 80 well with the sine-wave overlay (Fig. 7A, bottom graph).

we The other well-developed peak (59 m) is also prominently visual in the sub-

Po 60 146 m aerial-facies ratio as the highest frequency fluctuation between a low and high ratio for subaerial facies (Fig. 7B, top graph). It represents a gradual increase 59 m and decrease through a number of subsequent cyclothems. In the coal-per- 40 centage record, the separation of subsequent peaks is of the same order, and many peaks line up well with the overlay, although a bit offset in places. Again 20 the cyclicity is less pronounced than in the subaerial-facies ratio data set (Fig. 7B, bottom graph). The subdued peaks representing wavelengths of 146 m 0 (subaerial-facies ratio) and 114 m (coal percentage) could not be recognized 00.005 0.01 0.015 0.02 0.025 visually in the data sets. Frequency (cycles/m) Absolute cycle periods were determined using recent U/Pb age determina- tions of volcanic-ash layers in the Duckmantian Fire Clay coal (314.6 Ma) and in B 120 Coal percentage the Langsettian Upper Banner coal (316.1 Ma; Lyons et al., 2006). The position of the Fire Clay coal is known (Fig. 7C), and the approximate position of the Upper­ 100 Banner coal bed was extrapolated from a nearby gas well (Rice et al., 1987) to slightly below the base of the Dutch composite succession. The ~1.5-m.y.-long 245 m r 80 interval defined by the two ash-fall deposits contains ~3.8 large-scale cycles

we (256 m), giving a cycle period of ~395 k.y. This is close to the 413-k.y. period Po 60 of the long-eccentricity cycle. The period for the short-term cycle (59 m) then 114 m equals ~96 k.y.; this matches the main period of the short eccentricity. The cyclicity interpretation of the power spectra in terms of time is shown 40 74 64 m in detail in Figures 7D and 7E. The subdued peaks at wavelengths of 146 m and 114 m are interpreted as first-order harmonics of the long-eccentricity cycle 20 with cycle periods close to half of 413 k.y. and/or twice 96 k.y. (cf. Weedon, 1989). This harmonic relation is particularly clear when peaks are plotted ver- 0 sus cycle period (Fig. 7E), instead of frequency (Fig.7D). The subdued peaks 00.005 0.01 0.015 0.02 0.025 with wavelengths of 74 m and 64 m and periods of 120 k.y. and 104 k.y. are Frequency (cycles/m) within the short-eccentricity band (95–125 k.y.; De Boer and Smith, 1994). Figure 6. Blackman-Tukey power spectra for the Dutch succession (A) for the The 145 individual cyclothems in the Dutch succession have a highly vari- subaerial-facies ratio and (B) for the coal percentage. able thickness, all on a sub-eccentricity scale. The complete succession is 1728 m long, and it equals ~7 long-eccentricity or 31 short-eccentricity cycles, which amounts to ~2.9 m.y. Based on a linear depth-thickness relation, cyclo- is repeated as a well-defined peak in the coal-percentage spectrum, although them duration ranges between 5 and 32 k.y.; cyclothem periods are evenly at a slightly reduced thickness of 245 m. Higher-frequency peaks in the coal-­ distributed, and there is no dominant period. Some cyclothems have higher percentage data set are poorly resolved; minor peaks were detected at periods estimated durations up to ~60 k.y. The average cyclothem measures 12.5 m, of 193 m, 74 m, and 46 m. which equals 21 k.y. Sine-wave overlays were used to visualize the sedimentary cyclicity in the The highly variable thickness of individual cyclothems suggests no specific Dutch succession. Because the results for the two data sets were very com­ control by precession or obliquity but points to cycle interference (De Boer, parable­ but more accurate and reliable for the subaerial-facies ratio, the wave- 1991; Sageman et al., 1997). The average duration of the cyclothems (21 k.y.) lengths determined for that specific spectrum were used to construct the sine is close to the main precession period, which equaled 17 k.y. during the Penn- waves (256 m and 59 m). sylvanian (Berger and Loutre, 1994), and the maximum duration for the bulk of

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A . D 100 120 80 Subaerial-facies

cle (%) 254 m 60 ratio cy 100 40 per Subaerial fac 20

60 r 80 0 we cle (%) 40 cy Po 146 m 20 60 0 59 m

oal in subaerial 114 m

C 0 200 400 600 8001000 1200 1400 1600 1800 40

facies per 74 m64 m B 100 80 20

cle (%) 60 cy 40 0 per 20 00.005 0.01 0.015 0.02 0.025 Subaerial facies

l 0 60 Cycles/m

cle (% ) 40 Subaerial-fac.

cy 413 237 96 20 0 398 185 120 104 al in subaeria Coal percent. 0 200 400 600 8001000 1200 1400 1600 1800 Co facies per Radiometric age dates volcanic ashfalls (U/Pb) Long eccentricity C 314. 6 316. 1 Harmonics (~413/2) Short ecc. band

E 413 Long eccentricity Banner ashfall reclay ashfall Fi U. Harmonic (~413/2) 0 200 400 600 8001000 1200 1400 1600 1800 Bolsovian (Westphalian C) Duckmantian (Westphalian B) Langsettian (Westph. A) Short ecc. Time (Ma)

U/Pb based 39 8 23 7 18 5 12 0 314315 316 96 4 8 MagofffinBKendrick 6 etsie Marine bands KY (USA) Europe (UK terminology) Aegiranum Maltby Vanderbeckei 0 314. 314. 315. 500 400 300 200 100 0

Figure 7. (A) Subaerial-facies ratio and coal percentage for the Dutch composite section. Sine-wave overlay with a 256 m wavelength matches the large-scale trend in the subaerial ratio. The large- scale trend is less well defined in the coal-percentage data (coal in subaerial facies per cycle; wave reversed). (B) Sine-wave overlay with a wavelength of 59 m. Also peaks in the coal-percentage data line up relatively well (sine-wave reversed). (C) Absolute-time interpretation based on Middle Pennsylvanian radiometric age dates (U/Pb) from the United States. (D) Time interpretation of power spectra. (E) Interpreted cycle periods plotted against linear time.

the cyclothems (32 k.y.) is close to the main obliquity period (34 k.y.). This may surfaces mark the base of cycles in the Appalachian Basin (Aitken and Flint, indicate that the amplitude of precession-driven, sea-level fluctuations was 1995). Chesnut (1997) noted that areas of low subsidence in the Appalachian sufficiently high to prevent obliquity and short eccentricity cycles from being Basin are characterized by 400 k.y. cycles; whereas in areas of higher sub­ recorded. The observation that 63 cycles in the Dutch section are represented sidence in the same basin, 100 k.y. cycles have been preserved. If this trend of by only 17 cycles in Kentucky indicates that only one out of almost four cyclo- increased likelihood of preservation of shorter cycles is extrapolated to areas­ thems (on average) was preserved in the Kentucky succession. Absence of part of even higher subsidence, it is expected that at some point sub-eccentricity of the cycles is in line with the observation that regionally extensive erosion cycles are preserved.

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The comparable thickness of cyclothems in the two study areas indicates bed from the Appalachian Basin. For the Fire Clay coal bed, both an Ar/Ar age that cyclothem thickness was probably not controlled by subsidence rate, but (310.9 Ma) and an U/Pb age (314.6 Ma) are available (Lyons et al., 2006), which instead by glacio-eustatic sea-level fluctuations. Because these were global indicates that 3.7 m.y. must be added to Ar/Ar dates to fit the U/Pb scale. Note and of higher magnitude (~50–100 m) than typical subsidence rates (Soreghan that the Fire Clay level (Late Duckmantian) is an interesting calibration point, and Dickinson, 1994; Soreghan and Giles, 1999; Rygel et al., 2008), different because its U/Pb age of 314.6 Ma is very close to the U/Pb age of 314.4 Ma de- areas experienced the formation of accommodation space at relatively com­ termined for the base Moscovian in Eastern Europe (Eros et al., 2012; Schmitz parable rates during periods of long-term sea-level rise. This likely resulted and Davydov, 2012) and could therefore serve as a tie point for North Ameri- in the formation of cyclothems of relatively comparable thickness in differ- can, Western European, and Eastern European stratigraphy (Fig. 8). ent areas on the globe. During subsequent periods of overall sea-level fall, It was found that the Duckmantian substage (Westphalian B) measures non-deposition and/or erosion occurred. In areas of low subsidence these three long- and 13 short-eccentricity cycles, which amounts to 1.2 m.y. (Figs. ­periods of non-deposition lasted longer than in areas where subsidence rates 7 and 8). If the Fire Clay coal bed is taken as a reference level (314.6 Ma), the where high, resulting in less complete successions. marine band at the base of the Duckmantian has an age of ca. 315.6 Ma, and the marine band at the base of the Bolsovian has an age of ca. 314.4 Ma. The ­intra-Duckmantian marine band (Maltby/Kendrick) then lines up at ca. 314.8 Ma IMPLICATIONS FOR PENNSYLVANIAN CHRONOLOGY (Fig. 7). The Bolsovian substage (Westphalian C) in the Dutch succession rep- Chronological interpretations of Pennsylvanian stratigraphy are based on resents at least three long-eccentricity cycles, which equals 1.2 m.y. However, an integration of conodont (Boardman and Heckel, 1989; Barrick et al., 2004; the Dutch succession has been erosionally truncated, and the duration of the Heckel et al., 2007; Boardman et al., 2009) and ammonoid (“”) (Rams- Bolsovian substage thus must be longer. Numerous Ar/Ar age determinations bottom et al., 1978; Riley and Turner, 1995; Greb and Chesnut, 2009) zonations­ of volcanic ash-fall layers are available from the Bolsovian of Central Europe with radiometric ages (Burger et al., 1997; Davydov et al., 2004; Davydov (Hess and Lippolt, 1986; Burger et al., 1997; Gradstein et al., 2004), and based et al., 2010; Schmitz and Davydov, 2012) and cyclostratigraphic interpretations on these, the total duration of the Bolsovian is estimated at ~2.0 m.y. (Fig. 8). (Heckel, 2008; Falcon-Lang et al., 2011). This has yielded a high-resolution time This places the base of the Asturian at ca. 312.4 Ma. Extrapolation of radio­ scale, which is of limited use however in the mainly terrestrial, and often bar- metric ages based on Burger et al. (1997) places the youngest Asturian rocks, ren, Middle and Upper Pennsylvanian successions of Europe and the Appa- which are truncated by a major , at ca. 310.8 Ma. Downward ex- lachian Basin. In those parts, stratigraphic subdivisions are based primarily trapolation from Stephanian radiometric age data gives a base Stephanian age on palynology and (Ramsbottom et al., 1978; Cleal and Thomas, of ca. 307.9 Ma and indicates that the duration of the Westphalian–Stephanian 1996; Peppers, 1996), and uncertainty exists as to how these successions tie hiatus, in this case in the German Saar Basin, lasted some three million years into the global stratigraphic framework. This is reflected in many different cor- (Burger et al., 1997). An Asturian-Stephanian hiatus characterizes the entire relations of the Westphalian substages to global Eastern European stages and European Variscan foreland (Ziegler, 1990; Corfield et al., 1996; Schroot and North American regional stages, and in differences in interpreted duration of De Haan, 2003), although commonly not shown in stratigraphic columns, and the individual substages (Heckel and Clayton, 2006; Greb et al., 2008; Heckel, it relates to late Westphalian culmination of thrusting in the Variscan orogen 2008; Falcon-Lang et al., 2011; Van Hoof et al., 2013). (Ziegler, 1990). In the United States, a late Westphalian unconformity and asso- The large-scale cycle framework presented in this study was integrated ciated hiatus are not recognized, or at least not thought to be as extensive as with published radiometric ages for volcanic ash (“tonstein”) layers to re- in Europe (Falcon-Lang et al., 2011). fine the correlation of the Western European Westphalian substages, which Only a small part of the Langsettian (Westphalian A) substage is covered by are commonly used in the (terrestrial) Appalachian Basin as well (Greb et al. the studied cores, and radiometric ages are not available below the Late Lang- 2008). Because radiometric ages were determined using different methods settian Upper Banner coal bed. Therefore an accurate estimate of the duration (Ar/Ar and U/Pb), results cannot be easily compared and integrated (Davydov of the Langsettian is not possible. However, when the Langsettian thickness et al., 2004; Villeneuve, 2004). Most of the available radiometric ages are from of 1200–1350 m (Drozdzewski, 1993) from the nearby Ruhr Basin in Germany the Ar/Ar isotope system (Fig. 8). They are consistent internally and between (gray square in Fig. 2C) is extrapolated and constant subsidence is assumed, ­basins (Lyons et al., 1992, 2006). Recent radiometric ages are based on the the Langsettian substage has an estimated duration of ~2.0 m.y. This gives an U/Pb isotope system (Lyons et al., 2006; Eros et al., 2012). These are more estimated age for the base Langsettian of ca. 317.6 Ma (Fig. 8). accurate; but due to a different standard, they yield systematically older ages Based on the above discussion, the total duration of the Westphalian (Davydov et al., 2004). , at least the portion that has been preserved in Western Europe, lasted To integrate ages from both isotope systems, Ar/Ar age determinations ~6.8 m.y. The duration of the hiatus between the youngest Westphalian sedi- were shifted to match the U/Pb time scale, based on the Fire Clay reference ments (Asturian) and the overlying Stephanian section was ~2.9 m.y., giving

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Radiom. successions Studied Eastern North Euramerica Radiometric age Eastern North Western Age Western Europe Europe (U/Pb) America (terrestrial) Europe America Europe (marine) (marine) This study (marine) (marine) (terrestrial) East. (Ar/Ar) (U/Pb) Perm. Eur. TIme (U/Pb) TIme (U/Pb) 299.0 299.0 299.0 299.0 299.0 299.0 298.9 Netherlands Kentuck 300 300 300

(300.3) 304.0 Stephanian

Uppe r Virgilian Gzhelian Virgilian y (USA

303.4 303.0 Stephanian 303.4 303.0 (Saar Basin, ) Missourian 306.0 Missourian Stephanian 305 (302.9) 306.6 305 Germany) 305 Kasimovian 305.4 305.4

PENNSY 306.6 306.6 307.3 Desmoinesian Desmoin. Asturian ~307.9 M (308.0) 311.7 ? iddle 309.4 (hiatus) ? 309.4 (hiatus)

310 LV (309.0) 312.7 310 310 Moscovian 310.6 ~310.8 unconformity Moscovian

ANIA N Bolsovian

(310.1) 313.8 W 312.0 Atokan ~1.6 (D) Asturian Atokan Asturian 312.2 (310.9) 314.6 ~312.4 estphalian 312.4 313.2 Duckmantian ~2.0 (C) Bolsovian Bolsovian 314.6 314.4 314.4 314.6 314.4 315 316.1 315 1.2 (B) Duckmantian 315 Duckmantian Langsettian 315.6 315.6 Lowe ~2.0 (A) Langsettian Bashkirian Morrowan Langsettian Bashkirian Morrowan ~317.6 Namuria ~317.6 r Namurian 320 320 320 n

Figure 8. Chronostratigraphic interpretation of the European Westphalian stage and substages based on U/Pb ages from the Appalachian Basin and Eastern Europe. Gray horizontal bar indicates 314.4 U/Pb tie point between Eastern Europe, Western Europe, and North America. Based on Hess and Lippolt (1986), Burger et al. (1997), Hess et al. (1999), Heckel and Clayton (2006), Lyons et al. (2006), Greb et al. (2008), Heckel (2008), Falcon-Lang et al. (2011), and Eros et al. (2012).

a maximum duration of Westphalian time of ~9.7 m.y. This is considerably TERRESTRIAL-CARBON (COAL) STORAGE shorter than the earlier estimate of 11.5 m.y. by Menning et al. (2000). The shortening is primarily due to the newly available age data for the Late Lang- The Duckmantian and Bolsovian stages are the most prolific coal inter- settian Upper Banner coal bed. In the 2004 of Gradstein vals in the Pennsylvanian and represent a large percentage of the terrestrial et al. (2004), only 7.0 m.y. are assigned to the Westphalian stage, which is at- carbon buried during the late Paleozoic ice-house period (Berner, 2003). The tributed to base Westphalian age estimation based on interpolation between accurately dated sedimentary record from the Netherlands allows a precise de- Bolsovian (Westphalian C) and Namurian ash-fall ages and assuming similar termination of the long-term burial of carbon (as coal) in one of the largest and sedimentation rates for the deeper marine Namurian and the paralic West­ fastest subsiding Pennsylvanian basins (Fig. 9). The cumulative-coal patterns phalian depositional systems. are correlatable between wells and show low terrestrial-carbon accumulation The Desmoinesian stage in the Midcontinent United States and the Upper rates (~5 m coal/m.y.) before ca. 315.1 Ma (U/Pb) after which accumulation Moscovian stage in Eastern Europe are commonly interpreted to partly over- accelerated to ~20 m coal/m.y. lap with the (Upper) Westphalian in Western Europe (Greb et al., 2008; Heckel, The cumulative-coal pattern in Kentucky, although showing lower values, 2008; Falcon-Lang et al., 2011; Eros et al., 2012). However, the age determina- features a similar instant increase at 315.1 Ma. The patterns are almost iden- tions presented here place the entire Westphalian stage below the base Des- tical when the Kentucky coal-abundance values are multiplied by the strati- moinesian (309.4 Ma) of Heckel (2008). graphic stretching factor of 2.8 (i.e., correcting for subsidence and/or preser-

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Bolsovian Duckmantian Langsettian observed cycles. When many cyclothems are missing, cycle duration is grossly (Westph. C) (Westph. B) (Westph. A) overestimated. This means that estimated cycle periods could be too long al- though still falling in the Milankovitch range (Algeo and Wilkinson, 1988). It has been shown that Milankovitch signatures can be revealed by quan-

ness (m) titatively analyzing variations in cyclothem composition through time, such as the subaerial-facies ratio and the coal percentage per cycle when done in high-subsidence areas where stratigraphic successions are most complete. In 25 m coal/M combination with radiometric ages, the data show a strong short- and long-ec- oal thick centricity control, which is in agreement with current ideas (Eros et al., 2012; e c Netherlands Waters and Condon, 2012). However, the data also show that the 100 k.y. esti- KPK-1 y mate is too high for individual cyclothems and includes missed beats and/or RLO-1 5 m coal/My eroded stratigraphy. Individual cyclothems have a sub-eccentricity duration,

umulativ JOP-1

C which is possibly the result of interference of precession, obliquity, and ec- HGV-1 centricity signals. The interpreted dominance of precession cycles is remark- Kentucky (actual) able when compared with δ18O records from the Quaternary; these records Kentucky (standardized subsidence) point to a dominance of obliquity (before 0.7 Ma) and short eccentricity (after 314 315316 0.7 Ma). The influence of precession-controlled climate fluctuations is partic- Time (m.y.; U/Pb scale) ularly strong at low latitudes (De Boer and Smith, 1994), and it is therefore not expected to play an important role during ice-house periods. However, a Figure 9. Cumulative-coal accumulation through time for the Dutch and Kentucky intervals. number of studies suggest that late Paleozoic ice sheets extended into low- Open circles represent Kentucky dataset standardized (× 2.8) to Dutch subsidence rates. latitude­ areas (Frakes et al., 1992; Poulsen et al., 2007; Soreghan et al., 2008), perhaps down to 30°–40° S during the Westphalian. At such low latitudes, pre- vation) that was required to align the marine bands in the high-subsidence cession-driven climate fluctuations may have been important in partially con- Dutch succession and the low-subsidence Kentucky succession (Fig. 9). This trolling or modulating the waxing and waning of ice caps and may have had suggests that overall coal accumulation was externally controlled by climate sufficiently high amplitudes to break up obliquity cycles into smaller units. In and/or sea level, and was comparable between the areas, the amounts of bur- a number of recent studies, however, the extent of ice sheets into relatively ied coal depending on subsidence, which also controlled the percentage of low-latitude areas is questioned; and especially during the late Westphalian cycles deposited and preserved. From outcrops, it is known that coal thickness and Stephanian, ice extent may have been limited (Isbell et al., 2003; Fielding may show rapid lateral changes, but the results of this study show that this did et al., 2008a; Fielding et al., 2008b). not significantly affect the overall long-term coal-accumulation patterns. As an alternative, variations in sediment supply, either regional (allocyclic [cf. Cecil et al., 2014]) or local (autocyclic [e.g., delta-lobe switching; cf. Field- ing, 1984]), may have been responsible for the splitting of sea-level cycles into DISCUSSION AND CONCLUSIONS shorter subcycles. Integration of the cycle interpretations presented here with recent U/Pb Since the beginning of the twentieth century, the cyclicity in Euramerica ages from the Appalachian Basin allowed chronostratigraphic dating of the coal basins has been related to sea-level changes associated with late Paleo- main marine bands at the base, middle, and top of the Duckmantian substage zoic glaciations (e.g., Udden, 1912; Wanless and Shepard, 1936). Although it at 315.6, 314.8, and 314.4 Ma. This makes a robust chronostratigraphic frame- seems more than a coincidence that cyclothem formation was widespread work for the Late Langsettian to Early Bolsovian interval that links the coal and coeval with late Paleozoic glaciation, there was as yet no evidence that basins from Europe and North America. Based on Ar/Ar ages from Europe unambiguously demonstrates Milankovitch control. This is attributed here to (recalculated to U/Pb), it is estimated that the entire Westphalian stage lasted the fact that previous analyses were based on cyclothem thickness, which is ~9.8 m.y. at most (including an ~2.9 m.y. hiatus at its top) and is entirely older unlikely to reflect the sea-level fluctuations that shaped them, because—de- than the Midcontinent Upper Pennsylvanian key section of Heckel (2008). pending on the ratio between sea-level change, subsidence, and sediment ac- The observation that the pattern of carbon (coal) storage through time cumulation—cyclothem boundaries may be formed almost anywhere during a can be correlated between the Dutch wells, and even between basins after sea-level cycle. Furthermore, previous studies were carried out in areas where correction for subsidence and missing cycles, is intriguing. It requires further the Pennsylvanian succession is relatively thin and incomplete, and cycle du- study to establish whether the recorded patterns are indeed global rather than ration is typically estimated by dividing succession duration by the number of the result of local sedimentary conditions. If indeed correlatable over larger

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distances, coal patterns may be an interesting correlation tool and a possible Cecil, C.B., 1990, Paleoclimate controls on stratigraphic repetition of chemical and siliciclastic proxy of paleoclimate and sea level. rocks: Geology, v. 18, p. 533–536. Cecil, C.B., Dulong, F.T., West, R.R., Stamm, R., Wardlaw, B., and Edgar, N.T., 2003, Climate con- The methodology applied here has the advantage that it is quantitative trols on the stratigraphy of a Middle Pennsylvanian cyclothem in North America, in Cecil, and therefore leaves less room for speculation when it comes to the inter- C.B., and Edgar, N.T., eds., Climate Controls on Stratigraphy: SEPM (Society for Sedimentary pretation of cycle periods. However, it requires thick, continuous stratigraphic Geology) Special Publication 77, p. 151–180. Cecil, C.B., DiMichele, W.A., and Elrick, S.D., 2014, Middle and Late Pennsylvanian cyclothems, successions in high-subsidence areas with a relatively complete sedimentary American Midcontinent: Ice-age environmental changes and terrestrial biotic dynamics: record. Based on a few good-quality sections, such as the early Langsettian Comptes Rendus Geoscience, v. 346, p. 159–168, doi:​10​.1016​/j​.crte​.2014​.03​.008​. “” sections of Nova Scotia, it may be possible to extend the Duckman- Chesnut, D.R., 1997, Eustatic and tectonic control of the Lower and Middle Pennsylvanian strata of the Central Appalachian Basin, in Podemski, M., ed., Proceedings of the XIII International Con- tian–Bolsovian chronology presented here to the base of the Langsettian and gress on the Carboniferous and : Krakow, Poland, Polish Geological Institute, p. 33–41. into the Asturian, thus covering the entire Westphalian coal interval and giving Cleal, C.J., and Thomas, B.A., 1996, Introduction and general background, British Upper Carbonif- a high-resolution time framework for a the major coal interval of the late Paleo­ erous Stratigraphy: Geological Conservation Review Series 11, p. 3–14. zoic glaciation. Corfield, S.M., Gawthorpe, R.L., Gage, M., Fraser, A.J., and Besly, B.M., 1996, Inversion tectonics of the Variscan foreland of the British Isles: Journal of the Geological Society of London, v. 153, p. 17–32, doi:​10​.1144​/gsjgs​.153​.1​.0017​. Davies, H., Burn, M., Budding, M., and Williams, H., 1992, High-resolution sequence stratigraphic ACKNOWLEDGMENTS analysis of fluvio-deltaic cyclothems: The Pennsylvanian Breathitt Group, east Kentucky: An- nual Meeting Abstracts, American Association of Petroleum Geologists and Society of Eco- We are thankful to Thomas Algeo and William DiMichele for their constructive reviews and to nomic Paleontologists and Mineralogists, p. 27–28. Poppe de Boer for his comments on an earlier version of the manuscript. Discussions with Hemmo Davydov, V.I., Wardlaw, B.R., and Gradstein, F.M., 2004, The Carboniferous period, in Gradstein, Abels, Haefa Abdul Aziz, and Frits Hilgen (University of Utrecht) helped to improve the ­cyclicity F.M., Ogg, J.G., and Smith, A.G., eds., A Geologic Time Scale 2004: Cambridge, UK, Cam- analysis. Stephen Greb and Cortland Eble of the Kentucky Geological Survey (Lexington) are bridge University Press, p. 222–248. thanked for their assistance during our field trips and for sharing their ideas and expertise on the Davydov, V.I., Crowley, J.L., Schmitz, M.D., and Poletaev, V.I., 2010, High-precision U-Pb zircon cyclothem successions of the Appalachian Basin. age calibration of the global Carboniferous time scale and Milankovitch band cyclicity in the Donets Basin, eastern Ukraine: Geochemistry Geophysics Geosystems, v. 11, Q0AA04, doi:​ 10​.1029​/2009GC002736​. 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