Abstract Cyclothems are stratigraphic sequences deposited during glacial-eustatic transgressive–regressive inundations of land. Major cyclothems are most complete on lower shelves and become separated by exposure surfaces higher on the shelf. Minor cyclothems extend only onto lower shelves or are parasequences reflecting a reversal of sea level during general phases of transgression or regression. In Midcontinent North America, highstand condensed intervals of major cyclothems are conodont-rich black shales correlated eastwards into the Illinois and Appalachian basins. The number of cyclothems decreased by loss of lesser cyclothems across these basins, signifying an eastwards increase in their depositional elevations. Generalized palaeogeographical maps show that facies successions developed across these basins during a single major interglacial transgression and regression. The control of glacial eustasy by the interaction of Earth's orbital parameters, along with radiometric dating, allows subdivision of the cyclothem succession into c. 400 kyr groupings, which reflect the longest eccentricity cycle and facilitates global correlation. Delineation of the basinward extents of regression from the disappearance of exposure surfaces elucidates the history of basin-margin development. Major cyclothems that underwent reversals of general sea-level trend display ‘splays’ of lesser cycles onto the higher shelf. Geochemical cycles ‘nested’ within deepest-water shales on low shelves appear as thin nearshore facies between exposure surfaces at their high-shelf shorelines.

Pennsylvanian cyclothems of Midcontinent North America represent a repetitive succession of widespread marine beds, upon which widespread paleosols in the overlying terrestrial beds show that they resulted from extensive marine regressions as well as transgressions over a large land surface. Classic widespread late middle to late Pennsylvanian major cyclothems in this region consist of a thin transgressive limestone and thin offshore dark phosphatic shale (which contains the maximum flooding surface), followed upward by a thicker regressive shallowing-upward limestone and a variety of nearshore marine and terrestrial detrital facies as well as paleosols. Cyclothems of intermediate scale lack the black facies in the offshore shale and are less widespread, and those of minor scale lack much differentiation of facies. The greatest number of cyclothems of all scales is along the shelf-basin margin in the Kansas-Oklahoma border region, and the total number decreases as most minor cycles pinch out northward into Iowa, several intermediate cycles disappear eastward into Illinois, and only some of the major cycles extend farther into the shelfward Appalachian Basin. Cycles of all scales can be grouped around each major cyclothem to produce a succession of ~400-k.y.-long groupings, which can be used to calibrate the Pennsylvanian time scale with the few radiometric dates that are available. Conodont-based biostratigraphic correlation of the Midcontinent cyclothems with those of the Illinois and Appalachian Basins and the north Texas shelf and Paradox Basin in Utah has been extended to the cyclothems now recognized on the Russian Platform and in the Donets Basin of Eastern Europe. This biostratigraphic zonation of the Pennsylvanian pantropical zone provides the framework for incorporating the radiometric dates now becoming available from fossiliferous marine successions that contain volcanics into the named units of the Pennsylvanian time scale. This framework ultimately should allow the Gondwana succession with entirely endemic biotas to be correlated more accurately with the pantropical zone. The current lack of apparent correlation of times of major cyclothem formation in the pantropical zone with widespread glacial deposits on Gondwana relates to the fact that only large-scale withdrawals of the sea off of the tropical shelves would correlate with widespread glacial deposits, whereas a succession of major cyclothems that are separated by regressions that only approached the edge of the shelf would appear to be simply a long-term interglacial episode in most of Gondwana.

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Abstract Pennsylvanian major marine cyclothems in midcontinent North America comprise the sequence: thin transgressive limestone, thin offshore gray to black phosphatic shale, and thick regressive limestone. Typically, the cyclothems are separated from one another by well-developed paleosols across an area of perhaps 500,000 km 2 from southern Kansas to Iowa and Nebraska. Southward, the offshore shales extend into the foreland basin of Oklahoma, and the regressive limestones and paleosols grade into deltaic to fluvial clastics derived from the Ouachita detrital source. Texas, Illinois, and Appalachian marine cyclothems are detrital-rich like those in Oklahoma, but appear to be separated by paleosols like those in the northern midcontinent. Because the black phosphatic offshore shales of the midcontinent record sediment-starved, condensed deposition below a thermocline in about 100 m of water, sea-level rise and fall of at least that amount is required over the entire northern midcontinent region to account for the widespread dark shale-paleosol cyclicity. Sparsity to absence of deltas between most cycles on the northern shelf rules out delta shifting as a control over major cyclothem formation there. Continuity of all major cyclothems across both the Forest City basin and adjacent Nemaha uplift rules out local differential tectonics on the northern shelf as a major control. Confinement of all reasonable estimates of cyclothem periods within the Milankovitch band of orbital parameters (20 ky to 400 ky), which controlled Pleistocene glacial fluctuation, points to glacial eustasy as the major control over midcontinent cyclicity. Moreover, only the documented late Quaternary post-glacial rates of sea-level rise significantly greater than 3 mm/yr are sufficient to exceed carbonate accumulation consistently and produce the characteristic thin transgressive limestone overlain by the widespread thin subthermocline black shale in each major cyclothem. Although tectonic subsidence helped provide space for sediment accumulation, tectonic control over cyclothem deposition would require both subsidence and uplift of the midcontinent (or an equally large region) at Milankovitch band frequencies. However, currently developed cyclic tectonic mechanisms that can achieve the required depths repeatedly in a cratonic area act at periods at the very least 5 times greater (2 my+) and at rates of sea-level rise at least 30 times too slowly (maximum of 0.1 mm/yr). Firm biostratigraphic correlation of major midcontinent Upper Pennsylvanian cyclothems with similar depositional cycles in Texas and Illinois allows a strong glacio-eustatic signal to be identified in those regions, with little evidence so far of temporally differential tectonism among them. The lithic differences between carbonate-rich midcontinent cyclothems and detrital-rich cyclothems in Texas, Illinois, and the Appalachians are attributable directly to the greater detrital influx in the latter areas, which could relate as much to appropriate climate and accessibility to detrital provenance as to tectonic activity. Preliminary correlations showing that only certain bundles of major marine transgressions extended into the Appalachian basin suggest that the absence of the others may reflect tectonic uplift there, and that with more definite correlation, a longer-term tectonic signal can be isolated in that area.

Abstract This quadruple site (Fig. 1) illustrates typical examples of Kansas cyclothems of Pennsylvanian age. Site 10: Iola and Wyandotte cyclothems (Figs. 2, 6). I-435 exit at Holliday Road, NE¼NW¼, Sec.6, T.12S., R.24E., Ed-wardsville 7½-minute Quadrangle, Johnson County, Kansas. The best way to get to this section is to proceed south on I-435 from Kansas 32, cross the Kansas River and take the Holli-day Road exit around to the right, pulling off to park on the shoulder before meeting Holliday Road. The lower part of this section (up to the lower Argentine) is easily accessible on the east side of this ramp road, the upper part is accessible on the west side of this road, but requires more careful climbing. Site 11: Swope and Dennis cyclothems (Figs. 2, 7). U.S. 69 roadcut by Jingo, SW¼SE¼, Sec.31, T.l8S., R.25E., New Lancaster 7½-minute Quadrangle, Miami County, Kansas. This section is exposed continuously along the east side of U.S. 69 and the north side of a gravel section-line road that crosses U.S. 69, 13 mi (21 km) south of Kansas 68 (Louisburg) exit and 6 mi (9.6 km) north of Kansas 135 (LaCygne) exit. Park along the section-line road east of U.S. 69. Site 12: Plattsburg cyclothem (Figs. 2, 8). Kansas 47 Altoona lower roadcut, near NW corner, Sec. 17, T.29S., R.16E., Altoona 7½-minute Quadrangle, Wilson County, Kansas.