Keith B. Miller
Department of Geology
Kansas State University
Manhattan, KS 66506

Fieldtrip Guidebook
2001 Meeting of the American Scientific Affiliation

(Modified and updated in October, 2011)

All text and figures Keith B. Miller copyright 2011


This fieldtrip focuses on a nearly continuous exposure of the lower Permian (Wolfcampian) stratigraphic interval that includes the entire Council Grove Group and the lower half of the overlying Chase Group.  The outcrop exposures are all within the Manhattan area in Riley County, northeastern Kansas (Figures 1 and 2).

    During the Wolfcampian the mid-continent of North American lay within the low relief interior of the supercontinent Pangea in near equatorial latitudes.  Throughout the Permian and into the Triassic this landmass drifted slowly to the north into higher latitudes (Rowley et al., 1985; Scotese, 1986; Witzke, 1990).  In the Wolfcampian, the study area would have been relatively far from areas of active tectonism.  The highlands of the ancestral Rockies lay ~500 km to the west and the Ouachita and Wichita uplifts were an approximately equal distance to the south.  A broad low lying cratonic area probably lay to the north and east.  The carbonate and fine clastic facies of the Council Grove and Chase Groups in northeastern Kansas suggest a vast shallow marine to marginal marine shelf periodically exposed during relative sealevel lowstands.

    The facies of the Wolfcampian are in many ways transitional between those of the Late Pennsylvanian (Virgilian) and the later Permian.  During this time black shales and coal beds decline, and red beds and evaporites increase in abundance (West et al. 1997).  These facies changes reflect a long term climatic change from more humid to more arid conditions.  The trend toward increased aridity begun in the Late Pennsylvanian can also be followed in the paleobotanical record (Phillips & Peppers, 1984; Phillips et al., 1985; Cross & Phillips, 1990; DiMichele & Aronson, 1992).  In addition, the Pennsylvanian and Early Permian was a time of widespread continental glaciation that subsequently declined later in the Permian (Crowell, 1978; Veevers & Powell, 1987; Frakes et al., 1994).  The waxing and waning of these glaciers, probably driven by cyclic changes in the Earth's orbital parameters (Denton & Hughes, 1983), is the likely cause for the repeated sedimentary cycles characteristic of the Pennsylvanian and Permian in the mid-continent.


    The term "cyclothem" was introduced by Wanless and Weller (1932) to describe Pennsylvanian cyclicity of the Illinois Basin.  The term was subsequently applied to the description of Permian cyclicity within the mid-continent by Jewett (1933).  This description was modified and elaborated by Elias (1937), who placed all the major facies encountered within Permian cycles into an idealized depth-related sequence.  A number of detailed sedimentary and paleontological studies of individual Lower Permian cylothems and their member-scale lithologic units followed (Imbrie, 1955; Hattin, 1957; Lane, 1958; Laporte, 1962; McCrone, 1963; Imbrie et al., 1964).

    The facies sequence of Lower Permian (Wolfcampian) cyclothems typically begins with a thin marine limestone overlain by a gray fossiliferous shale/mudstone.  One or more additional limestone-shale (mudstone) alternations may follow.  An interval of variegated red and green mudstones with extensive paleosol development lies above these shallow marine facies.  Cyclothem boundaries are here recognized at the base of the stratigraphically lowest fossiliferous fully marine limestone occurring above a paleosol-bearing interval.  Commonly, these marine limestones directly overlie and partially truncate the uppermost paleosol profiles.  The contacts often appear to be erosive, although little or no relief is evident at an outcrop scale, and are typically overlain by intraclastic beds up to 20cm thick.  As thus defined, the cyclothem-bounding surfaces are equivalent to the transgressive surfaces of depositional sequences (Van Wagoner et al., 1988).  These sufaces thus provide a basis for understanding these cycles in a sequence stratigraphic framework (Miller & West, 1998). 

    Meter-scale cycles are both ubiquitous and prominent within the Wolfcampian cyclothems of eastern Kansas (Miller & West, 1993; Miller & West, 1998).  These small-scale cycles are bounded by flooding surfaces and can be defined as parasequences (Van Wagoner et al., 1988) or punctuated aggradational cycles (Goodwin & Anderson, 1985).  Flooding surfaces overlie paleosol profiles and other indicators of subaerial exposure, or mark sharp changes in depth as indicated by lithology and fossil content.  Thin (<2 cm thick) skeletal and/or intraclastic lags mark these cycle-bounding flooding surfaces.  The inferred positions of both flooding surfaces and transgressive surfaces are indicated on the stratigraphic columns provided (Figures 3 through 7).

    Most of the meter-scale cycles throughout the Wolfcampian are capped by subaerial exposure surfaces.  These range from well-developed paleosol profiles that may have required 100,000 yrs to form, to desiccation cracked surfaces.  The criteria used to identify and classify ancient soil profiles are nicely summarized by Retallack (1988, 1990).  Within the more carbonate-dominated parts of cyclothems, meter-scale cycles may be capped by tepee structures or boxwork structures.  These latter features can be seen in the Johnson Shale, Morrill Mbr. of the Beattie Limestone, Eiss Mbr. of the Bader Limestone, Havensville Mbr. of the Wreford Limestone, and the Holmesville Shale. 

    Of particular interest is the consistent carbonate-to-siliciclastic pattern exhibited by the meter-scale cycles.  Within the variegated mudstone intervals of cyclothems, flooding surfaces are typically overlain by thin micritic carbonates.  Carbonate deposition thus follows inundation of the exposed land surface during relative sealevel rise and is replaced by the influx of siliciclastic sediments during subsequent sealevel fall.  Pedogenesis begins with the subaerial exposure of these clastic sediments during sealevel lowstand.  The carbonate-to-clastic pattern is also clearly apparent for meter-scale cycles within the dominantly marine part of cyclothems.  Here, bioclastic marine wackestones are overlain by fossiliferous gray shales or calcareous mudstones.  This meter-scale cyclicity is also apparent within the thick Barneston Limestone.


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