GEOLOGY
OF THE KANSAS FLINT HILLS:
ANCIENT ICE AGES, SEA LEVELS,
AND CLIMATE CHANGE
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
PALEOGEOGRAPHIC
AND CLIMATIC CONTEXT
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.
CYCLE
PATTERNS
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.
CONTINUE
KANSAS FLINT HILLS GEOLOGY
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