Validation of Sediment Accumulation Regions in Kansas, USA
351
clastic-dominated in the lower half and carbonate-dominated in the upper portion southeast of boundary E.
SAR boundary F is associated with abrupt southeastward thickening of the
shale between the Toronto and Douglas Limestone units. The upper Muncie
Creek GS abruptly thickens to the southeast, thickening basinward in steps that
began so noticeably at boundary D.
SAR boundary G is associated with abrupt thickening of the shale between
the Heebner Shale, a condensed section, the datum of the cross section, and the
succeeding condensed section, the Queen Hill Shale. The Nuyaka Creek GS continues to thicken southeastward, but more significantly, the lithofacies in this interval dramatically changes near boundary G. Southeast of boundary G, the carbonate units that remain in the Nuyaka Creek GS at this low position on the shelf
pass abruptly southeastward to clastics. Unlike the apparent downlapping of
carbonates in the lower Muncie Creek genetic set, each individual GSUs appears
to be correlatable across the boundary linking carbonate and clastic facies of
each. The actual internal temporal relationships are not known, but it appears
from outcrop analogs that the clastics came later at the end of each GSU as reciprocal sedimentation during low-stand conditions (Watney et al. 1989). The
Dennis Limestone is very clean on the shelfward side of boundary G before its
abrupt change to sandstone with its attendant higher gamma radiation.
4
Discussion of the Northwest to Southeast Cross Section
4.1
Nuyaka Creek genetic Set
The Upper Pennsylvanian section undergoes significant lithofacies and thickness changes along this cross-section ranging from thinner carbonate-dominated GSUs on the northwestern, the higher shelf side, to thicker clastic-dominated
GSUs along the basinward side in the southeast. The Nuyaka Creek GS is more
uniform through the entire section compared to the Muncie Creek GS, yet with
notable changes in lithofacies and, locally, thickness within particular GSUs in
conjunction with region boundaries. Mixed clastics and carbonates are common
in the Nuyaka Creek GS along the northwestern reaches of the cross-section with
the lower and upper sections containing the most clastics. In contrast, the central and lower shelf region in the southeast is carbonate-dominated. Only the
upper portion of the Nuyaka Creek GS is dominated by carbonates in the lower
reaches of the shelf. The lithofacies is entirely comprised of clastics on the lowest
reach of the shelf, probably representing a boundary between shelf and basin.
Lower shelf carbonates in the Stark GSU are unusually thick compared to
landward sites and extended out over the thicker lower clastics, suggesting lateral accretion later in the Nuyaka Creek genetic set. This could be attributed at
least in part to a fall in relative sea level or an extended time of the seafloor in
the photic zone at that elevation of the shelf during the Stark GSu.
351
clastic-dominated in the lower half and carbonate-dominated in the upper portion southeast of boundary E.
SAR boundary F is associated with abrupt southeastward thickening of the
shale between the Toronto and Douglas Limestone units. The upper Muncie
Creek GS abruptly thickens to the southeast, thickening basinward in steps that
began so noticeably at boundary D.
SAR boundary G is associated with abrupt thickening of the shale between
the Heebner Shale, a condensed section, the datum of the cross section, and the
succeeding condensed section, the Queen Hill Shale. The Nuyaka Creek GS continues to thicken southeastward, but more significantly, the lithofacies in this interval dramatically changes near boundary G. Southeast of boundary G, the carbonate units that remain in the Nuyaka Creek GS at this low position on the shelf
pass abruptly southeastward to clastics. Unlike the apparent downlapping of
carbonates in the lower Muncie Creek genetic set, each individual GSUs appears
to be correlatable across the boundary linking carbonate and clastic facies of
each. The actual internal temporal relationships are not known, but it appears
from outcrop analogs that the clastics came later at the end of each GSU as reciprocal sedimentation during low-stand conditions (Watney et al. 1989). The
Dennis Limestone is very clean on the shelfward side of boundary G before its
abrupt change to sandstone with its attendant higher gamma radiation.
4
Discussion of the Northwest to Southeast Cross Section
4.1
Nuyaka Creek genetic Set
The Upper Pennsylvanian section undergoes significant lithofacies and thickness changes along this cross-section ranging from thinner carbonate-dominated GSUs on the northwestern, the higher shelf side, to thicker clastic-dominated
GSUs along the basinward side in the southeast. The Nuyaka Creek GS is more
uniform through the entire section compared to the Muncie Creek GS, yet with
notable changes in lithofacies and, locally, thickness within particular GSUs in
conjunction with region boundaries. Mixed clastics and carbonates are common
in the Nuyaka Creek GS along the northwestern reaches of the cross-section with
the lower and upper sections containing the most clastics. In contrast, the central and lower shelf region in the southeast is carbonate-dominated. Only the
upper portion of the Nuyaka Creek GS is dominated by carbonates in the lower
reaches of the shelf. The lithofacies is entirely comprised of clastics on the lowest
reach of the shelf, probably representing a boundary between shelf and basin.
Lower shelf carbonates in the Stark GSU are unusually thick compared to
landward sites and extended out over the thicker lower clastics, suggesting lateral accretion later in the Nuyaka Creek genetic set. This could be attributed at
least in part to a fall in relative sea level or an extended time of the seafloor in
the photic zone at that elevation of the shelf during the Stark GSu.