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Kansas Geological Survey Open-file Report 2003-82 |
Chapter Four : Sequence Stratigraphy of the Cherokee Group
4.1 Sequence Stratigraphic Nomenclature
Sequence stratigraphic concepts provide a framework to better explain and predict the lateral distribution, relative thickness and ash content of coal beds in the Cherokee Group. Although a complete review of sequence stratigraphy concepts and nomenclature are beyond the scope of this study, a brief summary of basic concepts and terminology is provided.
Sequence stratigraphy is the study of genetically related facies within a framework of chronostratigraphically significant surfaces, where the depositional sequence is considered to be the fundamental unit for sequence-stratigraphic analysis (Van Wagoner et al., 1990). The depositional sequence is defined as a genetically related succession of strata bounded by unconformable surfaces and their correlative conformities (Mitchum et al., 1977). An alternative method to divide the rock record would be the genetic sequence, defined as strata bounded by surfaces that reflect the depositional hiatus occurring during maximum marine flooding (Galloway, 1989). This study applies the Mitchum et al. (1977) and Van Wagoner et al. (1990) approach to the definition of depositional sequences in the Cherokee Group of southeastern Kansas. It is much easier to map intervals of the Cherokee Group separated by “core” shales, which can be interpreted as flooding surfaces. Some of these flooding surfaces are also interpreted as maximum flooding surfaces (sensu Galloway, 1989).
4.1.1 Identification of Parasequences
Parasequences are the stratal building blocks of sequences. The parasequence is a relatively conformable succession of genetically related beds or bedsets bounded by marine-flooding surfaces (FS) or their correlative surfaces (Van Wagoner et al., 1990). A marine flooding surface (parasequence boundary) has a correlative surface in the coastal plain as well as on the shelf. The correlative surface on the coastal plain may be marked by local erosion or evidence of subaerial exposure such as soil or root horizons, whereas the correlative surface on the shelf is marked by thin pelagic of hemipelagic deposits (Van Wagoner et al., 1990). In this study, well-log cross-sections of the Cherokee Group aided in determining flooding surfaces, as well as helping to define the transition of coals or paleosols into deeper marine rocks. Well log data are abundant throughout the study area with over 930 wells incorporated in the study. However, core control is very limited, and was not sufficient to correlate individual beds, so parasequences and parasequence sets were not correlated.
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Last updated December 2003
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