Stratigraphy, Depositional Environments and Coalbed Methane Resources of Cherokee Group Coals (Middle Pennsylvanian)--Southeastern Kansas
Kansas Geological Survey
Open-file Report 2003-82

5.2 Modern Analogs

Comparison of modern peat forming environments to the inferred depositional environments in the Cherokee Group of the Cherokee basin aids in understanding the depositional controls on peatland growth and development in the ancient. Several works on modern environments such as that of the Orinoco Delta of South America (Andel, 1967), a Malaysian tropical delta (Coleman et al., 1970), and the Snuggedy swamp (Staub and Cohen, 1979) are analogs that have resemblance to environments during the Middle Pennsylvanian throughout southeastern Kansas.

The Orinoco Delta is situated off the coast of northeastern South America in Venezuela, Colombia and Brazil, and appears analogous to many of the coastal plain settings of the Cherokee basin. The Orinoco delta has built the entire coastal plain during a rapid coastal accretion that resulted in a wide zone of swamps and marshes with local chenier plains that merge into extensive tidal mud flats (Andel, 1967). Due to the low gradient, streams are not considered as significant transporters of sediment, and the coastal plain is subject to tidal flooding. Marine processes such as long shore drift supply clastic sediments to the coastal plain. The outer delta is described as a featureless marsh plain traversed by many swamp streams, estuaries, and distributary channels (Andel, 1967). Lithologies are similar to that of those described for Cherokee Group coastal plains and consist of sandy clays, mud flats, silty clays and peaty clays.

The Snuggedy swamp of South Carolina is analogous to coals associated with coastal plains and estuaries of the Cherokee basin. Peat development in these settings is described as thick extensive deposits underlain by a kaolonite rich underclay within a back-barrier estuarine depositional environment (Staub and Cohen, 1979). Similar to many of the coals in the Cherokee Group, coals in the Snuggedy swamp are formed above coarsening upward sands and shales described as lagoonal deposits, and thick well developed underclay’s interpreted as soils. Peatlands are also dissected by crevasse and fire splays. In the ancient, the presence of fusinite within a coal bed is interpreted as the product of fire (Staub and Cohen, 1979). The presence of fusinite ranging from 0 up to more than 3.5 percent has been noted in many of the Cherokee Group coals of eastern Kansas (Bensley et al., 1990). Many of these peat fires can result in localized thin coals replaced by clastic “fire splay” deposits.

Peat accumulation in the Snuggedy swamp is controlled by sea level rise, rate of sediment influx and or basin subsidence, related to an increase in accommodation (Staub and Cohen, 1979). The preservation of peat in the Snuggedy swamp is related to rapid flooding. A similar condition of rapid transgression occurred with many of the Cherokee Group coals where deep marine deposits directly overly coal. The distribution and thickness of Snuggedy swamp peat is also a function of topographic relief, fresh water versus brackish water, and relation to barrier islands. According to Staub and Cohen (1979) the thickest and most continuous peat forms in fresh water, near barrier islands and in areas with a slightly higher topography. Areas near tidal channels are also higher in sulfur content due to marine influence.

A Malaysian compound delta of the Klang and Langat Rivers located off the west coast of the Malay Peninsula in southeast Asia is also analogous to many of the coastal environments formed during deposition of the Cherokee Group. This compound delta is described as a complex network of tidal passes that function as an open-ended estuary in which large mangroves and freshwater swamps form between channels (Coleman et al., 1970). Seaward, the delta transitions into irregular and extensive tidal mud flats that typically do not have any beach development. Much of the coastal mangrove swamps formed in the above settings are colonized on top of the muddy tidal flats at or just above the neap high water (Coleman et al., 1970). Tides and tidal current processes are considered as the primary control on the delta morphology. The widespread distribution of the Malay swamps parallels the shoreline and is rapidly prograding (Coleman et al., 1970). Cherokee coals such as the Weir-Pittsburg have similar distributions.

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Last updated December 2003