Kansas Geological Survey, Subsurface Geology 12, p. 71-72
by
R. R. West1, D. R. Suchy2, and V J. Voegeli1
1Kansas State University
2McGill University
The Marmaton Group (Desmoinesian) in Kansas is composed of four limestone formations: the Fort Scott, Pawnee, Altamont, and Lenapah, and four mudstone formations: the Labette, Bandera, Nowata, and Holdenville (fig. 1). The Fort Scott, Altamont, and Lenapah are each composed of three members: a lower limestone, a middle mudrock/shale, and an upper limestone. The Pawnee is more complex (fig. 1). Traditionally, three members have been interpreted as a cyclothem with the lower limestone interpreted as a transgressive phase, the middle unit as a deeper water phase, and the upper limestone as a regressive phase. Knight (1985) recognized two lithostratigraphic packages (cyclothems), rather than one in the Fort Scott. Within all these cyclothems studied to date, it is possible to recognize within these cyclothems correlative genetic sequences which provide a better understanding of the geologic history (Suchy, 1987).
Figure 1--Stratigraptuc columm of the Marmaton Group (modified from Zeller, 1968).
Such genetic sequences are the chaetetid intervals in the Houx-Higginsville Limestone Member of the Fort Scott Limestone and in the Amoret Limestone Member of the Altamont Limestone. Other such genetic sequences may be the chaetetid intervals in the Blackjack Creek Limestone of the Fort Scott Limestone, Myrick Station and Laberdie Limestone Members of the Pawnee Limestone, and Worland Limestone Member of the Altamont Limestone. Chaetetids are unknown from the Lenapah Limestone, although they are known from younger rocks (Missourian) in Texas. Chaetetid-bearing limestones are sought for use in road construction and produce hydrocarbons in Kansas, Oklahoma, and Texas.
Genetic surfaces, and thus genetic sequences, may be recognized by subtle changes in lithologic and biologic characteristics. Taphonomic aspects and features associated with subaerial exposure are particularly useful. Whereas autocyclic surfaces and events may be local, any surfaces and events for which the controlling mechanism is extrabasinal are allocyclic.
Our studies of the Fort Scott and Altamont formations indicate that allocyclic genetic sequences, at a scale smaller than the lithostratigraphic cyclothem, are recognizable and greatly enhance understanding of these intervals. The lithostratigraphic cyclothem itself represents a shorter interval of time (on the order of 300 to 500 ka) than can be recognized biostratigraphically (Rollins et al., in press). We are now able to accurately differentiate genetic sequences within a given cyclothem and with this finer temporal framework and enhanced stratigraphic resolution are better able to reconstruct ancient paleogeography and palaeoceanography. Using these, and similar data, it should also be possible to model more realistic situations for less well studied intervals.
Five transgressive surfaces occur within the "Upper Fort Scott cyclothem" as recognized by Knight (1985). These surfaces delineate four complete and two partial other sixth-order (time frame for each sixth-order unit is approximated at from 50 to 130 ka, Rollins et al., in press) transgressive-regressive units as defined by Busch and Rollins (1984). Chaetetid masses occur in only one of these sixth-order transgressive-regressive units. In the Amoret Limestone Member of the Altamont Limestone, two genetic events (an oncolite bed and an apparent exposure surface) suggest that seafloor topography localized the occurrence of chaetetid "patch reefs" (Voegeli, 1989). Thus, clearly the chaetetids are not randomly distributed in the limestones of the Marmaton Group. Rather, they occur in predictable stratigraphic and paleoecologic sequences that are discernible and predictable using detailed genetic stratigraphy.
Modeling of genetic sequences will benefit greatly from studies such as those reviewed here. As stratigraphic and environmental models are developed, data from such studies must be available for testing and refining the models. Finally, the fullest possible integration of the often subtle changes in lithologic and biologic characteristics are essential for the interpretation and modeling of sedimentary sequences.
Busch, R. M. and Rollins, H. B., 1984, Correlation of Carboniferous strata using a hierarchy of transgressive-regressive units: Geology, v. 12, p. 471-474
Knight, K. L., 1985, Stratigraphy, depositional and diagenetic history of three Middle Pennsylvanian cyclothems (Breezy Hill and Fort Scott limestones), midcontinent North America: Ph.D. dissertation, The University of Iowa, Iowa City, Iowa, 340 p.
Rollins, H. B., West, R. R., and Busch, R. M., in press, Hierarchical genetic stratigraphy and marine paleoecology: Paleontological Society, Special Publication 5
Suchy, D. R., 1987, Sixth-order transgressive-regressive units in the Fort Scott cyclothem of southeast Kansas: Geological Society of America, Abstracts with Program, v. 19, no. 3, p. 178
Voegeli, V. J., 1989, Local variations within the Altamont Limestone Formation (Middle Desmoinesian), southeastern Kansas: Geological Society of America, Abstracts with Program, v. 21 . no. 1, p. 42
Zeller, D. E. (ed.), 1968, The stratigraphic succession in Kansas: Kansas Geological Survey, Bulletin 189, 81 p. [available online]
Kansas Geological Survey
Comments to webadmin@kgs.ku.edu
Web version May 12, 2010. Original publication date 1989.
URL=http://www.kgs.ku.edu/Publications/Bulletins/Sub12/West/index.html