Fig. 5. Thickness of beds 1 to 258 in the Tonganoxie Sandstone Member at the Buildex Quarry. (A) Unit A1, (B) Unit A2, (C) Unit A3, (D) Facies CL (adapted from Lanier, 1993; adapted from Lanier et al., 1993).
Archer, Lanier et al. (1994), Archer and Feldman (1995), and Feldman et al. (1995) discussed the problems associated with the recognition of system tracts within the Tonganoxie incised valley system (fig. 6). In the present study, the definitions of Dalrymple et al. (1992) were used to determine boundaries between system tracts. However, if the terminology of Van Wagoner et al. (1990) were used, the boundary between the lowstand and transgressive system tracts would be placed further up in the sequence (at the base of the Westphalia Limestone Member). The basal erosion surface represents a type 1 sequence boundary (Van Wagoner et al., 1990) resulting from sea-level fall and subaerial exposure. The lowstand system tract is recorded by coarse-grained, fluvial channel deposits at the base of the Tonganoxie Sandstone Member (type I sandstone of Feldman et al., 1995). Dalrymple et al. (1992) suggested that the boundary between lowstand and transgressive system tracts should be placed at the lowest evidence of marine influence. Accordingly, Archer, Lanier et al. (1994) and Feldman et al. (1995) placed the boundary near the top of the type I sandstone package within the Tonganoxie Sandstone Member, where clay-draped bedforms indicate the onset of estuarine deposition. Upwards in the sequence, however, a widespread transgression is suggested by deposition of the Westphalia Limestone Member. Above this limestone, retrogradational parasequence sets are stacked (Westphalia Limestone, Vinland Shale, and Haskell Limestone Members), culminating with an open-marine, condensed section in the lowermost part of the Robbins Shale Member (Archer, Lanier et al., 1994). Because they judged this condensed section to represent the maximum flooding surface, Archer, Lanier et al. (1994) regarded the remainder of the Robbins Shale Member as the highstand system tract.
Fig. 6. Sequence stratigraphic model for the Tonganoxie paleovalley (adapted from Archer, Lanier et al., 1994). Placement of system-tract boundaries based upon the definitions of Dalrymple et al. (1992).
The Buildex Quarry succession is situated at the eastern edge of the Tonganoxie paleovalley (Feldman et al., 1995) and is part of the transgressive system tract. At this locality, the boundary between the Tonganoxie Sandstone Member and the Ottawa coal represents a coplanar surface of lowstand erosion and flooding.
Kansas Geological Survey
Web version March 19, 1998
http://www.kgs.ku.edu/Current/1998/buatois/buatois5.html
email:lbrosius@kgs.ku.edu