Current Research--Buatois et al.--page 2 of 13

Kansas Geological Survey, Current Research in Earth Sciences, Bulletin 241, part 1
Allostratigraphic and Sedimentologic Applications of Trace Fossils to the Study of Incised Estuarine Valleys--page 2 of 13

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Introduction

The sedimentary facies, depositional dynamics, and sea-level history of estuarine paleovalleys have received increased attention during the last few years (e.g., Dalrymple et al., 1990, 1992, 1994; Allen, 1991; Nichols et al., 1991; Allen and Posamentier, 1993; Zaitlin et al., 1994). The ichnology of estuarine depositional systems is also becoming a focus of intense research (e.g., Bjerstedt, 1987; Wightman et al., 1987; Pattison, 1992; Benyon and Pemberton, 1992; Pemberton and Wightman, 1992; Ranger and Pemberton, 1992; Pemberton, Reinson et al., 1992; Greb and Chesnut, 1994; MacEachern and Pemberton, 1994). Studies of organism-sediment interactions in such environments provide valuable information on the role of salinity as a controlling factor in benthic faunal distributions, allowing the recognition of estuarine deposits and discontinuity surfaces due to estuarine valley incision.

The Tonganoxie Sandstone Member (Stranger Formation, Douglas Group) of eastern Kansas records sedimentation within an estuarine paleovalley that was incised during a late Missourian (Late Carboniferous) drop in sea level and was later infilled during a Virgilian (Late Carboniferous) transgressive episode (Lins, 1950; Lanier et al., 1993; Archer, Lanier et al., 1994; Archer and Feldman, 1995; Feldman et al., 1995). At Buildex Quarry (fig. 1), well-exposed deposits of the Tonganoxie Sandstone Member are interpreted as having been formed in a fluvio-estuarine transitional setting (Bandel, 1967; Lanier, 1993; Lanier et al., 1993). These deposits host a rich and very well preserved vertebrate and invertebrate trace-fossil assemblage. The Buildex ichnofauna was first analyzed by Bandel (1967), who described some arthropod traces and suggested deposition in a river valley close to the river's mouth. Subsequently, Buildex trace fossils were mentioned or briefly discussed in a series of sedimentologic papers (Lanier et al., 1993; Archer, 1993; Archer, Feldman et al., 1994; Archer, Lanier et al., 1994; Feldman et al., 1995; Tessier et al., 1995).

Figure 1. Map showing surficial distribution of the Douglas Group and location of Buildex Quarry (adapted from Lanier et al., 1993).

This paper deals with the sedimentologic and stratigraphic implications of the Tonganoxie Sandstone ichnofauna at Buildex Quarry (fig. 1). Our conclusions on the paleoenvironmental significance of this ichnofauna are based on the study of 65 rock slabs collected by the authors and 12 samples from Bandel's original collection. The aim of this paper is threefold: (1) to discuss the relevance of the Buildex ichnofauna for facies delineation of estuarine valley systems, in particular at the fluvio-estuarine transition; (2) to analyze the allostratigraphic implications of this ichnofauna; and (3) to emphasize the regional significance of the Buildex trace-fossil assemblage.

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