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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 12 of 13

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The Buildex ichnofauna was produced by a terrestrial and freshwater biota and represents a mixture of the nonmarine Scoyenia and Mermia ichnofacies. The presence of such an assemblage in tidal rhythmites indicates deposition on tidal flats in the most proximal zone of the inner estuary. This zone is situated between the landward limit of tidal currents and the salinity limit further towards the sea.

Although lithofacies distribution within estuarine valleys is mostly salinity-independent, the distribution of organisms is not. Accordingly, ichnologic analysis of estuarine systems can provide the high-resolution data necessary to delineate fluvio-estuarine transitions and may help to refine facies models based only on physical evidence.

In terms of sequence stratigraphy, Buildex-type ichnofaunas characterize the lower part of the transgressive system tract, immediately overlying a coplanar surface. As transgression proceeds, tide-influenced freshwater facies are replaced by backstepping brackish-water deposits, and the mixed Scoyenia and Mermia ichnofacies may be replaced by a Skolithos and impoverished Cruziana ichnofacies. The coplanar surface (flooding surface and sequence boundary) at the base of the Tonganoxie sequence at Buildex Quarry lacks the Glossifungites ichnofacies, which is restricted to the limits of marine influence within the valley system. The coals and paleosols with upright plant remains that typify the surface represent erosional truncation and nondeposition close to the valley interfluves and may be regarded as the landward equivalent of the Glossifungites ichnofacies.

Comparisons with other trace fossil assemblages from marginal marine environments suggest that Buildex-type ichnofaunas are widespread in Pennsylvanian tidal rhythmites of the United States Midcontinent. Recognition of such ichnofaunas may be useful in the identification of freshwater inner estuarine facies and help to delineate fluvioestuarine transitions in incised valley systems.


LAB and MGM thank the Argentinian Research Council (CONICET) for financial support and the Kansas Geological Survey for technical and logistical facilities. We also would like to thank Scott Beaty and Lynn Watney for carefully reading this manuscript, Ron Pickerill and Andrew Rindsberg for reviewing the paper, Mark Schoneweis for the drawings, and Al Kamb for lending us Bandel's collection housed at The University of Kansas.

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Kansas Geological Survey
Web version March 19, 1998