6-3 Revisiting Ancient Behavior at Fielder Ridge: Estuarine Ichnology at a Classic Site in the Upper Mississippian Hartselle Sandstone of Alabama

Session: Advances in ichnology: walking in Memphis and other records of behavior

Presenting Author:

Authors:

Abstract:

For more than thirty years, the roadcut at Fielder Ridge (Colbert County, Alabama) has yielded more information on trace fossils of the Mississippian Hartselle Sandstone than all other exposures combined. Although trace fossils are common in the Hartselle, this outcrop is unusual because it exposed a complete section of the formation including alternating beds of shale and sandstone: perfect conditions for preserving burrows, trackways, and trails in lithologic contrast. When Rindsberg (1994) presented the systematic ichnology of the formation, specimens from Fielder Ridge made up the majority of the material. New ichnotaxa were erected and we thought that they would soon be recognized widely in the North American Mississippian.

            However, this expectation has not been fulfilled, perhaps because the predominantly estuarine setting of the Hartselle at Fielder Ridge is unusual. Hartsellea sursumramosa, the most widespread trace fossil within the Hartselle Sandstone, is a multibranched, dendritic, lined burrow that branches upward and includes actively filled segments; its makers may have been predatory polychaetes. Hartsellea has not been reported in any other formation. Alph hartselleanus is a crustacean resting trace preserved in such exquisite detail that the evidence supports a possible nesting function; it is rare at Fielder Ridge, but more poorly preserved specimens are common in the overlying Bangor Limestone. Well-preserved Nereites missouriensis and Olivellites implexus – two iconic locomotion burrows or trails – turn out to be closely related, and may have shared an arthropod maker. Unlike some of the others, these have worldwide distribution, but their appearance at Fielder Ridge may be at the edge of their environmental range. We hope that more geologists will recognize these trace fossils in their own studies.

            The hazards of deriving our understanding about trace fossils from the best-preserved specimens are unavoidable. Broad-based studies are advisable to prevent distorted views of ancient behavior.

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