THE INGERSOLL SHALE, AN UPPER CRETACEOUS KONSERVAT-LAGERSTÄTTE IN THE EUTAW FORMATION OF EASTCENTRAL ALABAMA

The Ingersoll shale lens, within the Eutaw Formation in Russell Co., Alabama, contains unique preservation of soft-tissue fossils along with a great diversity and abundance of Santonian age flora and fauna. Both marine and terrestrial fossils, including plants such as the angiosperm Manihotites georgiana and conifers of an unknown species, are found preserved as carbon films. Among the soft-bodied fossil preservations are: a theropod down feather (possibly non-avian); a theropod feather with vein-forming interlocking barbs, a feature suggesting it was used for flight; insect wings (possibly neuropteran); and many small ammonite aptychi assumed to be from Placenticeras benningi. The carbonaceous Ingersoll shale lens is bracketed by light-colored, non-carbonaceous sediments with a normal marine biota.

Exceptional preservation of organic matter within the Ingersoll shale is attributed to sediment deposition in an anoxic environment, which did not permit rapid breakdown of organic matter. In addition to the anoxic conditions, the rate of fine-grain sediment accumulation exceeded the rate of biological decay, leaving the fossils well-preserved and intact. The quality and completeness of the carbon films that constitute the fossils indicate little bioturbation during or after deposition. Pyrite nodules and sulphur-filled fractures within the shale are further evidence of deposition within a reducing environment. This new Konservat-Lagerstätte in the Upper Cretaceous offers a rare view of soft-body fossils from the Santonian age that has not been observed in other eastern USA sediments. No other theropod feather fossils have been discovered in the Southeast, and apparently within an Upper Cretaceous shale in the USA.