BIOTIC COMPOSITION AND TAPHONOMY OF AN UPPER CRETACEOUS KONSERVAT-LAGERSTÄTTE (INGERSOLL SHALE, EUTAW FORMATION, EASTERN ALABAMA)

The Ingersoll shale is a thin (<1m), laterally restricted clay lens within the Upper Cretaceous (Santonian) Eutaw Formation, Russell County, eastern Alabama. Excavation of this marginal marine konservat-lagerstätte has produced an abundant, diverse, and extraordinarily well-preserved biotic assemblage, which is dominated by terrestrial plants but includes invertebrates and vertebrates. The macroflora consists of leaves from dicotyledonous and monocotyledon angiosperms (over two dozen species), gymnosperms, and a variety of water plants (ferns and lycopsids). Although most plant tissues are carbonized and/or pyritized, some leaf cuticle is unmineralized, flexible, and easily removed from the matrix. Conifer stems are often preserved in three-dimensions via early authigenic pyritization. Some of these reveal in situ amber rods. The shale lens also contains a variety of plant reproductive organs (e.g., cones, and seedpods), megaspores from heterosporous isoetalean lycopsids and water ferns, a variety of fungal spores, pollen, acritarchs, and marine dinoflagellates. Amber is very abundant in the lower portions of the lens and often contains inclusions, some of which are insect appendages, mites, and fungal hyphae. In the reducing environment represented by the Ingersoll shale, carbonates are completely absent, and phosphatic components such as vertebrate bones have yet to be found. However, well-preserved vertebrate integumentary structures, such as theropod feathers and fish scales, have been found. These structures represent the preservation of protein-based tissues (e.g., beta-keratin and collagen).

The Ingersoll-shale biota is more diverse than any previously documented Gulf coast Santonian deposit and provides a unique look into a Late Cretaceous terrestrial community. In particular, the feathers from the Ingersoll shale are the only Mesozoic feathers from North America found in a sedimentary host. Furthermore, understanding the taphonomy of the Ingersoll shale biota provides insight into the conditions that govern the preservation of refractory soft tissues, thus enhancing future prospecting methods for other nearshore konservat-lagerstätten.