Paper No. 3
Presentation Time: 8:45 AM
EXTRAORDINARILY PRESERVED TERRESTRIAL BIOTA IN THE INGERSOLL SHALE, A COMPACT ESTUARINE CLAY LENS IN THE UPPER CRETACEOUS EUTAW FORMATION, EASTERN ALABAMA
The Ingersoll shale, a small clay lens in the lower part of the Upper Cretaceous Eutaw Formation in eastern Alabama, contains an unusually well-preserved, mainly terrestrial fossil biota that includes a diverse plant assemblage, amber, and feathers. Deposition of the Ingersoll shale occurred in a shallow, narrow tidal channel within a distal bayhead delta setting. Accumulation and extraordinary preservation of fossil components in this isolated depocenter were favored by close proximity to coastal swamps, rapid tidal deposition of clay-rich, carbonaceous sediment, anoxic pore waters, and early diagenetic pyrite mineralization. Plant fossils include 55 leaf morphotypes, representing angiosperms, gymnosperms, and ferns and often articulated on stems, and various other plant organs (e.g., flowers, cones, and megaspores), some of which contain in situ amber rods. Detrital amber clasts are abundant (up 360 g/m3 of sediment) and contain common fungal, plant, and arthropod inclusions (e.g., scale insects, spiders). Fossil feathers, fourteen in all, preserve ultrastructural detail, including carbonized melanin rods. Ongoing studies of this compact lagerstatte will provide a clearer picture of Cretaceous coastal ecosystems, plant-resin and plant-arthropod relations, and aspects of theropod evolution, including feather coloration. Similar, as yet undiscovered, compact lagerstatten may reside in other isolated carbonaceous clay-dominated bodies common in marginal marine successions throughout the coastal plain provinces of the southeastern U.S.