WETLAND PLANT ASSEMBLAGES OF THE TROUT VALLEY FORMATION, MIDDLE DEVONIAN, MAINE

The Trout Valley Formation of Middle Devonian age is located in Baxter State Park, northcentral Maine. These rocks consist of terrestrial (granule and coarse sandstones), estuarine (siltstones), and near-shore marine (quartz arenites) deposits. Plant fossils are common in terrestrial and estuarine settings, having been used previously to reconstruct early-middle Devonian ecosystems. In the summer of 2002, all available plant bearing assemblages in the sequence were examined. Assemblage outcrops were described in detail and samples collected for cm-scale stratigraphic descriptions and thin section analysis.

Detailed plant taphonomic analyses of fossil-bearing outcrops have revealed that there is a spectrum of assemblage types. Autochthonous assemblages characterized by dense mat-like intervals of concentrated axes that are both flat lying, inclined upwards, and vertically cross-cutting bedding occur in interpreted paleosol deposits. Parautochthonous assemblages consisting of concentrated, parallel aligned flat lying plants are found in the troughs of ripple structures and channel-fill sequences of fluvial and tidal channel deposits. Allochthonous assemblages are characterized by disordered, litholateral plant fragments having been deposited as lag deposits in large-scale channel forms within both fluvial and estuarine environments.

Based on previous reports and present identifications it appears that systematic partitioning of taxa occurs in these assemblages. Three plant taxa are exclusive to fluvial environments, six to estuarine environments, and five plant taxa occur in both fluvial and estuarine environments.