EARLY MIDDLE DEVONIAN TERRESTRIAL ECOSYTEMS OF MAINE: THE TROUT VALLEY FORMATION REVISITED

The transition from the Early to Middle Devonian within the terrestrial landscape witnesses a marked change not only in systematic biodiversity, but also in ecosystem structure. As several new plant clades originated in the Siegenian and Emsian, the landscape is envisioned to have become colonized by a mosaic of r-strategists. The Trout Valley flora of Maine has been used by many authors as the archetype of such Early Devonian assemblages because extensive, detailed systematic and morphologic studies were published in the 1970s based upon material originating from these outcrops. Using spatial relationships as determined from the field, the Trout Valley assemblage has been described as consisting of low-diversity patches of vegetation, with patch size varying but usually composed of 3-4 taxa. Although used as the prima facie model for Middle Devonian ecosystems, the Trout Valley Formation, and the fossils preserved therein, is nearly an unknown entity. Plant assemblages were reported to be fairly common locally in thin zones, occurring within "black sandy shale lenses in granule or pebble conglomerate," with better preserved material originating from the "finer shale beds...sandstones and siltstones," but the geological context and framework within which these fossil assemblages were preserved were never well documented, analyzed, or used as the basis for published interpretations. Preliminary field investigations in Baxter State Park on the series of outcrops along Trout Brook and South Branch Ponds Brook have revealed that most fossil plant assemblages are preserved as parautochthonous assemblages, either in the waning stages of tidal channel infill sequences or along bedding surfaces of accretionary foresets within a tidally influenced regime. Hence, the absence of any detailed stratigraphic or sedimentologic analysis coupled with a lack of taphonomic data on the plant fossil assemblages can only lead to the conclusion that presently there are few data to substantiate the widely cited vegetational community scenario for the Early-Middle Devonian.