MIDDLE DEVONIAN (EMSIAN-EIFELIAN) MIXED TERRESTRIAL, ESTUARINE, AND MARINE-INVERTEBRATE ASSEMBLAGES FROM THE TROUT VALLEY FORMATION, BAXTER STATE PARK, MAINE

The Trout Valley Formation hosts early land plants preserved primarily in parautochthonous and allochthonous assemblages in a foreland basin formed during the last phases of Acadian deformation. Published reports have focused on outcrops along Trout and South Branch Ponds brooks in northwestern Baxter State Park, Maine, where a fluvial to tidally influenced estuarine (intertidal) sequence is documented. The construction of Wadleigh Road within the Scientific Forest Management Area north of Trout Brook has unearthed pavement exposures in which both terrestrial plant and nearshore invertebrate assemblages occur in fine-grained siliciclastic deposits.

Fossiliferous lithologies range from moderately sorted, olive gray (5Y 4/1) silty sandstone, with symmetrical ripples defining bed contacts, to olive and dark gray (N3) sandy siltstone. Plants are preserved prostrate on bedding, and consist of subaerial axes in an array of decay states ranging from minimal degradation where fine structures are discernible to unidentifiable axial remains. Taxa include: the trimerophyes Pertica quadrifaria, Psilophyton forbesii, and P. dapsile; the zosterophyllophyte Serrulacaulis furcatus; and lycophytes of unidentifiable generic affinity. These occur either in heteromeric plant-fossil assemblages or in assemblages interspersed with invertebrates.

To date, rare isolated invertebrates are reported from along Trout Brook and include the bivalve Phthonia sectifrons, small spiral and planispiral gastropods, and a juvenile eurypterid cf. Parahughmilleria. New invertebrate collections from Wadleigh Road include concentrated shelly assemblages of the bivalve Modiomorpha concentrica, isolated bivalves assigned to Nuculites corrugatus, and a scale impression of the eurypterid Pterygotus sp. all of which are interpreted as having inhabited estuarine conditions. The first open-marine brachiopod taxon, assigned to Coleospira sp., also was collected from the formation. This is represented by a single specimen that may have been transported shoreward during storm activity, similar to what has been interpreted for the presence of P. sectifrons in the sequence. These new collections extend our knowledge of Middle Devonian biodiversity in both the continental and marine realms.