RELATIONSHIPS BETWEEN EMSIAN PALEOSOLS, PARA- AND ALLOCHTHONOUS PLANT ASSEMBLAGES, AND MACROINVERTEBRATE-AND-TRACE FOSSIL ASSEMBLAGES IN THE TROUT VALLEY FORMATION, MAINE

Higher plant colonization set the stage for revolutionary adaptations that impacted Earth Systems. By Middle Devonian, coastal wetlands were turfed in by rhizomatous clades growing in freshwater and estuarine conditions. These ecosystems contributed organic matter to marshes, intertidal, and subtidal environments. Fossil assemblages in these settings occur in the Trout Valley Formation (TVF), Maine.

The TVF contains granule-and-pebble conglomerate, lithic wacke interbedded with quartz arenite, sandy siltstone, and both coarse-and-fine siltstone. Disarticulated plants are found in most facies, but rooting in paleosols is restricted to fine clastics. The presence of aerial and secondary axes indicates that taphonomic conditions promoted preservation across the coarse-to-fine clastic spectrum. Burial was not instantaneous as evidenced by silt-filled axial remains. Rapidly buried plant parts include vertical rooting in at least two paleosols, differentiated by the presence or absence of small carbonate-cemented nodules. Stable isotope data of the latter indicate formation in wetland, low latitude conditions, and thin rooting structures indicate periodic dysoxia/anoxia that promoted their isolation and preservation, albeit without evidence of overlying or attached rhizomatous structures.

Few macroinvertebrates are known, and a single locality preserves trace fossils. Invertebrates are restricted and preserved in sandy siltstone, in which fragmentary plant taxa occur. The most abundant assemblage is of a monotypic bivalve and differs systematically from other invertebrate-bearing horizons. Trace fossils include vertical burrows and single-story, spiral feeding structures. The former are associated with shelly debris; the latter are not. Comparison with time-equivalent Middle Devonian plant-bearing localities in North America indicates that the TVF conforms more closely to the Emsian Battery Point Formation, Gaspé, than to the Campbellton Formation, New Brunswick, Canada.