PALEOENVIRONMENTS OF EARLY DEVONIAN LAND PLANTS, GASPÉ, QUEBEC: RESEARCH INSPIRED BY J.R. BEERBOWER

Dick Beerbower's abiding interest in the origin of terrestrial ecosystems inspired our multidisciplinary analysis of the classic Lower Devonian plant-bearing beds of Gaspé, Quebec, which, though preliminary, provides a baseline for comparison with subsequent ecosystem development in the Paleozoic. Detailed sedimentological and paleoecological examination of the lower portion of the Battery Point Formation (Emsian) exposed near d'Aiguillon, on the north shore of Gaspé Bay, elucidates Early Devonian land plant paleoecology. In situ land plant megafossils are primarily preserved in mudstone-dominant strata representing distributary channel bar, crevasse splay/levee, interdistributary basin and marsh deposits associated with a delta-tidal flat complex. The absence of unambiguous marine fossil indicators (e.g. marine acritarchs, articulate brachiopods) and marine sedimentary structures within in situ plant horizons suggests that they inhabited freshwater habitats in close proximity to brackish and fully marine subenvironments. Evidence in the lower Battery Point supports the concept of clade-related niche partitioning among these plants: trimerophytes and certain rhyniopsids (Huvenia) occupied more ephemeral near-channel settings and propagated quickly over freshly deposited mud surfaces by means of abundant spore production, whereas zosterophylls apparently preferred somewhat wetter interdistributary basins where they developed comparatively long-term stands through vegetative propagation. Thus, we see in the Early Devonian the origin of the marked niche-partitioning observed in Late Devonian and Carboniferous floras, especially as observed in the lycophyte descendants of zosterophylls. Although preservation of plant megafossils is biased toward low-lying coastal environments, root traces in paleosols, as well as fragmentary plant material and spore assemblages from intervals of multistory fluvial channel sandstones, suggest that embryophytes were occupying drier upland environments as well. Existence of an Emsian upland megaflora is also supported by analysis of upper Battery Point root traces and paleosol carbonate chemistry by Elick et al. (1998, 1999).