Abstract

The Paleozoic spread of plants, beginning in the Ordovician and reaching a phase of accelerated diversity and dispersal in the Early Devonian, was a critical episode in Earth history. The Lower Devonian (Emsian) Campbellton Formation represents a subtropical basin comprising coastal and fluvial–lacustrine intermontane environments. Although the formation has been recognized for a rich fossil assemblage since the mid-19th century, this is the first attempt to correlate the tracheophyte fossil record with physical attributes of the environment as inferred from the sedimentology. Marginal lacustrine beds contain a parautochthonous collection of plants interpreted as dislodged from lakeside plant stands and buried by density flows. Shallow, oxygen-depleted lakes or ponds subjected to fluctuations in water level collected a more diverse assemblage from the surrounding flooded marsh. Plants within fluvial sandstones were transported by ephemeral flows, and typically display poorer preservation. Although some plants showed adaptations to drier environments, there is little evidence of the environmental partitioning identified at contemporaneous localities between rhyniaceans, basal euphyllophytes (trimerophytes), zosterophylls, and lycopsids, all of which are here found in nearly every identified setting. Plant occupation of basin margins or upland areas is suggested by the occurrence of plant-bearing strata within blocks transported cohesively by hyperconcentrated flows.

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