Coastal-fluvial palaeoenvironments and plant palaeoecology of the Lower Devonian (Emsian), Gaspe Bay, Quebec, Canada

The Cap-aux-Os Member (of Emsian age) of the Battery Point Formation, Gaspe Bay, Quebec, comprises coastal and fluvial deposits containing abundant, well-preserved remains of early land plants (embryophytes). Metres-thick sandstone bodies represent the deposits of the main river channels, including some that were tidally influenced. Thinner sandstone bodies within mudstone successions represent deposits of crevasse splays-levees, lacustrine deltas, tidal channels, flood-tidal deltas and washovers. Mudstone-dominant strata represent backswamps and marshes, lakes, coastal bays and tidal flats. Certain plants (trimerophytes, Huvenia and Scyadophyton) are particularly common on the moist, upper parts of near-coastal channel bars. They apparently germinated and grew rapidly on freshly exposed muds deposited during floods or exceptionally high tides. In situ zosterophylls are most common in backswamp and marshy areas, where they formed extensive, relatively long-lived stands. It is uncertain whether these plants were tolerant of brackish water or killed by it. However, absence of acritarchs in these in situ plant horizons suggests that they occupied primarily freshwater habitats. Transported Prorotaxites and Spongiophyton, both interpreted as possible fungi, are the main components of fully non-marine channel deposits. It is no coincidence that the best-preserved plants are those that lived in moist, oxygen-poor settings. However, the occurrence of root traces in palaeosols and sparse fossil evidence suggests that embryophytes also occupied drier settings.