TERRESTRIAL-MARINE TELECONNECTIONS IN THE DEVONIAN - LINKS BETWEEN THE EVOLUTION OF LAND PLANTS, WEATHERING PROCESSES, AND MARINE ANOXIC EVENTS

The Devonian Period was characterized by major changes in both the ter restrial biosphere, e.g. the evolution of trees and seed plants and th e appearance of multi-storied forests, and in the marine biosphere, e. g. an extended biotic crisis that decimated tropic al marine benthos, especially the stromatoporoid-tabulate coral reef community. Teleconne ctions between these terrestrial and marine events are poorly understo od, but a key may lie in the role of soils as a geochemical interface between the lithosphere and atmosphere/hydrosphere, and the role of la nd plants in mediating weathering processes at this interface. The eff ectiveness of terrestrial floras in weathering was significantly enhan ced as a consequence of increases in the size and geographic extent of vascular land plants during the Devonian. In this regard, the most im portant palaeobotanical innovations were (1) arborescence (tree statur e), which increased maximum depths of root penetration and rhizoturbat ion, and (2) the seed habit, which freed land plants from reproductive dependence on moist lowland habitats and allowed colonization of drie r upland and primary successional areas. These developments resulted i n a transient intensification of pedogenesis (soil formation) and to l arge increases in the thickness and areal extent of soils. Enhanced ch emical weathering may have led to increased riverine nutrient fluxes t hat promoted development of eutrophic conditions in epicontinental sea ways, resulting in algal blooms, widespread bottomwater anoxia, and hi gh sedimentary organic carbon fluxes. Long-term effects included drawd own of atmospheric pCO(2) and global cooling, leading to a brief Late Devonian glaciation, which set the stage for icehouse conditions durin g the Permo-Carboniferous. This model provides a framework for underst anding links between early land plant evolution and coeval marine anox ic and biotic events, but further testing of Devonian terrestrial-mari ne teleconnections is needed.