TRACKING THE IMPACT OF LAND PLANTS ON EARTH SYSTEMS ON THE NORTHWESTERN LAURENTIAN MARGIN

The diversification and spread of terrestrial plants was one of the most profound changes in the history of Earth. Plants affect Earth’s climate and the global hydrologic cycle through evapotranspiration and by altering planetary albedo. While it is long accepted that the evolution of terrestrial plants had considerable impact on Earth systems, there are still widely varying views about the extent to which the emergence of land plants increased global productivity, drove atmospheric oxygenation, and altered the global marine redox landscape. The goals of this project are to connect and evaluate the effects of plant evolution on the marine redox record through palynology, paleobotany, and geochemistry.

Sampling efforts have focused on the Silurian-Devonian transition along the Alaska-Yukon border, which records continental margin sedimentation on the northwestern margin of Laurentia. Stratigraphic sections of the Ordovician-Silurian Road River Group at the Tatonduk River, and the Devonian McCann Hill Chert at its type section near Hillard Peak, Alaska, were measured and sampled. Here new programmed pyrolysis data constraining the thermal maturity of the sections will be presented and future plans for palynology, conodont biostratigraphy, Re-Os geochronology, and organic (biomarkers) and inorganic geochemical analyses will be discussed. If palynomorph and plant macrofossil diversity and abundance correlate with shifts in geochemical redox tracers this will allow for the detailed, high-resolution linkage of plant evolution and marine geochemistry through the Silurian-Devonian interval. The geochemical and palaeobotanical data from these Alaskan successions will provide well-calibrated records of redox change through the Silurian-Devonian transition, directly connected to palaeobotanical records, and thus one of the strongest tests to date of whether terrestrial evolution is temporally associated with redox changes in the marine realm.