Biostratigraphy, Phytogeography and Evolution of Middle Ordovician-Earlier Silurian Land Plants Based on their Spores

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Mid-Ordovician/Early Silurian land plant spores can contribute to the resolution of two important problems. Land plant spores provide the only entrance into terrestrial and fresh H2O environments in this interval of Phanerozoic time. The research described in this proposal is the first to attempt to establish a Late Ordovician/Early Silurian nonmarine biostratigraphy and phytogeography. Throughout the post-Silurian Phanerozoic, land plant spores/pollen have proved vital in stratigraphic zonation of nonmarine and shallow-water, nearshore marine rocks. Only local attempts have been made to extend spore biostratigraphy into the Late Silurian, and none effectively into the pre-Late Silurian. It now appears possible to establish a continuous biostratigraphy for shallow-water nearshore marine and nonmarine rocks from the mid-Ordovician to the Devonian. This will be the first zonation possible for nonmarine rocks; it will also provide the only precise means of correlating shallow-water, nearshore, Late Ordovician-Silurian strata since marine invertebrates/organic microfossils are absent or not presently biostratigraphically useful in the nearshore facies. Equally important is the fact that the spore-producing plants represent a hitherto unknown group of land plants that placed an important source of vegetation into continental habitats well before the traditional Early Devonian benchmark commonly considered to mark the major, initial radiation of the tracheophytes.