PRE-DEVONIAN PALYNOLOGY IN THE APPALACHIAN BASIN: A NEW LOOK AT LITHOFACIES

Palynological analysis of “unfossiliferous” sections has the potential to equal or exceed biostratigraphic resolution, provenance analysis, and paleoecological analysis based on conventional invertebrate body fossils. In particular, the recovery of microscopic remains with a mix of marine and nonmarine origins allows detection of changes in depositional settings that can be checked against lithostratigraphic interpretations. In Silurian rocks exposed at Allenport, Pennsylvania, sediments were deposited in a range of shallow basin (Rose Hill and Mifflintown Formations), shelf shoal (Keefer), and tidal flat settings (Bloomsburg to Tonoloway). Outward lithologic differences between nearshore and questionably nonmarine deposits are often slight. Invertebrate fossils are absent, rare, or restricted to transported storm beds. Tight palynological sampling of interbedded shales and siltstones throughout this sequence reveals, however, that all lithofacies (including the Bloomsburg) contain a mix of autochthonous marine and allochthonous nonmarine microfossils. Multivariate ordination techniques applied to the palynological data reveal cryptic facies similarities, both within and between formations at the same or disparate locations. Gradational contacts between formations (e.g. Rose Hill-Keefer) are readily quantified, as are age correlations with reference sections. The rich spore and cryptospore record of the Appalachian Basin shows that tracheophytes diversified rapidly during late Mifflintown/early Bloomsburg time (latest Homerian/Gorstian to early Ludfordian). This evoultionary event lags behind a similar basal diversification seen in the Avalonian terrane by about a stage.