PALYNOLOGICAL CORRELATION OF A LATE DEVONIAN DROPSTONE IN KENTUCKY WITH DIAMICTITE-BEARING SECTIONS IN MARYLAND AND PENNSYLVANIA

Well-preserved palynomorph assemblages are described from organic rich fissile shales at the top of the Cleveland Member of the Upper Devonian Ohio Shale and from the overlying Upper Devonian Bedford Shale in Logan Hollow Branch, approximately 8 km northwest of Morehead, Kentucky; both units occur in the S. praesulcata Conodont Biozone. At this locality, the granitic 'Robertson dropstone' is embedded in the uppermost part of the Cleveland Shale. Miospore assemblages from samples immediately below, above, and adjacent to the dropstone can be confidently assigned to the late Famennian Retispora lepidophyta - Verrucosisporites nitidus (LN) Biozone. LN Biozone assemblages have also been recovered from the overlying Bedford Shale at this locality.

Highly carbonized palynomorphs have also been recovered from sections that include diamictites at three localities, ca. 500 km to the east, at Sideling Hill, Maryland, La Vale, Maryland, and Crystal Spring, Pennsylvania. Although these palynomorphs are poorly preserved, stratigraphically important taxa can still be recognized, allowing the diamictite units in these sections to be assigned to the LN Miospore Biozone and the preceding Retispora lepidophyta - Indotriradites explanatus (LE) Biozone. The palynologic evidence supports previous lithostratigraphic and gamma-ray correlations between the Kentucky and Appalachian sections. It also provides firm evidence of a late Famennian age for the alpine glaciation/deglaciation responsible for deposition of the diamictites and related sediments.

The sections studied can be correlated palynologically with Gondwanan, high-paleolatitude, marine diamictites, such as those at Bermejo, Bolivia. They can also be correlated with well-known sections in Belgium, permitting calibration against the 'standard' Famennian conodont zonation. Late Famennian miospore assemblages from Euramerica are similar to those from western Gondwana, though some distinctive taxa are restricted to the latter. However, some of the index species of the European-based miospore zonation are relatively rare in both western Euramerica (USA) and western Gondwana (Bolivia / Brazil) compared to eastern Euramerica (Europe).