Palynology, dacryoconarids and the lower Eifelian (Middle Devonian) Basal Choteč Event: case studies from the Prague and Appalachian basins
Abstrakt
During recent studies of the Basal Choteč Event (BCE) at its type locality (Na Škrábku Quarry at Choteč Village, Prague Basin of the Barrandian area, Czech Republic) and selected sections of time-equivalent strata in the Appalachian Basin (USA), palynomorphs and dacryoconarids have proven responsive to changing environmental conditions. To date, there have been no detailed reports of dacryoconarids from the Appalachian Basin (AB) and none of palynomorphs from Bohemia or elsewhere.
Palynomorphs of the Barrandian area comprise a more or less monospecific assemblage of prasinophycean algae interpreted here to represent an ecological epibole. Mazuelloids and scolecodonts are also present, whereas acritarchs, spores and chitinozoans are accessory components.
Prasinophytes also predominate in coeval strata of the Appalachian Basin's northern region, whereas a chitinozoan species and morphotypes possibly assignable to fungi abound in the central region. Scolecodonts and acritarchs are regionally variable throughout the interval.
The former are rare in the central region of the basin but are ubiquitous and sometimes abundant in the northern region. Dacryoconarids of the Appalachian Basin are also regionally variable.
The dacryoconarid fauna of the northern region, however, descended from a previous Emsian fauna that diversified during the BCE and subsequently functioned as the foundation of the upper Eifelian faunas, while dacryoconarids of the central region represent an incursion epibole of Old World forms that entered the basin at the onset of the event interval and became extinct at its close. Among the dacryoconarids there are key taxa that serve as excellent biostratigraphic markers to identify the BCE in the Appalachian Basin.
In both the Prague and Appalachian basins, the BCE occurs near the maximum transgression of the Devonian Ic sequence. Additional faunal changes are found in the Appalachian Basin leading up to the main body of the event.