Abstract

The main facies distribution in the Devonian of western Europe is shown to result from the broad geographical and morphological pattern created by late-Caledonian (late Silurian to early Devonian) movements. Within the area of the Caledonian mountain chain a continental, molasse-like facies prevails (Old Red Sandstone facies). The general features of the succession in the marine realm are essentially controlled by the presence or absence of nearby emergent areas acting as source areas for the supply of terrigenous material, particularly in early Devonian times. The resulting lithological and faunal differences roughly correspond with the distinction between the Rhenish and the Bohemian (or Hercynian) facies. Factors taken into account by previous authors to explain the differences between these two marine facies (e.g. well-aerated vs. restricted conditions, or near-shore vs. off-shore deposition) may be of local or even regional importance, but are of secondary importance in the broad continental picture.

The distinction between the Rhenish and the Bohemian facies has, moreover, been confused because previous explanations failed to distinguish between carbonate rocks of fundamentally different origin. Usually carbonate rocks have been considered to constitute a characteristic feature of the Bohemian facies, although in fact many of them are more closely related to the Rhenish facies. The growing importance of carbonates in the course of the Devonian in areas with a Rhenish Lower Devonian, is simply due to a decrease in terrigenous supply as the emergent source areas gradually disappeared.