Paleogeography and Paleoclimate at the Deposition Sites of the Devonian Catskill and Old Red Facies
The reassembled circum–North Atlantic landmass was an equatorial one, characterized during the Middle and Late Devonian by deposition on it of the Catskill–Old Red continental facies on coastal plains and in intermontane basins. Shelf seas were contiguous with much of this landmass.

That part of the Catskill-Old Red coastal plain nearest the sea was marked by an indistinct shoreline, meandering streams, minor relief, and land slopes of 0.3 to 1.0 m per km (1 to 3 ft per mi). The more distal parts of the coastal plain were characterized by low-angle piedmont fans and, less commonly, by steeper sloped alluvial fans with braided streams and minor relief. Old Red facies developed also in intermontane basins as alluvial fans and lacustrine deposits associated with volcanic rocks.

Over much of the landmass, the climate was hot and semiarid. The most arid part was in the south where the formation of calcareous soils was enhanced, dipnoan fish aestivated, and evaporites formed in contiguous shelf seas. The northern part of the landmass, with its more even pattern of annual rainfall, supported a more extensive growth of plants and the formation of coal. On large parts of the coastal plains and intermontane basins, evaporation was great enough to lower the water table and thus provide a distinct zone of aeration in which sediments reddened.

Vegetation on the coastal plains and in intermontane basins was concentrated near shorelines and streams. Because grasses did not exist, floods were highly erosive and introduced large amounts of sediment onto the coastal plains and contiguous shelves.