Cross Section Along Line A-B of the Old Red Sandstone Continent
During the mid to late Devonian, North America, a part of the Old Red Sandstone supercontinent (Larussia), lay on the equator with the area east of the present Mississippi river mostly in the southern hemisphere. Most of North America lay under the Kaskaskia epicontinental sea.
Along the eastern margin (modern direction) the Kaskaskia sea deepened into the narrow Catskill foreland basin, before climbing up into the Acadian mountains. East of the Acadian mountains, and the Avalon terrane, is the Rheic ocean.
Acadian Climatic Patterns
The Acadian mountains were built when the Avalon terrane collided with the east coast as a hinterland. Note the suture in the cross section where Larussia and Avalone join. During the Devonian, eastern North America lay in the southern trade wind belt between 10-20 degrees south (Old Red Map). Winds blowing across the Rheic ocean picked up moisture, but were forced to rise when they hit the mountains. As the winds rose they cooled, formed clouds, and dumped all their moisture as rain and snow, a process called orographic rainfall. The trade winds that got over the mountain were dry and so the foreland Basin was in a rain shadow, resulting in an arid to semiarid climate. Or, it may have been monsoonal (heavy seasonal rains followed by many dry months.) Under these conditions the rivers feeding the clastic wedge and Kaskaskia sea may have been ephemeral, that is dry most of the year and flowing only with the occasional storms that brought heavy rain. Out in the Kaskaskia sea (Old Red Map) toward the equator and the doldrums (a zone of no winds) calm conditions prevailed.
Detail of Catskill Foreland Basin
Contributed by Lynn Fichter