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Global Devonian Geology
Paleoclimatic Indicators and Inferred Devonian Paleolatitudes of Euramerica
Paleolatitudinal inferences for Euramerica and adjacent continental blocks in the Devonian can be drawn from paleomagnetic, paleoclimatic, paleobiogeographic, and tectonic lines of evidence. The necessity for independent latitudinal tests in the Devonian is underscored by recent re-evaluation (Miller & Kent, 1986) of Catskill paleomagnetic data, heretofore the primary source of Late Devonian data for North America. Paleomagnetic latitudes shown on some published Devonian maps of Euramerica introduce notable climatic or biogeographic anomalies and need to be reconsidered.
Zonal climatic belts (humid equatorial, arid tropical, and humid temperate) are modified by land masses in potentially predictable ways (orographic and monsoonal effects), providing constraints on paleolatitudes. Our approach attempts to: 1) confine climate-sensitive sedimentary indicators to respective climatic belts; and 2) establish a temporally consistent pattern of continental migration across these belts. Resulting patterns are checked against independent paleobiogeographic and paleomagnetic data.
Devonian carbonate-evaporite facies occur over large areas of Euramerica and are constrained to a single arid belt at low latitudes. Two humid belts are delimited for the Middle and Late Devonian, separated by 35–40° of paleolatitude. The northern belt (Arctic Canada, Svalbard, and Urals) is interpreted as equatorial, where thick detrital sediments are associated in places with coal, bauxite, and thick local carbonates. The southern belt (eastern U.S.) is dominated by thick detrital sediments with minor carbonate and some coal; it probably was an orographic wet belt along the Acadians in warm temperate latitudes.
Placement of Devonian Euramerica (Laurussia) in the southern hemisphere has advantages for global paleogeography. There is room to position the Devonian evaporites of Siberia north of Euramerica in an arid climatic belt (5–35°N), instead of their anomalous position in temperate latitudes (30–70°N) shown on paleomagnetic-based maps. A major seaway separating Euramerica and Gondwana on some Devonian maps creates serious paleobiogeographic anomalies, particularly for Appalachian Realm faunas. Southern Euramerica should occupy a position close to northwest Gondwana in order to keep North and South American parts of the Appalachian Realm together, and to keep both separated from the coeval Old World Realm.
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