Ordovician: Tectonics and Paleoclimate

During the Ordovician, most of the world's land was collected together in the super-continent Gondwana. Gondwana consisted of Southern Europe, Africa, South America, Antarctica, and Australia. Throughout the Ordovician, Gondwana moved towards the South Pole where it finally came to rest at the end of this period. In the Early Ordovician, North America roughly straddled the equator and almost all of that continent lay underwater. However, by the Middle Ordovician North America became land with a karst topography on exposed carbonate rocks that developed. Taconica, a tectonic highland, formed along the margin of eastern North America. Also at this time, Western and Central Europe were separated and located in the Southern Tropics; Europe shifted towards North America from higher to lower latitudes.

During the Middle Ordovician, uplifts took place in most of the areas that had been under shallow shelf seas. These uplifts are seen as the precursor to glaciation. Also during the Middle Ordovician, latitudinal plate motions appear to have taken place, including the northward drift of the Baltoscandian Plate (northern Europe). Increased sea floor spreading and ridge activity accompanied by volcanic activity occurred in the Llanvirnian. Ocean currents changed as a result of lateral continental plate motions causing the opening of the Atlantic ocean. Sea levels underwent regression and transgression globally. Because of sea level transgression, flooding of the Gondwana craton occurred as well as regional drowning which caused carbonate sedimentation to stop.

During the Ashgillian (Late Ordovician), a major glaciation centered in Africa occurred. Because of this global disturbance, oxygenation, ocean erosion, and a severe drop in sea level resulted. In addition, aggressive circulation, then shrinking, of tropical belts also resulted. This glaciation caused a dramatic regression of ocean waters which drained nearly all craton platforms. More specifically, this glaciation contributed to ecological disruption and mass extinctions. Nearly all conodonts disappeared in the North Atlantic Realm while only certain lineages became extinct in the Midcontinental Realm. Asaphoid larvae-bearing trilobites, echinoderms, brachiopods, bryozoans, graptolites, and chitinozoans also became extinct. The Atlantic Ocean closed as Europe moved towards North America. Climatic fluctuations were extreme as glaciation continued and became more extensive. Cold climates with floating marine ice developed as the maximum glaciation was reached.

For additional maps of the Ordovician world, visit the Ordovician page at the Paleogeography Through Geologic Time site by Dr. Ron Blakey of Northern Arizona University.

Read about the Ordovician Mass Extinction at the Hooper Virtual Paleontology Museum.

Find out more about the Ordovician paleontology and geology of North America at the Paleontology Portal.

C. Barnes & Z. Ji, 1993. A major conodont extinction event during the Early Ordovician within the Midcontinental realm. Paleogeography, Paleoclimatology, Paleoecology, pp. 37-47.

T. N. Koren, 1991. Evolutionary Crisis of the Ashgill Graptolites. Geological Survey of Canada, pp. 157-164

J. R. Laurie & B. D. Webby, 1992. Preliminary correlation of latest Cambrian to Early Ordovician sea level events in Australia and Scandinavia. Global Perspectives on Ordovician Geology, pp. 381-394.

J. D. Marshall, P. J. Brenchley, P. Mason, G. A. Wolff, R. A. Astini, L. Hints, & T. Meidla, 1997. Global Carbon Isotopic Events Associated with Mass Extinction and Glaciation in the Late Ordovician. Paleogeography, Paleoclimatology, Paleoecology, pp. 195-210.