TECTONIC AND CLIMATIC IMPLICATIONS OF CLASTIC DISPERSAL PATHWAYS IN THE PERMIAN MID-CONTINENT (Invited Presentation)

Over 30 new and previously acquired detrital-zircon analyses from silt- and sandstones of mid-continent North America record sediment dispersal during Permian time. These data are from units interpreted to record eolian-transported sediment ultimately deposited in either continental or shallow epeiric environments, and subordinate fluvial environments, and provide a comprehensive view of spatial and temporal changes in source regions during the Permian.

Data were collected by LA-ICPMS at the University of Arizona from randomly picked detrital zircon grains (n ranges from <100-200 per sample) from both outcrop and core. The U-Pb ages range from Archean to Permian (the approximate depositional age of the corresponding unit). The older Archean grains compose a small but consistent percentage of grains in the samples, and likely reflect either reworking of lower Paleozoic strata or erosion of emergent cratonal areas. The rare young grains (<300 Ma) appear to be volcanic zircons reflecting either coeval eruptions or reworking of penecontemporaneous ash beds. However, three age groups dominate (44-74%) the U-Pb spectra of zircons in all samples: 1) 1300-900 Ma (Grenville); 2) 790-570 Ma (Neoproterozoic); and 3) 480-360 Ma (early to mid Paleozoic). Finally, zircons with ages between 1600-1800 Ma, which likely represent the Yavapai-Mazatzal basement of the southwestern U.S., compose <15% of the total zircons in most samples.

The data suggest that the Central Pangaean Mountains were a dominant source of sediment to the mid-continent region during the Permian, which seems to be a pervasive conclusion from research on Permian strata ranging from the Appalachian basins to the western Pangaean margin. The Ancestral Rocky Mountains— cored by Yavapai-Mazatzal basement— were less important sources during Permian time.

Although the Central Pangaean Mountains, and in particular the Grenville-age basement rocks were a dominant source of sediment to the mid-continent, changes in the relative proportions of Neoproterozoic and Paleozoic grains relative to the Grenville-aged grains vary through time and space, presumably recording docking and uplift of various Appalachian terranes, overprinted by paleoclimatic controls through the Permian.