DETRITAL-ZIRCON POPULATIONS AND MISSISSIPPIAN–PERMIAN SEDIMENT DISPERSAL PATHWAYS IN EASTERN LAURENTIA

Sandstones from Upper Mississippian through Lower Permian in eastern Laurentia have distinctive detrital-zircon populations, which are grouped by ages of zircon-generating events in the provenance. Distributions of detrital-zircon populations suggest sediment dispersal pathways. New zircon analyses of 11 sandstone samples from the Illinois (KY) and Michigan (MI) intracratonic basins and the Appalachian foreland basin (KY, VA), along with published data, provide a regional perspective of sediment dispersal from the Appalachian orogen onto the eastern part of the Laurentian craton.

Zircons with ages of the Grenville orogen (1200–950 Ma) dominate all of the samples. Less abundant zircon ages correspond to the Superior (2400+ Ma), TransHudson-Penokean (1900–1800 Ma), Mazatzal-Yavapai-Central Plains (1800–1620 Ma), Granite-Rhyolite (1500–1320 Ma), and early Grenville (1320–1200 Ma) provinces of the Laurentian craton. Even less abundant zircon ages represent Iapetan synrift and/or accreted PanAfrican/Brasiliano terranes (750–530 Ma), which are indistinguishable by age; accreted TransAmazonian terranes (2200–1900 Ma); and unidentified sources (530–490 Ma, 1620–1500 Ma, and 2400–2200 Ma). Most samples have some zircons with ages of the Taconic (490–415 Ma) and Acadian (415–340 Ma) orogens; zircons with ages of the Alleghanian orogen (340–273 Ma) are very rare.

Mesoproterozoic and older zircons in Appalachian foreland synorogenic sandstones commonly are interpreted to record recycling from Neoproterozoic–Cambrian synrift or younger passive-margin strata in the Appalachian orogen; Grenville rocks in Appalachian basement massifs provide a first-cycle source. Greater concentrations of Paleoproterozoic–Archean zircons in some sandstones in the distal Appalachian foreland (in contrast to more proximal Appalachian sandstones) and in the Michigan and Illinois basins may reflect dispersal by large rivers from primary sources in the continental shield or recycling from sedimentary cover deposits around the shield. TransAmazonian, Taconic, and Acadian zircons in those same sandstones, however, indicate mixing from Appalachian sources. The paucity of Alleghanian zircons suggests time lag in unroofing, limited zircon production, and/or diversion of drainage from the orogenic hinterland.