Document Type
Article
Publication Date
4-2-2020
Publication Title
Geosphere
Abstract
Results of detrital-zircon analyses (U-Pb ages and initial Hf values, εHft) of Mississippian–Pennsylvanian sandstones in the Michigan, Illinois, and Forest City basins are remarkably similar to data for coeval sandstones in the Appalachian basin, indicating dispersal of sediment from the Appalachian orogen through the Appalachian basin to the eastern Midcontinent during the late Paleozoic. The similarities of results include matches of the two most prominent age groups (1300–950 Ma and 490–350 Ma), as well as matches of the less abundant age groups. Comparisons of the data are from observations of probability density plots and multidimensional scaling of U-Pb age data and of εHft values. Despite the dominance of an Appalachian signature in all samples, some samples contain grains with ages that suggest intermittent additional sources.
Four samples (three ranging in depositional age from Morrowan to Atokan–Desmoinesian in the Illinois basin, and one of Desmoinesian age in the Forest City basin), in addition to typical Appalachian age distributions, have prominent age modes between 768 and 525 Ma, corresponding in age to Pan-African/Brasiliano rocks in Gondwanan accreted terranes in the Appalachian orogen, suggesting intermittent dispersal from the Moretown terrane of the northern Appalachians.
Sandstones in the Appalachian basin and those in the Midcontinent basins have very few grains with ages that correspond to the Alleghanian orogeny in the Appalachian orogen. Nevertheless, three sandstones each in the Illinois basin and Forest City basin with depositional ages of 312–308 Ma have a few zircon grains in the age range of 321 ± 5 to 307 ± 4 Ma. The nearly identical crystallization and depositional ages suggest reworking at the depositional sites of air-fall volcanic ash from the Alleghanian orogen, rather than fluvial transport from the orogen.
The basal Pennsylvanian sandstones lap onto a regional unconformity around the northern rims of the Illinois and Forest City basins, suggesting sources for recycled grains. Along the northern edge of the Illinois basin, Ordovician sandstones beneath the unconformity may have contributed minor concentrations of Superior-age zircons in the basal Pennsylvanian sandstones. Basal Pennsylvanian sandstones in the Forest City basin lap onto Mississippian strata, suggesting possible recycling of zircons from eroded Mississippian sandstones.
Funding Source
Sample collecting and analyses have been funded by National Science Foundation award EAR-1304980 to Gehrels and Thomas. All analyses were conducted at the Arizona LaserChron Center with the support of NSF awards EAR-1338583 and EAR-1649254.
DOI
https://doi.org/10.1130/GES02152.1
Recommended Citation
William A. Thomas, George E. Gehrels, Kurt E. Sundell, Stephen F. Greb, Emily S. Finzel, Ryan J. Clark, David H. Malone, Brian A. Hampton, Mariah C. Romero; Detrital zircons and sediment dispersal in the eastern Midcontinent of North America. Geosphere 2020;; 16 (3): 817–843. doi: https://doi.org/10.1130/GES02152.1
Supplemental Table S1
ges02152_supptabs2.xlsx (70 kB)
Supplemental Table S2
ges02152_supptabs3.xlsx (12832 kB)
Supplemental Table S3
ges02152_supptabs4.xlsx (107 kB)
Supplemental Table S4
ges02152_supptabs5.xlsx (4907 kB)
Supplemental Table S5
ges02152_supptabs6.xlsx (107 kB)
Supplemental Table S6
ges02152_supptabs7.xlsx (26 kB)
Supplemental Table S7
Comments
This article was originally published in Geosphere (2020), 16 (3), 817–843. https://doi.org/10.1130/GES02152.1.
Gold Open Access: This paper is published under the terms of the CC-BY-NC license.