Geochronology of Cambrian Sedimentary and Volcanic Rocks in the Illinois Basin: Defining the Illinois Aulacogen

Abstract

The Wabash #1 well, drilled for the Wabash CarbonSAFE Project and located in Vigo County, Indiana, USA, was drilled in early 2020 as a stratigraphic test well to characterize and evaluate the basal Cambrian Mt. Simon Sandstone for carbon dioxide storage (TD=8750 ft; 2667 m). The Wabash #1 well is located along the eastern flank of a newly interpreted Cambrian aulacogen that occurs in western Indiana and eastern Illinois. Here we present 938 new detrital zircon U-Pb ages (LA-ICPMS) from early Cambrian sandstones sampled near the base of the well. A basalt lava flow was penetrated at ~8530 ft (2600 m) and has an 40Ar/39Ar age of 525.03 +/- 1.10 Ma, which represents the first known Cambrian crust in the Illinois Basin. The two sandstone samples from beneath the basalt are dominated by zircons derived from the Midcontinent Granite-Rhyolite terrane. The sandstone samples from above the basalt reflect a mixture of these locally derived Mazatzal and Granite-Rhyolite terrane zircons, but also distal Archean, Grenville, and Yavapai zircons. Each sample has small numbers of Cambrian zircons, which is consistent with those in basal Cambrian sandstones in other deep wells to the west. These early Cambrian detrital zircons and early Cambrian age of the basalt, combined with sediment thickness patterns permit the interpretation of the Illinois aulacogen, which formed during the final stage of Rodinian rifting.

Cratonic basins as effective sediment barriers in continent-scale sediment routing systems of Paleozoic North America

“…The upper Paleozoic strata of the Michigan Basin have similar zircon signatures that support increased mixing associated with sediment bypass. Although it is possible that the Michigan Basin represents an anomaly of early Paleozoic sediment routing patterns in the US Midcontinent, a regional survey compiled from previously published data sets suggests that localized sediment routing systems may have been common throughout the continent prior to Alleghenian mountain building 3 , 5 , 14 – 16 , 40 . This is also consistent with observations of localized sedimentation patterns in Cambrian strata of the southwestern US along low-relief landforms following the Great Unconformity 58 .…”

“…However, the effect of cratonic basins, if any, on sediment routing systems during the early Paleozoic prior to these Appalachian orogenic events is mostly untested 15 , 16 and sediment routing reconstructions interpret much of the Midcontinent as zones of sediment bypass interpolating hundreds of kilometers across entire basins. Clastic units including the Mt.…”

Petrologic relationship between lamprophyres, carbonatites, and heavy rare‐earth element enriched breccias at Hicks Dome

“…The WIP in Illinois hosts igneous rocks including lamprophyre diatremes, sills, and dikes within the Reelfoot Rift and Rough Creek Grabens (Figure 1a), near Hicks Dome in Illinois and in western Kentucky (Bradbury & Baxter, 1992;Brock & Heyl Jr., 1961;Denny & Seid, 2014;Diller, 1885). These Illinois aulacogen-related structures formed during the Neoproterozoic-Cambrian rifting of Rodinia (Freiburg et al, 2020(Freiburg et al, , 2022. Episodic reactivation of basement faults deformed overlying Palaeozoic strata and produced one of the most structurally complex areas in the Appalachian-Ouchita foreland (Craddock et al, 2018).…”