Late Paleoproterozoic Climate, Tectonics, and Metamorphism in the Southern Lake Superior Region and Proto–North America: Evidence from Baraboo Interval Quartzites

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to The Journal of Geology. A B S T R A C TRed, supermature quartzites of the Baraboo interval of the Lake Superior region contain detrital zircon that ranges in age from 1782 to 1712 Ma. Deposition clearly occurred after the geon 18 Penokean orogeny. These late Paleoproterozoic sedimentary rocks consist largely of quartz, kaolinite or pyrophyllite, and hematite; detrital feldspar and muscovite are rare or absent. Their Chemical Index of Alteration ranges from 96.8 to 98.6, among the most chemically mature clastic sediments in the geological record. The quartzites are underlain by mature, feldspar-free paleosols, accounting for the absence of feldspar in the overlying sediments and indicating the presence of first-cycle quartzose detritus. Such physical and chemical characteristics imply that late Paleoproterozoic deposition in the Lake Superior region occurred in a stable tectonic setting with subdued topographic relief in a warm, humid climate. Folding and low-grade metamorphism of the quartzites is thought to reflect ∼1630 Ma foreland deformation related to the Mazatzal orogeny. Younger hydrothermal alteration is widespread in the Baraboo and Sioux quartzites and, based on 40 Ar/ 39 Ar dating of low-temperature minerals, is attributed to the migration of fluids along permeable channels in response to the thermal effects of magmatism associated with the 1465 Ma Wolf River batholith. Much of the Paleo-and Mesoproterozoic crust of Proto-North America may have been affected by areally extensive, but stratigraphically restricted, hydrothermal alteration related to the influence of geon 14 transcontinental A-type granitic magmatism.

Low Mid-Proterozoic atmospheric oxygen levels and the delayed rise of animals

“…The Freedom Formation in the Midwest of the USA lies conformably above the Seeley Slate, which is above the Baraboo Quartzite (44). The Freedom Formation is at its maximum 300 meters thick and includes ferruginous shales, ferruginous cherts, and ironrich dolostones.…”

“…The mineralogy is relatively simple with the unit containing only quartz, dolomite, hematite, magnetite, and chlorite. The Baraboo Quartzite and Seeley Slate are both supermature sedimentary units deposited in a shallow marine environment adjacent to a rhyolitic/granitic landmass that had undergone intense and sustained tropical weathering (44). The youngest detrital zircons in the Baraboo Quartzite are 1710 Ma, providing a maximum age for the underlying unit (44).…”

“…The Baraboo Quartzite and Seeley Slate are both supermature sedimentary units deposited in a shallow marine environment adjacent to a rhyolitic/granitic landmass that had undergone intense and sustained tropical weathering (44). The youngest detrital zircons in the Baraboo Quartzite are 1710 Ma, providing a maximum age for the underlying unit (44). There are no direct constraints on the ages of the overlying units nor on the timing of regional metamorphism and folding.…”

The Great Grenvillian Sedimentation Episode: Record of Supercontinent Rodinia's assembly

“…Some of the thickest and most extensive of these dominantly terrestrial deposits occur above regionally extensive unconformities that are developed on the crystalline rocks of broad and stable Precambrian cratons (Eriksson and Donaldson, 1986). This period is marked by Earth's earliest examples of thick (sometimes exceeding 1000 m), widespread deposits of mature sandstone (mainly quartzarenite), many of which show evidence of deposition in broad, braided river channels (e.g., Athabasca Group of northern Saskatchewan, Ramaekers and Catuneanu, 2004), Dubawnt Supergroup of Thelon and Baker basins (Rainbird et al, 2003); Baraboo interval of north-central United States (Medaris et al, 2003(Medaris et al, , 2007; Roraima Supergroup of southern Venezuela (Santos et al, 2003); and the Huron Supergroup of south-central Canada , to name a just a few (North American examples located on Figure 29.2). These deposits contain a relatively high proportion of coarse, bedload material and there is little evidence of the existence of deep channels.…”

Remote sensing and GIS investigation of glacial features in the region of Devil's Lake State Park, South-Central Wisconsin, USA

“…1) is a doubly-plunging syncline comprised mostly of Precambrian quartzite (Defrates, 2007). The Baraboo and six correlative red quartzites are the remnants of a once vast clastic wedge that covered much of the southern margin of the Superior Province (Medaris et al, 2003). Detrital zircons obtained from the quartzite yield U/Pb ages that cluster around 1754, 1850 and 2550 Ma (Van Wyck and Norman, 2004).…”