Detrital zircon record of magmatism and sediment dispersal across the North American Cordilleran arc system (28–48°N)

The Bell River hypothesis proposes that an ancestral, transcontinental river occupied much of northern North America during the Cenozoic Era, transporting water and sediment from the North American Cordillera to the Saglek Basin on the eastern margin of the Labrador Sea. To explore this hypothesis and reconstruct Cenozoic North American drainage patterns, we analyzed detrital zircon grains from the Oligocene−Miocene Mokami and Saglek formations of the Saglek Basin and Oligocene−Miocene fluvial conglomerates in the Great Plains of western Canada. U-Pb detrital zircon age populations in the Mokami and Saglek formations include clusters at <250 Ma, 950−1250 Ma, 1600−2000 Ma, and 2400−3200 Ma. Detrital zircons with ages of <250 Ma were derived from the North American Cordillera, supporting the transcontinental Bell River hypothesis. Oligocene−Miocene fluvial strata in western Canada contain detrital zircon age populations similar to those in the Saglek Basin and are interpreted to represent the western headwaters of the ancient Bell River drainage. Strontium-isotope ratios of marine shell fragments from the Mokami and Saglek formations yielded ages between 25.63 and 18.08 Ma. The same shells have εNd values of −10.2 to −12.0 (average = −11.2), which are consistent with values of Paleozoic strata in western North America but are more radiogenic than the modern Labrador Current, Labrador Sea Water, and North Atlantic Deep Water values (εNd ∼−12 to −25). As a freshwater source, the existence and termination of the Bell River may have been important for Labrador Sea circulation, stratification, and chemistry.

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Early Pennsylvanian sediment routing to the Ouachita Basin (southeastern United States) and barriers to transcontinental sediment transport sourced from the Appalachian orogen based on detrital zircon U-Pb and Hf analysis

Geosphere ◽

10.1130/ges02408.1 ◽

2021 ◽

Author(s):

Isaac J. Allred ◽

Michael D. Blum

Keyword(s):

United States ◽

Detrital Zircon ◽

Eastern United States ◽

Ouachita Mountains ◽

Sediment Dispersal ◽

Continental Scale ◽

The North ◽

Sediment Routing ◽

Proximal Site ◽

Central United States

Carboniferous sediment dispersal from the Appalachian orogenic system (eastern United States) has become a topic of widespread interest. However, the actual pathways for continental-scale, east-to-west sediment transfer have not been documented. This study presents detrital zircon (DZ) U-Pb ages and Hf isotopic values from the Lower Pennsylvanian (Morrowan) Jackfork Group and Johns Valley Shale of the synorogenic Ouachita deepwater basin of Arkansas to document provenance and delineate the likely sediment-routing systems within the broader context of sediment dispersal across Laurentia. Twelve (12) DZ U-Pb age distributions are interpreted to indicate that sediments were derived from the Appalachians to the east and northeast, as well as the midcontinent region to the north. All samples display prominent ca. 500– 400 Ma, 1250–950 Ma, 1550–1300 Ma, and 1800–1600 Ma grains, consistent with ultimate derivation from the Appalachian, Grenville, Midcontinent, and Yavapai-Mazatzal provinces. DZ Hf values obtained from the Ouachita Basin are similar to published Hf values from Pennsylvanian samples in the Appalachian and Illinois Basins. Age distributions are generally consistent for seven samples collected from the Jackfork Group and Johns Valley Shale in the southern Ouachita Mountains through ~2400 m of stratigraphic section and are interpreted to indicate little change in provenance during the Morrowan in this part of the system. However, samples from the most northern and most source-proximal site in Little Rock, Arkansas, exhibit modest percentages of Appalachian ages and elevated contributions of Yavapai-Mazatzal ages when compared with samples collected farther to the south and west. We interpret differences between DZ signatures to indicate distinct sediment-routing pathways to the Ouachita Basin. We infer the strong Appalachian and Grenville signals to represent an axial system flowing through the Appalachian foredeep, whereas the more diverse signals represent a confluence of rivers from the northeast through the backbulge of southern Illinois and western Kentucky and from the north across the Arkoma shelf. Collectively, the Ouachita Basin represents a terminal sink for sediments derived from much of the eastern and central United States.

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Detrital zircon geochronology and provenance of the southeastern Yukon–Tanana terrane

Canadian Journal of Earth Sciences ◽

10.1139/e06-105 ◽

2007 ◽

Vol 44 (3) ◽

pp. 297-316 ◽

Cited By ~ 26

Author(s):

JoAnne Nelson ◽

George Gehrels

Keyword(s):

North American ◽

Detrital Zircon ◽

Ocean Basin ◽

Detrital Zircons ◽

Late Paleozoic ◽

Data Set ◽

North American Continent ◽

The North ◽

Two Samples ◽

Formed Part

Two samples of late Paleozoic grit and Late Mississippian quartzite–chert conglomerate collected from southeastern Yukon–Tanana terrane (YTT) — a composite thrust sheet resting structurally above North American parautochthonous strata and intervening imbricate sheets of the late Paleozoic oceanic Slide Mountain terrane — yielded, respectively, 89 and 74 concordant or nearly concordant (<20% discordant) U–Pb ages on single detrital zircons. They provide constraints on the provenance of this allochthonous pericratonic terrane. Zircons in the grit range from 1770 to 2854 Ma, with a well-defined Early Proterozoic peak between 1800 and 2100 Ma. Precambrian zircons in the conglomerate also show a dominant peak between 1800 and 2100 Ma and smaller peaks between 2200 and 3200 Ma, with a few older grains, and younger grains with ages of 998, 1219, 1255, 1256, and 1417 Ma. The conglomerate also yielded three Devonian grains, with ages of 366 ± 23, 373 ± 12, and 379 ± 23 Ma. Their ages are approximately coeval with the oldest felsic to intermediate arc- and rift-related magmatism in the YTT. The age spectra from southeastern YTT units compare closely with those from Mississippian and older pericratonic units in the Coast Mountains, confirming correlations previously made on lithologic grounds. They also strongly resemble detrital zircon populations from craton-derived Paleozoic units of the northern North American autochthon. This robust U–Pb data set lends support to the idea that YTT once formed part of the outer, active margin of the North American continent, prior to Mississippian rifting and marginal ocean basin development.

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