Detrital zircon geochronology from the Bighorn Basin, Wyoming, USA: Implications for tectonostratigraphic evolution and paleogeography

Abstract

Tectonostratigraphic assemblages record phases of basin history during which the fundamental controls of tectonic setting, sub sidence style, and basin geometry are relatively similar. Because these fundamental controls, in combination with climate and eustasy, infl uence paleogeography and sediment-dispersal patterns, they should also yield similar patterns, or facies, of detrital zircon age spectra . Such age-distribution patterns should be documented on the craton in order to make meaningful comparisons to sedimentary rocks from suspect terranes along continental margins. The Rocky Mountains of western North America provide excellent outcrops of sedimentary rocks that record >500 m.y. of tectonostratigraphic evolution. One such Phanerozoic section is exposed along the margins of the Bighorn Basin in northwest Wyoming, from which we report over 4000 U/Th/Pb detrital zircon ages from 48 samples that span a stratigraphic interval from the Middle Cambrian Flathead Sandstone through the Eocene Willwood Formation. These data provide one of the most complete records of detrital zircon age patterns from this part of cratonic North America.The stratigraphic record of the Bighorn Basin is subdivided into four tectonostratigraphic assemblages (TSA1-TSA4). These assemblages record an initial passive margin, followed by a transition to a convergent margin, followed by a marine-dominated retroarc foreland basin, followed by a retroarc foreland segmented by local basement uplifts. This tectonostratigraphic architecture is expressed as four, fi rst-order patterns within the detrital zircon age distributions.TSA1 represents a Paleozoic-Triassic proximal continental margin assemblage dominated by Proterozoic zircons with abundant grains in the 1600-1950 Ma range, a Grenville population at ca. 1100 Ma, and a Phanerozoic population at ca. 420 Ma. TSA2 is a transitional assemblage associated with the Jurassic-Early Cretaceous organization of a west-facing convergent margin and Cordilleran orogen. The TSA2 detrital zircon age distribution is characterized by the appearance of Mesozoic grains, age peaks at ca. 420 and 600 Ma, and a dominant population of Grenville (1.0-1.1 Ga) grains with a suite of Proterozoic grains diminishing in abundance as age increases to 1.9 Ga. TSA3 sedimentary rocks were deposited in the Cretaceous Interior Seaway in a retroarc foreland basin and are dominated by zircons for which ages are close to the depositional age of the strata, refl ecting input from the active Idaho Batholith and Sierran segments of the Cordilleran magmatic arc. The older zircon fractions from TSA3 sedimentary rocks are characterized by a dominant detrital zircon age peak at 1.7-1.8 Ga, which probably refl ects reworking of Belt Supergroup metasedimentary rocks from the northwest into the Cretaceous foreland, based on regional paleogeographic patterns. TSA4 refl ects the phase of basin fi ll associated with Paleogene structural segmentation of the retroarc foreland during the Laramide orogeny. Detrital zircon age spectra from this a...

A Late Jurassic to Early Cretaceous record of orogenic wedge evolution in the Western Interior basin, USA and Canada

“…The distribution of zircon populations is consistent with recycling of sedimentary strata uplifted along the Mogollon highlands and incipient Cordilleran foldthrust belt in the southwestern United States ( Fig. 7; Dickinson andGehrels, 2008a, 2009b;Leier and Gehrels, 2011;Laskowski et al, 2013;May et al, 2013). Group 1 samples are also characterized by a Jurassic detrital zircon population from primary igneous sources in the Cordillera (Fig.…”

“…Therefore, to preserve Mesozoic-dominated detrital zircon spectra in the foreland, rivers that supplied sediment to the Western Interior basin from the magmatic hinterland would need to have traversed the fold-thrust belt without incorporating detrital zircon grains from pre-foreland sedimentary strata, which in aggregate yield diverse detrital zircon spectra (Fig. 7) (Ross and Villeneuve, 2003;Dickinson and Gehrels, 2009b;May et al, 2013;Gehrels and Pecha, 2014;Golding et al, 2015). Aerial delivery of Early Cretaceous zircon to the basin is possible or even probable; however, most of the zircon in these samples is Jurassic in age, supporting an interpretation that fluvial sediment routing was an important process (Figs.…”

“…Texturally, framework grains of the Swift, Morrison, and Kootenai Formations have been reported as round to subround, which supports the hypothesis of second-cycle deposition of these units (Ballard, 1966). Given the limitations of this data set, it is difficult to rule out these local sources; however, north-directed paleoflow for the Swift, Morrison, and Cut Bank units, and the continuity of similar Morrison Formation (Dickinson and Gehrels, 2008a;May et al, 2013) and Early Cretaceous (Leier and Gehrels, 2011) detrital zircon spectra with samples south of the Great Falls area support southern provenance as most likely. The Sunburst Member is unique in that it is characterized by an average paleoflow direction to the west, which is difficult to reconcile with detrital zircon spectra that suggest a source area to the south (Fig.…”

Detrital zircons from Cretaceous midcontinent strata reveal an Appalachian Mountains–Cordilleran foreland basin connection

“…Paleocurrent indicators and provenance studies from Albian and Cenomanian strata in the Bighorn Basin demonstrate that the development of the foldand-thrust belt created new sediment sources and increased sediment flux from the western margin of the evolving Cordilleran foreland basin (DeCelles, 2004). Existing detrital zircon data from the Bighorn Basin provide evidence that most of the sediment in the foredeep was derived from the adjacent fold-and-thrust belt (May et al, 2013).…”

Pairwise sample comparisons and multidimensional scaling of detrital zircon ages with examples from the North American platform, basin, and passive margin settings

“…Dissimilarities in abundances of different age components in any population of zircon grains potentially reflect changes in the tectonic history of basins or of variations in climate and sea level, all of which possibly impact paleogeography and sediment dispersal patterns. May et al (2013) compiled and qualitatively interpreted zircon age data from Phanerozoic units exposed in the Bighorn Basin of Wyoming to better understand the tectonostratigraphic evolution of that region. Based on 4104 U-Pb detrital zircon ages from 44 samples, May et al subdivided Upper Mississippian through Paleocene units into four "tectonostratigraphic assemblages" based on perceived patterns in sample zircon age frequency distributions: (1) a Paleozoic-Triassic proximal continental margin assemblage;…”