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Abstract Middle to Upper Jurassic strata in the Paradox Basin and Central Colorado trough (CCT; southwestern United States) record a pronounced change in sediment dispersal from dominantly aeolian deposition with an Appalachian source (Entrada Sandstone) to dominantly fluvial deposition with a source in the Mogollon and/or Sevier orogenic highlands (Salt Wash Member of the Morrison Formation). An enigmatic abundance of Cambrian (ca. 527–519 Ma) grains at this provenance transition in the CCT at Escalante Canyon, Colorado, was recently suggested to reflect a local sediment source from the Ancestral Front Range, despite previous interpretations that local basement uplifts were largely buried by Middle to Late Jurassic time. This study aims to delineate spatial and temporal patterns in provenance of these Jurassic sandstones containing Cambrian grains within the Paradox Basin and CCT using sandstone petrography, detrital zircon U-Pb geochronology, and detrital zircon trace elemental and rare-earth elemental (REE) geochemistry. We report 7887 new U-Pb detrital zircon analyses from 31 sandstone samples collected within seven transects in western Colorado and eastern Utah. Three clusters of zircon ages are consistently present (1.53–1.3 Ga, 1.3–0.9 Ga, and 500–300 Ma) that are interpreted to reflect sources associated with the Appalachian orogen in southeastern Laurentia (mid-continent, Grenville, Appalachian, and peri-Gondwanan terranes). Ca. 540–500 Ma zircon grains are anomalously abundant locally in the uppermost Entrada Sandstone and Wanakah Formation but are either lacking or present in small fractions in the overlying Salt Wash and Tidwell Members of the Morrison Formation. A comparison of zircon REE geochemistry between Cambrian detrital zircon and igneous zircon from potential sources shows that these 540–500 Ma detrital zircon are primarily magmatic. Although variability in both detrital and igneous REE concentrations precludes definitive identification of provenance, several considerations suggest that distal sources from the Cambrian granitic and rhyolitic provinces of the Southern Oklahoma aulacogen is also likely, in addition to a proximal source identified in the McClure Mountain syenite of the Wet Mountains, Colorado. The abundance of Cambrian grains in samples from the central CCT, particularly in the Entrada Sandstone and Wanakah Formation, suggests northwesterly sediment transport within the CCT, with sediment sourced from Ancestral Rocky Mountains uplifts of the southern Wet Mountains and/or Amarillo-Wichita Mountains in southwestern Oklahoma. The lack of Cambrian grains within the Paradox Basin suggests that the Uncompahgre uplift (southwestern Colorado) acted as a barrier to sediment transport from the CCT. 

This paper explores an inverse approach to the problem of characterizing sediment sources' (“source” samples) age distributions based on samples from a particular depocenter (“sink” samples) using non-negative matrix factorization (NMF). It also outlines a method to determine the optimal number of sources to factorize from a set of sink samples (i.e., the optimum factorization rank). We demonstrate the power of this method by generating sink samples as random mixtures of known sources, factorizing them, and recovering the number of known sources, their age distributions, and the weighting functions used to generate the sink samples. Sensitivity testing indicates that similarity between factorized and known sources is positively correlated to 1) the number of sink samples, 2) the dissimilarity among sink samples, and 3) sink sample size. Specifically, the algorithm yields consistent, close similarity between factorized and known sources when the number of sink samples is more than ∼3 times the number of source samples, sink data sets are internally dissimilar (cross-correlation coefficient range >0.3, Kuiper V value range >0.35), and sink samples are well-characterized (>150–225 data points). However, similarity between known and factorized sources can be maintained while decreasing some of these variables if other variables are increased. Factorization of three empirical detrital zircon U–Pb data sets from the Book Cliffs, the Grand Canyon, and the Gulf of Mexico yields plausible source age distributions and weights. Factorization of the Book Cliffs data set yields five sources very similar to those recently independently proposed as the primary sources for Book Cliffs strata; confirming the utility of the NMF approach. The Grand Canyon data set exemplifies two general considerations when applying the NMF algorithm. First, although the NMF algorithm is able to identify source age distribution, additional geological details are required to discriminate between primary or recycled sources. Second, the NMF algorithm will identify the most basic elements of the mixed sink samples and so may subdivide sources that are themselves heterogeneous mixtures of more basic elements into those basic elements. Finally, application to a large Gulf of Mexico data set highlights the increased contribution from Appalachian sources during Cretaceous and Holocene time, potentially attributable to drainage reorganization. Although the algorithm reproduces known sources and yields reasonable sources for empirical data sets, inversions are inherently non-unique. Consequently, the results of NMF and their interpretations should be evaluated in light of independent geological evidence. The NMF algorithm is provided both as MATLAB code and a stand-alone graphical user interface for Windows and macOS (.exe and .app) along with all data sets discussed in this contribution. 

Abstract The Ancestral Rocky Mountains system consists of a series of basement-cored uplifts and associated sedimentary basins that formed in southwestern Laurentia during Early Pennsylvanian–middle Permian time. This system was originally recognized by aprons of coarse, arkosic sandstone and conglomerate within the Paradox, Eagle, and Denver Basins, which surround the Front Range and Uncompahgre basement uplifts. However, substantial portions of Ancestral Rocky Mountain–adjacent basins are filled with carbonate or fine-grained quartzose material that is distinct from proximal arkosic rocks, and detrital zircon data from basins adjacent to the Ancestral Rocky Mountains have been interpreted to indicate that a substantial proportion of their clastic sediment was sourced from the Appalachian and/or Arctic orogenic belts and transported over long distances across Laurentia into Ancestral Rocky Mountain basins. In this study, we present new U-Pb detrital zircon data from 72 samples from strata within the Denver Basin, Eagle Basin, Paradox Basin, northern Arizona shelf, Pedregosa Basin, and Keeler–Lone Pine Basin spanning ∼50 m.y. and compare these to published data from 241 samples from across Laurentia. Traditional visual comparison and inverse modeling methods map sediment transport pathways within the Ancestral Rocky Mountains system and indicate that proximal basins were filled with detritus eroded from nearby basement uplifts, whereas distal portions of these basins were filled with a mix of local sediment and sediment derived from marginal Laurentian sources including the Arctic Ellesmerian orogen and possibly the northern Appalachian orogen. This sediment was transported to southwestern Laurentia via a ca. 2,000-km-long longshore and aeolian system analogous to the modern Namibian coast. Deformation of the Ancestral Rocky Mountains slowed in Permian time, reducing basinal accommodation and allowing marginal clastic sources to overwhelm the system. 

Abstract Three drivers of subsidence are recognized in the Western Interior Basin: Mesozoic–early Cenozoic flexure adjacent to the thin‐skinned, eastward propagating Sevier Orogeny, Late Cretaceous–Eocene flexure associated with thick‐skinned Laramide Uplifts and Late Cretaceous dynamic subsidence. This study combines outcrop lithofacies, palaeocurrent measurements, detrital zircon geochronology, biostratigraphy, stratigraphic correlations and isopach maps of Coniacian–Maastrichtian (89–66 Ma) units to identify these subsidence mechanisms impact on basin geometry and stratigraphic architecture in the northern Utah to southwestern Wyoming segment of the North American Cordillera. Detrital zircon maximum depositional ages and biostratigraphy support that the Maastrichtian Hams Fork Conglomerate was deposited above the Moxa unconformity in the wedgetop and foredeep depozones. The Moxa unconformity underlies the progradational Ericson Formation in the distal foredeep. The Hams Fork, however, is younger than the Ericson Formation, and instead equivalent to upper Almond Formation. Therefore, the hiatus associated with the Moxa unconformity continued for several million years longer in the fold belt and proximal basin than in the distal foredeep, with Ericson Formation‐equivalent strata onlapping the Moxa unconformity towards the west. Regional thickness patterns record and constrain the timing of the transition from Sevier to Laramide‐style tectonic regimes. From 88 to 83 Ma (upper Baxter Formation) a westward‐thickening stratigraphic wedge characterized the foredeep developed by lithospheric flexure by thrust‐belt loading. Nevertheless, the presence of >500 m of subsidence >200 km from the thrust front suggests a long‐wavelength subsidence mechanism consistent with dynamic subsidence. By 83 Ma (Blair Formation) the long‐wavelength depocentre shifted away from the thrust belt, with no evidence of a Sevier foredeep. This depocentre continued migrating eastward during the early‐mid Campanian (ca. 81–77 Ma). The late Campanian–Maastrichtian (ca. 74–66 Ma) is marked by narrow sedimentary wedges adjacent to the Wind River, Granite and Uinta Mountain uplifts and attributed to flexural loading by Laramide deformation. 

Abstract The timing of crustal thickening in the northern Central Andean Plateau (CAP), at 13–20°S, and its relationship to surface uplift is debated. Zircon qualitatively records crustal thickness as its trace element chemistry is controlled by the growth of cogenetic minerals and relative uptake of light and heavy Rare Earth Elements. Jurassic to Neogene zircons from volcanic rocks, sandstones, and river sediments reveal shifts in trace element ratios suggesting major crustal thickening at 80–55 Ma and 35–0 Ma, coincident with high‐flux magmatism. An intervening magmatic lull due to shallow subduction obscures the magmatic record from 55 to 35 Ma during which thickening continued via crustal shortening. Protracted thickening since the Late Cretaceous correlates with early elevation gain of the CAP western margin, but contrasts with Miocene establishment of near modern elevation in the northern CAP and the onset of hyperaridity along the Pacific coast, highlighting their complex spatial and temporal relationship. 

Abstract This paper investigates the causes of the Late Cretaceous transition from “Sevier” to “Laramide” orogenesis and the spatial and temporal evolution of effective elastic thickness (EET) of the North American lithosphere. We use a Monte Carlo flexural model applied to 34 stratigraphic profiles in the Laramide province and five profiles from the Western Canadian Basin to estimate model parameters which produce flexural profiles that match observed sedimentary thicknesses. Sediment thicknesses come from basins from New Mexico to Canada of Cenomanian–Eocene age that are related to both Sevier and Laramide crustal loads. Flexural models reveal an east‐to‐west spatial decrease in EET in all time intervals analyzed. This spatial decrease in EET may have been associated with either bending stresses associated with the Sevier thrust belt, or increased proximity to attenuated continental crust at the paleocontinental margin. In the Laramide province (i.e., south of ~48°N) there was a coeval, regional decrease in EET between the Cenomanian–Santonian (~98–84 Ma) and the Campanian–Maastrichtian (~77–66 Ma), followed by a minor decrease between the Maastrichtian and Paleogene. However, there was no decrease in EET in the Western Canada Basin (north of ~48°N), which is consistent with a lack of Laramide‐style deformation or flat subduction. We conclude that the regional lithospheric weakening in the late Santonian–Campanian is best explained by hydration of the North American lithosphere thinned by bulldozing by a shallowly subducting Farallon plate. The weakening of the lithosphere facilitated Laramide contractional deformation by focusing end‐loading stresses associated with flat subduction. Laramide deformation in turn may have further reduced EET by weakening the upper crust. Finally, estimates of Campanian–Maastrichtian and Paleogene EET are comparable to current estimates indicating that the modern distribution of lithospheric strength was achieved by the Campanian in response to flat subduction. 

Abstract Between 81°30ʹE and 83°E, the Himalayan range's “perfect” arcuate shape is interrupted by an embayment. We hypothesize that thrust geometry and duplexing along the megathrust at midlower‐crustal depths play a leading role in growth of the embayment as well the southern margin of the Tibetan plateau. To test this hypothesis, we conducted thermokinematic modeling of published thermochronologic data from the topographic and structural embayment in the western Nepal Himalaya to investigate the three‐dimensional geometry and kinematics of the megathrust at midlower‐crustal depths. Models that can best reproduce observed cooling ages suggest that the megathrust in the western Nepal Himalaya is best described as two ramps connected by a long flat that extends further north than in segments to the east and west. These models suggest that the high‐slope zone along the embayment lies above the foreland limb of an antiformal crustal accretion zone on the megathrust with lateral and oblique ramps at midlower‐crustal depths. The lateral and oblique ramps may have initiated by ca. 10 Ma. This process may have controlled along‐strike variation in Himalayan‐plateau growth and therefore development of the topographic embayment. Finally, we analyze geological and morphologic features and propose an evolution model in which landscape and drainage systems across the central‐western Himalaya evolve in response to crustal accretion at depth and the three‐dimensional geometry of the megathrust. Our work highlights the importance of crustal accretion at different depths in orogenic‐wedge growth and that the midlower crustal accretion determines the location of plateau edge.