The nature of subsidence in the Western Interior evolved in the Late Cretaceous from a contiguous (Sevier) foreland to partitioned (Laramide) basins coeval with an increase in long-wavelength “dynamic” subsidence. This evolution is interpreted by many as indicators of flat slab subduction. However, the timing and geographic location of changing subsidence mechanisms remains poorly documented. To better assess the geodynamic mechanisms responsible for this transition, we have mapped active elements versus time, including classic foredeeps, intra-basinal uplifts, long-wavelength subsidence, and local flexural wedges adjacent to rising Laramide structures. Criteria include isopachs, paleogeography, geohistory analysis, unconformities/exhumation, and sediment dispersal patterns.
The analysis identifies a continuous foredeep along the Sevier Thrust Front through the Santonian, but not subsequently. Long-wavelength “dynamic” subsidence in the basin commences in the Coniacian, but is spatially and temporally quite variable. Short-wavelength Laramide structures first begin growing in the Ceno-Turonian. The influence of Laramide uplifts increases over time, with associated flexures becoming a dominant subsidence mechanism by the Maastrichtian.
Thirteen flexural stratigraphic wedges, associated with both Sevier and Laramide uplifts, have been used to quantitatively model loads (uplift height/width) and effective elastic thicknesses (EET). EET is a measure of the integrated strength of the lithosphere. Results indicate that EET decreases over time, enhancing Laramide basin partitioning. The decrease in effective elastic thickness of the lithosphere is consistent with lithospheric weakening by the introduction of volatiles during flat slab subduction. Calculated Maastrichtian EET’s are consistent with modern EET, supporting the hypothesis that flat slab subduction preconditioned the lithosphere for subsequent Cenozoic tectonic and magmatic events. Large-scale petroleum system play elements are correlated with the distribution of these tectonic elements and associated subsidence. Examples include the Lance reservoir at Pinedale Field, Lewis source/seal in the Washakie Basin and the Niobrara source/reservoir in the Sand Wash, eastern Piceance and Denver Basins.
more »
« less
Effects of contemporaneous orogenesis on sedimentation in the Late Cretaceous Western Interior Basin, northern Utah and southwestern Wyoming
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.
more » « less- Award ID(s):
- 1824538
- NSF-PAR ID:
- 10361829
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Basin Research
- Volume:
- 34
- Issue:
- 1
- ISSN:
- 0950-091X
- Page Range / eLocation ID:
- p. 366-392
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The nature of subsidence in the Western Interior evolved in the Late Cretaceous from a contiguous (Sevier) foreland to partitioned (Laramide) basins coeval with an increase in long-wavelength “dynamic” subsidence. This evolution is interpreted by many as indicators of flat slab subduction. However, the timing and geographic location of changing subsidence mechanisms remains poorly documented. To better assess the geodynamic mechanisms responsible for this transition, we have mapped active elements versus time, including classic foredeeps, intra-basinal uplifts, long-wavelength subsidence, and local flexural wedges adjacent to rising Laramide structures. Criteria include isopachs, paleogeography, geohistory analysis, unconformities/exhumation, and sediment dispersal patterns. The analysis identifies a continuous foredeep along the Sevier Thrust Front through the Santonian, but not subsequently. Long-wavelength “dynamic” subsidence in the basin commences in the Coniacian, but is spatially and temporally quite variable. Short-wavelength Laramide structures first begin growing in the Ceno-Turonian. The influence of Laramide uplifts increases over time, with associated flexures becoming a dominant subsidence mechanism by the Maastrichtian. Thirteen flexural stratigraphic wedges, associated with both Sevier and Laramide uplifts, have been used to quantitatively model loads (uplift height/width) and effective elastic thicknesses (EET). EET is a measure of the integrated strength of the lithosphere. Results indicate that EET decreases over time, enhancing Laramide basin partitioning. The decrease in effective elastic thickness of the lithosphere is consistent with lithospheric weakening by the introduction of volatiles during flat slab subduction. Calculated Maastrichtian EET’s are consistent with modern EET, supporting the hypothesis that flat slab subduction preconditioned the lithosphere for subsequent Cenozoic tectonic and magmatic events. Large-scale petroleum system play elements are correlated with the distribution of these tectonic elements and associated subsidence. Examples include the Lance reservoir at Pinedale Field, Lewis source/seal in the Washakie Basin and the Niobrara source/reservoir in the Sand Wash, eastern Piceance and Denver Basins.more » « less
-
more » « less
Abstract Understanding the effects of flat slab subduction on mountain building, arc magmatism, and basin evolution is fundamental to convergent‐margin tectonics, with implications for potential feedbacks among geodynamic, magmatic, and surface processes. New stratigraphic and geochronological constraints on Cenozoic sedimentation and magmatism in the southern Central Andes of Argentina (31°S) reveal shifts in volcanism, foreland/hinterland basin development, sediment accumulation, and provenance as the retroarc region was structurally partitioned during slab flattening. Detrital zircon U‐Pb age distributions from the western (Calingasta basin), central (Talacasto and Albarracín basins), and eastern (Bermejo foreland basin) segments of the retroarc basin system preserve syndepositional volcanism and orogenic unroofing of multiple tectonic provinces. Initial shortening‐related exhumation of the Principal Cordillera at 24–17 Ma was recorded by the accumulation of distal eolian deposits bearing Oligocene–Eocene zircons from the Andean magmatic arc. The Calingasta basin chronicled volcanism and basement shortening in the Frontal Cordillera at ~17–11 Ma, as marked by an upward coarsening succession of fluvial to alluvial fan deposits with a sustained zircon U‐Pb age component that matches pervasive Permian‐Triassic bedrock in the hinterland. An ~450 km eastward inboard sweep of volcanism at 11 Ma coincided with the inception of flat slab subduction, and subsequent thin‐skinned shortening in the Precordillera fold‐thrust belt that exhumed wedge‐top deposits and induced cratonward (eastward) advance of flexural subsidence into the Bermejo foreland basin. This foreland basin was structurally partitioned as basement uplifts of the Sierras Pampeanas transformed a fluvial megafan sediment routing network into smaller isolated alluvial fan systems fed by adjacent basement blocks.
-
more » « less
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.
-
more » « less
Abstract Crystalline basement rocks of southwestern Montana have been subjected to multiple tectonothermal events since ∼3.3 Ga: the Paleoproterozoic Big Sky/Great Falls orogeny, Mesoproterozoic extension associated with Belt‐Purcell basin formation, Neoproterozoic extension related to Rodinia rifting, and the late Phanerozoic Sevier‐Laramide orogeny. We investigated the long‐term (>1 Ga), low‐temperature (erosion/burial within 10 km of the surface) thermal histories of these tectonic events with zircon and apatite (U‐Th)/He thermochronology. Data were collected across nine sample localities (
n = 55 zircon andn = 26 apatite aliquots) in the northern and southern Madison ranges, the Blacktail‐Snowcrest arch, and the Tobacco Root uplift. Our zircon (U‐Th)/He data show negative trends between single aliquot date and effective uranium (a radiation damage proxy), which we interpreted with a thermal history model that considers the damage‐He diffusivity relationship in zircon. Our model results for these basement ranges show substantial cooling from temperatures above 400°C to near surface conditions between 800 and 510 Ma. Subsequent Phanerozoic exhumation culminated by ∼75 Ma. Late Phanerozoic cooling is coincident with along‐strike Sevier belt thin‐skinned thrusting in southeastern Idaho, and older than exhumation in basement‐involved uplifts of the Wyoming Laramide province. Our long‐term, low‐temperature thermal record for these southwestern Montana basement ranges shows that: (a) these basement blocks have experienced multiple episodes of upper crustal exhumation and burial since Archean time, possibly influencing Phanerozoic thrust architecture and (b) the late Phanerozoic thick‐skinned thrusting recorded by these rocks is among the earliest thermochronologic records of Laramide basement‐involved shortening and was concomitant with Sevier belt thin‐skinned thrusting.
