Both the surface processes associated with large intracontinental basins and their underlying geodynamic mechanisms remain unclear. Proposed models include flexural deformation due to orogenic loading, isostatic subsidence in response to lithosphere extension, and dynamic subsidence arising from sublithospheric mantle downwelling. Here we use forward landscape evolution modeling to quantitatively investigate the surface process response to various types of tectonic subsidence during intraplate sedimentation. We find that isostatic subsidence causes continuous accumulation of sediment through time with a largely stable pattern of fluvial drainage. In contrast, dynamic subsidence results in fast intraplate sedimentation followed by regional unconformities and continental‐scale reorganization of fluvial networks. Our quantitative simulations reveal that the traditional 1‐D isostatic backstripping approach may lead to erroneous estimates of the past tectonic subsidence from the preserved sedimentary records: for lithospheric elastic thickness (
- Award ID(s):
- 1554554
- NSF-PAR ID:
- 10325487
- Date Published:
- Journal Name:
- GSA Bulletin
- Volume:
- 133
- Issue:
- 1-2
- ISSN:
- 0016-7606
- Page Range / eLocation ID:
- 347 to 361
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract T eT e -
null (Ed.)Dynamic topography refers to the vertical deflection (i.e., uplift and subsidence) of the Earth’s surface generated in response to mantle flow. Although dynamic subsidence has been increasingly invoked to explain the subsidence and migration of depocenters in the Late Cretaceous North American Cordilleran foreland basin (CFB), it remains a challenging task to discriminate the effects of dynamic mantle processes from other subsidence mechanisms, and the spatial and temporal scales of dynamic topography is not well known. To unravel the relationship between sedimentary systems, accommodation, and subsidence mechanisms of the CFB through time and space, a high-resolution chronostratigraphic framework was developed for the Upper Cretaceous strata based on a dense data set integrating >600 well logs from multiple basins/regions in Wyoming, Utah, Colorado, and New Mexico, USA. The newly developed stratigraphic framework divides the Upper Cretaceous strata into four chronostratigraphic packages separated by chronostratigraphic surfaces that can be correlated regionally and constrained by ammonite biozones. Regional isopach patterns and shoreline trends constructed for successive time intervals suggest that dynamic subsidence influenced accommodation creation in the CFB starting from ca. 85 Ma, and this wave of subsidence increasingly affected the CFB by ca. 80 Ma as subsidence migrated from the southwest to northeast. During 100−75 Ma, the depocenter migrated from central Utah (dominantly flexural subsidence) to north-central Colorado (dominantly dynamic subsidence). Subsidence within the CFB during 75−66 Ma was controlled by the combined effects of flexural subsidence induced by local Laramide uplifts and dynamic subsidence. Results from this study provide new constraints on the spatio-temporal footprint and migration of large-scale (>400 km × 400 km) dynamic topography at an average rate ranging from ∼120 to 60 km/m.y. in the CFB through the Late Cretaceous. The wavelength and location of dynamic topography (subsidence and uplift) generated in response to the subduction of the conjugate Shatsky Rise highly varied through both space and time, probably depending on the evolution of the oceanic plateau (e.g., changes in its location, subduction angle and depth, and buoyancy). Careful, high-resolution reconstruction of regional stratigraphic frameworks using three-dimensional data sets is critical to constrain the influence of dynamic topography. The highly transitory effects of dynamic topography need to be incorporated into future foreland basin models to better reconstruct and predict the formation of foreland basins that may have formed under the combined influence of upper crustal flexural loading and dynamic subcrustal loading associated with large-scale mantle flows.more » « less
-
more » « less
Abstract The Lower Cretaceous Blackleaf Formation in southwestern Montana records sedimentation in the Idaho‐Montana retroforeland basin of the North American Cordillera. Regional‐scale sedimentology suggests that during Albian time southwestern Montana was partially flooded by an early marine incursion of the Western Interior Seaway during deposition of the Blackleaf Formation. We use sandstone petrography, large‐
n (n = 600) U‐Pb detrital zircon geochronology and mixture modelling to determine the provenance of these strata. Our analysis suggests three distinct provenance groups: Group 1 sandstones occur in the eastern region of the study area, are quartz‐rich and have zircon age‐probability peaks of ca. 110, 160, 420–450, 1050 and 1160 Ma; these sandstones match with a primarily Appalachian provenance. Group 2 sandstones occur in the western region of study area, are lithic‐rich and have peaks of ca. 110, 160, 1780, 1840, 1920, 2080 and 2700 Ma; the primary source for these sandstones was exhumed lower‐middle Palaeozoic strata from the Idaho sector of the Sevier belt. Group 3 sandstones occur in the western region of the study area, are lithic‐rich and have prominent peaks of ca. 115, 170, 430, 600, 1085, 1170, 1670 and 1790 Ma; the primary source for these sandstones was exhumed Triassic‐upper Palaeozoic strata from the Idaho sector of the Sevier belt. Our provenance data record a sharp change that coincides with the western shoreline of the seaway, and we infer that it may indicate the position of an irregular, submarine forebulge depozone influenced by dynamic subsidence during a period of reduced thrusting in the adjacent fold‐thrust belt. Albian‐aged sediments in southwestern Montana were delivered by rivers with headwaters in the Sevier belt as well as transcontinental river systems with headwaters in eastern North America. In southwestern Montana, west‐flowing transcontinental fluvial systems were flooded by the Western Interior Seaway as it encroached from the north. -
more » « less
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.
-
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
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1130/B35653.1
