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Abstract Mantle‐induced dynamic topography (i.e., subsidence and uplift) has been increasingly recognized as an important process in foreland basin development. However, characterizing and distinguishing the effects (i.e., location, extent and magnitude) of dynamic topography in ancient foreland basins remains challenging because the spatio‐temporal footprint of dynamic topography and flexural topography (i.e., generated by topographic loading) can overlap. This study employs 3D flexural backstripping of Upper Cretaceous strata in the central part of the North American Cordilleran foreland basin (CFB) to better quantify the effects of dynamic topography. The extensive stratigraphic database and good age control of the CFB permit the regional application of 3D flexural backstripping in this basin for the first time. Dynamic topography started to influence the development of the CFB during the late Turonian to middle Campanian (90.2–80.2 Ma) and became the dominant subsidence mechanism during the middle to late Campanian (80.2–74.6 Ma). The area influenced by >100 m dynamic subsidence is approximately 400 by 500 km, within which significant (>200 m) dynamic subsidence occurs in an irregular‐shaped (i.e., lunate) subregion. The maximum magnitude of dynamic subsidence is 300 ± 100 m based on the 80.2–74.6 Ma tectonic subsidence maps. With the maximum magnitude of dynamic uplift being constrained to be 200–300 m, the gross amount of dynamic topography in the Late Cretaceous CFB is 500–600 m. Although the location of dynamic subsidence revealed by tectonic subsidence maps is generally consistent with isopach map trends, tectonic subsidence maps developed through 3D flexural backstripping provide more accurate constraints of the areal extent, magnitude and rate of dynamic topography (as well as flexural topography) in the CFB through the Late Cretaceous. This improved understanding of dynamic topography in the CFB is critical for refining current geodynamic models of foreland basins and understanding the surface expression of mantle processes.
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Reversible subsidence on the North West Shelf of Australia
The Northwest Shelf (NWS) of Australia is characterized by offshore basins associated with Permian and Jurassic rifting and was only slowly subsiding by the Neogene. International Ocean Discovery Program (IODP) Expedition 356 targeted this region by coring four sites in the Northern Carnarvon and Roebuck Basins and two sites in the Perth Basin to the south on the Australian western margin. We use detailed lithological, physical property and age data with paleobathymetric interpretations, to infer tectonic subsidence apparently confined to the NWS that reverses (uplifts) with about the same amplitude and rate as an earlier subsidence event. About 300 m of tectonic subsidence occurred over one million years from 6 to 5 million years ago and then reverses when 300 m of tectonic uplift occurred from 2 to 1 Ma. The along strike extent of this subsidence pattern is ∼ 400 km. The similarity of magnitude and duration of the subsidence and uplift phases suggest that the subsidence is reversible. The results cannot be explained by glacial eustatic variability nor can the uplift event be attributed to sediments filling the accommodation space generated earlier. Reversible subsidence is a key fingerprint of dynamic topography. Although the rates of subsidence and uplift are roughly ∼ 300 m/Myr, a substantial portion of the changes occur over less than 1 Myr and the rates inferred from a detailed least squares analysis can reach up to about 500 m/Myr. These rates are incompatible with dynamic topography associated with motion of Australia over large-scale convection (10 to 40 m/Myr) or that associated with instability of the base of the lithosphere (<15 m/Myr). The vertical motions are too large to be associated with simple flexure of a plate and plate buckling in that the required amplitudes would lead to permanent deformation of the plate. A new geodynamic mechanism is required to fit the observations.
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- Award ID(s):
- 1645775
- PAR ID:
- 10228141
- Date Published:
- Journal Name:
- Earth and planetary science letters
- Volume:
- 534
- ISSN:
- 0012-821X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.epsl.2020.116070
