Jakob Skogseid

Reconstruction of tectonic events on the northern Eurasia margin of the Arctic, from U-Pb detrital zircon provenance investigations of late Paleozoic to Mesozoic sandstones in southern Taimyr Peninsula

The Taimyr fold-and-thrust belt records late Paleozoic compression, presumably related to Uralian orogenesis, overprinted by Mesozoic dextral strike-slip faulting. U-Pb detrital zircon analyses of 38 sandstones from southern Taimyr were conducted using laser ablation–inductively coupled plasma–mass spectrometry to investigate late Paleozoic to Mesozoic sediment provenance and the tectonic evolution of Taimyr within a regional framework. The Pennsylvanian to Permian sandstones contain detrital zircon populations of 370–260 Ma, which are consistent with derivation from the late Paleozoic Uralian orogen in northern Taimyr and/or the polar Urals. Late Neoproterozoic through Silurian ages (688–420 Ma), most consistent with derivation from Timanian and Caledonian age sources, suggest an ultimate Baltica source. Southern Taimyr represents the proforeland basin of the bivergent Uralian orogen in the late Paleozoic. Triassic sedimentary rocks contain detrital zircon populations of Carboniferous–Permian (355–260 Ma), late Neoproterozoic to Early Devonian (650–410 Ma), and minor Neoproterozoic (1000–700 Ma) ages, which suggest a similar provenance as the Carboniferous to Permian strata. The addition of a Permian–Triassic (260–220 Ma) zircon population indicates derivation of detritus from Siberian Trap–related magmatism. Jurassic samples have a dominant age peak at 255 Ma and a distinct reduction in Carboniferous–Permian and late Neoproterozoic to Early Devonian input, suggesting that erosion and contributions from Uralian sources ceased while greater input from Siberian Trap–related rocks of Taimyr dominated. Comparison of these results to the published literature demonstrates that detritus from the Uralian orogen was deposited in Taimyr, Novaya Zemlya, and the New Siberian Islands in the Permian, but not in the Lisburne Hills or Wrangel Island. In the Triassic, Taimyr, Chukotka, Wrangel Island, the Kular Dome in the northern Verkhoyansk of Siberia, Lisburne Hills, Franz Josef Land, and Svalbard shared sources from Taimyr, the Siberian Traps, and the polar Urals, indicating that there were no geographic barriers among these locations prior to opening of the Amerasia Basin. Detritus from the Uralian orogen in Taimyr was shed northward into the retroforeland basin and was then transported farther 20–30 m.y. after Uralian orogenesis. The widespread distribution of material eroded from Taimyr and the polar Urals during the Triassic is likely due to the arrival of, and sublithospheric spreading associated with, the Siberian mantle plume head at ca. 250 Ma. The subsequent motion of the lithosphere relative to the plume-swell likely caused a northwestward migration of the uplifted regions. Taimyr and the polar Urals were probably affected. In the Jurassic, detrital zircon spectra from Taimyr, Chukotka, the Kular Dome, and Svalbard show great differences, suggesting that these locations no longer shared the same provenance from Taimyr and the Urals. The restricted distribution of detritus from Taimyr and the Urals indicates that erosion of the Uralian orogen was reduced. In the Late Jurassic, the depositional setting of southern Taimyr probably changed from a foreland to an intracratonic basin.

4DPlates: On the fly visualization of multilayer geoscientific datasets in a plate tectonic environment

This paper presents the 4DPlates, an application designed to display high resolution data and reconstruct their positions in the geologic past. 4DPlates makes use of level of detail (LoD) grids with a 4-8 tree structure to store the data so only the required resolution for a particular viewpoint is used. This facility means that the user can interact with large data sets on the fly, achieving between 30 and 50 frames per second with a large test data set. The article presents the design and functionality of the application from view-dependent visualization to the ability to reconstruct data in the distant past. Finally, we apply the application in two geoscientific settings. In the first, we calculate the tectonic subsidence from sediment loading and test the variation of the sediment density to the resulting subsidence grid. Secondly, we examine two South Atlantic reconstructions and highlight minor differences between them visible in the closeness of the fit of the topographic grids. The application excels at providing an interactive manipulation of high resolution data, whether it be reconstructing the data, setting the lighting angle or vertical exaggeration, or modifying parameters in the underlying formulas.

Rapid Cenozoic subsidence in the Gulf of Mexico resulting from Hess Rise conjugate subduction

Enigmatic surface deflections occurred in North America starting from the Cretaceous, including the continental-scale drainage reorganization and the long-wavelength subsidence in the Western Interior Seaway. These surface undulations cannot be simply explained by sea level change or flexure loading. Coinciding with the large-scale surface deflection, the Gulf of Mexico (GOM) has an immense Paleocene sediment deposition probably caused by tectonic subsidence. Increasing evidence indicates a distinct seismic anomaly localized in the mantle below the GOM. With geodynamic models, we show that the Hess Rise conjugate coincides with the position of the seismic anomaly. The basalt-eclogite transition in the Hess conjugate can lead to a localized dynamic subsidence in the GOM, which is superimposed on the broad surface deflection caused by the Farallon slab. The Hess conjugate, transformed to eclogite, could tilt the surface southward in the U.S. and help frame the GOM as a main depocenter in the Cenozoic.