Double dating sedimentary sequences using new applications of in-situ laser ablation analysis

Sedimentary rocks can provide important insights regarding the evolution of Earth's surface environments through deep time. Such sequences are pervasive through the geological record and currently cover >70% of the planet's surface. They are also a key repository for energy and mineral resources. However, absolute chronology of sedimentary rocks can be difficult to constrain using conventional methods due to their typically low abundances of radiogenic elements. Establishing chronology is particularly challenging for Precambrian sedimentary rocks, where the lack of a diverse fossil record makes biostratigraphic correlations ambiguous. In this study, we use shale and carbonate samples from the Proterozoic greater McArthur Basin in northern Australia as a case study to demonstrate two emerging in-situ laser-based methods that have the potential to quickly and accurately resolve the minimum depositional age of a sedimentary package. The first method provides a tool to constrain the formation of authigenic clay minerals in shales using in-situ laser ablation Rbsingle bondSr geochronology. The second method demonstrates an approach for dating carbonate sedimentation using Usingle bondPb geochronology via a laser isotopic mapping approach. Laser rasters are compiled into isotopic maps, and this spatial and geochemical information is used to target representative subdomains within the sample. Detrital or altered regions can be avoided by monitoring chemical signatures and pixels, and to the most authigenic domains are then subdivided that give the best spread of data on an isochron. Both approaches provide the key advantage of preserving, and through the mapping approach further resolving, sample petrographic context, which together with complementary geochemical data can be triaged to yield a more appropriate age and interpretation

Adelaide Superbasin Detrital Geochronology, Tectonics, and Palaeogeography

Research on the tectonics and palaeogeography of the Neoproterozoic to middel Cambrian Adelaide Superbasin utisiling detrital geochronology and geochemistry, Nd isotopes, and Rb-Sr in-situ dating

pvermees/IsoplotR: 5.6

<p>Adds KDE mode identification option; improves robustness of Ludwig regression for U-Pb formats 1, 2 and 3.</p&gt

pvermees/IsoplotR: 6.0

<p>Adds anchored regression option to Pb-Pb, Th-Pb, Ar-Ar, K-Ca, Rb-Sr, Sm-Nd, Re-Os, Lu-Hf and U-Th-He isochrons; automatically attributes the uncertainty of the anchors to dispersion under model-3 regression; flips the 208Pb/206Pb and 208Pb/207Pb ratios in the settings; adds option to anchor the common Pb composition of a U-Pb isochron to the Stacey-Kramers mantle evolution model.</p&gt

Early Evolution of the Adelaide Superbasin

Continental rifts have a significant role in supercontinent breakup and the development of sedimentary basins. The Australian Adelaide Superbasin is one of the largest and best-preserved rift systems that initiated during the breakup of Rodinia, yet substantial challenges still hinder our understanding of its early evolution and place within the Rodinian supercontinent. In the past decade, our understanding of rift and passive margin development, mantle plumes and their role in tectonics, geodynamics of supercontinent breakup, and sequence stratigraphy in tectonic settings has advanced significantly. However, literature on the early evolution of the Adelaide Superbasin has not been updated to reflect these advancements. Using new detrital zircon age data for provenance, combined with existing literature, we examine the earliest tectonic evolution of the Adelaide Superbasin in the context of our modern understanding of rift system development. A new maximum depositional age of 893 ± 9 Ma from the lowermost stratigraphic unit provides a revised limit on the initiation of sedimentation and rifting within the basin. Our model suggests that the basin evolved through an initial pulse of extension exploiting pre-existing crustal weakness to form half-grabens. Tectonic quiescence and stable subsidence followed, with deposition of a sourceward-shifting facies tract. Emplacement and extrusion of the Willouran Large Igneous Province occurred at c. 830 Ma, initiating a new phase of rifting. This rift renewal led to widespread extension and subsidence with the deposition of the Curdimurka Subgroup, which constitutes the main cyclic rift sequence in the Adelaide Superbasin. Our model suggests that the Adelaide Superbasin formed through rift propagation to an apparent triple junction, rather than apical extension outward from this point. In addition, we provide evidence suggesting a late Mesoproterozoic zircon source to the east of the basin, and show that the lowermost stratigraphy of the Centralian Superbasin, which is thought to be deposited coevally, had different primary detrital sources