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[Display omitted] • High-resolution ID-TIMS geochronology of tuff beds reveal unconformity in Surat Basin. • Traceable diachronous regional unconformity spans 3 to 10 Ma within a fluvial-dominated depositional system. • Differential deformation trend coeval with intensified tectonic activity in eastern Gondwana. New high-resolution ID-TIMS geochronology of zircon from tuff horizons reveals a regionally traceable temporal hiatus of ∼ 3–10 Ma in sedimentation along the contact between the Middle-Upper Jurassic Walloon Coal Measures (WCM) and the Upper Jurassic Springbok Sandstone (SS), Surat Basin, Australia. Undecompacted sedimentation rates of 15–65 m.Ma −1 in the WCM drop to apparent sedimentation rates of 0 to 7 m.Ma −1 near the WCM-SS transition, rising again to 15–51 m.Ma −1 during SS deposition. U-Pb geochronology identifies a hiatus – either a cessation in sedimentation or an erosional event defining a regional unconformity – not discernable from sedimentary features, highlighting the need for high-resolution geochronology in defining key bounding surfaces in sequence stratigraphy of intracratonic basins. Determining the exact position of lithological contacts and characterizing petrophysical properties of units below and above the WCM-SS transition are particularly important in quantifying connectivity between the gas-bearing units below with regional aquifers above the unconformity. As exploration for coal-seam and shale gas in intracratonic sedimentary basins expands globally, identification of major stratigraphic transitions through high-resolution geochronology will help assessing the economic potential and environmental vulnerabilities of such systems. [ABSTRACT FROM AUTHOR] more...

Terrestrial supergene goethites of known ages record information on changes in weathering conditions through time. Here we present a database of (U-Th)/He ages and U and Th contents of goethites from different weathering environments around the globe. By consolidating published data collected at four different laboratories and unpublished data collected at the Noble Gas Laboratory at Caltech, we aim to give an overview of the work carried out by geochronologists and geochemists in the last 20 years. The database contains 2597 (U-Th)/He ages of goethites from 10 countries; most of the ages come from Brazil and Australia. [ABSTRACT FROM AUTHOR] more...

Increases in temperature and pressure caused by rapid burial of sediments seaward of the Sumatra subduction zone have been hypothesized to trigger dehydration reactions that diagenetically strengthen sediments and contribute to the formation of an over‐pressured pre‐décollement, which together facilitate the occurrence of large shallow earthquakes. We present paleomagnetic, rock magnetic, and electron microscopic analyses from drill cores collected offshore Sumatra at Site U1480 during IODP Expedition 362 that support this hypothesis. The older pre‐fan units (Late Cretaceous to early Paleocene) were deposited when Site U1480 was moving rapidly northward with the Indian plate from a paleolatitude of 50° to 30°S, which would equate to expected absolute paleomagnetic inclinations of 70°–43°. Most of the older pre‐fan sediments, however, have shallow observed inclinations (shallower than ±20°), indicating that the sediments were overprinted when Site U1480 was located near the paleoequator, as it has been since the early Oligocene. Electron microscopic observations reveal that the pre‐existing detrital magnetite grains have undergone pervasive dissolution and alteration by hydrothermal fluids. The diagenesis observed is consistent with mineral dehydration, possibly driven by rapid burial of pelagic sediments by the ∼1250 m thick Nicobar Fan sequence. In addition, the elevated burial temperature also facilitated the smectite to illite conversion reaction. We hypothesize that chemical reactions resulted in the formation of fine‐grained magnetite that records a chemical remanent magnetization overprint. This overprint is consistent with the alteration occurring after burial by the thick Nicobar Fan sequence sometime in the past few million years. Plain Language Summary: Sediments and rocks commonly contain magnetic minerals that record the direction and intensity of Earth's magnetic field as they are being emplaced, thus preserving an ancient record of the geomagnetic field. Subsequent alteration of the magnetic minerals caused by heating and/or fluid circulation can result in the acquisition of secondary magnetizations (i.e., remagnetization) that may overprint or completely reset the primary ancient magnetization. Such remagnetization provides evidence of the physical and chemical changes that have occurred. Here through paleomagnetic, rock magnetic, and microscopic analyses of the deeper older (pre‐fan) stratigraphic sequence cored offshore Sumatra, we find that hydrothermal fluids, resulting from mineral dehydration driven by rapid burial of this sequence by younger, thick Nicobar Fan sediments, led to pervasive secondary remagnetization. Consequently, the newly formed magnetite recorded a much younger paleomagnetic field, leaving a shallow overprint that probably occurred sometime in the past few million years. The dehydration reactions also increased the strength of the sediments entering the subduction zone and aided in the formation of slip surfaces (called décollements), possibly contributing to the shallow, large earthquakes that have generated tsunamis off Sumatra. Key Points: The 60–67 Ma pre‐fan sediments offshore Sumatra were most likely remagnetized since deposition of the Nicobar Fan sediments, which began at ∼9 MaRemagnetization of pre‐fan sediments caused by mineral dehydration may be linked to shallow seismogenic slip off SumatraMagnetic properties of input sediments in the subduction margin record conditions that may have facilitated the generation of earthquakes [ABSTRACT FROM AUTHOR] more...

Lithology plays a fundamental role in rock weathering and erosion, and in landscape evolution. When weathering‐ and erosion‐prone lithologies are protected from erosion by more resilient rock types (e.g., quartzites and banded iron formations) unusual weathering products result. At the Southern Espinhaço Range, Minas Gerais, Brazil, bauxitic weathering profiles are found in a unique geomorphological–lithological–climatic setting. Resistant quartzites acted as a barrier against erosion of interbedded hematite‐phyllite lenses, channelling solution flows and facilitating the formation of deep weathering profiles. The long‐term exposure of the hematite‐phyllites under alternating wet and dry tropical climates favoured widespread bauxitization. Here we investigate the geochemical, mineralogical, geochronological and micromorphological signatures of scaffolded bauxites in order to reconstruct their evolutionary history. Our data suggest that recurrent aluminium and iron mobilization within the profiles were mainly driven by mineral dissolution‐reprecipitation mediated by bioturbation and the influx of vegetation‐derived organic species. (U–Th)/He geochronology of Al‐goethite reveals that bauxitization started at least since the Lower Miocene, with important intensification of weathering in the Upper Miocene and Lower Pleistocene. The adjacent resilient quartzites acted as scaffolds for bauxitization and supported the preservation of more erodible weathering profiles developed over phyllites. Surface waters that could not infiltrate into the impermeable adjacent quartzites preferentially infiltrated into the more weathereable phyllites, enhancing their porosity and permeability, further enhancing weathering. The evolutionary history of Southern Espinhaço Range bauxites suggests a new model of bauxitization in ancient land surfaces evolution underlain by quartzites, where erosion‐prone lithologies are scaffolded by resilient quartzites and survive long‐term weathering with minimum erosion, producing bauxites. [ABSTRACT FROM AUTHOR] more...

We use a recently completed airborne magnetic and gamma-ray spectrometric survey, and new U/Pb and 40Ar/39Ar age determinations, to revise and clarify several aspects of Brook Street Terrane geology in the Takitimu Mountains. Steeply dipping and homoclinal Permian Takitimu Subgroup formations defined in the central part of the range can, with moderate confidence, be traced along strike to other parts of the range where they are more complexly folded and faulted. We report intrusion ages for three Brook Street plutonic suites: pyroxene-bearing White Hill Intrusives (306-270 Ma, U/Pb zircon), amphibole-bearing Mackinnon Peak Intrusives (261 ± 1 Ma, 40Ar/39Ar amphibole), and shoshonitic Wether Hill Dikes (254 ± 1 Ma, 40Ar/39Ar plagioclase). Geological relationships between these intrusions and the host Takitimu Subgroup reinforce the Early Permian age of the latter, which is distinct from the overlying Late Permian Productus Creek Group. The Wether Hill Dikes mark the cessation of igneous activity in the Brook Street Terrane at c. 254 Ma. A large (n = 499) dataset of detrital zircon U/Pb ages from the nonmarine Jurassic Barretts Formation confirms a local Median Batholith-Tuhua Intrusives provenance and supports a post-Permian fore-arc tectonic setting along the Gondwana margin. [ABSTRACT FROM AUTHOR] more...

(U-Th)/He dating of late-stage authigenic goethite, combined with corrections for diffusive loss of [sup.4]He by the [sup.4]He/[sup.3]He methodology, reveals strong correlation between a sample's age and its depth in ferruginized channel sediments from the Yandicoogina deposit, Western Australia. Corrected ages, ranging from ca. 18 Ma near the surface to ca. 5 Ma at the bottom of the profile, indicate that ferruginization of the aggraded channels becomes progressively younger with depth. This trend is consistent with goethite precipitation at the groundwater-atmosphere interface during water table drawdown driven by the aridification of Western Australia during the Neogene. The results demonstrate that the (U-Th)/He system is ideal for dating goethite if diffusive loss corrections are applied. The approach is suitable for dating weathering reactions on Earth and should also be suitable for dating Fe oxyhydroxides in the Martian regolith. Keywords: (U-Th)/He dating, goethite, weathering geochronology, channel iron deposits, iron ore. more...