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U-Pb geochronology by isotope dilution−thermal ionization mass spectrometry (ID-TIMS) has the potential to be the most precise and accurate of the deep time chronometers, especially when applied to high-U minerals such as zircon. Continued analytical improvements have made this technique capable of regularly achieving better than 0.1% precision and accuracy of dates from commonly occurring high-U minerals across a wide range of geological ages and settings. To help maximize the long-term utility of published results, we present and discuss some recommendations for reporting ID-TIMS U-Pb geochronological data and associated metadata in accordance with accepted principles of data management. Further, given that the accuracy of reported ages typically depends on the interpretation applied to a set of individual dates, we discuss strategies for data interpretation. We anticipate that this paper will serve as an instructive guide for geologists who are publishing ID-TIMS U-Pb data, for laboratories generating the data, the wider geoscience community who use such data, and also editors of journals who wish to be informed about community standards. Combined, our recommendations should increase the utility, veracity, versatility, and “half-life” of ID-TIMS U-Pb geochronological data.

New rock dredge samples supply key information to establish the tectonic and geological framework of the northern two-thirds of the 95% submerged Zealandia continent. The R/V Investigator voyage IN2016T01 to the Fairway Ridge, Coral Sea, obtained poorly sorted poly-lithologic pebbly to cobbly sandstones, well sorted fine grained sandstones, mudstones, bioclastic limestones, and basaltic lavas. Post-cruise analytical work comprised petrography, whole rock geochemical and Sr and Nd isotopic analyses, and U-Pb zircon, Rb-Sr, and Ar-Ar geochronology. A Fairway Ridge cobbly sandstone has a ∼95 Ma (early Late Cretaceous) depositional age; two biotite granite cobbles are 111 ± 1 and 128 ± 1 Ma in age, and some volcanic pebbles are also likely Early Cretaceous. Fairway Ridge basalts have intraplate alkaline chemistry and are of Late Eocene age (∼40–36 Ma). By analogy with South Zealandia, we interpret strong positive continental magnetic anomalies of North Zealandia to mainly result from Late Cretaceous to Cenozoic intraplate basalts, many of them rift-related lavas. A new basement geological map of North Zealandia shows the position of the Mesozoic Gondwana magmatic arc axis (Median Batholith) and other major geological units. This study completes onland and offshore reconnaissance geological mapping of the entire 5 Mkm2 Zealandia continent.

New rock dredge samples supply key information to establish the tectonic and geological framework of the northern two-thirds of the 95% submerged Zealandia continent. The R/V Investigator voyage IN2016T01 to the Fairway Ridge, Coral Sea, obtained poorly sorted poly-lithologic pebbly to cobbly sandstones, well sorted fine grained sandstones, mudstones, bioclastic limestones, and basaltic lavas. Post-cruise analytical work comprised petrography, whole rock geochemical and Sr and Nd isotopic analyses, and U-Pb zircon, Rb-Sr, and Ar-Ar geochronology. A Fairway Ridge cobbly sandstone has a ∼95 Ma (early Late Cretaceous) depositional age; two biotite granite cobbles are 111 ± 1 and 128 ± 1 Ma in age, and some volcanic pebbles are also likely Early Cretaceous. Fairway Ridge basalts have intraplate alkaline chemistry and are of Late Eocene age (∼40–36 Ma). By analogy with South Zealandia, we interpret strong positive continental magnetic anomalies of North Zealandia to mainly result from Late Cretaceous to Cenozoic intraplate basalts, many of them rift-related lavas. A new basement geological map of North Zealandia shows the position of the Mesozoic Gondwana magmatic arc axis (Median Batholith) and other major geological units. This study completes onland and offshore reconnaissance geological mapping of the entire 5 Mkm2 Zealandia continent.

Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC). The time of origin of the geodynamo has important implications for the thermal evolution of the planetary interior and the habitability of early Earth. It has been proposed that detrital zircon grains from Jack Hills, Western Australia, provide evidence for an active geodynamo as early as 4.2 billion years (Ga) ago. However, our combined paleomagnetic, geochemical, and mineralogical studies on Jack Hills zircons indicate that most have poor magnetic recording properties and secondary magnetization carriers that postdate the formation of the zircons. Therefore, the existence of the geodynamo before 3.5 Ga ago remains unknown.

The end-Triassic is characterized by one of the largest mass extinctions in the Phanerozoic, coinciding with major carbon cycle perturbations and global warming. It has been suggested that the environmental crisis is linked to widespread sill intrusions during magmatism associated with the Central Atlantic Magmatic Province (CAMP). Sub-volcanic sills are abundant in two of the largest onshore sedimentary basins in Brazil, the Amazonas and Solimões basins, where they comprise up to 20% of the stratigraphy. These basins contain extensive deposits of carbonate and evaporite, in addition to organic-rich shales and major hydrocarbon reservoirs. Here we show that large scale volatile generation followed sill emplacement in these lithologies. Thermal modeling demonstrates that contact metamorphism in the two basins could have generated 88,000 Gt CO2. In order to constrain the timing of gas generation, zircon from two sills has been dated by the U-Pb CA-ID-TIMS method, resulting in 206Pb/238U dates of 201.477 ± 0.062 Ma and 201.470 ± 0.089 Ma. Our findings demonstrate synchronicity between the intrusive phase and the end-Triassic mass extinction, and provide a quantified degassing scenario for one of the most dramatic time periods in the history of Earth.

The end-Triassic is characterized by one of the largest mass extinctions in the Phanerozoic, coinciding with major carbon cycle perturbations and global warming. It has been suggested that the environmental crisis is linked to widespread sill intrusions during magmatism associated with the Central Atlantic Magmatic Province (CAMP). Sub-volcanic sills are abundant in two of the largest onshore sedimentary basins in Brazil, the Amazonas and Solimões basins, where they comprise up to 20% of the stratigraphy. These basins contain extensive deposits of carbonate and evaporite, in addition to organic-rich shales and major hydrocarbon reservoirs. Here we show that large scale volatile generation followed sill emplacement in these lithologies. Thermal modeling demonstrates that contact metamorphism in the two basins could have generated 88,000 Gt CO2. In order to constrain the timing of gas generation, zircon from two sills has been dated by the U-Pb CA-ID-TIMS method, resulting in 206Pb/238U dates of 201.477 ± 0.062 Ma and 201.470 ± 0.089 Ma. Our findings demonstrate synchronicity between the intrusive phase and the end-Triassic mass extinction, and provide a quantified degassing scenario for one of the most dramatic time periods in the history of Earth.

The end-Triassic is characterized by one of the largest mass extinctions in the Phanerozoic, coinciding with major carbon cycle perturbations and global warming. It has been suggested that the environmental crisis is linked to widespread sill intrusions during magmatism associated with the Central Atlantic Magmatic Province (CAMP). Sub-volcanic sills are abundant in two of the largest onshore sedimentary basins in Brazil, the Amazonas and Solimões basins, where they comprise up to 20% of the stratigraphy. These basins contain extensive deposits of carbonate and evaporite, in addition to organic-rich shales and major hydrocarbon reservoirs. Here we show that large scale volatile generation followed sill emplacement in these lithologies. Thermal modeling demonstrates that contact metamorphism in the two basins could have generated 88,000 Gt CO2. In order to constrain the timing of gas generation, zircon from two sills has been dated by the U-Pb CA-ID-TIMS method, resulting in 206Pb/238U dates of 201.477 ± 0.062 Ma and 201.470 ± 0.089 Ma. Our findings demonstrate synchronicity between the intrusive phase and the end-Triassic mass extinction, and provide a quantified degassing scenario for one of the most dramatic time periods in the history of Earth.

Dinosaur skeletal remains are almost unknown from northern South America. One of the few exceptions comes from a small outcrop in the northernmost extension of the Andes, along the western border of Venezuela, where strata of the La Quinta Formation have yielded the ornithischian Laquintasaura venezuelae and other dinosaur remains. Here, we report isolated bones (ischium and tibia) of a small new theropod, Tachiraptor admirabilis gen. et sp. nov., which differs from all previously known members of the group by an unique suite of features of its tibial articulations. Comparative/phylogenetic studies place the new form as the sister taxon to Averostra, a theropod group that is known primarily from the Middle Jurassic onwards. A new U–Pb zircon date (isotope dilution thermal-ionization mass spectrometry; ID-TIMS method) from the bone bed matrix suggests an earliest Jurassic maximum age for the La Quinta Formation. A dispersal–vicariance analysis suggests that such a stratigraphic gap is more likely to be filled by new records from north and central Pangaea than from southern areas. Indeed, our data show that the sampled summer-wet equatorial belt, which yielded the new taxon, played a pivotal role in theropod evolution across the Triassic–Jurassic boundary., Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (Grant 2014/03835–3), Venezuelan Science, Technology, and Innovation Ministry (Project IVIC-1096)

A mid-Permian (Guadalupian epoch) extinction event at approximately 260 Ma has been mooted for two decades. This is based primarily on invertebrate biostratigraphy of Guadalupian-Lopingian marine carbonate platforms in southern China, which are temporally constrained by correlation to the associated Emeishan Large Igneous Province (LIP). Despite attempts to identify a similar biodiversity crisis in the terrestrial realm, the low resolution of mid-Permian tetrapod biostratigraphy and a lack of robust geochronological constraints have until now hampered both the correlation and quantification of terrestrial extinctions. Here we present an extensive compilation of tetrapod-stratigraphic data analysed by the constrained optimization (CONOP) algorithm that reveals a significant extinction event among tetrapods within the lower Beaufort Group of the Karoo Basin, South Africa, in the latest Capitanian. Our fossil dataset reveals a 74-80% loss of generic richness between the upper Tapinocephalus Assemblage Zone (AZ) and the mid-Pristerognathus AZ that is temporally constrained by a U-Pb zircon date (CA-TIMS method) of 260.259 ± 0.081 Ma from a tuff near the top of the Tapinocephalus AZ. This strengthens the biochronology of the Permian Beaufort Group and supports the existence of a mid-Permian mass extinction event on land near the end of the Guadalupian. Our results permit a temporal association between the extinction of dinocephalian therapsids and the LIP volcanism at Emeishan, as well as the marine end-Guadalupian extinctions.

TIMS and SHRIMP U-Pb analyses of zircons from Milford Orthogneiss metadiorite (P = 1-1.4 GPa; T ≥ 750°C) of the Arthur River Complex of northern Fiordland reveal a bimodal age pattern. Zircons are predominantly either Paleozoic (357.0 ± 4.2 Ma) and pr

Le Guerroue´ and others (this issue) highlight several questions regarding the Neoproterozoic stratigraphy of Oman in response to the publication of Bowring and others (2007). We take this opportunity to respond to each of their points, to reiterate some of the conclusions made in our original paper, stress the importance of understanding all sources of uncertainty in geochronological data, and re-emphasize the distinction between geochronological constraints and predictive models.

Le Guerroue´ and others (this issue) highlight several questions regarding the Neoproterozoic stratigraphy of Oman in response to the publication of Bowring and others (2007). We take this opportunity to respond to each of their points, to reiterate some of the conclusions made in our original paper, stress the importance of understanding all sources of uncertainty in geochronological data, and re-emphasize the distinction between geochronological constraints and predictive models.

The Huqf Supergroup, Sultanate of Oman, contains an important record of Neoproterozoic history, including evidence for two glaciations, a massive reorganization of the global carbon cycle, and the Ediacaran-Cambrian transition. New U-Pb geochronologic data provide precise constraints on the age of several key stratigraphic levels in the Neoproterozoic Huqf Supergroup and its subjacent crystalline basement rocks. The basement ages constrain an interval of felsic magmatism to have occurred from at least 840 Ma to approximately 810 Ma. Detrital zircons from several stratigraphic levels within the Huqf Supergroup yield ages in excess of 2.5 Ga, suggesting proximity of Archean crust during the Neoproterozoic evolution of the eastern Arabian Peninsula. Volcanic ash beds intercalated within the Huqf Supergroup were dated in the Oman Mountains, and in several subsurface wells (South Oman Salt Basin). Glacial deposits of the Abu Mahara Group in the Oman Mountains (Ghubrah Formation) contain volcaniclastic rocks that are approximately 713 Ma; overlying syn-glacial turbiditic sandstones of the Fiq Formation yield a suite of detrital zircon dates ranging from 920 to 664 Ma so that deposition of at least the upper Fiq must have post-dated 664 Ma. In the South Oman Salt Basin, volcaniclastic deposits intercalated within glaciogenic strata of the Fiq Formation yielded zircons, the youngest of which is about 645 Ma. These data indicate two distinct episodes of glaciation at approximately 713 and <645 Ma. The uppermost Ara Group of the Huqf Supergoup contains multiple ash beds within its carbonate strata, where an age of roughly 547 Ma is reported for rocks that occur above strata marked by a pronounced negative (-12‰) to positive (4‰) excursion in carbon isotope composition. Higher in the Ara sequence, three distinct ash beds dated at about 543 Ma, 542 Ma, and 541 Ma closely approximate the Ediacaran-Cambrian boundary in Oman. The dramatic carbon isotope excursion of 16 permil in t

The Huqf Supergroup, Sultanate of Oman, contains an important record of Neoproterozoic history, including evidence for two glaciations, a massive reorganization of the global carbon cycle, and the Ediacaran-Cambrian transition. New U-Pb geochronologic data provide precise constraints on the age of several key stratigraphic levels in the Neoproterozoic Huqf Supergroup and its subjacent crystalline basement rocks. The basement ages constrain an interval of felsic magmatism to have occurred from at least 840 Ma to approximately 810 Ma. Detrital zircons from several stratigraphic levels within the Huqf Supergroup yield ages in excess of 2.5 Ga, suggesting proximity of Archean crust during the Neoproterozoic evolution of the eastern Arabian Peninsula. Volcanic ash beds intercalated within the Huqf Supergroup were dated in the Oman Mountains, and in several subsurface wells (South Oman Salt Basin). Glacial deposits of the Abu Mahara Group in the Oman Mountains (Ghubrah Formation) contain volcaniclastic rocks that are approximately 713 Ma; overlying syn-glacial turbiditic sandstones of the Fiq Formation yield a suite of detrital zircon dates ranging from 920 to 664 Ma so that deposition of at least the upper Fiq must have post-dated 664 Ma. In the South Oman Salt Basin, volcaniclastic deposits intercalated within glaciogenic strata of the Fiq Formation yielded zircons, the youngest of which is about 645 Ma. These data indicate two distinct episodes of glaciation at approximately 713 and <645 Ma. The uppermost Ara Group of the Huqf Supergoup contains multiple ash beds within its carbonate strata, where an age of roughly 547 Ma is reported for rocks that occur above strata marked by a pronounced negative (-12‰) to positive (4‰) excursion in carbon isotope composition. Higher in the Ara sequence, three distinct ash beds dated at about 543 Ma, 542 Ma, and 541 Ma closely approximate the Ediacaran-Cambrian boundary in Oman. The dramatic carbon isotope excursion of 16 permil in t