Use of U–Pb ages of detrital zircons to infer maximum depositional ages of strata: A test against a Colorado Plateau Mesozoic database

The aftermath of the great end-Permian period mass extinction 252 Myr ago shows how life can recover from the loss of >90% species globally. The crisis was triggered by a number of physical environmental shocks (global warming, acid rain, ocean acidification and ocean anoxia), and some of these were repeated over the next 5-6 Myr. Ammonoids and some other groups diversified rapidly, within 1-3 Myr, but extinctions continued through the Early Triassic period. Triassic ecosystems were rebuilt stepwise from low to high trophic levels through the Early to Middle Triassic, and a stable, complex ecosystem did not re-emerge until the beginning of the Middle Triassic, 8-9 Myr after the crisis. A positive aspect of the recovery was the emergence of entirely new groups, such as marine reptiles and decapod crustaceans, as well as new tetrapods on land, including — eventually — dinosaurs. The stepwise recovery of life in the Triassic could have been delayed either by biotic drivers (complex multispecies interactions) or physical perturbations, or a combination of both. This is an example of the wider debate about the relative roles of intrinsic and extrinsic drivers of large-scale evolution. from a much more devastated planet and biota than the others. With only some 10% of species surviving, the EPME was much harsher than the other mass extinctions, during which global species diversity reduced to only about 50% of the pre-extinction total 1,2,24-26 . This means that the Triassic recovery has two profound implications: first, it may show qualitative, as well as quantitative, differences from the other post-extinction recoveries; and, second, it can act as an exemplar of what to expect, at its most extreme, when global biodiversity is pushed to the brink. There are obvious implications for current concerns about biodiversity loss and recovery resulting from human impacts 27,28 . In the past ten years, attention has focused on the sedimentary successions in south China. These are enormously laterally extensive, with some formations extending more than 2,000 km from the Zhejiang to Yunnan provinces. The huge exposures, length of the sections and improving dating open up the opportunity to explore physical environmental and biotic changes through the extinction and recovery times in varied marine habitats, and compare these with patterns elsewhere in the world (Fig. 1). A fine- scale, forensic analysis of this extraordinary time in Earth's history now becomes possible. The end-Permian mass extinction The EPME killed 80-96% of marine animal species and 70% of terrestrial vertebrate species

The timing and pattern of biotic recovery following the end-Permian mass extinction

• Plants have utterly transformed the planet, but testing hypotheses of causality requires a reliable time-scale for plant evolution. While clock methods have been extensively developed, less attention has been paid to the correct interpretation and appropriate implementation of fossil data. • We constructed 17 calibrations, consisting of minimum constraints and soft maximum constraints, for divergences between model representatives of the major land plant lineages. Using a data set of seven plastid genes, we performed a cross-validation analysis to determine the consistency of the calibrations. Six molecular clock analyses were then conducted, one with the original calibrations, and others exploring the impact on divergence estimates of changing maxima at basal nodes, and prior probability densities within calibrations. • Cross-validation highlighted Tracheophyta and Euphyllophyta calibrations as inconsistent, either because their soft maxima were overly conservative or because of undetected rate variation. Molecular clock analyses yielded estimates ranging from 568-815 million yr before present (Ma) for crown embryophytes and from 175-240 Ma for crown angiosperms. • We reject both a post-Jurassic origin of angiosperms and a post-Cambrian origin of land plants. Our analyses also suggest that the establishment of the major embryophyte lineages occurred at a much slower tempo than suggested in most previous studies. These conclusions are entirely compatible with current palaeobotanical data, although not necessarily with their interpretation by palaeobotanists.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.2011.03794.x

Establishing a time-scale for plant evolution

Triassic climates — State of the art and perspectives

U-Pb ages for 1655 individual detrital zircon grains in 18 samples of eolian and associated marine and fluvial sandstones of the Glen Canyon and San Rafael Groups from the Colorado Plateau and contiguous areas shed light on patterns of Jurassic sediment dispersal within Laurentia. Most detrital zircon grains in Jurassic eolianites were derived ultimately from basement provinces older than 285 Ma in eastern and central Laurentia, rather than from rock assemblages of the nearby Cordilleran margin. The most prominent peaks of constituent age populations at 420 Ma, 615 Ma, 1055 Ma, and 1160 Ma reflect derivation from Paleozoic, Neoproterozoic, and Grenvillian sources within the Appalachian orogen or its sedimentary cover. Sediment was transported to a position upwind to the north of the Colorado Plateau by a transcontinental paleoriver system with headwaters in the central to southern Appalachian region, but subordinate non-Appalachian detritus was contributed by both northern and southern tributaries during sediment transit across the continent. Subordinate detrital zircons younger than 285 Ma in selected Middle to Upper Jurassic eolianites were derived from the Permian-Triassic East Mexico and the Mesozoic Cordilleran magmatic arcs. Lower Jurassic fluvial sandstones typically contain a mixture of detrital zircons redistributed from eolian sand and derived from the East Mexico arc, which lay up-current to the southeast. Zircons in marine Curtis sandstone were largely reworked from underlying Entrada eolianite, with minor contributions from the Jurassic backarc igneous assemblage of the Great Basin. Once mature quartzose detritus was dispersed widely across southwest Laurentia by a transcontinental paleoriver system and paleowinds, which deposited extensive Jurassic ergs, durable zircon grains were recycled by multiple intraregional depositional systems. Lower Jurassic fluvial sand is locally composed, however, of detritus derived from the nearby Cordilleran magmatic arc assemblage and its Precambrian basement.

U-Pb ages of detrital zircons in Jurassic eolian and associated sandstones of the Colorado Plateau: Evidence for transcontinental dispersal and intraregional recycling of sediment

The Global boundary Stratotype Section and Point （GSSP） of the Ladinian Stage （Middle Triassic） at Bagolino （Southern Alps, Northern Italy） and its implications for the Triassic time scale

Nicora

Papers

The Global boundary Stratotype Section and Point （GSSP） of the Ladinian Stage （Middle Triassic） at Bagolino （Southern Alps, Northern Italy） and its implications for the Triassic time scale