Ross N. Mitchell

• PhD
• Research Associate at Curtin University

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Plate tectonics and mantle plumes are two of the most fundamental solid-Earth processes that have operated through much of Earth history. For the past 300 million years, mantle plumes are known to derive mostly from two large low shear velocity provinces (LLSVPs) above the core-mantle boundary, referred to as the African and Pacific superplumes, bu...

The Great Unconformity, a profound gap in Earths stratigraphic record often evident below the base of the Cambrian system, has remained among the most enigmatic field observations in Earth science for over a century. While long associated directly or indirectly with the occurrence of the earliest complex animal fossils, a conclusive explanation for...

The Great Unconformity, a profound gap in Earth’s stratigraphic record often evident below the base of the Cambrian system, has remained among the most enigmatic field observations in Earth science for over a century. While long associated directly or indirectly with the occurrence of the earliest complex animal fossils, a conclusive explanation fo...

The James Ross Basin, in the northern Antarctic Peninsula, exposes which is probably the world thickest and most complete Late Cretaceous sedimentary succession of southern high latitudes. Despite its very good exposures and varied and abundant fossil fauna, precise chronological determination of its infill is still lacking. We report results from...

A central prediction of the Snowball Earth hypothesis is that glacial onset should be synchronous at low latitudes, and its termination should be rapid and synchronous globally. Synchronous onset of the Sturtian (ca. 716 to ca. 660 Ma) has been robustly shown on multiple continents through the application of high precision U-Pb zircon dating. Succe...

A palaeomagnetic study was carried out on the newly identified 1888 ± 9 Ma Boonadgin dyke swarm of the Yilgarn Craton in Western Australia. The Bonnadgin dykes yield a mean direction of magnetisation of D = 143°, I = 13°, k = 37 and α95 = 8°, based on samples from 10 diabase dykes, with a corresponding palaeopole at 47° S, 235° E, A95 = 6°. A posit...

The concentration of atmospheric oxygen (pO2) is thought to have increased throughout Earth history, punctuated by rapid increases ca. 2.4 and 0.8 billion years ago near the beginning and end of the Proterozoic Eon. As photosynthesis is the largest source of free O2, the reigning paradigm of rising O2 levels centres around biologic metabolism. Here...

A geometrically quantitative plate-kinematic model, based on paleomagnetism, for the initial assembly of Laurentia has taken form in the past few decades. Within this framework, there remains but one problematic interval of data predominantly from the Slave craton, which is the 1.96–1.87Ga Coronation apparent polar wander path (APWP). The Coronatio...

The Derim Derim Suite of magmatic sills (1324 ± 4 Myr1) intrude Mesoproterozoic sediments of the Roper Group, McArthur Basin. While intersected by numerous mineral and petroleum wells, no volcanic equivalents have been identified, but these sills have been correlated1,2 with the Galiwinku Dykes (1325 ± 36 Myr3). Intruding at multiple stratigraphic...

Earth's magnetic field is generated in the outer core, where an electrically conducting dynamic fluid mainly composed of iron and nickel acts as a geodynamo. Features like polarity reversals (~10 kyr in duration), geomagnetic excursions (<10 kyr in duration), secular variation (~0.2˚/year), and geomagnetic jerks (several years in duration) are all...

The concentration of atmospheric oxygen (O2) is thought to have increased throughout Earth history, punctuated by rapid increases ca. 2.4 and 0.8 billion years ago at the beginning and end of the Proterozoic Eon. As photosynthesis is the largest source of free O2, the reigning paradigm of rising O2 levels centers around biologic metabolism. Here we...

Of ∼35 Archean cratons that have been identified around the globe, only one, the Superior craton of the Canadian Shield, has a reasonably well-defined apparent polar wander (APW) path for much of Paleoproterozoic time based on ‘key’ (i.e., well-defined and precisely dated) paleopoles. As a result it has been difficult to compare the drift of these...

Charles Darwin suspected that the Cambrian “explosion” might be an artifact of fossil preservation. A more recent, initially controversial hypothesis that repeated true polar wander (TPW) triggered the Ediacaran-Cambrian explosion of animal life has been supported by numerous paleomagnetic and geochronologic refinements. These data imply ∼75° of TP...

Large collections of well-preserved specimens of the ammonite Baculites inornatus Meek (1862) from two lower to middle Campanian localities on the Pacific coast of North America are analyzed quantitatively to examine both variability and evolutionary change of species-level distinguishing characters. To this end, we present a new method of describi...

The amplitude of true polar wander events is shown to occur in cycles out of phase with the formation of supercontinents over the past 3 Gyr. Associated with small-amplitude true polar wander, supercontinents act to stabilize the spin axis. Stabilization can be explained by reduced lithospheric elasticity and/or the triaxial (oblate) figure of the...

Laurentia, the core of Paleo- to Mesoproterozoic supercontinent Nuna, has remained largely intact since assembly 2.0 to 1.8 billion years ago [Ga]. For earlier times, previous paleomagnetic data on poorly dated Paleoproterozoic mafic intrusions yielded ambiguous estimates of the amount of separation between key cratons within Nuna such as the Slave...

A rover-borne magnetometer can characterize ancient martian lightning strikes, constraining paleoclimate and informing biomarker sample selection.

Although abundant evidence now exists for a massive bolide impact coincident with the Cretaceous–Paleogene (K–Pg) mass extinction event (~65.5 Ma), the relative importance of this impact as an extinction mechanism is still the subject of debate. On Seymour Island, Antarctic Peninsula, the López de Bertodano Formation yields one of the most expanded...

Traditional models of the supercontinent cycle predict that the next supercontinent--'Amasia'--will form either where Pangaea rifted (the 'introversion' model) or on the opposite side of the world (the 'extroversion' models). Here, by contrast, we develop an 'orthoversion' model whereby a succeeding supercontinent forms 90° away, within the great c...

New biostratigraphic data obtained from measured stratigraphic sections of Santonian through Maastrichtian age located along the west coast of North America necessitate changes to the currently accepted chronostratigraphic framework for this region of the North Pacific biotic province. We recognize and/or define 12 molluscan zones over this interva...

Hotspot tracks represent plate motions relative to mantle sources, and paleomagnetic data from magmatic units along those tracks can quantify motions of those mantle anomalies relative to the Earth's magnetic field and rotational axis. The Ediacaran Period is notable for rapid and large paleomagnetic apparent polar wander (APW) for many continents....

Idealized conceptual models of supercontinent cyclicity must be tested against the geologic record using pre-Pangean reconstructions. We integrate tectonostratigraphic records and paleomagnetic data from Siberia, Laurentia, and Baltica to produce a quantitative reconstruction of the core of the Nuna supercontinent at 1.9-1.3 Ga. In our model, the p...

The Archean Wyoming craton is mostly buried beneath Phanerozoic sediments in the Rocky Mountains of the west central United States. Exposures of the craton are entirely in thrust-bounded Laramide uplifts and contain numerous swarms of Neoarchean-Proterozoic mafic dikes. U-Pb ages from these dikes include ~2685 Ma from a dike in the Owl Creek Mounta...

Where will the next supercontinent form? Traditional `introversion' and `extraversion' models of supercontinent succession predict that Super Asia will respectively form whence Pangea was or on the opposite side of the world. We develop the `orthoversion' model whereby a succeeding supercontinent forms 90° away: somewhere along the great circle of...

Detailed magnetostratigraphic resampling of the Central Italian Scaglia Rossa limestones spanning the entirety of magnetic polarity Chron 33r and its boundaries (ca. 85-70 Ma) reveals previously undocumented long-wavelength (~1 Myr) oscillations in inclination as large as 20° that are not attributable to inclination flattening, remagnetization, or...

Is the Archean-Proterozoic transition characterized by a single Kenorland supercontinent, or separate independently drifting supercratons? Two ``type'' cratons, Superior and Kaapvaal, of hypothesized Superia and Vaalbara supercratons, have previously yielded satisfactory paleomagnetic apparent polar wander (APW) paths that allow robust reconstructi...

Based on the history of Mesozoic-Cenozoic plate motions, as well as simple dynamical considerations, a "speed limit" for tectonic plates has been suggested at ~20 cm/yr. Previous paleomagnetic data from the Early Cambrian of Gondwana are conflicting but generally imply rapid motions approaching that limit. Herein we describe results from a continuo...

The Coronation loop is a 110° arcuate sweep of 15 paleomagnetic poles with ages of ca. 1950–1850 Ma, derived from contemporaneous basins on the western (Coronation), southern (Great Slave) and eastern (Kilohigok) margins of the Slave craton in the northwestern Canadian shield. Although the paleomagnetic results are either demonstrated as primary or...

The prelude to the second global oceanic–anoxic event of the Cretaceous (OAE 2), as recorded in the classic sections of the Scaglia Bianca Formation in the Umbria–Marches region of Italy, is characterized by an oscillation between black to gray, organic-rich cherts and white pelagic limestones. Spectral analysis of these lithologic alternations rev...

Central to the Baja BC conundrum is the problem of comparing paleomagnetic data from the Insular Superterrane with coeval data from lithologically similar North American cratonic units. We report a first step toward that comparison by presenting new paleomagnetic data from marine claystone, siltstone, and calcareous concretions of flat-lying Pierre...

Plate-tectonic assembly of Laurentia, during the surprisingly brief interval of 1.9-1.8 Ga, has been appreciated by the geological community for more than two decades (Hoffman, 1988). Nonetheless, the only rigorously quantitative method for reconstructing Precambrian cratons and supercontinents, paleomagnetism, has yet to fulfill its potential in d...