Untangling Ediacaran Paleomagnetism to Contextualize Immense Global Change

Informazioni relative al progetto

EPIC

ID dell’accordo di sovvenzione: 101043844

DOI

10.3030/101043844

Data della firma CE 19 Aprile 2022

Data di avvio 1 Ottobre 2022

Data di completamento 30 Settembre 2027

Finanziato da

• European Research Council (ERC)

Costo totale

€ 1 963 575,00

Contributo UE

€ 1 963 575,00

Coordinato da

UNIVERSITETET I OSLO
Norway

Periodic Reporting for period 1 - EPIC (Untangling Ediacaran Paleomagnetism to Contextualize Immense Global Change)

Periodo di rendicontazione: 2022-10-01 al 2025-03-31

Sintesi del contesto e degli obiettivi generali del progetto

During the Ediacaran and early Cambrian periods, about 635 to 520 million years ago, dramatic changes occurred in Earth's climate, in the biosphere, and in global geochemical systems. These included the end of a series of protracted, global-scale glaciations, the seemingly abrupt appearance and rapid diversification of modern metazoan life, a rise in atmospheric oxygen and the recording of one of the most significant and mysterious carbon isotope anomalies in Earth's history. Given the immensity and abruptness of these events, they are important to an understanding of the development of life, the history of climatic change and the evolution of the carbon and oxygen cycles.

Great effort has been dedicated to acquiring better temporal constraints to investigate these changes through time, but we presently lack the ability to reconstruct and study the records of these changes in a spatial context. Because the orientation of Earth's magnetic field is latitude-dependent, we can normally use paleomagnetic directions (records of the local orientation of Earth's magnetic field preserved in rocks from when they formed) to reconstruct paleogeography. However, Ediacaran and early Cambrian paleomagnetic data exhibit strange behavior, including exceptionally rapid rates of directional change, the meaning of which remains unknown. Four alternative hypotheses have been put forward to explain these unusual data: (1) the tectonic plates were moving ultra-fast, (2) the entire solid Earth was tilted rapidly about an equatorial axis (a process called 'true polar wander'), (3) the data have been pervasively corrupted, or (4) the geomagnetic field was acting anomalously at this time. Each of these hypotheses has far-reaching implications, but until we know which (or which combination) is correct, the paleomagnetic data cannot be reliably applied to make paleogeographic reconstructions for this time.

With EPIC, we will identify the origin(s) of the enigmatic Ediacaran-early Cambrian paleomagnetic data through direct testing of the alternative hypotheses formulated to explain them. This will be accomplished through a multi-pronged approach organized around the collection of new paleomagnetic, geochronologic and paleointensity data. With the knowledge gleaned from the hypothesis tests, we will decode the paleomagnetic data and apply it to build robust reconstructions for this critical interval of Earth's history.

Lavoro eseguito dall’inizio del progetto fino alla fine del periodo coperto dalla relazione e principali risultati finora ottenuti

To initiate EPIC on a firm foundation, at the project outset we conducted a review and analysis of the existing Ediacaran-early Cambrian paleomagnetic data and laid out the specific hypothesis tests to be executed by the project. A preliminary execution of these tests using the extant paleomagnetic constraints demonstrated ultra-fast plate motions and/or true polar wander to be unlikely—although not dismissible—explanations of the observations.

The main project efforts have subsequently been dedicated to the acquisition of new observational data to meet three core objectives: (1) resolve the rate and spatial pattern of Ediacaran-early Cambrian paleomagnetic directional change, (2) determine the strength and stability of the geomagnetic field at this time, and (3) evaluate the fidelity of magnetization carriers in key Ediacaran-early Cambrian units. Work toward objective (1) has proceeded through sampling campaigns to Ediacaran-early Cambrian sedimentary successions in northern and central Norway, Spain, and Paraguay, in addition to the re-dating of Ediacaran volcanic units from Morocco that have yielded key paleomagnetic constraints. The latter has yielded an early breakthrough: demonstrating that mid-late Ediacaran paleomagnetic directions shifted by more than 90 degrees in just a few million years. Work toward objective (2) has been made through sampling campaigns to a coeval set of early Ediacaran dike swarms in southwestern Norway and northeastern Canada, for which new paleointensity and geochronological analyses are underway. Preliminary results have revealed hitherto unrecognized complexities in the magnetizations of the Norwegian dikes, further reinforcing the notion that geomagnetic field may have been complex at this time. Work toward objective (3) has proceeded through sampling campaigns to similarly aged carbonatite complexes in Norway and Sweden, as well as Ediacaran volcanic rocks in eastern North America—all of which have previously yielded complex magnetic signals. Our reinvestigations of these units are presently ongoing, but we have made important progress in identifying and dissecting both remagnetizations and likely primary signals in these complex records.
In the near-term, our efforts will be dedicated to bringing these ongoing, multipronged analyses to completion, and in selecting key targets for focused follow-up analyses to best refine our understanding of the paleomagnetic changes from this time.

Progressi oltre lo stato dell’arte e potenziale impatto previsto (incluso l’impatto socioeconomico e le implicazioni sociali più ampie del progetto fino ad ora)

Our finding that the rate of paleomagnetic directional change in the mid-late Ediacaran was greater than 10 degrees per million years is a breakthrough in demonstrating that these changes could not have arisen principally from ultra-fast plate motions or rapid episodes of solid Earth tilting ('true polar wander'). Because the associated paleomagnetic data have also passed field tests indicating that they represent primary magnetizations of high-fidelity, the directional changes are not attributable to differential remagnetizations. This leaves the conclusion that the directional changes are due to changes in the magnetic field itself—and possibly to the temporary existence of a geomagnetic field that was oriented at high angle to the planetary rotation axis (along which the geomagnetic field is otherwise assumed to have remained aligned). Although this was one of the initial hypotheses that we set out to test, a past orientation of the geomagnetic field at high angle to the planetary rotation axis has not been anticipated by numerical models of Earth's magnetic field, nor is it readily explainable by them. This result will therefore serve as an impetus for further dedicated work to understand this phenomenon and the history of the geomagnetic field in general, as well as the potential consequences this could have had for the biosphere and atmosphere.

We have discovered that some of the Ediacaran-early Cambrian sedimentary successions that we are investigating have been pervasively remagnetized (the primary magnetization that was acquired when the rock formed has been replaced by one or more younger, secondary magnetizations). Remagnetizations are a widespread problem in paleomagnetism, notably because their mechanisms and timing are often unconstrained or only speculative. Because one of EPIC's objectives is to better characterize the history and fidelity of the magnetization carriers in Ediacaran and early Cambrian units, we have developed new methods to unravel the mechanisms of remagnetization through paired rock magnetic and geochemical analyses jointly evaluated with machine-learning. These tools have already yielded important insights concerning the specific history of the units that we are investigating, but we plan to explore how they may be deployed more widely and used in conjunction with geochronometers to directly constrain the age of remagnetization events.