Brunhes–Matuyama reversal

Brunhes–Matuyama reversal
Name	Brunhes–Matuyama reversal
Type	Geomagnetic reversal
Epoch	Pleistocene
Age	~780,000 years ago
Also known as	Matuyama–Brunhes boundary

Brunhes–Matuyama reversal

The Brunhes–Matuyama reversal marks the most recent major reversal of Earth's magnetic field when the axial dipole switched polarity during the Pleistocene. This reversal is a primary chronostratigraphic marker used across Quaternary geology, paleomagnetism studies, archaeology, and tephrochronology because it is recorded broadly in marine sediments, volcanic rocks, and speleothems from locations such as Vostok Station, Lake Baikal, and the Santa Rosa Island lava flows.

Overview

The boundary between the Brunhes Chron and the Matuyama Chron is recognized globally as a reversal of the geomagnetic field recorded in lithologies studied by pioneers such as Bernard Brunhes and Motonori Matuyama. Identification relies on correlations among records from the Mediterranean Sea, North Atlantic Ocean, Pacific Ocean, and continental sequences like the Loess Plateau (China), the Punaré Formation, and the Olduvai Gorge stratigraphy. Geomagnetic polarity time scales compiled by teams associated with institutions like the United States Geological Survey, Lamont–Doherty Earth Observatory, and the British Geological Survey place the reversal as a key tie-point for synchronizing marine isotope stages and chronologies used by investigators from organizations such as the International Union for Quaternary Research and the National Oceanic and Atmospheric Administration.

Timing and duration

Numerical ages for the reversal have been refined by radiometric methods including argon–argon dating and correlation with oxygen isotope stratigraphy from cores drilled by programs like the Integrated Ocean Drilling Program and its successor, the International Ocean Discovery Program. Estimates cluster near ~780,000 years ago, with earlier studies citing ~730,000–790,000 years. High-resolution magnetostratigraphy tied to Santa Rosa Island and Mount Etna lava sequences and paleoclimate proxies from Greenland Ice Sheet Project cores constrain the transition to a few thousand years, although some volcanic sequences indicate transition intervals as short as a few hundred years or as protracted as several thousand years according to research teams from California Institute of Technology, ETH Zurich, and Scripps Institution of Oceanography.

Paleomagnetic evidence

Key paleomagnetic signatures derive from marine sediment cores such as those obtained by the Deep Sea Drilling Project, the Ocean Drilling Program, and the Chikyu expeditions, augmented by continental records from loess sequences in China, speleothems in European caves, and basalt flows on islands including Canary Islands, Hawaii, and Iceland. Investigators from institutions like the Paleomagnetic Research Group at University of Liverpool and the Geological Survey of Japan document directional inclinations and declinations, paleointensity lows, and excursions recorded by magnetometers and cryogenic magnetometers produced by companies collaborating with Natural History Museum, London and Uppsala University. Cross-checks with tephra layers identified by volcanologists from Kīlauea, Mount Vesuvius, and Mount St. Helens assist stratigraphic correlation alongside chronologies developed by researchers affiliated with the Max Planck Institute for Chemistry and the Smithsonian Institution.

Mechanisms and geodynamo interpretations

The Brunhes–Matuyama event informs theoretical work on the geodynamo in the Earth's core, drawing on computational models from research groups at Princeton University, University of Oxford, University of Cambridge, and Université Paris-Saclay. Hypotheses invoke interactions among thermal convection, compositional buoyancy, and rotational forces, tested using numerical codes developed by teams connected to the National Center for Atmospheric Research, Los Alamos National Laboratory, and the French Alternative Energies and Atomic Energy Commission. Studies reference analogues in planetary magnetism such as the paleomagnetic histories of Mars and Mercury and compare with dynamo simulations used by researchers at NASA Goddard Space Flight Center and the European Space Agency. Interpretations of polarity reversal dynamics consider scenarios including multipolar transitional fields, stochastic perturbations, and excursions influenced by mantle convection patterns, as explored by scientists at Caltech, University of Tokyo, and the Woods Hole Oceanographic Institution.

Global environmental and climatic effects

Analyses of marine isotope stages, ice-core records from EPICA and GRIP, and pollen assemblages studied by palynologists at University of Cambridge and University of Pennsylvania examine whether the reversal coincided with climatic change. Some investigators link paleointensity minima and increased cosmic ray flux hypotheses to transient increases in cosmogenic isotopes such as beryllium-10 and carbon-14 recorded in archives from Greenland and Antarctica, with work performed by teams at Swiss Federal Institute of Technology Zurich and Columbia University. Other studies by researchers at University of California, Santa Cruz and University of Bergen find little evidence for major biospheric disruption, noting resilience in faunal records from Olduvai Gorge, marine microfossil assemblages cataloged by Scripps Institution of Oceanography, and archaeological layers at Zhoukoudian and Boxgrove.

Geological and archeological implications

The Brunhes–Matuyama boundary serves as a chronostratigraphic marker in volcanic, sedimentary, and archaeological contexts, aiding age models in sites examined by teams from University College London, Harvard University, University of Witwatersrand, and the Max Planck Institute for Evolutionary Anthropology. It constrains timing in hominin sites including Olduvai Gorge and Dmanisi, helps calibrate marine terraces studied by coastal geologists at University of California, Santa Barbara and University of Sydney, and supports eruption chronologies for volcanic centers like Mount Etna and Santorini researched by volcanologists from University of Florence and University of Athens. The boundary also underpins magnetostratigraphic frameworks used by petroleum geoscientists at Royal Dutch Shell and paleoclimatologists at National Center for Atmospheric Research for basin analysis and correlation across continental platforms such as the European Plate and the Eurasian Basin.

Category:Geomagnetic reversals Category:Pleistocene