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Research shows how Gulf of Mexico escaped ancient mass extinction

Examples of radiolarians, a type of microplankton. These tiny lifeforms need normal salinity seawater with plenty of nutrients including silica to grow and maintain their glassy shells. Researchers at the University of Texas Institute for Geophysics found fossilized radiolarians in geologic samples dating back 56 million years, proving that life persisted in the Gulf of Mexico despite global warming that left many oceans barren. Credit: U.S. Geological Survey
Examples of radiolarians, a type of microplankton. These tiny lifeforms need normal salinity seawater with plenty of nutrients including silica to grow and maintain their glassy shells. Researchers at the University of Texas Institute for Geophysics found fossilized radiolarians in geologic samples dating back 56 million years, proving that life persisted in the Gulf of Mexico despite global warming that left many oceans barren. Credit: U.S. Geological Survey

An ancient bout of global warming 56 million years ago that acidified oceans and wiped-out marine life had a milder effect in the Gulf of Mexico, where life was sheltered by the basin’s unique geology — according to research by the University of Texas Institute for Geophysics (UTIG).

Published in the journal Marine and Petroleum Geology, the findings not only shed light on an ancient mass extinction, but could also help scientists determine how current climate change will affect marine life and aid in efforts to find deposits of oil and gas.

And although the Gulf of Mexico is very different today, UTIG geochemist Bob Cunningham, who led the research, said that valuable lessons can be drawn about climate change today from how the Gulf was impacted in the past.

“This event known as the Paleocene-Eocene Thermal Maximum or PETM is very important to understand because it’s pointing towards a very powerful, albeit brief, injection of carbon into the atmosphere that’s akin to what’s happening now,” he said.

Cunningham and his collaborators investigated the ancient period of global warming and its impact on marine life and chemistry by studying a group of mud, sand, and limestone deposits found across the Gulf.

They sifted through rock chips brought up during oil and gas drilling and found an abundance of microfossils from radiolarians — a type of plankton — that had surprisingly thrived in the Gulf during the ancient global warming. They concluded that a steady supply of river sediments and circulating ocean waters had helped radiolarians and other microorganisms survive even while Earth’s warming climate became more hostile to life.

“In a lot of places, the ocean was absolutely uninhabitable for anything,” said UTIG biostratigrapher Marcie Purkey Phillips. “But we just don’t seem to see as severe an effect in the Gulf of Mexico as has been seen elsewhere.”

The reasons for that go back to geologic forces reshaping North America at the time. About 20 million years before the ancient global warming, the rise of the Rocky Mountains had redirected rivers into the northwest Gulf of Mexico — a tectonic shift known as the Laramide uplift — sending much of the continent’s rivers through what is now Texas and Louisiana into the Gulf’s deeper waters.

When global warming hit and North America became hotter and wetter, the rain-filled rivers fire-hosed nutrients and sediments into the basin, providing plenty of nutrients for phytoplankton and other food sources for the radiolarians.

The findings also confirm that the Gulf of Mexico remained connected to the Atlantic Ocean and the salinity of its waters never reached extremes — a question that until now had remained open. According to Phillips, the presence of radiolarians alone — which only thrive in nutrient-rich water that’s no saltier than seawater today — confirmed that the Gulf’s waters did not become too salty. Cunningham added that the organic content of sediments decreased farther from the coast, a sign that deep currents driven by the Atlantic Ocean were sweeping the basin floor.

The research accurately dates closely related geologic layers in the Wilcox Group (a set of rock layers that house an important petroleum system), a feat that can aid in efforts to find undiscovered oil and gas reserves in formations that are the same age. At the same time, the findings are important for researchers investigating the effects of today’s global warming because they show how the water and ecology of the Gulf changed during a very similar period of climate change long ago.

The study compiled geologic samples from 36 industry wells dotted across the Gulf of Mexico, plus a handful of scientific drilling expeditions including the 2016 UT Austin-led investigation of the Chicxulub asteroid impact, which led to the extinction of non-avian dinosaurs.

For John Snedden, a study coauthor and senior research scientist at UTIG, the study is a perfect example of industry data being used to address important scientific questions.

“The Gulf of Mexico is a tremendous natural archive of geologic history that’s also very closely surveyed,” he said. “We’ve used this very robust database to examine one of the highest thermal events in the geologic record, and I think it’s given us a very nuanced view of a very important time in Earth’s history.”

Snedden is also program director of UT’s Gulf Basin Depositional Synthesis, an industry-funded project to map the geologic history of the entire Gulf basin, including the current research. UTIG is a research unit of UT Jackson School of Geosciences.

Reference:
Robert Cunningham, Marcie Purkey Phillips, John W. Snedden, Ian O. Norton, Christopher M. Lowery, Jon W. Virdell, Craig D. Barrie, Aaron Avery. Productivity and organic carbon trends through the Wilcox Group in the deep Gulf of Mexico: Evidence for ventilation during the Paleocene-Eocene Thermal Maximum. Marine and Petroleum Geology, 2022; 140: 105634 DOI: 10.1016/j.marpetgeo.2022.105634

Note: The above post is reprinted from materials provided by University of Texas at Austin.

Ancient ocean floors could help in the search for critical minerals

Examining ocean floors key to minerals needed for renewable energy. Image: Supplied
Examining ocean floors key to minerals needed for renewable energy. Image: Supplied

Studying ancient ocean floors could help discover minerals needed to produce electric cars and solar panels.

Researchers at The University of Queensland led a collaborative study that examined the remnants of ocean floors in eastern Australia and central Asia and applied a method to date the age of calcite trapped inside.

Dr Renjie Zhou from UQ’s School of Earth and Environmental Sciences said the findings could make it easier to source critical minerals used in renewable and clean technologies.

“Calcite and other hydrothermal minerals are often observed in critical mineral deposits and form under mineralising fluid activities,” Dr Zhou said.

“Our work shows that we can trace the history of fluids in the Earth’s crust and see when and what mineral resources they might generate.”

The renewable energy sector is continuing to grow rapidly with increasing demand for technologies like wind turbines, solar panels, electric vehicles and batteries.

“These often require large quantities of critical minerals,” he said.

“Electric vehicles need up to four times more copper than conventional cars and a single wind turbine uses several tonnes of permanent magnets made of rare earth metals.”

Dr Zhou said being able to study and discover these minerals was going to become increasingly important.

“Researchers across many institutions are doing excellent work in this field, including UQ’s Centre for Geoanalytical Mass Spectrometry,” Dr Zhou said.

“Our hope is to expand our collaboration with industry and academia to increase the understanding and discovery of critical minerals in the future.”

References:

  • Johannes Rembe, Renjie Zhou, Edward R. Sobel, Jonas Kley, Jie Chen, Jian-Xin Zhao, Yuexing Feng, Daryl L. Howard. Calcite U–Pb dating of altered ancient oceanic crust in the North Pamir, Central Asia. Geochronology, 2022; 4 (1): 227 DOI: 10.5194/gchron-4-227-2022
  • Goran Andjić, Renjie Zhou, David M. Buchs, Jonathan C. Aitchison, Jianxin Zhao. Paleozoic ocean plate stratigraphy unraveled by calcite U-Pb dating of basalt and biostratigraphy. Communications Earth & Environment, 2022; 3 (1) DOI: 10.1038/s43247-022-00446-1

Note: The above post is reprinted from materials provided by University of Queensland.

The link between temperature, dehydration and tectonic tremors in Alaska

Tectonic map of the Alaska subduction zone
Tectonic map of the Alaska subduction zone
The thick blue solid line outlines the Yakutat terrane. The white circle indicates the epicentre of the low-frequency tectonic tremors, and the light blue dashed line shows the area where the tectonic tremors occurred, which is used in Figures 2 to 4. The area inside the pink dashed box is the model region used in this study, and the pink dashed line down the center of the box divides the model region into northeast and southwest areas, and represents the boundary between the subducted Yakutat terrane and the subducted Pacific plate in the model. The black lines indicate the isodepth contours of the upper surface of the subducted oceanic plate (with a contour interval of 20 km), red arrows show the plate motion velocity in the Aleutian Trench, and the red triangles indicate volcanoes.

A Kobe University research group has shed light on how low-frequency tectonic tremors occur; these findings will contribute towards better predictions of future megathrust earthquakes.

In addition to the subducting Pacific plate, the Alaska subduction zone is also characterized by a subducting oceanic plateau called the Yakutat terrane. Low-frequency tectonic tremors, which are a type of slow earthquake, have only been detected in the subducted Yakutat terrane area. However, the mechanism by which these events occur is not well understood.

Researchers at Kobe University performed a 3D numerical thermomechanical simulation of thermal convection in the Alaska subduction zone with the aim of revealing the mechanism behind these low-frequency tremors. Based on the 3D thermal structure obtained from the simulation, and the indications of hydrous minerals contained in the slab, the researchers calculated the water content distribution and compared the results of these calculations in the area where the tremors occur.

The results revealed high levels of dehydration in the marine sediment layers and ocean crust in the earthquake region. The researchers believe that the reason the tremors only occur in the Yakutat terrane is because the marine sediment layers and ocean crust are thicker there, which means that the level of dehydration is higher than in the western adjacent Pacific plate (where tectonic tremors don’t occur).

The Kobe University research group consisted of 2nd year Master’s student IWAMOTO Kaya (Department of Planetology, Graduate School of Science), Academic Researcher SUENAGA Nobuaki and Professor YOSHIDA Shoichi (both of the Research Center for Urban Safety and Security).

These results were published in the British online scientific journal ‘Scientific Reports’ (Nature Publishing Group) on April 14, 2022.

Main Points

  • Elucidating the mechanism by which low-frequency tremors occur is important for understanding the plate subduction process. It is believed that this will also help illuminate how shallower megathrust earthquakes occur.
  • In this study, the research group constructed a 3D thermomechanical model of the Alaska subduction zone and calculated the subducting plate’s maximum water content and level of dehydration.
  • The dehydration levels from the subducting plate’s marine sediment layers and ocean crust were highest in the region where low-frequency tremors occur. Therefore, it is thought that the water expelled from the subducted plate contributes towards the occurrence of these tectonic tremors.

Research Background

An oceanic plateau called the Yakutat terrane is subducting in the Alaska subduction zone. Low-frequency tectonic tremors occur at this subducting plateau. The region where slow earthquakes (such as low-frequency tectonic tremors) occur is deeper and adjacent to the area where megathrust earthquakes occur, which suggests a connection between the two. Revealing the mechanism behind how low-frequency tectonic tremors occur is therefore important for understanding the occurrence of various earthquake events in subduction zones. This research group constructed a 3D thermomechanical model of the Alaska subduction zone so that they could investigate the temperature and level of dehydration in the areas near where low- frequency tremors occur.

Research Methodology

The researchers performed a 3D numerical thermomechanical simulation in accordance with the subduction of the Yakutat terrane and Pacific plate in the Alaska subduction zone. It is thought that as the Pacific plate subducts, it brings the hydrous minerals in the slab into the deep high temperature and high pressure regions, and these conditions cause a dehydration reaction where water is expelled from the hydrous minerals. Based on the 3D thermal structure obtained from the numerical simulation, the researchers determined dehydration levels of the hydrous minerals in the slab. From these results, it was understood that in the region where low- frequency tremors occur, a large amount of water is expelled due to the high temperature and high pressure conditions that cause the dehydration degradation reactions. It is thought that low frequency earthquakes don’t occur in the Pacific plate because it has thin layers and therefore experiences little dehydration. On the other hand, the Yakutat terrane’s ocean crust and marine sediment layers are comparatively thicker, meaning that it experiences high levels of dehydration. The researchers concluded that this is why low-frequency tectonic tremors only occur in the Yakutat terrane.

Further Research

In 1964, a megathrust earthquake occurred in Alaska. This is the biggest earthquake that has occurred in the Alaska subduction zone and the second most powerful earthquake recorded in world history. The low-frequency tectonic tremors that were the subject of this research occur close to the epicenter of the 1964 earthquake, at the downdip of the plate interface. Next, the research group will continue to make thermomechanical models of various subduction zones to search for universal and regional characteristics of the causal mechanisms behind undersea megathrust earthquakes and slow earthquakes. This research will contribute towards improving understanding of how earthquakes occur and our ability to predict future megathrust earthquakes.

Glossary

1. Low-frequency tectonic tremors: A seismic event that is characterized by lower-frequency seismic waves than a regular earthquake.
2. Slow earthquake: A phenomenon where a fault slips at a slower speed than in a regular earthquake.
3. Oceanic plateau: A comparatively flat area of the seabed.
4. Slab: refers to the subducted plate.
5. Hydrous mineral: Minerals that contain OH groups in their crystal structure.
6. Dehydration degradation reaction: As the plate subducts, the resulting temperature and pressure causes phase transformations of hydrous minerals and they expel water.

Reference:
Kaya Iwamoto, Nobuaki Suenaga, Shoichi Yoshioka. Relationship between tectonic tremors and 3-D distributions of thermal structure and dehydration in the Alaska subduction zone. Scientific Reports, 2022; 12 (1) DOI: 10.1038/s41598-022-10113-2

Note: The above post is reprinted from materials provided by Kobe University.

A new 225-million-year-old reptile from Brazil

Partial skull of Maehary bonapartei (CAPPA/UFSM 0300), left side, highlighting the maxilla. Photo: Rodrigo Temp Müller.
Partial skull of Maehary bonapartei (CAPPA/UFSM 0300), left side, highlighting the maxilla. Photo: Rodrigo Temp Müller.

In a new study published in PeerJ — Reassessment of Faxinalipterus minimus, a purported Triassic pterosaur from southern Brazil resulted in the description of a new taxon — researchers present Maehary bonapartei a small reptile that is considered to be the most basal of the evolutionary lineage that gave rise to pterosaurs. The study also demonstrates that Faxinalipterus minimus is not a winged reptile, contrary to what was previously supposed.

Maehary bonapartei represents a small reptile that is considered to be the most basal of the evolutionary lineage that gave rise to pterosaurs. The study also demonstrates that Faxinalipterus minimus is not a winged reptile, contrary to what was previously supposed.

Researchers from the National Museum/UFRJ, the Federal University of Santa Maria, the Catalan Institute of Paleontology, the Regional University of Cariri, the Federal University of Pampa, the Federal University of Rio Grande do Sul and COPPE/UFRJ presented a review of a small reptile named Faxinalipterus minimus, from Triassic rocks (about 225 million years ago) in Rio Grande do Sul. Faxinalipterus was described more than a decade ago (2010), being assigned to the Pterosauria, a group which includes the first vertebrates to develop active flight. The original fossil of Faxinalipterus was composed by bones from the postcranial sleleton and a part of the skull (an upper jaw with several teeth), found separately in two field expeditions, carried out in 2002 and 2005, at the Linha São Luiz fossil site, located in the municipality of Faxinal do Soturno. Thus, it was not possible to say with certainty whether all parts belonged to the same type of animal and species. Despite this, it was assumed at the time that all the bones belonged to a single species, named Faxinalipterus minimus.

The new study of Faxinalipterus established that there were two distinct species, with the isolated jaw representing another animal. This was possible based on the comparison with a new fossil recently found at the same site (Linha São Luiz). The new material is composed of an incomplete skull, whose maxilla exhibits the same features of the maxilla attributed to Faxinalipterus. In addition, there are parts of the mandible, scapula and some vertebrae. The maxilla of Faxinalipterus can therefore be incorporated into the description of the new fossil, that was named Maehary bonapartei.

“There was always a great doubt whether the two specimens attributed to Faxinalipterus represented the same species, and whether this was a flying reptile,” commented Alexander Kellner, a specialist in pterosaurs who currently directs the Museu Nacional/UFRJ. Having examined the specimen shortly after publication in 2010, he saw that several bones could be misidentified and the lack of diagnostic features of pterosaurs, including the absence of specific features on the humerus (forelimb bone), such as a large and projected deltopectoral crest, which is typical of pterosaurs. Borja Holgado, also a specialist in pterosaurs from the Catalan Institute of Paleontology and currently a researcher at the Regional University of Cariri (Ceará), analyzed the material and agreed with the initial conclusions. “It was clear to me that this is a primitive reptile that did not belong to pterosaurs, as it did not present any unequivocal features of this lineage” explained Holgado and pointed out: “But the present knowledge of the faunas at the end of the Triassic indicates that the disparity of animals at that time was so great that animals that might resemble pterosaurs at first glance, but really they are not flying reptiles. This is what happened to Faxinalipterus and Maehary.”

“The material on which Faxinalipterus is based is very fragile and very incomplete. In addition, parts of the bones were covered by rock matrix, which required a more detailed preparation” commented Cesar Schultz, from UFRGS and one of the authors of the 2010 work and of the new research that has just been published.

The preparation of the original material required a lot of experience and was carried out at the National Museum. “Fortunately, we were able to photograph the entire specimen in detail,” said Orlando Grillo, who took care to reproduce in the form of drawings each anatomical detail of the bones of Faxinalipterus.

It was with the help of a CT scanner that the enigma was revealed. “Computed tomography has been an increasingly used tool in paleontological studies” highlights Ricardo Lopes from COPPE/UFRJ. “It is a non-destructive analysis that allows the visualization of anatomical details still covered by the sedimentary rock where the fossil is preserved” adds Olga Araújo, also from COPPE.

“In the original work from 2010, we found that the teeth present in the maxilla of Faxinalipterus were very closely spaced, which is a characteristic of early Triassic pterosaurs. However, tomography of the maxilla showed that the teeth were not as separated as initially thought, since many teeth had been lost during the fossilization process. As a result, the dentition pattern and the close-spacing between the alveoli (cavities where the teeth are inserted) were not consistent with pterosaurs,” highlights Marina Soares.

After these studies, there was still a doubt about who, after all, Faxinalipterus was. The solution came from the finding of a new specimen that had been collected in the same region where the specimens of Faxinalipterus came from. “Systematic collections have been carried out by CAPPA (Support Center for Paleontological Research of the Fourth Colony), from UFSM, revealing a series of new fossil species for the Triassic of Rio Grande do Sul” commented Flávio Pretto. At the Linha de São Luiz fossil site, in the municipality of Faxinal do Soturno, several fossils have already been found, such as close relatives of mammals, dinosaurs and other reptiles. The region where the excavations were carried out is located in the territory of the Quatro Colônia — that is seeking to become an UNESCO Geopark.

“When we had access to the study that was being developed by the National Museum team, it became clear that the maxilla, until then referred to Faxinalipterus, was very similar to the material we were studying,” added Leonardo Kerber. “They were definitely not examples of a pterosaur,” reinforced Felipe Pinheiro, from UNIPAMPA, a researcher who is also an expert in winged reptiles.

Using an anatomical database, the team established that Faxinalipterus would be closely related to lagerpetids, a branch considered to be a sister group to Pterosauria in more recent studies. Together, lagerpetids and pterosaurs form a broader group called Pterosauromorpha. In this context, the new species Maehary bonapartei was positioned as the most primitive member within Pterosauromorpha. “That is, Faxinalipterus and Maehary are not pterosaurs, but are related to them. Especially Maehary is configured as a key element in the elucidation of how the anatomical characteristics evolved along the lineage of pterosauromorphs to the pterosaurs themselves, fully adapted to the flight,” points out Rodrigo Müller. “These species, with an estimated length of 30 cm for Faxinalipterus and 40 cm for Maehary, demonstrate the importance of continuing to collect fossils in this region.”

The genus name of the new species comes from Ma’ehary, an expression of the original Guarani-Kaiowa people, which means “who looks at the sky” in allusion to its position in the evolutionary line of reptiles, being the most primitive of the Pterosauromorpha, group which includes the fascinating pterosaurs. The specific name is a fitting tribute to the main researcher of fossil vertebrates in Argentina, José Fernando Bonaparte (1928-2020), who died recently, and who worked actively together with Brazilian paleontologists in outcrops of Rio Grande do Sul, in the collection and description of many extinct vertebrates that lived during the Triassic period, including Faxinalipterus.

Now researchers are looking for new findings that help to understand how the first forms of this fascinating group of pterosaurs came to be.

Reference:
Alexander W.A. Kellner, Borja Holgado, Orlando Grillo, Flávio Augusto Pretto, Leonardo Kerber, Felipe Lima Pinheiro, Marina Bento Soares, Cesar Leandro Schultz, Ricardo Tadeu Lopes, Olga Araújo, Rodrigo Temp Müller. Reassessment of Faxinalipterus minimus, a purported Triassic pterosaur from southern Brazil with the description of a new taxon. PeerJ, 2022; 10: e13276 DOI: 10.7717/peerj.13276

Note: The above post is reprinted from materials provided by PeerJ.

Volcanoes at fault if the Earth slips

One of the strombolian explosions that have occurred at Stromboli about every 10 minutes for at least 2000 years. © UNIGE, Luca Caricchi
One of the strombolian explosions that have occurred at Stromboli about every 10 minutes for at least 2000 years. © UNIGE, Luca Caricchi

The 2016 Kumamoto earthquakes shocked inhabitants of the western island of Kyushu, causing hundreds of casualties and serious damage to vital infrastructure. The epicenter of the quake was traced to the Futagawa fault in a region neighboring Mount Aso, an active volcano in Kumamoto Prefecture that last erupted in October 2021.

An investigation of earth displaced by the series of quakes has offered potentially new clues into seismic activity in regions close to volcanoes. The study has also attributed the root cause of the 7.3-magnitude mainshock to specific geological damage.

The Futagawa strike-slip fault is a vertical break in the ground tracing a line southwest originating from Mount Aso, where the two sides of the fault point straight down and brush against each other side to side during an earthquake.

The research team had anticipated that any rupturing would occur exclusively near the strike-slip fault system. But as Weiren Lin of KyotoU’s Graduate School of Engineering says, ”Our discovery of a relatively large dip-slipdisplacement at the site was unexpected.”

As part of the team’s exploration around the epicenter of the 2016 quakes, scientists drilled a series of bore holes, including one that measured more than 600 meters deep. By extracting and analyzing the types of rocks present in these cores, they were able to reconstruct the different layers of earth around the fault.

Surprisingly, at two boreholes 80 meters apart, the scientists noticed that the same layer of rock sediment was appearing at different depths and separated by more than 200 meters vertically. This large gap could only be explained by the current strike-slip motion, where the two sides of the fault move up and down with respect to each other.

The team has attributed this dramatic change in the fault slip mode to eruption activity of Aso occurring around this time. Such observations from the Aso volcanic region could apply more broadly to similar volcanic areas near other subduction zones.

Lin concludes, ”Until about 87,000 years ago, this fault was moving in a completely different way. We hope that our results increase understanding of interactions between faulting and volcanic activities in other regions of the world.”

Reference:
Susumu Shibutani, Weiren Lin, Koichiro Sado, Akihiro Aizawa, Katsuaki Koike. An Ancient >200 m Cumulative Normal Faulting Displacement Along the Futagawa Fault Dextrally Ruptured During the 2016 Kumamoto, Japan, Earthquake Identified by a Multiborehole Drilling Program. Geochemistry, Geophysics, Geosystems, 2022; 23 (1) DOI: 10.1029/2021GC009966

Note: The above post is reprinted from materials provided by Kyoto University.

Researchers discover overlooked Jurassic Park of lizards

The fossil of Jurassic lizard Eichstaettisaurus. Credit: Jorge Herrera Flores
The fossil of Jurassic lizard Eichstaettisaurus. Credit: Jorge Herrera Flores

New research published today in eLife by researchers from the Institut Català de Paleontologia Miquel Crusafont (ICP) and the University of Bristol (UB) moves back the moment of the radiation of squamates — the group of reptiles that includes lizards, snakes and worm lizards — to the Jurassic, a long time before current estimates.

The Squamata is the largest order of reptiles, including lizards, snakes and worm lizards. Squamates are all cold-blooded, and their skins are covered by horny scales. They are key parts of modern terrestrial faunas, especially in warmer climates, with an astonishing diversity of more than 10,000 species. However, understanding the evolutionary paths that forged their success are still poorly understood.

There is consensus that all the main squamate groups had arisen before the event that wiped out dinosaurs and other groups of reptiles at the end of the Mesozoic era. Before that global catastrophic event, through the Cretaceous, many terrestrial tetrapod groups like mammals, lizards and birds, apparently underwent a great diversification during the so-called Cretaceous Terrestrial Revolution, triggered by the rise of flowering plants. The scarcity of fossil remains of squamates through the Jurassic suggested that the main burst of squamate evolution happened in the Cretaceous (between 145 and 66 Myr.), when their fossil record dramatically improves.

Now, a new paper published in eLife, led by Arnau Bolet, paleontologist at the Institut Català de Paleontologia Miquel Crusafont and the University of Bristol, however, challenges this view by suggesting a much earlier radiation of squamates. Along with colleagues from the University of Bristol Michael Benton, Tom Stubbs and Jorge Herrera-Flores, their research concludes that this group of reptiles probably achieved a diverse array of adaptations in the Jurassic (between 201 and 145 Myr.), long before previously thought. “Even though Jurassic squamates are rare, reconstructed evolutionary trees show that all the main specializations of squamates evolved then, and it’s possible to distinguish adaptations of geckoes, iguanas, skinks, worm lizards, and snakes some 50 million years earlier than had been thought,” explains Michael Benton, co-author of the research.

But how could the scarce Jurassic fossils suggest an early burst in evolution? The key is in their anatomy. The few Jurassic squamates do not show primitive morphologies as would be expected, but they relate directly to the diverse modern groups. “Instead of finding a suite of generalized lizards on the stem of the squamate tree, what we found in the Jurassic were the first representatives of many modern groups, showing advanced morphological features,” says Arnau Bolet, lead author of the article.

The observed times of divergence, morphospace plots and evolutionary rates, all suggest that the Jurassic was a time of innovation in squamate evolution, during which the bases of the success of the group were established. According to these results, the apparent sudden increase in diversity observed in the Cretaceous could be related to an improved fossil record, capable of recording a larger number of species, or to a burst of origins of new species related to the new kinds of forests and insects.

Establishing the timing and mode of radiation of squamates is key for not only understanding the dynamics of terrestrial ecosystems in the Mesozoic, but also for deciphering how the group achieved an astonishing diversity of more than 10,000 species, only rivalled by birds among tetrapods.

Reference:
Arnau Bolet, Thomas L Stubbs, Jorge A Herrera-Flores, Michael J Benton. The Jurassic rise of squamates as supported by lepidosaur disparity and evolutionary rates. eLife, 2022; 11 DOI: 10.7554/eLife.66511

Note: The above post is reprinted from materials provided by University of Bristol.

Dinosaur extinction changed plant evolution

The large, woody fruits of the Manicaria saccifera palm that depend on large animals for their dispersal. (Picture: John Dransfield, Royal Botanic Gardens, Kew)
The large, woody fruits of the Manicaria saccifera palm that depend on large animals for their dispersal. (Picture: John Dransfield, Royal Botanic Gardens, Kew)

With the extinction of large, non-flying dinosaurs 66 million years ago, large herbivores were missing on Earth for the subsequent 25 million years. Since plants and herbivorous animals influence each other, the question arises whether, and how this very long absence and the later return of the so-called “megaherbivores” affected the evolution of the plant world.

To answer this question, a research team led by iDiv and Leipzig University analysed fossil and living palms today. Genetic analyses enabled the researchers to trace the evolutionary developments of plants during and after the absence of megaherbivores. Thus, they first confirmed the common scientific assumption that many palm species at the time of the dinosaurs bore large fruits and were covered with spines and thorns on their trunks and leaves.

However, the research team found that the “evolutionary speed” with which new palm species with small fruits arose during the megaherbivore gap decreased, whereas the evolutionary speed of those with large fruits remained almost constant. The size of the fruits themselves, however, also increased. So, there were palms with large fruits even after the extinction of the dinosaurs. Apparently, much smaller animals could also eat large fruits and spread the seeds with their excretions. “We were thus able to refute the previous scientific assumption that the presence of large palm fruits depended exclusively on megaherbivores,” says the study’s first author Dr Renske Onstein from iDiv and Leipzig University. “We therefore assume that the lack of influence of large herbivores led to denser vegetations in which plants with larger seeds and fruits had an evolutionary advantage.”

However, the defence traits of the plants; spines and thorns on leaves and stems, showed a different picture: the number of palm species with defence traits decreased during the megaherbivore gap. “Defence traits without predators apparently no longer offered evolutionary advantages,” says Onstein, who heads the junior research group Evolution and Adaptation at iDiv. “However, they returned in most palm species when new megaherbivores evolved, in contrast to the changes in fruits, which persisted.”

With their work, the researchers shed new light on evolution and adaptation during one of the most enigmatic and unique periods in the history of plant evolution, during and after megaherbivore extinctions. Understanding how megaherbivore extinctions affected plant evolution in the past can also help predict future ecological developments. For example, the authors have noted the loss of traits during the megaherbivore gap. This loss can affect important ecosystem functions and processes, such as seed dispersal or herbivory. The ongoing extinction of large animals due to human hunting and climate change may thus also affect trait variation in plant communities and ecosystems today and in the foreseeable future.

Reference:
Renske E. Onstein, W. Daniel Kissling, H. Peter Linder. The megaherbivore gap after the non-avian dinosaur extinctions modified trait evolution and diversification of tropical palms. Proceedings of the Royal Society B: Biological Sciences, 2022; 289 (1972) DOI: 10.1098/rspb.2021.2633

Note: The above post is reprinted from materials provided by German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig. Original written by Urs Moesenfechtel.

Earliest geochemical evidence of plate tectonics found in 3.8-billion-year-old crystal

Creative destruction: a thinner ocean plate sides under a continental plate, melting and recycling the ocean crust into the Earth’s interior and birthing volcanoes in this illustration of subduction, a consequence of modern plate tectonics. A new study reports evidence of a transition in multiple locations around the world, 3.8-3.6 billion years ago, from stable “protocrust” to pressures and processes that look a lot like modern subduction, suggesting a time when plates first got moving. Credit: Nikolas Midttun, CC-BY
Creative destruction: a thinner ocean plate sides under a continental plate, melting and recycling the ocean crust into the Earth’s interior and birthing volcanoes in this illustration of subduction, a consequence of modern plate tectonics.
A new study reports evidence of a transition in multiple locations around the world, 3.8-3.6 billion years ago, from stable “protocrust” to pressures and processes that look a lot like modern subduction, suggesting a time when plates first got moving.
Credit: Nikolas Midttun, CC-BY

A handful of ancient zircon crystals found in South Africa hold the oldest evidence of subduction, a key element of plate tectonics, according to a new study published today in AGU Advances, AGU’s journal for high-impact, open-access research and commentary across the Earth and space sciences.

These rare time capsules from Earth’s youth point to a transition around 3.8 billion years ago from a long-lived, stable rock surface to the active processes that shape our planet today, providing a new clue in a hot debate about when plate tectonics was set in motion.

Earth’s crust and the top layer of mantle just under it are broken up into rigid plates that move slowly on top of viscous but mobile lower layers of mantle rock. Heat from Earth’s core drives this slow but inexorable motion, responsible for volcanoes, earthquakes, and the uplift of mountain ranges.

Estimates for when this process revved up and modern crust formed range from over 4 billion years ago to just 800 million years ago. Uncertainty arises because the geologic record from Earth’s youth is sparse, due to the surface recycling effect of plate tectonics itself. Almost nothing remains from the Hadean Eon, Earth’s first 500 million years.

“The Hadean Earth is this big mystery box,” said Nadja Drabon, a geologist at Harvard University and the lead author of the new study.

Tiny time capsules

In an exciting step forward in solving this mystery, in 2018 Drabon and her colleagues unearthed a chronological series of 33 microscopic zircon crystals from a rare, ancient block of crust in the Barberton Greenstone Belt in South Africa, that formed at different times over a critical 800-million-year span from 4.15 to 3.3 billion years ago.

Zircon is a relatively common accessory mineral in Earth’s crust, but ancient representatives from the Hadean Eon, 4 to 4.56 billion years ago, are exceedingly rare, found in only 12 places on Earth, and usually in numbers fewer than three at each location.

Hafnium isotopes and trace elements preserved in the Greenstone Belt zircons told a story about the conditions on Earth at the time they crystalized. Zircons 3.8-billion-years-old and younger appeared to have formed in rock experiencing pressures and melting similar to modern subduction zones, suggesting the crust may have started moving.

“When I say plate tectonics, I’m specifically referring to an arc setting, when one plate goes under another and you have all that volcanism — think of the Andes, for example, and the Ring of Fire,” Drabon said, describing a classic example of subduction.

“At 3.8 billion years there is a dramatic shift where the crust is destabilized, we have new rocks forming and we see geochemical signatures becoming more and more similar to what we see in modern plate tectonics,” Drabon said.

In contrast, the older zircons preserved evidence of a global cap of “protocrust” derived from remelting mantle rock that had remained stable for 600 million years, the study found.

Signs of global change

The new study found a similar transition to conditions resembling modern subduction in zircons from other locations around the world, dating to within about 200 million years of the South African zircons.

“We see evidence for a significant change on the Earth around 3.8 to 3.6 billion years ago and evolution toward plate tectonics is one clear possibility.” Drabon said.

While not conclusive, the results suggest a global change may have begun, Drabon said, possibly starting and stopping in scattered locations before settling into the efficient global engine of constantly moving plates we see today.

Plate tectonics shapes Earth’s atmosphere as well as its surface. Release of volcanic gasses and production of new silicate rock, which consumes large amounts carbon dioxide from the atmosphere, temper large temperature swings from too much or too little greenhouse gas.

“Without all of the recycling and new crust forming, we might be going back and forth between boiling hot and freezing cold,” Drabon said. “It’s kind of like a thermostat for the climate.”

Plate tectonics has, so far, only been observed on Earth, and may be essential to making a planet livable, Drabon said, which makes the origins of plate motions of interest in research into the early development of life.

“The record we have for the earliest Earth is really limited, but just seeing a similar transition in so many different places makes it really feasible that it might have been a global change in crustal processes,” Drabon said. “Some kind of kind of reorganization was happening on Earth.”

Reference:
Nadja Drabon, Benjamin L. Byerly, Gary R. Byerly, Joseph L. Wooden, Michael Wiedenbeck, John W. Valley, Kouki Kitajima, Ann M. Bauer, Donald R. Lowe. Destabilization of Long‐Lived Hadean Protocrust and the Onset of Pervasive Hydrous Melting at 3.8 Ga. AGU Advances, 2022; 3 (2) DOI: 10.1029/2021AV000520

Note: The above post is reprinted from materials provided by American Geophysical Union.

Major 2020 Alaska quake triggered neighboring 2021 temblor

Map shows location of the Shumagin Gap, location of the 2020 Simeonof and 2021 Chignik earthquakes. Map courtesy Alaska Earthquake Center.
Map shows location of the Shumagin Gap, location of the 2020 Simeonof and 2021 Chignik earthquakes. Map courtesy Alaska Earthquake Center.

A study of two powerful earthquakes in adjacent areas off the Alaska Peninsula in 2020 and 2021 shows a connection between the two. It also suggests they may be a part of an 80-year rupture cascade along the fault.

The research was published today by the journal Science Advances in a paper jointly led by University of Alaska Fairbanks Geophysical Institute associate professor Ronni Grapenthin and Michigan State University assistant professor Julie Elliott. UAF postdoctoral researcher Revathy M. Parameswaran is among the four co-authors.

The researchers also conclude that the two deep earthquakes on the Aleutian-Alaska megathrust fault, where the Pacific plate is sliding beneath the North American plate, may have brought shallow portions of the fault closer to failure.

They add that their research will help scientists better understand stress transfer and earthquake triggering in the region and in general.

“One large earthquake increases the stress on the neighboring part of the megathrust fault. This patch then ruptures and increases the stress on the next patch in the fault, like delayed dominos,” Grapenthin said. “And that’s what we’re seeing here.”

The first of the two major quakes, known as the Simeonof event, occurred July 21, 2020. It registered at magnitude 7.8, struck near the Shumagin Islands south of the Alaska Peninsula and ruptured westward.

The second quake, the Chignik event, occurred just over one year later on July 28, 2021. It registered at magnitude 8.2, was located south of the Alaska Peninsula and northeast of the Simeonof quake and ruptured eastward.

The two quakes and their aftershocks occurred in the Shumagin Gap, a spot near the Shumagin Islands in a known band of historical ruptures. That 1,900-mile subduction zone, where the Pacific tectonic plate slides under the North American plate, starts at the tip of the Aleutian Islands. It continues along the south side of the islands and the Alaska Peninsula, curves upward across the Kenai Peninsula and encompasses the Anchorage area and Prince William Sound.

No major earthquakes had been recorded in the Shumagin Gap, a space about 100 miles long in the subduction zone, until the 2020 and 2021 quakes.

“This could be a case study to understand how adjacent earthquake patches could be activated by a significant release of energy that has accumulated through plate motion,” Parameswaran said.

The researchers studied data to assess the impact of the stress changes caused by the 2020 Simeonof quake, particularly as they might relate to the Chignik quake’s rupture site.

Modeling the Simeonof quake’s stress buildup shows that the Chignik hypocenter, the location inside the earth at which an earthquake rupture begins, is embedded in an area of increased stress change, consistent with what scientists know about how earthquakes are triggered.

The work also indicated some notable areas of “very high” stress loading of the fault, especially in the shallower regions of the model fault plane. That area didn’t rupture during this earthquake, according to the research paper.

The researchers added that the two earthquakes may be part of an 80-year cascade of large subduction earthquakes along this major plate boundary and that the cascade has now concluded, with the most recent large event prior to the 2020 Simeonof quake being the 1965 magnitude 8.7 earthquake off the Rat Islands in the Aleutian Chain.

Prior to 1965, five earthquakes of magnitude 8 or greater occurred within 30 years from the farthest Aleutian Islands to Southcentral Alaska.

“In the concept of cascades, the entire Aleutian-Alaska megathrust has now ruptured and released most of the stress that has accumulated since the onset of that most recent cascade,” Grapenthin said.

Reference:
Julie L. Elliott, Ronni Grapenthin, Revathy M. Parameswaran, Zhuohui Xiao, Jeffrey T. Freymueller, Logan Fusso. Cascading rupture of a megathrust. Science Advances, 2022; 8 (18) DOI: 10.1126/sciadv.abm4131

Note: The above post is reprinted from materials provided by University of Alaska Fairbanks. Original written by Rod Boyce.

Landslides can have a major impact on glacier melt and movement

Using satellite imagery (shown above) to study the effects of a 2019 landslide on the Amalia Glacier in Patagonia, a University of Minnesota-led research team found the landslide helped stabilize the glacier and caused it to grow by about 1,000 meters over the last three years. Photo credit: Max Van Wyk de Vries
Using satellite imagery (shown above) to study the effects of a 2019 landslide on the Amalia Glacier in Patagonia, a University of Minnesota-led research team found the landslide helped stabilize the glacier and caused it to grow by about 1,000 meters over the last three years. Photo credit: Max Van Wyk de Vries

A team led by University of Minnesota Twin Cities researchers has revealed, for the first time, that landslides can have a major impact on the movement of glaciers. Using satellite imagery to study the effects of a 2019 landslide that occurred on the Amalia Glacier in the Patagonia region of Chile, the researchers found that the landslide caused the glacier to grow in size and has since slowed down its melting process.

This information could help scientists more accurately predict the size of glaciers in the future and better understand the risks of living in areas with both glaciers and landslides.

The study is published in Geology, a peer-reviewed geoscience journal published by the Geological Society of America.

Glaciologists have been monitoring the recession of glaciers due to global warming around the world for decades. The 150-square-kilometer Amalia Glacier has been receding steadily — or losing ice and becoming smaller — having shrunk by more than 10 kilometers over the past 100 years. Until now, the effect of landslides on this movement was largely unknown.

The University of Minnesota-led research team found that after the 2019 landslide in question, the Amalia Glacier immediately began to “advance” or grow at a fast rate. Although its flow has since slowed down to half its pre-landslide speed, over the last three years the glacier has grown by about 1,000 meters.

“These landslides are actually fairly common,” explained Max Van Wyk de Vries, lead author of the study and a recent Ph.D. graduate of the University of Minnesota’s N.H. Winchell School of Earth and Environmental Sciences. “If they’re able to stabilize glaciers, then it might affect projections of how large certain glaciers will be in the future. There’s the context of global warming and climate change here, which is causing glaciers all around the world to retreat at unprecedented rates. That’s affecting essentially everyone around the world because as these glaciers get smaller, they cause the sea levels to rise.”

The researchers found that the landslide pushed ice from the glacier downstream, causing it to immediately advance and increase in size. Then, sediment and rock from the landslide built up where the glacier borders the ocean, preventing icebergs from breaking off into the sea and effectively stabilizing the glacier.

This study also gave researchers an idea of how proximity to glaciers can unfortunately enhance the impact of landslides on neighboring communities.

“The combination of glaciers and landslides can be extremely dangerous,” said Van Wyk de Vries, a recipient of the University of Minnesota’s CSE and Doctoral Dissertation fellowships. “Glaciers can allow landslides to fluidize and flow much further than they would have originally. They only affect people who live in these high-mountain areas where steep slopes and glaciers co-exist. But we still have a limited understanding of these processes, so being able to investigate events like this can give us a better idea of the risk associated with living in these glacierized, high-mountain areas.”

Using satellite imagery allowed the researchers to monitor the movement of the glacier in real time without being physically on site. In the future, this method could be used more often to monitor glaciers in remote locations. The University of Minnesota research team, along with other scientists, is currently studying satellite data from the last 20-30 years to see if they can spot previously unrecorded landslides that occurred on glaciers. They aim to increase their data pool so they can better understand this phenomenon.

In addition to Van Wyk de Vries, the research team included University of Minnesota School of Earth and Environmental Sciences McKnight Land-Grant Associate Professor Andy Wickert; Macalester College Geology Professor Kelly MacGregor; University of Magallanes, Chile Assistant Professor Camilo Rada; and University of Colorado Boulder Assistant Professor Michael Willis.

This research was funded by the National Science Foundation.

Reference:
Maximillian Van Wyk de Vries, Andrew D. Wickert, Kelly R. MacGregor, Camilo Rada, Michael J. Willis. Atypical landslide induces speedup, advance, and long-term slowdown of a tidewater glacier. Geology, 2022; DOI: 10.1130/G49854.1

Note: The above post is reprinted from materials provided by University of Minnesota.

Sampling the deep graveyard of Earth’s earliest crust

Basalt mit frischen Klinopyroxenen (credit Jonas Tusch)
Basalt mit frischen Klinopyroxenen (credit Jonas Tusch)

In an international collaboration, Earth scientists at the University of Cologne and Freie Universität Berlin discovered that some magmas on Earth, which made their way through the deep terrestrial mantle and erupted at Earth’s surface, originate from mantle portions that contain remnants of Earth’s earliest crust. This ancient material must have been buried in a ‘graveyard’ of old and cold crust more than 4 billion years ago and survived since then, maybe since the giant impact event forming the Moon.

This finding is unexpected because the plate tectonic regime of our planet progressively recycles crustal material via large-scale mantle convection at much smaller time scales. Therefore, it has been assumed that vestiges of early geological processes on Earth can only be found as analogues, on other terrestrial planets (Mercury, Venus, and Mars), asteroids, or the Moon. However, according to their study ‘Long-term preservation of Hadean protocrust in Earth’s mantle’, which has recently appeared in the Proceedings of the National Academy of Sciences (PNAS), magmatic rocks that erupted throughout Earth’s history can still carry signatures that provide detailed information about the nature of the first crust, its long-term preservation in a graveyard in the lower-most mantle, and its resurrection via younger volcanism.

For their study, the geologists investigated up to 3.55 billion years old rocks from southern Africa. The analysis of these rocks revealed small anomalies in the isotope composition of the element tungsten (W). The origin of these isotope anomalies, namely the relative abundance of 182W, relates to geological processes that must have occurred immediately after the formation of the Earth more than 4.5 billion years ago.

Model calculations by the authors show that the observed 182W isotope patterns are best explained by the recycling of Earth’s earliest crust into mantle material that ascends via plumes from the lower mantle to generate lavas erupting at Earth’s surface. Intriguingly, the study shows that similar isotope patterns can be observed in distinct types of modern volcanic rocks (ocean island basalts), which demonstrates that Earth’s earliest crust is still buried in the lowermost mantle.

‘We assume that the lower layers of the crust — or the roots of the primordial continents — became heavier than their surroundings due to a geological maturation process and therefore sank into the Earth’s underlying mantle. Similar to a lava lamp,’ geochemist Dr Jonas Tusch from the University of Cologne’s Institute of Geology and Mineralogy remarked. ‘This fascinating insight provides a geochemical fingerprint of the young Earth, allowing us to better understand how large continents formed over the history of our planet. It also explains how our current, oxygen-rich atmosphere evolved — setting the stage for the origin of complex life,’ Dr Elis Hoffmann of Freie Universität Berlin added.

The geochemical fingerprint of the early Earth can also be compared with findings about other planets obtained during space missions. For example, data from Mars missions and studies of Martian meteorites show that Mars still has a very old surface due to the lack of plate tectonics, and that its composition may correspond to that of the young Earth.

Reference:
Jonas Tusch, J. Elis Hoffmann, Eric Hasenstab, Mario Fischer-Gödde, Chris S. Marien, Allan H. Wilson, Carsten Münker. Long-term preservation of Hadean protocrust in Earth’s mantle. Proceedings of the National Academy of Sciences, 2022; 119 (18) DOI: 10.1073/pnas.2120241119

Note: The above post is reprinted from materials provided by University of Cologne.

Large Mesozoic Marine Reptile Described

Vertebrate bones exposed during fieldwork in the Zhebao region of Guangxi ProvinceThe arrows indicate ribs, exposed in cross-section
Vertebrate bones exposed during fieldwork in the Zhebao region of Guangxi
ProvinceThe arrows indicate ribs, exposed in cross-section

Ichthyosaurs are a group of successful Mesozoic marine reptiles that have a worldwide distribution, but their evolutionary origin is still unclear. In recent years, many new marine reptiles related to ichthyosaurs, and called early ichthyosauromorphs, have been found in rocks of Early Triassic age and shed light on the origin of ichthyosaurs. These early ichthyosauromorphs have been discovered in many countries, but most of them are from China, including Cartorhynchus, Chaohusaurus, and several members of an ichthyosauromorph subgroup called the Hupehsuchia. They are generally small (about 1m long) and are from the eastern and central regions of China.

In a new paper published in the journal PeerJ, researchers from China and Canada report a new large early ichthyosauromorph, named Baisesaurus robustus, from the southwest of China, extending the known geographic distribution of this group.

In 2017, Guizhou Geological Survey field crews found some vertebrate bones exposed in limestone in the Zhebao region of Guangxi Province, southwest China, and they invited researchers (Haishui Jiang and Fenglu Han) from China University of Geosciences (Wuhan) to join them in studying the specimen. Jiang and Han confirmed that the fossil was that of a marine reptile, possibly a relative of ichthyosaurs. The specimen was collected by the joint research team in 2018, and was prepared in the Wuhan Centre of the China Geological Survey.

The specimen comprises only the front part of the trunk skeleton, including some vertebrae and ribs, a limb bone, and abdominal bones called gastralia. This made classification difficult, but the researchers compared the fossil comprehensively with other marine reptiles from the Early Triassic and ultimately identified it as an ichthyosauromorph. “The dorsal ribs and gastralia are more similar to those of other early ichthyosauromorphs, such as Chaohusaurus, than to sauropterygians,” said Long Cheng, a coauthor on the study.

In general, Baisesaurus robustus shares more similarities with Utatsusaurus from Japan, another early ichthyosauromorph, than with other marine reptiles. The researchers also found some unusual features that were unknown in other early ichthyosauromorphs, such as deep depressions on the sides of the vertebrae, and a robust radius with two distinct joint facets for contact with wrist bones. These new features indicate that the fossil belongs to a previously unknown species, which the researchers named Baisesaurus robustus. Moreover, Baisesaurus is estimated to have been about 3m long, making this newly discovered marine reptile significantly larger than any other Early Triassic ichthyosauromorph from China. Finally, Baisesaurus has a more robust radius than many other early ichthyosauromorphs, suggesting strong swimming abilities that might have been used for long-distance migrations along the eastern margin of an ancient ocean known as the Paleo-Tethys.

“I’m inclined to take Baisesaurus as a reminder that there’s still a lot to be discovered about the tremendous evolutionary explosion of vertebrate diversity that took place in the Triassic,” said Corwin Sullivan, a coauthor on the study. Sullivan is an associate professor at the University of Alberta in Edmonton, Canada, and curator of the Philip J. Currie Dinosaur Museum in nearby Wembley.

Reference:
Jicheng Ren, Haishui Jiang, Kunpeng Xiang, Corwin Sullivan, Yongzhong He, Long Cheng, Fenglu Han. A new basal ichthyosauromorph from the Lower Triassic (Olenekian) of Zhebao, Guangxi Autonomous Region, South China. PeerJ, 2022; 10: e13209 DOI: 10.7717/peerj.13209

Note: The above post is reprinted from materials provided by PeerJ.

Seafloor spreading has been slowing down

Painting of the Mid-Ocean Ridge with rift axis by Heinrich Berann based on the scientific profiles of Marie Tharp and Bruce Heezen (1977).
Painting of the Mid-Ocean Ridge with rift axis by Heinrich Berann based on the scientific profiles of Marie Tharp and Bruce Heezen (1977).

A new global analysis of the last 19 million years of seafloor spreading rates found they have been slowing down. Geologists want to know why the seafloor is getting sluggish.

New oceanic crust forms continuously along rifts thousands of miles long on the seafloor, driven by plate tectonics. As subduction pulls old crust down, rifts open up like fissures in an effusive volcano, drawing hot crust toward the surface. Once at the surface, the crust begins to cool and gets pushed away from the rift, replaced by hotter, younger crust.

This cycle is called seafloor spreading, and its rate shapes many global processes, including sea level and the carbon cycle. Faster rates tend to cause more volcanic activity, which releases greenhouse gases, so deciphering spreading rates helps contextualize long-term changes in the atmosphere.

Today, spreading rates top out around 140 millimeters per year, but peaked around 200 millimeters per year just 15 million years ago in some places, according to the new study. The study was published in the AGU journal Geophysical Research Letters, which publishes high-impact, short-format reports with immediate implications spanning all Earth and space sciences.

The slowdown is a global average, the result of varying spreading rates from ridge to ridge. The study examined 18 ridges, but took a particularly close look at the eastern Pacific, home to some of the globe’s fastest spreading ridges. Because these slowed greatly, some by nearly 100 millimeters per year slower compared to 19 million years ago, they dragged down the world’s average spreading rates.

It’s a complex problem to solve, made more difficult by the seafloor’s slow and steady self-destruction.

“We know more about the surfaces of some other planets than we do our own seafloor,” said Colleen Dalton, a geophysicist at Brown University who led the new study. “One of the challenges is the lack of perfect preservation. The seafloor is destroyed, so we’re left with an incomplete record.”

The seafloor is destroyed in subduction zones, where oceanic crust slides under continents and sinks back into the mantle, and is reforged at seafloor spreading ridges. This cycle of creation and destruction takes about every 180 million years, the age of the oldest seafloor. The crust’s magnetic record tracks this pattern, producing identifiable strips every time the Earth’s magnetic field reverses.

Dalton and her co-authors studied magnetic records for 18 of the world’s largest spreading ridges, using seafloor ages and their areas to calculate how much ocean crust each ridge has produced over the last 19 million years. Each ridge evolved a little differently: some lengthened, some shrank; some sped up, but almost all slowed down. The overall result of Dalton’s work is that average seafloor spreading slowed down by as much as 40% over that time.

The driver here might be located at subduction zones rather than spreading ridges: for example, as the Andes grow along the western edge of the South American continent, the mountains push down on the crust.

“Think of it as increased friction between the two colliding tectonic plates,” Dalton said. “A slowdown in convergence there could ultimately cause a slowdown in spreading at nearby ridges.” A similar process could have operated underneath the Himalaya, with the rapidly growing range slowing spreading along the ridges in the Indian Ocean.

However, Dalton points out, this added friction can’t be the only driver of the slowdown, because she found slowing rates globally and mountain growth is regional. Larger-scale processes, like changes in mantle convection, could also be playing a role. In all likelihood, she concludes, it’s a combination of both. To learn more, Dalton hopes to collect absolute plate speeds, rather than the relative speeds used in this study, which will better allow her to determine the cause of the slowdown.

Reference:
Colleen A. Dalton, Douglas S. Wilson, Timothy D. Herbert. Evidence for a Global Slowdown in Seafloor Spreading Since 15 Ma. Geophysical Research Letters, 2022; 49 (6) DOI: 10.1029/2022GL097937

Note: The above post is reprinted from materials provided by American Geophysical Union.

Million-year-old Arctic sedimentary record sheds light on climate mystery

Lake El´gygytgyn. Credit: UMass Amherst
Lake El´gygytgyn. Credit: UMass Amherst

New research, led by the University of Massachusetts Amherst and published recently in the journal Climate of the Past, is the first to provide a continuous look at a shift in climate, called the Mid-Pleistocene Transition, that has puzzled scientists. Kurt Lindberg, the paper’s first author and currently a graduate student at the University at Buffalo, was only an undergraduate when he completed the research as part of a team of climate scientists at UMass Amherst.

Somewhere around 1.2 million years ago, a dramatic shift in the Earth’s climate, known as the Mid-Pleistocene Transition, or MPT, happened. Previously, ice ages had occurred, with relative regularity, every 40,000 years or so. But then, in a comparatively short window of geological time, the time between ice ages more than doubled, to every 100,000 years. “It’s a real puzzle,” says Isla Castañeda, professor of geosciences at UMass Amherst and one of the paper’s co-authors. “No one really knows why this shift occurred.”

One of the big barriers to understanding the MPT is that very little data exists. The oldest Arctic ice cores only go back approximately 125,000 years. And older sedimentary cores are almost nonexistent, because as ice ages have come and gone, the advancing and retreating ice sheets have acted like enormous bulldozers, scraping much of the exposed land down to bedrock.

However, there is one place in the world, in far northeastern Russia, that is both above the Arctic Circle and which has never been covered by glaciers: Lake El’gygytgyn. This is where the polar scientist, Julie Brigham-Grette, professor of geosciences at UMass Amherst and one of the paper’s co-authors, comes in.

In 2009, Brigham-Grette led an international team of scientists to Lake El’gygytgyn, where they drilled a 685.5 meter sediment core, representing approximately the last 3.6 million years of Earth’s history. Lindberg and his co-authors used the portion of this sedimentary core that spanned the MPT and looked for specific biomarkers that could help them ascertain temperature and vegetation. With this information, they were able to reconstruct, for the first time, climactic conditions in the Arctic during the MPT.

While the team did not solve the mystery of the MPT, they did make a few surprising discoveries. For example, an interglacial period, or era when ice was in retreat, known as MIS 31 is widely recognized as having been abnormally warm — and yet the records at Lake El’gygytgyn show only moderate warmth. Instead, three other interglacial periods, MIS 21, 27 and 29 were as warm or warmer. Finally, the team’s research shows a long-term drying trend throughout the MPT.

Reference:
Kurt R. Lindberg, William C. Daniels, Isla S. Castañeda, Julie Brigham-Grette. Biomarker proxy records of Arctic climate change during the Mid-Pleistocene transition from Lake El’gygytgyn (Far East Russia). Climate of the Past, 2022; 18 (3): 559 DOI: 10.5194/cp-18-559-2022

Note: The above post is reprinted from materials provided by University of Massachusetts Amherst.

A swarm of 85,000 earthquakes at the Antarctic Orca submarine volcano

Seismogram
Representative Image: Seismogram

Volcanoes can be found even off the coast of Antarctica. At the deep-sea volcano Orca, which has been inactive for a long time, a sequence of more than 85,000 earthquakes was registered in 2020, a swarm quake that reached proportions not previously observed for this region. The fact that such events can be studied and described in great detail even in such remote and therefore poorly instrumented areas is now shown by the study of an international team published in the journal “Communications Earth and Environment.” Led by Simone Cesca from the German Research Centre for Geosciences (GFZ) Potsdam, researchers from Germany, Italy, Poland and the United States were involved. With the combined application of seismological, geodetic and remote sensing techniques, they were able to determine how the rapid transfer of magma from the Earth’s mantle near the crust-mantle boundary to almost the surface led to the swarm quake.

The Orca volcano between the tip of South America and Antarctica

Swarm quakes mainly occur in volcanically active regions. The movement of fluids in the Earth’s crust is therefore suspected as the cause. Orca seamount is a large submarine shield volcano with a height of about 900 metres above the sea floor and a base diameter of about 11 kilometres. It is located in the Bransfield Strait, an ocean channel between the Antarctic Peninsula and the South Shetland Islands, southwest of the southern tip of Argentina.

“In the past, seismicity in this region was moderate. However, in August 2020, an intense seismic swarm began there, with more than 85,000 earthquakes within half a year. It represents the largest seismic unrest ever recorded there,” reports Simone Cesca, scientist in GFZ’s Section 2.1 Earthquake and Volcano Physics and lead author of the now published study. At the same time as the swarm, a lateral ground displacement of more than ten centimetres and a small uplift of about one centimetre was recorded on neighbouring King George Island.

Challenges of research in a remote area

Cesca studied these events with colleagues from the National Institute of Oceanography and Applied Geophysics — OGS and the University of Bologna (Italy), the Polish Academy of Sciences, Leibniz University Hannover, the German Aerospace Centre (DLR) and the University of Potsdam. The challenge was that there are few conventional seismological instruments in the remote area, namely only two seismic and two GNSS stations (ground stations of the Global Navigation Satellite System which measure ground displacement). In order to reconstruct the chronology and development of the unrest and to determine its cause, the team therefore additionally analysed data from farther seismic stations and data from InSAR satellites, which use radar interferometry to measure ground displacements. An important step was the modelling of the events with a number of geophysical methods in order to interpret the data correctly.

Reconstructing the seismic events

The researchers backdated the start of the unrest to 10 August 2020 and extend the original global seismic catalog, containing only 128 earthquakes, to more than 85,000 events. The swarm peaked with two large earthquakes on 2 October (Mw 5.9) and 6 November (Mw 6.0) 2020 before subsiding. By February 2021, seismic activity had decreased significantly.

The scientists identify a magma intrusion, the migration of a larger volume of magma, as the main cause of the swarm quake, because seismic processes alone cannot explain the observed strong surface deformation on King George Island. The presence of a volumetric magma intrusion can be confirmed independently on the basis of geodetic data.

Starting from its origin, seismicity first migrated upward and then laterally: deeper, clustered earthquakes are interpreted as the response to vertical magma propagation from a reservoir in the upper mantle or at the crust-mantle boundary, while shallower, crustal earthquakes extend NE-SW triggered on top of the laterally growing magma dike, which reaches a length of about 20 kilometres.

The seismicity decreased abruptly by mid November, after about three months of sustained activity, in correspondence to the occurrence of the largest earthquakes of the series, with a magnitude Mw 6.0. The end of the swarm can be explained by the loss of pressure in the magma dike, accompanying the slip of a large fault, and could mark the timing of a seafloor eruption which, however, could not yet be confirmed by other data.

By modeling GNSS and InSAR data, the scientists estimated that the volume of the Bransfield magmatic intrusion is in the range 0.26-0.56 km³. That makes this episode also the largest magmatic unrest ever geophysically monitored in Antarctica.

Simone Cesca continues: “Our study represents a new successful investigation of a seismo-volcanic unrest at a remote location on Earth, where the combined application of seismology, geodesy and remote sensing techniques are used to understand earthquake processes and magma transport in poorly instrumented areas. This is one of the few cases where we can use geophysical tools to observe intrusion of magma from the upper mantle or crust-mantle boundary into the shallow crust — a rapid transfer of magma from the mantle to almost the surface that takes only a few days.”

Reference:
Simone Cesca, Monica Sugan, Łukasz Rudzinski, Sanaz Vajedian, Peter Niemz, Simon Plank, Gesa Petersen, Zhiguo Deng, Eleonora Rivalta, Alessandro Vuan, Milton Percy Plasencia Linares, Sebastian Heimann, Torsten Dahm. Massive earthquake swarm driven by magmatic intrusion at the Bransfield Strait, Antarctica. Communications Earth & Environment, 2022; 3 (1) DOI: 10.1038/s43247-022-00418-5

Note: The above post is reprinted from materials provided by GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre.

The oxidation of volcanoes—a magma opus

One of the strombolian explosions that have occurred at Stromboli about every 10 minutes for at least 2000 years. © UNIGE, Luca Caricchi
One of the strombolian explosions that have occurred at Stromboli about every 10 minutes for at least 2000 years. © UNIGE, Luca Caricchi

A new, Yale-led study unlocks the science behind a key ingredient—namely oxygen—in some of the world’s most violent volcanoes.

The research offers a new model for understanding the oxidation state of arc magmas, the lavas that form some volcanoes, such as the one that erupted dramatically in Tonga earlier this year.

The plume from Tonga’s underwater volcanic eruption on Jan. 15 rose 36 miles into the air. Ash from the volcano reached the mesosphere, Earth’s third layer of atmosphere.

“These eruptions occur in volcanic arcs, such as the Aleutian island chain, which are well known in the circum-Pacific region and produce the world’s most explosive volcanic eruptions,” said Jay Ague, the Henry Barnard Davis Memorial Professor of Earth & Planetary Sciences at Yale.

Ague is first author of the new study, published in the journal Nature Geoscience. Ague is also curator-in-charge of mineralogy and meteoritics for the Yale Peabody Museum of Natural History.

Scientists have long known that arc magmas have a higher oxidation state than rocks in most of the Earth’s mantle (its upper, rocky layer). This is surprising, they say, because arc magmas form in the mantle. There has been no consensus on the origins of the oxidizing signature.

Ague and his colleagues say the process begins with a layer of sediment that covers tectonic plates beneath the ocean floor. Tectonic plates are large slabs of rock that jockey for position in the Earth’s crust and upper mantle.

The sediment covering these ocean plates is largely made up of weathered materials shed from continents or produced as a result of seafloor hydrothermal vent activity. Giant tube worms and other exotic sea creatures commonly thrive near these vents. But regardless of origin, the sediments covering oceanic plates are often highly oxidized.

Tectonic plates are constantly in motion, moving at about the rate that fingernails grow. Oceanic plates are generated at mid-ocean ridges and sink sharply into Earth’s interior—in a process called subduction.

That’s where things get interesting for arc volcanism, Ague said.

When an ocean plate subducts, Ague explained, it heats up, is compressed, and begins to dehydrate. This metamorphism produces hot, water-rich fluids that rise toward the surface.

As these materials move upward through the oxidized sediment layer on top of slabs, the fluids themselves become oxidized—setting the stage for an arc magma.

“As the fluids continue to rise they leave the slab behind and enter Earth’s mantle,” Ague said. “There, the fluids drive mantle melting, producing oxidized magmas that ascend and can ultimately erupt as lava from volcanoes.”

Beyond the dramatic effects of volcanic eruptions, the oxidized character of arc magmas is also geologically significant, Ague said. Oxidation is critical for making certain kinds of ore deposits, particularly copper and gold, such as those found in western South America.

Also, the injection of highly-oxidized, sulfur-bearing gases into the atmosphere after an eruption can lead to transient global cooling of the troposphere, the lowest level of Earth’s atmosphere.

“This was the case with the 1991 eruption of Mount Pinatubo in the Philippines,” Ague said. “It also occurred in a number of famous historical cases, such Mount Tambora in Indonesia in 1815. That was the most powerful volcanic eruption in human history and led to the so-called ‘Year Without a Summer’ in 1816.”

Santiago Tassara, a Bateman Postdoctoral Associate in Yale’s Department of Earth & Planetary Sciences, is a co-author of the new study. Other co-authors include researchers from Cornell University, the Chinese Academy of Sciences, the National Museum of Natural History at the Smithsonian Institution, Freie Universität Berlin, and the University of Crete.

Reference:
Jay Ague, Slab-derived devolatilization fluids oxidized by subducted metasedimentary rocks, Nature Geoscience (2022). DOI: 10.1038/s41561-022-00904-7.

Note: The above post is reprinted from materials provided by Yale University.

Newly identified softshell turtle lived alongside T. rex and Triceratops

An imagined scene from the end of the Cretaceous Period, more than 66 million years ago, has the newly identified softshell turtle Hutchemys walkerorum dwelling alongside iconic species from the Age of the Dinosaurs. (Image: Sergey Krasovskiy)
An imagined scene from the end of the Cretaceous Period, more than 66 million years ago, has the newly identified softshell turtle
Hutchemys walkerorum
dwelling alongside iconic species from the Age of the Dinosaurs. (Image: Sergey Krasovskiy)

A newly described softshell turtle that lived in North Dakota 66.5 million years ago at the end of the Cretaceous Period, just before the end-Cretaceous mass extinction,is oneof the earliest known species of the genus, according to new research shared in the journal Cretaceous Research.

Hutchemys walkerorum lived during a period when large and well-known dinosaurs also roamed Earth, including Tyrannosaurus rex and Triceratops. The find adds important information to scientists’ understanding of softshell turtles more broadly, including the potential effects of the end-Cretaceous mass extinction, which took place in this same time period, on their evolution.

Steven Jasinski, who recently completed his Ph.D. in Penn’s Department of Earth and Environmental Sciences in the School of Arts & Sciences, led the research, collaborating with advisor Peter Dodson of the School of Veterinary Medicine and Penn Arts & Sciences. The research team included Andrew Heckert and Ciara Sailar of Appalachian State University and Asher Lichtig and Spencer Lucas of the New Mexico Museum of Natural History and Science.

Hutchemys walkerorum belongs to a particular group of softshell turtles in the Trionychidae family called plastomenines. These turtles are similar to the softshell turtles that exist today, although the plastron of plastomenine turtles — the bones covering their stomach and abdominal area — are more strongly sutured together and often larger and more robust than in other softshell turtles.

Plastomenines lived during the Cretaceous and Paleogene periods, around 80 million to 50 million years ago. Members of this group first appear in the fossil record during the Late Cretaceous, and a single species continues into the Eocene Epoch, 50 million years ago, but they are at their peak diversity before and after the Cretaceous-Paleogene boundary.

“Until recently we didn’t understand these softshell turtles very well,” says Jasinski. “However, we are starting to get more information on this extinct group of turtles and further understanding their evolution, including how they dealt with the mass extinction.”

The fossil specimen of the new species, a partial carapace — the bones that cover the back and what people think of as a turtle’s “shell” — was discovered in 1975 in southwestern North Dakota. A field crew from Appalachian State University led by Frank K. McKinney and John E. Callahan collected the specimen, along with a specimen of Triceratops, that summer. The fossil turtle specimen remained at Appalachian State until 2013, when Heckert discussed it with Jasinski, a master’s student at East Tennessee State University at the time.

Research started in earnest around that time and continued as Jasinski was at Penn for his doctoral studies. Based on the structure of the specimen, he and colleagues determined this fossil belonged to a genus of turtles from the American West known as Hutchemys. Hutchemys walkerorum represents one of the rare occurrences of these turtles prior to the mass extinction event that brought the Age of Dinosaurs to an end. It also represents the easternmost occurrence of the genus during the Cretaceous Period.

“With this study we gain further insight into winners and losers during the cataclysm that ended the Age of Dinosaurs,” says Dodson. “The mighty dinosaurs fell, and the lowly turtle survived.”

A phylogenetic analysis, comparing the new species with other known trionychids, or softshell turtles, gave the scientists a better understanding of the group’s evolutionary relationships. Their analysis placed Hutchemys walkerorum with other known species of Hutchemys and several other turtles in a distinct group of derived plastomenines, which they named Plastomenini. In addition, the researchers found a group of early trionychids, placing them in a newly established subfamily, Kuhnemydinae. Kuhnemydines are fossil species from Asia, and the team’s analysis suggests the family Trionychidae originated in Asia before migrating to North America sometime in the Late Cretaceous.

The researchers’ investigations also led them to another new classification in the Trionychidae family, a subfamily they named Chitrainae. This group encompasses modern softshell turtles, including the narrow-headed and giant softshell turtles found in southern Asia.

The species name walkerorum honors Greg and Susan Walker, whose philanthropy created The Greg and Susan Walker Endowment in 2006. Under the terms of that gift, students in the Department of Earth and Environmental Science (EES) may apply for funds to undertake research projects for which no other source of support is immediately available.

“The Greg and Susan Walker Endowment awards research support, typically for projects costing up to $5,000, in response to proposals submitted to the endowment through the Department of Earth and Environmental Science,” says Robert Giegengack, professor emeritus.

“The professors and advisors who approve the endowment do an awesome job in helping the students thrive,” says Joan Buccilli, an administrator in the EES department who assists students seeking support. “However, I really do feel I have the best job, getting to navigate through their awards with them and getting to see firsthand how excited they are and what they have accomplished.”

Jasinski was awarded Walker Research Grant funds for this project as well as others describing new species of dinosaurs, turtles, dogs, and investigations of dinosaurs and carnivorous mammals. “The Walkers’ generous support helped me get the most out of my time while at Penn,” says Jasinski, “and I know they were vital to the research of other students as well. This was one of the major reasons we wanted to name this new species in their honor.”

Hermann Pfefferkorn, professor emeritus, says, “Research funds like the one established by the Walkers allow both undergrad and graduate students to pursue research that is not funded by the grants of their professors. This means that their creativity can bear fruits very early in their career. In this way they learn to be scientists in their own right.”

Reference:
Steven E. Jasinski, Andrew B. Heckert, Ciara Sailar, Asher J. Lichtig, Spencer G. Lucas, Peter Dodson. A softshell turtle (Testudines: Trionychidae: Plastomeninae) from the uppermost Cretaceous (Maastrichtian) Hell Creek Formation, North Dakota, USA, with implications for the evolutionary relationships of plastomenines and other trionychids. Cretaceous Research, 2022; 135: 105172 DOI: 10.1016/j.cretres.2022.105172

Note: The above post is reprinted from materials provided by University of Pennsylvania.

Giant impact crater in Greenland occurred a few million years after dinosaurs went extinct

Zircon Crystals of the mineral zircon are tiny time-capsules that record the age of many events in Earth’s history. Dating zircon crystals like this was one of the two methods used to calculate the age of the Hiawatha impact crater. Illustration: Gavin Kenny, Swedish Museum of Natural History.
Zircon Crystals of the mineral zircon are tiny time-capsules that record the age of many events in Earth’s history. Dating zircon crystals like this was one of the two methods used to calculate the age of the Hiawatha impact crater. Illustration: Gavin Kenny, Swedish Museum of Natural History.

Danish and Swedish researchers have dated the enormous Hiawatha impact crater, a 31 km-wide meteorite crater buried under a kilometer of Greenlandic ice. The dating ends speculation that the meteorite impacted after the appearance of humans and opens up a new understanding of Earth’s evolution in the post-dinosaur era.

Ever since 2015, when researchers at the University of Copenhagen’s GLOBE Institute discovered the Hiawatha impact crater in northwestern Greenland, uncertainty about the crater’s age has been the subject of considerable speculation. Could the asteroid have slammed into Earth as recently as 13,000 years ago, when humans had long populated the planet? Could its impact have catalyzed a nearly 1,000-year period of global cooling known as the Younger Dryas?

New analyses performed on grains of sand and rocks from the Hiawatha impact crater by the Natural History Museum of Denmark and the GLOBE Institute at the University of Copenhagen, as well as the Swedish Museum of Natural History in Stockholm, demonstrate that the answer is no. The Hiawatha impact crater is far older. In fact, a new study published in the journal Science Advances today reports its age to be 58 million years old.

“Dating the crater has been a particularly tough nut to crack, so it’s very satisfying that two laboratories in Denmark and Sweden, using different dating methods arrived at the same conclusion. As such, I’m convinced that we’ve determined the crater’s actual age, which is much older than many people once thought,” says Michael Storey of the Natural History Museum of Denmark.

“Determining the new age of the crater surprised us all. In the future, it will help us investigate the impact’s possible effect on climate during an important epoch of Earth’s history” says Dr. Gavin Kenny of the Swedish Museum of Natural History.

As one of those who helped discover the Hiawatha impact crater in 2015, Professor Nicolaj Krog Larsen of the GLOBE Institute at the University of Copenhagen is pleased that the crater’s exact age is now confirmed.

“It is fantastic to now know its age. We’ve been working hard to find a way to date the crater since we discovered it seven years ago. Since then, we have been on several field trips to the area to collect samples associated with the Hiawatha impact,” says Professor Larsen

Age revealed by laser beams and grains of sand

No kilometer-thick ice sheet draped Northwest Greenland when the Hiawatha asteroid rammed into Earth surface releasing several million times more energy than an atomic bomb. At the time, the Arctic was covered with a temperate rainforest and wildlife abounded — and temperatures of 20 degrees Celsius were the norm. Eight million years earlier, an even larger asteroid struck present-day Mexico, causing the extinction of Earth’s dinosaurs.

The asteroid smashed into Earth, leaving a thirty-one-kilometer-wide, one-kilometer-deep crater. The crater is big enough to contain the entire city of Washington D.C. Today, the crater lies beneath the Hiawatha Glacier in Northwest Greenland. Rivers flowing from the glacier supplied the researchers with sand and rocks that were superheated by the impact 58 million years ago.

The sand was analyzed at the Natural History Museum of Denmark by heating the grains with a laser until they released argon gas, whereas the rock samples were analyzed at the Swedish Museum of Natural History using uranium-lead dating of the mineral zircon.

Clear evidence that the Hiawatha impact disrupted global climate is still lacking. However, the crater’s dating allows the international research team working on the crater to begin testing various hypotheses to better understand what its impact was on both the local and global climate.

Facts:

  • At 31 km across, the Hiawatha impact crater is larger than about 90% of the roughly 200 previously known impact craters on Earth.
  • Although the Hiawatha impact crater is much smaller than the approximately 200 km-wide Chicxulub impact crater in present-day Mexico, which led to the demise of the dinosaurs, it would have devastated the region and may even have had wider consequences for the climate and plant and animal life.
  • When the Hiawatha impact occurred 58 million years ago the Earth had recovered from the catastrophic effects of the Chicxulub impact eight million years earlier and was entering a long-term warming trend that was to last about 5 million years.

Reference:
Gavin G. Kenny, William R. Hyde, Michael Storey, Adam A. Garde, Martin J. Whitehouse, Pierre Beck, Leif Johansson, Anne Sofie Søndergaard, Anders A. Bjørk, Joseph A. MacGregor, Shfaqat A. Khan, Jérémie Mouginot, Brandon C. Johnson, Elizabeth A. Silber, Daniel K. P. Wielandt, Kurt H. Kjær, Nicolaj K. Larsen. A Late Paleocene age for Greenland’s Hiawatha impact structure. Science Advances, 2022; 8 (10) DOI: 10.1126/sciadv.abm2434

Note: The above post is reprinted from materials provided by University of Copenhagen – Faculty of Science.

Hidden weaknesses within volcanoes may cause volcano collapse

The unstable southern flank of the Merapi volcano during a partial collapse in 2019. Photograph: GFZ Potsdam
The unstable southern flank of the Merapi volcano during a partial collapse in 2019.
Photograph: GFZ Potsdam

Lava domes form at the top of many volcanoes when viscous lava erupts. When they become unstable, they can collapse and cause a hazard. An international team of researchers has analysed summit dome instabilities at Merapi Volcano, Indonesia. The researchers hope that by understanding the inner processes, volcano collapses can be better forecasted.

Catastrophic volcano collapses and associated explosions, like the famous collapse of Mt St Helens in 1980, are widely considered as unpredictable. This is because the physical properties, stress conditions, and internal structure of volcanoes and the lava domes on top of many volcanoes are not well understood and can change rapidly from one day to another.

A new study jointly led by Gadja Mata University in Yogyakarta Indonesia, Uppsala University in Sweden, and the German Research Center GFZ at Potsdam is now able to explain summit dome instabilities and associated pyroclastic flows at Merapi volcano, Indonesia. The study combines novel drone-based photogrammetry surveillance over several years with mineralogical, geochemical, and mechanical rock strength measurements.

The research demonstrated that a horseshoe-shaped fracture zone in the volcanoes summit region that formed in 2012 and which guided intense gas emission in the past was subsequently buried by renewed lava outpourings in 2018. The new lava dome that has been forming since 2018 started to show signs of instability in 2019 and the researchers were able to show that the summit dome of the volcano is currently collapsing along this now-hidden fracture zone. The research team then considered the changes that must have occurred along this now buried fracture zone from long term gas flux by measuring the composition and physical properties along similar fracture zones in the volcano’s summit region, and concludes that weakened rocks of the hidden fracture zone are likely the main cause for the location of the ongoing summit instabilities at Merapi.

Reference:
Herlan Darmawan, Valentin R. Troll, Thomas R. Walter, Frances M. Deegan, Harri Geiger, Michael J. Heap, Nadhirah Seraphine, Chris Harris, Hanik Humaida, Daniel Müller. Hidden mechanical weaknesses within lava domes provided by buried high-porosity hydrothermal alteration zones. Scientific Reports, 2022; 12 (1) DOI: 10.1038/s41598-022-06765-9

Note: The above post is reprinted from materials provided by Uppsala University. Original written by Linda Koffmar.

A slow-motion section of the San Andreas fault may not be so harmless after all

California’s San Andreas Fault. The “creeping” central section, subject of a new study, is in yellow. Rock samples from almost 2 miles down were taken at the San Andreas Fault Observatory at Depth, or SAFOD, marked by the red star. (Adapted from Coffey et al., Geology, 2022)
California’s San Andreas Fault. The “creeping” central section, subject of a new study, is in yellow. Rock samples from almost 2 miles down were taken at the San Andreas Fault Observatory at Depth, or SAFOD, marked by the red star. (Adapted from Coffey et al., Geology, 2022)

Most people have heard about the San Andreas Fault. It’s the 800-mile-long monster that cleaves California from south to north, as two tectonic plates slowly grind against each other, threatening to produce big earthquakes.

Lesser known is the fact that the San Andreas comprises three major sections that can move independently. In all three, the plates are trying to move past each other in opposing directions, like two hands rubbing against each other. In the southern and the northern sections, the plates are locked much of the time — stuck together in a dangerous, immobile embrace. This causes stresses to build over years, decades or centuries. Finally a breaking point comes; the two sides lurch past each other violently, and there is an earthquake. However in the central section, which separates the other two, the plates slip past each other at a pleasant, steady 26 millimeters or so each year. This prevents stresses from building, and there are no big quakes. This is called aseismic creep.

At least that is the story most scientists have been telling so far. Now, a study of rocks drilled from nearly 2 miles under the surface suggests that the central section has hosted many major earthquakes, including some that could have been fairly recent. The study, which uses new chemical-analysis methods to gauge the heating of rocks during prehistoric quakes, just appeared in the online edition of the journal Geology.

“This means we can get larger earthquakes on the central section than we thought,” said lead author Genevieve Coffey, who did the research as a graduate student at Columbia University’s Lamont-Doherty Earth Observatory. “We should be aware that there is this potential, that it is not always just continuous creep.”

The threats of the San Andreas are legion. The northern section hosted the catastrophic 1906 San Francisco magnitude 7.9 earthquake, which killed 3,000 people and leveled much of the city. Also, the 1989 M6.9 Loma Prieta quake, which killed more than 60 and collapsed a major elevated freeway. The southern section caused the 1994 M6.7 Northridge earthquake near Los Angeles, also killing about 60 people. Many scientists believe it is building energy for a 1906-scale event.

The central section, by contrast, appears harmless. Only one small area, near its southern terminus, is known to produce any real quakes. There, magnitude 6 events — not that dangerous by most standards — occur about every 20 years. Because of their regularity, scientists hoping to study clues that might signal a coming quake have set up a major observatory atop the fault near the city of Parkfield. It features a 3.2-kilometer-deep borehole from which rock cores have been retrieved, and monitoring instruments above and below ground. It was rock from near the bottom of the borehole that Coffey and her colleagues analyzed.

When earthquake faults slip, friction along the moving parts can cause temperatures to spike hundreds of degrees above those of surrounding rocks. This cooks the rocks, altering the makeup of organic compounds in any sedimentary formations along the fault path. Recently, study coauthors Pratigya Polissar and Heather Savage figured out how to take advantage of these so-called biomarkers, using the altered compositions to map prehistoric earthquakes.They say that by calculating the degree of heating in the rock, they can spot past events and estimate how far the fault moved; from this, they can roughly extrapolate the sizes of resulting earthquakes. At Lamont-Doherty, they refined the method in the U.S. Northeast, Alaska, and off Japan.

In the new study, the researchers found many such altered compositions in a band of highly disturbed sedimentary rock lying between 3192 and 3196 meters below the surface. In all, they say the blackish, crumbly stuff shows signs of more than 100 quakes. In most, the fault appears to have jumped more than 1.5 meters (5 feet). This would translate to at least a magnitude 6.9 quake, the size of the destructive Loma Prieta and Northridge events. But many could well have been larger, say the researchers, because their method of estimating earthquake magnitude is still evolving. They say quakes along the central section may have been similar to other large San Andreas events, including the one that destroyed San Francisco.

The current official California earthquake hazard model, used to set building codes and insurance rates, does include the remote possibility of a big central-section rupture. But inclusion of this possibility, arrived at through mathematical calculations, was controversial, given the lack of evidence for any such prior event. The new study appears to be the first to indicate that such quakes have in fact occurred here. The authors say they could have originated in the central section, or perhaps more likely, started to the north or south, and migrated through the central.

So, when did these quakes happen? Trenches dug by paleoseismologists across the central section have revealed no disturbed soil layers that would indicate quakes rupturing the surface in the last 2,000 years — about the limit for detection using that method in this region. But 2,000 years is an eye blink in geologic terms. And, the excavations could be missing any number of quakes that might not necessarily have ruptured the surface at specific sites.

The researchers used a second new technique to address this question. The biomarkers run along very narrow bands, from microscopic to just a couple of centimeters wide. Just a few inches or feet away, the rock heats only enough to drive out some or all of the gas argon naturally present there. Conveniently for the authors, other scientists have long used the ratio of radioactive potassium to argon, into which potassium slowly decays, to measure the ages of rocks. The more argon compared to potassium, the older the rock. Thus, if some or all of the argon is driven out by quake-induced heat, the radioactive “clock” gets reset, and the rock appears younger than identical nearby rock that was not heated.

This is exactly what the team found. The sediments they studied were formed tens of millions of years ago in an ancient Pacific basin that was subducted under California. Yet the ages of rocks surrounding the thin quake slip zones came out looking as young as 3.2 million years by the potassium-argon clock. This sets out a time frame, but only a vague one, because the scientists still do not know how to judge the amount of argon that was driven out, and thus how thoroughly the clock may have been reset. This means that 3.2 million years is just an upper age limit for the most recent quakes, said Coffey; in fact, some could have taken place as little as a few hundred or a few thousand years ago, she said. The group is now working on a new project to refine the age interpretations.

“Ultimately, our work points to the potential for higher magnitude earthquakes in central California and highlights the importance of including the central [San Andreas Fault] and other creeping faults in seismic hazard analysis,” the authors write.

William Ellsworth, a geophysicist at Stanford University who has led research at the drill site, pointed out that while a possible big quake is included in the state’s official hazard assessment, “Most earthquake scientists think that they happen rarely, as tectonic strain is not accumulating at significant rates, if at all, along it at the present time,” he said.

Morgan Page, a seismologist with the U.S. Geological Survey who coauthored the hazard assessment, said the study breaks new ground. “The creeping section is a difficult place to do paleoseismology, because evidence for earthquakes can be easily erased by the creep,” she said. “If this holds up, this is the first evidence of a big seismic rupture in this part of the fault.” She said that if a big earthquake can tear through the creeping section, it means that it is possible — though chances would be remote — that one could start at the very southern tip of the San Andreas, travel through the central section and continue all the way on up to the end of the northern section — the so-called “Big One” that people like to speculate about. “I’m excited about this new evidence, and hope we can use it to better constrain this part of our model,” she said.

How much should this worry Californians? “People should not be alarmed,” said Lamont-Doherty geologist and study coauthor Stephen Cox. “Building codes in California are now quite good. Seismic events are inevitable. Work like this helps us figure out what is the biggest possible event, and helps everyone prepare.”

The study’s other coauthors are Sidney Hemming and Gisela Winckler of Lamont-Doherty, and Kelly Bradbury of Utah State University. Genevieve Coffey is now at New Zealand’s GNS Science; Pratigya Polissar and Heather Savage are now at the University of California Santa Cruz.

Reference:
Genevieve L. Coffey, Heather M. Savage, Pratigya J. Polissar, Stephen E. Cox, Sidney R. Hemming, Gisela Winckler, Kelly K. Bradbury. History of earthquakes along the creeping section of the San Andreas fault, California, USA. Geology, 2022; DOI: 10.1130/G49451.1

Note: The above post is reprinted from materials provided by Columbia Climate School. Original written by Kevin Krajick.

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