Earth

New research shows the permanent rise of oxygen in our atmosphere, which set the stage for life as we know it, happened 100 million years later than previously thought.

A significant rise in oxygen occurred about 2.43 billion years ago, marking the start of the Great Oxidation Episode -- a pivotal moment in Earth's history. 

An international research team including a UC Riverside scientist analyzed rocks from South Africa formed during this event. Findings, published this week in the journal Nature, include the discovery that oxygen fluctuated dramatically after its early appearance until it became a permanent constituent of the atmosphere much later.

These fluctuations reinforce a direct link between atmospheric oxygen and concentrations of greenhouse gases such as methane, helping to explain some of the most extreme climate changes in the planet's past.

During the same period, ancient Earth experienced four glaciations -- periods when the whole planet was covered with ice and snow for millions of years. According to UC Riverside geologist Andrey Bekker, changes in atmospheric oxygen levels began and ended these events. 

Scientists have often wondered how the planet could have emerged from the periods in which ice and snow covered everything, including the oceans. According to Bekker, increases in atmospheric oxygen levels resulted in low concentrations of greenhouse gases, such as methane and carbon dioxide. This ushered in global glaciations by maintaining surface conditions below the water-freezing temperature. 

Volcanoes also continued to erupt on the frozen planet, building required high levels of carbon dioxide in the atmosphere to exit from climatic catastrophe by warming the planet and melting the snow and ice.

"Before this work, we all wondered why the fourth glacial event happened if oxygen was already a steady component in the atmosphere," Becker said. "We found it was not steady. The permanent rise of oxygen actually occurred after the fourth, final glaciation in the Paleoproterozoc Era, and not before it, and this solves what had previously been a major puzzle in our understanding." 

The Great Oxidation Episode ushered in a 1.5 billion-year period of subsequent environmental stability, which lasted until a second major transitional period, marked by rising atmospheric oxygen and similar climatic changes at the end of the Precambrian time. 

"We thought once oxygen increased it wouldn't ever return back to lower levels," Bekker said. "Now we have learned it fluctuated to very low levels and this could have dramatic implications in terms of understanding extinction events and the evolution of life."

Open questions include the reasons for these multiple fluctuations, and whether complex life could have evolved and then died out again in response to them, said Simon Poulton, a biogeochemist at Leeds University who led the research. 

"We cannot begin to understand the causes and consequences of atmospheric oxygenation, the most significant control on Earth's habitability, if we do not know when permanent atmospheric oxygenation actually occurred," he said. "Now at last we have that piece of the puzzle."

WASHINGTON, April 5, 2021 -- Forever chemicals are known for being water-, heat- and oil-resistant, which makes them useful in everything from rain jackets to firefighting foams. But the chemistry that makes them so useful also makes them stick around in the environment and in us -- and that could be a bad thing: https://youtu.be/tqKEG5LxPiY.

A lot of people think regret must be a good thing because it helps you not repeat a mistake, right?

But that turns out not to be the case. Not even when it comes to casual sex, according to new research from the Norwegian University of Science and Technology's (NTNU) Department of Psychology.

"For the most part, people continue with the same sexual behaviour and the same level of regret," says Professor Leif Edward Ottesen Kennair.

So, we repeat what we thought was a mistake, and we regret it just as much the next time around.

Professor Kennair and colleagues professor Mons Bendixen and postdoctoral fellow Trond Viggo Grøntvedt have investigated whether sexual regret is functional, that is, whether it contributes to any change in behaviour.

The participants in the study answered a questionnaire about sexual regret two times, at approximately 4.5 month intervals. This approach makes it possible to study changes over shorter periods of time.

Both women and men might regret what they did the last time an opportunity for casual sex arose. But they often regret completely different choices.

Women tend to regret having had casual sex more than men. Men, on the other hand, regret not taking advantage of a casual sex opportunity markedly more than women.

"We wanted to examine if their level of regret contributed to a change in behaviour the next time around," says Bendixen.

"A lot of emotions are functional, like disgust that protects against infection and fear that protects against danger. An evolutionary approach has helped us understand anxiety by understanding the function of fear: fight-flight-freeze is about avoiding danger and defending ourselves against it," says Kennair.

Many people assume that emotions have a function

Many psychologists assume that regret and other emotions have a function: that they'll influence our behaviour so that we modify it. For example, after experiencing negative emotions, we will change our behaviour to reduce the risk of having those negative feelings later.

"Researchers have found that most people believe this is true for regret. They assume that regret is actually a helpful negative feeling. People assume it guides them not to repeat what they regretted," says Grøntvedt.

If regret works that way, then wouldn't men more often have casual sex the next time the opportunity arose? And, you would think that women's regret would lead them to choose better partners, have less frequent casual sex or try harder to get into steady relationships.

But no, that's not what happens. The findings from the study show that we don't learn from what we perceived as a mistake.

So why is that? Why don't we learn from our mistakes?

Probably because our behaviour depends on our personality, which is something quite different and more complicated than a shorter or more prolonged feeling of regret.

We are mostly just who we are, and when the opportunity arises and horniness take over, or doesn't, we probably react just like the time before.

"We are not that surprised," Kennair says. "If regret helped, would not most sinners eventually become saints? What do you regret the most often? Has it changed your behaviour?" he asks.

Regret is flexible, not constant. Or, as psychologists say, regret is adaptive. It changes according to the conditions.

"We have repeated that regret is adaptive in all our articles on the subject in recent years. And now we have tested it," says Kennair.

No one else has tested regret for sexual behaviour. Perhaps researchers have assumed that they knew enough? Even outstanding people in the field have assumed that regret would help us learn.

"We found little information on this topic. But both most researchers and people in general believe that regret is wise," says Grøntvedt.

Do you really need to spend so much time being regretful?

"Maybe it would be smart instead to think about what we regret in everyday life, and what we actually do so often that we get ample opportunity to regret it," Kennair says.

Have you exercised enough lately? Did you eat too much? Done everything you should? Said something you shouldn't have said? Does it help to regret things sometimes? No? This is a bit like ruminating, which a lot of people with depression assume is a smart thing to do, even if they become more depressed from doing it.

"And yet, there are some folks who think that depressive ruminating and worry are a good idea. But the way we treat depression and generalized anxiety disorders is by helping people to stop ruminating and to stop worrying. Not everything people do, think or feel is an evolutionary adaptation - sometimes it is not appropriate either," Kennair says.

Piping plover breeding groups in the Northern Great Plains are notably connected through movements between habitats and show lower reproductive rates than previously thought, according to a new U.S. Geological Survey study. These new findings point to a need for further studies and suggest the species may show a higher extinction risk than currently presumed.

Piping plovers are small-bodied, short-distance migratory shorebirds. The Northern Great Plains population has been listed as a threatened species under the U.S. Endangered Species Act since 1985. Previously, wildlife managers had assumed four separate breeding groups within the Northern Great Plains and that individuals from these groups moved infrequently between habitats. Earlier studies based on this assumption resulted in a low extinction risk for the species.

Scientists analyzed movement, survival and renesting rates in two of the assumed breeding groups of piping plovers over four distinct management units along the Missouri River and alkaline wetlands distributed throughout the prairie pothole region from 2014 - 2019. Piping plover reproductive rates were studied between 2014 - 2016. The study areas are within North Dakota, South Dakota and Montana and include the U.S. alkali wetlands, Lake Sakakawea, the Garrison Reach of the Missouri River, and Lake Oahe.

Results show river and alkali wetland habitats appear to be of higher quality than reservoir habitats, which had lower annual survival, increased movement away from the habitat, lower renesting success, and lower reproductive output.

Habitat availability affected nearly every parameter examined in this study. In general, when more habitat was available, piping plover vital rates improved. These findings support the current focus of managing the Missouri River for abundant breeding habitat for piping plovers.

Study findings show managing for successful first nests for Northern Great Plains piping plovers is key to improving reproductive output. Piping plovers are intensively managed throughout their range, and in the Northern Great Plains, management of habitat, water and predation, including vegetation removal and protective fences around nests, are common conservation strategies. Therefore, intensive management focused on the protection of early nests or first nest attempts would likely be more effective than strategies that assume equivalent productivity from renests.

The study also shows that piping plovers move between the northern Missouri River habitat and the U.S. alkali wetlands at a rate that is substantially higher than previously assumed. Further, movement rates were unbalanced and varied between hatch-year and adult plovers. Adults were more likely to forego breeding altogether than to relocate to alternate management units and breed. This implies that either the rates of movement or the way local bird populations are managed may need to be reevaluated.

A new study shows a correlation between the end of solar cycles and a switch from El Nino to La Nina conditions in the Pacific Ocean, suggesting that solar variability can drive seasonal weather variability on Earth.

If the connection outlined in the journal Earth and Space Science holds up, it could significantly improve the predictability of the largest El Nino and La Nina events, which have a number of seasonal climate effects over land. For example, the southern United States tends to be warmer and drier during a La Nina, while the northern U.S. tends to be colder and wetter.

"Energy from the Sun is the major driver of our entire Earth system and makes life on Earth possible," said Scott McIntosh, a scientist at the National Center for Atmospheric Research (NCAR) and co-author of the paper. "Even so, the scientific community has been unclear on the role that solar variability plays in influencing weather and climate events here on Earth. This study shows there's reason to believe it absolutely does and why the connection may have been missed in the past."

The study was led by Robert Leamon at the University of Maryland-Baltimore County, and it is also co-authored by Daniel Marsh at NCAR. The research was funded by the National Science Foundation, which is NCAR's sponsor, and the NASA Living With a Star program.

Applying a new solar clock

The appearance (and disappearance) of spots on the Sun -- the outwardly visible signs of solar variability -- have been observed by humans for hundreds of years. The waxing and waning of the number of sunspots takes place over approximately 11-year cycles, but these cycles do not have distinct beginnings and endings. This fuzziness in the length of any particular cycle has made it challenging for scientists to match up the 11-year cycle with changes happening on Earth.

In the new study, the researchers rely on a more precise 22-year "clock" for solar activity derived from the Sun's magnetic polarity cycle, which they outlined as a more regular alternative to the 11-year solar cycle in several companion studies published recently in peer-reviewed journals.

The 22-year cycle begins when oppositely charged magnetic bands that wrap the Sun appear near the star's polar latitudes, according to their recent studies. Over the cycle, these bands migrate toward the equator -- causing sunspots to appear as they travel across the mid-latitudes. The cycle ends when the bands meet in the middle, mutually annihilating one another in what the research team calls a terminator event. These terminators provide precise guideposts for the end of one cycle and the beginning of the next.

The researchers imposed these terminator events over sea surface temperatures in the tropical Pacific stretching back to 1960. They found that the five terminator events that occurred between that time and 2010-11 all coincided with a flip from an El Nino (when sea surface temperatures are warmer than average) to a La Nina (when the sea surface temperatures are cooler than average). The end of the most recent solar cycle -- which is unfolding now -- is also coinciding with the beginning of a La Nina event.

"We are not the first scientists to study how solar variability may drive changes to the Earth system," Leamon said. "But we are the first to apply the 22-year solar clock. The result -- five consecutive terminators lining up with a switch in the El Nino oscillation -- is not likely to be a coincidence."

In fact, the researchers did a number of statistical analyses to determine the likelihood that the correlation was just a fluke. They found there was only a 1 in 5,000 chance or less (depending on the statistical test) that all five terminator events included in the study would randomly coincide with the flip in ocean temperatures. Now that a sixth terminator event -- and the corresponding start of a new solar cycle in 2020 -- has also coincided with an La Nina event, the chance of a random occurrence is even more remote, the authors said.

The paper does not delve into what physical connection between the Sun and Earth could be responsible for the correlation, but the authors note that there are several possibilities that warrant further study, including the influence of the Sun's magnetic field on the amount of cosmic rays that escape into the solar system and ultimately bombard Earth. However, a robust physical link between cosmic rays variations and climate has yet to be determined.

"If further research can establish that there is a physical connection and that changes on the Sun are truly causing variability in the oceans, then we may be able to improve our ability to predict El Nino and La Nina events," McIntosh said.

NEW YORK, APRIL 5, 2021 -- Nine of the hottest years in human history have occurred in the last decade. Without a major shift in this climate trajectory, the future of life on Earth is in question. Should humans, whose fossil-fueled society is driving climate change, use technology to put the brakes on global warming?

Every month since September 2019 the Climate Intervention Biology Working Group, a team of internationally recognized experts in climate science and ecology, has gathered remotely to bring science to bear on that question and the consequences of geoengineering a cooler Earth by reflecting a portion of the sun's radiation away from the planet -- a climate intervention strategy known as solar radiation modification (SRM).

The group's seminal paper, "Potential ecological impacts of climate intervention by reflecting sunlight to cool Earth," was published in the most recent Proceedings of the National Academy of Sciences of the United States (PNAS).

"Participating in this working group has been quite eye-opening for me," said co-author Peter Groffman, an ecosystem ecologist at the Advanced Science Research Center at The Graduate Center, CUNY and the Cary Institute of Ecosystem Studies. "I was unaware that modeling climate intervention was so advanced, and I think that climate modelers were unaware of the complexities of the ecological systems being affected. It is a strong reminder of the importance of the need for multi-disciplinary analysis of complex problems in environmental science."

The interdisciplinary team is co-led by Phoebe Zarnetske, community ecologist and associate professor in Michigan State University's Department of Integrative Biology and the Ecology, Evolution, and Behavior program, and ecologist Jessica Gurevitch, distinguished professor in the Department of Ecology and Evolution at Stony Brook University.

Conversations between Gurevitch and climate scientist Alan Robock, distinguished professor in the Department of Environmental Sciences at Rutgers University, gave rise to the pioneering group, which is more aware than most that geoengineering Earth's atmosphere is more than just a science-fiction scenario.

"There is a dearth of knowledge about the effects of climate intervention on ecology," said Zarnetske. "As scientists, we need to understand and predict the positive and negative effects it could have on the natural world, identify key knowledge gaps, and begin to predict what impacts it may have on terrestrial, marine, and freshwater species and ecosystems if it were adopted in the future."

The costs and technology needed to reflect the Sun's heat back into space are currently more attainable than other climate intervention ideas like absorbing carbon dioxide (CO2) from the air. The working group anticipates their lively discussions and open access paper will encourage an explosion of scientific investigation into how a climate intervention strategy known as solar radiation modification (SRM), in tandem with greenhouse gas emissions reduction, would affect the natural world.

The feasibility of planetary-wide SRM efforts hinge on accurate predictions of its myriad outcomes provided by the well-established computer simulations of the Geoengineering Model Intercomparison Project (GeoMIP). The PNAS paper lays the foundation for expanding GeoMIP's scope to include the incredible range and diversity of Earth's ecosystems.

"While climate models have become quite advanced in predicting climate outcomes of various geoengineering scenarios, we have very little understanding of what the possible risks of these scenarios might be for species and natural systems," Gurevitch explained. "Are the risks for extinction, species community change, and the need for organisms to migrate to survive under SRM greater than those of climate change, or does SRM reduce the risks caused by climate change?"

"Most of the GeoMIP models only simulate abiotic variables, but what about all of the living things that are affected by climate and rely on energy from the sun?" Zarnetske added. "We need to better understand the possible impacts of SRM on everything from soil microorganisms to monarch butterfly migrations to marine systems."

Zarnetske's Spatial and Community Ecology Lab (SpaCE Lab) specializes in predicting how ecological communities respond to climate change across scales from the microcosm to the global, making it uniquely poised to assist the working group in illuminating vital data for future SRM scenarios such as stratospheric aerosol intervention (SAI), the focus of the paper.

SAI would reduce some of the Sun's incoming radiation by reflecting sunlight back into space, similar to what happens after large volcanic eruptions. Theoretically, it would be possible to continuously replenish the cloud and control its thickness and location to achieve a desired target temperature.

But the paper reveals the under-researched complexity of cascading relationships between ecosystem function and climate under different SAI scenarios. In fact, they argue, climate change mitigation must continue regardless of whether SRM is adopted, and the question remains whether some or any SRM can be beneficial in addition to decarbonization efforts.

"Although SAI may cool Earth's surface to a global temperature target, the cooling may be unevenly distributed, affecting many ecosystem functions and biodiversity," Zarnetske said. "Rainfall and surface ultraviolet radiation would change, and SAI would increase acid rain and would not mitigate ocean acidification."

In other words, SRM is not a magic bullet for solving climate change. Until the working group's efforts inspire new research into the effects of different climate intervention scenarios, SRM is more akin to a shot in the dark.

"We hope that this paper will spark a lot more attention to this issue and greater cooperation between scientists in the fields of climate science and ecology," added Gurevitch.

On-surface synthesis has received great attention as a method to create atomically-precise one-dimensional (1D) and two-dimensional (2D) polymers with intriguing properties. In particular, graphene nanoribbons (GNRs), a category of quasi-1D nanomaterials derived from graphene, have been widely studied due to their tunable electronic properties and potential applications in semiconductor devices, such as field-effect transistors and spintronics. A series of top-down approaches have been pursued to produce GNRs, but a lack of control over the ribbon width and edge structure has hindered their further development.

In 2010, Cai et al. firstly reported the fabrication of an atomically-precise armchair GNR (AGNR) on the Au(111) surface using a bottom-up approach. The basic mechanism involves thermally-activated dehalogenation, surface-assisted polymerization and finally cyclodehydrogenation.

In the following decade, this bottom-up approach has been extended to synthesize a wide variety of GNRs, including AGNRs with different widths, zigzag GNRs, GNR heterojunctions, chiral GNRs and chemically- doped GNRs. Based on the periodic similarity of their electronic structures, AGNRs can be classified into three families, 3p, 3p+1 and 3p+2 (representing the number of carbon atoms in the narrow direction).

So far, few studies have focused on GNR synthesis on Cu(111) due to the stronger surface interaction, despite the lower temperature for dehalogenation. It has been shown that chiral GNRs can be synthesized on Cu(111) using the same precursor which yields non-chiral 7-AGNR on Au(111) and that dehalogenation can be reversible on Au(111) but not Cu(111), which implies that the reaction pathway and products achieved could be controlled through the choice of substrate.

A second approach to tailor the reaction pathway in surface-confined synthesis is to introduce different atomic species, which has been considered in only a few recent studies. Exposure to iodine creates a monolayer intercalated between the polymers and the Ag(111) surface that decouples their electronic interactions. In addition, hydrogen was shown to remove halogen by-products and to induce covalent coupling, and sulphur to switch the surface-confined Ullmann reaction on or off.

Prof. Lifeng Chi's research group in Soochow University recently investigated the effect of oxygen on the synthesis of 3-AGNRs by surface-confined Ullmann coupling and determined that it, instead, caused a 1D to 2D transformation of the organometallic (OM) structures.

Here, their objective was to investigate the synthesis of 3p-AGNRs on Cu(111), extending from the previous study on Au(111), and to examine the effect of oxygen on lateral fusion of 3-AGNRs, inspired by their potential to promote C-H activation.

Their investigation demonstrated the successful synthesis of 3p-AGNRs on Cu(111) via lateral fusion of poly(para-phenylene) (i.e. 3-AGNR). Introduction of co-adsorbed atomic oxygen substantially reduced the temperature required to induce the lateral fusion reaction. The identification of this catalytic effect could benefit on-surface synthesis that applies dehydrogenation reactions, not restricting to GNRs, and highlights the potential of additional atomic adsorbates to steer surface reactions.

A new technique that mimics the ancient Japanese art of kirigami may offer an easier way to fabricate complex 3D nanostructures for use in electronics, manufacturing and health care.

Kirigami enhances the Japanese artform of origami, which involves folding paper to create 3D structural designs, by strategically incorporating cuts to the paper prior to folding. The method enables artists to create sophisticated three-dimensional structures more easily.

"We used kirigami at the nanoscale to create complex 3D nanostructures," said Daniel Lopez, Penn State Liang Professor of Electrical Engineering and Computer Science, and leader of the team that published this research in Advanced Materials. "These 3D structures are difficult to fabricate because current nanofabrication processes are based on the technology used to fabricate microelectronics which only use planar, or flat, films. Without kirigami techniques, complex three-dimensional structures would be much more complicated to fabricate or simply impossible to make."

Lopez said that if force is applied to a uniform structural film, nothing really happens other than stretching it a bit, like what happens when a piece of paper is stretched. But when cuts are introduced to the film, and forces are applied in a certain direction, a structure pops up, similar to when a kirigami artist applies force to a cut paper. The geometry of the planar pattern of cuts determines the shape of the 3D architecture.

"We demonstrated that it is possible to use conventional planar fabrication methods to create different 3D nanostructures from the same 2D cut geometry," Lopez said. "By introducing minimum changes to the dimensions of the cuts in the film, we can drastically change the three-dimensional shape of the pop-up architectures. We demonstrated nanoscale devices that can tilt or change their curvature just by changing the width of the cuts a few nanometers."

This new field of kirigami-style nanoengineering enables the development of machines and structures that can change from one shape to another, or morph, in response to changes in the environment. One example is an electronic component that changes shape in elevated temperatures to enable more air flow within a device to keep it from overheating.

"This kirigami technique will allow the development of adaptive flexible electronics that can be incorporated onto surfaces with complicated topography, such as a sensor resting on the human brain," Lopez said. "We could use these concepts to design sensors and actuators that can change shape and configuration to perform a task more efficiently. Imagine the potential of structures that can change shape with minuscule changes in temperature, illumination or chemical conditions."

Lopez will focus his future research on applying these kirigami techniques to materials that are one atom thick, and thin actuators made of piezoelectrics. These 2D materials open new possibilities for applications of kirigami-induced structures. Lopez said his goal is to work with other researchers at Penn State's Materials Research Institute (MRI) to develop a new generation of miniature machines that are atomically flat and are more responsive to changes in the environment.

"MRI is a world leader in the synthesis and characterization of 2D materials, which are the ultimate thin-films that can be used for kirigami engineering," Lopez said. "Moreover, by incorporating ultra-thin piezo and ferroelectric materials onto kirigami structures, we will develop agile and shape-morphing structures. These shape-morphing micro-machines would be very useful for applications in harsh environments and for drug delivery and health monitoring. I am working at making Penn State and MRI the place where we develop these super-small machines for a specific variety of applications."

The kangaskhan, Australia's only species of endemic Pokemon in Pokemon Go, is commonly poached within its natural habitat by Pokemon trainers for use in fighting contests

Researchers used several species distribution modeling algorithms to predict how climate change, on top of the already existing human-induced pressures, would impact the distribution of the kangaskhan in the future

In addition to this, they found a way to measure how biased commonly used species distribution models are, and found that some models are so biased that their results weren't influenced by the data at all

The researchers compared these results to previously published models for hundreds of species of Australian mammals and found similar biases

This research has highlighted specific problems with common species distribution models, and has given scientists new statistical tools to refine them in the future

Kangaskhan (Garura kangaskhani) are two-meter-tall Pokemon, endemic to Australia. Although commonly spotted around cities and other urban areas, information is lacking about their basic biology and wider range distribution. Much of what is known is based on anecdotes from the public, especially unlicensed breeders, many of whom are not trained in scientific research. Today, kangaskhan are believed to be threatened due to frequent poaching of adults and eggs. The poaching is primarily motivated by the demand for these animals to be used in fighting contests. This pressure, combined with the fact that climate change is predicted to have a large impact in Australia over the next few decades, has resulted in a bleak outlook for this majestic Pokemon species.

Now, researchers in the Biodiversity and Biocomplexity Unit at the Okinawa Institute of Science and Technology Graduate University (OIST) have taken an extensive look at how climate change will impact the existence of suitable habitat for kangaskhan. This study was published today in Methods in Ecology and Evolution.

"Apart from seeming to prefer partly cloudy weather, very little is known about the species' climatic preferences," said lead author Dr. Dan Warren, who previously worked as a researcher in Australia. "This makes it difficult to estimate the response of kangaskhan to environmental change, or how climate change might combine with the effects of poaching to impact the species' long-term survival. For this research, we used several well-known modeling methods to gain insight into how threatened kangaskhan really are."

With data that was initially recorded by hobbyists and professional trainers seeking out kangaskhan for exploitation, the researchers attempted to shed light on what the future holds for this species. Species distribution models were the obvious way to go. These models are a common way for scientists to predict changes in the availability of suitable habitat for a species, in response to estimated shifts in environmental parameters like rainfall, humidity, temperature, and vegetation cover.

In terms of the results, the models differed on what they predicted the future to be for the kangaskhan depending on the algorithms used. Three of the models predicted a decrease in habitat suitability, though differed substantially on the magnitude of this decline. Two other models switched their answer depending on the climate estimates used, and a sixth model predicted an increase in suitability of habitat. Policymakers and stakeholders should take this uncertainty into account and err on the side of caution when it comes to safeguarding the future of kangaskhan.

Aside from revealing uncertainty surrounding the long-term survival of kangaskhan, the research has also shed light on how scientists can calculate the biases that come with species distribution models. Every one of these models comes with a level of bias and uncertainty, depending on the choices made in the modeling process. For example, when predicting the implications of climate change, the amount of future CO2 emissions needs to be considered, and yet estimating this can be tricky as it's based on human behavior. Differences in these estimates can interact with other aspects of the modeling process, resulting in biases in predictions of how climate change will affect threatened and endangered species. Scientists know about these biases but have never found a way to measure them before, until now.

"We found that we could determine the level of bias with a simple statistical test," said Dr. Warren. "And, in doing so, we realized that some of these models could be so biased that the data didn't have much effect on their results... effectively the conclusion was picked based on study design regardless of what the data actually showed," said Dr. Warren.

In addition to the kangaskhan, the researchers demonstrated similar biases for these models by reexamining a previous study that built models for 220 species of Australian mammals, as well as a study that simulated artificial organisms in order to understand how well models estimated species' environmental tolerances. The researchers hope that by revealing these biases they are providing a more secure future for kangaskhan and the rest of the world's biodiversity.

Dr. Warren emphasized that although the study itself might seem strange, what it's revealed will actually go on to help other researchers create more robust estimates of species distribution. His primary reason for choosing to do this research on a Pokemon character was to engage a broader audience with issues that conservation scientists regularly need to think about.

"It's a bit silly but it's also cool science," said Dr. Warren. "Stakeholders use these models for predicting a number of important ecological phenomena, from the effects of climate change, to the dispersal of diseases and invasive species, so having a firm understanding of the biases the models might have is important. We've just scratched the surface of what we can do with this method so I think this could be a useful tool for a whole bunch of things."

His final point was a word of caution with respect to the culture that surrounds Pokemon. "It's specifically based around over-exploitation with the tagline 'gotta catch them all.' The rarer they get, the more valuable they get. This is like some of the larger tuna species, which are in serious danger of going extinct. We might have focused on climate change in this study but, for many Pokemon (and many species around the world), overexploitation should also be a concern."

Oak Brook, IL - The April edition of SLAS Discovery is a special issue on advances in protein degradation curated by guest editors M. Paola Castaldi, Ph.D., and Stewart L. Fisher, Ph.D.

Targeted protein degradation has generated interest within the drug discovery arena due to the inhibition of one particular function of a protein not often delivering the successful results that comes from whole-protein depletion. The pharmacology of PROTACs present challenges, however, namely for the development of orally bioavailable drugs. In the article "Target Validation Using PROTACs: Applying the Four Pillars Framework" authors Rados?aw P. Nowak, Ph.D., and Lyn H. Jones, Ph.D., describe the application of a translational pharmacology framework (the four pillars) to expedite PROTAC development by informing pharmacokinetic-pharmacodynamic (PKPD) understanding and helping clarify structure-activity relationships. Nowak and Jones hope that the four pillars will serve as a useful guideline to those developing targeted protein degraders and help establish PROTAC molecules as target validation chemical probes.

The April issue of SLAS Discovery includes three articles of original research.

These include:

Exploring the Biology of Degraders -- Simultaneous Detection of Protein Target Engagement and Functional Readout for In-Depth Characterization of Targeted Protein Degraders

A Method for Determining the Kinetics of Small Molecule Induced Ubiquitination

CDK Family PROTAC Degradation Profiling Reveals Differential Family Member Responses and Cell-Cycle Dependent Degradation of CDK

Other articles include:

Target Validation Using PROTACs: Applying the Four Pillars Framework

E3 Ligase Ligands for PROTACs: How They Were Found and How to Discover New Ones

Delivering Best Practice PROTACs Projects -- Lessons from AZ Experience.

High-Throughput Assay Technologies for Accelerating the Discovery and Optimization of Targeted Protein Degradation Therapeutics

The Vital Role of Proteomics in Characterizing Novel Protein Degraders

Non PROTAC Small Molecule Degraders -- An Exciting Novel Modality?

Development of a Novel SNAP-Epitope Tag/Near Infrared Imaging Assay to Quantify G Protein-Coupled Receptor Degradation in Human Cells

The current method of manufacturing carbon nanotubes--in essence rolled up sheets of graphene--is unable to allow complete control over their diameter, length and type. This problem has recently been solved for two of the three different types of nanotubes, but the third type, known as 'zigzag' nanotubes, had remained out of reach. Researchers with Japan's National Institutes of Natural Sciences (NINS) have now figured out how to synthesize the zigzag variety.

Their method is described in the journal Nature Chemistry, published on January 25.

Thanks to carbon's unique capacity to combine with other atoms to form molecules, when it combines with itself, it can do so in many structurally different ways (such as diamonds and graphite) with different properties. In recent decades, shapes such as graphene--a layer of carbon one atom thick formed from a hexagonal honeycomb-like lattice--have been produced. Another of these different forms, or 'allotropes,' that can be produced is a hollow cylinder of graphene known as a nanotube.

When the hexagons of carbon in the nanotube come together in this honeycomb lattice, they form either an armchair, zigzag or chiral configuration. The name 'zigzag' is used for the configuration in which the 'path' of each molecular bond between carbon atoms is directed first leftward by 60 degrees, then rightward by 60 degrees, then left 60 degrees, then right 60 degrees again: a zigzag pattern. The name 'armchair' describes a path that moves twice left, then twice right, before repeating. This pathway supposedly looks a bit like an armchair, hence the name. A third type, chiral, sits between these two forms, along with its mirror image.

If one were able to take a knife and slice through these tubes twice horizontally against the lengthwise axis, one could produce a 'belt' of nanotube, composed of 12 carbon hexagonal rings. Such a belt is called a 'nanobelt'.

Efforts at production of these nanobelts have been the subject of much scholarly investigation. This is because of the limitations of conventional manufacture of nanotubes, which takes what is termed a 'top-down' form. Top-down manufacture involves the pulverizations of a bulk mass of carbon into a powder, after which the nanotubes randomly form themselves into one or more of the three configuration types.

"The problem here is that you can't control which configuration type is formed, or the diameter, or even the length," said Yasutomo Segawa, of the Institute for Molecular Science at NINS and corresponding author for the paper. "But if you can build a nanotube from the bottom up, from the 'seed' of a nanobelt, then you control all these three aspects."

Previous research in 2019 had been able to produce armchair and chiral nanobelts, but not the third type - the zigzag.

And now for the first time, the researchers were able to form a zigzag nanobelt. The key to the nanobelt synthesis strategy was the bridging of the hexagonal rings by an oxygen atom (the addition of an oxanorbornadiene unit). They were then able to use X-ray crystallography to confirm that this structure, which had been predicted by theoretical calculations, was indeed forming in the real world.

With this third nanobelt synthesis, all three types of nanotubes--armchair, chiral, and zigzag--are in principle now available. This is a great step towards the bottom-up synthesis of carbon nanotubes made to order.

The next step is to take this proof of concept through to actual structure-selective bottom-up synthesis of carbon nanotubes, by using the synthesis of carbon nanotubes using their nanobelts as seeds.

A study led by Queen Mary University of London researchers has compared the performance and acceptability of a urine test and four different vaginal self-sampling collection devices to detect high risk Human Papilloma Virus (HPV).

Corresponding author Professor Jack Cuzick from Queen Mary University of London said: "Uptake of cervical screening has been declining in the UK in recent years, and self-sampling is an attractive alternative to clinician collected samples, initially in non-attenders but potentially for all women as the primary option.

"Cost and simplicity of use are important factors, and in low- and middle-income countries self-sampling may prove to be the only practical cost-effective option. High performance and acceptability of self-sampling is essential if this is to become the first option. Understanding preferences for a urine rather than a vaginal sample is important, and perhaps a choice should be offered."

The trial recruited women referred to the Royal London Hospital colposcopy clinic because of a positive cervical screening result. Those who joined the study were asked to provide a urine sample and to take two vaginal self-samples, using either a dry flocked swab and dacron swab, or a HerSwab and Qvintip device.

Of 600 vaginal sample pairs suitable for analysis, 505 were accompanied by a urine sample. All samples were tested at Queen Mary's Wolfson Institute of Preventive Medicine, with HPV determined using the Becton Dickinson Onclarity test.

All methods except HerSwab gave similar HPV positivity rates, but the highest sensitivity for abnormal cancer precursor lesions was seen with either the dry flocked swab or the dacron swab. Cellularity of the collected sample was highly variable for Herswab, but not for the other devices.

Survey results evaluating the women's experiences with sampling showed that there were no clear user preferences between devices, but that they found urine easy to collect and were more confident they had taken the sample correctly.

Many slopes in the Campania region are covered with layers of volcanic soil, the result of repeated eruptions over the course of millennia. As the impacts of climate change worsen, including the occurrence of very intense and short rainfall in localized areas, there is a growing need, especially in this and other Italian regions that are vulnerable to landslides, to understand the dynamics that induce such events more precisely and develop models that can predict them. When employed through adequate early warning systems, these tools can support decision-makers in adopting effective and efficient measures to protect people and the areas themselves from landslides.

To this end, the study Exploring ERA5 reanalysis potentialities for supporting landslide investigations: a test case from Campania Region (Southern Italy) by the CMCC Foundation identifies the potential of the fifth generation of atmospheric models (known as reanalysis dataset ERA5) developed by the European Centre for Medium-Range Weather Forecasts for improving the performance of early warning systems used, for example, by the Civil Protection (Protezione Civile).

On a slope covered by pyroclastic soil landslides are usually caused by a combination of two factors: the antecedent slope wetness conditions and the triggering condition represented by an intense precipitation event. The early warning system currently used by the Campania region uses the latter as the only indicator, ignoring the antecedent conditions of the soil. As a result, every time a precipitation event of a certain intensity is forecasted, whatever the state of the ground at that specific moment, the system returns a state of alert, pre-alarm or alarm. This increases the likelihood of false alarms and therefore of decisions - such as road closures - which may cause interruptions to services that in some cases could be avoided.

"Reanalyses are atmospheric models, the same ones that are used for forecasting. But they are usually used in back-analysis to reconstruct past weather conditions," explains Guido Rianna, CMCC researcher and co-author of the study. "Because of this characteristic, the purpose of reanalyses is not to forecast, but to homogenize, from a spatial and temporal point of view, data from different in situ monitoring systems - such as weather stations - or from remote sensing, such as satellites."

The fifth generation of reanalysis (ERA5) has a much better spatial resolution than the previous ones, providing atmospheric variables on grid cells of about 30 km side. In addition, it is possible to access free daily updated data through the Climate Data Store of the Copernicus Climate Change Service. This data ranges from 1979 up to 5 days before the consultation. Such a short time of data release allowed the authors of the study to assume - and then verify - a good performance of the tool not only for back-analysis studies but also for operational purposes such as the development of early warning systems.

"We first verified the reliability of the ERA5 reanalysis in reproducing rainfall histories leading to landslide events that actually occurred in the studied area," says Alfredo Reder, CMCC researcher and first author of the publication. "Next, we analysed the specific landslide event that occurred in Nocera Inferiore (Campania) on 4 March 2005. We verified that, at that event, the soil moisture estimations offered by ERA5, although not free of constraints and limitations, would have been able to observe a very high value in terms of water content along the entire cover. Thus, we have been able to take the final step of evaluating the possibility of using these reanalyses operationally for an early warning system. In the last phase of our research, we verified that the ERA5 datasets, if used as a proxy to support a decision, could improve the reliability of the forecasting model currently used in Campania, because they can provide information on antecedent slope wetness conditions, which are a predisposing factor for a landslide event."

The results of the study suggest the potential of this tool especially for minimizing false alarms, while avoiding missed alarms.

"Any expert on landslides in pyroclastic soils would say that the occurrence of an intense precipitation event in September in Campania, happening on a soil in dry condition, can rarely trigger a landslide," concludes Rianna. "But to date there is a lack of quantitative observational support to affirm this. Today, a Civil Protection decision-maker, on the basis of existing studies in the literature, could not fail to sound the alarm in the event of a forecast of a precipitation event with certain characteristics: he could not support this choice with data on the state of the soil in the prior period (except for a few limited slopes). Our research shows that ERA5 could fill this gap and therefore minimize the number of false alarms."

The results of this research apply to the case of pyroclastic landslides, which are characteristic of the studied area. The next step will be to verify the suitability of ERA5 reanalyses for the same purpose but in the case of other soil types, such as clay soils leading to slow landslides, which are characteristic of various areas of Italy, such as the southern Apennines and some areas of Basilicata and Campania.

In the 1960s, a national focus on hunger was essential to address major problems of undernutrition after World War II. In the 1990s, the nation shifted away from hunger toward "food insecurity" to better capture and address the challenges of food access and affordability.

Now, a new Viewpoint article argues that today's health and equity challenges call for the U.S. to shift from "food insecurity" to "nutrition insecurity" in order to catalyze appropriate focus and policies on access not just to food but to healthy, nourishing food.

The Viewpoint, by Dariush Mozaffarian of the Friedman School of Nutrition Science & Policy at Tufts University, Sheila Fleischhacker of Georgetown Law School, and José Andrés of World Central Kitchen, was published online in JAMA this week.

The concept of food security focuses on access to and affordability of food that is safe, nutritious, and consistent with personal preferences. In reality, however, the "nutritious" part often has been overlooked or lost in national policies and solutions, with resulting emphasis on quantity, rather than quality, of food, say the authors.

"Food is essential both for life and human dignity. Every day, I see hunger, but the hunger I see is not only for calories but for nourishing meals. With a new focus on nutrition security, we embrace a solution that nourishes people, instead of filling them with food but leaving them hungry," said Chef José Andrés, founder of World Central Kitchen.

The authors define nutrition security as having consistent access to and availability and affordability of foods and beverages that promote well-being, while preventing -- and, if needed, treating -- disease. Nutrition security provides a more inclusive view that recognizes that foods must nourish all people.

"'Nutrition security' incorporates all the aims of food security but with additional emphasis on the need for wholesome, healthful foods and drinks for all. COVID-19 has made clear that Americans who are most likely to be hungry are also at highest risk of diet-related diseases including obesity, diabetes, heart disease, and many cancers - a harsh legacy of inequities and structural racism in our nation. A new focus on nutrition security for all Americans will help crystallize and catalyze real solutions that provide not only food but also well-being for everyone," said first author Dariush Mozaffarian, dean of the Friedman School of Nutrition Science & Policy at Tufts University.

"It's the right time for this evolution," said Sheila Fleischhacker, adjunct professor at Georgetown Law School, who has drafted food, nutrition and health legislation and campaign positions at the local, state, tribal and federal levels. "By prioritizing nutrition security, we bring together historically siloed areas - hunger and nutrition - which must be tackled together to effectively address our modern challenges of diet-related diseases and disparities in clinical care, government food and food assistance policies, public health investments, and national research."

"The current approach is not sufficient," the authors write, and "traditionally marginalized minority groups as well as people living in rural and lower-income counties are most likely to experience disparities in nutrition quality, food insecurity, and corresponding diet-related diseases."

Boulder, Colo., USA: The Geological Society of America regularly publishes
articles online ahead of print. For March, GSA Bulletin topics
include multiple articles about the dynamics of China and Tibet; the ups
and downs of the Missouri River; the Los Rastros Formation, Argentina; the
Olympic Mountains of Washington State; methane seep deposits; meandering
rivers; and the northwest Hawaiian Ridge. You can find these articles at

https://bulletin.geoscienceworld.org/content/early/recent

.

Transition from a passive to active continental margin setting for the
NE Asian continental margin during the Mesozoic: Insights from the
sedimentary formations and paleogeography of the eastern Jiamusi
Massif, NE China

Yini Wang; Wenliang Xu; Feng Wang

Abstract:
The Mesozoic tectonic evolution of the NE Asian continental margin has
received much attention in recent years. However, previous studies focused
mainly on the petrogenesis of igneous rocks and their relationship with
Mesozoic tectonics, and there have been few studies of the Mesozoic
sedimentary formations of the NE Asian continental margin. We combined
zircon U-Pb ages with Hf isotopic and biostratigraphic data to reconstruct
the Mesozoic paleogeography of the NE Asian continental margin. The results
indicate that Mesozoic strata of the eastern Jiamusi Massif, NE China,
include the Upper Triassic Nanshuangyashan Formation (Norian), Lower
Jurassic volcanic rocks, and Lower Cretaceous Longzhaogou Group. The Upper
Triassic Nanshuangyashan Formation consists of a suite of alternating
marine and terrestrial sedimentary rocks with abundant fossils that formed
in a passive continental margin setting. The Lower Jurassic strata comprise
a suite of calc-alkaline volcanic rocks that include basaltic andesites,
andesites, and rhyolites that formed in an active continental margin
setting related to initial subduction of the Paleo-Pacific Plate beneath
Eurasia. The Lower Cretaceous Longzhaogou Group belong to alternating
marine and terrestrial sedimentary formations that formed in an active
continental margin setting related to subduction of the Paleo-Pacific
Plate. Here, we integrate these data to reconstruct the Mesozoic tectonic
history of the NE Asian continental margin, which comprises a Late Triassic
passive continental margin, the initiation of subduction of the
Paleo-Pacific Plate in the Early Jurassic, and westward subduction and
rollback of the Paleo-Pacific Plate in the Early Cretaceous.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35850.1/595823/Transition-from-a-passive-to-active-continental

Low-δ18O A-type granites in SW China: Evidence for the interaction
between the subducted Paleotethyan slab and the Emeishan mantle plume

Jian Xu; Xiao-Ping Xia; Qiang Wang; Christopher J. Spencer; Bin He ...

Abstract:
The mechanisms and processes by which subducted slab interacted with mantle
plume remain controversial, as direct observation of such interaction is
difficult to impossible. Compositional heterogeneity of large igneous
provinces (LIPs) additionally makes plume-slab interaction hard to detect.
Oxygen isotopes are sensitive enough to trace the source of magmas. Here we
provide evidence for plume-slab interaction mainly based on in situ zircon
Hf-O isotope analyses, as well as whole-rock elemental and Sr-Nd-Hf isotope
analyses, on the Late Permian and Early Triassic A-type granites on the
margin of the Emeishan LIP in SW China. These granites show typical A-type
geochemical characters, such as high total alkali (7.93−9.68 wt%) and field
strength element (HFSE, e.g., Zr and Nb) contents, and high FeOT
/(FeOT+MgO) (0.87−0.98) and Ga/Al (3.67−5.06) values. The Late
Permian (ca. 259 Ma) and Early Triassic (ca. 248 Ma) granites show high
Nb/Th (>3.0) and low Y/Nb (<1.2) and Yb/Ta (<2.0) ratios similar
to the oceanic island basalts and have near-zero εNd(t) (−0.83
to −0.13 and −0.15 to +0.16, respectively) and depleted εHf(t)
(+2.71 to +3.39 and +2.62 to +3.55, respectively). In situ zircon O-Hf
analyses yielded anomalously low δ18O (0.2−2.0‰ and 3.2−4.8‰,
respectively) and positive εHf(t) (1.6−7.0 and 3.9−8.8,
respectively), suggesting varying proportions of hydrothermally altered
oceanic crust in their source region. Our results imply that significant
amounts of altered Paleotethyan oceanic crust have been subducted in the
upper mantle beneath the western South China Block. The nearby rising
Emeishan mantle plume may have rapidly entrained and incorporated these
oceanic crustal materials to the shallow mantle so that their low-δ 18O isotope feature was preserved. Subsequent
decompression-related partial melting of this hybrid source formed parental
rocks of the low-δ18O A-type granites. Our findings also suggest
that LIPs could obtain their compositional (especially oxygen isotope)
diversity through the interaction between the subducting slab and rising
mantle plume.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35929.1/595807/Low-18O-A-type-granites-in-SW-China-Evidence-for

The ups and downs of the Missouri River from Pleistocene to present:
Impact of climatic change and forebulge migration on river profiles,
river course, and valley fill complexity

Justin Anderson; John Holbrook; Ronald J. Goble

Abstract:
The Missouri River is a continent-scale river that has thus far escaped a
rigorous reporting of valley fill trends within its trunk system. This
study summarizes evolution of the lower Missouri River profile from the
time of outwash in the Last Glacial Maximum (LGM) until establishment of
the modern dominantly precipitation-fed river. This work relies on
optically stimulated luminescence (OSL) dating, water-well data, and a
collection of surficial geological maps of the valley compiled from U.S.
Geological Survey EDMAP and National Science Foundation Research Experience
for Undergrads projects. Mapping reveals five traceable surfaces within
valley fill between Yankton, South Dakota, USA, and Columbia, Missouri,
USA, that record two cycles of incision and aggradation between ca. 23 ka
and ca. 8 ka. The river aggraded during the LGM to form the Malta Bend
surface by ca. 26 ka. The Malta Bend surface is buried and fragmented but
presumed to record a braided outwash plain. The Malta Bend surface was
incised up to 18 m between ca. 23 ka and ca. 16 ka to form the Carrolton
surface (ca. 16 ka to ca. 14 ka). The Carrollton surface ghosts a braided
outwash morphology locally through overlying mud. Aggradation followed (ca.
14 ka to ca. 13.5 ka) to within 4 m of the modern floodplain surface and
generated the Salix surface (ca. 13.5 to ca. 12 ka). By Salix time, the
Missouri River was no longer an outwash river and formed a single-thread
meandering pattern. Reincision at ca. 12 ka followed Salix deposition to
form the short-lived Vermillion surface at approximately the grade of the
earlier Carrolton surface. Rapid aggradation from ca. 10 ka to ca. 8 ka
followed and formed the modern Omaha surface (ca. 8 ka to Present). The
higher Malta Bend and Omaha profiles are at roughly the same grade, as are
the lower Carrolton and Vermillion surfaces. The Salix surface is in
between. All surfaces converge downstream as they enter the narrow and
shallow bedrock valley just before reaching Columbia, Missouri. The maximum
departure of the profiles is 18 m near Sioux City, Iowa, USA, at ∼100 km
downstream from the James Lobe glacial input near Yankton, South Dakota.
Incision and aggradation appear to be driven by relative changes in input
of sediment and water related to glacial advance and retreat and then later
by climatic changes near the Holocene transition. The incision from the
Malta Bend to the Carrolton surface records the initial breakdown of the
cryosphere at the end of the LGM, and this same incisional event is found
in both the Ohio and Mississippi valleys. This incisional event records a
“big wash” that resulted in the evacuation of sediment from each of the
major outwash rivers of North America. The direction and magnitude of
incision from the LGM to the modern does not fit with modeled
glacioisostatic adjustment trends for the Missouri Valley. Glaciotectonics
likely influenced the magnitude of incision and aggradation secondarily but
does not appear to have controlled the overall timing or magnitude of
either. Glaciotectonic valley tilting during the Holocene, however, did
likely cause the Holocene channel to consistently migrate away from the
glacial front, which argues for a forebulge axis south of the Missouri
Valley during the Holocene and, by inference, earlier. This is at least 200
km south of where models predict the Holocene forebulge axis. The Missouri
Valley thus appears to reside in the tectonic low between the ice front and
the forebulge crest. The buffer valley component of incision caused by
profile variation could explain as much as 25 m of the total ∼40 m of
valley incision at Sioux City, Iowa. The Missouri Valley also hosted a
glacial lobe as far south as Sioux City, Iowa, in pre-Wisconsinan time,
which is also a factor in valley excavation.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35909.1/595763/The-ups-and-downs-of-the-Missouri-River-from

Segmentation of the Wassuk Range normal fault system, Nevada (USA):
Implications for earthquake rupture and Walker Lane dynamics

Ben Surpless; Sarah Thorne

Abstract:
Normal faults are commonly segmented along strike, with segments that
localize strain and influence propagation of slip during earthquakes.
Although the geometry of segments can be constrained by fault mapping, it
is challenging to determine seismically relevant segments along a fault
zone. Because slip histories, geometries, and strengths of linkages between
normal fault segments fundamentally control the propagation of rupture
during earthquakes, and differences in segment slip rates result in
differential uplift of adjacent footwalls, we used along-strike changes in
footwall morphology to detect fault segments and the relative strength of
the mechanical links between them. We applied a new geomorphic analysis
protocol to the Wassuk Range fault, Nevada, within the actively deforming
Walker Lane. The protocol examines characteristics of footwall morphology,
including range-crest continuity, bedrock-channel long profiles, catchment
area variability, and footwall relief, to detect changes in strike-parallel
footwall characteristics. Results revealed six domains with significant
differences in morphology that we used to identify seismically relevant
fault segments and segment boundaries. We integrated our results with
previous studies to determine relative strength of links between the six
segments, informing seismic hazard assessment. When combined with recent
geodetic studies, our results have implications for the future evolution of
the Walker Lane, suggesting changes in the accommodation of strain across
the region. Our analysis demonstrates the power of this method to
efficiently detect along-strike changes in footwall morphology related to
fault behavior, permitting future researchers to perform reconnaissance
assessment of normal fault segmentation worldwide.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35756.1/595764/Segmentation-of-the-Wassuk-Range-normal-fault

Widespread hydrothermal vents and associated volcanism record prolonged
Cenozoic magmatism in the South China Sea

Fang Zhao; Christian Berndt; Tiago M. Alves; Shaohong Xia; Lin Li ...

Abstract:
The continental margin of the northern South China Sea is considered to be
a magma-poor rifted margin. This work uses new seismic, bathymetric,
gravity, and magnetic data to reveal how extensively magmatic processes
have reshaped the latter continental margin. Widespread hydrothermal vent
complexes and magmatic edifices such as volcanoes, igneous sills, lava
flows, and associated domes are confirmed in the broader area of the
northern South China Sea. Newly identified hydrothermal vents have crater-
and mound-shaped surface expressions, and occur chiefly above igneous sills
and volcanic edifices. Detailed stratigraphic analyses of volcanoes and
hydrothermal vents suggest that magmatic activity took place in discrete
phases between the early Miocene and the Quaternary. Importantly, the
occurrence of hydrothermal vents close to the present seafloor, when
accompanied by shallow igneous sills, suggest that fluid seepage is still
active, well after main phases of volcanism previously documented in the
literature. After combining geophysical and geochemical data, this study
postulates that the extensive post-rift magmatism in the northern South
China Sea is linked to the effect of a mantle plume over a long time
interval. We propose that prolonged magmatism resulted in contact
metamorphism in carbon-rich sediments, producing large amounts of
hydrothermal fluid along the northern South China Sea. Similar processes
are expected in parts of magma-poor margins in association with CO 2/CH4 and heat flow release into sea water and
underlying strata.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35897.1/595765/Widespread-hydrothermal-vents-and-associated

Tectonically conditioned record of continental interior paleoclimate
during the Carnian Pluvial Episode: The Upper Triassic Los Rastros
Formation, Argentina

C.A. Benavente; A.C. Mancuso; R.B. Irmis; K.M. Bohacs; S. Matheos

Abstract:
Discerning paleoclimate parameters in depositional systems of the
continental interior is challenging because the system response and
stratigraphic record of climate are controlled by tectonic processes and
are mediated through landscape and hydrological evolution of fluvial
lacustrine systems. Climate and tectonic signals cannot be deconvolved from
stratigraphic patterns alone but require additional information or data
sets that directly record climate or tectonic influence. The Carnian Los
Rastros Formation in northwest Argentina provides an excellent case study
that integrates an appropriate range of information in a system with strong
climate and tectonic signals, being deposited in part during the Carnian
Pluvial Episode and spanning the active rift phase of the
Ischigualasto−Villa Unión Basin. We examined the stratigraphic and spatial
patterns of carbon (C) and oxygen (O) stable isotopes in lacustrine
carbonates from the Los Rastros Formation in multiple parts of the basin to
constrain paleohydrological conditions and paleotemperatures. Practically
all C and O isotope values are characterized by negative values: δ 18Ocarb −11.6‰ and −15.7‰ (χ average −13.1‰; 1σ =
1.6) and δ13Ccarb −2.6‰ to −8.0‰ (χ average −5.1‰; 1σ
= 2.1), reflecting the latitude, altitude, and continentality of the lake
system and its vegetated and humid catchment area. Stratigraphic patterns
of stable isotope data from two different localities (Cerro Bola North and
Cerro Bola South) show a change from short water-residence time to long
residence time and back to short residence time. This contrasts with
sedimentologic, organic geochemical, and small-scale stratigraphic patterns
that indicate an overfilled lake basin, which is expected to contain a
completely open-hydrology isotopic signature. Paleotemperatures calculated
from marginal lacustrine carbonates show a warm and quite variable
paleothermal range consonant with their continental interior position and
with Global Climate Model estimates for high paleolatitudes. Warmer
paleotemperatures (linked to aridity, probably smaller lake size, and less
thermal mass) precede the Carnian Pluvial Episode, whereas relatively
cooler paleotemperatures coincide with the Carnian Pluvial Episode (linked
to humidity, probably larger lake size, and more thermal mass). Carbon and
oxygen stable isotope signatures integrated with sedimentologic and
physiographic information allow us to propose that tectonics, specifically,
half-graben tilting during the active synrift phase, dominated over climate
effects as the cause of hydrological fluctuations of this system, even
during the Carnian Pluvial Episode. Without appropriate
stratigraphic-tectonic context, single-proxy reconstructions of
continental-interior paleoclimate can be misleading. A robust
interpretation of climate effects requires characterization of tectonic
effects, geomorphology, paleohydrology, and sedimentary system responses.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35847.1/595766/Tectonically-conditioned-record-of-continental

An intracontinental orogen exhumed by basement-slice imbrication in the
Longmenshan Thrust Belt of the Eastern Tibetan Plateau

Zhenhua Xue; Wei Lin; Yang Chu; Michel Faure; Yan Chen ...

Abstract:
The Longmenshan Thrust Belt in Eastern Tibet resulted from a Mesozoic
orogeny and Cenozoic reworking. It is generally believed that the Cenozoic
tectonics along the Longmenshan Thrust Belt are mostly inherited from the
Mesozoic. Reconstructing the Mesozoic tectonics of the Longmenshan Thrust
Belt is therefore important for understanding its evolutionary history. On
the basis of detailed structural analysis, we recognized a Main Central
Boundary that divides the Longmenshan Thrust Belt into a Southeastern Zone
and a Northwestern Zone. Both zones underwent a main D1 event
characterized by D1E top-to-the-SE thrusting in the Southeastern
Zone and D1W top-to-the-NW/N thrusting in the Northwestern Zone.
In the Southeastern Zone, a D2 top-to-the-NW/N normal faulting
that cuts the D1E structures is developed along the NW boundary
of the basement complexes. Newly obtained and previous geochronological
data indicate that the D1E and D1W events occurred
synchronously at ca. 224−219 Ma, and the D2 top-to-the-NW/N
normal faulting was episodically activated at ca. 166−160 Ma, 141−120 Ma,
81−47 Ma, and 27−25 Ma. Episodic and synchronously activated top-to-the-NW
normal faulting and top-to-the-SE thrusting along the northwestern and
southeastern boundaries of the basement complexes, respectively, leads us
to propose that the basement slices were episodically imbricated to the SE
during the Late Jurassic−Early Cretaceous and Late Cretaceous−earliest
Paleocene. The D1 amphibolite facies metamorphic rocks above the
basement complexes recorded fast exhumation during the Late Jurassic−Early
Cretaceous. We propose that the early Mesozoic northwestward basement
underthrusting along a crustal “weak zone” was responsible for the D 1 double-vergent thrusting and amphibolite facies metamorphism.
Subsequent basement-slice imbrications reworked the Longmenshan Thrust Belt
and exhumed the amphibolite facies rocks. Our results highlight the
importance of basement underthrusting and imbrication in the formation and
reworking of the intracontinental Longmenshan Thrust Belt in Eastern Tibet.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35826.1/595732/An-intracontinental-orogen-exhumed-by-basement

Mo isotope records from Lower Cambrian black shales, northwestern Tarim
Basin (China): Implications for the early Cambrian ocean

Guangyou Zhu; Tingting Li; Kun Zhao; Chao Li; Meng Cheng ...

Abstract:
The widely developed black shales deposited during the early Cambrian
recorded paleoenvironmental information about coeval seawater. Numerous
studies have been conducted on these shales to reconstruct the paleomarine
environment during this time period. However, most research has been
conducted on stratigraphic sections in South China, and equivalent studies
of sections from other cratons are relatively rare. Here, we report Mo
isotopic compositions as well as redox-sensitive trace-element and iron
(Fe) speciation data for black shales of the Lower Cambrian Yuertusi
Formation from the Tarim block (i.e., a small craton). The Fe speciation
data show high FeHR/FeT and Fepy/Fe HR ratios, indicating roughly sustained euxinic bottom-water
conditions during their deposition. Based on Mo isotopic compositions (δ 98/95Mo), we further classified the euxinic black shales into
two intervals: a lower interval (0−21.3 m) and an upper interval (21.3−32.3
m). The lower interval is characterized by variable Mo isotopic
compositions (−2.12‰ to +0.57‰, mean = −0.52‰ ± 0.72‰), with an obvious
negative excursion in its middle portion. The overlying upper interval has
relatively heavy δ98/95Mo values up to +1.42‰ (mean = +0.62‰ ±
0.37‰). We ascribe δ98/95Mo differences in the lower and upper
intervals to inadequate aqueous H2S concentrations for
quantitative thiomolybdate formation under euxinic conditions. The most
negative Mo isotope excursion may have been caused by upwelling
hydrothermal inputs during a transgression, consistent with significantly
elevated total organic carbon (TOC) contents, Mo and U enrichments, and Fe
supply. Relatively positive δ98/95Mo values in the upper
interval have roughly similar variations with other coeval sections,
indicating such variations were common for early Cambrian euxinic deposits,
and they were most likely caused by local differences in [H2S] aq. Compilation of Mo isotope data from the early Cambrian and
earlier times further indicates relatively oxygenated seawater, especially
the deep-marine areas during the early Cambrian before reaching a state
like modern seawater.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35726.1/595658/Mo-isotope-records-from-Lower-Cambrian-black

Quantitative analysis of the sedimentary architecture of eolian
successions developed under icehouse and greenhouse climatic conditions

Grace I.E. Cosgrove; Luca Colombera; Nigel P. Mountney

Abstract:
The continental terrestrial record preserves an archive of how ancient
sedimentary systems respond to and record changes in global climate. A
database-driven quantitative assessment reveals differences in the
preserved sedimentary architectures of siliciclastic eolian systems with
broad geographic and stratigraphic distribution that developed under
icehouse versus greenhouse climatic conditions. Over 5600 geological
entities, including architectural elements, facies, sediment textures, and
bounding surfaces, have been analyzed from 34 eolian systems of
Paleoproterozoic to Cenozoic ages. Statistical analyses have been performed
on the abundance, composition, preserved thickness, and arrangement of
different eolian lithofacies, architectural elements, and bounding
surfaces. Results demonstrate that preserved sedimentary architectures of
icehouse and greenhouse systems differ markedly. Eolian dune, sand sheet,
and interdune architectural elements that accumulated under icehouse
conditions are significantly thinner relative to their greenhouse
counterparts; this is observed across all basin settings, supercontinents,
geological ages, and dune field physiographic settings. However, this
difference between icehouse and greenhouse eolian systems is exclusively
observed for paleolatitudes <30°, which suggests that climate-induced
changes in the strength and circulation patterns of trade winds may have
partly controlled eolian sand accumulation. These changes acted in
combination with variations in water table levels, sand supply, and sand
transport, ultimately influencing the nature of long-term sediment
preservation. During icehouse episodes, Milankovitch cyclicity resulted in
deposits typified by glacial accumulation and interglacial deflation.
Greenhouse conditions promoted the accumulation of eolian elements into the
geological record due to elevated water tables and biogenic- and
chemical-stabilizing agents, which could protect deposits from wind-driven
deflation. In the context of a rapidly changing climate, the results
presented here can help predict the impact of climate change on Earth
surface processes.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35918.1/595649/Quantitative-analysis-of-the-sedimentary

Late Eocene post-collisional magmatic rocks from the southern Qiangtang
terrane record the melting of pre-collisional enriched lithospheric
mantle

Yue Qi; Qiang Wang; Gang-jian Wei; Xiu-Zheng Zhang; Wei Dan ...

Abstract:
Diverse rock types and contrasting geochemical compositions of
post-collisional mafic rocks across the Tibetan Plateau indicate that the
underlying enriched lithospheric mantle is heterogeneous; however, how
these enriched mantle sources were formed is still debated. The accreted
terranes within the Tibetan Plateau experienced multiple stages of
evolution. To track the geochemical characteristics of their associated
lithospheric mantle through time, we can use mantle-derived magmas to
constrain the mechanism of mantle enrichment. We report zircon U-Pb ages,
major and trace element contents, and Sr-Nd isotopic compositions for Early
Cretaceous and late Eocene mafic rocks in the southern Qiangtang terrane.
The Early Cretaceous Baishagang basalts (107.3 Ma) are characterized by low
K2O/Na2O (<1.0) ratios, arc-like trace element
patterns, and uniform Sr-Nd isotopic compositions [(87Sr/ 86Sr)i = 0.7067−0.7073, εNd(t) = −0.4 to
−0.2]. We suggest that the Baishagang basalts were derived from partial
melting of enriched lithospheric mantle that was metasomatized by subducted
Bangong−Nujiang oceanic material. We establish the geochemistry of the
pre-collisional enriched lithospheric mantle under the southern Qiangtang
terrane by combining our data with those from other Early Cretaceous mafic
rocks in the region. The late Eocene (ca. 35 Ma) post-collisional rocks in
the southern Qiangtang terrane have low K2O/Na2O
(<1.0) ratios, and their major element, trace element, and Sr-Nd
isotopic compositions [(87Sr/86Sr)i =
0.7042−0.7072, εNd(t) = −4.5 to +1.5] are similar to those of
the Early Cretaceous mafic rocks. Based on the distribution, melting
depths, and whole-rock geochemical compositions of the Early Cretaceous and
late Eocene mafic rocks, we argue that the primitive late Eocene
post-collisional rocks were derived from pre-collisional enriched
lithospheric mantle, and the evolved samples were produced by assimilation
and fractional crystallization of primary basaltic magma. Asthenosphere
upwelling in response to the removal of lithospheric mantle induced the
partial melting of enriched lithospheric mantle at ca. 35 Ma.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35864.1/595453/Late-Eocene-post-collisional-magmatic-rocks-from

Reappraisal of the Mesozoic tectonic transition from the Paleo-Tethyan
to Paleo-Pacific domains in South China

Chengshi Gan; Yuzhi Zhang; Yuejun Wang; Xin Qian; Yang Wang

Abstract:
The southeastern (SE) South China Block was mainly influenced by the
Paleo-Tethyan and Paleo-Pacific dynamic domains during the Mesozoic. The
initial timing of the tectonic transition between these two domains in the
SE South China Block still remains debated. The transition would affect the
nature of the lithosphere and material provenance of sediments, and,
therefore, igneous and sedimentary rocks in the area could record such
dynamic processes. In this study, published geochronological and
geochemical data of the Triassic and Jurassic igneous rocks and detrital
zircon data of contemporaneous sedimentary rocks in the SE South China
Block were compiled, aiming to provide constraints on the tectonic
transition via tracing the spatial-temporal variations in the nature of the
lithosphere and sedimentary provenance signals. The compiled results
suggest that the magmatic intensity and volume decreased significantly from
the Late Triassic to Early−Middle Jurassic, with an obvious magmatic
quiescence between them, and increased from the Early−Middle Jurassic to
Late Jurassic. The εNd(t) and
zircon εHf(t) values of mafic
rocks, granitoids, and shoshonitic rocks remarkably increased from the Late
Triassic to Early−Middle Jurassic, indicative of variations in the
lithospheric mantle and continental crust. Such variations suggest that the
initial tectonic transition occurred at the earliest Early Jurassic. Based
on the southward paleocurrents from Early Jurassic sandstone, E-W−trending
extension of Early−Middle Jurassic mafic and shoshonitic rocks, and similar
sedimentary provenances of Late Triassic and Early−Middle Jurassic
sedimentary rocks, these features imply that the SE South China Block was
not immediately influenced by the Paleo-Pacific domain during the
Early−Middle Jurassic. However, from the Early−Middle Jurassic to Late
Jurassic and Early Cretaceous, the spatial distribution, geochemical
signatures, magmatic intensity, and magmatic volume of igneous rocks and
provenance of sedimentary rocks exhibit obvious variations, and the
regional fold hinge direction changed from E-W−trending to NE-trending,
suggesting significant effects from Paleo-Pacific subduction on the SE
South China Block. Thus, the Mesozoic tectonic transition from the
Paleo-Tethyan to the Paleo-Pacific dynamic domain in the SE South China
Block likely occurred during the Early−Middle Jurassic.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35755.1/595454/Reappraisal-of-the-Mesozoic-tectonic-transition

Two key switches in regional stress field during multi-stage
deformation in the Carboniferous−Triassic southernmost Altaids
(Beishan, NW China): Response to orocline-related roll-back processes

Zhonghua Tian; Wenjiao Xiao; Brian F. Windley; Peng Huang; Ji’en Zhang ...

Abstract:
The orogenic architecture of the Altaids of Central Asia was created by
multiple large-scale slab roll-back and oroclinal bending. However, no
regional structural deformation related to roll-back processes has been
described. In this paper, we report a structural study of the Beishan
orogenic collage in the southernmost Altaids, which is located in the
southern wing of the Tuva-Mongol Orocline. Our new field mapping and
structural analysis integrated with an electron backscatter diffraction
study, paleontology, U-Pb dating, 39Ar-40Ar dating,
together with published isotopic ages enables us to construct a detailed
deformation-time sequence: During D1 times many thrusts were
propagated northwards. In D2 there was ductile sinistral
shearing at 336−326 Ma. In D3 times there was top-to-W/WNW
ductile thrusting at 303−289 Ma. Two phases of folding were defined as D4 and D5. Three stages of extensional events (E1−E3) separately occurred during D1−D 5. Two switches of the regional stress field were identified in
the Carboniferous to Early Permian (D1-E1-D 2-D3-E2) and Late Permian to Early
Triassic (D4-E3-D5). These two switches in
the stress field were associated with formation of bimodal volcanic rocks,
and an extensional interarc basin with deposition of Permian-Triassic
sediments, which can be related to two stages of roll-back of the
subduction zone on the Paleo-Asian oceanic margin. We demonstrate for the
first time that two key stress field switches were responses to the
formation of the Tuva-Mongol Orocline.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35898.1/595455/Two-key-switches-in-regional-stress-field-during

Structural styles, deformation, and uplift of the Olympic Mountains,
Washington: Implications for accretionary wedge deformation

M. James Aldrich

Abstract:
The Olympic subduction complex is the exposed subaerial Cascadia
accretionary wedge in the Olympic Mountains of Washington State. Uplift of
the mountains has been attributed to two competing models: margin-normal
deformation from frontal accretion and underplating, and margin-parallel
deformation from the clockwise rotation and northward movement of the
Oregon Coast Range block compressing the Olympic Mountains block against
the Canadian Coast Range. East-northeast−oriented folds and Quaternary
thrust faults and paleostress analysis of faults in the Coastal Olympic
subduction complex, west of the subduction complex massif, provide new
evidence for north-south shortening in the Coastal Olympic subduction
complex that fills a large spatial gap in the north-south shortening
documented in prior studies, substantially strengthening the block rotation
model. These new data, together with previous studies that document
north-south shortening in the subduction complex and at numerous locations
in the Coast Range terrane peripheral to the complex, indicate that
margin-parallel deformation of the Cascadia forearc has contributed
significantly to uplift of the Olympic Mountains. Coastal Olympic
subduction complex shallow-level fold structural style and deformation
mechanisms provide a template for analyzing folding processes in other
accretionary wedges. Similar-shaped folds in shallow-level Miocene
turbidite sediments of the Coastal Olympic subduction complex formed in two
shortening phases not previously recognized in accretionary wedges. Folds
began forming by bed-parallel flow of sediment into developing hinges. When
the strata could no longer accommodate shortening by flexural flow, further
shortening was taken up by flexural slip. Similar-shaped folds in the
deeper accretionary wedge rocks of the subduction complex massif have a
well-developed axial-surface cleavage that facilitated shear folding with
sediment moving parallel to the axial surface into the hinges, a structural
style that is common to accretionary wedges. The pressure-temperature
conditions and depth at which the formation of similar folds transitions
from bed-parallel to axial-surface−parallel deformation are bracketed.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35729.1/595422/Structural-styles-deformation-and-uplift-of-the

Late Paleogene paleotopographic evolution of the northern Cordilleran
orogenic front: Implications for demise of the orogen

Majie Fan; Kurt N. Constenius; Rachel F. Phillips; David L. Dettman

Abstract:
The paleotopographic history of the North American Cordilleran orogen holds
the key to understanding mechanisms of orogenesis and subsequent orogenic
collapse. It has been suggested that the orogenic front in western Montana
(USA) and Alberta (Canada) was more than 4 km high during Late
Cretaceous−early Eocene contractional deformation and during the initial
phase of extension in the middle Eocene; however, the late Eocene−Oligocene
topographic evolution during continued extensional collapse remains poorly
constrained. Here we extend the paleotopographic record in the Kishenehn
Basin in northwestern Montana and southeastern British Columbia (Canada) to
the late Oligocene by studying δ18O values of fossil mollusks
and cement and paleosol carbonates. The molluscan taxa changed from three
sympatric groups with preferred habitats ranging from tropical wet,
semi-arid subtropical, and temperate during the middle and late Eocene, to
mainly a single group associated with temperate environment during the
Oligocene, reflecting a decline in molluscan biodiversity induced by
climate cooling across the Eocene−Oligocene transition. Reconstructed δ 18O values of alpine snowmelt and basinal precipitation
decreased by 1.4‰ and 3.8‰, respectively, from the middle to late Eocene,
reflecting climate cooling and ∼1 km surface uplift of the basin floor. The
reconstructed alpine snowmelt δ18O values then increased by 2.9‰
in the Oligocene suggesting a ∼0.5 km drop in elevation of the orogenic
front. Collectively, the results of our new and previously published δ 18O data chronicle the paleotopographic response to the change
from flat-slab subduction to slab rollback over a 45 m.y. period. These
data suggest that the orogenic front was characterized by high elevation
(>4 km) in the ancestral Lewis-Clark-Livingston ranges during latest
Cretaceous−early Eocene (ca. 75−52 Ma) contraction. The initial phase of
extension related to the Kishenehn Basin created a lowland basin with a
surface elevation of only ∼1.5 km during the early middle Eocene (ca. 46−44
Ma) whereas the ranges remained >4 km high. The high range elevations
were sustained for at least 12 m.y. in the middle to late Eocene concurrent
with extension, while the basin floor elevation was uplifted to ∼2.5 km by
the latest Eocene (ca. 36−34 Ma). Basin aggradation can explain at most
half of the 1 km basin floor uplift. The remaining amount (at least 0.5 km)
and sustained high range elevation suggest that range denudation and
crustal extension was compensated by the isostatic and thermal effects of
slab rollback and/or passage of a slab window and infusion of hot
asthenosphere beneath the continent. The range elevation in the orogenic
front decreased ∼0.5 km by the late Oligocene (ca. 28 Ma), associated with
a decrease in rock uplift rate associated with extension. A post-Oligocene
elevation drop of ∼1 km resulted in both the ranges and basin floor
reaching modern topography in the Kishenehn Basin drainage, likely due to
the regional effect of Neogene Basin and Range extension. This study, along
with the previous investigation of the Kishenehn Basin by Fan et al.
(2017), are the first studies that systematically investigate paleorelief
of the orogenic belt by reconstructing paleoelevations of the mountains and
the basin at the same time. The results highlight that the Cordilleran
orogenic front of northern Montana and southern British Columbia sustained
its high elevation edifice for at least 12 m.y. after the start of
extension. We suggest that initial crustal extension did not result in
orogenic demise because of concurrent thermal and isostatic uplift.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35919.1/595423/Late-Paleogene-paleotopographic-evolution-of-the

The role of slab geometry in the exhumation of cordilleran-type orogens
and their forelands: Insights from northern Patagonia

Marie C. Genge; Massimiliano Zattin; Elisa Savignano; Marta Franchini;
Cécile Gautheron ...

Abstract:
In cordilleran-type orogens, subduction geometry exerts a fundamental
control on the tectonic behavior of the overriding plate. An integrated
low-temperature, large thermochronological data set is used in this study
to investigate the burial and exhumation history of the overriding plate in
northern Patagonia (40°−45°S). Thermal inverse modeling allowed us to
establish that a ∼2.5−4-km-thick section originally overlaid the
Jurassic−Lower Cretaceous successions deposited in half-graben systems that
are presently exposed in the foreland. Removal of the sedimentary cover
started in the late Early Cretaceous. This was coeval with an increase of
the convergence rate and a switch to a westward absolute motion of the
South American Plate that was accompanied by shallowing of the subducting
slab. Unroofing was probably further enhanced by Late Cretaceous to early
Paleogene opening of a slab window beneath the overriding plate. Following
a tectonically quiescent period, renewed exhumation occurred in the orogen
during relatively fast Neogene plate convergence. However, even the highly
sensitive apatite (U-Th)/He thermochronometer does not record any coeval
cooling in the foreland. The comparison between Late Cretaceous and Neogene
exhumation patterns provides clear evidence of the fundamental role played
by inter-plate coupling associated with shallow slab configurations in
controlling plate-scale deformation. Our results, besides highlighting for
the first time how the whole northern Patagonia foreland was affected by an
exhumation of several kilometers since the Late Cretaceous, provide
unrivalled evidence of the link between deep geodynamic processes affecting
the slab and the modes and timing of unroofing of different sectors of the
overriding plate.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35767.1/595424/The-role-of-slab-geometry-in-the-exhumation-of

Flow of Devonian anatectic crust in the accretionary Altai Orogenic
Belt, central Asia: Insights into horizontal and vertical magma
transfer

Sheng Wang; Yingde Jiang; Roberto Weinberg; Karel Schulmann; Jian Zhang ...

Abstract:
Flow of partially molten crust is a key contributor to mass and heat
redistribution within orogenic systems, however, this process has not yet
been fully understood in accretionary orogens. This issue is addressed in a
Devonian migmatite-granite complex from the Chinese Altai through
structural, petrological, and geochronological investigations presented in
this study. The migmatite-granite complex records a gradual evolution from
metatexite, diatexite to granite and preserves a record of two main
Devonian phases of deformation designated D1 and D2. The D1 phase was
subdivided into an early crustal thickening episode (D1B) and a
later extensional episode (D1M) followed by D2 upright folding.
The D1M episode is associated with anatexis in the deep crust.
Vertical shortening, associated with D1M, gave rise to the
segregation of melt and formation of a sub-horizontal layering of stromatic
metatexite. This fabric was reworked by the D2 deformation associated with
the migration of anatectic magma in the cores of F2 antiforms.
Geochronological investigations combined with petro-structural analysis
reveal that: (1) D1M partial melting started probably at 420−410
Ma and formed sub-horizontal stromatic metatexites at ∼30 km depth; (2) The
anatectic magma accumulated and migrated when a drainage network developed,
as attested by the pervasive formation of massive diatexite migmatites, at
410−400 Ma; (3) Soon after, massive flow of the partially molten crust from
orogenic lower to orogenic upper crustal levels, assisted by the interplay
between D2 upright folding and magma diapirism, led to migmatite-granite
emplacement in the cores of regional F2 antiforms that lasted until at
least 390 Ma; (4) a terminal stage was manifested by the emplacement of
370−360 Ma granite dykes into the surrounding metamorphic envelope. We
propose that Devonian anatexis assisted by deformation governed first the
horizontal and then the vertical flow of partially molten orogenic lower
crust, which drove crustal flow, mass redistribution, and crustal
differentiation in the accretionary system of the Chinese Altai.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35645.1/595395/Flow-of-Devonian-anatectic-crust-in-the

Three stages of arc migration in the Carboniferous-Triassic in northern
Qiangtang, central Tibet, China: Ridge subduction and asynchronous slab
rollback of the Jinsha Paleotethys

Yin Liu; Wenjiao Xiao; Brian F. Windley; Kefa Zhou; Rongshe Li ...

Abstract:
Carboniferous-Triassic magmatism in northern Qiangtang, central Tibet,
China, played a key role in the evolution of the Tibetan Plateau yet
remains a subject of intense debate. New geochronological and geochemical
data from adakitic, Nb-enriched, and normal arc magmatic rocks, integrated
with results from previous studies, enable us to determine the
Carboniferous-Triassic (312−205 Ma), arc-related, plutonic-volcanic rocks
in northern Qiangtang. Spatial-temporal relationships reveal three periods
of younging including southward (312−252 Ma), rapid northward (249−237 Ma),
and normal northward (234−205 Ma) migrations that correspond to distinct
slab geodynamic processes including continentward slab shallowing, rapid
trenchward slab rollback, and normal trenchward rollback of the Jinsha
Paleotethys rather than the Longmuco-Shuanghu Paleotethys, respectively.
Moreover, varying degrees of coexistence of adakites/High-Mg andesites
(HMAs)/Nb-enriched basalt-andesites (NEBs) and intraplate basalts in the
above-mentioned stages is consistent with the magmatic effects of slab
window triggered by ridge subduction, which probably started since the Late
Carboniferous and continued into the Late Triassic. The
Carboniferous-Triassic multiple magmatic migrations and ridge-subduction
scenarios provide new insight into the geodynamic processes of the Jinsha
Paleotethys and the growth mechanism of the Tibetan Plateau.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35906.1/595412/Three-stages-of-arc-migration-in-the-Carboniferous

Magnetostratigraphic study of a Late Cretaceous−Paleogene succession in
the eastern Xining basin, NE Tibet: Constraint on the timing of major
tectonic events in response to the India-Eurasia collision

Chi-Cheng He; Yue-Qiao Zhang; Shao-Kai Li; Kai Wang; Jian-Qing Ji

Abstract:
Cretaceous-Cenozoic basins developed in the NE Tibetan Plateau contain key
archives to unravel the growth history of the plateau in response to the
India-Eurasia collision. Here we present magnetostratigraphic results of a
Late Cretaceous to Paleogene succession of the Zhongba section outcropping
at the southern margin of the eastern Xining basin. This succession
consists of three lithological units punctuated by two stratigraphic
unconformities, which best recorded the deformation history of this
foreland basin. Detailed magnetostratigraphic investigation show that the
lower terrestrial sedimentary rock unit, the Minhe Group, was deposited in
latest Cretaceous in the time span of ca. 74.5−69.2 Ma; the middle unit was
deposited in Paleogene in the time span of ca. 49.3−22 Ma; and the upper
conglomeratic unit, not dated, possibly was deposited in early Miocene.
Accordingly, the Cretaceous−Paleogene unconformity, widely observed in the
foreland basins of NE Tibet, represents a sedimentary hiatus duration of
∼19.9 m.y., from ca. 69.2 Ma to ca. 49.3 Ma, which possibly recorded the
far-field response to the tectonic transition from Neo-Tethys oceanic plate
subduction to the India-Eurasia collision in southern Tibet. Changes in
provenance, sedimentary accumulation rate, and mean susceptibility value at
ca. 33−30 Ma, and the total prolate anisotropy of magnetic susceptibility
(AMS) ellipsoids and provenance shifting since ca. 23−19 Ma, point to the
pulsed growth of West Qinling, and rapid uplift of Laji Shan, respectively,
indicating an enhanced effect of the India-Eurasia collision in Oligocene
and early Miocene. AMS results show a clockwise rotation of the shortening
direction from NEN-SWS in latest Cretaceous to NE-SW in Paleogene.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35874.1/595413/Magnetostratigraphic-study-of-a-Late-Cretaceous

Temperatures of Late Cretaceous (Campanian) methane-derived authigenic
carbonates from the Western Interior Seaway, South Dakota, USA, using
clumped isotopes

Yang Gao; Gregory A. Henkes; J. Kirk Cochran; Neil H. Landman

Abstract:
Methane seep deposits, comprising large, carbonate-rich mounds formed from
hydrocarbon seepage, were widely distributed in the Late Cretaceous Western
Interior Seaway (WIS) of North America. Well-preserved, methane-derived
authigenic carbonates (MDACs) from these deposits have been shown to retain
petrological, paleontological, and geochemical imprints of their ancient
depositional setting, all of which are important for understanding the
dynamics and evolution of the shallow, epeiric WIS. To better characterize
the environmental conditions of WIS seeps, we applied clumped isotope
paleothermometry to magnesium calcite MDAC samples from five seep
localities in the upper Campanian Pierre Shale, South Dakota, USA. We
measured 21 subsamples, including 18 micritic carbonates and demonstrated
apparent clumped isotope equilibrium between MDACs and WIS bottom waters.
Extreme 13C depletion in most samples (δ13C ranging
to −45.44‰) indicates they were precipitated with oxidized methane as a
major source of dissolved inorganic carbon, which itself implies a close
association with ancient methanotrophic metabolism. The average clumped
isotope paleotemperature from the micritic carbonates is 23 ± 7 °C (1σ
standard deviation), which agrees with bottom water paleotemperatures
inferred from δ18O measurements of MDACs and well-preserved
mollusk shells at similar localities in the WIS. The calculated average δ 18Ow value for these samples is −0.5 ± 1.7‰ (1σ SD),
which is indistinguishable from previously reported calculation on
Campanian seawater δ18Ow from fossil mollusk shells,
but elevated above younger fossils collected from other locations in the
WIS. Our conclusions are inconsistent with previously hypothesized
disequilibrium for WIS MDAC clumped isotope and therefore we propose that
fossil MDAC deposits may be used as paleotemperature archives.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35846.1/595396/Temperatures-of-Late-Cretaceous-Campanian-methane

Autogenic translation and counter point bar deposition in meandering
rivers

Z. Sylvester; P.R. Durkin; S.M. Hubbard; D. Mohrig

Abstract:
Although it has long been recognized that deposition along meandering
rivers is not restricted to convex banks (i.e., point bars), the consensus
is that sediment deposition on concave banks of channel bends mostly occurs
when meander bends translate downstream because erosion-resistant barriers
inhibit their lateral migration. Using a kinematic model of channel
meandering and time lapse satellite imagery from the Mamoré River in
Bolivia, we show that downstream translation and associated concave bank
deposition are essential, autogenic parts of the meandering process, and
resulting counter point bars are expected to be present whenever
perturbations such as bend cutoffs and channel reoccupations create short
bends with high curvatures. The implication is that zones of concave bank
deposition with lower topography, finer-grained sediment, slack water, and
riparian vegetation that differs from point bars are more common than
previously considered.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35829.1/595343/Autogenic-translation-and-counter-point-bar

Stratigraphy, age, and provenance of the Eocene Chumstick basin,
Washington Cascades; implications for paleogeography, regional
tectonics, and development of strike-slip basins

Erin E. Donaghy; Paul J. Umhoefer; Michael P. Eddy; Robert B. Miller;
Taylor LaCasse

Abstract:
Strike-slip faults form in a wide variety of tectonic settings and are a
first-order control on the geometry and sediment accumulation patterns in
adjacent sedimentary basins. Although the structural and depositional
architecture of strike-slip basins is well documented, few studies of
strike-slip basins have integrated depositional age, lithofacies, and
provenance control within this context. The Chumstick basin formed in
central Washington during a regional phase of dextral, strike-slip faulting
and episodic magmatism associated with Paleogene ridge-trench interaction
along the North America margin. The basin is bounded and subdivided by
major strike-slip faults that were active during deposition of the
intra-basinal, non-marine Chumstick Formation. We build on the existing
stratigraphy and present new, detailed lithofacies mapping, conglomerate
clast counts (N = 16; n = 1429), and sandstone detrital zircon analyses (N
= 16; n = 1360) from the Chumstick Formation to document changes in
sediment provenance, routing, and deposition. These data allow us to
reconstruct regional Eocene paleo-drainage systems of Washington and Oregon
and suggest that drainage within the Chumstick basin fed a regional river
system that flowed to a forearc or marginal basin on the newly accreted
Siletzia terrane. More generally, excellent age control from five
interbedded tuffs and high sediment accumulation rates allow us to track
the evolving sedimentary system over the Formation’s ca. 4−5 m.y.
depositional history. This is the first time lithofacies and provenance
variations can be constrained at high temporal resolution (0.5−1.5 m.y.
scale) for an ancient strike-slip basin and permits a detailed
reconstruction of sediment routing pathways and depositional environments.
As a result, we can assess how varying sediment supply and accommodation
space affects the depositional architecture during strike-slip basin
evolution.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35738.1/595282/Stratigraphy-age-and-provenance-of-the-Eocene

Progressive spatial and temporal evolution of tectonic triggers and
metasomatized mantle lithosphere sources for orogenic gold
mineralization in a Triassic convergent margin: Kunlun-Qinling Orogen,
central China

Hesen Zhao; Qingfei Wang; David I. Groves; Jun Deng

Abstract:
Whether orogenic gold deposits formed from crustal or subcrustal sources is
debated, and their link to orogenic processes is ambiguous. Gold
mineralization in the Triassic East Kunlun−West Qinling Orogen, China,
displays a spatial zonation in terms of its ages and stable isotope
compositions. In the West Qinling segment, most gold deposits formed in a
back-arc setting at 220∼210 Ma during a collisional episode within late
slab rollback. These deposits have dominant δ34S of 5∼15‰ and δ 18Ofluid of 10∼14‰, whereas those formed in the
suture zone at 210∼170 Ma, during a post-collisional episode after slab
break-off, have lower δ34S of −5∼+5‰ and δ18O fluid of 6∼10‰. In the East Kunlun segment, those deposits that
formed in a continental-arc setting and its related suture zone at 240∼200
Ma, in collisional to post-collisional episodes associated with slab
break-off, have δ34S and δ18Ofluid values
that are essentially similar to those in the West Qinling suture. δ 34S values of ore sulfide separates and rims of zoned pyrites
that have mantle-like signatures, in contrast with crustal signatures of
host rocks, are indicative of subcrustal ore-fluid sources. The combined
chronological and stable isotope shifts are consistent with a model in
which ore fluids for gold mineralization in a back-arc setting were sourced
from mantle lithosphere that was metasomatized by subducted oceanic
sediment; whereas those in a continental-arc setting—including its suture
zone—were sourced from fluid derived from altered oceanic crust. This study
thus provides new insights into the complexity of orogenic gold systems in
evolving orogens.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35754.1/595219/Progressive-spatial-and-temporal-evolution-of

Late Mesozoic−Cenozoic cooling history of the northeastern Tibetan
Plateau and its foreland derived from low-temperature thermochronology

Chen Wu; Andrew V. Zuza; Jie Li; Peter J. Haproff; An Yin ...

Abstract:
The growth history and formation mechanisms of the Cenozoic Tibetan Plateau
are the subject of an intense debate with important implications for
understanding the kinematics and dynamics of large-scale intracontinental
deformation. Better constraints on the uplift and deformation history
across the northern plateau are necessary to address how the Tibetan
Plateau was constructed. To this end, we present updated field observations
coupled with low-temperature thermochronology from the Qaidam basin in the
south to the Qilian Shan foreland in the north. Our results show that the
region experienced a late Mesozoic cooling event that is interpreted as a
result of tectonic deformation prior to the India-Asia collision. Our
results also reveal the onset of renewed cooling in the Eocene in the
Qilian Shan region along the northern margin of the Tibetan Plateau, which
we interpret to indicate the timing of initial thrusting and plateau
formation along the plateau margin. The interpreted Eocene thrusting in the
Qilian Shan predates Cenozoic thrust belts to the south (e.g., the Eastern
Kunlun Range), which supports out-of-sequence rather than
northward-migrating thrust belt development. The early Cenozoic deformation
exploited the south-dipping early Paleozoic Qilian suture zone as indicated
by our field mapping and the existing geophysical data. In the Miocene,
strike-slip faulting was initiated along segments of the older Paleozoic
suture zones in northern Tibet, which led to the development of the Kunlun
and Haiyuan left-slip transpressional systems. Late Miocene deformation and
uplift of the Hexi corridor and Longshou Shan directly north of the Qilian
Shan thrust belt represent the most recent phase of outward plateau growth.

View article:

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35879.1/595220/Late-Mesozoic-Cenozoic-cooling-history-of-the

Distinct responses of late Miocene eolian and lacustrine systems to
astronomical forcing in NE Tibet

Zhixiang Wang; Chunju Huang; David B. Kemp; Ze Zhang; Yu Sui

Abstract:
East Asian summer monsoon (EASM) and winter monsoon (EAWM) variability on

Journal

ACM SIGSAM Bulletin