Cretaceous-Paleogene clay in the Geulhemmergroeve tunnels near Geulhem, The Netherlands. Credit: Mark A. Wilson
What is K-T Boundary?
The Cretaceous–Tertiary extinction event, now called the Cretaceous–Palaeogene extinction event. It may be called the K/T extinction event or K/Pg event for short. This is the famous event which killed the dinosaurs at the end of the Cretaceous period.
Sixty-five million years ago about 70% of all species then living on Earth disappeared within a very short period. The disappearances included the last of the great dinosaurs. Paleontologists speculated and theorized for many years about what could have caused this “mass extinction,” known, as the K-T event (Cretaceous-Tertiary Mass Extinction event). Then in 1980 Alvarez, Alvarez, Asaro, and Michel reported their discovery that the peculiar sedimentary clay layer that was laid down at the time of the extinction showed an enormous amount of the rare element iridium.
First seen in the layer near Gubbio, Italy, the same enhancement was soon discovered to be world wide in that one particular 1-cm (0.4-in.) layer, both on land and at sea. The Alvarez team suggested that the enhancement was the product of a huge asteroid impact. On Earth most of the iridium and a number of other rare elements such as platinum, osmium, ruthenium, rhodium, and palladium are believed to have been carried down into Earth’s core, along with much of the iron, when Earth was largely molten.
Primitive “chondritic” meteorites (and presumably their asteroidial parents) still have the primordial solar system abundances of these elements. A chondritic asteroid 10 km (6 mi.) in diameter would contain enough iridium to account for the worldwide clay layer enhancement. This enhancement appears to hold for the other elements mentioned as well.
Since the original discovery, many other pieces of evidence have come to light that strongly support the impact theory. The high temperatures generated by the impact would have caused enormous fires, and indeed soot is found in the boundary clays. A physically altered form of the mineral quartz that can only be formed by the very high pressures associated with impacts has been found in the K-T layer.
Geologists who preferred other explanations for the K-T event said, “show us the crater.” In 1990 a cosmochemist named Alan Hildebrand became aware of geophysical data taken 10 years earlier by geophysicists looking for oil in the Yucatan region of Mexico. There a 180-km (112-mi.) diameter ring structure called “Chicxulub” seemed to fit what would be expected from a 65-million-year-old impact, and further studies have largely served to confirm its impact origin. The Chicxulub crater has been age dated (by the 40Ar/39Ar method) at 65 million years! Such an impact would cause enormous tidal waves, and evidence of just such waves at about that time has been found all around the Gulf.
One can never prove that an asteroid impact “killed the dinosaurs.” Many species of dinosaurs (and smaller flora and fauna) had in fact died out over the millions of years preceding the K-T events. The impact of a 10-km asteroid would most certainly have been an enormous insult to life on Earth. Locally, there would have been enormous shock wave heating and fires, tremendous earthquake, hurricane winds, and trillions of tons of debris thrown everywhere. It would have created months of darkness and cooler temperatures globally. There would have been concentrated nitric acid rains worldwide. Sulfuric acid aerosols may have cooled Earth for years. Life certainly could not have been easy for those species which did survive. Fortunately such impacts occur only about once every hundred million years.
What killed the dinosaurs?
Dinosaur fossils are only found below the K/T boundary. This shows they became extinct before, or during the event. Mosasaurs, plesiosaurs, pterosaurs and many species of plants and invertebrates also became extinct.
Mammalian and bird groups got through the event with some extinctions. Those that survived became widespread and varied during their later evolutionary radiation.
Scientists think the K/T extinctions were caused by something sudden and powerful, such as one or more massive asteroid or meteor impacts, and increased volcanic activity.
Scientists study what happened to the dinosaurs and other groups to learn what caused the K/T extinction event. How quickly they died out around the world is an important clue.
Scientists also study patterns in rocks to learn the causes. Several impact craters and massive volcanic activity, such as that in the Deccan Traps in India, are dated to about the same time as the extinctions. Those impacts and volcanoes would have reduced sunlight and hindered photosynthesis, disrupting Earth’s ecology.
Badlands near Drumheller, Alberta, where erosion has exposed the K-Pg boundary. Credit: Glenlarson/public domain
What is the K-Pg Boundary?
The Cretaceous–Paleogene (K–Pg) extinction event, was a sudden mass extinction of some three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the exception of some ectothermic species such as the leatherback sea turtle and crocodiles, no tetrapods weighing more than 25 kilograms (55 lb) survived. It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era that continues today.
In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows high levels of the metal iridium, which is rare in the Earth’s crust, but abundant in asteroids.
As originally proposed in 1980 by a team of scientists led by Luis Alvarez and his son Walter Alvarez, it is now generally thought that the K–Pg extinction was caused by the impact of a massive comet or asteroid 10 to 15 km (6 to 9 mi) wide, 66 million years ago, which devastated the global environment, mainly through a lingering impact winter which halted photosynthesis in plants and plankton.
The impact hypothesis, also known as the Alvarez hypothesis, was bolstered by the discovery of the 180-kilometer-wide (112 mi) Chicxulub crater in the Gulf of Mexico’s Yucatán Peninsula in the early 1990s, which provided conclusive evidence that the K–Pg boundary clay represented debris from an asteroid impact. The fact that the extinctions occurred simultaneously provides strong evidence that they were caused by the asteroid.
A 2016 drilling project into the Chicxulub peak ring, confirmed that the peak ring comprised granite ejected within minutes from deep in the earth, but contained hardly any gypsum, the usual sulfate-containing sea floor rock in the region: the gypsum would have vaporized and dispersed as an aerosol into the atmosphere, causing longer-term effects on the climate and food chain.
Other causal or contributing factors to the extinction may have been the Deccan Traps and other volcanic eruptions, climate change, and sea level change.
A wide range of species perished in the K–Pg extinction, the best-known being the non-avian dinosaurs. It also destroyed a plethora of other terrestrial organisms, including certain mammals, pterosaurs, birds, lizards, insects, and plants. In the oceans, the K–Pg extinction killed off plesiosaurs and the giant marine lizards (Mosasauridae) and devastated fish, sharks, mollusks (especially ammonites, which became extinct), and many species of plankton.
It is estimated that 75% or more of all species on Earth vanished. Yet the extinction also provided evolutionary opportunities: in its wake, many groups underwent remarkable adaptive radiation—sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches. Mammals in particular diversified in the Paleogene, evolving new forms such as horses, whales, bats, and primates. Birds, fish, and perhaps lizards also radiated.
K-Pg Boundary Extinction
The K–Pg extinction event was severe, global, rapid, and selective, eliminating a vast number of species. Based on marine fossils, it is estimated that 75% or more of all species were made extinct.
The event appears to have affected all continents at the same time. Non-avian dinosaurs, for example, are known from the Maastrichtian of North America, Europe, Asia, Africa, South America, and Antarctica, but are unknown from the Cenozoic anywhere in the world. Similarly, fossil pollen shows devastation of the plant communities in areas as far apart as New Mexico, Alaska, China, and New Zealand.
Despite the event’s severity, there was significant variability in the rate of extinction between and within different clades. Species that depended on photosynthesis declined or became extinct as atmospheric particles blocked sunlight and reduced the solar energy reaching the ground. This plant extinction caused a major reshuffling of the dominant plant groups. Omnivores, insectivores, and carrion-eaters survived the extinction event, perhaps because of the increased availability of their food sources. No purely herbivorous or carnivorous mammals seem to have survived. Rather, the surviving mammals and birds fed on insects, worms, and snails, which in turn fed on detritus (dead plant and animal matter).
In stream communities, few animal groups became extinct because such communities rely less directly on food from living plants and more on detritus washed in from the land, protecting them from extinction. Similar, but more complex patterns have been found in the oceans. Extinction was more severe among animals living in the water column than among animals living on or in the sea floor. Animals in the water column are almost entirely dependent on primary production from living phytoplankton, while animals on the ocean floor always or sometimes feed on detritus. Coccolithophorids and mollusks (including ammonites, rudists, freshwater snails, and mussels), and those organisms whose food chain included these shell builders, became extinct or suffered heavy losses. For example, it is thought that ammonites were the principal food of mosasaurs, a group of giant marine reptiles that became extinct at the boundary. The largest air-breathing survivors of the event, crocodyliforms and champsosaurs, were semi-aquatic and had access to detritus. Modern crocodilians can live as scavengers and survive for months without food, and their young are small, grow slowly, and feed largely on invertebrates and dead organisms for their first few years. These characteristics have been linked to crocodilian survival at the end of the Cretaceous.
After the K–Pg extinction event, biodiversity required substantial time to recover, despite the existence of abundant vacant ecological niches.
Radiolaria have left a geological record since at least the Ordovician times, and their mineral fossil skeletons can be tracked across the K–Pg boundary. There is no evidence of mass extinction of these organisms, and there is support for high productivity of these species in southern high latitudes as a result of cooling temperatures in the early Paleocene. Approximately 46% of diatom species survived the transition from the Cretaceous to the Upper Paleocene, a significant turnover in species but not a catastrophic extinction.
The occurrence of planktonic foraminifera across the K–Pg boundary has been studied since the 1930s. Research spurred by the possibility of an impact event at the K–Pg boundary resulted in numerous publications detailing planktonic foraminiferal extinction at the boundary; however, there is ongoing debate between groups that think the evidence indicates substantial extinction of these species at the K–Pg boundary, and those who think the evidence supports multiple extinctions and expansions through the boundary.
Numerous species of benthic foraminifera became extinct during the event, presumably because they depend on organic debris for nutrients, while biomass in the ocean is thought to have decreased. As the marine microbiota recovered, however, it is thought that increased speciation of benthic foraminifera resulted from the increase in food sources. Phytoplankton recovery in the early Paleocene provided the food source to support large benthic foraminiferal assemblages, which are mainly detritus-feeding. Ultimate recovery of the benthic populations occurred over several stages lasting several hundred thousand years into the early Paleocene.
Duration of K–Pg extinction
The rapidity of the extinction is a controversial issue, because some theories about the extinction’s causes imply a rapid extinction over a relatively short period (from a few years to a few thousand years) while others imply longer periods.
The issue is difficult to resolve because of the Signor–Lipps effect; that is, the fossil record is so incomplete that most extinct species probably died out long after the most recent fossil that has been found. Scientists have also found very few continuous beds of fossil-bearing rock that cover a time range from several million years before the K–Pg extinction to a few million years after it.
The sedimentation rate and thickness of K–Pg clay from three sites suggest rapid extinction, perhaps less than ten thousand years. At one site in the Denver Basin of Colorado, the ‘fern spike’ lasted about one thousand years (no more than 71 thousand years); the earliest Cenozoic mammals appeared about 185,000 years (no more than 570,000 years) after the K–Pg boundary layer was deposited.
Fossilized fish piled one atop another, suggesting that they were flung ashore and died stranded together on a sand bar after the wave from the seiche withdrew. Credit: Photo courtesy of Robert DePalma
The beginning of the end started with violent shaking that raised giant waves in the waters of an inland sea in what is now North Dakota.
Then, tiny glass beads began to fall like birdshot from the heavens. The rain of glass was so heavy it may have set fire to much of the vegetation on land. In the water, fish struggled to breathe as the beads clogged their gills.
The heaving sea turned into a 30-foot wall of water when it reached the mouth of a river, tossing hundreds, if not thousands, of fresh-water fish — sturgeon and paddlefish — onto a sand bar and temporarily reversing the flow of the river. Stranded by the receding water, the fish were pelted by glass beads up to 5 millimeters in diameter, some burying themselves inches deep in the mud. The torrent of rocks, like fine sand, and small glass beads continued for another 10 to 20 minutes before a second large wave inundated the shore and covered the fish with gravel, sand and fine sediment, sealing them from the world for 66 million years.
This unique, fossilized graveyard — fish stacked one atop another and mixed in with burned tree trunks, conifer branches, dead mammals, mosasaur bones, insects, the partial carcass of a Triceratops, marine microorganisms called dinoflagellates and snail-like marine cephalopods called ammonites — was unearthed by paleontologist Robert DePalma over the past six years in the Hell Creek Formation, not far from Bowman, North Dakota. The evidence confirms a suspicion that nagged at DePalma in his first digging season during the summer of 2013 — that this was a killing field laid down soon after the asteroid impact that eventually led to the extinction of all ground-dwelling dinosaurs. The impact at the end of the Cretaceous Period, the so-called K-T boundary, exterminated 75 percent of life on Earth.
“This is the first mass death assemblage of large organisms anyone has found associated with the K-T boundary,” said DePalma, curator of paleontology at the Palm Beach Museum of Natural History in Florida and a doctoral student at the University of Kansas. “At no other K-T boundary section on Earth can you find such a collection consisting of a large number of species representing different ages of organisms and different stages of life, all of which died at the same time, on the same day.”
In a paper to appear next week in the journal Proceedings of the National Academy of Sciences, he and his American and European colleagues, including two University of California, Berkeley, geologists, describe the site, dubbed Tanis, and the evidence connecting it with the asteroid or comet strike off Mexico’s Yucatan Peninsula 66 million years ago. That impact created a huge crater, called Chicxulub, in the ocean floor and sent vaporized rock and cubic miles of asteroid dust into the atmosphere. The cloud eventually enveloped Earth, setting the stage for Earth’s last mass extinction.
“It’s like a museum of the end of the Cretaceous in a layer a meter-and-a-half thick,” said Mark Richards, a UC Berkeley professor emeritus of earth and planetary science who is now provost and professor of earth and space sciences at the University of Washington.
Richards and Walter Alvarez, a UC Berkeley Professor of the Graduate School who 40 years ago first hypothesized that a comet or asteroid impact caused the mass extinction, were called in by DePalma and Dutch scientist Jan Smit to consult on the rain of glass beads and the tsunami-like waves that buried and preserved the fish. The beads, called tektites, formed in the atmosphere from rock melted by the impact.
Tsunami vs. seiche
Richards and Alvarez determined that the fish could not have been stranded and then buried by a typical tsunami, a single wave that would have reached this previously unknown arm of the Western Interior Seaway no less than 10 to 12 hours after the impact 3,000 kilometers away, if it didn’t peter out before then. Their reasoning: The tektites would have rained down within 45 minutes to an hour of the impact, unable to create mudholes if the seabed had not already been exposed.
Instead, they argue, seismic waves likely arrived within 10 minutes of the impact from what would have been the equivalent of a magnitude 10 or 11 earthquake, creating a seiche (pronounced saysh), a standing wave, in the inland sea that is similar to water sloshing in a bathtub during an earthquake. Though large earthquakes often generate seiches in enclosed bodies of water, they’re seldom noticed, Richards said. The 2011 Tohoku quake in Japan, a magnitude 9.0, created six-foot-high seiches 30 minutes later in a Norwegian fjord 8,000 kilometers away.
“The seismic waves start arising within nine to 10 minutes of the impact, so they had a chance to get the water sloshing before all the spherules (small spheres) had fallen out of the sky,” Richards said. “These spherules coming in cratered the surface, making funnels — you can see the deformed layers in what used to be soft mud — and then rubble covered the spherules. No one has seen these funnels before.”
The tektites would have come in on a ballistic trajectory from space, reaching terminal velocities of between 100 and 200 miles per hour, according to Alvarez, who estimated their travel time decades ago.
“You can imagine standing there being pelted by these glass spherules. They could have killed you,” Richards said. Many believe that the rain of debris was so intense that the energy ignited wildfires over the entire American continent, if not around the world.
“Tsunamis from the Chicxulub impact are certainly well-documented, but no one knew how far something like that would go into an inland sea,” DePalma said. “When Mark came aboard, he discovered a remarkable artifact — that the incoming seismic waves from the impact site would have arrived at just about the same time as the atmospheric travel time of the ejecta. That was our big breakthrough.”
At least two huge seiches inundated the land, perhaps 20 minutes apart, leaving six feet of deposits covering the fossils. Overlaying this is a layer of clay rich in iridium, a metal rare on Earth, but common in asteroids and comets. This layer is known as the K-T, or K-Pg boundary, marking the end of the Cretaceous Period and the beginning of the Tertiary Period, or Paleogene.
Iridium
In 1979, Alvarez and his father, Nobelist Luis Alvarez of UC Berkeley, were the first to recognize the significance of iridium that is found in 66 million-year-old rock layers around the world. They proposed that a comet or asteroid impact was responsible for both the iridium at the K-T boundary and the mass extinction.
The impact would have melted the bedrock under the seafloor and pulverized the asteroid, sending dust and melted rock into the stratosphere, where winds would have carried them around the planet and blotted out the sun for months, if not years. Debris would have rained down from the sky: not only tektites, but also rock debris from the continental crust, including shocked quartz, whose crystal structure was deformed by the impact.
The iridium-rich dust from the pulverized meteor would have been the last to fall out of the atmosphere after the impact, capping off the Cretaceous.
“When we proposed the impact hypothesis to explain the great extinction, it was based just on finding an anomalous concentration of iridium — the fingerprint of an asteroid or comet,” said Alvarez. “Since then, the evidence has gradually built up. But it never crossed my mind that we would find a deathbed like this.”
Key confirmation of the meteor hypothesis was the discovery of a buried impact crater, Chicxulub, in the Caribbean and off the coast of the Yucatan in Mexico, that was dated to exactly the age of the extinction. Shocked quartz and glass spherules were also found in K-Pg layers worldwide. The new discovery at Tanis is the first time the debris produced in the impact was found along with animals killed in the immediate aftermath of the impact.
“And now we have this magnificent and completely unexpected site that Robert DePalma is excavating in North Dakota, which is so rich in detailed information about what happened as a result of the impact,” Alvarez said. “For me, it is very exciting and gratifying!”
Tektites
Jan Smit, a retired professor of sedimentary geology from Vrije Universiteit in Amsterdam in The Netherlands who is considered the world expert on tektites from the impact, joined DePalma to analyze and date the tektites from the Tanis site. Many were found in near perfect condition embedded in amber, which at the time was pliable pine pitch.
“I went to the site in 2015 and, in front of my eyes, he (DePalma) uncovered a charred log or tree trunk about four meters long which was covered in amber, which acted as sort of an aerogel and caught the tektites when they were coming down,” Smit said. “It was a major discovery, because the resin, the amber, covered the tektites completely, and they are the most unaltered tektites I have seen so far, not 1 percent of alteration. We dated them, and they came out to be exactly from the K-T boundary.”
The tektites in the fishes’ gills are also a first.
“Paddlefish swim through the water with their mouths open, gaping, and in this net, they catch tiny particles, food particles, in their gill rakers, and then they swallow, like a whale shark or a baleen whale,” Smit said. “They also caught tektites. That by itself is an amazing fact. That means that the first direct victims of the impact are these accumulations of fishes.”
Smit also noted that the buried body of a Triceratops and a duck-billed hadrosaur proves beyond a doubt that dinosaurs were still alive at the time of the impact.
“We have an amazing array of discoveries which will prove in the future to be even more valuable,” Smit said. “We have fantastic deposits that need to be studied from all different viewpoints. And I think we can unravel the sequence of incoming ejecta from the Chicxulub impact in great detail, which we would never have been able to do with all the other deposits around the Gulf of Mexico.”
“So far, we have gone 40 years before something like this turned up that may very well be unique,” Smit said. “So, we have to be very careful with that place, how we dig it up and learn from it. This is a great gift at the end of my career. Walter sees it as the same.”
Reference:
DePalma, Robert A.; Smit, Jan; Burnham, David; Kuiper, Klaudia; Manning, Phillip; Oleinik, Anton; Larson, Peter; Maurrasse, Florentin; Vellekoop, Johan; Richards, Mark A.; Gurche, Loren; Alvarez, Walter. Prelude to Extinction: a seismically induced onshore surge deposit at the KPg boundary, North Dakota. PNAS, 2019
Young’s team collecting samples from a site once submerged under ancient oceans west of Nashville, Tennessee. Former FSU master’s student Andrew Kleinberg is pictured in the plaid shirt. Credit: Stephen Bilenky
Roughly 430 million years ago, during the Earth’s Silurian Period, global oceans were experiencing changes that would seem eerily familiar today. Melting polar ice sheets meant sea levels were steadily rising, and ocean oxygen was falling fast around the world.
At around the same time, a global die-off known among scientists as the Ireviken extinction event devastated scores of ancient species. Eighty percent of conodonts, which resembled small eels, were wiped out, along with half of all trilobites, which scuttled along the seafloor like their distant, modern-day relative the horseshoe crab.
Now, for the first time, a Florida State University team of researchers has uncovered conclusive evidence linking the period’s sea level rise and ocean oxygen depletion to the widespread decimation of marine species. Their work highlights a dramatic story about the urgent threat posed by reduced oxygen conditions to the rich tapestry of ocean life.
The findings from their study were published in the journal Earth and Planetary Science Letters.
Although other researchers had produced reams of data on the Ireviken event, none had been able to definitively establish a link between the mass extinction and the chemical and climatic changes in the oceans.
“The connection between these changes in the carbon cycle and the marine extinction event had always been a mystery,” said lead author Seth Young, an assistant professor in FSU’s Department of Earth, Ocean and Atmospheric Science.
To address this old and obstinate question, Young and his co-authors deployed new and innovative strategies. They developed an advanced multiproxy experimental approach using stable carbon isotopes, stable sulfur isotopes and iodine geochemical signatures to produce detailed, first-of-their-kind measurements for local and global marine oxygen fluctuation during the Ireviken event.
“Those are three separate, independent geochemical proxies, but when you combine them together you have a very powerful data set to unravel phenomena from local to global scales,” Young said. “That’s the utility and uniqueness of combining these proxies.”
Young and his team applied their multiproxy approach to samples from two geologically important field sites in Nevada and Tennessee, both of which were submerged under ancient oceans during the time of the extinction event. After analyzing their samples at the FSU-based National High Magnetic Field Laboratory, the connections between changes in ocean oxygen levels and mass extinction of marine organisms became clear.
The experiments revealed significant global oxygen depletion contemporaneous with the Ireviken event. Compounded with the rising sea level, which brought deoxygenated waters into shallower and more habitable areas, the reduced oxygen conditions were more than enough to play a central role in the mass extinction. This was the first direct evidence of a credible link between expansive oxygen loss and the Ireviken extinction event.
But, Young found, that oxygen loss wasn’t universal. Only about 8 percent or less of the global oceans experienced significantly reducing conditions with very little to no oxygen and high levels of toxic sulfide, suggesting that these conditions didn’t need to advance to whole-ocean scale to have an outsized, destructive effect.
“Our study finds that you don’t necessarily need the entire ocean to be reducing to generate these kind of geochemical signatures and to provide a kill mechanism for this significant extinction event,” Young said.
Today, like 430 million years ago, sea level is on the rise and ocean oxygen is hemorrhaging at an alarming rate. As parallels continue to emerge between today’s changes and past calamities, peering into the Earth’s distant past could be a critical tool in preparing for the future.
“There are common threads with other climatic and extinction events throughout Earth’s history, and future work will continue to help us understand the similarities and differences of these events to constrain future climate predictions,” said co-author Jeremy Owens, an assistant professor in FSU’s Department of Earth, Ocean and Atmospheric Science who has worked on other extinction events in the Jurassic and Cretaceous periods.
“I think it’s important to see how these events played out all the way from extinction interval through recovery period, how severe they were and their connections to the ancient environment along the way,” added Young. “That could help us figure out what’s in store for our future and how we can potentially mitigate some of the negative outcomes.”
This study was funded by the National Science Foundation and the Geological Society of America.
Reference:
Seth A. Young, Andrew Kleinberg, Jeremy D. Owens. Geochemical evidence for expansion of marine euxinia during an early Silurian (Llandovery–Wenlock boundary) mass extinction. Earth and Planetary Science Letters, 2019; 513: 187 DOI: 10.1016/j.epsl.2019.02.023
Aerial photo of the San Andreas Fault in the Carrizo Plain, northwest of Los Angeles. Credit: Wikipedia.
A new high-resolution map of a poorly known section of the northern San Andreas Fault reveals signs of the 1906 San Francisco earthquake, and may hold some clues as to how the fault could rupture in the future, according to a new study published in the Bulletin of the Seismological Society of America.
Samuel Johnson of the U.S. Geological Survey and Jeffrey Beeson of Fugro USA Marine Inc. compiled the map for the 35-kilometer-long section of the fault between Tomales Point and Fort Ross, California. They discovered two large zones, each covering about two square miles, of slope failure on the seafloor offshore of the Russian River, marked by lobes that appear to have formed when the intense shaking of the 1906 earthquake caused sand liquefaction.
The mapping also demonstrates that there are two active strands of the fault within the northern part of Bodega Bay, each of which has moved tens of meters within the past 10,000 years.
The findings “are not going to affect what we know about the recurrence interval or slip rate” on the Northern San Andreas Fault, “but it will affect what we know about how the northern San Andreas fault ruptures,” Johnson said.
“Normally if you were studying a fault zone on land and found a prominent fault strand, you would probably assume that was the strand that has most recently ruptured,” he explained. “Because we found two here, it’s a cautionary tale for earthquake geologists to comprehensively map fault zones. You may only capture part of the earthquake history or slip rate along a fault if you only know about one strand in a multi-strand zone”
The northern offshore areas of the fault have been intensively studied only within the past eight years, said Johnson. While much of the rest of the San Andreas fault has become a natural laboratory for studying earthquakes, “it’s a major geoscience oversight that these northern areas have not been studied before,” said Johnson. “We have been waiting for technology to produce the tools to look at these areas in high resolution.”
The researchers used data drawn from several techniques, including high-resolution seismic reflection profiles and multibeam bathymetry, both of which use multiple directed sound waves to image layers on or below the seafloor. Collection of some of the bathymetry data was funded by the California Ocean Protection Council as part of its work to designate and develop monitoring strategies for Marine Protected Areas, and by the National Oceanic and Atmospheric Administration (NOAA) to improve nautical charts.
The liquefaction lobes, which are similar to the ground failure seen offshore of the Klamath River delta during the magnitude 7.2 Eureka earthquake in northern California in 1980, were one of the surprises uncovered during the mapping, said Johnson.
The researchers were lucky to have caught a glimpse of the lobes before they disappeared, as some of the features are already being smoothed over by sediments deposited after 1906, Johnson said. “If you came back in another 50 to 100 years, you might not see these features because they would be all covered up. You can see their lifespan in the data and images we have now.”
Other insights from the map include a look at how movement along this portion of the fault has affected the onshore landscape, including the uplift of marine terraces and rapid formation of beaches and coastal sand dunes. For instance, the researchers noted that uplift west of the Northern San Andreas Fault has blocked the southward drift of sediment from the Russian River and Salmon Creek, leading to the swiftly growing South Salmon Creek Beach and its background of high coastal sand dunes.
Reference:
Samuel Y. Johnson, Jeffrey W. Beeson. Shallow Structure and Geomorphology along the Offshore Northern San Andreas Fault, Tomales Point to Fort Ross, California. Bulletin of the Seismological Society of America, 2019 DOI:10.1785/0120180158
Deep below the Earth in the Tonga-Fiji region of the South Pacific, one enormous earthquake triggered another. Credit: David Broad.
In the waning months of 2018, two of the mightiest deep earthquakes ever recorded in human history rattled the Tonga-Fiji region of the South Pacific.
In the first-ever study of these deep earthquakes — generally defined as any earthquake occurring 350 kilometers or more below the Earth’s surface — a Florida State University-led research team characterized these significant seismological events, revealing new and surprising information about our planet’s mysterious, ever-changing interior.
The team’s findings, published in the journal Geophysical Research Letters, delineate the complex geological processes responsible for the earthquakes and suggest that the first powerful perturbation may have actually triggered the second.
“We don’t have these kind of large earthquakes too often,” said study author Wenyuan Fan, an earthquake seismologist in FSU’s Department of Earth, Ocean and Atmospheric Science. “These deep earthquakes, especially larger earthquakes, aren’t really promoted by the ambient environment. So why is this happening? It’s a compelling question to ask.”
While deep earthquakes are rarely felt on the Earth’s surface, studying these titanic events can help researchers better understand the systems and structures of the inner Earth.
But the precise mechanisms of deep earthquakes have long been a mystery to earthquake scientists. The extreme temperature and pressure conditions of the deep Earth aren’t suitable for the kinds of mechanical processes typically responsible for earthquakes — namely the movement and sudden slippage of large plates.
Instead, the extraordinary pressure holds things firmly in place, and the soaring temperatures make rocky material behave like chocolate — moving around viscously instead of like ice cubes as is seen in the shallow surface.
“We did not expect to have deep earthquakes,” Fan said. “It should not happen. But we do have observations of deep earthquakes. So why? How? What kind of physical processes operate under such conditions?”
Using advanced waveform analyses, Fan and his team found that the first quake — a behemoth clocking in at magnitude 8.2, making it the second-largest deep earthquake ever recorded — was the product of two distinct physical processes.
The earthquake, they found, began in one of the region’s seismically important slabs, a portion of one tectonic plate subducted beneath another. Slab cores are cooler than their seething hot surroundings, and therefore more amenable to earthquake nucleation.
Once the earthquake began forming in the slab core, it propagated out into its warmer and more ductile surroundings. This outward propagation moved the earthquake from one mechanical process to another.
“This is interesting because before Tonga was thought to predominantly only have one type of mechanism, which is within the cold slab core,” Fan said. “But we’re actually seeing that multiple physical mechanisms are involved.”
The dual mechanism propagation pattern present in the magnitude 8.2 earthquake wasn’t wholly surprising to Fan and his team. The process was reminiscent of a similarly deep, 7.6 magnitude quake that shook the region in 1994. These recognizable patterns were a promising sign.
“To see that something is predictable, like the repeated patterns observed in the magnitude 8.2 earthquake, is very satisfying,” Fan said. “It brings up the hope that we do know something about this system.”
But the second earthquake, which occurred 18 days after the first, was more of a puzzle. The magnitude 7.9 convulsion struck in an area that previously experienced very little seismic activity. The distinct physical mechanisms present in the second quake shared more similarities with South American deep earthquakes than with the massive quakes that rock the South Pacific. And, puzzlingly for researchers, the magnitude 7.9 earthquake produced surprisingly few aftershocks relative to its considerable size.
Somehow, Fan said, a large earthquake was triggered in a previously aseismic region that then immediately returned to normal.
It’s this triggering process that most interests Fan going forward. He said this earthquake “doublet” illustrates the dynamic and interrelated nature of deep-Earth processes and the urgent need to better understand how these complicated processes operate.
“It’s important that we address the question of how large earthquakes trigger other large earthquakes that are not far away,” he said. “This is a good demonstration that there seem to be physical processes involved that are still unknown. We’ve gradually learned to identify the pattern, but not to a degree where we know exactly how it works. I think this is important to any kind of hazard forecast. It’s more than an intellectual interest. It’s important for human society.”
This study was funded by the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution.
Reference:
Wenyuan Fan, S. Shawn Wei, Dongdong Tian, Jeffrey J. McGuire, Douglas A. Wiens. Complex and Diverse Rupture Processes of the 2018 Mw 8.2 and Mw 7.9 Tonga‐Fiji Deep Earthquakes. Geophysical Research Letters, 2019 DOI: 10.1029/2018GL080997
Massachusetts State Geologist Stephen Mabee and colleagues recently annoucned that newly digitized surficial geology maps of the entire state are available online now. They provide details of what Mabee calls the ‘kitty litter’ mix of glacial tills, various sands and gravels on the earth’s surface. Credit: USGS/MassGIS
Anyone who digs in the earth needs a geologic map, says State Geologist Stephen Mabee at the University of Massachusetts Amherst, and now he and colleagues have finished a federal-state collaboration that began 81 years ago to create the first complete set of 189 surficial geologic maps of Massachusetts in 7.5-minute quadrangles, the same useful scale as the topographical maps used by hikers.
Civil engineers, geotechnology firms, state, county and town planners, transportation engineers, geologists, developers, “anyone who disturbs the ground for any project needs this resource,” Mabee says, “because running into an unexpected obstacle can cost tens of thousands, even millions of dollars. That’s the benefit of this information now publicly available. It’s been estimated that the benefit-to-cost ratio of such maps is 34/1, so every dollar spent on mapping saves the taxpayer $34.”
The newly digitized maps available online this month provide details of what Mabee calls the “kitty litter” mix of glacial tills, various sands and gravels on the earth’s surface. The uniform, portable maps use a unique standard color for each geologic material, with legends and supporting notes, and are “not just more accurate, but more convenient,” he adds. “You can use GIS to overlay them with any number of layers of other information for all kinds of spatial analyses.”
“These are very detailed for a statewide map,” he says. Another plus is that the maps are in a layered vector format, which means that the superimposed geologic units will be shown in the correct place on the Earth’s surface.
The senior lecturer in geosciences collaborated with research geologists Janet and Byron Stone and Mary DiGiacomo-Cohen at the U.S. Geological Survey (USGS) office in East Hartford, Conn. and others at the Massachusetts Bureau of Geographic Information (MassGIS) to resurrect this project that was begun in 1938. It was abandoned for many years, with roughly half the maps published on paper, when the USGS reorganized in 1978.
Mabee recalls, “I became the state geologist in 2002 and the first thing I did was tell the USGS ‘let’s get started again.’ All it took was someone to say we need to finish the job. There was once a great partnership between USGS and the state and I’m really glad to have helped to revive it. This is a huge accomplishment and one of my main goals when I started.”
At its peak, the project had been pumping out up to 18 quadrangles per decade, Mabee says, and by 1980 the Massachusetts Department of Public Works and USGS partners had mapped the entire state but only 105 maps were published on paper, a little more than half of what would be needed to cover the state. “We saw the last few maps published in the 1980s, then nothing,” he notes.
When Congress passed the National Environmental Policy Act of 1970, the Clean Water Act of 1972 and Superfund legislation in 1980, plus other environmental regulations, many environmental and consulting groups urgently needed surficial geologic maps but couldn’t find them, Mabee says. “For 20 years we had almost nothing, and what we had was only on paper. I had worked in consulting, so I knew the frustration.”
With the project revived in 2002 and supported by the USGS National Cooperative Geologic Mapping Program, MassGIS scanned all the paper maps on hand, while “squads” of Mabee’s UMass Amherst geosciences students hand-traced every map and created digital versions. The USGS professionals used old field notes to fill in gaps, digitized all the unpublished maps, matching all areas where different materials met, and added legends and definitions.
“They had to match the work done by people in the 1940s to what was produced by the next generation in the 1970s for all 189 quads,” he adds. “It was a huge undertaking, and finally, 17 years later, we got it done. People have been screaming for this data that once was all on paper, and now it’s all digital and online.”
A QUT geologist has published a new theory on the thermal evolution of Earth billions of years ago that explains why diamonds have formed as precious gemstones rather than just lumps of common graphite.
In the study, published in the journal Chemical Geology, the researchers looked at the magnesium oxide levels in thousands of volcanic rocks, dating at least 2.5 billion years old, that had been collected from around the world.
Professor Balz Kamber, from QUT’s Earth, Environmental and Biological Sciences School, co-authored the study with Professor Emma Tomlinson, from the Department of Geology at Trinity College Dublin. The research challenges a common theory about the evolution of the Earth and offers an explanation as to why the Earth’s mantle was cool enough to produce diamonds in the Archaean era between 4 billion and 2.5 billion years ago.
Professor Kamber said the analysis of the magnesium oxide levels in rock samples from the Archaean era contradicts the conventional belief that the Earth’s mantle was a lot hotter than it is in the current day.
“We know for a fact that the Earth produced a lot more heat back then — three to two-and-a-half times,” Professor Kamber said.
The prevailing theory among petrologists who study the origin, structure and composition of rocks, is that the Earth’s whole mantle was significantly hotter until 2.5 billion years ago.
But Professor Kamber’s analysis is that the prevailing theory is only half right. He said that while the lower mantle was significantly hotter, the upper mantle which is the area down to 670km was no hotter than it is in the present day.
“It’s the upper mantle that matters because the volcanic rocks that we observe, they come from the upper mantle,” Professor Kamber said.
To explain the theory, Professor Kamber uses the analogy of someone trying to warm their bedroom in winter by turning up the heater but failing to close the windows.
“You can produce as much heat as you like but it doesn’t get any warmer,” he said.
“So what we’re actually interested in is not how much heat we’re producing, but how warm it was in the interior of the earth.
“The assumption has been: more heat, therefore it was hotter. But what we show is: more heat but not hotter.
“The Earth was producing more heat but was also getting rid of it, opening more windows so to speak.”
The theory comes from the evidence stored in the ancient rocks on their level of magnesium oxide. Professor Kamber said the magnesium oxide levels in the vast majority of rock samples from that date similar to modern lavas, which indicated the temperatures were similar.
“Experimentalists can recreate the conditions that lead to the melting of the mantle,” Professor Kamber said. “And these experiments inform us without any doubt that the hotter the mantle at which it melts, the more magnesium in the melt.
“Our assumption had been we would find more magnesium in the older rocks compared to today.
“There are rocks that have more magnesium but they don’t come from the upper mantle.”
The cool upper mantle theory helps to explain the formation of diamonds, most of which were formed during this time period and would have turned into lumps of graphite if the upper mantle was too hot.
Professor Kamber’s paper outlining how evidence that the upper mantle was relatively cool has since been supported by a study coincidently published a few days later in the journal AGU100 by a team of German, American and British geologists who put forward a similar theory.
The understanding that the upper mantle 2.5 billion years ago was a lot cooler than previously thought also answers another long-standing area of dispute that has split geologists concerning the movement of tectonic plates.
If the upper mantle had been much hotter 2.5 million years ago, then the oceanic plates would have been thicker and difficult to move under each other.
The new evidence of a cooler upper mantle, which would have been churning hot rocks from the lower mantle upwards towards the surface to release the heat, explains how the plates riding on top of this would have moved fast and collided with each other.
Professor Kamber said understanding the thermal evolution of the Earth was critical to understanding the many aspects of our planet, such as the evolution of the atmosphere, the emergence of land, and the evolution of life.
“A geologist views the present state as the accumulated history of more than 4 billion years,” Professor Kamber said.
“We can’t understand the present fully if we don’t understand this journey.”
Reference:
Balz S. Kamber, Emma L. Tomlinson. Petrological, mineralogical and geochemical peculiarities of Archaean cratons. Chemical Geology, 2019; 511: 123 DOI: 10.1016/j.chemgeo.2019.02.011
Cross-sections of Earth’s mantle down to 1,400 km depth showing changes in its flow as ancient ocean beds fall into Earth’s deep interior. Credit: Ana M. G. Ferreira et al.
As ancient ocean floors plunge over 1,000 km into the Earth’s deep interior, they cause hot rock in the lower mantle to flow much more dynamically than previously thought, finds a new UCL-led study.
The discovery answers long-standing questions on the nature and mechanisms of mantle flow in the inaccessible part of deep Earth. This is key to understanding how quickly Earth is cooling, and the dynamic evolution of our planet and others in the solar system.
“We often picture the Earth’s mantle as a liquid that flows but it isn’t — it’s a solid that moves very slowly over time. Traditionally, it’s been thought that the flow of rock in Earth’s lower mantle is sluggish until you hit the planet’s core, with most dynamic action happening in the upper mantle which only goes to a depth of 660 km. We’ve shown this isn’t the case after all in large regions deep beneath the South Pacific Rim and South America,” explained lead author, Dr Ana Ferreira (UCL Earth Sciences and Universidade de Lisboa).
“Here, the same mechanism we see causing movement and deformation in the hot, pressurised rock in the upper mantle is also occurring in the lower mantle. If this increased activity is happening uniformly over the globe, Earth could be cooling more rapidly than we previously thought,” added Dr Manuele Faccenda, Universita di Padova.
The study, published today in Nature Geoscience by researchers from UCL, Universidade de Lisboa, Universita di Padova, Kangwon National University and Tel Aviv University, provides evidence of dynamic movement in the Earth’s lower mantle where ancient ocean floors are plunging towards the planet’s core, crossing from the upper mantle (up to ~660 km below the crust) to the lower mantle (~660 — 1,200 km deep).
The team found that the deformation and increased flow in the lower mantle is likely due to the movement of defects in the crystal lattice of rocks in the deep Earth, a deformation mechanism called “dislocation creep,” whose presence in the deep mantle has been the subject of debate.
The researchers used big data sets collected from seismic waves formed during earthquakes to probe what’s happening deep in Earth’s interior. The technique is well established and comparable to how radiation is used in CAT scans to see what’s happening in the body.
“In a CAT scan, narrow beams of X-rays pass through the body to detectors opposite the source, building an image. Seismic waves pass through the Earth in much the same way and are detected by seismic stations on the opposite side of the planet to the earthquake epicentre, allowing us to build a picture of the structure of Earth’s interior,” explained Dr Sung-Joon Chang, Kangwon National University.
By combining 43 million seismic data measurements with dynamic computer simulations using the UK’s supercomputing facilities HECToR, Archer and the Italian Galileo Computing Cluster, CINECA the researchers generated images to map how the Earth’s mantle flows at depths of ~1,200 km beneath our feet.
They revealed increased mantle flow beneath the Western Pacific and South America where ancient ocean floors are plunging towards Earth’s core over millions of years.
This approach of combining seismic data with geodynamic computer modelling can now be used to build detailed maps of how the whole mantle flows globally to see if dislocation creep is uniform at extreme depths.
The researchers also want to model how material moves up from the Earth’s core to the surface, which together with this latest study, will help scientists better understand how our planet evolved into its present state.
“How mantle flows on Earth might control why there is life on our planet but not on other planets, such as Venus, which has a similar size and location in the solar system to Earth, but likely has a very different style of mantle flow. We can understand a lot about other planets from revealing the secrets of our own,” concluded Dr Ferreira.
The study was funded by the Leverhulme Trust, NERC, the Korea Meteorlogical Administration Research and Development Program, the Progetto di Ateneo FACCPTRAT12 granted by the Università di Padova and by the ERC StG #758199 NEWTON.
Reference:
Ana M. G. Ferreira, Manuele Faccenda, William Sturgeon, Sung-Joon Chang, Lewis Schardong. Ubiquitous lower-mantle anisotropy beneath subduction zones. Nature Geoscience, 2019; DOI: 10.1038/s41561-019-0325-7
Scientists from The Australian National University have discovered the have discovered that 558 million-year-old Dickinsonia fossils do not reveal all of the features of the earliest known animals, which potentially had mouths and guts. Credit: Ilya Bobrovskiy, The Australian National University (ANU)
Scientists from The Australian National University (ANU) have discovered that 558 million-year-old Dickinsonia fossils do not reveal all of the features of the earliest known animals, which potentially had mouths and guts.
ANU PhD scholar Ilya Bobrovskiy, lead author of the study, said the study shows that simple physical properties of sediments can explain Dickinsonia’s preservation, and implies that what can be seen today may not be what these creatures actually looked like.
“These soft-bodied creatures that lived 558 million years ago on the seafloor could, in principle, have had mouths and guts — organs that many palaeontologists argue emerged during the Cambrian period tens of millions of years later,” said Mr Bobrovskiy from the ANU Research School of Earth Sciences.
“Our discovery about Dickinsonia — and many other Ediacaran fossils — opens up new possibilities as to what they actually looked like.”
Ediacara biota were strange creatures that lived on the seafloor 571 to 541 million years ago. They grew up to two metres long and include the earliest known animals as well as colonies of bacteria.
The fact that Dickinsonia and other Ediacara biota fossils were preserved at all in the geological record has been a big mystery — until now.
The team, which includes scientists from Russian institutions, discovered how Ediacara biota fossils were preserved, despite the macroorganisms not having skeletons or shells.
“As the organisms decayed, softer sediment from below gradually flowed into the forming void, creating a cast,” Mr Bobrovskiy said.
“Now we know that what we are looking at is an impression of a soft organic skeleton that may have been anywhere within Dickinsonia’s body. What we’re seeing could be a part of Dickinsonia’s bottom, the inside of its body or part of its back.”
Mr Bobrovskiy said Dickinsonia had different types of tissues and must have been a true animal, a Eumetazoa, the lineages eventually leading to humans.
Co-researcher and RSES colleague Associate Professor Jochen Brocks said the team used a melting cast of a Death Star made of ice to show the physical properties of sediments that enabled the soft-bodied Ediacara biota to be preserved.
“This process of fossilisation could tell us more about what Ediacara biota were and how they lived,” he said.
“These fossils comprise our best window into earliest animal evolution and are the key to understanding our own deep origins.”
Reference:
Ilya Bobrovskiy, Anna Krasnova, Andrey Ivantsov, Ekaterina Luzhnaya, Jochen J. Brocks. Simple sediment rheology explains the Ediacara biota preservation. Nature Ecology & Evolution, 2019; DOI: 10.1038/s41559-019-0820-7
Earth’s mantle (dark red) lies below the crust (brown layer near the surface) and above the outer core (bright red). Credit: CC image by Argonne National Laboratory via Flickr
The solid Earth breathes as volcanoes “exhale” gases like carbon dioxide (CO2) — which are essential in regulating global climate — while carbon ultimately from CO2 returns into the deep Earth when oceanic tectonic plates are forced to descend into the mantle at subduction zones. However, the amount of carbon in the sediments and ocean crust that subducts is poorly constrained, as is the fraction of that breaks down in the mantle and contributes to volcanic CO2.
Most subduction zones in the world are complex: the amount of sediment and carbon (C) concentration frequently varies along their length, and at many, some of the sediment reaching the subduction zone is scraped off, so the C in it never gets returned into the Earth. Developing a way to figure out how C cycles at complex subduction margins is therefore critical to understanding our planet.
To establish such a method, researchers Brian M. House and colleagues focused on the Sunda margin along Indonesia, a subduction zone where the amount of sediment changes dramatically as does the proportion of organic and inorganic C, and very little of the sediment actually stays attached to the subducting plate.
Erosion from the Himalayas and underwater sediment “avalanches” bring a tremendous amount of sediment that is rich in organic C to the northeast section of the margin while the southwest portion is inundated by sediment rich in calcium carbonate (CaCO3) microfossils from the Australian continental shelf.
To account for this the team made a 3D model of the sediments and their composition across thousands of square kilometers outboard of the margin, which allowed us to more accurately quantify C in sediments throughout the region. House says they “estimate that only about a tenth of the C reaching the margin makes it past the subduction zone while the rest is scraped off the plate into the enormous wedge of sediment offshore of Sumatra and Java.”
House and colleagues estimate that the C returning into the Earth is much less — maybe only a fifth — of what volcanoes expel each year, meaning that the margin represents a net source of C into the atmosphere and that C from something other than the subducting sediments is released. “The sediments subducted into the Earth also have a different C isotope composition than that of volcanic CO2, so we think that inorganic CaCO3 in the ground underneath Sumatra and Java as well as C in the oceanic plate that carries sediment into the subduction zone release CO2 that travels back into the atmosphere.”
These are two possible CO2 sources that, while extremely large, haven’t received much scientific attention. By presenting a new method for investigating tectonic C cycling in a place as complicated as the Sunda margin, says House, “We hope to spur new interest in understanding the full range of processes by which the solid Earth breathes over geologic timescales.”
Reference:
Brian M. House, Gray E. Bebout, and David R. Hilton. Carbon cycling at the Sunda margin, Indonesia: A regional study with global implications. Geology, 2019
Fossil whale barnacles from the Pleistocene were retrieved from the Burica Peninsula of Panama for analyses. Credit: Larry Taylor
Many whales take long journeys each year, spending summers feeding in cold waters and moving to warm tropical waters to breed. One theory suggests that these long-distance migrations originated around 5 million years ago, when ocean productivity became increasingly patchy. But patterns of ancient whale migrations have, until recently, been shrouded in mystery. Scientists from the Smithsonian Tropical Research Institute (STRI) and the University of California, Berkeley approached this question with an ingenious technique: barnacles.
“Instead of looking for clues to migration patterns from the whale’s bones, we used hitch-hiking whale barnacles instead,” said Larry Taylor, STRI visiting scientist and doctoral student at UC Berkeley who led the study.
Barnacles are crustaceans (crabs, lobsters, shrimp) that live stuck in one place in a hard shell. Most glue themselves to rocks, but whale barnacles attach to a whale’s skin by sucking the skin in.
“Whale barnacles are usually species specific — one species of barnacle on one type of whale,” said Aaron O’Dea, staff scientist at STRI and co-author of the study. “This gives the barnacle several advantages — a safe surface to live on, a free ride to some of the richest waters in the world and a chance to meet up with others when the whales get together to mate.”
As whale barnacles grow, their shells record the conditions by taking up oxygen isotopes from the water. By carefully reading the unique isotope signatures left in the shells, the barnacles can reveal the water bodies the barnacle passed through, helping reconstruct the whale’s movements over time.
The study, published in Proceedings of the National Academy of Sciences looked at a number of fossil and modern whale barnacles from the Pacific coast of Panama and California.
“The signals we found in the fossil barnacles showed us quite clearly that ancient humpback and grey whales were undertaking journeys very similar to those that these whales make today,” Taylor said. “It seems like the summer-breeding and winter-feeding migrations have been an integral part of the way of life of these whales for hundreds of thousands of years.”
“We want to push the technique further back in time and across different whale populations,” said Seth Finnegan, co-author from UC Berkeley. “Hunting for fossil whale barnacles is easier than whales, and they provide a wealth of information waiting to be uncovered.”
Reference:
Larry D. Taylor, Aaron O’Dea, Timothy J. Bralower, Seth Finnegan. Isotopes from fossil coronulid barnacle shells record evidence of migration in multiple Pleistocene whale populations. Proceedings of the National Academy of Sciences, 2019; 201808759 DOI: 10.1073/pnas.1808759116
From the field on Svalbard, showing an ancient channel extending into the Barents Sea. Credit: Tore Grane Klausen.
The largest delta plain in Earth’s history formed along the northern coast of the supercontinent Pangea in the late Triassic. Its size out-scales modern counterparts by an order of magnitude, and approximates 1% of the total land area of the modern world. And although contenders are found in the rock record, no ancient counterpart exceeds the extent of the Triassic delta plain mapped in the subsurface Barents Sea either.
An important part of this study by, published in Geology, was to document and compare the size of the delta plain, but also to understand why it grew so large.
Aerially extensive 3-D seismic datasets and rock samples collected for petroleum exploration in the Barents Sea have revealed that delta plains covered the entire basin during the Triassic. Comparing the size of this delta plain to modern and—more challenging—ancient delta plains shows that the Triassic delta plains of the Barents Sea were the largest in Earth’s history that has been preserved in the rock record.
Its tremendous size accounts for nearly 1% of the land areas of the modern world, and was facilitated by a vast drainage area feeding sediments to a shallow basin were sediments accumulated.
Reference:
Tore Grane Klausen et al, The largest delta plain in Earth’s history, Geology (2019). DOI: 10.1130/G45507.1
Scientists say the fossils have been “exquisitely” preserved. Credit: Ao Sun
Scientists say they have discovered a “stunning” trove of thousands of fossils on a river bank in China.
The fossils are estimated to be about 518 million years old, and are particularly unusual because the soft body tissue of many creatures, including their skin, eyes, and internal organs, have been “exquisitely” well preserved.
Palaeontologists have called the findings “mind-blowing” – especially because more than half the fossils are previously undiscovered species.
The fossils, known as the Qingjiang biota, were collected near Danshui river in Hubei province.
More than 20,000 specimens were collected, and a total of 4,351 have been analysed so far, including worms, jellyfish, sea anemones and algae.
They will become a “very important source in the study of the early origins of creatures”, one of the fieldwork leaders, Prof Xingliang Zhang from China’s Northwest University, told the BBC.
The discovery is particularly remarkable because “the majority of creatures are soft-bodied organisms like jellyfish and worms that normally stand no chance of becoming fossilised”, Prof Robert Gaines, a geologist who also took part in the study, said in an email to the BBC.
The majority of fossils tend to be of hard-bodied animals, as harder substances, like bones, are less likely to rot and decompose.
The Qingjiang biota must have been “rapidly buried in sediment” due to a storm, in order for soft tissues to be so well preserved, Prof Zhang says.
Scientists are especially excited by the jellyfish and sea anemone fossils, which Prof Gaines describes as “unlike anything I have ever seen. Their sheer abundance and their diversity of forms is stunning”.
Meanwhile, Prof Allison Daley, a palaeontologist who was not part of the study but wrote an accompanying analysis in Science, told BBC’s Science in Action programme the find was one of the most significant in the last 100 years.
“It blew my mind – as a palaeontologist I never thought I’d get to witness the discovery of such an incredible site.
“For the first time we’re seeing preservation of jellyfish – [when] you think of jellyfish today, they’re so soft-bodied, so delicate, but they’re preserved unbelievably well at this site.”
The research team are now documenting the remaining specimens, and conducting more drilling in the region to find out more about the ancient local ecosystem, and the fossilisation process.
Prof Zhang says he looks forward to studying “all these new species – I’m always excited when we get something new”.
The fossils are from the Cambrian period, which began 541 million years ago and saw a rapid increase in animal diversity on Earth.
Prof Gaines hopes his work will also strike a chord with modern readers.
“Biotic diversity today is something that we take for granted, even though there are indications that extinction rates are sharply increasing.
“Yet most of the major animal lineages were established in a singular event in the history of life, the Cambrian explosion, the likes of which have never been seen before or after. It also reminds us of our deep kinship to all living animals.”
Reference:
Dongjing Fu et al. The Qingjiang biota—A Burgess Shale–type fossil Lagerstätte from the early Cambrian of South China, Science (2019). DOI: 10.1126/science.aau8800
The towering and battle-scarred ‘Scotty’ reported by UAlberta paleontologists is the world’s largest Tyrannosaurus rex and the largest dinosaur skeleton ever found in Canada. Credit: Amanda Kelley
University of Alberta paleontologists have just reported the world’s biggest Tyrannosaurus rex and the largest dinosaur skeleton ever found in Canada. The 13-metre-long T. rex, nicknamed “Scotty,” lived in prehistoric Saskatchewan 66 million years ago.
“This is the rex of rexes,” said Scott Persons, lead author of the study and postdoctoral researcher in the Department of Biological Sciences. “There is considerable size variability among Tyrannosaurus. Some individuals were lankier than others and some were more robust. Scotty exemplifies the robust. Take careful measurements of its legs, hips, and even shoulder, and Scotty comes out a bit heftier than other T. rex specimens.”
Scotty, nicknamed for a celebratory bottle of scotch the night it was discovered, has leg bones suggesting a living weight of more than 8,800 kg, making it bigger than all other carnivorous dinosaurs. The scientific work on Scotty has been a correspondingly massive project.
The skeleton was first discovered in 1991, when paleontologists including T. rex expert and UAlberta professor Phil Currie were called in on the project. But the hard sandstone that encased the bones took more than a decade to remove — only now have scientists been able to study Scotty fully-assembled and realize how unique a dinosaur it is.
It is not just Scotty’s size and weight that set it apart. The Canadian mega rex also lays claim to seniority.
“Scotty is the oldest T. rex known,” Persons explains. “By which I mean, it would have had the most candles on its last birthday cake. You can get an idea of how old a dinosaur is by cutting into its bones and studying its growth patterns. Scotty is all old growth.”
But age is relative, and T. rexes grew fast and died young. Scotty was estimated to have only been in its early 30s when it died.
“By Tyrannosaurus standards, it had an unusually long life. And it was a violent one,” Persons said. “Riddled across the skeleton are pathologies — spots where scarred bone records large injuries.”
Among Scotty’s injures are broken ribs, an infected jaw, and what may be a bite from another T. rex on its tail — battle scars from a long life.
“I think there will always be bigger discoveries to be made,” said Persons “But as of right now, this particular Tyrannosaurus is the largest terrestrial predator known to science.”
A new exhibit featuring the skeleton of Scotty is set to open at the Royal Saskatchewan Museum in May 2019.
Reference:
W. Scott Persons, Philip J. Currie, Gregory M. Erickson. An Older and Exceptionally Large Adult Specimen of Tyrannosaurus rex. The Anatomical Record, 2019; DOI: 10.1002/ar.24118
The string of volcanoes in the Cascades Arc, ranging from California’s Mt. Lassen in the south to Washington’s Mt. Baker in the north, have been studied by geologists and volcanologists for over a century. Spurred on by spectacular events such as the eruption of Mount Lassen in 1915 and Mount St. Helens in 1980, scientists have studied most of the Cascade volcanoes in detail, seeking to work out where the magma that erupts comes from and what future eruptions might look like.
However, mysteries still remain about why nearby volcanoes often have radically different histories of eruption or erupt different types of magma. Now scientists would like to find out why — both for the Cascades and for other volcanic ranges.
In a perspective essay published today (March 22) in Nature Communications, scientists argue for more “synthesis” research looking at the big picture of volcanology to complement myriad research efforts looking at single volcanoes.
“The study of volcanoes is fascinating in detail, and it has largely been focused on research into individual volcanoes rather than the bigger picture,” said Adam Kent, a volcano expert at Oregon State University and a co-author on the essay. “We now have the insight and data to go beyond looking at just Mount St. Helens and other well-known volcanoes. We can take a step back and ask why is St. Helens different from Mount Adams, why is that different from Mount Hood?”
The study takes a novel approach to this topic. “One way to do this is to consider the heat it took to create each of the volcanoes in the Cascades Arc, for example, and also compare this to the local seismic wave speeds and heat flow within the crust, Kent said. “Linking these diverse data sources together this way gives us a better glimpse into the past, but offer some guidance on what we might expect in the future.”
The need for studying volcanoes more thoroughly is simple, noted Christy Till of Arizona State University, lead author of the Nature Communications essay.
Worldwide almost a billion people live in areas at risk from volcanic eruptions, 90 percent of which live in the so-called Pacific Ring of Fire.
The subduction of the Juan de Fuca tectonic plate beneath the North American plate is the ultimate driver for the formation of the Cascade Range, as well as many of the earthquakes the Northwest has experienced. Subduction results in deep melting of the Earth’s mantle, and the magma then heads upward towards the crust and surface, eventually reaching the surface to produce volcanoes.
But there are differences among the volcanoes, the researchers note, including in the north and south of the Cascade Range.
“The volcanoes in the north stand out because they stand alone,” Kent said. “In the south, you also have recognizable peaks like the Three Sisters and Mount Jefferson, but you also many thousands of smaller volcanoes like Lava Butte and those in the McKenzie Pass area in between. Our work suggests that, together with the larger volcanoes, these small centers require almost twice the amount of magma being input into the crust in the southern part of the Cascade Range.”
Why is that important?
“If you live around a volcano, you have to be prepared for hazards and the hazards are different with each different type of volcano,” Kent said. “The northern Cascades are likely to have eruptions in the future, but we know where they’ll probably be — at the larger stratovolcanoes like Mount Rainier, Mount Baker and Glacier Peak. In the south the larger volcanoes might also have eruptions, but then we have these large fields of smaller — so called ‘monogenetic’ volcanoes. For these it is harder to pinpoint where future eruptions will occur.”
The field of volcanology has progressed quite a bit, the researchers acknowledge, and the need now exists to integrate some of the methodology of individual detailed studies to give a more comprehensive look at the entire volcanic system. The past is the best informer of the future.
“If you look at the geology of a volcano, you can tell what kind of eruption is most likely to happen,” Kent said. “Mount Hood, for example, is known to have had quite small eruptions in the past, and the impact of these is mostly quite local. Crater Lake, on the other hand, spread ash across much of the contiguous United States.
“What we would like to know is why one volcano turns out to be a Mount Hood while another develops into a Crater Lake, with a very different history of eruptions. This requires us to think about the data that we have in new ways.”
The 1980 eruption of Mt. St. Helens was a wake-up call to the threat of volcanoes in the continental United States, and though noteworthy, its eruption was relatively minor. The amount of magma involved in the eruption was estimated to be 1 kilometer cubed (enough to fill about 400,000 Olympic swimming pools), whereas the eruption of Mt. Mazama 6,000 years ago that created Crater Lake was 50 km cubed, or 50 times as great.
The researchers say the process of building and tearing down volcanoes continues today, though it is difficult to observe on a day-to-day basis.
“If you could watch a time-lapse camera over millions of years, you would see volcanoes building up slowly, and then eroding fairly quickly,” said Kent, who is in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “Sometimes, both are happening at once.”
Which of the Cascades is most likely to erupt? The smart money is on Mount St. Helens, because of its recent activity, but many of the volcanoes are still considered active.
“I can tell you unequivocally that Mount Hood will erupt in the future,” Kent said. “I just can’t tell you when.”
For the record, Kent said the odds of Mt. Hood erupting in the next 30 to 50 years are less than 5 percent.
Reference:
C. B. Till, A. J. R. Kent, G. A. Abers, H. A. Janiszewski, J. B. Gaherty, B. W. Pitcher. The causes of spatiotemporal variations in erupted fluxes and compositions along a volcanic arc. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-09113-0
Feathers revealed in a ~125 million-year-old fossil of a bird hatchling shows it came “out of the egg running”. Specimen MPCM-LH-26189 from Los Hoyas, Spain is preserved between two slabs of rock: (a) ‘counter’ slab under normal light (b) Laser-Stimulated Fluorescence (LSF) image combining the results from both rock slabs. This reveals brown patches around the specimen that include clumps of elongate feathers associated with the neck and wings and a single long vaned feather associated with the left wing. (c) Normal light image of the main slab. Scale is 5mm. Credit: Copyright Kaye et al. 2019
The ~125 million-year-old Early Cretaceous fossil beds of Los Hoyas, Spain have long been known for producing thousands of petrified fish and reptiles. However, one special fossil stands unique and is one of the rarest of fossils — a nearly complete skeleton of a hatchling bird. Using their own laser imaging technology, Dr Michael Pittman from the Department of Earth Sciences at The University of Hong Kong and Thomas G Kaye from the Foundation for Scientific Advancement in the USA determined the lifestyle of this ~3cm long hatchling bird by revealing the previously unknown feathering preserved in the fossil specimen.
Chickens and ducks are up and about within hours of hatching, they are “precocial.” Pigeons and eagles are “altricial,” they stay in the nest and are looked after by their parents. How do you tell if a hatchling came “out of the egg running” or was “naked and helpless in the nest”? Feathers. When precocial birds hatch they have developed down feathers and partly developed large feathers and can keep warm and get around without mum’s help. “Previous studies searched for but failed to find any hints of feathers on the Los Hoyas hatchling. This meant that its original lifestyle was a mystery,” says Dr Pittman.
Michael Pittman and Thomas Kaye brought new technology to the study of Los Hoyas fossils in the form of a high power laser. This made very small chemical differences in the fossils become visible by fluorescing them different colours, revealing previously unseen anatomical details.
They recently had tremendous success with the first discovered fossil feather which they disassociated from the famous early bird Archaeopteryx by recovering the chemical signature of its fossil quill, a key part of the feather’s identification that had been previously unverified for ~150 years.
The new results on the hatchling bird finally answered the question about its lifestyle as it did indeed have feathers at birth and was thus precocial and out of the egg running. The feathers were made of carbon which has low fluorescence using Laser-Stimulated Fluorescence (LSF), but the background matrix did glow making the feathers stand out in dramatic dark silhouette.
“Previous attempts using UV lights and synchrotron beams failed to detect the feathers, underscoring that the laser technology stands alone as a new tool in palaeontology” added Tom Kaye, the study’s lead author.
This discovery via new technology demonstrates that some early birds adopted a precocial breeding strategy just like modern birds. Thus, in the time of the dinosaurs, some enantiornithine bird babies had the means to avoid the dangers of Mesozoic life perhaps by following their parents or moving around themselves.
“One of the feathers discovered was of a substantial size and preserves features seen in other hatchlings. It indicates that our hatchling had reasonably well-developed flight feathers at the time of birth,” says Jesús Marugán-Lobón, a co-author from the Universidad Autónoma of Madrid, Spain.
This and other “illuminating” discoveries are adding to our knowledge of ancient life with details surviving in the fossil record that were never thought possible even a couple decades ago.
Reference:
Thomas G. Kaye, Michael Pittman, Jesús Marugán-Lobón, Hugo Martín-Abad, José Luis Sanz, Angela D. Buscalioni. Fully fledged enantiornithine hatchling revealed by Laser-Stimulated Fluorescence supports precocial nesting behavior. Scientific Reports, 2019; 9 (1) DOI: 10.1038/s41598-019-41423-7
Volcano Credit: Jessica Johnson/University of East Anglia
New research led by the University of East Anglia (UEA) reveals that sharp variations of the surface of volcanoes can affect data collected by monitoring equipment.
The surfaces of many volcanoes feature steep walls or cliffs. These are often part of calderas — large craters left by a previous collapse — but can also be caused by the volcano ‘rifting’ — or splitting — or sector collapse, when part of the side of the volcano slides away.
However, the effect of these variations in landscape has not previously been considered in studies of surface deformation in volcanic regions, even though they are a common feature.
In addition, monitoring equipment such as tiltmeters are usually placed on caldera rims as they are often more accessible, especially if the caldera is lake-filled. Tiltmeters measure the horizontal gradient of vertical displacement and can emphasise small variations that go unnoticed using other monitoring methods.
Now researchers from UEA, the US Geological Survey and University of Bristol have found that features such as cliffs can cause a reversal in the pattern of deformation, leading to misleading data being recorded by the tiltmeters. Their findings are published in the journal Geophysical Research Letters.
The team studied Kilauea volcano in Hawaii, which erupted last April, resulting in a summit collapse that has reshaped the cliffs around the caldera. It now has near-vertical cliffs of up to 500 metres and terrace-like steps of 50-150 metres.
The researchers say these new structures may have an impact on tilt measured at the existing network of tiltmeters and have implications for any new monitoring equipment that is installed.
Lead researcher Dr Jessica Johnson, lecturer in geophysics at UEA’s School of Environmental Sciences, said: “Tilt measurements have played a significant role in the knowledge of volcanic processes on at least 40 volcanoes worldwide. Our analysis highlights the importance of considering surface features when assessing tilt measurements at active volcanoes, something that hasn’t generally been taken into account.
“While the inconsistent data at Kilauea cannot be completely explained by topography, it may have some influence. Following the most recent collapse at Kilauea this problem is likely to be even more pronounced and should be considered when new monitoring instruments are installed.”
The researchers investigated after finding anomalies in data collected from one of the tiltmeters on the caldera rim at Kilauea before the last eruption. They looked at whether this could be due to topography and found that the then 80 metre-high caldera wall caused data from one of the monitoring tiltmeters to rotate away from the true centre of deformation.
“These findings have implications for network design and ongoing monitoring,” said Dr Johnson, who visited Kilauea last July and previously spent two years on a research fellowship at the Hawaiian Volcano Observatory.
“They suggest that other tiltmeters around Kilauea and at volcanoes globally could be affected by caldera rims and other sharp variations in the landscape.”
Dr Johnson added: “If this this monitoring method is already being used there are things that can be done to fix the data stream. If new tilt monitors are being installed then we have got to be careful where they are deployed.”
Co-author Dr Juliet Biggs, from the University of Bristol, said: “Understanding what drives volcano deformation is critical for improving the interpretation of volcano monitoring data, and developing probabilisitic eruption forecasts. Tiltmeters are very sensitive to small changes in the volcanic conduit, but their measurements have been challenging to interpret.
“This study sheds new light on how these measurements are influenced by surface features such as steep cliffs, and will undoubtedly improve our ability to interpret the complex monitoring signals.”
Reference:
Jessica H Johnson, Michael P Poland, Kyle R Anderson, and Juliet Biggs. A cautionary tale of topography and tilt from Kilauea Caldera. Geophysical Research Letters, 2019
The Washington coast is geologically complex. The bubbles emerge from a region off the coast above where the Juan de Fuca ocean plate plunges beneath the North American continental plate.Credit: Paul Johnson/University of Washington
Off the coast of Washington, columns of bubbles rise from the seafloor, as if evidence of a sleeping dragon lying below. But these bubbles are methane that is squeezed out of sediment and rises up through the water. The locations where they emerge provide important clues to what will happen during a major offshore earthquake.
The study, from the University of Washington and Oregon State University, was recently published in the Journal of Geophysical Research: Solid Earth.
The first large-scale analysis of these gas emissions along Washington’s coast finds more than 1,700 bubble plumes, primarily clustered in a north-south band about 30 miles (50 kilometers) from the coast. Analysis of the underlying geology suggests why the bubbles emerge here: The gas and fluid rise through faults generated by the motion of geologic plates that produce major offshore earthquakes in the Pacific Northwest.
“We found the first methane vents on the Washington margin in 2009, and we thought we were lucky to find them, but since then, the number has just grown exponentially,” said lead author Paul Johnson, a UW professor of oceanography.
“These vents are a little ephemeral,” Johnson added. “Sometimes they turn off-and-on with the tides, and they can move around a little bit on the seafloor. But they tend to occur in clusters within a radius of about three football fields. Sometimes you’ll go out there and you’ll see one active vent and you’ll go back to the same location and it’s gone. They’re not reliable, like the geysers at Yellowstone.”
The authors analyzed data from multiple research cruises over the past decade that use modern sonar technology to map the seafloor and also create sonar images of gas bubbles within the overlying water. Their new results show more than 1,778 methane bubble plumes issuing from the waters off Washington state, grouped into 491 clusters.
“If you were able to walk on the seafloor from Vancouver Island to the Columbia River, you would never be out of sight of a bubble plume,” Johnson said.
The sediments off the Washington coast are formed as the Juan de Fuca oceanic plate plunges under the North American continental plate, scraping material off the ocean crust. These sediments are then heated, deformed and compressed against the rigid North American plate. The compression forces out both fluid and methane gas, which emerges as bubble streams from the seafloor.
The bubble columns are located most frequently at the boundary between the flat continental shelf and the steeply sloped section where the seafloor drops to the abyssal depths of the open ocean. This abrupt change in slope is also a tectonic boundary between the oceanic and continental plates.
“Although there are some methane plumes from all depths on the margin, the vast majority of the newly observed methane plume sites are located at the seaward side of the continental shelf, at about 160 meters water depth,” Johnson said.
A previous study from the UW had suggested that warming seawater might be releasing frozen methane in this region, but further analysis showed the methane bubbles off the Pacific Northwest coast arise from sites that have been present for hundreds of years, and are not related to global warming, Johnson said.
Instead, these gas emissions are a long-lived natural feature, and their prevalence contributes to the continental shelf area being such productive fishing grounds. Methane from beneath the seafloor provides food for bacteria, which then produce large quantities of bacterial film. This biological material then feeds an entire ecological chain of life that enhances fish populations in those waters.
“If you look online at where the satellite transponders show where the fishing fleet is, you can see clusters of fishing boats around these methane plume hotspots,” Johnson said.
To understand why the methane bubbles occur here, the authors used archive geologic surveys conducted by the oil and gas companies in the 1970s and 1980s. The surveys, now publicly accessible, show fault zones in the sediment where the gas and fluid migrate upward until emerging from the seafloor.
“Seismic surveys over the areas with methane emission indicate that the continental shelf edge gets thrust westward during a large megathrust, or magnitude-9, earthquake,” Johnson said. “Faults at this tectonic boundary provide the permeable pathways for methane gas and warm fluid to escape from deep within the sediments.”
The location of these faults could potentially provide new understanding of the earthquake hazard from the Cascadia Subduction Zone, which last ruptured more than 300 years ago. If the seafloor movement during a subduction-zone earthquake occurs closer to shore, and a major component of this motion occurs within the shallower water, this would generate a smaller tsunami than if the seafloor motion were entirely in deep water.
“If our hypothesis turns out to be true, then that has major implications for how this subduction zone works,” Johnson said.
Reference:
H. Paul Johnson, Susan Merle, Marie Salmi, Robert Embley, Erica Sampaga, Michelle Lee. Anomalous Concentration of Methane Emissions at the Continental Shelf Edge of the Northern Cascadia Margin. Journal of Geophysical Research: Solid Earth, 2019; DOI: 10.1029/2018JB016453
Explosive volcanic crater (maar) with small lake at the bottom close to Dilo. Credit: Giacomo Corti, National Research Council Italy
Continental rift valleys are huge fractures on the surface of our planet that progressively break continental plates with the eventual development of new oceans. The African rift valley between Ethiopia and Kenya is a classical example of this geodynamic process. There, volcanism, earthquakes, and fracturing of the Earth’s surface result from the enormous forces that tear the eastern portion of the African continent apart. This system of linear valleys extending for thousands of kilometers is believed to result from the growth and propagation of isolated rift segments that evolve into a continuous zone of deformation. However, although instrumental in driving climate and biosphere of that region which in turn may have influenced habitats and the pattern of migration of human species in East Africa, and possibly even conditioned hominin evolution, this process is poorly documented and understood.
In a study published in Nature Communications and funded by the National Geographic Society, an international group of scientists from universities and research institutions from Ethiopia, France, Germany, Italy, New Zealand and the United Kingdom, of which Sascha Brune from the GFZ German Research Centre for Geosciences was a part, has shed new light into the recent evolution of the African rift valley. Its focus was on the spatial and temporal sequence of the propagation, interaction and linking of the Ethiopian rift section with the Kenyan part of the rift fracture. By conducting fieldwork in a remote area at the border between Ethiopia and Kenya, and integrating the results of that field campaign with laboratory analysis of volcanic rocks, analysis of the seismicity, morphology and numerical modelling, the authors have been able to reconstruct the geological history of an almost unknown sector of the African rift valley: the Ririba rift in South Ethiopia. The scientists showed that the Ririba trench formed about 3.7 million years ago as the southernmost advance of the Ethiopian rift segment.
Sascha Brune says: “In my research group at the GFZ we were able to substantiate the geological observations with numerical experiments. To this end, we brought together regional structures, deformation laws and basic physical equations to modelling in a supercomputer. In this way, we were able to show how the focusing of the rift valley contributed to a direct connection between the Kenyan and Ethiopian Rift.”
In contrast with previous theories of rifting in the region, the new data indicate that the southward growth was short-lived and aborted around 2.5 million years ago. At this time, deformation migrated westward into the Lake Turkana region, where the Ethiopian and Kenyan sectors of the rift valley are now directly connected. A later phase of volcanism, expressed by numerous lava flows and impressive explosive volcanic craters (maars), have since affected the Ririba area; however, this volcanic activity was unrelated to tectonic activity, opening new questions on how volcanism and faulting interact during rifting.
Overall, the results of this work provide new insights into the break-up of continents: “In the East African rift, we can observe processes that are important far beyond the region,” says Sascha Brune. “The same dynamics that determine the rift development in East Africa led to the opening of the Atlantic and Indian Oceans many millions of years ago and thus had a decisive influence on the face of the Earth.”
Reference:
Giacomo Corti, Raffaello Cioni, Zara Franceschini, Federico Sani, Stéphane Scaillet, Paola Molin, Ilaria Isola, Francesco Mazzarini, Sascha Brune, Derek Keir, Asfaw Erbello, Ameha Muluneh, Finnigan Illsley-Kemp, Anne Glerum. Aborted propagation of the Ethiopian rift caused by linkage with the Kenyan rift. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-09335-2
