Sheath Folds

Evolution of different coastal systems with time

36 Years into 3.8 Seconds

In this animated GIF, you can see the changes over time in this river course. This is near Pucallpa, Peru. Here, 36 years of change are condensed into 3.8 seconds.

 

Effect of drainage density on the hydrograph

Classification of river deltas

Crystallography Rotoinversion Projection

Type-2 Superposed Folding Using Analogue Modelling

Anthropogenic Seismic Noise & COVID-19

Reduction of anthropogenic seismic noise due to COVID-19 lockdown

                                                                                                                                  -- Sandro Chatterjee

The Planet Earth is still trying its best to get rid of the unwanted guest, COVID-19. The impact of the virus is going to have a prolonged effect on the history of mankind. The down falling economies, joblessness, death of an entire generation are the harshest truth to stand with. But as the earth already refused to surrender in this battle vs. COVID -19, scientists all around the globe are looking for every positive impact in the upcoming days due to this deadly virus and the positive effects are now being signaled by the pulse of a seismometer.

The lack of human activities due to this prolonged lockdown caused human linked vibrations to be decreased by 50% between March and May 2020. The quiet period caused by the increasing social distancing, closure of industries, pubs, hotels, stadiums, and movies is the longest and most pronounced quiet period of Seismic noise ever recorded. The research work, led by Royal Observatory of Belgium and Imperial College London shows the dampening effects are most prominent in the densely populated areas. The quietness and the decreased human-generated noise are helping the researchers to accurately differentiate between natural and human seismic noises and are allowing them to detect previously concealed earthquake signals. The study also found the signatures of this lockdown measure on sensors buried hundreds of meters under the ground in remote areas. Researchers are eager to name this quiet period as “Anthropause”, as the anthropogenic activities are minimal and are the main causes to create this historical period. To read the full story Click Here.

The reduced anthropogenic noise in Brussels, Belgium after lockdown (source: Royal Observatory of Belgium)

Earth's Plate Tectonics Began Over 3.2 Billion Years Ago

Paleomagnetic evidence for modern-like plate motion velocities at 3.2 Ga

by  Alec R. Brenner et al.

An artistic cross-section through forming Earth's crust approximately 3-4 billion years ago. Image credit: Alec R. Brenner

Plate tectonics has been the dominant surface geodynamical regime throughout Earth’s recent geological history. One defining feature of modern plate tectonics is the differential horizontal motion of rigid lithospheric plates. The physiography and composition of Earth’s modern crust bear evidence for plate tectonic or “mobile-lid” processes including subduction, collisional orogeny, rifting, and ocean spreading. The case for the Archean Earth [4.0 to 2.5 billion years (Ga) ago] is not so clear. The surviving Archean crust consists of ~35 cratons, most with characteristic architecture of rounded granitoid intrusive domes rimmed by steeply dipping greenstone keels. The composition of extant Archean crust is substantially more mafic than modern oceanic crust, with a high fraction of ultramafic rocks such as komatiites. These structural and compositional differences have led to a number of proposals that the Archean crust was constructed by exotic processes, including plume tectonics, sagduction/drip tectonics, and a vertically overturning lithosphere. Since some of these processes are difficult to reconcile with plate mobility, alternative geodynamical regimes have been proposed for the Archean Earth, including stagnant-lid and sluggish-lid modes in which the lithosphere was rendered immobile, or at least slowed, due to decoupling from the asthenosphere under elevated geothermal gradients. Other studies argue for a uniformitarian model of the Archean Earth, in which some variant of modern plate tectonics was in operation at least locally throughout Earth history. Complete understanding of the Archean lithosphere, hydrosphere, atmosphere, and biosphere are predicated upon distinguishing between these proposed Archean geodynamic modes. Insights into these components of the early Earth are foundational to the inner workings of terrestrial planets generally and what surface conditions and environments hosted the development of the first life.

Arguments for alternative geodynamical regimes in the Archean are often based on inferences of a regime transition toward modern-style plate tectonics. Existing estimates for the age of such a transition range from the Neoproterozoic to the Hadean (see the Supplementary Materials) and invoke a range of observations including global and local geochemical records, field relations of possible syn-tectonic rocks, and paleomagnetic pole comparisons.  

A key discriminant between stagnant- and mobile-lid regimes is the rate of horizontal motion of plates over Earth’s surface. Absolute plate velocities have typically been ~2 to 10 cm/year (extremes from 0 to 25 cm/year) over the last 400 million years (Ma), while hypothesized velocities for stagnant- and sluggish-lid models are typically less than 2 cm/year. Paleomagnetic methods may constrain the velocity of crustal blocks in deep geological time by measuring their apparent polar wander histories. However, robust paleomagnetic evidence for latitudinal motion has been lacking thus far for times before 2.8 Ga. Here, we produce a new paleomagnetic pole from ~3180 Ma volcanics in the East Pilbara Craton of Western Australia and use this result to assess the presence of plate tectonic– like processes on Earth before that time.  

Original article: Paleomagnetic evidence for modern-like plate motion velocities at 3.2 Ga. DOI: 10.1126/sciadv.aaz8670. To read the article click here.

Earth’s oldest recognized meteorite impact structure

Precise radiometric age establishes Yarrabubba, Western Australia, as Earth’s oldest recognised meteorite impact structure (Research work by Erickson et al.)

Composite aeromagnetic anomaly map of the Yarrabubba impact structure within the Yilgarn Craton, Western Australia, showing the locations of key outcrops and samples used in this study. The image combines the total magnetic intensity (TMI, cool to warm colours) with the second vertical derivative of the total magnetic intensity (2VD, grayscale) data. The demagnetized anomaly centred on the outcrops of the Barlangi granophyre is considered to be the eroded remnant of the central uplift domain, which forms the basis of the crater diameter of 70 km. Prominent, narrow linear anomalies that cross-cut the demagnetized zone with broadly east-west orientations are mafic dykes that post-date the impact structure.  

The ~70 km-diameter Yarrabubba impact structure in Western Australia is regarded as among Earth’s oldest but has hitherto lacked precise age constraints. Here we present U–Pb ages for impact-driven shock-recrystallised accessory minerals. Shock-recrystallised monazite yields a precise impact age of 2229 ± 5 Ma, coeval with shock-reset zircon. This result establishes Yarrabubba as the oldest recognised meteorite impact structure on Earth, extending the terrestrial cratering record back >200 million years. The age of Yarrabubba coincides, within uncertainty, with temporal constraint for the youngest Palaeoproterozoic glacial deposits, the Rietfontein diamictite in South Africa. Numerical impact simulations indicate that a 70 km diameter crater into a continental glacier could release between 8.7 × 1013 to 5.0 × 1015 kg of H2O vapour instantaneously into the atmosphere. These results provide new estimates of impact-produced H2O vapour abundances for models investigating termination of the Paleoproterozoic glaciations and highlight the possible role of impact cratering in modifying Earth’s climate. The ~70 km-diameter Yarrabubba impact structure in Western Australia has previously been regarded as among Earth’s oldest meteorite craters but has hitherto lacked absolute age constraints. Here, the authors determine a precise impact age of 2229 ± 5 Ma, which extends the terrestrial cratering record back in time by > 200 million years and establishes Yarrabubba as the oldest recognised meteorite impact structure on Earth.

Original article: Precise radiometric age establishes Yarrabubba, Western Australia, as Earth’s oldest

recognised meteorite impact structure. DOI:  10.1038/s41467-019-13985-7. To read the article click here.

By 2025, carbon dioxide levels in Earth’s atmosphere will be higher than at any time in the last 3.3 million years

By 2025, carbon dioxide levels in Earth’s atmosphere will be higher than at any time in the last 3.3 million years

Source: GeologyPage

The composition of fossilised zooplankton shells has enabled the
reconstruction of past pH and CO2. Credit: University of Southampton  

By 2025, atmospheric carbon dioxide (CO2) levels will very likely be higher than they were during the warmest period of the last 3.3 million years, according to new research by a team from the University of Southampton published today in Nature Scientific Reports.

The team studied the chemical composition of tiny fossils, about the size of a pinhead collected from the deep ocean sediments of the Caribbean Sea. They used this data to reconstruct the concentration of CO2 in Earth’s atmosphere during the Pliocene epoch, around 3 million years ago when our planet was more than 3°C warmer than today with smaller polar ice caps and higher global sea-levels.

 

Dr. Elwyn de la Vega, who led the study, said: “Knowledge of CO2 during the geological past is of great interest because it tells us how the climate system, ice sheets and sea-level previously responded to the elevated CO2 levels. We studied this particular interval in unprecedented detail because it provides great contextual information for our current climate state.”

To determine atmospheric CO2, the team has used the isotopic composition of the element boron, naturally present as an impurity in the shells of zooplankton called foraminifera or ‘forams’ for short. These organisms are around half a millimetre in size and gradually accumulate in huge quantities on the seabed, forming a treasure trove of information on Earth’s past climate. The isotopic composition of the boron in their shells is dependent on the acidity (the pH) of the seawater in which the forams lived. There is a close relationship between atmospheric CO2 and seawater pH, meaning past CO2 can be calculated from the careful measurement of the boron in ancient shells.

 

Dr. Thomas Chalk, a co-author of the study, added: “Focussing on a past warm interval when the incoming insolation from the Sun was the same as today gives us a way to study how Earth responds to CO2 forcing. A striking result we’ve found is that the warmest part of the Pliocene had between 380 and 420 parts per million CO2 in the atmosphere. This is similar to today’s value of around 415 parts per million, showing that we are already at levels that in the past were associated with temperature and sea-level were significantly higher than today. Currently, our CO2 levels are rising at about 2.5 ppm per year,  meaning that by 2025 we will have exceeded anything seen in the last 3.3 million years.”

Professor Gavin Foster, who was also involved in the study, continued: “The reason we don’t see Pliocene-like temperatures and sea-levels yet today is that it takes a while for Earth’s climate to fully equilibrate (catch up) to higher CO2 levels and, because of human emissions, CO2 levels are still climbing. Our results give us an idea of what is likely in store once the system has reached equilibrium.”

Concluded Dr. de la Vega, “Having surpassed Pliocene levels of CO2 by 2025, future levels of CO2 are not likely to have been experienced on Earth at any time for the last 15 million years, since the Middle Miocene Climatic Optimum, a time of even greater warmth than the Pliocene.”

Original article: The paper, “Atmospheric CO2 during the Mid-Piacenzian Warm Period and the M2 glaciation” is published in Nature Scientific Reports. DOI: 10.1038/s41598-020-67154-8

How burning of coal contributed to End Permian Mass Extinction?

End Permian Mass Extinction

Source: Science News

An international team of geologists has found the first direct evidence that volcanic eruptions in the southern part of Siberian Traps region 252 million years ago burned a large volume of coal and vegetation.

Image Credit: Astrobiology Magazine

The end-Permian extinction, also known as the Permian-Triassic extinction event and the Great Dying, is the Earth’s most severe mass extinction that peaked about 252.3 million years ago. The catastrophe killed off nearly 96% of all marine species and 70% of terrestrial vertebrate species on the planet over the course of thousands of years. 

Calculations of seawater temperature indicate that at the peak of the extinction, the Earth underwent hot global warming, in which equatorial ocean temperatures exceeded 40 degrees Celsius (104 degrees Fahrenheit). 

Among the possible causes of this event, and one of the longest hypothesized is that massive burning coal led to catastrophic global warming, which in turn was devastating to live.....Read more.

The Missing Billion Years!!

The Missing Billion Years!!

By Harrison Tasoff 

Source: The Current (UC Santa Barbara)

A billion years is missing from the geologic record; one UC Santa Barbara scientist believes he knows where it may have gone. 

An exposed outcrop showing The Great Unconformity (Photo Credit: Rebecca Flowers)

The geologic record is exactly that: a record. The strata of rock tell scientists about past environments, much like pages in an encyclopedia. Except this reference book has more pages missing than it has remaining. So geologists are tasked not only with understanding what is there, but also with figuring out what’s not, and where it went. 

One omission, in particular, has puzzled scientists for well over a century. First noticed by John Wesley Powell in 1869 in the layers of the Grand Canyon, the Great Unconformity, as it’s known, accounts for more than one billion years of missing rock in certain places. 

Scientists have developed several hypotheses to explain how, and when, this staggering amount of material may have been eroded. Now, UC Santa Barbara geologist Francis Macdonald and his colleagues at the University of Colorado, Boulder and at Colorado College believe they may have ruled out one of the more popular of these. Their study appears in the Proceedings of the National Academy of Sciences.

“There are unconformities all through the rock record,” explained Macdonald, a professor in the Department of Earth Science. “Unconformities are just gaps in time within the rock record. This one’s called the Great Unconformity because it was thought to be a particularly large gap, maybe a global gap.” Read more.

A Congolese Escapade

A Congolese Escapade

                                     - Supratik Roy

I have a proclivity towards travelling and adventure and these are the major rationales that motivated me to pursue Geology as a career. So, when my institute issued a notice about some mining company based in the Democratic Republic of Congo, inviting students for a fully-funded internship in their country, I could not resist the crave of visiting Africa. My voyage began on the 8th of June, 2019. This was going to be my first overseas trip and not in the comforts of some luxurious country. It was going to be in the place where human civilization began, where there are people still detached from the comforts of city life, where there are wild animals still in their natural habitat.

The Democratic Republic of Congo is a country in the central part of the African continent. Despite having an unimaginable natural resource wealth, the country is fighting with poverty and diseases. A despondent colonial history, slavery, civil wars and systematic corruption have crippled the nation to the core of its spirit. However, things are slowly changing for the country and the new generation of educated and passionate Congolese will help them achieve their pipe dream.

A typical African landscape on the banks of the Congo river.

Geology is one of those professions which takes you to the rarest parts of the planet. I was posted deep inside the Congo Rainforest, near a small village named Mikengele. It was a typical African village with some shanty huts and lively people. The Congo River flows close to this village, acting as the source of water and a major source of food for the people in this area. The nearest hospital that could provide an anti-venom was hundreds of kilometres away and the road conditions only made it worse. 

The mining company had set foot here looking for cassiterite (Sn-ore), which is abundant in this country, along with many other conflict minerals like, cobalt, tungsten, coltan (columbite-tantalite), etc., which are responsible for Congo’s “resource curse”. As a Geologist, I was expected to help the company in the exploration planning and mapping of the concession area. The job was rather difficult because of several reasons including thick vegetation cover, venomous snakes, limited outcrops and language barrier. There were some Indian employees in the camp who taught me the life hacks of working in the forest and made my life easier in this otherwise hostile environment.

A lump of cassiterite extracted from the pegmatite belt.

The area was a part of the Mesoproterozoic Kibara belt. The major rock type was schist, regularly intruded by quartz veins that were present in two sets, regionally. These quartz veins were the primary source of cassiterite. Schist was overlain by a thick cover of alluvial and eluvial deposits, which hosted the secondary source of cassiterite. Pitting, logging and sampling at regularly spaced intervals, running along and across the strike of the bedding was a part of my daily routine, along with hiking around the area for mapping and identifying the structural controls. The other primary source of cassiterite was a pegmatite belt on the other side of the Congo river. I was accompanied by a professor from my institute for a few days. He taught me the tricks of the trade during his stay and was by far, the best companion to have on such a trip. Read the full story.