GeoLog

Tectonics and Structural Geology

Imaggeo on Mondays: Angular unconformity

Imaggeo on Mondays: Angular unconformity

It is not unusual to observe abrupt contacts between two, seemingly, contiguous rock layers, such as the one featured in today’s featured image. This type of contact is called an unconformity and marks two very distinct times periods, where the rocks formed under very different conditions.

Telheiro Beach is located at the western tip of the Algarve; Portugal’s southernmost mainland region and the most touristic too.

The area, famous for its famous rocky beaches and great seefood, shows a spectacular Variscan unconformity between the highly-folded greywackes and shales of the Brejeira Formation (Moscovian-Carboniferous) and the horizontally placed red sandstones and mudstones of the Group Grés de Silves (of Late Triassic age: 237 and 201.3 million years old). There is a hiatus of about 100 million years between the two formations.

The Variscan period ranges from 370 million to 290 million year ago and is named after the formation of a mountain belt which extends across western Europe, as a result of the collision between Africa and the North American–North European continents.

The imposing sea cliffs produce a privileged place to observe the end of the Variscan Cycle and the beginning of the Alpine Cycle.

It is possible to visit the outcrop on foot, from the top of the cliffs to the beach, although the path is of high degree of difficulty. When going down to the beach one can begin to visualise the typical lithologies of the Grés de Silves. Toward its top you can see red to green Mudstones (dominant) intercalated with rare dolomites and immediately above the unconformity plane it is possible to observe the red sandstone with cross stratification. The highly-folded turbidites (a type of sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean) of the Brejeira Formation are located below the unconformity.

The folds feature chevron geometries (where the rocks have well behaved layers, with straight limbs and sharp hinges, so that they look like sharp Vs). The folding is the result of the final deformation phase of the Variscan compression.

The beds of sedimentary rocks show sedimentary structures attributed to sedimentation in a turbidic environment (turbititic currents), namely the Bouma sequence and sole marks like flute, groove and load casts.

                                                                                                     By André Cortesão, Environmental Engineer and Geoscientist collaborator of the University of Coimbra Geosciences Centre

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/

October GeoRoundUp: the best of the Earth sciences from around the web


Carbon dioxide plays a significant role in trapping heat in Earth’s atmosphere. The gas is released from human activities like burning fossil fuels, and the concentration of carbon dioxide moves and changes through the seasons. Using observations from NASA’s Orbiting Carbon Observatory (OCO-2) satellite, scientists developed a model of the behavior of carbon in the atmosphere from Sept. 1, 2014, to Aug. 31, 2015. Scientists can use models like this one to better understand and predict where concentrations of carbon dioxide could be especially high or low, based on activity on the ground. Credit: NASA’s Goddard Space Flight Center/K. Mersmann, M. Radcliff, producers

Drawing inspiration from popular stories on our social media channels, as well as unique and quirky research news, this monthly column aims to bring you the best of the Earth and planetary sciences from around the web.

Major story

Our top pick for October is a late breaking story which made headlines across news channels world-wide. The World Meteorological Organization (WMO) announced that ‘Greenhouse gases in the atmosphere had surged to new records’ in 2016.

“Globally averaged concentrations of CO2 reached 403.3 parts per million in 2016, up from 400.00 ppm in 2015 because of a combination of human activities and a strong El Niño event,” reported the WMO in the their press release.

The last time Earth experienced a comparable concentration of CO2 was 3 to 5 million years ago (around the period of the Pliocene Epoch), when temperatures were 2-3°C warmer and sea level was 10-20 meters higher than now. You can put that into context by taking a look at this brief history of Earth’s CO2 .

Rising levels of atmospheric CO2  present a threat to the planet, most notably driving rising global temperatures. The new findings compromise last year’s Paris Climate Accord, where 175 nations agreed to work towards limiting the rise of global temperatures by 1.5 degrees celsius (since pre-industrial levels).

No doubt the issue will be discussed at the upcoming COP 23 (Conference of Parties), which takes place in Bonn from 6th to 17th of November in Bonn. Fiji, a small island nation particularly vulnerable to rising sea levels and extreme weather phenomena (a direct result of climate change), is the meeting organiser.

What you might have missed

The 2017 Hurricane season has been devastating (as we’ve written about on the blog previously), but in a somewhat unexpected turn of events, one of the latest storms to form over the waters of the Atlantic, took a turn towards Europe.

Storm Ophelia formed in waters south-west of the Azores, where the mid-latitude jet stream push the storm toward the UK and Ireland. By the time it made landfall it had been downgraded to a tropical storm, but was still powerful enough to caused severe damage. Ireland, battered by 160 kmph winds, declared a national emergency following the deaths of three people.

NASA-NOAA’s Suomi NPP satellite took this thermal image of Hurricane Ophelia over Ireland on Oct. 16 at 02:54 UTC (Oct. 15 at 10:54 p.m. EDT).
Credits: NOAA/NASA Goddard Rapid Response Team

The effects of the storm weren’t only felt across the UK and Ireland. In the wake of an already destructive summer fire season, October brought further devastating forest fires to the Iberian Peninsula. The blazes claimed 32 victims in Portugal and 5 in Spain. Despite many of the wildfires in Spain thought to have been provoked by humans, Ophelia’s strong winds fanned the fire’s flames, making firefighter’s efforts to control the flames much more difficult.

On 16th October many in the UK woke up to eerie red haze in the sky, which turned the Sun red too. The unusual effect was caused by Ophelia’s winds pulling dust from the Sahara desert northward, as well as debris and smoke from the Iberian wildfires.

And when you thought it wasn’t possible for Ophelia to become more remarkable, it also turns out that it became the 10th storm of 2017 to reach hurricane strength, making this year the fourth on record (and the first in over a century) to hit that milestone.

But extreme weather wasn’t only limited to the UK and Ireland this month. Cyclone Herwart brought powerful winds to Southern Denmark, Germany, Poland, Hungary and Czech Republic over the final weekend of October. Trains were suspended in parts of northern Germany and thousands of Czechs and Poles were left without power. Six people have been reported dead. Hamburg’s inner city area saw significant flooding, while German authorities are closely monitoring the “Glory Amsterdam”, a freighter laden with oil, which ran aground in the North Sea during the storm. A potential oil spillage, if the ship’s hull is damaged, is a chief concern, as it would have dire environmental concerns for the Wadden Sea (protected by UNESCO).

Links we liked

The EGU story

This month we released not one but two press releases from research published in our open access journals. The finding of both studies have important societal implications. Take a look at them below

Deforestation linked to palm oil production is making Indonesia warmer

In the past decades, large areas of forest in Sumatra, Indonesia have been replaced by cash crops like oil palm and rubber plantations. New research, published in the European Geosciences Union journal Biogeosciences, shows that these changes in land use increase temperatures in the region. The added warming could affect plants and animals and make parts of the country more vulnerable to wildfires.

Study reveals new threat to the ozone layer

“Ozone depletion is a well-known phenomenon and, thanks to the success of the Montreal Protocol, is widely perceived as a problem solved,” says University of East Anglia’s David Oram. But an international team of researchers, led by Oram, has now found an unexpected, growing danger to the ozone layer from substances not regulated by the treaty. The study is published in Atmospheric Chemistry and Physics, a journal of the European Geosciences Union.

Imaggeo on Mondays: Measuring the wind direction

Imaggeo on Mondays: Measuring the wind direction

Remote, rugged, raw and beautiful beyond measure, the island of South Georgia rises from the wild waters of the South Atlantic, 1300 km south east of the Falkland Islands.

The Allardyce Range rises imposingly, south of Cumberland Bay, dominating the central part of the island. At its highest, it towers 2935 m (Mount Paget) above the surrounding landscape. In the region of 150 glaciers carve their way down the rocky peaks, toward craggy clifftops and the emerald green waters of the ocean.

Geologically speaking, the territory is unique. South Georgia sits atop the place where the South American Plate and the Scotia Plate slide past one another; exactly which can claim ownership of the mountainous outpost is highly debated.

As East and West Gondwana split, about 185 million years ago, South Georgia was pulled away from Tierra del Fuego, an archipelago off the southernmost tip of mainland South American, and experienced severe volcanism.

The island is so remote and exposed, it creates its own weather system. It sits in the path of very strong winds, the westerlies, which flow through the subtropical highs in the Southern Hemisphere.  As air flows over the high mountains of South Georgia, they generate atmospheric gravity waves (which transfer energy from the troposphere – the layer closest to the Earth’s surface – to the upper layers of the atmosphere, including the stratosphere, where the ozone layer is found). Atmospheric gravity waves are responsible for the transfer of considerable amounts of energy over large distances, and thus have a substantial impact on weather and climate.

It is precisely to study South Georgia’s atmospheric gravity waves that Andrew Moss, the author of today’s photograph, journeyed to the remote island back in January 2015 as part of the South Georgia Wave Experiment (SG-WEX). The project was led by the University of Bath, in collaboration with the British Antarctic Survey, the University of Leeds, and the UK Met Office. As part of this project Andrew worked with a colleague at the University of Bath (UK) to release radiosondes – a small, expendable instrument package that is suspended below balloon which measures pressure, temperature and humidity – to better understand the atmospheric conditions and measure atmospheric gravity-wave activity above the island.

The chilly, often cloudy and wet landscape is a wildlife haven. It is home to a staggering five million seals and 65 million seabirds.  The wildlife is so rich, on and off the island, that large swathes of South Atlantic waters surrounding South Georgia are protected and onshore activities which might disturb wildlife require permits.

“Over the course of the two-week field campaign, King Penguins, fur seals and elephant seals often surrounded us while we worked,” describes Andrew.  “During the trip, I captured a group of penguins, with their backs to the wind, clustered together on a windy day.”

References and further reading:

Imaggeo on Mondays: Atmospheric gravity waves (GeoLog, EGU Blogs, April 2017)

Hoffmann, L., Grimsdell, A. W., and Alexander, M. J.: Stratospheric gravity waves at Southern Hemisphere orographic hotspots: 2003–2014 AIRS/Aqua observations, Atmos. Chem. Phys., 16, 9381-9397, https://doi.org/10.5194/acp-16-9381-2016, 2016.

South Georgia & the South Sandwich Islands Government website

Radiosondes – a guide by the National Weather Service (NOAA)

Find out more about Andrew, here: https://www.researchgate.net/profile/Andrew_Moss8