As readers of this blog know, geology is an awe-inspiring subject, dealing as it does with immensely powerful forces operating on time scales, pressures, and temperatures we can barely fathom. It is geological processes that are responsible for the continents, oceans, mountain ranges, indeed for all the landscapes we see around us. Even though many of these processes operate over deep time and dee ...[Read More]
Inverted River Channels in Alcaniz: Insights into Mars’ Fluvial History
Photograph showing roadcut view of an exposed inverted river channel in Alcaniz Spain
This edition of ‘Features from the field’ is brought to you by Faris Beg, a masters student on the EU Erasmus Mundus program. He will be talking about exhumed river channels in Alcaniz, Spain. Did you know one of the most striking pieces of evidence for the existence of water on ancient Mars comes from certain geological features cropped out from underneath the Earth surface as a resul ...[Read More]
Features from the Field: Dikes and Sills
Dikes and sills intruding Dalradian quartzites, Donegal, Ireland. Photo © Prof. Alan Cooper (University of Otago).
Volcanoes are everywhere along plate margins and on hot spots on the planet’s surface. Just in the past 2 years, we have witnessed enormous explosive eruptions such as that of the Hunga Tonga volcano which released an amount of energy equivalent to hundreds of atomic bombs, and massive lava flows, as at the Cumbre Vieja at La Palma, which was estimated to have a total volume of 80 million cubic me ...[Read More]
Features from the Field: Sheath Folds
Spectacular sheath folds in Cap de Creus (Spain), produced by deformation in a Variscan shear zone. Photo by Dr. Melanie Finch.
Shear zones are areas of intense deformation that localize the movement of one block of the crust with respect to another. In previous posts, we have seen that shear zones contain some very deformed rocks called mylonites, lineations that tell us the direction of movement, and useful kinematic indicators, such as S-C fabrics, that allow geologists to understand which way the rocks moved. However, ...[Read More]
Features from the Field: Stretching Lineations
Measuring stretching lineations is the base to understanding the kinematics of large structures, like this protomylonitic metasandstone from a shear zone in the Glengarry Basin (Western Australia). Rocks slid past each other either up or down along this lineation. Which way? We need to look at a section oriented parallel to this lineation. Photo by Rolinator via wikimedia.org.
Deep beneath our feet, deformation of rocks at high temperature produces impressive structures such as shear zones, that localize the movement of two volumes of rock with respect to one another. Shear zones are strongly deformed bands with strongly foliated structures (i.e., with rocks that look like a pile of leaves) and kinematic indicators, such as S-C fabrics, that tell us geologists which way ...[Read More]
Features from the Field: Shear Zones and Mylonites
Dextral, ductile shear zones crosscut foliated schist at Cap de Creus (Catalona, Spain). Photo © Jordi Carreras
The San Andreas Fault in California, the Alpine Fault in New Zealand, or the Main Frontal Thrust in the Himalayas are some of the most famous and largest fault zones that accommodate the relative displacement between two adjacent crustal blocks. Such faults, however, represent only the shallower expression of something much bigger: a crustal shear zone. In the first 10 kilometers or so of the crus ...[Read More]
Beyond Tectonics: Fishing for Continents in the Furious Fifties and Roaring Forties
Some of the research team of IN2020_V01 in front of the bridge of the R/V Investigator (credit: Paige Maroni)
This edition of “Beyond Tectonics” is brought to you by Dr. Derya Gürer and Luca Magri. Derya is a Lecturer in Earth Sciences at The University of Queensland in Brisbane, and Adjunct Lecturer at the University of Tasmania, and Luca is a PhD student at the University of Tasmania in Hobart, Australia. In early 2020, they participated in a research voyage to one of the most remote places on the plane ...[Read More]
Features from the Field: Angular Unconformities
The worldwide famous angular unconformity at Siccar Point, between vertical layers of Silurian graywacke (below) and gently dipping Devonian layers of the Old Red Sandstone Fm. (above). Photo © Dave Souza via Wikimedia.commons
An angular unconformity is an erosional surface that truncates older, tilted sedimentary layers and that is overlain by younger layers, oriented parallel to the unconformity. The discovery and interpretation of angular unconformities, like the famous Hutton’s unconformity at Siccar Point, Scotland, marked a paradigm shift in the geological theories of the 18th century. At that time, the theo ...[Read More]
Features from the field: Bedding/Stratification
Inclined bedding planes in Ladakh (India). Photo credits: Arjun Datta (Imaggeo)
Bedding (also called stratification) is one of the most prominent features of sedimentary rocks, which are usually made up of ‘piles’ of layers (called ‘strata‘) of sediments deposited one on top of another. Every stratum is characterized by its own lithology (composition), sedimentary structures, grain size and fossil content that make it unique and different from the stra ...[Read More]
Trieste, where the word Karst originates
The Gulf and city of Trieste viewed from the Strada Napoleonica. Credit: Simon Blondel.
The city of Trieste lies in north-eastern Italy along the border with Slovenia. It is positioned at the corner point between the Romance, Germanic and Slavic worlds and serves as an important seaport in the region. It is fascinating for both its history and geology. My relationship with Italy’s town of Science, as Trieste is often referred to, started about a year ago. I got the opportunity to st ...[Read More]