Features from the field

Inverted River Channels in Alcaniz: Insights into Mars’ Fluvial History

Faris Beg August 16, 2024

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: Columnar Basalts and why Hexagons are nature’s favourite shape

Hannah Davies May 26, 2023

What does an insect eye, Saturn’s North pole, beeswax, and a rock formation called columnar basalts all have in common? They are all hexagonal in shape. Why is this the case? Hexagons are the most efficient way to fill a space with the least amount of material The science of bubbles and bubble sculptures is very interesting and I do encourage you to go check out some other blogs that talk ab ...[Read More]

Features from the Field: Dikes and Sills

Samuele Papeschi and Hannah Davies May 30, 2022

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: Snow illuminates fault zones

Afroz Shah April 8, 2022

A fault zone illuminated by light snow cover in the Himalayan orogenic belt.

This guest post was contributed by Afroz Shah who is an Assistant Professor of Structural Geology at the Department of Geosciences, Universiti of Brunei Darussalam (UBD). He has completed Ph.D at James Cook University, Australia in 2010, post-doctorate at Earth Observatory of Singapore in 2013 and joined the first academic job as a Senior Lecture of Structural Geology at Curtin Sarawak, Miri, Mala ...[Read More]

Features from the Field: Sheath Folds

Samuele Papeschi and Hannah Davies October 4, 2021

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

Samuele Papeschi and Hannah Davies June 21, 2021

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: S-C fabrics

Sandra McLaren, Samuele Papeschi and Hannah Davies May 19, 2021

As we have seen in previous Features from the field posts, structural fabrics are both informative and spectacular. But many structural geologists will list a shear zone fabric, such as mylonite, as their favourite! As Samuele, Hannah and I wrote in a previous post, shear zones are regions of intense deformation where rocks have accommodated an extremely high amount of strain and that strain has b ...[Read More]

Features from the Field: Shear Zones and Mylonites

Samuele Papeschi, Sandra McLaren and Hannah Davies January 25, 2021

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]

Features from the Field: Angular Unconformities

Samuele Papeschi October 21, 2020

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: Pencil Cleavage

Sandra McLaren August 7, 2020

A selection of the author’s pencil shale collection, appropriately with a pencil for scale! Neoproterozoic Tapley Hill Formation from South Australia, Ordovician Liptrap Formation, Victoria, Balcanoona Formation shales from Mount Fitton, South Australia and a sample from an unknown location rescued from a departmental clean out (source: Sandra McLaren)

This edition of ‘Features from the field’ is brought to you by Sandra McLaren, a senior lecturer at the University of Melbourne. She will be talking about type of rock formation called “Pencil Cleavage” so called because it looks like pencils. Sandra even has a small collection of pencil/crayon shale which is the cover image of this post. I have seen quite a range of differ ...[Read More]