TS
Tectonics and Structural Geology

Samuele Papeschi

Samuele Papeschi is a postdoc at JAMSTEC (Kochi, Japan). As a researcher, he studies deformation in rocks combining field work with the analysis of rocks under the optical and electron microscopes. He constantly hears the call of the mountains, where he loves to hike and work, taking snapshots of impressive Features from the Field.

Features from the Field: Sheath Folds

Features from the Field: Sheath Folds

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

Features from the Field: Stretching Lineations

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

Features from the Field: S-C fabrics

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

Features from the Field: Shear Zones and Mylonites

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

Features from the Field: Angular Unconformities

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: Chevron Folds

Features from the Field: Chevron Folds

Folds are among the most strikingly beautiful structures we can observe in rocks. There are several ways folds may form in rocks. For instance, folds in sedimentary rocks may develop by liquefaction of soft sediments, but the most common way to produce folds – and also my favorite – is by deformation. When rocks are compressed by tectonic forces, layers (or foliations) bend and warp, p ...[Read More]

Features from the field: crenulation cleavage

Features from the field: crenulation cleavage

In one of the former episodes of the ‘Features from the field’ series we have talked about foliations, and how they develop when rocks are pushed together by the movement of tectonic plates. It is quite uncommon, however, that tectonic forces are active in the same direction for an unlimited period of time. The rule, rather than the exception, is that the orientation of tectonic forces ...[Read More]

Features from the field: Bedding/Stratification

Features from the field: Bedding/Stratification

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]

Features from the field: Ripple Marks

Features from the field: Ripple Marks

Earlier this year, Ian Kane, geologist at the University of Manchester, captured the iconic snapshot shown above. The picture reveals ripples, developed due to waves and currents in the sand of White Strand (near Killard, county Clare, Ireland) right next to Carboniferous sandstone that contains ‘petrified’ ripple marks! The image is powerful, because it shows the basic principle of geological act ...[Read More]

Features from the field: Foliation

Features from the field: Foliation

Have you ever walked on a mountain trail, passing past outcrops of rocks and noticed that many rocks appear to be split along a well-defined orientation? If you have, you might have seen one of the most important structures in metamorphic rocks – called foliation. The term ‘foliation’ derives from the Latin folium, meaning ‘leaf’. A rock with a foliation looks like a pile of R ...[Read More]