Tectonics and Structural Geology

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]

TS Must-Read – Wilson (1966) Did the Atlantic close and then re-open?

The Must-read team October 13, 2020

J.T. Wilson published “Did the Atlantic close and reopen?” in 1966, giving birth to the so called “Wilson Cycle”. The article is a key steppingstone for the theory of plate tectonics, and it is a must-read paper not only in tectonics studies but also in paleontology and stratigraphy. The questions raised can be generally abridged in two: “Why regions with similar fauna can be very far from each ot ...[Read More]

TS Must-Read – Mckenzie and Parker (1967) The North Pacific: an example of tectonics on a sphere

The Must-read team September 30, 2020

The paper describes how large, rigid, aseismic regions can be defined with Euler’s theorem, which describes the geometry of motion on a sphere, i.e. the Earth’s surface. Points on these large and rigid blocks move in relation to other blocks describing small circles set by their rotation pole. The paper describes this as “paving stone theory”, where tectonic plates are “paving stones”, and success ...[Read More]

Ana Margarida Neiva – A woman as hard as granite

Rita Solá September 24, 2020

An artists illustration of Ana Neiva, (credit: Annique van der Boon)

Ana Neiva was born on May 7 1941 in Cedofeita, Porto, northwest Portugal – a city carved in granite. Her childhood and youth were spent in Coimbra, where her father worked. João Cotelo Neiva was an eminent geologist and professor at the University of Coimbra, one of Europe’s oldest universities. His influence was decisive for her interest in geology and her scientific career. ...[Read More]

TS Must-Read – Wilson (1965) A New Class of Faults and their Bearing on Continental Drift

The Must-read team September 15, 2020

In 1965, JT Wilson published “A New Class of Faults and their Bearing on Continental Drift” (https://doi.org/10.1038/207343a0). This is one of the papers that led to a paradigm shift in Earth Sciences and would become one of the bases of plate tectonics. The concept of the transform fault, introduced in this paper in a very smart way, is fundamental in tectonics textbooks nowadays. Indeed many of ...[Read More]

TS Must-Read – Dietz (1961) Continent and ocean basin evolution by spreading of the sea floor

The Must-read team September 2, 2020

Dietz 1961 “Continent and Ocean Basin Evolution by Spreading of the Sea Floor” paper was ground-breaking for plate tectonics. Almost literally, as it discussed the sea-floor spreading theory. Certainly away from the consensus at the time, this article is a classic in divergent tectonic settings and it may be an interesting piece of work for ECS working in tectonics and, more particularly, in conti ...[Read More]

Marguerite Thomas Williams: The US’ first black person to obtain a doctorate in Geology

Anouk Beniest August 26, 2020

An artists illustration of Marguerite Thomas Williams (credit: Annique van der Boon)

On the day of Christmas Eve, five years before the turn of the century, Marguerite Thomas Williams (December 1895 – August 1991) was born. She was the youngest of her five siblings born to her parents Henry and Clara Thomas. We don’t know much about her early life. Perhaps her older brothers and sisters would take her by the hand when walking to school, maybe the family would g ...[Read More]

TS Must-Read – Hubbert and Rubey (1959)

The Must-read team August 13, 2020

“The Role of Fluid Pressure in Mechanics of Overthrust Faulting” by Hubbert and Rubey is a “groundbreaking” article from the end of the 1950s. It’s a remarkable piece of research, written in an old-fashioned way, for modern standards. Many ECS that may not have read the original paper yet are certainly familiar with its textbook content. Let’s go quickly through it! The article, as a key po ...[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]

100 years of Marie Tharp – The woman who mapped the ocean floor and laid the foundations of modern geology

Derya Gürer July 30, 2020

An artists illustration of Marie Tharp (credit: Annique van der Boon)

Marie Tharp (July 30, 1920 – August 23, 2006) would have turned 100 on this very day and she continues to live through her legacy of having mapped the world’s oceans. Similar to famous painters, some of whom only gain appreciation after their death, Marie Tharp is one of the most underappreciated scientists in the history of the earth sciences. Marie was born in Ypsilanti, Michigan. Due to h ...[Read More]