The 366 daily episodes in 2014 were chronological snapshots of earth history, beginning with the Precambrian in January and on to the Cenozoic in December. You can find them all in the index in the right sidebar. In 2015, the daily episodes for each month were assembled into monthly packages, and a few new episodes were posted. Now, the blog/podcast is on a weekly schedule with diverse topics, and the Facebook Page showcases photos on Mineral Monday and Fossil Friday. Thanks for your interest!

Tuesday, February 20, 2018

Episode 388 Folds in Algeria


You may have seen some of the spectacular images of the earth in southern Algeria, curves and colors like some Picasso in the opposite of his cubist period. If you haven’t, check out the one from NASA, below. 

The ovals and swirls, with their concentric bands, are immediately obvious to a geologist as patterns of folds, but not just linear folds like many anticlines and synclines form. These closed ovals represent domes and basins – imagine a large scale warping, both up and down, in a thick succession of diverse sedimentary rocks, like sets of nested bowls, some of them right-side up and some inverted, then all sliced off halfway through.

But “obvious to a geologist” has plenty of limitations in a space image. Without knowing more information, it’s difficult to be sure if an oval is a basin or a dome. And you can speculate, but without some ground truth, it’s challenging to be sure what the rock types are.

Ahnet-Mouydir, Hoggar Mountains, Algeria. NASA image - source

This area, called the Ahnet-Mouydir, on the flank of the Hoggar Mountains close to the middle of the Sahara Desert, is remote, inhospitable, and arid, and called the “land of terror” for a reason. The rocks represent a thick sequence of marine sandstones, shales, and limestones, spanning a huge range of ages, from at least the Ordovician to the early Carboniferous – 150 million years or more, a great chunk of the Paleozoic era.


The core of the Hoggar Mountains is an old Precambrian block, not as big as the cratons and shields that form the hearts of most of the continents, but otherwise similar. It might have been something like a microcontinent that became amalgamated into the growing supercontinent of Gondwana about 600 million years ago. After that amalgamation, seas came and went much like they did in western North America throughout much of the Paleozoic era, laying down the sediments that became the rocks we see today in the northern Hoggar Mountains.

That’s all well and good – but here’s the next question, how did the rocks get deformed into these oval domes and basins? If you imagine the kinds of collisions that are typical on earth, you think of linear or curvilinear things – island arcs, edges of continents and such – that when they collide, are likely to make linear belts of deformation. This is why so many mountain ranges are long, linear features, and the folds and faults that make them up also tend to be linear. Domes and basins happen, but that seems to be almost all we have here in these mountains.

We have to look for a deformational event that is later than the youngest rocks deformed. So if some of these rocks are as young as early Carboniferous, about 340 million years old, the mountain-building event that fills the bill is the Hercynian Orogeny, where ‘orogeny’ just means mountain-building.

The Hercynian, at about 350 to 280 million years ago, represents the complex collision between Gondwana and the combined North America and Europe, which were already more or less attached to each other. The leading edge of Gondwana that collided was in what is now North and West Africa, and the collision produced mountain ranges all over – the Alleghenies in the central Appalachians in North America, and a complex swath of mountains across central Europe, from Spain, across France to northern Germany and into Poland, as well as elsewhere. In Africa, the most intense squeezing was at the leading edge, in what is now Morocco and Mauritania, colliding with North America, and northern Algeria, impacting Iberia.

The basins and domes of southern Algeria that we’re trying to understand are 1500 kilometers or more from that leading edge of continental collision. So I think – and full disclosure, I’ve never really researched this area in detail – that what must have happened is that that distant hinterland wasn’t pushed into tight, linear belts like those we find along the lines of collision, but the force was enough to warp the sediments into these relatively small domes and basins. Alternatively, it might be possible that the brittle Precambrian rocks beneath the sedimentary layers broke from the force of the collision, so that the sedimentary layers draped over the deeper brittle surface like a carpet lying over a jumble of toy building blocks – some high, some low.

The latter idea, that the brittle basement rocks were broken and pushed upward with the sedimentary layers draped over them is supported by research published in the journal Terra Nova in 2001. Hamid Haddoum and colleagues studied the orientations of folds and faults in this area, trying to figure out the orientations of the stresses that caused them. Their data show a shortening direction – which means compression, or squeezing – during early Permian time oriented about northeast-southwest. That is consistent with the collision that was happening at that same time between what is now Senegal and Mauritania, in westernmost Africa, and the Virginia-Carolinas region of what is now the United States. Haddoum and his colleagues show cross-sections with basement upthrusts, basically high-angle reverse faults where older rocks are squeezed so much that they are pushed up and over younger rocks. This is quite similar to the Laramide Orogeny in the western United States about 80 to 50 million years ago, but this compression was happening about 280 million years ago as the supercontinent of Pangaea was assembled during the early Permian Period. Both represent deformation at relatively great distances from the lines of continental collision. In the case of the Laramide in western United States, one idea for transmitting the stress so far from the collision is that the subducting slab of oceanic crust began to go down at a relatively gentle angle, even close to horizontal, creating friction and stress further away from the subduction zone than normal. Whether that’s the case here in southern Algeria isn’t clear for this Hercynian collision.

I wouldn’t think of this area as high mountains, such as those that must have formed along the lines of Hercynian collision. Maybe more like warped, uplifted plateaus – but whatever they were, they were certainly subject to erosion. Erosion probably wore the domes and basins down to a common level, so that the nested bowls were exposed in horizontal cross-section – which for geologists is the equivalent of a geologic map. And that’s what the beautiful photos reveal.

The area might have been planed off even more by Permian glaciers during and after the Hercynian mountain-building events. But then, during the Mesozoic era, seas returned to the region and all this mess of eroded domes and basins was buried beneath even more sediments. Sometime relatively recently, during the Cenozoic era, the past 65 million years, everything was uplifted at least gently, so that the highest parts – including today’s Hoggar Mountains, were stripped of the younger Mesozoic sedimentary rocks, revealing the much older Paleozoic rocks in the domes and basins.

Thanks to Petr Yakovlev for pointing me to the 2001 paper by Haddoum and others.

—Richard I. Gibson

Link: 




Tuesday, February 13, 2018

Episode 387 Geology of Beer


It isn’t true that all geologists drink beer. But many do, and I’m one of them. Today I’m going to talk about the intimate connection between geology and beer.

Beer is mostly water, and water chemistry has everything to do with beer styles. And water chemistry itself depends mostly on the kinds of rocks through which the water flows. You know about hard and soft water – hard water has more dissolved chemicals like calcium and magnesium in it, and while salts of those chemicals can precipitate out of hard water, making a scum on your dishes, they also can be beneficial to development of bones and teeth. In the United States, the Midwest and Great Plains have some of the hardest water because of the abundant limestones there, and in Great Britain, southern and eastern England have harder water than Scotland for similar reasons.

But it wasn’t limestone that made Burton-upon-Trent a center of brewing in the 19th Century, when it was home to more than 30 breweries. The water there is rich in sulfate which comes from gypsum, calcium sulfate, in the sandstone underlying the region. Those sandstones are Permian and Triassic in age, representing a time when much of the earth was arid. Those dry conditions allowed gypsum to crystallize in the sediments. Gypsum is much more soluble than limestone, and the slightly acidic waters of Burton help with that. Burton water has ten times the calcium, three times the bicarbonate, and 14 times the sulfate of Coors’ “Rocky Mountain Spring water” in Colorado. That certainly makes Coors’ Burton brewery product rather different from that made in Colorado.

In fact, the addition of gypsum to beer is called “Burtonization.” This increases the hops flavor, but more important to history, sulfates act as preservatives in beer, enough so that Burton brews of pale ales could survive the long trip to British India, giving us the India Pale Ale style of beer. Not from India, but brewed with sulfates derived from gypsum in Britain’s rocks.

That slight acidity in Burton’s water depends on the calcium and magnesium content, and also lends itself to extracting sugars from malted barley in the mashing process. Calcium and magnesium also help yeast to work its magic. Today, home brewers can buy “Burton Water Salts” to imitate the product from England.

Truman, Hanbury, Buxton & Co., Black Eagle brewery, Derby Street, Burton-upon-Trent, in 1876,
from University of London
Less hoppy beers often originated in areas where the sulfate content of the water was low. Pilsen in the Czech Republic, home to pilsner beer, has almost no sulfate and only 7 parts per million calcium in its water, compared to around 300 for Burton. Pilsen is in an area of metamorphic rocks that don’t yield the typical hard-water-making elements.


The presence of Carboniferous age limestones in Ireland make waters that are high in calcium and carbonate, but they lack the sulfate of northern England. Together with other differences, that makes the area around Dublin ideal for making a stout porter known today as Guinness.

After water, it’s the soil that makes the most difference to beer. Hops can grow in a wide range of soils, even the decomposed granite we have here in Butte, but the thick, well-drained soils of Washington and Oregon, weathered from volcanic rocks, make those states the source of 70% of the hops grown in the United States.

The surge of craft breweries in the United States has given rise to some interesting geological names for brews. Great Basin Brewing in Reno and Sparks, Nevada, has Ichthyosaur IPA, known as Icky, as well as Orogenesis, a Belgian-style amber ale. Socorro Springs, in New Mexico, brews Isopod Pale Ale and Obsidian Stout is available from Deschutes in Oregon.  You can get Triceratops Double IPA at Ninkasi Brewing in Eugene, Oregon, and Pangaea Ale at Dogfish Head in Delaware. And even though it’s more chemical than geological, we shouldn’t leave out Atomic Ale’s Dysprosium Dunkelweizen, made in Richland, Washington. Dysprosium is a rare-earth element found in the phosphate mineral xenotime and other stranger minerals.

San Andreas Brewing Company, near the fault in California, boasts Oktoberquake and Aftershock Wheat.

And I’m undoubtedly prejudiced, because I’m the House Geologist at Quarry Brewing here in Butte, which probably has the best mineral collection in a brewery in the United States, but I think their collection of geological names for their beers is unexcelled: Shale Pale Ale, Galena Gold, Open Cab Copper, and Gneiss IPA, and seasonals including Albite, Basalt, Bauxite, Calcite, Epidote, Halite, Ironstone, Porphyry, Opal Oktoberfest, Schist Sour, Rhyolite Rye Pale Ale, Pyrite Pilsner, and more. Mia the bartender and I tried to come up with a fitting name for a 50-50 mix of basalt and gneiss. I wanted it to be charnockite, but we ended up calling it Mia’s Mixture.

Next time you enjoy a beer, thank geology!

—Richard I. Gibson

Image: Truman, Hanbury, Buxton & Co., Black Eagle brewery, Derby Street, Burton-upon-Trent, in 1876 from University of London


Sunday, February 11, 2018

Paleozoic Vertebrates compilation


Ganoid fish from an old textbook (public domain)
Running time, 1 hour. File size, 70 megabytes.


This is an assembly of the 15 episodes in the original series from 2014 that are about Paleozoic vertebrates.

I’ve left the references to specific dates in the podcast so that you can, if you want, go to the specific blog post that has links and illustrations for that episode. They are all indexed on the right-hand side of the blog.

Thanks for your interest and support!