Sedimentary, My Dear Watson

A 21-year-old geology (and Spanish and history) undergrad who loves rocks and wants other people to love them too! Here you'll find a diverse collection of all things geo and natural history related, targeted at varying levels of expertise.

*Please feel free to send in geo-related questions to the ASK page!*

amnhnyc:

Corythosaurus is a member of the group of duck-billed dinosaurs called hadrosaurs, which walked and ran on their two hind legs. The species’ strange skull is capped by a crescent-shaped helmet that contains extended tubes, which formed elaborate nasal passages.

Collected in 1912 in Alberta, Canada, this Corythosaurus is among the finest dinosaur specimens ever found. The preservation of fossilized skin impressions and a meshwork of calcified tendons that stiffened the tall vertebrae make it a rare find.

This specimen is located in the Hall of Ornithischian Dinosaurs.

Hello! Can you recommend any Geology books for those with the most rudimentary knowledge of science? Science was always a struggle for me growing up, but geology is so fascinating to me. Thank you!
Anonymous

I highly recommend Reading the Rocks: The Autobiography of the Earth by Marcia Bjornerud. (Plus, I personally know the author, and she’s magnificent!) I definitely enjoy reading it as a geologist, but it’s perfectly geared to those who have more of a beginning knowledge of science; it’s typically categorized as ‘popular science,’ which basically just means that even if you’re not a geologist, you’ll still enjoy and understand it!

Another author I very highly recommend is Stephen Jay Gould. His writing is so vivid and easily accessible, it makes the natural work and natural history so fascinating! (He’s probably a large reason for why I fell in love with geology!) Bully for Brontosaurus and Wonderful Life: The Burgess Shale and the Nature of History are two fantastic books of his.

Anyone else have any great geology book recommendations to share?

Geology of the Indiana Dunes

Located in northwestern Indiana along the southern shore of Lake Michigan, the Indiana Dunes are a fantastic display of aeolian (wind) processes at work.

Incredibly tall sand dunes line the shores, and dune fields from former lake highstands extend even further back away.

These impressive ‘beach mountains’ originated from glacially transported sediment post-last glacial maximum [Pleistocene, ~18-14,000 yrs ago]. Glacial deposits are typically very poorly sorted but can become sorted by water (outwash), wave action, and wind action.

The dunes are primarily medium-grained quartz with finer-grained magnetite, so they are rather well sorted by specific weight. It would require wind ~15 mph to move this sized-sediment. 

Dunes typically have gentle upwind faces and steeper downwind faces [which is what generates the classic look of cross-bedding].
image

However, some dunes may become ‘blowouts,’ which is when a pristine dune has been modified, potentially by human activity/movement. Instead of having a linear or slightly concave down front face, the dune can become concave up in the direction of the wind and have a much steeper front slope.

However, the Indiana Dunes are being starved at sediment and now are at risk. As is evidenced by the large number of blowouts, the dunes are not healing themselves too well. Due to longshore drift,
image
t
he source of the sand for the dunes comes from the NE. As there is a large nuclear power plant along the shore toward the NE, the plant is likely blocking and prohibiting sand from traveling past it. Combined with this fact, negative feedbacks, human use, and other factors may be causing the starvation of these dunes.

All photos by author; graphics are linked to original sources

houroftherose:

Moss Agate is one of the most beautiful and interesting stones I know of. They often contain beautiful little scenes like this that look like hand-drawn landscapes or nature scenes. They are the result of various minerals and metals and the reaction that occurs when those minerals and metals interact.

houroftherose:

Moss Agate is one of the most beautiful and interesting stones I know of. They often contain beautiful little scenes like this that look like hand-drawn landscapes or nature scenes. They are the result of various minerals and metals and the reaction that occurs when those minerals and metals interact.

earthstory:

Porphyritic Texture.Porphyritic is a term used in igneous petrology to describe texture in relation to crystal size. Porphryitic refers to one crystal size being much larger than the other, such as in the image below. The k-feldspar crystals are obviously much larger than the rest of the crystals making up the granite. There are two main types of porphyritic texture, the first, large crystals"floating" in a fine grained crystal groundmass, where it is not possible to differentiate the individual crystals of the ground mass with the naked eye, and the second, where it is possible to differentiate the differing crystals, but one group of crystals are obviously larger than the other.Porphyritic texture forms when magma cools in two stages. The first stage is slow, and elements that form at high temperatures are the first to crystallise, forming large individual crystals “floating” in a magma. The second stage is sudden rapid cooling, forming the smaller sized crystals. This rapid cooling can occur during an eruption from a volcano, or when a rising column of magma suddenly reaches shallow depths in the crust.-LLLinks;http://www.pitt.edu/~cejones/GeoImages/2IgneousRocks/IgneousTextures/4PorphyriticFineGrained.htmlhttp://geology.about.com/od/more_igrocks/ig/igroxtextures/igtexporphyritic.htmhttp://www.tulane.edu/~sanelson/eens212/textures_igneous_rocks.htmImage; Leah Lynham

earthstory:

Porphyritic Texture.

Porphyritic is a term used in igneous petrology to describe texture in relation to crystal size. Porphryitic refers to one crystal size being much larger than the other, such as in the image below. The k-feldspar crystals are obviously much larger than the rest of the crystals making up the granite. 

There are two main types of porphyritic texture, the first, large crystals"floating" in a fine grained crystal groundmass, where it is not possible to differentiate the individual crystals of the ground mass with the naked eye, and the second, where it is possible to differentiate the differing crystals, but one group of crystals are obviously larger than the other.

Porphyritic texture forms when magma cools in two stages. The first stage is slow, and elements that form at high temperatures are the first to crystallise, forming large individual crystals “floating” in a magma. The second stage is sudden rapid cooling, forming the smaller sized crystals. 

This rapid cooling can occur during an eruption from a volcano, or when a rising column of magma suddenly reaches shallow depths in the crust.

-LL

Links;
http://www.pitt.edu/~cejones/GeoImages/2IgneousRocks/IgneousTextures/4PorphyriticFineGrained.html

http://geology.about.com/od/more_igrocks/ig/igroxtextures/igtexporphyritic.htm

http://www.tulane.edu/~sanelson/eens212/textures_igneous_rocks.htm


Image; Leah Lynham

BONUS - THE ANTHROPOCENE (present day)
Severity: TBD
Cause: Fossil fuel combustion
Climate: Rapid climate change, sea level change, ocean acidification, ocean anoxia, ozone destruction
Aftermath: ??
Mass extinction aren’t just something of the past; it’s commonly accepted that we’re in one right now.
While the Anthropocene isn’t yet an official epoch, there is mounting evidence to suggest that human activity has caused such a perturbation to the system that there should be a departure from the Holocene.
It’s possible that up to 140,000 are going extinct each year, primarily as a result of human activities. 
HERE’s a nice TIME article on this sixth mass extinction.
Click HERE to see all Mass Extinction Monday posts

BONUS - THE ANTHROPOCENE (present day)

Severity: TBD

Cause: Fossil fuel combustion

Climate: Rapid climate change, sea level change, ocean acidification, ocean anoxia, ozone destruction

Aftermath: ??

Mass extinction aren’t just something of the past; it’s commonly accepted that we’re in one right now.

While the Anthropocene isn’t yet an official epoch, there is mounting evidence to suggest that human activity has caused such a perturbation to the system that there should be a departure from the Holocene.

It’s possible that up to 140,000 are going extinct each year, primarily as a result of human activities. 

HERE’s a nice TIME article on this sixth mass extinction.

Click HERE to see all Mass Extinction Monday posts

s-c-i-guy:

600 Million Years and Counting…

I was pretty bored so I decided to make some GIFs of the last 600 million years of our planet’s plate tectonics.

The first GIF is a global mollewide projection. The second one is of the Colorado Plateau and the North American Southwest. The next GIF is of the entire formation of the North American Continent. The fourth GIF is of geologic and tectonic evolution of Europe. And finally the last one is the same as the first except in rectangular format.

I obtained the images from Global Paleogeography and them compiled them one by one into Photoshop with the end result being the above GIFs.

Geology rocks

earthstory:

Turbidites!These rock layers may not look that distinctive, but to geologists these tell a really cool story. These are turbidites, the remnants of debris flows off the shore of an ancient ocean.Turbidites form when sediment piles up just off of a shoreline, often carried to the area by a river. Eventually, even underwater, big enough piles of sediment will collapse and avalanche downslope. Sometimes they do so under their own weight, sometimes an earthquake will set them off.The avalanche of debris produces a recognizable pattern to geologists. The heaviest particles, the biggest grains, settle out at the bottom of the debris flow, and the sequence “fines upward”, meaning the grain sizes get smaller.A typical turbidite will start at the bottom with sandy grains, maybe even larger stuff, and the grain size will decrease going upward as progressively finer grains settle out. Finally, each turbidite is topped by a layer of very fine grained clay particles that can even be a different color from the stuff below it. This sequence even has a name – the “Bouma” sequence.Turbidites show up throughout the geologic record because they’re easily preserved. They form in areas in the ocean that aren’t likely to be eroded and they form in areas with lots of sediment that can bury and protect them afterwards. This sequence photographed here is about 10 separate turbidites; the whole outcrop probably has a lot more.-JBBImage credit: Brian Romans (Creative commons):https://www.flickr.com/photos/bromans/4969233953Read more:https://courses.washington.edu/sicilia/pdf/JBturbidites_fans.pdfhttp://trg.leeds.ac.uk/

earthstory:

Turbidites!

These rock layers may not look that distinctive, but to geologists these tell a really cool story. These are turbidites, the remnants of debris flows off the shore of an ancient ocean.

Turbidites form when sediment piles up just off of a shoreline, often carried to the area by a river. Eventually, even underwater, big enough piles of sediment will collapse and avalanche downslope. Sometimes they do so under their own weight, sometimes an earthquake will set them off.

The avalanche of debris produces a recognizable pattern to geologists. The heaviest particles, the biggest grains, settle out at the bottom of the debris flow, and the sequence “fines upward”, meaning the grain sizes get smaller.

A typical turbidite will start at the bottom with sandy grains, maybe even larger stuff, and the grain size will decrease going upward as progressively finer grains settle out. Finally, each turbidite is topped by a layer of very fine grained clay particles that can even be a different color from the stuff below it. This sequence even has a name – the “Bouma” sequence.

Turbidites show up throughout the geologic record because they’re easily preserved. They form in areas in the ocean that aren’t likely to be eroded and they form in areas with lots of sediment that can bury and protect them afterwards. This sequence photographed here is about 10 separate turbidites; the whole outcrop probably has a lot more.

-JBB

Image credit: Brian Romans (Creative commons):
https://www.flickr.com/photos/bromans/4969233953

Read more:
https://courses.washington.edu/sicilia/pdf/JBturbidites_fans.pdf
http://trg.leeds.ac.uk/

rivermusic:

Around Jenny LakeGrand Teton National Park, Wyoming(gneiss, quartz, granite, garnet, schist)
photo by rivermusic, June 2013

rivermusic:

Around Jenny Lake
Grand Teton National Park, Wyoming
(gneiss, quartz, granite, garnet, schist)

photo by rivermusic, June 2013

END-CRETACEOUS (65 Ma)
[Also formerly known as the Cretaceous-Tertiary (K-T) and now as the Cretaceous-Paleogene (K-Pg) extinction]
Severity: 5th worst
Cause: Meteorite impact released CO2 from carbonates
Climate: Cold (SO2) then warm (CO2)
Aftermath: Mammals arise
Even though the End-Cretaceous is the least severe of all the mass extinctions, with 62% of species and 11% of families wiped out, it’s probably the most well-known. (Say goodbye to our dinosaur friends!) The hardest hit animals included: dinosaurs (except Aves), pterosaurs, corals, echinoids, ammonites and belemnites, brachiopods, bivalve molluscs, and foraminifera.
Luckily for us, mammals were among those that fared better, along with turtles, lizards and snakes, birds, amphibians, and fish.
Most people are familiar with the theory that a meteorite impact was the cause of this mass extinction, but what really did happen and what can be proven?
Back in 1980 in Gubbio, Italy, father-son duo of Luis and Walter Alvarez measured an iridium abundance in the K-Pg boundary clay. Iridium is not a very common element in the Earth’s crust, so they knew it must have come from an extraterrestrial source. This observation would lead to inferring that there must have been a massive meteorite impact, but they would have to find the actual impact crater.
In the K-Pg boundary layer around the Caribbean, tektites, shocked quartz, and tsunami deposits were discovered, all of which would be indicative of a nearby meteorite impact.
The half-submerged Chicxulub crater was soon discovered in the Yucatan of Mexico, and impact glass yielded a 39Ar/40Ar age of 65 Ma, the exact age of the K-Pg boundary, making it the perfect candidate.
A large portion of this impact’s deadliness would have been due to the target rocks, which are mainly carbonates and evaporites. Upon impact, the rocks would have been vaporized, releasing large amounts of CO2 and SO2.
However, this mystery still isn’t fully solved. Around the same time, the Deccan Traps in India were effusively erupting, and as we saw in the End-Permain extinction, flood basalt events can produce absolutely disastrous effects.
We then have to ask ourselves: Was the impact really the only (or primary) cause of the extinction? What would have been the actual kill mechanism? And what was the role of the Deccan Traps?
Click HERE to see all Mass Extinction Monday posts

END-CRETACEOUS (65 Ma)

[Also formerly known as the Cretaceous-Tertiary (K-T) and now as the Cretaceous-Paleogene (K-Pg) extinction]

Severity: 5th worst

Cause: Meteorite impact released CO2 from carbonates

Climate: Cold (SO2) then warm (CO2)

Aftermath: Mammals arise

Even though the End-Cretaceous is the least severe of all the mass extinctions, with 62% of species and 11% of families wiped out, it’s probably the most well-known. (Say goodbye to our dinosaur friends!) The hardest hit animals included: dinosaurs (except Aves), pterosaurs, corals, echinoids, ammonites and belemnites, brachiopods, bivalve molluscs, and foraminifera.

Luckily for us, mammals were among those that fared better, along with turtles, lizards and snakes, birds, amphibians, and fish.

Most people are familiar with the theory that a meteorite impact was the cause of this mass extinction, but what really did happen and what can be proven?

Back in 1980 in Gubbio, Italy, father-son duo of Luis and Walter Alvarez measured an iridium abundance in the K-Pg boundary clay. Iridium is not a very common element in the Earth’s crust, so they knew it must have come from an extraterrestrial source. This observation would lead to inferring that there must have been a massive meteorite impact, but they would have to find the actual impact crater.

In the K-Pg boundary layer around the Caribbean, tektites, shocked quartz, and tsunami deposits were discovered, all of which would be indicative of a nearby meteorite impact.

The half-submerged Chicxulub crater was soon discovered in the Yucatan of Mexico, and impact glass yielded a 39Ar/40Ar age of 65 Ma, the exact age of the K-Pg boundary, making it the perfect candidate.

A large portion of this impact’s deadliness would have been due to the target rocks, which are mainly carbonates and evaporites. Upon impact, the rocks would have been vaporized, releasing large amounts of CO2 and SO2.

However, this mystery still isn’t fully solved. Around the same time, the Deccan Traps in India were effusively erupting, and as we saw in the End-Permain extinction, flood basalt events can produce absolutely disastrous effects.

We then have to ask ourselves: Was the impact really the only (or primary) cause of the extinction? What would have been the actual kill mechanism? And what was the role of the Deccan Traps?

Click HERE to see all Mass Extinction Monday posts