The Earth Story

Vitrinite: Earth’s very own cooking timer

When looking for oil a key parameter to consider is how mature your source rock is. As we have mentioned in previous posts (http://on.fb.me/1zNI6Pc), source rocks contain organic matter that produce hydrocarbons upon heating. For oil this is generally around 70-110°C (the oil window) which represents burial to around 2-3km. If the rocks have not been heated to these temperatures then no hydrocarbons will form.

The temperature of a formation can be crudely estimated by using the distance to which it is buried and the local geothermal gradient. The geothermal gradient is the increase in temperature observed with increasing depth, and ranges from 18°C/km to 90°C/km globally, depending on the basin type and local crustal thickness.

However, rocks have a tendency to be buried, exhumed (exposed to the surface) and even buried again during their history and this only serves to complicate things. Who’s to say that the source rock that is currently sitting above the oil window has been there for the entirety of its existence?

This is where vitrinite comes in. Vitrinite is an organic component of coal and has a very interesting characteristic; as you heat it it becomes shinier! The higher the temperature the higher the amount of light that vitrinite reflects, and by measuring this we can calculate a maximum temperature it has been heated to.

Not only does this indicate whether a source rock has been ‘cooked’ but it can also help identify where sections of rock are ‘missing’ (eroded away) and even how much rock has been removed! Even with all the high tech equipment boasted by the oil industry today, it is something as simple as Vitrinite that can make all the difference.

Reference:http://bit.ly/1CI7uI6

Further Reading : http://bit.ly/1znhgyp Photo Credit: Corbis

Plants Bathed In Fire

We recently posted an article about plant remains being preserved within fine grained mud deposits (http://on.fb.me/1LhD4DX). However, they can also be preserved in volcanic deposits as shown below. These photos are from the Erill Castell formation in the Spanish Pyrenees and show plants that became preserved when they were buried by a pyroclastic flow between 272 - 303 million years ago.

The volcanic eruptions are associated with the Hercynian Orogeny (a collisional event associated with the formation of Pangea that produced a mountain chain), with felsic (silica rich) magmas producing numerous pyroclastic flows. These superheated flows of ash and other volcanic debris would bury any flora and fauna in their path, sealing them off from the atmosphere and aiding in preservation. In some parts of this rock unit black lignite and/or coal layers can be found, and it is thought these represented the charred remains of plants that remained exposed at the surface long enough to burn.

Image Credit: Watson References: http://www.repository.naturalis.nl/record/505597 http://www.britannica.com/EBchecked/topic/262841/Hercynian-orogenic-belt Further Reading: 300ma Forest Preserved in Ash in China http://www.bbc.co.uk/news/science-environment-17117223 http://www.pnas.org/content/109/13/4927.full

Under Ol' Smokey

Many of you may be familiar with the creepy horror movie Silent Hill, which was based, in part, on the coal seam fire that burns near Centralia, Pennsylvania (USA). That fire has been burning for 53 years after it was accidentally started (though no one is completely sure how) sometime in May or June 1962. The town of Centralia was eventually abandoned, but the coal fire continues to burn on.

But 53 years is nothing compared to the Mount Wingen (which means “fire” in the local Aboriginal language) fire, also known as Burning Mountain, which has been burning for 6,000 years.

According to the local Wanaruah people, the mountain has been used for warmth, to cook, and make tools for a long time, despite the noxious gases caused by the burning coal. Surface temperatures reach 350° C even though the blaze is contained 30 metres below the surface.

No one knows how this fire was started, though the first Europeans, who came to the area in 1828, thought the heat was from a volcano. In reality, the blaze could have been started by anything from lightning, a forest fire, or the Aboriginal people themselves. But once started, coal seams fires are nearly impossible to put out. In fact, there are around 1,000 coal seam fires burning in the world today.

Further reading on Centralia, PA:https://www.facebook.com/TheEarthStory/posts/521109511283431 Further reading: https://www.facebook.com/TheEarthStory/posts/652924618101919 and https://www.sciencealert.com/this-fire-in-australia-has-been-burning-for-6-000-years Photo credit: http://www.australiantraveller.com/hunter-valley/069-make-like-moses-at-burning-mountain/

-Colter

Cyclothems

Our last post showed the Persian Gulf, (http://tinyurl.com/pp6l5fp) a flooded foreland basin sitting in space formed when the Earth’s crust is dragged down by the weight of the Zagros Mountains.

These rocks come from the other side of the world and are hundreds of millions of years older, but they tell the exact same story. These strata outcrop in Kentucky and date back to the time when the Appalachian Mountains were growing. They’ve been tilted and are no longer flat lying, but they were deposited as the Appalachians grew.

The mass of the Appalachian Mountains, created when a series of island arcs and then eventually Africa and Europe ran into North America, were a huge weight on the Earth’s surface. That weight dragged down the Earth’s crust and created a basin running up and down the North American continent.

During much of the time when the Appalachians were growing, sea level globally was higher than today; a consequence of the presence of huge ice sheets in Antarctica and Greenland today. Higher sea levels allowed the oceans to flood onto the North American continent, creating a series of inland seaways behind the mountains, just as the Persian Gulf sits next to the Zagros today.

Cyclothems are packages of sediment created during these processes. When sea level would rise, the sediments deposited in the basin would change. They would start off as on-shore, river sediments. Beach sands and coal layers formed from near-ocean swamps would follow those. Finally, deep-water shales and limestones form as the waters inundated the land.

To create the cycle, the waters would then retreat, leading to erosion and the formation of unconformities. Finally, the waters come back in, repeating the same basic package of sediment over and over.

Sediments just like this cover much of the Eastern United States, as well as areas in Europe.

-JBB

Image credit: http://www.flickr.com/photos/universalpops/6194337959/i

Read more: http://eas.unl.edu/~tfrank/History%20on%20the%20Rocks/Nebraska%20Geology/Paleozoic%20Webpage/Cyclothems.htm http://www.britannica.com/EBchecked/topic/148194/cyclothem

Smoky mountain Located in Grand Staircase Escalante National Monument (see http://tinyurl.com/l6zwpew), a non volcanic mountain disgorges smoke and toxic gases into the clean desert air. The cause is a deep coal fire that started millennia ago that releases the toxic fumes that rise through fractures in the Cretaceous sandstones above. The rocks are the relics of the ancient shoreline of the inland sea that cut north America in half during the Mesozoic, recording the oscillations of marine and coastal sediments as it oscillated in size. Loz Image credit: David Rankin via EPOD

Pyramiden

The islands of the Svalbard Archipelago are located between Norway and the North Pole. The islands are low-lying and have been so through most of their geologic history. The rocks of Svalbard include a series of sedimentary rocks deposited in the Devonian and the Carboniferous, a time when many areas of the planet formed large coal seams from recently developed plants. There are similar coal seams found here, leading to the origin of this mining colony.

Pyramiden was a mining colony established by the Russians as a way to enforce a claim on the islands. In 1920, a treaty was signed giving Norway official control of the islands but giving economic access to other countries. In 1936, the Soviet Union established a mining claim and facilities here at Pyramiden. The coalmines were never profitable but the Soviet government supported them until the collapse of the USSR in 1991. That was followed by a plane crash in 1996 that killed 141 travelers on their way to the island, including family members of many of the miners. By the late 1990s, the miners departed, leaving behind most of the equipment and the structures, frozen alongside the nearby Nordenskiöld glacier.

-JBB

Image credits: https://flic.kr/p/ZTLNLk https://flic.kr/p/HisLEP https://flic.kr/p/Hisvfv https://flic.kr/p/22crrJ9

References: http://bit.ly/2io03ck http://www.npolar.no/en/themes/geology/arctic/_ _

The less grand Staircase

The uppermost layer in the package of sedimentary rocks representing the Grand Canyon is the Permian aged Kaibab Limestone, just over 250 million years old. That was not the last sedimentary unit deposited in what is today Arizona and Utah. That area continued to see sedimentary rock deposition until the Cretaceous – nearly 200 million years more sedimentary layers on top of the Grand Canyon layers.

Those layers aren’t exposed at the Canyon site any more; they’ve eroded away. To the north of the Grand Canyon, the sedimentary package gently folds and is faulted down, exposing layers that are stratigraphically above those at the Canyon. Some of these younger layers are eroded into their own spectacular features – the Navajo Sandstone, for example, makes up much of the exposure in Zion National Park. The Navajo Sandstone is just one of more than a dozen sedimentary units that formed in this area.

Just like in the Grand Canyon, these units vary in their properties. Some are well lithified and make steep cliffs like the Navajo Sandstone does, others are weaker and erode back easily. Just as in the Grand Canyon, this setup creates a “Stairstep” pattern, where the landscape steps upwareds at the edge of a resistant layer and then erodes away at a weaker layer.

Southern Utah, to the north of the Grand Canyon, therefore, is a gigantic geologic stairstep pattern. This area is nicknamed the “Grand Staircase”. You get that impression in this picture from the central part of the area – stairstepping geologic units.

In the 1990s, President Bill Clinton used the power of an early 20th century bill called the Antiquities Act to declare much of the Grand Staircase part of “Grand Staircase-Escalante National Monument”. The original power to declare National Monuments was established in part to allow rapid protection of historical relics without the approval of Congress, which is required to create a full national park, but Presidents have historically used this power to set aside large areas for protection. It is often controversial as setting aside territory for protection means that you can’t make money on the area by tearing it apart, but this power has been used in the past to protect areas including what is today Grand Canyon National Park just to the south - Congress often eventually turns National Monuments into National Park sites once enough visitors begin coming to the area.

On Monday, something that has never happened is apparently going to happen. No President has ever shrunk a National Monument – in fact none has ever tried to do so. President Donald Trump is coming to Utah on Monday to declare that he will shrink Grand Staircase-Escalante National Monument and one other, Bears Ears National Monument, created by President Obama just over a year ago.

We don’t yet have maps of the areas that will be removed from the national monuments, and some areas have been declared Wilderness areas and have additional protections against development, but there’s a good chance that this photo will not look the same in a few years. The central part of Grand Staircase covers a coal-bearing unit and if the geotag on this photo is correct, this photo sits right above that coal-bearing unit. There are other natural gas deposits in the park as well, and local officials who have submitted maps of new park boundaries typically make sure these areas are outside the National Monument so that they can be mined and drilled.

Earlier this year, the US Interior Secretary allowed public comments about what to do with these monuments and the comments were overwhelmingly in favor of keeping them as they were – a required step before making such a change. There are local officials who want to open these areas to drilling and grazing, and the changes will be basically choosing their voices over the voices of the people who submitted comments.

It is uncertain what will happen when they try to do this. The text of the Antiquities Act gives the President the ability to declare a monument but there is no law stating how a monument can be undeclared, so there will likely be a long legal case. But…if they do what they want to do, the area in this photo will one day host a coal mine.

-JBB

Image credit: https://flic.kr/p/KfLBNY

References: http://wapo.st/2j3q7q5 http://zion-gardner-bosch.weebly.com/plate-tectonics.html http://bit.ly/2io03ck