#cross bedding

Nevada’s Valley of Fire - The Valley That Was

Valley of Fire is a vivid land of bold cliffs of red and white sandstone set in the midst of the grandeur that is the Mojave Desert. So many stories of powerful earth forces, adapting life forms, and early man are all revealed in this Nevada State Park. Anyone visiting this park scarcely needs a reminder of the awesome power of the desert. The searing heat and lack of water seem almost unbearable, even in the winter the aesthetics of the place is overwhelming and the silence is profound. But in the past, the Valley was subjected to desert conditions even more demanding on life than the desert of today. For tens of millions of years the area that is now the park was a barren desert covered by lofty sand dunes.

Wind carved and swirled the sands into fantastic formations of multi-angled layers. Thousand of feet of sand piled up in the region, carried there by winds from the erosion of other areas of highland around Nevada. Today, almost half-mile thick, these “fossil” dunes comprise the beautifully shaped red and white sandstone bluffs, the most scenic aspects of Valley of Fire.

The perfectly-preserved, swirled layers of wind-blown sand illustrate a page of Mesozoic history more than 140 million years old. This sandstone, termed Aztec sandstone by geologists, extends over large areas of the Southwest. The sandstone varies in colour from deep reds and purples to tans and whites. Delicate and subtle changes in tones are thought to be the result of groundwater percolating through the sand and leaching the oxidized iron.

By tracing individual layers of sandstone, one can follow the paths of ancient, slow-moving, subterranean waters. The passage of these waters altered and transformed the chemistry of mineral grains. The result is a pleasing, artistic intermingling of colours. It is a rather poetic place as well as unbelievable past geological history.

~JM

Photo Credit: My Own

Wow. Just to stress - this area was removed from the National Monument just over a year ago.

Simple movements revealing great riches in a remote corner of (what was formerly) #bearsearsnationalmonument.  This is the kind of wealth that has fed the spirits of humans for thousands of years, the kind that will always eclipse short term profits for mineral extraction. ~ Follow @protectbearsears to learn more about hidden power of this place. ~ [Bears Ears personal collection shot with @kylor @djiglobal #inspire2 and the 50mm to compress the layers of 500-800ft tall towers!]

Lights, Camera, Action!

As a geologist I spend a vast amount of time staring at rocks, whether it be out in the field or in the lab. Whatever I'm doing I always take pictures, as proof of what I've seen, evidence to back up my assumptions or just because a professor has demanded diagrams and I am artistically limited.

Through my education I have come to realise one thing; no matter how good the rocks look the key is lighting. When mapping in the Spanish Pyrenees the best light was at dusk or dawn, when the sun sat lowest in the sky. As you can see it beautifully highlights the cross laminations (bottom photo: laminations produced by the flow of material; the height of each set can indicate water depth and the direction in which the lines dip is the direction of flow) and slickensides (top photo: precipitation of minerals, here calcite, along a fault plane as one piece of rock slides past another) on the Buntsandstein Formation. These rocks represent an ancient braided river that swept eroded material off the Hercynian mountain range 250 million years ago.

As every good scientist knows there should always be a scale as the processes that form these structures are fractalic (they can form on a variety of scales through similar processes and it is their scale as well as their shape that define what caused the structures to form e.g. a rain drop and a river will produce similar structures during flow, the only difference being the scale of the structure formed). In this case I have used my GPS and my finger (it was very early in the morning and I had forgotten my ruler) to define the scale.

Watson

Image Credit: Watson

Valley of Fire

These rocks are cross-bedded sandstones of the Aztec formation found in Valley of Fire State Park in Nevada.

This unit correlates in time with the Navajo Sandstone found in other parks throughout the Western U.S. The patterns of layers and cross bedding are similar to patterns we see forming in sand dunes today, implying that the rocks formed in giant sand dunes. In the early Jurassic when these rocks formed, this part of the North American continent was basically a giant sand sea known as an erg. The climate of the area gradually moistened during the Jurassic, allowing for preservation of these features. The colors are produced by iron oxides that were trapped in the sand dunes as they formed.

-JBB

Image credit: https://commons.wikimedia.org/wiki/File:Aztec_Sandstone_-_Valley_of_Fire1.jpg

細礫や泥岩偽礫を伴う斜交層理　強い波の力が働く浅海の環境　更新世

Original caption:

斜交層理の発達した砂質礫岩　　堆積したときの流れの向きは右から左　　更新世　長岡市