#clast

[pipers-pixels-and-papers]

Figuring out how to draw them

[drrockclub]

Clast-supported conglomerate

This is a type of sedimentary rock where clasts (pebbles, cobbles or boulders) dominate the volume of the rock and are resting on top of each other. The matrix makes up a small percentage of the volume and infills the gaps between the clasts and usually consists of fine to coarse sand.

Conglomerates are awesome rocks. Their clasts can indicate what types of rocks existed in the catchment of the river that deposited them. Very useful, as these rocks may no longer exist, and the clasts in the conglomerate could be all that is left of those rocks!

Just like finding random ripped out pages from the last copy of the book and your job is to tell everyone what the book was about.

Geologist’s job in a nutshell.

Example from northern NSW, Australia.

[earthstory]

The Tapeats Sandstone

Throughout the Grand Canyon area, the Great Unconformity represents about 200 million years of time where no rocks were deposited. The seas retreated, leaving the basement rocks to erode away. But, 525 million years ago, the seas returned and the geologic record resumed. The first unit deposited in the Cambrian was the previous Sixtymile formation, but it was found only in a few select spots. About 500 million years ago, much more extensive deposition of sediments began with this unit.

In many places throughout the Grand Canyon, this unit, the Tapeats Sandstone, is the first unit on top of the Great Unconformity. The unit represents a shallow marine deposit, made up of sediments deposited in settings like modern-day sand bars, beaches, and channels.

The unit’s maximum thickness is about 250 meters, but like the Sixtymile Formation, the Tapeats actually isn’t deposited everywhere. In some places, the next unit up is actually deposited directly on top of the Grand Canyon Supergroup rocks. That means at the time of Tapeats deposition, there was substantial topography in the area. There were mesas and hills made up of the strong quartzites of the Supergroup and of the Vishnu Schist basement standing as islands amongst the channels where the sandstone was deposited.

The Tapeats also, as you see here being pointed at by this helpful person from Flickr, contains a variety of larger pebble and cobble-sized clasts. Many of these are made of familiar rocks; components of the Vishnu Schist and the Shunimo Quartzite, strong units deposited previously, are reworked into the Tapeats. The presence of these large clasts also suggests high-energy flows, like debris flows or turbidites, carried the clasts out to sea. The ripple marks, visible in this shot, also testify to the flow of currents that carried the sediments of this unit.

The Tapeats contains a variety of Cambrian-era fossils and trace fossils, including tracks of creatures like trilobites. It also contains the mineral glauconite, an iron-bearing mineral that forms sand-sized grains and also is likely a remnant of life, either of waste or of bodies after death. Various other sedimentary structures, like cross bedding and ripple marks are found as well.

As a strong, hard to erode sandstone, the Tapeats stands out and forms the strong platform around the central gorge in many areas of the Canyon. The Tapeats also marks the beginning of a long period of marine deposition both here and throughout the Western U.S. Although the rock types change slightly, sandstones correlative to the Tapeats can be found throughout the West, again as far north as Montana, all indicating the seas rising and beginning to claim the continent.

-JBB

Image credits (Creative Commons): https://www.flickr.com/photos/alanenglish/3609981986 https://www.flickr.com/photos/ceedave/4647884862 References: http://3dparks.wr.usgs.gov/coloradoplateau/lexicon/tapeats.htm

References: http://3dparks.wr.usgs.gov/coloradoplateau/lexicon/tapeats.htm http://geology.swau.edu/faculty/tapeats.html http://hikearizona.com/dexcoder.php?PID=1942

Oh you have got to visit the Tapeats on Google Streetview. https://www.google.com/maps/views/view/streetview/colorado-river/tapeats-sandstone/jXK-DOmUBE4PPqCz6A7CBw?gl=u&heading=263&pitch=107&fovy=75

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[calitraditionalism]

Name: Redheart

Gender: Female

Age: Roughly 3 years old

Group/Family: Clast

Rank: Deputy

Relations: N/A

A tall, well-built, red-brown molly with orange eyes and a dark back.

Redheart is ambitious – this, everyone can agree on. She’s also overly serious and can be pretty annoying about her opinions, and everyone is also unanimous about that. There’s a sense of wit somewhere in her head, but it rarely peeks out. She was made a deputy almost immediately after her warrior ceremony (some cry foul, others who knew her as an apprentice are unsurprised) and she has since been trying to climb up the Clan’s hierarchy ladder, working tirelessly in her pursuit to serve directly under or as a head of the Clan. Redheart takes her job seriously and is a natural leader, almost charismatic in her drive and vision for the world. She’s often seen staring at the night sky and grimacing.

[relatetorocks]

Cobble made of brick, via Reddit.

[calitraditionalism]

Possible symbols for the various notable groups. I’m still on the fence on a couple of these, and I’m not sure how they’d be utilized in the Clan (if they’re utilized at all), but I like the idea of families having little marks like this. 

[calitraditionalism]

Families: Clast

Regular disclaimer that the information here may change over time.

Original Clan: CobbleClan (supposedly), along with an influx of loner and kittypet blood.

Location: In the village in the center of the valley.  

Appearance: There is no set visual standard for the Clast. Thanks to so many cats wandering in, mating, and then leaving, there is no guarantee of what a litter of kittens will look like. They can be any size, any shape, and any color. Even hair length is an unknown. Surprisingly, this appears to be a benefit for them when it comes to finding mates from other areas.

Culture: Despite being the most diverse family and friendliest to strangers in the Territory, there’s a sense of posturing similar to a prison yard. New cats are dismissed until they can prove themselves worthy of respect, which usually involves a “friendly” tussle with someone who’s already earned respect. Any cat can come in and stay for a bit, but they won’t be seen as “one of the family”. Fights that occur are mostly joking wrestling, but it can very quickly grow hostile and result in a screaming match. Most cats who have their own families and litters tend to leave the Clast for safety and peace. Naming styles tend towards birds and plants, as with suffixes.

Vernacular: Clast cats are influenced verbally by the visitors from the town. They say phrases that are more human and alien to the rest of the Territory (“up my alley”, for example) and have more casual, almost brash sort of accent, the sort you would expect from someone growing up in the thick of stone and concrete. 

Relationships: Hillock and Clast are the friendliest with each other thanks to proximity and shared diversity, as well as regular interactions with outsiders.  Scattered cats tend to avoid the village, however, and everyone else generally thinks pretty lowly of this particular family. The fact that they’ve only recently started to have deputies and a sense of structure barely helps matters. 

[earthstory]

Metaconglomerate

This texture is a particularly neat one to find in the field. These rocks are clearly metamorphic; there is a strong foliation pattern developed in the rock, but there is still a strong remnant of the protolith in the variation in chemistry from one spot to another.

This rock in northern France started off as a sedimentary conglomerate containing large chunks of rock >10 centimeters in length. That rock was then squished, squeezed and heated to the point that the rocks began to flow. The big clasts in the conglomerate were flattened and new minerals grew, but the metamorphism wasn’t intense enough to fully homogenize the rock. The clast chemistries started off distinct from the surrounding groundmass and they remained distinct throughout the metamorphism.

The shape of the clasts seen now can be used to reconstruct what happened during the metamorphism. On average, the cobbles that went into the conglomerate can be assumed to have started off life either round or randomly oriented. Measuring their length now can allow scientists to estimate how much strain has happened to this rock and how its shape changed during metamorphism.

-JBB

Image credit: Graeme Churchard https://flic.kr/p/tHwTaN

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