Photos of a variety of breccias or related phenomena

This is support material for an undergraduate research seminar at the University of Nebraska at Omaha into breccia porosity.

Colluvial breccias

This is an image from the Snowy Range just W of Laramie Wyoming, looking at well developed talus beneath a cliff of Precambrian white quartizites. The cliff was formed by glacial acitvity, and some of the debris down by the lakes represents morainal material (transported by the glacier) but the overlying talus material with a fan geometry has developed by various mass wasting processes since the glaciers melted away.

This is what some of the talus looks like close up. Large angular blocks with many relatively flat faces. As you can imagine the porosity of such talus is large. Most of the water as snow melt or rain will be 'captured' by the talus. Since there is not much fine grained material (such as clays) around not much sediment will infiltrate between the blocks to clog the porosity.

This is a close up of the cliff above the talus. Note the regular array of fractures that breaks the quartzite up into squarish blocks. These are joints and are a result of the tectonic forces during the long and complex history these rocks have experienced. The jointing plays a major role in talus clast shape and size. Surface processes such as frost wedging mainly serve to pry pieces loose, which then fall to accumulate as talus.

This collection or rubble is the result of collapse of the roof of a lava tube, the remnants of which can be seen in the center. These lava tubes are in relatively young volcanic flows in west-central New Mexico (Mal Pais). This very coarse talus material has very high porosity. It is interesting to speculate whether collapse was slow and piecemeal, or more catastrophic.

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Karst related breccias

This is a carbonate breccia from Carboniferous rocks in Spitsbergen which formed by gypsum-carbonate karst (solution) processes. Note the great range in grain sizes and shapes of clasts. Note also the clear subhorizontal boundary, indicating 2 different episodes of breccia deposition. Interestingly, the cement and appearance of the breccias above and below this boundary are different, with a pinkish cement below. This and the rather straight boundary suggest that cementation in the lower unit occurred before cementation in the upper. The finer grained browish sediment may represent internal cave sediment. Did these breccias result as mass wasting from the roof and wall or by some other process?

This is a view of the breccia locality the photo above was taken from (a mountain face called Wordiekammen and very near a locality known as Fortet). Note how the breccias are quite thick and crudely bedded. They also slope significantly. One good possibility is that the layers represent debris flows. Debris flows can occur within cave systems. If one looks carefull, the large rock spire turns out to be a large clast. What is more, it is a clast of breccia. The idea begins to evolve for this breccia that it involves multiple cycles of breccia clast formation, deposition, and cementation, and that the fragmentation process cannabalizes earlier formed breccia.

For the uninitiated this mountain side takes some explanation. The well layered and slightly dipping material is carbonate strata of the Carboniferous-Permian Wordiekammen Fm. The blunt finger of material that interurrupts the layer has a blocky and chaotic look to it. This is a breccia pipe that has been exposed in the wall of a glacial valley. Vertical conduits filled with breccia material are a common karst phenomena. The vertical relief here is on the order of several hundred meters, and so this is a good sized breccia body.

This is a diagram from a USGS web site (http://pubs.usgs.gov/bul/b2004/html/bull2004breccia_pipe_uranium_deposits.htm), which shows a breccia pipe from the Colorado plateau area. Some of these breccia pipes host U deposits. How water flowed through this system is critical for understanding the genesis of these U deposits.

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Impact related breccias.

This is an image of a moon-meteorite breccia from a NASA website (http://solarsystem.nasa.gov/multimedia/gallery/Moon_Meteorite.jpg ). Given that impact cratering is one of the major processes that shapes the surface of the moon, it is not surprising that impact ejecta (all the pulverized material that is created and distributed during an impact), is a common lunar deposit. If the impact is large enough it can actually cause produce some molten rock, which solidifies with lots of ejecta clasts captured in it, to form a rock type known as suevite. With the smaller size and lower escape velocities for the moon, larger impacts can also hurl ejecta away so that it eventually reaches the earth, which what happened with the specimen in this image.

This is a moon rock, carried back by one of the Apollo astronauts. Note the fragmental, breccia character, and the fact that it is only poorly held together. This is from the lunar highlands and represents some impact ejecta, breccia, regolith (thats a mouthful). Image source: http://pds.jpl.nasa.gov/planets/captions/earth/breccia.htm.

This photo is from the rim or lip of Meteor (Barringer) Crater in Arizona. The reddish layers represent in place, uplifted and tiled sediments. The blocky material above represents tens of meters of coarse ejecta deposits. These very proximal deposits have a lobate form and likely were transported by coherent basal surge deposits instead of individual airfall.

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Deformation related breccias (hydrothermal, fault, other)

This is an image of a hydrothermal fault related breccia from the Kenai peninsula of Alaska. These rocks have been generally tortured deformatoin wise, because of Alaska's long history of subduction plate tectonics. In this particular case the surface on the very right of the image has fault striae on it, and the white material is mainly vein quartz. Repeated movement, and opening of cracks with quartz precipitating in the racks has produced this breccia.

This breccia, also from the Kenai region of Alaska, has a very complicated history. It basically consists of subduction melange material. Note the very different clast characters. A diversity of clasts is described as polymict. Here sedimentary chert, metamorphosed volcanics, and plutonic rocks are all mixed together. The initial material was likely coarse, submarine debris flow material. However, close inspection shows an abundance of brittle slip surfaces of a variety of orientations. So brittle deformation has also contributed to the formation of angular clasts.

This is a close up of the outcrop above. Note especially the dark chert clast, which has been sliced by two brittle slip surfaces. A close inspection will show several tens of such brittle slip surfaces that have helped modify and/or produce the clast geometries. So this is essentially a fault-like breccia of a colluvial breccia that formed in a very active tectonic region.

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Breccias associated with igneous activity

This is some of the Bandelier tuff associated with Jemez volcanic center in New Mexico. These deposits resulted from a variety of volcanic pyroclastic (fragmental and exlosive eruptions) debris flows. Many of the light colored clasts here are very vesicular (lots of holes from interior volcanic gases present as they cooled) pumice clasts. Others area shallow intrusives, while others are fragmental pyroclastic deposits themselves. The finer lighter debris is volcanic ash material. Note the inequant nature of the clasts and the their good alignment.

This is a basaltic agglomerate, a breccia like deposit of blocks deposited aa part of cinder cones that can be found at the edge of the inner gorge of the Grand Canyon at a place called Vulcan's throne. It is basicaly a collection of volcanic bombs and tephra from a mildly explosive volcanic eruption. Note the relatively significant porosity evident.