Logging Tasks
- Please let me know the GC code and the people that you are submitting the cache answers for (if one is submitting the answers for the group), everyone should have visitied the site.
- Are all the clasts (rocks) inside the "cement" in this rock the same?
- Is it Clast supported or Matrix supported? Why do you say?
- Are the clasts even in size? and are they smooth or rough?
- Based on this, is this rock conglomorate, or Brecca?
- Add a photo of you from the location or of an identifiable item (paper with trackable name). Posting a photo pulled from the internet, or photoshopped will result in instant deletion.
At the cache site there is a large boulder. It is made up of a cement of Limestone with many smaller rocks packed inside. This rocks has traveled many miles to get here. Most of the limestones are many miles from this location.
The rock is made up of many clasts. Clasts are the name for a fragment of another rock tack is eventually bound together. Cement has a clast in it. The gravel that you see in cement would be considered a clast.
Clast or Matrix Supported
There are two ways that these types of materials form. One is Clast supported. Think of filling a bucket with gravel, then dumping in a plaster mix. In this cast the rocks are sitting on top of each other, they touch, and the plaster fills the holes. So the weight is supported by the rocks.
The other option is matrix supported. The matrix refers to the "cement" that holds all the rocks together. Using the example like before, this time we take the plaster and fill a bucket. Then drop the rocks inside, or you may pour some plaster, drop in some rocks, then pour some more plaster, then more rocks. In the end the rocks do not touch, or do not touch as much. In these types there is usually more "cement" or matrix than there is rocks.
Conglomorate
Conglomerate forms in a very energetic environment, where rocks are eroded and carried downhill so swiftly that they aren't fully broken down into sand. Another name for conglomerate is puddingstone, especially if the large clasts are well rounded and the matrix around them is very fine sand or clay.
Brecca
Brecca is actually a type of conglomorate, though many consider it something seperate. Breccia is a term most often used for clastic sedimentary rocks that are composed of large angular fragments (over two millimeters in diameter). Breccia forms where broken, angular fragments of rock or mineral debris accumulate. One possible location for breccia formation is at the base of an outcrop where mechanical weathering debris accumulates. Another would be in stream deposits near the outcrop such as an alluvial fan. Some breccias form as debris flow deposits. The angular particle shape reveals that they have not been transported very far (transport wears the sharp points and edges of angular particles into rounded shapes).