Please enjoy this EarthCache from the trail system.
There should be no need to climb or explore further than a few feet from the trail.
Remember we'll be watching.
A conglomerate is a sedimentary rock formed from round gravel or larger sized clasts cemented together in a matrix. The rounding of the clasts indicates that they have been transported some distance by a river or glacier, or that they have resided in a high energy environment for some time like a beach or shoreline. The cement that binds the clast is generally made up of calcite, silica, or iron oxide. The matrix can consist of the cementing material, but may also contain sand and/or silt sized clasts cemented together among the coarser clasts.
Classification
Conglomerates can be classified by their texture, clast composition, and there clast size.
Texture (Class):
- Paraconglomerate (Clast supported) where the clast touch each other and the matrix fills the voids.
- Orthoconglomerate (Matrix supported) where the clast are not in contact and the matrix surrounds each clast.
Clast Composition:
- Monomict - clasts with only a single rock type (lithology) is represented.
- Oligomict - clasts with only a few different rock types (lithologies) are represented.
- Polymict - clasts with many different rock types (lithologies) are represented.
- Granule conglomerate 2 - 4 mm (0.08" - 0.15")
- Pebble conglomerate 4 - 64 mm (0.15" - 2.5")
- Cobble conglomerate 64 - 256 mm (2.5" - 10")
- Boulder conglomerate > 256 mm (10")
Logging Requirements
Explore the conglomerates along the trail, and email me the following information with the text "GC4ZXVC Conglomerate" on the first line of the email:
- Classify the conglomerates by their texture, clast composition and clast size.
- Examine the matrix and describe its composition.
- Which rock type(s) are present as clast?
- Theorize why you think these conglomerates formed here or are found here?