|
Many area residents have traveled the highway between Lewiston and Juliaetta for years without knowing the geological significance along this route. This earthcache is designed to enlighten the locals and share some treasure with all who stop and explore the area. Please note it is not necessary to use tools, or remove any 'attached' mudrocks as they are present in the form of 'rubble' at the base of the hillside .
The parking is very limited for this cache so please approach at your own risk. There is ample space to pull off the highway and park a couple vehicles at N46° 31.408 W116° 44.670
LOGGING REQUIREMENTS
- Much of the the 'rubble' on the hillside is considered mudstone or mudrock. It comes in many colors as you will read below. What color is the mudrock at the posted coordinates?
- Many of the mudrocks at this location contain partial or complete fossils. All the fossils are categorized as: plant life, marine life or shells?
- Did you find a fossil? yes/no
In order to log this earthcache you must answer the questions above. Please do not post the answers in your log entry as they will be deleted. You can email me your answers via the link provided -OR- you can message me through my geocaching.com profile. Pictures posted with your log entry are encouraged, but not required. Have fun searching for a souvenir and feel free to share your prize with others via a photo!
Over the past year since discovering this location, I've queried several experts and earth science teachers to determine some facts about how these fossils were formed and the likelihood of their appearance in this location. What I've pieced together is outlined below and sourced from Wikipedia & Encyclopedia Britannica:
|
| What are mudrocks? |
|
Mudrocks are a class of fine grained siliciclastic sedimentary rocks. The varying types of mudrocks include: siltstone, claystone, mudstone, slate and shale. Most of the particles are less than 0.0625 mm (1/16th mm or 0.0025 inches) and are too small to study readily in the field. At first sight the rock types look quite similar; however, there are important differences in composition and nomenclature. There has been a great deal of disagreement involving the classification of mudrocks. There are a few important hurdles to classification, including:
|
 |
 |
- Mudrocks are the least understood, and one of the most understudied sedimentary rocks to date
- It is difficult to study mudrock constituents, due to their diminutive size and susceptibility to weathering on outcrops
- And most importantly, there is more than one classification scheme accepted by scientists
|
|
Mudrocks make up fifty percent of the sedimentary rocks in the geologic record, and are easily the most widespread deposits on Earth. Fine sediment is the most abundant product of erosion, and these sediments contribute to the overall omnipresence of mudrocks. With increased pressure over time the platy clay minerals may become aligned, with the appearance of fissility or parallel layering. This finely bedded material that splits readily into thin layers is called shale, as distinct from mudstone. The lack of fissility or layering in mudstone may be due either to original texture or to the disruption of layering by burrowing organisms in the sediment prior to lithification.
|
 |
| How'd they get here? |
|
Below is a listing of various environments that act as sources, modes of transportation to the oceans, and environments of deposition for mudrocks.
|
|
Fluvial environments Fluvial processes comprise the motion of sediment and erosion or deposition (geology) on the river bed.
Erosion by moving water can happen in two ways. Firstly, the movement of water across the bed exerts a shear stress directly onto the bed. If the cohesive strength of the substrate is lower than the shear exerted, or the bed is composed of loose sediment which can be mobilized by such stresses, then the bed will be lowered purely by clearwater flow. However, if the river carries significant quantities of sediment, this material can act as tools to enhance wear of the bed (abrasion). At the same time the fragments themselves are ground down, becoming smaller and more rounded (attrition).
Sediment in rivers is transported as either bedload (the coarser fragments which move close to the bed) or suspended load (finer fragments carried in the water). There is also a component carried as dissolved material..
|
Deep, eroding glaciofluvial deposits
alongside the Matanuska River, Alaska
|
 |
Glaciers Vast quantities of mud and till are generated by glaciations and deposited on land as till and in lakes. Glaciers can erode already susceptible mudrock formations, and this process enhances glacial production of clay and silt.
The Northern Hemisphere contains 90-percent of the world’s lakes larger than 500 km (310 mi), and glaciers created many of those lakes. Lake deposits formed by glaciation, including deep glacial scouring, are abundant.
|
|
MY GUESS...
Glacial Lake Missoula was a prehistoric proglacial lake in western Montana that existed periodically at the end of the last ice age between 15,000 and 13,000 years ago. The lake measured about 7,770 square kilometers (3,000 sq mi) and contained about 2,100 cubic kilometers (500 cu mi) of water, half the volume of Lake Michigan.
The lake was the result of an ice dam on the Clark Fork caused by the southern encroachment of a finger of the Cordilleran Ice Sheet into the Idaho Panhandle (at the present day location of Clark Fork, Idaho at the east end of Lake Pend Oreille). The height of the ice dam typically approached 610 meters (2,000 ft), flooding the valleys of western Montana approximately 320 kilometers (200 mi) eastward. It was the largest ice-dammed lake known to have occurred.
The periodic rupturing of the ice dam resulted in the Missoula Floods -- cataclysmic floods that swept across Eastern Washington and down the Columbia River Gorge approximately 40 times during a 2,000 year period. The cumulative effect of the floods was to excavate 210 cubic kilometers (50 cu mi) of loess, sediment and basalt from the channeled scablands of eastern Washington and to transport it downstream. These floods are noteworthy for producing canyons and other large geologic features through cataclysms rather than through more typical gradual processes.
|
|
Non-glacial lakes Although glaciers formed 90-percent of lakes in the Northern Hemisphere, they are not responsible for the formation of ancient lakes. Ancient lakes are the largest and deepest in the world, and hold up to twenty percent of today’s petroleum reservoirs. They are also the second most abundant source of mudrocks, behind marine mudrocks. Ancient lakes owe their abundance of mudrocks to their long lives and thick deposits. These deposits were susceptible to changes in oxygen and rainfall, and offer a robust account of paleoclimate consistency.
|
 |
 |
Deltas A delta is a subaerial or subaqueous deposit formed where rivers or streams deposit sediment into a water body. Deltas, such as the Mississippi and Congo, have massive potential for sediment deposit, and can move sediments into deep ocean waters. One can find delta environments at the mouth of a river, where its waters slow as they enter the ocean, and silt and clay are deposited.
We can locate low energy deltas, which deposit a great deal of mud, in lakes, gulfs, seas, and small oceans, where coastal currents are also low. Sand and gravel-rich deltas are high-energy deltas, where waves dominate, and mud and silt are carried much farther from the mouth of the river. |
|
Coastlines Coastal currents, mud supply, and waves are a key factor in coastline mud deposition. The Amazon River supplies 500 million tons of sediment, which is mostly clay, to the coastal region of northeastern South America. 250 tons of this sediment moves along the coast and is deposited. Much of the mud accumulated here is more than 20 meters (65 feet) thick, and extends 30 kilometers (19 mi) into the ocean.
|
 |
| Important Properties |
|
Color
Mudrocks form in various colors, including: red, purple, brown, yellow, green and grey, and even black. Shades of grey are most common in mudrocks, and darker colors of black come from organic carbons. Green mudrocks from in reducing conditions, where organic matter decomposes along with ferric iron. They can also be found in marine environments, where pelagic, or free-floating species, settle out of the water and decompose in the mudrock. Red mudrocks form when iron within the mudrock becomes oxidized, and depending on the intensity red one can determine if the rock has fully oxidized.
|
Fossils
Fossils are well preserved in mudrock formations, because the fine-grained rock protects the fossils from erosion, dissolution, and other processes of erosion. Fossils are particularly important for recording past environments. Paleontologists can look at a specific area and determine salinity, water depth, water temperature, water turbidity, and sedimentation rates with the aid of type and abundance of fossils in mudrock
|
|
Petroleum and natural gas
Mudrocks, especially black shale, are the source and containers of precious petroleum sources throughout the world. Since mudrocks and organic material require quiet water conditions for deposition, mudrocks are the most likely resource for petroleum. Mudrocks have low porosity, they are impermeable, and often, if the mudrock is not black shale, it remains useful as a cork to petroleum and natural gas reservoirs. In the case of petroleum found in a reservoir, it must be noted the rock surrounding the petroleum is not the source rock, whereas black shale is a source rock.
|
Household items
There are a few basic uses of mudrocks in one's household, including: toothpaste, face powder, adhesives, clean-up products, cat box filler, and potting soil. Metamorphosed shale can hold emerald and gold, and mudrocks can host ore metals such as lead and zinc. Mudrocks are important in the preservation of petroleum and natural gas, due to their low porosity, and are commonly used by engineers to inhibit harmful fluid leakage from landfills. |