Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g., kaolin, Al2Si2O5(OH)4) and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite. Shale is characterized by its tendency to split into thin layers (laminae) less than one centimeter in thickness. This property is called fissility. Shale is the most common sedimentary rock.
The term shale is sometimes applied more broadly, as essentially a synonym for mudrock, rather than in the narrower sense of clay-rich fissile mudrock.
Most clay must be deposited as aggregates and floccules, since the settling rate of individual clay particles is extremely slow. Flocculation is very rapid once the clay encounters highly saline sea water. Whereas individual clay particles are less than 4 microns in size, the clumps of clay particles produced by flocculation vary in size from a few tens of microns to over 700 microns in diameter. The floccules start out water-rich, but much of the water is expelled from the floccules as the clay minerals bind more tightly together over time (a process called syneresis). Clay pelletization by organisms that filter feed is important where flocculation is inhibited. Filter feeders produce an estimated 12 metric tons of clay pellets per square kilometer per year along the Coast
As sediments continue to accumulate, the older, more deeply buried sediments begin to undergo diagenesis. This mostly consists of compaction and lithification of the clay and silt particles. Early stages of diagenesis, described as eogenesis, take place at shallow depths (a few tens of meters) and are characterized by bioturbation and mineralogical changes in the sediments, with only slight compaction.
Credit: From Wikipedia, the free encyclopedia
Exposure: Mount Tzouhalem is a high point of land that overlooks Cowichan Bay. Much of the mountain is forested, and some of it is protected by an ecological reserve, but the northern side of the mountain, originally intended as a golf course, is slowly being developed into single family homes. High on the mountain, in undeveloped areas, fossils are found in the rock and in concretions; hiking steep inclines is required. Where subdivision construction is in progress, lower down, fossils can be collected on newly excavated flat lots and in debris piles beside newly paved streets with ample parking. The matrix is black shale, ranging from very hard to extremely friable. Preservation of shell is typically black in colour. Fossils at this locality are characteristic of the older part of the Haslam, including the typical ammonites (Haeuriceras, Eupachydiscus, and the heteromorphs Eubostrychoceras and Glyptoxoceras). A wide variety of clams and snails can also be found. Along with the more standard fare, the exposures here have yielded some rarities, such as the crinoids Uintacrinus and the spiny ammonite Urakawites, which are unknown from most other Haslam localities. In 2021 an impression of Pseudoxybeleceras was collected, which is pending donation to the Royal BC Museum. Plant material is common in some areas, mainly Metasequoia (dawn redwood); a well-preserved flowering cone collected at the site by a VicPS.
Equipment: The ground is uneven so wear sturdy shoes, dress for all weather (rain, wind) and bring drinking water and snacks.
Credit: Victoria Paleontology Society website. (VicPS)
Caution should be exercized while at / near GZ there are virtical faces and loose material.
To claim this Earth Cache as a find, and prove you were actualy here, you must answer the following and email the appropriate responses to the CO. Failing to do so may result in the log being deleted.
a) Estimate the altitude of GZ ? (this was sea bed at one time)
b) In your own words; Briefly describe the formation process of shale.
c) What is the dominent colour of the nearby rock face ?
d) While on site were you fortunate to discover a marine fossil ? if so, which one ?
d) Attach a photo of your GPSr / phone and or yourself in the same frame as the shale face.
I hope you enjoy the adventure and have learned more about our earth.