Manistee and Lake County Quarries
The layers of earth between the bedrock and the surface are known as the soil profile or regolith. These layers, also called horizons, are differentiated by their distinct physical and chemical properties.
There are four main soil horizons from the surface down to the bedrock:
A Horizon, known as topsoil, is a layer of dark, nutrient-rich mixture of minerals and decomposed organic matter (humus). It has the highest level of biological activity, and most plant roots are concentrated here.
B Horizon, known as subsoil, is a layer of accumulated materials. It is generally lighter in color and contains less organic matter than the topsoil.
C Horizon is the parent material from which the upper layers developed. It consists of unconsolidated, slightly weathered bedrock, and unlike the soil layers above it, it has not undergone significant soil-forming processes. It contains very little organic material.
R Horizon, the final layer of a soil profile, is the hard, unweathered bedrock, which is a continuous mass of solid rock. This consolidated layer is not considered soil because it cannot be excavated by hand.
This location is at the junction of three bedrock geologies. A vein from the Michigan Formation bedrock traverses northwesterly across the Marshall Formation bedrock to its border with the Coldwater Shale bedrock.
Coldwater Shale, the oldest bedrock in the area, is a Mississippian-aged shale located below the Marshall Formation bedrock. It is a widespread and thick unit of gray to bluish-gray shale that conformably underlies the Marshall Formation.
Marshall Formation is a Mississippian-aged sandstone located above the Coldwater Shale. This formation consists primarily of sandstone with highly angular quartz grains.
Michigan Formation, the youngest bedrock in the area, is a Mississippian-aged unit consisting of shale, limestone, and dolomite that lies above the Marshall Formation.
The Manistee and Lake County Quarries are open-pit mines where gravel and limestone are extracted from the earth's surface for use in construction and other purposes, such as building materials. The Manistee Quarry (north of the paved road) is accessible by foot traffic only. It is considered to be a "shallow" quarry because excavation there was at surface-level. It is currently inactive. The Lake County Quarry (south of the paved road) is accessible by two track; however, it is highly recommended to park along the paved road, since the two track is very soft till. This quarry is considered to be a "deep" quarry because excavation there was done with in layers or benches.
This is an earthcache with a lesson in geology. To log this cache, send answers to the following questions and post a picture:
1) From both the reading and observation of the Manistee Quarry (north side of road):
a) What is the soil profile (Horizon) that was harvested here (give letter(s) followed by your explanation)?
b) Is this a type of bedrock? If so, describe which type and how it is different from the Lake County Quarry.
2) From both the reading and observation of the Lake County Quarry (south side of the road):
a) What is the soil profile (Horizon) that was harvested here (give letter(s) followed by your explanation)?
b) Is this a type of bedrock? If so, describe which type and how it is different from the Manistee County Quarry.
3) How can you tell which geological bedrock these quarries have reached or are close to reaching? If excavation continues, what is the next geological bedrock that they would reach?