Principles of relative dating of geologic events
Today, perched or winding ridges (Figure 4.) that appear of a glacial origin are called eskers and are considered to be valuable resources to a region.These rich deposits of sand, gravel, and rock are often mined by businesses or governmental agencies because they support a variety of construction needs including the creation and maintenance of roads and highways.Using your knowledge of the Blue Ridge Esker, the Michigan Basin, maps of glacial lobes, bedrock maps, and the relative direction of both ice and water flow, where do you think the metamorphic and igneous rocks came from that are found in the Blue Ridge Gravel Pit?At least two stories of climatic change can be told by reading the content held within the fossiliferous orange-brown sandstone boulders and fragments that are easily found at the Blue-Ridge Gravel Pit.Exceptions to this rule can be found in nature but are extremely rare and often relate to the burial or encapsulation of a life-form in a very fine sediment or substance that represent a low-energy environment.If a time-traveler had the ability to transport himself back in time to the Mississippian, he would probably enjoy walking along the beaches of the Michigan Basin with his toes in the warm salty-surf.The first tells about the environmental conditions and fauna of the Mississippian Period when Michigan lay near the equator (Figures 10.) and was covered with a vast inland sea about 330 million years ago known as the Michigan Basin (Figure 11).
The Blue Ridge Esker appears on the map as a narrow brown feature with contour lines that are in close proximity to each other.
The main storyline of this exercise will examine the Orange-Brown Sandstone boulders and related plate-like fragments (Figure 9.) that are easily found along the floor or at the base of any slope within the Blue Ridge Gravel Pit.
The orange-brown sandstone boulders have at least two stories that can be read from the rocks.
Secondly, when cephalopods and ammonites die, their shelly remains may have enough buoyancy to be carried by waves and currents until such a time that they might wash up onto a beach and/or be buried in the sand.
In general terms, animals or plants with hard parts that have been buried quickly or have died in environments without abundant oxygen or scavengers have the best chance of becoming preserved as fossils.