Ohio's Physiographic Regions
This Earthcache brings you to an informational sign that describes Ohio’s five physiographic regions (see attached image if the sign becomes illegible). You will need to use the information on this sign, some basic observations about stones found at the rest stop, and your critical thinking skills to infer the provenance (geological source) of these stones. If you fully engage with this exercise, which asks you to connect a known (the information on the sign) to an unknown (the types of rocks present and their sources), then you should develop an enriched understanding of Ohio’s diverse geologic landscape.
Questions:
At the nearby waypoints you will find three stones. Use the informational sign at the posted coordinates, the information provided in the lesson below, and observations you make at the three waypoints to answer the following questions.
1) Three of Ohio’s physiographic regions were heavily sculpted by glaciers over the 2-million-year period of the Ice Age. The surface geology of these regions is dominated by poorly sorted glacial till and outwash, including sediments that range in size from the finest clays to the largest boulders.
a) Which of the three physiographic regions are dominated by glacial sediments?
b) Which of the three waypoints (A, B, or C) contains a heavily rounded and weathered glacial erratic like those found in these physiographic regions?
2) Two of Ohio’s physiographic regions are dominated by surface bedrock formations consisting of the sedimentary rocks described below.
a) Waypoint A contains a stone marked “Cumberland 153”. Does this stone consist of grains of sand cemented together (sandstone) or crystals of calcite growing into one another (limestone)?
b) Based upon your answer to a), from which of Ohio’s five physiographic regions was this stone most likely mined?
c) Based upon the information on the Ohio's Physiographic Regions sign, was the rock used to manufacture the Department of Transportation dedicatory marker located at the remaining waypoint obtained from a surface bedrock formation in Ohio? Why or why not?
3) Based upon the information on the Ohio's Physiographic Regions sign, in which of Ohio’s physiographic regions are you currently standing? Take a moment to observe the natural landscape visible in the distance from the rest area. Do your observations confirm your answer to this question? Why or why not?
4) Post a picture of yourself or an item of your choice at the rest stop.
The Lesson:
A physiographic region is a large geographic area that is separated from adjacent regions by shared geology and topographic features. Ohio has five major physiographic regions that are largely defined by the kinds of glacial sediments and exposed bedrock formations that are present.
The following rock and sediment types dominate Ohio's surface geology:
a) Glacial Sediments - These are unconsolidated, poorly sorted deposits of weathered and rounded rocks and sediments that range in size from the finest clays to the largest boulders. Since glaciers sometimes carried these materials hundreds of miles, they can include any rock types. Nevertheless, they are easily identified by their rounded to subrounded appearance.
b) Sandstone - This rock type consists of thousands of sand grains that have been naturally cemetered together by a kind of 'rock glue' (typically silica but sometimes calcium carbonate or iron oxides). Typically, the individual sand grains are visible to the naked eye.
c) Limestone/Dolomite - These rocks form on the ocean floor and are crystalline in nature, meaning they consist of calcite crystals that grow together to form the rock. Dolomite forms from limestone when some of the calcium in the stone is replaced by magnesium, making it less susceptible to weathering. Because they form on the ocean floor, both often contain fossils. They are typically a grey or bluish-grey color.
d) Shale - This sedimentary rock has a high clay content and will often contain many organics, causing it to be dark grey or black in color. The clay particles align with one another, forming very thin bands in the rock that will peel apart from one another like pages in a book. Geologists call this property fissility.