Surficial Geology of Findlay EarthCache
Surficial Geology of Findlay
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An earthcache placed for International Earthcaching Day 2016, and is located at Emory Adams Park. Placed with permission of Findlay's Recreation Department, please restrict caching to posted hours.
We will be using the Surficial Geology of the Findlay 30x60 Minute Quadrangle, found in the related link or here. It is a large file so it may not load on a phone.
SURFICIAL GEOLOGY
'Surficial Geology' is the study of the land, specifically of the sediment and bedrock. Sediments, such as clay or gravel, are not the soils immediately beneath your feet; there are sandwiched between the soil at 'ground level' and the bedrock far beneath. As you can see from the map, the area is far from uniform, due to a variety of factors. Typically, water is the main source of sediment being moved around. Glaciers have played by far the biggest role, moving sediment anywhere from 21,000 to 13,500 years ago. Rivers, lakes, and other bodies of water have had more recent effects on sediment displacement. Even humans can have an impact on sediment migration- typically with labor projects. A local example would be construction of the Findlay airport.
SURFICIAL UNITS
Also known as lithographic units, surficial units refer to a standardized definition of a particular combination of sediments from a specific time frame. For example, a common unit in the Findlay Quadrangle is Clay Loam/Loamy Till, an unsorted mix of silt, clay, gravel, and sand. It is formed from an overlap of several glacial movements. These units are used on a state and federal level (i.e. maps of nearby quadrangles or states would also use the same name and definitions for Clay Loam/Loamy Till).
This map also depicts Bedrock Units- measurements of the solid rock beneath the sediment. The same standardized definitions are in place. In the Findlay quadrangle, four types of Bedrock are found- Shale, Limestone, a Shale/Limestone hybrid, and Dolomite- the predominant bedrock found in the area.
DATA COLLECTION & GENERAL FEATURES
Maps like these rely on numerous data sources (see the extensive references list on the map). County soil surveys (which document the first 5 feet of sediment) were used as a foundation for research. The information was then updated using a wide variety of other sources (water well logs, EPA records, field notes, etc.) This latter data helped form the surficial units on the map. The depth of the surificial deposits was calculated based on local topographic maps. The bedrock data is based on previous bedrock mapping projects. Finally, all the data is condensed and drawn into the map you now see.
This map of surficial geology is broken down into 4 key aspects:
- Geologic deposits (of sediment)
- The depth of these deposits
- The area covered by a particular sediment
- A cross-section of the layers of sediment and bedrock
This information can be useful for a variety of reasons- agriculture, construction, construction, and research, just to name a few uses. The map summarizes geologic features, engineering properties, depositional environment, geomorphology, and geographic location.
READING THIS MAP
The map provides a lot of information, which is broken down into several major elements. The most important ones are the black text throughout the map, written like a division problem (with a numerator and denominator). The cross section near the bottom of the map can help you interpret these readings. Here's an example:
The map includes major roads and county lines (both in light gray) and water features, which can be used to find your location on the map. The major elements are as follows:
- Surficial Units- displayed on the map as both the color of a given area, as well as the numerator (top half) of the black text readings taken throughout the region. A key is listed on the far left side of the map, including a description of the unit, as well as its time period of origin. Note: There can be multiple layers of different sediments in one place- each layer as its own line in the black text readings.
- Bedrock Unit- displayed on the map as the denominator (bottom half) of the black text readings on the map, measured throughout the quadrangle. Its descriptions and time periods are listed on the left side of the map, beneath the Surficial Unit information.
- Depth Numbers- Next to some Surficial Units, there is a number. This denotes the depth of the sediment in multiples of ten feet- for example, a reading of S4 implies forty feet of Sand. No number implies a default of 10 feet of sediment.
- Explanations- A legend of additional markings on the map, such as organic deposits, quarries, sand/gravel pits, and boundaries between surficial areas.
- Scale- Immediately below the map, this provides the ratio of distance on the map to real world distances, as well as a translation of inches to miles or kilometers. This map's scale is 1:100,000- that is, 1 inch on the map is 100,000 inches in real life, or approximately 1.57 miles.
- Cross Section- a side view of terrain- a slice of a hypothetical piece of land to see a vertical perspective to the black text readings' meaning.
- Mapping Responsibilities- a representation of the townships on the map, colored to which member of the Ohio Geological Survey took, complied, or researched measurements for that area.
- Acknowledgements/References- a list of people and sources that were utilized in constructing the map.
Please answer the following questions to complete this earthcache. Send your answers via the email link or message link on my profile- logs without an email or message will be deleted.
- What are the Surficial Unit and Bedrock Unit at the posted coordinates? If you need help locating yourself on the map, see the hint.
- What is the depth of the Surficial Unit at this location?
- Why do you think this particular Surficial Unit is here? What brought it here & when?
- There is exposed rock in the water just east of the coordinates. Describe it in your email. Do you think this is the surficial unit, bedrock unit, or neither?
Additional Hints
(Decrypt)
[Finding your Location]: Ybbx sbe gur Svaqynl Nvecbeg be gur Svaqynl Erfreibve gb svaq lbhe trareny nern ba gur znc, gura ybbx sbe Rntyr Perrx.