SIOUX QUARTZITE in Wahoo EarthCache

This EarthCache is located at the SAUNDERS COUNTY HISTORICAL SOCIETY MUSEUM in Wahoo NE. The coordinates for this EarthCache will take you to a large Sioux Quartzite Rock in front of the museum.  By studying this Rock you will learn about geological dating and Sioux Quartzite. 

Information needed to Log this Cache must be obtained at the entrance desk to the museum. At the front desk ask for the hand out: “TWIN ROCK MARKER”. This handout contains information necessary to answer some of the required questions.

PERMISSION TO PLACE THIS CACHE was provided by the Saunders County Historical Society.

You MUST visit the museum during OPEN hours to obtain the handout. For hours check the website: http://www.saunderscomuseum.org. The Museum is closed on Mondays and is usually open from 10am to 4pm. From October through March it is also closed on the weekends. If you are traveling through the area and wish to Log this EarthCache during closed hours you may arrange to meet the CO and get a copy of the Handout.

LOGGING REQUIREMENTS

Answers will be found in the text, in the handout available at the museum and by physical examination of the “Twin Rock” in front of the museum entrance. Send your answers by email to the CO of this EarthCache. Do not post the answers with your Log. Share a picture if you would like (optional) and post a note in your log if you spent time at the Museum.

1) What type of “Dating” process was used to determine the Absolute Age of the Sioux Quartzite in Pipestone, MN. ______________________________

2) a. What is the geological EON when Sioux Quartzite was formed? __________________

b. Is this an example of Absolute Time or Relative Time? _________________________

3) a. How much does the Sioux Quartzite in front of the museum weigh? _______________

b. Estimate the height, width, and length of this rock. Hgt ______ Wdt ______ Lgt _______

4). Where was this Rock moved from to its present location? __________________________

5). This Rock was one of two markers along what Trail? __________________________

GEOLOGICAL TIME

Time is measured in a number of ways. For example: A decade is 10 years. 1 Year is 12 Months or 365/6 days; 1 Day is 24 hours; 1 hour is 60 minutes; and 1 minute is 60 seconds. Geological Time is also measured in units of time within units of time. The major units of Geological time use the following classifications: Eon, Era, Period, Epoch, and Age. Following are examples of the breakdown of some of these time periods.

1) EON: Two or more geological “ERAS” form and “EON”, which is the largest division of geological time, lasting hundreds of millions of years.

2) ERA: “EONS” are divided in to smaller divisions called “ERAS”.

3) PERIOD: “ERAS” are divided up into “PERIODS” which are smaller units of time.

4) EPOCH: “PERIODS” are divided up into smaller units called “EPOCHS”.

5) AGE: “EPOCHS” are further divided up into still smaller time units call “AGES”.

ABSOLUTE TIME – DATING

Trying to figure out the age of a rock isn’t easy, but it can be determined. Absolute Dating is a process to determine the geological age of an object, such as a type of rock formation. Through the development of Radioactive Decay, Radiocarbon dating is used to measure the span of time it takes certain radioactive isotopes to decay. One method that is commonly used is Uranium-Lead dating which allows the determination of absolute ages for some of the oldest rocks on earth. Potassium-Argon Dating is another method used for earlier periods.

RELATIVE TIME – DATING

Geologist will date earth and rock formations by comparing similar types to one another in relationship to the layers they form in the Earth’s surface. By comparison of layers geologist can date one layer in relationship to another. It is the science of determining the relative order of past events without necessarily determining their absolute age. One obvious conclusion of note, is the older layers will be deeper than more recent layers.

SIOUX QUARTZITE

“The Sioux Quartzite is a Proterozoic Quartzite that is found in region around the intersection of Minnesota, South Dakota, and Iowa, and correlates with other rock units throughout the upper Midwestern and southwestern United States .

[The Proterozoic Time is a geological eon representing the time just before the proliferation of complex life on Earth.]

It was formed by braided river deposits, and its correlative units are thought to possibly define a large sedimentary wedge that once covered the passive margin on the then-southern side of the North American craton. In human history, it provided the catlinite, or pipestone, that was used by the Plains Indians to carve ceremonial pipes. With the arrival of Europeans, it was heavily quarried for building stone, and was used in many prominent structures in Sioux Falls, SD and shipped to construction sites around the Midwest. Sioux Quartzite has been and continues to be quarried in Jasper, MN at the Jasper Stone Company and Quarry, which itself was posted to the National Register of Historic Places on January 5, 1978. Jasper MN contains many turn-of-the-century quartzite buildings, including the school, churches and several other public and private structures, mostly abandoned.”²

“Quartzite is a metamorphic rock formed from layers of small to medium rounded grains of quartz that have been cemented together by silica, it is so strong that it breaks across the grain instead of around it. Quartzite is between 1.6 and 1.7 billion years old, making it some of the oldest and hardest rock in the world. Though commonly pink or red, the color varies over a wide range due to the presence of a thin film of iron oxide coating the grains of quartz. Quartzite that has been exposed is an outcropping that has been caused by some element of erosion, primarily water, taking away the “blanket” of glacial drift.

Sioux quartzite outcroppings are the area’s most unique geological feature. The outcrops of Sioux quartzite start at Redstone in East New Ulm, MN and extend 180 miles west to Rockport Colony along the James River, south of Mitchell, SD. The north-south band of outcrops is about 40 miles wide. The unexposed quartzite, a sub crop, covers a much broader area extending west of the Missouri River. The whole area is referred to as The Sioux Ridge Quartzite is a metamorphic rock formed from layers of small to medium rounded grains of quartz that have been cemented together by silica, it is so strong that it breaks across the grain instead of around it. Quartzite is between 1.6 and 1.7 billion years old, making it some of the oldest and hardest rock in the world. Though commonly pink or red, the color varies over a wide range due to the presence of a thin film of iron oxide coating the grains of quartz. Quartzite that has been exposed is an outcropping that has been caused by some element of erosion, primarily water, taking away the “blanket” of glacial drift.

Sioux quartzite outcroppings are the area’s most unique geological feature. The outcrops of Sioux quartzite start at Redstone in East New Ulm, MN and extend 180 miles west to Rockport Colony along the James River, south of Mitchell, SD. The north-south band of outcrops is about 40 miles wide. The unexposed quartzite, a sub crop, covers a much broader area extending west of the Missouri River. The whole area is referred to as The Sioux Ridge.”³

GEOLOGY OF THE SIOUX QUARTZITE

“The Sioux Quartzite is a red to pink Proterozoic quartzite. It is a thick stratigraphic unit (~3000 m‬) that crops out in southwestern Minnesota, southeastern and south-central South Dakota, northwestern Iowa, and a small part of northeastern Nebraska. It is correlated with other sandstone and quartzite units across Wisconsin (at Rib Mountain, Baraboo, Barron, Waterloo, and Flambeau), southeastern Iowa, southern Nebraska, and north-central New Mexico and southeast-central Arizona (Ortega, Mazatzal, and Deadman Quartzite).

Its age is constrained to be between 2280 ± 110 Ma from the URANIUM-LEAD DATING of a Rhyolite that underlies it in northwestern Iowa, and 1120 Ma from a POTASSIUM-ARGON DATING of deformation of the Sioux Quartzite in Pipestone, Minnesota.

[Ma (for megaannus), is a unit of time equal to one million years.]¹

Its ABSOLUTE AGE age can be better-constrained by extrapolation correlative units to between 1760 ± 10 Ma.‬ and 1640 ± 40 Ma.

This period in which The Sioux Quartzite and its correlative units were deposited is known as the Baraboo interval, in which high relative sea levels covered a large amount of North America. The Sioux quartzite was primarily formed by braided river deposits, of quartz arenite composition, with 95% of the rock being composed of rounded, fine to medium (0.125–0.5 mm) sand-size quartz grains. The rivers are believed to flow southeast, at a relatively shallow gradient. Its basal conglomerate is thought to be braided stream deposits that are more proximal to the source, and there is possible marine influence on the upper part of the unit – this interpretation is supported by evidence of marine sediments (shales and banded iron formations atop its correlative unit in Baraboo, Wisconsin.

In addition, the unit contains ~1 meter beds of claystone, which are known as Catlinite or Pipestone, because these beds were used by the natives of the area to carve pipe bowls. It is thought that the Sioux Quartzite and its correlative units are parts of a once-laterally-extensive sedimentary wedge that covered the then-southern passive margin of the North American craton.

The Sioux Quartzite is extremely resistant to erosion, and has formed a topographic high through most of Phanerozoic time. It was inundated by Phanerozoic seas during the periods of maximum sea level, and subsequent erosion removed these sedimentary units. For this reason, the only geologic units to sit atop the Sioux Quartzite are of Cretaceous age, deposited when a large portion of North America was covered by the Cretaceous Interior Seaway.

Many present-day outcrops of Sioux Quartzite were exposed by glacial erosion during the Quaternary. Some of these have been dated with the cosmogenic radionuclides and aluminum-26 to determine how long ago the Laurentide Ice Sheet retreated from the Upper Midwest. These dates show that southwestern Minnesota was last covered in glacial ice at least 500,000 years ago.”²

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This EarthCache was designed as part of the EarthCache Academy project for the Course GEOLOGICAL TIME designed by Gary Lewis. For more information on the EarthCache Academy goto: www.earthcacheacademy.org.

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Footnote References:

1: https://en.wikipedia.org/wiki/Year#SI_prefix_multipliers

2: https://en.wikipedia.org/wiki/Sioux_Quartzite

3: http://siouxquartzite.com/what-is-sioux-quartzite/

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