Sioux Quartz EarthCache EarthCache
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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 (mega annum -
million years ago) from the Uranium-Lead dating of a rhyolite that
underlies it in northwestern Iowa, and 1120 Ma from a
Potassium-Argon date of deformation of the Sioux Quartzite in
Pipestone, Minnesota. Its 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 Federal Building in Sioux Falls, South Dakota was constructed
with Sioux quartzite from nearby quarries.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. To
log this find you must perform the following tasks:
To log this EarthCache you MUST perform the following tasks:
Note: Additional waypoints have been supplied.
Any logs without the following questions answered will be
deleted. You must visit all 3 locations to be able to log this
EarthCache.
Location A (EarthCache Location):
1) QUESTION - Read the sign and Email me (or via the message
button) answers to the following question: How old is the
Precambrian Rock?
2) OPTIONAL PHOTO - Post a photo in your log showing the Sioux
Quartz Paving Stones. Please be careful of any traffic. The photo
does not need to be taken on the road.
Location B (Old Court House Museum - ( N 43° 33.073 W 096° 43.742
)
1) QUESTIONS - Examine the Sioux Quartz on the Old Court House
Museum and Email me (or via the message button) answers to the
following question:
a. Do you see any cross-bedding in the Sioux Quartzite on the Old
Court House Museum?
b. Do you see any weathering to the Quartz?
2) OPTIONAL PHOTO - Post a photo in your log showing the Sioux
Quartz at the Minnehaha County Old Court House Museum.
Location C ( N 43° 32.580 W 096° 43.599 )
1) QUESTION: Read the infornmation sign & Email me (or via the
message button) the answer to the following question: - Which
quarry supplied the Sioux Quartz for this building?
2) QUESTION: Just south of the information sign on a wall made of
Sioux Quartz you will find an old rusty sign. What are the words on
this sign?
Additional Question: (This information can be found on this page):
Email me (or via the message button) the answer to the following:
Name the period in which the Sioux Quartzite and its correlative
units were deposited?
Additional Hints
(No hints available.)
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