Contact of Morton Gneiss and Sacred Heart Granite

New Ulm Quartzite Quarry

Dan Chies and Amanda Shield: Stop #1b

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Location: New Ulm Quartzite Quarry, south east of New Ulm in Nicollet County, just south of Highway 14.  SW Section 35, Township 110, Range 30 west.

Location 1B is an abandoned quarry, slightly south of the main quarry 

Brief Description: In the abandoned south end of the New Ulm Quartzite Quarry lie some unique outcrops.  Made up of a weathered purplish-pink meta-sedimentary crystalline rock, it is, of course, a continuation of the Sioux Quartzite as seen in stop 1A.  It consists of inter-locking quartz grains and occurs in repeated graded beds up to two meters thick.  Generally, the outcrop is a deeper purple color and finer grained toward the top and a lighter purple and courser grained towards the bottom (Fig 1b-A).  There are also occasional clay/shale layers interbedded with the quartzite. These shale layers are one to two feet thick.

(Fig. 1b-A) the rock up-close

More Info: However, this site offers another interesting aspect that the northern part of the quarry does not. The top of the outcrop remains untouched from the mining and still displays signs of ancient glaciations and water flow in the area.  Well-defined hummocks and swales run the length of the top of the outcrop, along with occasional mud cracks, and cross-trough stratification is visible on the side of the outcrop.(Fig. 1b-D)  The hummocks are a result of the outwash from ancient Lake Agassiz and Glacial River Warren, whose waters ripped through the area roughly 10,000 years ago (Dogwiler 2003).

^(Fig. 1b-B) A map of Lake Agassiz ~10,000 yrs. BP (www.dnr.state.mn.us, 2003)^

Geologic History of the Area:

During the last ice age, the Laurentide Ice Sheet advanced slowly across the continent.  Many glacial lakes formed at this time, and one that covered a large chunk
northwestern Minnesota, the Dakotas, and portions of Manitoba was Lake Agassiz (Fig 1b-B)(Hu 1997).  The Glacial River Warren drained this lake toward the south. As the last ice age wound down, Lake Agassiz and River Warren underwent dramatic change.  When the ice dam blocking Lake Agassiz could not hold her contents anymore, her waters surged down Glacial River Warren.  River Warren turned from a peaceful outflow river (Fig 1b-C) to a gushing torrent of muddy sediments (Clarke 2003).

^(Fig. 1b-C) Remnants of Glacial River Warren?, with outcrop in foreground.^

Effects of the Outwash:

This tremendous outflow traveled southeast toward what would one day be known as the New Ulm Quartzite Quarry.  Our poor outcrop stood in the path of billions upon billions of gallons of rapidly moving water. Lake Agassiz discharged enough water to lower a lake larger than 110,000 square miles by 46 meters (Fisher 1993).  This water was moving so fast and so hard that it gouged out hummocks in the hard metamorphic quartzite See Fig. 1b-E and 1b-F.

^(Fig 1b-D) view of outcrop from the North^

^(Fig 1b-E) close-up of hummocks^

^(Fig 1b-F) more hummocks^

References: 

Clarke, G., Leverington, D., Teller, J., and Dyke, A., 2003.  Superlakes, Megafloods, and Abrupt Climate Change:  Science Vol. 301, p.922-923.

Fisher, Timothy G., and Smith, D.G., 1993.  Glacial Lake Agassiz: The northwestern outlet and paleoflood:  Geology v.21, Jan. 1993, p. 9-12. 

 Hu, Feng Sheng, Wright, Jr H. E., Ito, E., and Lease, K., 1997.  Climatic effects of glacial Lake Agassiz in the Midwestern United States during the last deglaciation:  Geology, v. 25, no.3, p. 207-210.

 No author listed, last updated 2003.  “Glacial Lake Agassiz Map.”  http://www.dnr.state.mn.us/rprp/claycounty/lakeagassiz.html.  Accessed on 11/20/2003.

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