Monday, April 16, 2012

Minnesota Geology Monday - Conglomerate

On the south side of US highway 14 near New Ulm, justwest of the intersection of County Road 37 is a small outcrop of Proterozoic conglomerate.  The location is across the Minnesota River from New Ulm, though within the river valley.  The outcrop itself is small, fairly covered by grasses, mosses and other plants.

The conglomerate is lies above Archean gneisses and is the base of the early Proterozoic Sioux Quartzite.  The 1,700 million year old Sioux Quartzite is found throughout SW Minnesota, NE Iowa and South Dakota and correlates well with other quartzites in other states like the Baraboo Quartzite in Wisconsin.

Pieces of the Archean gneisses are incorporated into the conglomerate.  Over one billion years of weathering of these gneisses occurred before being cemeted into the conglomerate.  This basal conglomerate is interpreted to be braided stream deposits close to the source rock.

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