Pebbles in tills of Minnesota
Simplified bedrock over topography
Simplified map of ice lobe sources
Generalized provenance and till character
Deposits left by glaciers are the "footprints" that allow geologists to retrace the history of glacier movement. Till of a particular color and containing distinct rock types may indicate the direction from which the glacier advanced. In Minnesota, where the glacial history is complex, it is important to be able to determine where and when a glacier originated.(from: Minnesota at a Glance: Quaternary Glacial Geology.)
Additional information:
Use of 1-2 mm sand grain composition in Minnesota Quaternary Studies; From_RI 49, page 193.
End member example of Riding Mountain provenance; 8-16 mm fraction from
site N4 of Thorleifson et al. (2007);
from left to right, Cretaceous shale, Paleozoic carbonate, felsic intrusive
and high grade metamorphic, dark metasedimentary
and metavolcanic, and from top down, reddish volcanic, ironstone, and
quartzite.
WINNIPEG PROVENANCE---Northern Source Area
End member example of Winnipeg provenance; 8-16 mm fraction from site
U13 of Thorleifson et al. (2007);
from left to right, Cretaceous shale, Paleozoic carbonate, felsic intrusive
and high grade metamorphic, above mafic intrusive and high
grade metamorphic, and from top down, dark metasedimentary and metavolcanic,
quartzite, reddish volcanic,and ironstone.
RAINY PROVENANCE---North-Northeastern Source Area
End member example of Rainy provenance; 8-16 mm fraction from site S10
of Thorleifson et al. (2007);
from left to right, felsic intrusive and high grade metamorphic, dark
metasedimentary and metavolcanic,
and from top down, sandstone and quartz; elsewhere, felsics may dominate.
SUPERIOR PROVENANCE---Northeastern Source Area
End member example of Superior provenance; 8-16 mm fraction from site
O11 of Thorleifson et al. (2007);
from left to right, felsic intrusive and high grade metamorphic above
ironstone, dark metasedimentary and metavolcanic,
and from top down, mafic intrusive and high grade metamorphic, quartzite,
and sandstone and finally, reddish volcanic rocks.
