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|Time divisions
divisions of geologic time based on intervals of interpreted contrasting climates; boundaries are not synchronous
glacial/interglacial
stage & substage: e.g. Wisconsin Stage; early , middle & late substages
stadial/interstadial within substages
phases: geologic events, not time periods
Late Ice Age divisions
Illinoian Glaciation: 302,000- 132,000 YBP
Early Illinoian and Late Illinoian
Sangamon Interglacial: 132,000 - 115,000 YBP or 75,000 YBP
Wisconsin Glaciation 115,000 or 75,000 - 10,000 YBP
Early Wisconsin
Middle Wisconsin
Late Wisconsin: 25,000-10,000 YBP
Lithostratigraphic units
formation: fundamental unit in stratigraphy
defined by lithology; e.g. color, grain size distribution, mineralogy
and defined by stratigraphic position; conforms to Law of Superposition
sufficiently widespread to be mappable at regional scale
member: a named unit within a formation; names are geographical
has characteristics that distinguish it from neighboring parts of formation
not all formations have named members
some formations may have only certain parts defined as named members (i.e. the entire formation may not be divided into named members)
law of superposition: younger units overlie older units
younger units truncate older units
younger units are behind older units
Pierce Formation: grey to brown; silt-rich; kaolinite-rich
Kinnickinnic Member: lacustrine silt & clay from pro-glacial lakes
Hersey Member: till
Woodville Member: till (first recognized ice advance in Wisconsin)
Eau Galle Member: lake sediment; possible pro-glacial lake from advance that deposited Woodville Member
Marathon Formation: thin, discontinuous; calcareous, silt-rich, highly weathered
Edgar Member: till; Marshfield moraine
Medford Member: till
Wausau Member: silt-rich, highly weathered till
River Falls Formation: reddish brown, sandy till; basalt & red sandstone clasts from Lake Superior region
deeply weathered during Sangamon
extensively eroded; no primary glacial topography
overlies Pierce formation
Lincoln Formation: reddish brown, sandy till; basalt & red sandstone clasts from Lake Superior region
Bakerville Member: till
not deeply weathered, but extensively eroded; no primary glacial topography
Walworth Formation: yellowish brown, silt-rich to sandy till; abundant dolomite
from Lake Michigan lowland
- become more eroded from east to west
Pre 25 ka YBP; pre early- and middle-Wisconsinan
Lincoln Formation: reddish-brown, sandy till
little-moderate stream incision; mildly weathered; units Ltr, gm & gmh
Merrill Member: some low hummocky topography & streamlined landforms
till plain: gently rolling topography (unit gm) or slightly hilly (unit gmh)
Zenda Formation
Capron Member
Introduction
ice crossed southern Lake Superior drainage divide ~26,000 YBP
Green Bay and Langlade Lobes advanced over northeastern Wisconsin by ~20,000 YBP
ice reached maximum extent by~ 20,000-18,000 YBP
ice stayed at maximum until ~15,000 YBP
ice sheet melted from northeastern Wisconsin before ~12,000 YBP
Woodfordian substage
Superior Lobe - Copper Falls Formation
Poskin Member: till; indistinct landforms
Sylvan Lake Member: St. Croix moraine; hummocks, ice-walled lake plains, tunnel channels; dominated by sand
Superior Lobe - Miller Creek Formation
silt & clay rich till derived from lake sediments
After Clayton et al. (2006) WGNHS Ed. Series 36
Copper Falls Formation: yellowish-red to reddish brown till; slightly to gravelly sandy loam; leached of carbonates; very coarse sand & pebble fractions predominantly igneous & metamorphic
Chippewa Lobe - Copper Falls Formation
end moraines: Late Chippewa, Perkinstown
sharp-crested ridge; ahead: outwash fans; behind: up to 20 km wide band hummocky topography, ice-walled lake plains, supraglacial sediment; another ridge & outwash fans; tunnel channels
Wisconsin Valley Lobe - Copper Falls Formation (Wildcat Lake Member)
end moraines: Harrison (truncates Parrish moraine)
ridge; hummocky topography; ice-walled lake plains
Langlade Lobe - Copper Falls Formation (Nashville Member)
end moraines: Parrish (truncates Hancock); Summit Lake
ridge; hummocky topography; ice-walled lake plains
zone of drumlins farther up-glacier (north) oriented NE to SW
in places underlain by Lincoln, Marathon, and Holy Hill Formations
Holy Hill Formation: brown sandy till
Green Bay Lobe - Holy Hill Formation
Wisconsin Valley, Chippewa & Superior Lobes melted back prior to Green Bay and Langlade Lobes
Ice flowed northwestward at the northwestern margin of the lobe
Mapleview Member: yellowish-brown or brown, sandy till, calcareous, granitic clasts from Wolf River Batholith
Hancock end moraine; Almond recessional moraine
single ridge end moraines; 10-20 m high & 0.5-1.0 km wide; steep front; tunnel channels
Keene Member:
Arnott end moraine
non- to slightly calcareous, brown to reddish brown sandy till, granitic clasts from Wolf River Batholith
more weathered and eroded than Mapleview Member
most likely Illinoian or older in age
Horicon Member: brown till; gravelly, clayey and silty sand; dolomite is generally most common pebble type
compared to Mapleview, Horixon is slightly finer textured, contains less quartz & more dolomite
Johnstown end moraine: sharp-crested ridge, 5-10 m high & 20-100 m wide
- ~10 km wide hummocky zone
stubby drumlins: 0.2-0.4 km wide, 0.5-2.0 km long, 10-30 m high, length/width ratios of 2:1 to 10:1, non-uniform orientation
spindly drumlins: several m high, up to 10 m wide, up to 3.0 km long, length/width ratios may be >100:1, uniform orientation
Green Bay Lobe - Kewaunee Formation: reddish-brown clayey till
ice retreated to north end of Lake Michigan basin; water & reddish-brown sediment flowed from Lake Superior basin into Lake Michigan basin
Silver Cliff Member: reddish brown sandy till
Kirby Lake Member: reddish brown, dolomitic, silty-clayey till; gently rolling low relief topography
Middle Inlet Member: reddish brown, less clay than Kirby Lake; relatively flat topography
Intersection of Green Bay & Lake Michigan Lobes - Kewaunee Formation
Age relationships (from youngest to oldest)
Green Bay: Middle Inlet & Glenmore = Lake Michigan: Two Rivers
Green Bay: Kirby Lake & Chilton = Lake Michigan: Valders
Green Bay: Silver Cliff = Lake Michigan: Ozaukee
Two Creeks buried forest sequence:
Lacustrine sediments
Two Rivers Member Kewaunee Fm
Lacustrine sediments
Two Creeks buried forest & paleosol in lacustrine sediments
Valders Member Kewaunee Fm
Image credit: NOAA National Geophysical Data Center. http://www.ngdc.noaa.gov/mgg/greatlakes/lakemich_cdrom/html/geomorph.htm
After Clayton et al. (2006) WGNHS Ed. Series 36
Green Bay Lobe - Oak Creek Formation: grey silty-clay till
Des Moines, Superior, Chippewa, Wisconsin Valley, & Langlade Lobes
Miller Creek Formation
red silt & clay-rich till from Lake Superior basin
topography modified by lake or wave action
Copper Falls Formation
reddish-brown, sandy till, slightly calcareous, igneous & metamorphic clasts from Lake Superior basin
broad hummocky end moraines with ice-walled lake plains & tunnel channels
River Falls Formation & Lincoln Formation
reddish-brown sandy till, basalt & red sandstone clasts from Lake Superior basin
no primary glacial topography; extensively eroded
Marathon Formation & Pierce Formation
yellowish or greyish-brown, silt-rich till or lacustrine sediment
no primary glacial topography
Green Bay & Lake Michigan Lobes
Kewaunee Formation
reddish clay till
subdued topography
Oak Creek Formation: grey silty-clay till
Holy Hill Formation
brown, sandy till, calcareous, clasts from Wolf River Batholith
single-crest moraines, tunnel channels; drumlins behind end moraines where bed wasn't frozen
After Clayton et al. (2006) WGNHS Ed. Series 36
