Pleistocene -Pleistocene -the Ice Agesthe Ice AgesSleeping Bear Dunes National LakeshoreSleeping Bear Dunes National LakeshorePleistocene - the Ice Ages•• Stage is now set to Stage is now set tounderstand the nature ofunderstand the nature offlora and vegetation offlora and vegetation ofNorth America and GreatNorth America and GreatLakesLakes•• Pliocene (end of Tertiary) Pliocene (end of Tertiary)- most genera had already- most genera had alreadyoriginated (in palynofloras)originated (in palynofloras)•• Flora was in place Flora was in place•• Vegetation units (biomes) Vegetation units (biomes)already derivedalready derivedVegetationFloraThe vegetation and flora as we see it now (Holocene) was dramaticallyThe vegetation and flora as we see it now (Holocene) was dramaticallyaffected by Pleistocene eventsaffected by Pleistocene eventsPleistocene - the Ice Ages•• In the Pleistocene, earth In the Pleistocene, earthexperienced intensification towardsexperienced intensification towardsclimatic coolingclimatic cooling•• Culminated with a series of glacial- Culminated with a series of glacial-interglacial cyclesinterglacial cyclesPleistocene - the Ice Ages•• North American flora and North American flora andvegetation profoundly influenced byvegetation profoundly influenced bythese these ““ice-ageice-age”” events events•• Wisconsin glaciation (last epoch) Wisconsin glaciation (last epoch)most importantmost important•• Assembly of Assembly of floraflora and and vegetationvegetation of ofmost Great Lakes was during the latemost Great Lakes was during the latePleistocene and Holocene - (18,000Pleistocene and Holocene - (18,000years ago to present)years ago to present)Pleistocene - the Ice Ages•• In the Pleistocene, earth In the Pleistocene, earthexperienced intensification towardsexperienced intensification towardsclimatic coolingclimatic cooling•• Culminated with a series of glacial- Culminated with a series of glacial-interglacial cyclesinterglacial cycles•• North American flora and North American flora andvegetation profoundly influenced byvegetation profoundly influenced bythese these ““ice-ageice-age”” events eventsLouis Agassiz [1807-1873]•• Swiss geologist who studied mountain Swiss geologist who studied mountainglaciation in Europeglaciation in Europe•• First scientist to articulate continental First scientist to articulate continentalglaciation in the northern hemisphereglaciation in the northern hemispherebased on landscape features he based on landscape features he ““readread””in eastern North Americain eastern North America•• His subsequent studies of North His subsequent studies of NorthAmerican glacial evidence beganAmerican glacial evidence beganthe study of the field ofthe study of the field ofcontinental glaciationcontinental glaciation•• Evidence for continental Evidence for continentalglaciation is overwhelmingglaciation is overwhelmingPleistocene - the Ice AgesWhat evidence did Agassiz see?•• ice scouring (rock markings, flat ice scouring (rock markings, flatplains,U-shaped river valleys, erratics)plains,U-shaped river valleys, erratics)•• glacial till (outwash, direct deposit) glacial till (outwash, direct deposit)•• drainage channels drainage channels•• temporary glacial lakes temporary glacial lakes•• kettles (permanent lakes formed by ice kettles (permanent lakes formed by icechunks)chunks)•• moraines moraines•• perched dunes perched dunes•• plant and animal plant and animal ““disjunctdisjunct”” distributions distributionsPleistocene - the Ice Ages•• Terminal moraines are some of the most are some of the mostvisible visible ““footprintsfootprints”” of glaciers of glaciers•• formed as ice front formed as ice front ““stagnatedstagnated”” for a time for a timeand deposited large amounts of unsortedand deposited large amounts of unsortedrock, pebbles, sand, and clayrock, pebbles, sand, and clayPleistocene - the Ice Ages•• Terminal moraines (often (oftenfrom different lobes) arefrom different lobes) areevident from past glacialevident from past glacialstages - before the laststages - before the lastWisconsin stageWisconsin stageLast 3 glacial and interglacialLast 3 glacial and interglacialstages in Illinoisstages in IllinoisPleistocene - the Ice Ages•• Glacial lakes - now gone or - now gone orreduced - formed as glaciers firstreduced - formed as glaciers firstbegan meltingbegan melting•• Wisconsin Dells and Devil Wisconsin Dells and Devil’’s Lakes Lakegeology is largely due to suchgeology is largely due to suchglacial eventsglacial eventsPleistocene - the Ice Ages•• Perched dunes —— as in Sleeping as in SleepingBear Dunes National Landscape Bear Dunes National Landscape ——provide evidence of higher Lakeprovide evidence of higher LakeMichigan water levels during iceMichigan water levels during iceretreatretreatPleistocene - the Ice Ages•• Erratic boulders - such as this boulders - such as thisPetoskey Stone at the top of aPetoskey Stone at the top of aSleeping Bear Dune moraine -Sleeping Bear Dune moraine -also are evidence of glacialalso are evidence of glacialactivityactivityPleistocene - the Ice Ages•• Perched dunes —— as in Sleeping as in SleepingBear Dunes National Landscape Bear Dunes National Landscape ——provide evidence of higher Lakeprovide evidence of higher LakeMichigan water levels during iceMichigan water levels during iceretreatretreatLake sediment pollenLake sediment pollenprofile through timeprofile through time•• Pollen profiles in lake or bog sediments/peat show sweep of vegetation in lake or bog sediments/peat show sweep of vegetationand flora through time in once ice-covered regionsand flora through time in once ice-covered regionsPleistocene - the Ice Ages•• Disjunct distributions of arctic species at edges of glacial advances inof arctic species at edges of glacial advances inWisconsin River Dells and Kickapoo River valley a lot further southWisconsin River Dells and Kickapoo River valley a lot further souththan expected for the species suggest than expected for the species suggest ““left behindleft behind”” scenarios scenariosArctic Arctic ““birdbird’’s-eye-primroses-eye-primrose”” distribution in Wisconsin distribution in WisconsinPleistocene - the Ice AgesEvidence for Pleistocene glaciation cycles?Evidence for