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The Anatomy of a Glacial Cycle

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The Anatomy of a Glacial Cycle Pleistocene Glaciations Jarðsaga 2 Ólafur Ingólfsson Háskóli Íslands Classical glacial stratigraphy NW Europe N America Age Holocene interglacial Holocene interglacial 10-0 ka Weichselian glacial Wisconsinan glacial 120-10 ka Eemian Sangamonian 130-120 ka Saalian Illinoian 300-130 ka Holsteinian Yarmothian 430-300 ka Elsterian Kansan 560-430 ka Cromerian complex Aftonian 630-560 ka Until the 1970's it was believed that 4-5 Pleistocene glacial-interglacial cycles had occurred. This was based on the classical stratigraphy of Europe and N America. Quaternary stratigraphy After (Zagwijn, 1957) PLEISTOCENE STAGES Weichselian g g=GLACIAL - regression Eemian i i =INTERGLACIAL - transgression Saalian g Holsteinian i Elsterian g Cromerian i About 750000 yr BP Bavelian/Menapian gi Waalian ig Eburonian gi Tiglian ig Praetiglian gi ICE AGE CYCLES www.museum.state.il.us/exhibits/ice_ages/ Weichselian Saalian. Å Pre-Saalian Æ G =glaciations Classical stratigraphic division of the Quaternary From: Lowe & Walker 1998: Reconstructing Quaternary Environments. Harlow, Longman. >30 glacial- interglacial cycles We now know from deep sea sediments and ter- restrial stratigraphy that at least 8 glacial- interglacial cycles have occurred for the past 800 ka, and probably >30 such cycles since late Pliocene. Stratigraphy and environments of older glaciations poorly known... The information is often from mining pits or boreholes. Clay mine at Jaroszów, southwestern Poland. Tertiary clay (gray) is overlain by glacial sediments (brown). Such geology is typical through-out much of central Europe between the Baltic Sea and alpine mountains. Photo date 8/93; ©; by J.S. Aber. LITHOSTRATIGRAPHIC LOGGING 15 m structures scale •stratigraphy 10 • sedimentary structures • deformation structures •bed contacts 5 • colour • fossil content lithology fossils •erratics • lateral variations 0 f m c clay/silt sand pebbles mean grain size Sea level signatures Isostatic signature: The weight of kilometers of ice depresses continental crust. Localized sea level changes alters coastlines significantly. Relative sea level change due to loading and unloading. Rebound of crust after the ice melts can take thousands of years. Therefore: deglaciation signaled by transgression Eustatic sea level controlled by volume of ice At height of last interglacial, the sea stood 5-7 m higher than today. At the Last Glacial Maximum (LGM) global sea level was at -120 m. The figure shows oxygen isotopes and sea level changes for the last 140 ka, from late in the previous glacial period to the present. Increased glaciation means falling sea levels, deglaciation means rising sea levels and transgressions Composite stratigraphy, Kapp Ekholm, Svalbard The stratigraphy shows four till units, deposited by glaciers during glaciations. They are sparated by four coarsening up- wards marine-littoral units, showing de- glaciation and marine regression. RELATIVE AND ABSOLUTE DATING METHODS 1. Sidereal (calender/annual) varves, Tree-rings 2. Isotopic δ18O K/Ar or Ar/Ar-method Th/U Fission track (U/U isotopes) 3. Radiogenic 14C Thermoluminescence (TL), optical stimulated luminescence (OSL) electro spin resonance (ESR) 4. Chemical/biological pollen, amino-acid, lichenometry, tephra 5. Geomorphic Weathering, relative position 6. Correlations Lithostratigraphy, magnetostratigraphy Kapp Ekholm chronology based on 14C, TL/OSL and amino-acid datings Stratigraphic data used for constructing time- distance diagrams for glacial oscillations PRAETIGLIAN 1st Pleistocene cold stage (2,4 MY) • pollen spectra resemble Weichselian • trees: Betula, Pinus, Alnus • herbs and grasses dominate pollen diagrams The onset of true cold climates in the Praetiglian caused a marked change in depositional style with the input of gravel and sand; glaciation may already have been established in the Alps; ice-rafted blocks occur in Rhine sediments. TIGLIAN =Tegelen clay • Major Quaternary transgression • Poorly known environments, more stratigraphic information needed trees: Fagus (beech) herbs: water fern fauna: warm molluscs Also ice wedges (cold) CROMERIAN (~500 ka) Complex Originally named after Cromerian Forest Beds (UK), which are actually of Tiglian Age CROMERIAN I, A, II, B, III, C, IV Letters = glacials Numbers = interglacials We know that there was a continental ice sheet over NW Europe during the Cromerian... ELSTERIAN COLD STAGE (OIS 12, ~400-500 ka BP) Ice extent unknown: most till eroded by Saalian ice • Change in regional drainage (e.g. Elbe, Ice-dammed lakes) • Incised subglacial tunnel channels + troughs Origin: fluvioglacial/glacial/liquefaction ??? • Late-glacial glaciolacustrine clays (up to 150 m) UK: Anglian Glaciation Thames valley = southern margin Norfolk: interaction Scandinavian and British ice 5 tills but no interglacial N-Am: PRE-ILLINOIAN (formerly Kansan) The Elsterian middle Pleistocene glaciation We know that continental ice sheets advanced onto lowland NW Europe during the Elsterian glaciation. stages. The areas overridden by the ice were subjected to total landscape remodelling. Kansan glaciation landscape View over glaciated landscape, Wabaunsee County, northeastern Kansas. Erratic boulders of Sioux Quartzite are scattered in the foreground. The glaciation of Kansas took place >0.5 MY ago. Photo date 10/89; © by J.S. Aber. HOLSTEINIAN INTERGLACIAL Typesite= Sleswick-Holstein Major transgression: onset by isostatic depression Sites with Holsteinian deposits widespread Fossil soils, lacustrine and organic strata (diatoms), pollen UK: Hoxnian Interglacial typesite= Hoxne (Suffolk) Vegetational succession similar to the ‘continental’ N-Am: YARMOUTH Æ Typesite SE Indiana Æ organic deposits climate warmer and drier than Holocene SAALIAN COLD STAGE Start = nonglacial prolonged cold 2 ice advances (Drenthe and Warthe) MOIS stages 6-9 (?) Older, Middle and Younger Saalian Till UK: Wolstonian glaciation typesite= Wolston on Avon (Warwickshire) Limited ice extent compared to continent (why?) No contact between British and Scandinavian Ice sheets? N-Am: ILLINOIAN Æ Typesite Illinois: 8 tills/4 fossil soils Æ2 major glaciations ÆToronto: York Till ÆHudson Bay: 4 tills The Saalian Glaciation Glaciation during the Saalian had comparable effects to those seen in the prevois Elsterian Glaciation, causing major drainage diversion and landscape remodelling. Major ice- pushed ridges in the Netherlands and Maximum extent of the glaciation during the Germany forced the Saalian (late Middle Pleistocene - Marine Rhine to follow a more Isotope Stage 6 or ?8). southerly course. Saalian in NW Europe OLDER SAALIAN ADVANCE: PUSH MORAINES OF THE REHBURG PHASE From: Van der Wateren, 1995 and 1987 Saalian meltwater channel Subglacial meltwater channel (N-type) of Saalian age in Welzow Süd open-cast mine, Eastern Germany (Photo by J.A. Piotrowski) Saalian in Eurasia The Saalian glaciation was the most extensive glaciation recorded in Eurasia, particularily in the high arctic. Europe 150 ka BP The Great Glaciation The Illinoian or Great glaciation was the big one in N America, covering all but the highest summits of the Rockies, and burying Canada and the northern United States below ice. The last interglacial-glacial cycle We know very little about older glacial-interglacial cycles, and information on anything older than the second before the last (the Saalian) glaciation is very fragmentary. The Eemian was: • Oxygen isotope stage 5 (130,000-75,000 BP) or just substage 5e (130,000-115,000 BP) • Rapid warming at onset. 2-3°C warmer during the climate optimum than Holocene. Mid-latitudes slightly warmer than today, high latitudes considerably warmer. • Globally, ice volumes were smaller than during Holocene • Global sea levels were ~2-5 m higher than any time during the Holocene • Faunal and floral zones were considerably displaced towards North compared to Holocene. Widespread paleosols • Gradual cooling The Eemian-Sangamon interglacial Ice-core, marine and and paleobotanical data show Eemian warmer than Holocene Icecorerecordssuggestwarm Eemian on Greenland Greenland Inland Ice smaller than present during the Eemian – contributed to high global sea levels Biostratigraphical records from NE Greenland suggest Eemian was con- siderably warmer than Holocene. Birch grew on 72°N Eemian N America Eemian-Sangamon coastal waters considerably warmer than during Holocene – particularily at high latitudes. High arctic tundra areas considerably reduced compared to Holocene – tree line much further north, Eemian N America Birch and picea (“greni”) much further north than during Holocene. Birch forest in the arctic. Warm and moist airmasses penetrated the N American continent. Eemian Ocean warmer than present Thedifferencebetweenmodernandestimated February SST (in °C) during the Eemian, 120 ka BP. High Eemian sea level left Scandi- navia an island... References used for this presentation Stanley, Earth System History. Benn, DI & Evans, DJA (1998) Glaciers & Glaciation. Arnold, London. Clark & Mix (2002) Ice sheets & sea level of the Last Glacial Maximum. Quaternary Science Reviews. 21, 1-7. Lowe, JJ & Walker, MJC (1997) Reconstructing Quaternary Environments. 2nd edition. Longman, London. Siegert, MJ (2001) Ice sheets & Late Quaternary Environmental Change. Wiley, London. Svendsen et al. 2004: Late Quaternary ice sheet history of northern Eurasia. Quaternary Science Reviews 23, 1229-1271. http://www.joiscience.org/USSSP/Pubs/GreatHits/PDFs/Rhythms/Linsley.pdf http://www.pbs.org/wgbh/nova/vinson/ice-10.html#fea_top http://museum.state.il.us/exhibits/ice_ages/index.html http://pubs.acs.org/hotartcl/est/99/apr/learn.html#0043-99scho1.ev http://www.gps.caltech.edu/~jess/Adkins5eNature.pdf http://www.ngdc.noaa.gov/paleo/globalwarming/interglacial.html http://climchange.cr.usgs.gov/info/lite/results.html http://www-qpg.geog.cam.ac.uk/research/nweurorivers/.
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