Introduction to Quaternary Geology (MA-Modul 3223) Prof. C. Breitkreuz, SS2012, TU Freiberg

Transcription

1 Introduction to Quaternary Geology (MA-Modul 3223) Prof. C. Breitkreuz, SS2012, TU Freiberg 1. Introduction: - Relevance, and relations to other fields of geoscience - Lower stratigraphic boundary and subdivision of the Quaternary 2. The paleoclimatic evolution: - paleoclimatic proxies and controlling parameters 3. Stratigraphic methods and age dating of Quaternary processes: non-radiometric and radiometric methods 4. Glacials: glacial and periglacial processes on land, deposits and structures 5. Glacio-marine processes 6. Interglacials, including the Holocene, the Pleistocene-Holocene transition : one-day Field trip to Quaternary outcrops (put your name into list at Frau Klocke s office) : written test / Klausur

2 Non-radiometric methods - Paleomagnetic analysis - Continental loess profiles - Varve stratigraphy and paleoclimatology - Corals - Dendrochronology - Lichen chronology - Alkenone paleo-temperature proxy - Tephrostratigraphy/-chronology

3 Quaternary paleomagnetics Magnetic remanence: thermal R. (lava, contact metamorphism) depositional R. (small deep lakes) chemical R. (pedogenesis, diagenesis, hydrothermal overprint) Relative Paleomagnetic intensity (RPI) Susceptibility: volcanic ash soil horizons aeolian deposits

4 Singer et al Magnetic events

5 Matuyama > Brunhes transition VGP = virtual Geomagnetic pole Strength of Earth magnetic field decreases during transitions and excursion events Oda et al. 2000

6 Variation in relative magnetic paleointensity: another stratigraphic tool! Channell et al. 2009, EPSL

7 Loess: eolian deposits, mainly accumulated during glacials; predominantly silt size Quaternary loess areas Sandomierz, Poland Pye 1987

8 A Yuangquan, TU München B Ehlers 1994 A) Susceptibility peaks caused by pedogenic magnetic minerals (predominantly authigenic magnetite) B) Paleopolarity: chemical remanence in soil horizons

9 Correlation of Marine Isotope Stages (MIS) with Chinese loess profiles Bradley 1999

10 Warve* chronology and Paleoclimatology Example from the Holzmaar in the western Eifel GFZ Potsdam *warve = annual sediment layer

11 Example of a Holzmaar warve with seasonal variation

12 Current ICDP: A 3.6 million year old impact crater lake with a diameter of 12 km and a water depth of 170 m (Melles et al.)

13 Corals: Annual growth and multiple temperature proxies Bradley 1999

14 Dendrochronology: -paleoclimatology and wild fires

15 Stable isotopes (C, H, O) in tree rings: multi-paleoclimate proxy (air moisture, droughts etc.) reconstructions with perfect annual resolution (Carroll & Loader 2003, Quat. Sci. Rev.)

16 Lichenometry: < 6 ka Processes to be dated Land slides Marine regression Glacier retreat Bradley 1999 Cotopaxi, Ecuador

17 Alkenone ratios (C 37 -C 39 ), measured at organic remains of nanno plankton = proxy for paleowater temperature (back to 110 Ma!) Broecker 2000, ESR

18 Tephrochronology: relative and absolute time markers - good for marine-continent correlation Campanian Eruption, 37 ka Wulf 2005

19 Physical and chemical dating methods on Quaternary samples Geyh 1983

20 14 C age dating: Very important multiuse tool, with some problems Half-live = 5730 a Traditional: Counting decay events (< 50 ka) Since 1980: AMS (Accelerator-mass spectrometer); Less sample necessary, < 125 ka + biogenic debris in or below sediments / volcanic deposits Lex. Geowiss.

21 Causes of variation in atmospheric 14 C (selection): Variation in extra-terrestrial radiation: Solar wind, magnetic field, supernovae Variation of exchange rates between C-reservoirs Dilution effects due to exhumation of old carbon Causes of variation of the 14 C in the sample (selection): Contamination with modern C, e.g. during recrystallisation of aragonite to calcite Contamination with very old carbon (apparent age, water hardness effect) 14 C Variation im Ozeanwasser (fractionation atmosphere > hydrosphere: 1,5 %; as a consequence, ocean water has apparent ages of more than 1 ka, in places) Fractionation during biogenic metabolism (up to 5%, correction with 13 C possible, since 14 C ~ 13 C)

22 Calibration of 14C ages by age dating of tree rings of known age (< 11.4 ka BP)

23 U/Th decay series: After 450 ka radioactive equilibrium is achieved: then, the amount of intermediate decay products is only controlled by the decay constants

24 U, Th, Pa disequilibrium dating methods Catt 1992 e.g., Daughter isotope deficit or excess methods U tends to form water-soluble complexes, whereas Th becomes quickly adsorbed by clay Daughter isotope deficit methods (5-350 ka): Cave carbonates (UO 2 2+ precipitates with the carbonate); prerequisite: Th must have been adsorbed by clay minerals (test: absence of 232 Th)

25 Geyh & Schleicher 1990

26 Radiation damage methods: Electron shell phenomena (electrons become lifted to the conducting band): e.g. TL and ESR Lattice phenomena (e.g. fission track) Thermoluminescence (TL): clock reset by heat (lava!) or sunlight (sand, loess, volcanic glass, ceramics, fire places etc.): Age is calculated by measuring the luminescence of the sample upon heating Electron spin resonance (ESR): amount of electrons in the conducting band can be measured by ESR (corals, thick-walled moluscs, forams, travertine, caliche)