GEOL 4010 QUATERNARY GEOLOGY Instructor: Dr' Hester Jiskoot

1
GEOL 4010QUATERNARY GEOLOGYInstructor Dr.
Hester Jiskoot
LECTURE 8
Dating methods (2)
2
Radiometric dating Radio-isotopes (14C, U, K,
etc.) Luminescence dating (TL, OSL,ESR
etc.) Relative chronologies based on processes
of chemical alteration Amino-acid
geochronology Fluorine, uranium nitrogen
content of fossil bones Obsidian hydration
Weathering characteristics of rock surfaces
Pedogenesis
3
Incremental methods Dendrochronology
Varve chronology Lichenometry Annual
layers in glacier ice Age-equivalent
stratigraphic markers Palaeomagnetism
Tephrochronology Oxygen isotope
chronostratigraphy Palynology
(http//www.kv.geo.uu.se/pc-intro.html)
4
Lichenometry
Lichen growth rates vary with elevation,
proximity to sea, aspect, rock type
5
Lichenometry max 5000 y BP.
Rhizocarpon geographicum ? Most commonly used for
lichenometry ? Growth 1-4 mm/yr
Caloplaca ignea ? NOT used for lichenometry
dating
6
Palynology

• count and identify 200 pollen grains/sample
• divide census into three parts
• -- arboreal pollen (AP)
• -- non-arboreal pollen (NAP)
• -- spores
• express results as of total pollen or total AP
  at that particular depth
• plant assemblage at a particular horizon ? pollen
  spectrum
• histograms of successive spectra ? pollen curve
• curves from a series of stratigraphic positions ?
  pollen diagram
• age dates are determined by carbon-14 dating
• history of vegetation change linked to climate,
  environment and anthropological influences

7
Pollencurves
8
Pollendiagram
9
Dating techniques for the glacial record
Which methods can we use for glaciation
record Which methods can we use for deglaciation
record? Which methods good for ice
proximal? Which methods good for ice distal?
10
SUMMARY

• No absolute date, only age estimates.
• Incremental radiometric dates provide dates
  in years - important for Quaternary scientist.
• Dating methods valuable where calibrated/cross
  correlated to provide dates in years.
• Certain methods only practicable for particular
  materials within a certain age range.
• Use more than one dating technique to provide a
  more reliable chronology.
• Challenge is to improve reliability of existing
  dating techniques and to develop new ones.

11
Reading for Friday p. 70-86.