Dating Methods in Quaternary
1) Methods that provide direct age estimates
* Radiometric methods (using isotopic decay)
* Incremental methods (counting layers)
2) Methods that Establish age ‐equivalence
* Through certain well dated stratigraphy markers
3) Relative Age methods
* Using the relative Position Of each stratigraphy units
This process, known as radioactive decay, is time-dependent, and if the
rate of decay for a given element can be determined, then the ages of the
host rocks and fossils can be established.
Potassium Argon / Argon Argon
Electron spin resonance
Incremental Dating methods
Annual layers in ice
Age - equivalent dating methods
•Oxygen Isotope Chronology
Relative dating methods
•Weathering characteristics of rock surfaces
Carbon-14 (Radiocarbon) dating
-Uses natural decay of C-14 organic material
K-Ar and Ar-Ar dating
-Uses decay of K and Ar
Uranium series dating
-Uses natural decay of Uranium isotopes
Fission track dating
-Due to the radioactive marks on mineral lattice
-Other mineral nearby nuclear disintegration
-Exposure of rock surface
Radioactive decay, also known as nuclear decay or radioactivity, is the
process by which a nucleus of an unstable atom loses energy by emitting
particles of ionizing radiation.
A material that spontaneously emits this kind of radiation—which includes
the emission of energetic alpha particles, beta particles, and gamma
rays—is considered radioactive.
A typical radiometric dating method
This isotopic method has been in use since the late 1950s and has greatest
utility for the study of late Quaternary deposits containing organic residues. The
radioactive half-life of 14-C is 5,730 years (as it decays to 12-C).
The radioactive form of carbon is generated by cosmic ray interactions with
atmospheric nitrogen and oxygen, and possibly a trace from earth and ocean
matter. 14-C is incorporated into all organic mater through respiration.
Therefore, living tissue is in equilibrium with carbon isotope concentrations in
the biosphere. When an organism dies and some of its organic material
becomes isolated from bacterial decay, it no longer takes in "fresh" carbon and
the progressive decline in the 14-C isotope begins.
Uranium Series Methods
This methodology involves the measurement of isotopes of uranium (238-U
and 235-U), thorium (232-Th), and certain members of their daughter nuclides.
Uranium series geochronology is typically used to date authigenic minerals in
sediments or fossils, but has also been used to date speleothems, calcite
veins, rock varnishes, salts, and other materials.
Time determinations "windows" vary for the different radiogenic isotopes, but
applications are typically used for Quaternary deposits.
Uranium Series Methods
Age of deposition using ratios of intermediate daughters, 234U, 230Th.
Age range: several thousand to approximately 500,000 years, with greater
precision from higher U content and younger age sample.Extremely young
material can be dated given sufficient 234U (hundreds of years).
Most commonly applied to carbonates, opal, or other high-U, low-Th mineral
Potassium / 40Argon Geochronology
geochronology is one of the most widely used absolute-dating
The method relies on samples rich in mineral grains containing potassium,
typically an igneous volcanic rock rich in sanidine feldspar. 40-K undergoes
natural radiogenic decay through time (converting to argon-40 at a known
As the potassium gradually decays to argon, the naturally inert gas
accumulates, confined within the mineral crystal lattice.
As a result, the ratio of 40-K to 40-Ar derived from mineral grains is compared
with the known rate of radiogenic decay of 40-K.
By eliminating possible sources of error, this absolute dating method can be
used of on selected rock samples typically ranging in ages from ~10,000
years on back in time to billions of years.
methodology overcomes many of the problems intrinsic to
the 40-K/39-Ar, primarily the potential for radiogenic argon to escape form
minerals and/or rocks due to thermal processes (igneous or metamorphic)
This absolute dating method can be used on selected rock samples
typically ranging in ages from ~10,000 years on back in time to billions of
Based on radiation damage (tracks) due to spontaneous fission of 238U.
When combined with temperature required for annealing of the tracks in
specific minerals can yield cooling ages (e.g. age of most recent uplift,
pluton emplacement and cooling, etc.).
These tracks come from the spontaneous fission of 238U present in the
mineral. By determining the number of tracks present on a polished
surface of a grain and the amount of uranium present in the grain, it is
possible to calculate how long it took to produce the number of tracks
Fission track dating is a radiometric dating technique based on analyses of
the damage trails, or tracks, left by fission fragments in certain uraniumbearing minerals and glasses.
Fission-track dating is a relatively simple, but robust method of radiometric
dating that has made a significant impact on understanding the thermal
history of continental crust, the timing of volcanic events, and the source and
age of different archeological artifacts.
The method involves using the number of fission events produced from the
spontaneous decay of uranium-238 in common accessory minerals to date
the time of rock cooling below closure temperature.
Fission tracks are sensitive to heat, and therefore the technique is useful at
unraveling the thermal evolution of rocks and minerals.
Most current research using fission tracks is aimed at: a) understanding the
evolution of mountain belts;
b) determining the source or provenance of sediments;
c) studying the thermal evolution of basins;
d) determining the age of poorly dated strata; and
e) dating and provenance determination of archeological artifacts
This image shows the appearance of etched ﬁssion tracks in a crystal of apatite etched for
20 seconds in 5N Nitric acid at 20°C. The tracks appear as randomly oriented dark
straight lines on the surface of the mineral that also show variable focus along their length
due to the fact that they are 3-dimensional structures dipping at various orientations. Very
faint polishing scratches can also be seen traversing right across the surface of the grain
in various directions. Each etched ﬁssion track represents a single 238U nucleus that
has undergone spontaneous ﬁssion, so that counting the individual tracks is actually
counting individual atoms, an extreme detection sensitivity which makes ﬁssion-track
dating feasible despite the extraordinarily long half-life for this decay scheme.
The technique of fission track dating is based on the infrequent, but
predictable, break-up of the most abundant isotope of uranium, 238U, in
a fission reaction. The process leads to high-energy collisions between
the fission fragments and neighbouring atoms and creates damage
tracks or trails in the enclosing crystal lattice.
Precisely how this occurs is not completely understood, but it seems
that as two positively charged fission fragments are driven apart, they strip
electrons from atoms in the host lattice and, after passage of the fission
fragment, a zone of positively charged ions remain which mutually repel
Optical stimulated luminescence (OSL) and thermoluminscence (TL)
are dating methods that involve the analysis of the optical properties of
minerals exposed to environmental radiation.
Radiation damage to the crystal lattice of mineral grains produces
defects or "electron traps."
These "traps" can be stimulated to produce measurable luminescence.
However, these traps are highly sensitive to both sunlight and/or heat.
Rocks exposed even to a few hours of sunlight can loose their
As a result, the measurable luminescence a rock produces is directly
proportional to the amount of radiation exposure since the time of
burial. The OSL and TL methods are suitable for studying terrestrial
deposits up to about 500,000 years (late Quaternary).
This emission of light is known as thermoluminescence (TL) and is the
basis of thermoluminescence dating. Alternatively, the electrons can
be released from traps by shining a beam of light onto the sample, and
again the luminescent signal is a reflection of
the number of electrons trapped within the crystal lattice.
This is optically stimulated luminescence (OSL), and hence the
technique is generally referred to as optically stimulated
luminescence dating, although the abbreviated term optical dating
As time passes, the luminescence signal increases through exposure to the ionizing
radiation and cosmic rays.
Luminescence dating is based on quantifying both the radiation dose received by a
sample since its zeroing event, and the dose rate which it has experienced during the
Electron Spin Resonance Dating
ESR Dating, sometimes referred to as Electron Paramagnetic Dating (EPR),
has a greater time range than most of the other Quaternary dating methods
described in this book, extending from a few thousand years to about 2 million
years in the case of tooth enamel.
In general, the most important applications lie in the time range between 40
000 and 200 000 years, although a number of valuable age estimates of up to
500 000 years have also been obtained.
The basic principles of ESR dating are very similar to those for
luminescence in that it is based on measurements of the trapped
electrons in crystal lattices of rocks, sediments or other materials. In this
case, however, the electrons are not released by heat or by light.
Rather their abundance is estimated on the basis of their paramagnetic
properties. The sample is placed in a strong, steady magnetic field and
exposed to high-frequency electromagnetic radiation.
The magnetic field is slowly changed and at a certain frequency the
electrons (or spins) become ‘excited’ and resonate. The strength of this
resonance signal can be determined using an ESR spectrometer.
When the electrons are in resonance, electromagnetic power is absorbed
in direct proportion to the number of electrons present, and hence the
greater the number of electrons, the greater the absorption (Aitken, 1990).
The latter is a reflection of the time that has elapsed since the onset of
electron trapping, and hence is a measure of age.
Stable Isotope Records
Stable isotope data derived from mineral and biological materials can provide a
variety of insights into environmental conditions (past and present), and can be
used in geochronology and correlation.
Oxygen isotopes (18-O/16-O) are widely used in correlation of Quaternary marine
sediments. Oxygen isotope concentrations in mollusk shell and calcareous algal
material normalize with seawater while the organisms are alive.
During periods of glaciation, large volumes of 16-O become trapped in glacial ice,
enriching ocean water in the heavier oxygen isotope.
As a result, oxygen isotope data extracted from shell-bearing sediments can
provide information about cycles of glaciation (and climate change), and can be
used for relative dating. To a lesser degree, other stable isotopes are used for
correlation (such as 13C/12C and 36-S/34-S).
The dating and study of annual rings in trees. The word comes from
The science that uses tree rings dated to their exact year of formation to
analyze temporal and spatial patterns of processes in the physical and
A correlation of varve series and records that together have a uniform
numbering system and apply to a broader region than a varve sequence,
perhaps from different lakes or valleys.
A varve chronology will grow as it incorporates series and smaller
chronologies over time.
These varves were deposited in a position very distal to the receding glacier and
also are from the relatively shallow flanks of Lake Vermont where less sediment
was deposited during the summer than in deeper parts of the basin.
As a result, winter layers are thicker here than summer layers
Lichens are a symbiotic relationship between an alga and a fungus.
dating that uses lichen growth to determine the age of exposed rock,
based on a presumed specific rate of increase in radial size over time.
As a relative-age technique it is based on the assumption that some index
of lichen size increases over time.
Lichenometry has been used for dating many types of surfaces including
raised beaches, river terraces, talus, rockfalls, trimlines , snow-avalanche
activity and outwash plains .
Age: the size of the lichen thallus increases with age. assume growth
begins soon after the deposit stabilized growth rate slows with age
The Earth's magnetic north pole can change in orientation (from north to
south and south to north), and has many times over the millions of years
that this planet has existed. The term that refers to changes in the Earth's
magnetic field in the past is paleomagnetism
Paleomagnetic and rock magnetic techniques provide means of
understanding the Earth's ancient geomagnetic field by using the magnetic
record contained in rocks and archeological materials.
When the magma from which igneous rocks form is still molten, iron-rich minerals can orient
themselves in line with the local magnetic field in the same way that a compass needle does.
As the magma cools, the tiny iron-rich crystals are “frozen” in position, recording the orientation of
the local magnetic field at that time. Iron minerals in sediments can also align themselves with the
magnetic field, then become fixed as the sediment turns to rock.
The orientation of the magnetic crystals in rocks can be used to infer two pieces of information—the
direction of the magnetic pole from the point where the rock formed, and the polarity (reversed or
normal) of the magnetic field at the time the rock formed.
Tephra is a term used to describe all of the solid material produced from a
volcano during an eruption
Tephrachronology ist he study of volcanic ash deposits.
Volcanic ash layers often have unique chemical and physical characteristics
that can be used for correlation.
The chemical and physical characteristics of volcanic ash, select igneous
minerals in the ash can be used for absolute dating
As the deposition of the tephra layers is essentially instantaneous on a
geological timescale, these horizons provide distinctive and often widespread
isochronous (i.e. of the same age) marker horizons that offer a valuable basis
for inter-site correlation.
Each tephra horizon contains a unique geochemical fingerprint relating it to
the source of the eruption.
Tephra layers are excellent time-stratigraphic markers, but, to establish a
chronology, it is necessary to identify and correlate as many tephra units as
possible over the widest possible area.
- Quaternary Dating Methods – Mike Walker (2005)
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