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Topic:

Surface Exposure Dating,

methods and

applications

by Muhammad Haseeb Durrani

2Content

Define surface exposure dating Example Methods

I. Absolute

II. Relative

Explanation of some methods Applications

3Surface exposure dating:

It is collection of geochronological techniques for estimating the length of time that a rock has been exposed or near earth’s surface. It is used to date geological events such as:

o Glacial advanceso Erosion history

o Lava flowso Meteorite impactso Rocks sideso Faults scraps

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Example

Cosmogenic radionuclide dating:

Cosmogenic nuclides are created through the collision of cosmic rays with atomic nuclei.

These nuclei can be atmospheric (N,O) or terrestrial relies on terrestrially. Surface exposer dating formed nuclide and soil dating relies on atmospherically

from nuclides. Basic principal is that these radio nuclide are produce at known rate through this

scientist can date how long a particular surface has been exposed, how long a certain piece of material has been buried or how quickly a location is eroding.

The excess relative to natural abundance of cosmogenic nuclide in rock sample is usually measured by means of accelerator mass spectrometry.

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• Methods of surface exposure dating

Basically there are two Major methods

Absolute Dating

AndRelative Dating

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• Relative vs absolute dating

o Absolute Dating• it gives accurate dating of any material.

o Relative dating• determining the relative order of past

events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age.

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• Absolute DatingIt is further divided into following

Amino acid racemisation Archaeomagnetic dating Dendrochronology Ice core Incremental dating Lichenometry Paleomagnetism Radiometric dating  Radiocarbon Uranium-lead Potassium-argon Tephrochronology Luminescence dating

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• Relative Dating

It is further divided into following

Fluorine absorption Obsidian hydration Seriation Stratigraphy There are many methods of Dating. We will discuss few of them.

9 Absolute Dating By:

DEF

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• Absolute dating

It is the process of determining the age on a specified time scale in geology and archaeology i.e. it gives accurate dating of any material.

It is based upon physical, chemical, & life properties of the materials, materials of the artefacts, buildings etc.

Techniques include tree rings in timber, radiocarbon dating of wood or bones & trapped charge dating i.e. thermoluminescence dating.

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• Radio metric dating

The process of determining the age of rock from the decay of their radioactive elements.

There are over forty such techniques, each using a different way of measuring them. It is accurate because there is complete agreement between radiometric dates and

other dating methods.

The radio active methods we are discussing are:

1. Radio carbonation

2. K-Ar Dating

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• Radiocarbon Dating One of the most widely used & well known dating technique. Based on radioactive decay of C-14. Half life of C-14 is 5730 years. Plants take C-14 from CO2 and this C-14 circulates in food chain. With death, the uptake of C-14 stops. By measuring C-14 in organic material, scientists can determine the date of death of that

organism.

• Limitations

C-14 as a very short half life of about 5730 years. Due to this short life it is reliable only up to 75,000 years. Thus it is not highly effective. Still highly effective when calibrated with other techniques like tree ring dating.

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• Potassium- Argon Dating

Potassium-40 is a radioactive isotope of potassium that decays to argon-40. Half life of K-40 is 1.3 billion years. Potassium is common in rocks and minerals. The date measured reveals the last time the object was heated past the closure

temperature at which Argon can escape. The graph shows the age K-Ar method and other methods can find.

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• Luminescence Dating

It is the type of dating methodology that measures the amount of light emitted from energy stored in certain rock types and derived soils to obtain an absolute date for specific event that occurred in past.

Luminescence dating may be:

1. Thermoluminescence dating

2. Optically stimulated luminescence (OSL) dating

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• Thermoluminescence dating

It dates items to the last time they were heated. Based on the principle that all objects absorb light from the environment. This process frees the electrons within the mineral that remain caught in them. Heating to 500 degree C or Higher releases the trapped electrons & produces

light. The produced light is measured to determine the last time the item was heated.

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• Optically stimulated luminescence (OSL) dating

Constrains the time when sediment was last exposed to light. During sediment transport, exposure to sunlight ‘zeros’ the luminescence signal

as natural ambient radiation gradually ionizes mineral grains. Carefully sampling under dark conditions allow the sediments to be exposed to

artificial light in the laboratory which releases the OSL signal. The amount of luminescence released is used to calculate the age.

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• Dendrochronology (Tree ring Dating)

It is also called as tree ring dating. Scientific dating based on analysis of pattern of free rings (growth rings). One ring indicates one year. It has three areas of application.

I. Paleoecology (used to determine certain aspects of ecologies).

II. Archaeology (Used to date old buildings).

III. Radiocarbon dating (Used to calibrate radiocarbon ages).

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• Amino Acid Dating

Used to estimate age of specimen in pale biology, archaeology, sedimentary geology and other fields.

It relates changes in amino acid molecules, to time elapsed since they were formed. Amino acids have two different configurations D & L (Mirror images of each

other).

Living organisms keep all their amino acids in the "L" configuration. When an organism dies, control over the configuration of amino acid ceases, and

the ratio of D to L moves from a value near 0 towards an equilibrium value near 1 The measuring ratio of D to L in a sample enables one to estimate how long ago the

specimen died.

20 Relative Dating By:

GHI

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• Relative Dating

Before the use of absolute dating, archaeologists & geologists used this technique to determine ages of materials.

It can only determine the events in sequential order (in which not the event occurred).

It is still useful technique especially in that materials lacking radioactive isotopes. Based on law of superposition. Law of superposition states that older layers will be deeper in a site than more

recent layers.

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• Stratigraphy

A technique for relative dating based on organizing remains by means of strata.

There are many horizontal layers, which are called strata.

Based on law of super position. Like a layer cake. (Shown in the diagram below).

Objects in lower strata are older than objects in higher strata.

It is the oldest of the relative methods.

Using a few basic principles, it is possible to work out the relative ages of rocks.

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• Seriation

A technique for relative dating by putting groups of objects into sequence in relation to one another.

It is the standard method of dating in archaeology.

Used to date stone tools pottery fragments 7 other art-facts.

In Europe it has been used frequently to reconstruct the chronological sequence of graves in cemetery.

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• Fluorine Absorption Dating

It is a method used to determine the amount of time an object has been underground.

Fluorine absorption dating can be carried out based on the fact that groundwater contains fluoride ions.

Items such as bone that are in the soil will absorb fluoride from the groundwater over time. From the amount of absorbed fluoride in the item, the time that the item has been in the soil can be estimated.

Also a method that measures the amount of fluorine, nitrogen, and uranium in bones.

As not all objects absorb fluorine at the same rate, this also undermines the accuracy of such a dating technique.

It has a large margin of error.

27 Applications BY:

JKL

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• Applications Surface exposure dating is used for the following.

1) Glacial chronologies (alpines, ice sheets)

2) Fluvial chronology (Terraces, inclusion)

3) Shoreline chronology (terraces, lacustrine, marine)

4) Hillslope rates

5) Catchment wide denudation rates

6) Burial chronologies (caves, terraces, paleosols)

7) Landslide chronologies

8) Fault scrap chronologies

9) Volcanic eruptions

10)Desert chronologies

11)Alluvial fan chronologies

12)Archaeology

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The End