Dating methods for quaternary deposits

Biostratigraphy does not directly provide an absolute age determination of a rock, but merely places it within an interval of time at which that fossil assemblage is known to have coexisted.Both disciplines work together hand in hand however, to the point where they share the same system of naming rock layers and the time spans utilized to classify layers within a stratum.

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Luminescence dating refers to a group of methods of determining how long ago mineral grains were last exposed to sunlight or sufficient heating.

It is useful to geologists and archaeologists who want to know when such an event occurred.

Geochronology is the science of dating and determining the time sequence of events in the history of the Earth.

This web page provides an overview of selected geochronology methods used by USGS scientists.

The trapped charge accumulates over time at a rate determined by the amount of background radiation at the location where the sample was buried.

Stimulating these mineral grains using either light (blue or green for OSL; infrared for IRSL) or heat (for TL) causes a luminescence signal to be emitted as the stored unstable electron energy is released, the intensity of which varies depending on the amount of radiation absorbed during burial and specific properties of the mineral.Many methods are only useful for a limited period of time (for radiocarbon, for example, 40,000 years is the maximum age possible).Scientists dating Quaternary glacial sediments in Antarctica most commonly use one of the methods outlined below, depending on what kind of material they want to date and how old it is.These slowly decay over time and the ionizing radiation they produce is absorbed by mineral grains in the sediments such as quartz and potassium feldspar.The radiation causes charge to remain within the grains in structurally unstable "electron traps".Unfortunately, glacial sediments are typically difficult to date.

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