Pollen dating method

Stratified cores are sampled both within the stratified units and the point of change above and below these stratifications.

The samples removed from the cores then go through a series of chemical preparations which are quite complex.

Pollen was first recognised at the beginning of the 20th century by Lennart von Post, using a simple microscope with a natural light source, and pollen analysis was later to be used by a wide range of people from archaeologists, apiarists and geologists to environmental scientists, paleoenvironmentalists and forensic scientists.

In archaeology, pollen analysis is used as a tool to estimate an approximate date of sequence, and to help reconstruct the context of an environment surrounding a site looking at the type and number of samples found.

Combining centrifugations in two Cs Cl solutions, one of higher density and one of lower density than pollen, a pure pollen fraction was successfully prepared.

Data on the isodensity and sedimentation rate of ‘fossilized’ recent pollen from twelve tree taxa are also presented, and the potential for separating a single taxon from pollen assemblages is demonstrated.

Methods of preparative centrifugation eliminate many of the difficulties involved in preparing pollen concentrates from deposits rich in resistant organic material.

The prepared pollen is then suspended in glycerol or silicon oil and mounted on a microscope slide in preparation for identification and counting the grains.

AMS samples can be sent to a dating facility, such as the Center for Accelerator Mass Spectrometry (CAMS, Lawrence Livermore National Laboratory), or returned to the requester in acidified water.

Sediment samples (usually 4-5) are placed in pre-burned 40 m L glass centrifuge tubes and treated sequentially, as shown in the flow chart below, with centrifuging and water rinses between each of the steps to clear the sediment of the treatment solution.

Very often the core sample may be described by the Troels and Smith (1955) method whereby the core is sampled according to the visible evidence it contains, for instance, an obvious over-burden at the top (youngest) level, leading through a middle sequence, and finally a base level sequence representing the oldest level.

Sometimes a decision can be made on this simple sampling strategy, whereas cores of homogenous material may be sampled at arbitrary levels.

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Pollen in bogs may have been blown in from some distance; not all plants produce a lot of pollen; and differences between the aquatic pollen and wind borne pollen in a lake, can have a skewed result, with an increase in the number of aquatic pollens outweighing the airborne ones. An excellent PDAS training day was held at the University of Plymouth in April, under the tutorship of Ann Kelly, Science Officer in the School of Geography.

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