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--- sample_processing [05/05/2023 12:51] – mike_gss
+++ sample_processing [13/05/2023 14:09] (current) – mike_gss
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 ==== Sample Processing & Sample Selection ====
+All studies in biostratigraphy, no matter the reason, require rock samples from which to obtain the fossils. Some fossils are found whole in the rocks and can be extracted in one piece (hopefully). Microscopic fossils however - those used most often in applied biostratigraphy - require to be "liberated" from the surrounding sediments in one way or another and concentrated to make it convenient for the analyst to examine as many specimens as possible. It is important that biostratigraphers have a good degree of control over their samples in that they need to know (a) from where exactly the sample was obtained and (b) that the sample is not contaminated with material that has come from anywhere else. This control is often easy to deliver when sampling outcrops at the surface or near surface but much less so when dealing with samples that are obtained by drilling. The drilling process imparts many variables and unknowns into sample generation and collection and anyone who relies on data of any kind from these samples must be aware of such uncertainties.
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+//Samples in commercial biostratigraphy normally originate from the drilling process. However, other sample types are also analysed for biostratigraphy including outcrop samples and sea-bed cores or "grab" samples.//
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+//What can effect sample quality from drilled sediments? The choice of drill-bit, mud-type and method of drilling can affect the recovery potential of microfossils from the samples and thus influence data quality.//
 The three main microfossil groupings – in addition to the scientific differences between them – are each also distinguished by the basic processing methods used to liberate the microfossil specimens from the rock matrix, although there are various other detailed differences within the main three methods depending on additional factors. One of the most important factors which determines the likelihood of good microfossil recovery is sample lithology:
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 As a general guide – the finer the grain size, the more microfossils can expect to be recovered.
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+Sample spacing also has an influence on, for example, the degree of biostratigraphic resolution that can be achieved. As particle-physicists will tell you - "One can only resolve objects down to the wavelength of the light that is shone upon them."
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 The most common forms of sample processing techniques are:
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   * Suspension – a slower but more precise method for preparing nannofossils involving a suspension of lithic dust in water and allowing it to settle (or be centrifuged) before placing on a slide. Some of the smaller diatom species may also be visible this way
   * Chemical extraction – a means of extracting organic-walled microfossils (palynomorphs) essentially by dissolving away siliceous rock from un-, semi- and fully-consolidated sediments and then oxidising the residues to make the palynomorphs visible. Several different toxic and corrosive chemicals are used which requires a specialist laboratory to perform.
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