A direct comparison of three palynological preparation techniques

Two samples of palynomorph-rich Upper Jurassic (Lower Oxfordian) mudstone from western Scotland were quantitatively prepared using the traditional hydrochloric and hydrofluoric acid based palynological preparation technique and two non-acid procedures. The latter are protocols using sodium hexametaphosphate [(NaPO₃)₆] and hydrogen peroxide (H₂O₂). These non-acid techniques have previously been validated only in terms of the absolute numbers of palynomorphs extracted. By contrast, this study aimed to assess the numbers of palynomorphs extracted in terms of absolute numbers of the individual taxa present to test for any taxonomic biases. The (NaPO₃)₆ method proved around 50% as efficient as acid digestion in terms of absolute numbers of palynomorphs extracted. It produced clean residues, which are eminently suitable for most palynological studies. The majority of the taxa present were recovered in representative relative proportions, and no taxonomic biases were noted. The absolute numbers of most taxa decrease in a stepwise fashion from acid digestion via the (NaPO₃)₆ procedure to the H₂O₂ method. However, the concentrations of bisaccate pollen were apparently relatively unaffected by the three methods used. Similarly, the Meiourogonyaulax caytonensis group appears to be unusually resistant to oxidation damage by H₂O₂. It is considered that the (NaPO₃)₆ preparation method is an eminently viable alternative to acid digestion, especially in remote operational settings such as rigsites. The H₂O₂ technique proved to be significantly less effective, at approximately 10% of the extraction level of acid digestion which appears to be largely due to oxidation. Hydrogen peroxide is an aggressive oxidant. Therefore the (NaPO₃)₆ technique is deemed to be both safer and more effective than the H₂O₂ method.