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Further testing of a non‐acid palynological preparation procedure

Abstract The extraction of palynomorphs from sedimentary rocks and unconsolidated sediments has traditionally used hydrochloric acid (HCl) and hydrofluoric acid (HF) to remove the matrix by dissolution. The use of these, and other, acids in palynological preparation requires significant laboratory infrastructure, and may produce hazardous and potentially environmentally damaging waste. An effective technique of palynomorph preparation using sodium hexametaphosphate [(NaPO3)6] was recently developed. This technique was initially demonstrated on a suite of samples of Early Jurassic to Quaternary age. In this study, non‐acid preparation techniques were tested on 11 samples of Ordovician, Carboniferous, Jurassic and Paleogene age from the UK. In four of the six case studies described herein, the rock was prepared quantitatively using both the traditional mineral acid technique and the (NaPO3)6 procedure. In the Carboniferous case study, the two samples were prepared quantitatively using HCl/HF, (NaPO3)6 and hydrogen peroxide (H2O2). In the quantitative preparations, the concentrations of palynomorphs can be directly compared. Two non‐quantitative case studies were undertaken using (NaPO3)6 only, in order to demonstrate that this method is of practical utility. The (NaPO3)6 and H2O2 methods generally proved to be as effective as the mineral acid procedure. However the results from the three Paleozoic samples proved somewhat variable. The Early Ordovician sample 1 did not break down in (NaPO3)6, and consequently the palynomorph yield from this sample was extremely poor, compared to the acid preparation. Two Lower Carboniferous samples were prepared using all three methods. In sample 2, all the methods were effective, although the H2O2 technique proved less effective than those using mineral acids and (NaPO3)6. In this sample, both the non‐acid methods produced palynomorph assemblages cleaner of extraneous woody material than the residue produced by the acid digestion method. By contrast, in Carboniferous sample 3, the acid preparation was far better than those from the two non‐acid preparations. It appears that mudrocks which are relatively indurated are not consistently disaggregated using (NaPO3)6 and/or H2O2. It may be possible to adapt these non‐acid techniques so that they are more efficient on these relatively hard lithotypes. The samples would need to be softened prior to treatment with (NaPO3)6 and/or H2O2. Even on relatively hard lithotypes, some palynomorphs were extracted using (NaPO3)6 and H2O2. This confirms that non‐acid methods can be used on harder rocks if a preliminary age assessment is required and/or the full laboratory facilities are unavailable. The (NaPO3)6 technique proved extremely effective in the two quantitative Jurassic case studies. These were on the Oxford Clay and Kimmeridge Clay formations (Callovian‐Oxfordian and Kimmeridgian respectively). In samples 4, 6 and 7, both methods gave similar palynomorph yields. However in sample 5 from the Oxford Clay Formation, the acid preparation proved less palynologically productive than the material prepared using (NaPO3)6. Palynomorph diversity was also higher in Oxford Clay Formation samples 4 and 5, prepared with (NaPO3)6. In samples 6 and 7 from the Kimmeridge Clay Formation, the palynomorph diversity, preservation and yield were closely comparable. However, the HCl/HF preparations proved extremely rich in amorphous organic material as compared to the (NaPO3)6 slides. It therefore appears that (NaPO3)6 is effective at disaggregating amorphorgen in addition to clay minerals. This means that this reagent may be used as an alternative to nitric acid (HNO3) and other strong oxidizing agents for cleaning organic residues of amorphous organic material. More studies should be done using (NaPO3)6 to prove its effectiveness in dispersing amorphogen. The two non‐quantitative case studies prepared only using (NaPO3)6 were also successful. Three samples (8–10) of Early, Mid and Late Jurassic age and sample 11 of Paleogene age all produced abundant, well‐preserved and diverse palynofloras. This indicates that the (NaPO3)6 procedure can prepare palynomorph assemblages from Mesozoic and Cenozoic mudrocks as effectively as the HCl/HF procedure.