A Procedure for Extracting Palynomorphs (Pollen and Spores) from Clastic Sediments

Abstract

The traditional palynomorph extraction technique, which has been developed for organic deposits, employs chemical treatments that are too harsh for the often poorly preserved and widely dispersed palynomorphs present within clastic sediments. An extraction procedure that utilizes non-corrosive heavy-liquid techniques has been developed. In contrast to other existing heavy-liquid techniques, this procedure permits processing of large-volume samples and offers relative simplicity and considerable flexibility. It has been extremely successful in facilitating the processing of a wide variety of clastic deposits for their palynomorph content. The extraction, identification, and interpretation of pollen and spores, or palynomorphs, has traditionally been associated with deposits comprised almost entirely of organic peat. However, in recent years, palynologists have extended their work to the extraction of palynomorphs from clastic sediments, such as those comprising archaeological middens, soils, loess, alluvium, and glacial till. Palynomorphs in clastic sediments differ from those in peat in that the former are typically extremely fragile and in low concentrations. Present extraction techniques for clastic deposits, however, are often problematic because they incorporate caustic reagents which attack fragile grains, or permit the processing of only small amounts of sediment. The procedure utilized in the study of palynomorphs from organic deposits is actually one of concentration rather than extraction. The technique primarily involves the disintegration and dissolution of the nonpollen matrix. Since the peat environment is usually one of low pH and reduction, the palynomorphs are well-preserved. The grains can therefore withstand the harsh chemical treatment involved in their concentration. Four chemical processes are typically utilized: (1) potassium hydroxide digestion, (2) acetolysis (acid hydrolysis using a mixture of acetic anhydride and sulfuric acid), (3) hydrofluoric acid treatment, and (4) hydrochloric acid treatment. Occasionally, further treatment involving the use of chloric oxides as oxidizing This content downloaded from 157.55.39.170 on Wed, 19 Oct 2016 04:05:55 UTC All use subject to http://about.jstor.org/terms 52 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE agents is incorporated. The general procedure for the concentration of palynomorphs from organic deposits is described in several sources but is best presented in Faegri and Iverson (1975) and Moore and Webb (1978). All treatments, with the exception of hydrochloric acid, are extremely corrosive, but, if used prudently, none will damage the typically well-preserved palynomorphs which occur in the acid, anaerobic environment of a peat deposit. However, palynomorphs preserved in clastic sediments such as soils and river alluvium are often very fragile due to the higher pH (e.g., Dimbleby, 1957) and oxidizing conditions (e.g., Tschudy, 1969) usually present in such deposits. Therefore, the above chemical treatments are destructive to these palynomorphs, and may completely obliterate them. Although it has been recognized that palynomorphs in clastic deposits require a different extraction procedure because of their state of preservation, some of the harsh chemical treatments found in the standard procedure for organic deposits have persisted. There has been an understandable reluctance to abandon completely the traditional procedures. In order to assess the utility of different procedures for use with clastic sediments, Woosley (1978) using prepared archaeological samples compared four procedures: the Mehringer method; heavy liquid-hydrofluoric acid, nitric acid method; Chevron method; and modified Chevron method. The study indicated the modified Chevron method produced the lowest pollen mortality rates; the results were attributed to the fact that the method utilized fewer caustic chemical procedures than the others. Ideally one should avoid all treatments utilizing harsh reagents. Hydrochloric acid is frequently necessary, however, to remove calcium carbonate cementation that encases palynomorphs. This acid is used in low concentrations and apparently does not damage even the most fragile of grains. Approaches to palynomorph separations that do not employ harsh chemical treatments include sieving (e.g., Cwynar et al., 1979), vibration (e.g., Dumait, 1962; Tschudy, 1960), controlled centrifugation (e.g., Brown, 1960; Funkhouser and Evitt, 1959), panning or swirling (e.g., Faegri and Iversen, 1975; Funkhouser and Evitt, 1959), settling or decantation (e.g., Horowitz, 1979; MacInnis and Rukavina, 1977; Faegri and Iversen, 1975), and heavy-liquid flotation (e.g., Bryant and Holloway, 1983; U.S. Geological Survey, 1980; Horowitz, 1979; Gray, 1965). With the exception of the first and last techniques, all depend upon differential settling velocities of clastics and organics as determined by their densities. Individually considered, these techniques are somewhat tricky, require considerable patience, or are limiting in regard to the type and/or amount of sediment that can be processed.