Sieving techniques in palynological sample processing with special reference to the MRA System

Sieving techniques used in palynological sample processing, including the Modified Reissinger Apparatus sieving system, are described. MRA is useful for the removal of fine particles undesirable in palynological residues. It can also be used for filtration during various chemical treatments. MRA uses sintered glass filter discs fitted into Biichner funnels. Size-frequency studies using Schott type-3 filter funnels show that 98% of particles in filtrates are < 15-16 Am, and filtration rates of over 100 ml/min are easily obtained. These funnels are efficient for most palynological sample sieving. Finer filters may be necessary for samples containing smaller palynomorphs. INTRODUCTION AND HISTORY Sieving (screening or filtering) has long been used as a part ofpalynological sample processing, primarily to separate different size fractions of both organic and inorganic constituents of rock samples. Removal of the very fine or very coarse "undesired" particles, as well as separation of certain size fractions of palynomorphs and other dispersed organics is a common procedure. Various sieve types, mesh sizes and sorts of apparatus have been used (table 1). Sieving procedures vary considerably, depending upon the purpose of the study, the sedimentological characteristics of the samples and the processing method. Bennie and Kidston (1886) were apparently the first to adopt sieving techniques for palynological purposes. This paper can also be regarded as "the first serious contribution dealing solely with fossil spores isolated from the matrix" (Chaloner 1968). Bennie and Kidston (1886) extracted megaspores by washing and sieving naturally weathered shales and impure coals. Later, in his method called bulk maceration, Harris (1926) used a series of wire gauzes after oxidizing the shale samples to concentrate megafossils. Although sieving has long been used during coal maceration, the first serious attempt to use it for the removal of fines and for rinsing residues seems to be that of Reissinger (1939). The present MRA (Modified Reissinger Apparatus) is based on Reissinger's methods. McCulloch (1939) used a comparatively primitive type of sieving technique to concentrate Quaternary pollen to remove coarse particles by sieving the residue through a cheesecloth, which retained the sand grains. Sieving was later introduced more broadly in Europe and North America (Reissinger 1950; Kosanke 1950). The purpose of sieving, up to this point, had been mostly to remove coarse, coal-like particles, to separate megaspores and to concentrate certain size fractions ofpalynological residues. Mostly, 65-mesh (210 gm) brass screens were used for removal of very coarse particles (Kosanke 1950; Gray 1965). Churchill (1957) used 60-mesh wire gauze in a filtering system, in which he combined alkali treatment and filtering for the concentration of small spores/pollen. Dettmann (1965) used 100-mesh (149 jim) copper and steel screens, to concentrate megaspores. Hughes (1955) suggested the use of 40(420 ,m), 80(177 Am), and 100(149 Am) mesh screens to separate organic residues into various size fractions. Robbins (1982) separated her residues by sieving into 25-125 tm size fractions and studied the organic content. Sieving was also used for concentrating dinoflagellates with 200-mesh (64 Aim) sieves (Eagar and Sarjeant 1963). Eagar and Sarjeant developed a special filter assembly with a handoperated vacuum pump. A similar system based on this method was summarized by Doher (1980). Because of possible corrosive action of zinc-chloride and/or zinc-bromide solutions and their high cost, the disintegrated residue was passed through different sieves to remove clay particles instead of using heavy liquid separation (Bond 1964). Screening to replace short centrifugation or swirling has also been applied by using a series of screens (180, 38, and 20 tm) to prevent clogging in the finest sieve (Barss and Williams 1973). Sieving techniques in palynology expanded in usefulness with the availability of special metal screens with openings down to 5 Am (?2 Aim) (Kidston and Williams 1969). Before this, the smallest opening available was 37 jum, and such screens could not hold smaller angiosperm pollen and small spores. The use of an ultrasonic generator along with sieving and checks for contamination of sieves by staining the residue were techniques introduced by Kidson and Williams. However, metal screens clog easily and are relatively expensive and fragile (Cwynar et al. 1979). Ordinary filter papers (Whatman #4) have been used occasionally to remove suspended clays finer than 10 um (Schopf 1965). Paper filters attached to a special device are also used to remove the organicsolvent-soluble bitumen and asphalt of crude oil for the concentration of fossil palynomorphs for genesis studies (Sanders 1937; Artamonova and Medvedeva 1963). However, these papers, as well as borosilicate glass fiber filter papers, are not efficient, because they tend to clog and to contaminate the residue with fibers (Gray 1965). Most recently published sieving techniques employ nylon screens (Heusser 1978; Cwynar et al. 1979; Hansen and Gudmundsson 1979), and a special nickel screen (Caratini 1980). Nylon or polyester mesh screens are also used to remove or concentrate organic debris within selected size ranges in palynofacies analyses (Batten and Morrison 1983). Cwynar et al. (1979) tested the effectiveness of nylon screens with 5-, 7-, 10-, and 15-,um openings and found that 7-gm screens micropaleontology, vol. 32, no. 3, pp. 256-270, pls. 1-4,, 1986 256 This content downloaded from 157.55.39.138 on Sun, 26 Jun 2016 07:23:16 UTC All use subject to http://about.jstor.org/terms Micropaleontology, vol. 32, no. 3, 1986 were best for the concentration of pollen and spores from fine-grained, mineral-rich sediments of Quaternary age. Nylon screens (= nylon bolting cloth) have recently begun to be used routinely, because they are inexpensive (cost of screen per sample is about $0.40), durable and easy to use and recover the greatest amount of pollen (pollen loss is only about 0.4% with a 7-pum sieve, according to Cwynar et al. 1979). However, the pores tend to enlarge, and samples require relatively long sieving time. The difficulty of using such filters in any kind of vacuum system and for alkali-acid treatment during sieving are also important disadvantages. Also the sieves can only be used once; this increases their cost relative to that of glass filters. On the other hand, Caratini's nickel-perforated screens used with a filtration device called ultrasonic microfilter have openings of 5-100 pm, are very expensive (about $500 per screen) and disintegrate rapidly in either acids or basic solutions. (Caratini 1985 in a personal communication to A. Traverse reported that his laboratory now uses nylon cloth with an ultrasonic apparatus.)