Journal of Archaeological Science (1999) 26, 31–44 Article No. jasc.1998.0304, available online at http://www.idealibrary.com on An Assessment of Techniques for the Deflocculation and Removal of Clays from Sediments Used in Phytolith Analysis C. J. Lentfer and W. E. Boyd School of Resource Science and Management, Southern Cross University, Lismore, NSW, Australia (Received 25 May 1997, revised manuscript accepted 21 March 1998) This paper describes an experiment in which a comparison is made between two techniques of deflocculation and clay removal generally used for palynological extraction. In the experiment, methods used commonly for pollen extraction are applied to phytolith extraction. The palynological products of the different preparation techniques are compared by reference to several attributes: the time and efficiency in the preparation method; the weight of residue resulting from each method; the palynological composition; clarity of the palynomorphs on the slides; and measures of differential loss and selection by palynomorph shape and size. The results are compared and discussed in relation to the still-settling technique which is most commonly used for phytolith extraction. It is concluded that centrifugation is a reliable and fast method that can be used to remove clays from fine-grained sediments for the extraction of phytoliths and other silica microfossils. High levels of diversity were recorded for morphotypes across all size classes. It produced superior results to the sieving technique and there is no reason to assume that it cannot be used to produce results comparable with still-settling if calculations of settling times consider the implications of sediment density on fluid viscosity. Adoption of the centrifugation method for clay removal from palynological sediment samples can greatly reduce extraction times and, therefore, it is a recommended procedure.  1999 Academic Press Keywords: PHYTOLITH EXTRACTION, CLAY REMOVAL, DEFLOCCULATION, CENTRIFUGATION, SIEVING. Introduction P rocedures used to extract microfossils from sediments aim to produce residues with high concentrations of microfossils to allow reliable identifications of taxa to be made in minimal time. Several extraction procedures have been developed by palynologists with mixed results. It is notable that the most varied, difficult and time-consuming process, especially for fine-grained sediments, is the removal of clays and fine silts. To make it possible to produce clean residues with high concentrations of microfossils for analysis, disaggregation and deflocculation pro- cedures must be used. Chemical treatment and other procedures such as sonication, can reduce clay-binding potential and cause clay platelets to repel each other (Bates, Coxon & Gibbard, 1978). This allows free minerals and silt-sized particles, including organic microfossils, to be released from the clay aggregate matrix (Emerson, 1977; Norrish & Pickering, 1977). Clay can then be suspended in solution and removed by decantation. This paper compares two techniques of deflocculation and clay removal generally used for palynological extraction. In this case, methods used commonly for pollen extractions are applied to phyto- lith extraction. The results are compared and discussed in relation to the still-settling technique which is most commonly used for phytolith extraction. Standard pollen extraction procedures use defloccu- lation followed by hydrofluoric acid treatment to remove silica and silicates (Assarson & Granlund, 1924; Faegri & Iversen, 1989; Moore, Webb & Collinson, 1991). Chemical deflocculants used include EDTA (ethylenediaminetetraacetic acid-disodium salt), Calgon (sodium hexametaphosphate) and sodium silicate (Phipps & Playford, 1984), boiling water, sodium hydroxide, hydrochloric, nitric and sulfuric acids, and methanol (Brown, 1960), sodium pyro- phosphate (Bates, Coxon & Gibbard, 1978), sodium bicarbonate, ammonia and sodium carbonate in a ratio of 1:1, hydrogen peroxide, sodium tripolyphosphate and similar compounds used in detergents and water softeners (Pearsall, 1989), and ethanol (Faegri & Iversen, 1989). Of the above, sodium pyrophosphate, Calgon and other chain phosphate compounds are most commonly used amongst Quaternary palynolo- gists, often following pretreatment with one or more of the other chemicals listed above. Usually the HF technique requires only a single decantation of the supernatant following deflocculation. For very clay-rich sediments, however, the HF solution becomes quickly saturated and repeated treatments are 31 0305–4403/99/010031+14 $30.00/0  1999 Academic Press