SEM and Light Microscope Mounting and Specimen Location Technique for Same-Specimen Study of Palynological Strew Mounts

Abstract

A reliable and efficient technique has been developed for the mounting, location and quick re-location of palynological specimens in strew mounts for SEM (scanning electron microscope) and subsequent LM (light microscope) examination. Specimen locations are recorded with reference to a numbered location grid, which has been inked onto a glass coverslip and is visible, both under the SEM and in light. After SEM examination, a permanent LM slide can be made by removing the coverslip from the aluminum stub and inverting it into a non-aqueous mounting medium. Specimens can be quickly re-located under the SEM or the light microscope by referring to grid map records. With this method, both surface (SEM) and internal (LM) features of palynomorphs are readily available for the accurate description and identification of specimens. The resolution of gold coated specimens in LM compares favorably with conventionally mounted specimens. INTRODUCTION Although the SEM (scanning electron microscope) and LM (light microscope) offer different and complimentary types of information, the use of both techniques for same-specimen taxonomic study of palynomorphs is an uncommon practice. During the past 15 years very few studies have utilized both techniques (Doyle et al. 1975; Schrank 1983, 1987; Zippi 1987). SEM observations are clearly valuable for taxonomic and stratigraphic information (Reyre 1971; Doyle et al. 1975; Hughes et al. 1979; Schrank 1983, 1987; Chapman 1986, 1987), but the routine use of SEM observations in palynological taxonomy and stratigraphy has been hindered by the difficulty in relating features observed on the SEM to those seen under light (Reyre 1971; Chapman 1986). Many features observed under SEM are too small to be resolved in light and similar features on different specimens viewed under different imaging systems may often appear surprisingly dissimilar. The scarcity of published studies incorporating same-specimen observation under SEM and LM may, in part, be a consequence of technical difficulties associated with preparing and viewing mounts suitable for both microscope systems. Mounting techniques used for same-specimen study with the SEM and LM previously relied on time consuming single grain mounts, or strew mounts with location coordinates that were difficult or impossible to transfer from the SEM to a light microscope. A quick and easy method for the study of the same strew mounted specimens on both a SEM and a LM is described herein. MATERIALS Coverslips 0.75 inch diameter circular, #1 thinness. Pen K+E Leroy? 4x0 tip (o.d. 0.02) with waterproof ink. Grid template inch wide copper strips soldered inches apart for 0.1 inch spaced lines (see text-figure 1). Strips can be cut from copper sheet or any suitable material that will keep a straight edge with repeated use. Grid maps large scale replicas of the inked coverslip grid printed on sheets of paper for recording comments and positions of specimens. Elvacite? 2044 (Dupont) 65 grams of Elvacite dissolved in 110 ml of xylene. Other materials SEM sample stubs, double-sided adhesive tape, carbon paint, microscope slides. Coverslip preparation 1. Clean a #1 thinness, 0.75 inch diameter circular coverslip. 2. Draw an ink grid on the coverslip. Use the template to draw six evenly spaced parallel lines, then turn template 90? and draw six more lines to form a grid of squares. Number the outer left column and bottom row of squares as X and Y axes and mark the center square with a reference mark as shown in text-figure 2. The ink will dry in a few seconds. SEM sample preparation 3. Start with a concentrated palynological residue in distilled water or another medium that will evaporate without precipitating solids. Mix the residue in a vial so that the density of the suspended residue approaches the final density desired for slide making. 4. Place an appropriate amount of the suspended residue/water mixture onto the coverslip (inked side up) and adjust the density micropaleontology, vol. 37, no. 4, pp. 407-413, plates 1-2, text-figures 1-5, 1991 407 This content downloaded from 157.55.39.141 on Mon, 18 Jul 2016 05:11:49 UTC All use subject to http://about.jstor.org/terms P. A. Zippi: SEM and light microscope mounting and specimen location techniquefor study ofpalynological strew mounts 0.09 copper strips 1 / solder strips 0.12 apart I^ ^ EA Coverslip Aluminum stub A /A TCfC)72 (?b~fi TEXT-FIGURE 1 Copper template for drawing evenly spaced ink grid lines on coverslips.