Waco Gem and Mineral Club, Waco, Tx

16.6 Collecting Preparing and Storing Microfossils

 

16.6: Collecting, Preparing, and Storing Microfossils

Collecting microfossils. In areas of recent marine deposits, microfossils might be mixed loose with soft sediments (sand and mud), requiring only that you scoop up a sample and sift it through a screen. Or microfossils might be embedded in limestone, sandstone, or shale. To check sediment or rock samples, take a 10X or 20X loupe into the field. If you detect small fossils in a sediment sample, take home a supply in zip-lock baggies; if in matrix of hard rock, take several hand pieces home. Use the same tools already listed in Activities 16.4 and 16.5, but add sifting screens of various mesh sizes. You can purchase stackable graduated screens from geological supply houses such as Ward‘s, or you can do like I did and make your own with wooden frames and screens of various sizes purchased from a hardware store, starting with quarter-inch down to window screen and smaller. Small trowels and hand rakes are handy for sifting through soft sediments and dirt containing fossils that may have weathered out of a limestone, sandstone, or shale bank. It‘s always a good idea to sift through dirt surrounding such "hard rock" outcrops.

Preparing microfossils. For microfossils in soft sediment and for those that are weathered free in the dirt around hard sediments, all that‘s required is sifting away the sediment with a series of graduated screens. You‘ll also want a bench magnifier that allows for hands-free work or even better, a binocular stereomicroscope, commonly called a dissecting microscope, along with stick pins and tweezers. Work should be done on a tray under good lighting so tiny specimens don‘t get dropped and lost. (Microfossils embedded in limestone may be freed in acid baths and those in shale can sometimes be freed by soaking samples in kerosene, but those techniques are best reserved for adults exercising due precautions; see the references listed below for specific techniques.)

Storing microfossils. Microfossils can be prepared as "micromounts" in the same manner as microminerals, within small micromount boxes (see Activity 16.3). Alternatively, professional geology supply houses, such as Ward‘s, sell small slides made especially to hold microfossils. These are made of two layers of cardboard, a glass top, and an aluminum frame to hold the glass atop the cardboard. Specimens may be glued in with a small dab of white glue or a droplet of gum tragacanth or gum arabic.

Although most reference books published about microfossils are pitched to an adult audience, they provide fine reference for any adult working with kids on this activity:

Brasier‘s Microfossils (1980). This one is detailed and technical!

MacFall & Wollin‘s Fossils for Amateurs: A Handbook for Collectors (1972). Now out of print, this was a longtime standard for amateurs and is in many libraries or used book shops. Chapter 12 is a nice overview of microfossil collecting.

Margaret Kahrs (editor), Microfossils: M.A.P.S. Digest Expo XXI Edition (Mid-America Paleontological Society, Vol. 22, No. 4, 1999).

Jim Brace-Thompson, 'Microfossil Techniques: Tools & Methods for All Budgets', in Kathleen Morner (ed), Paleotechniques: M.A.P.S. Digest Expo XXVI Edition (Mid-America Paleontological Society, Vol. 27, No. 2, 2004). (Call me for reprints.)

Note: Kids can use this activity to satisfy requirements toward earning the Collecting badge simultaneously (Activity 5.1).