Foraminifers
Sampling
Beginners
should concentrate on recent species first. Foraminifers are exclusively marine
organisms, usually benthic. We find the tests concentrated in the sands of the
so called "high water mark", that means in that area of the beach
which is abundantly covered with debris and dried seaweed. Collect approximately
100 grams of the upper layer of sand (1 cm) with a spoon, or rather with a small
trowel, and put the sample into a plastic bag. If the sample is dry, it can
be immediately processed. If it is wet wash it very thoroughly with tap water
and afterwards with distilled water. Damp samples must be kept wet because salt
crystals will destroy the tests.
Fossil species can be found in tertiary clays and in chalk layers of the cretacous era, but not each sediment of the tertiary era contains foraminifers - ask specialists!
Tertiary clays are broken into small pieces of about 1 cm length. These pieces are covered with hydrogen peroxide of 12% (use a big jar because of foaming!) The penetrating peroxide reacts mainly inside the small lumps producing gas bubbles of oxygen which gently press the sample apart. When the sample has become pulp, elutriate the fine clay particles, wash several times with tap water, then with distilled water and dry the sample on blotting paper. Professionals rinse the sample through a set of sieves (mesh size 2 mm to 0.05 mm), but such sets are expensive.
Chalk is also broken into small pieces, then covered with water-free (!) acetic acid ( "glacial acetic acid "), which is mixed with 10 grams of anhydrous (!) copper sulfate per 100 ml to absorb the water formed by chemical reactions. Water free acetic acid dissolves the matrix of the chalk without destroying the foraminifers, although the tests are sensitive against acids! When the process has finished pour off the acid and wash quickly (!) with tap water until there is no longer any acidic reaction (pH paper!). Elutriate fine particles, wash the sediment with distilled water and dry on blotting paper. A set of sieves is recommended.
Selecting foraminifers
Studying foraminifers is not expensive! You need a simple binocular microscope, some PETRIE dishes and a fine pointed sable paintbrush, also about 100 "PLUMMER cells" for storing the specimens selected.
Cover the bottom of a PETRIE dish loosely with a small portion of the sample, put it on a dark surface and pick out the interesting objects under the stereo microscope by touching them with the damp paintbrush. Transfer them into a PLUMMER cell. It is more convenient to use a special picking tray with ists bottom being marked like a checkerboard to make a quantitative selection easier. Even better is a special picking tray with a perforated bottom: Make a small frame for a PLUMMER cell, place the dish with its first hole directly above the cell, then push each foraminifer into the hole with a needle. Move the dish to the next marked square and do the same.
As a sample does not only contain foraminifers but many other organisms (small shells, small mussels, parts of echinoderms, elements of sponges and corals, skin teeth of sharks, conodonts, ostracodes and much more), the beginner should first separate everything. Then try to distribute the elements found to different PLUMMER cells. All cells are labelled with the date and the locality and the bulk of the sample should be kept in a glass jar for subsequent investigations. Later it is recommended to fill one PLUMMER cell with all foraminifers of one location to get a quantitative section and to prepare cells containing only tests of identical species.
How foraminifers are identified
Foraminifers always show internal compartments that can be easily recognized in transparent forms. Opaque forms must be soaked with castor oil, which makes them transparent. Many tests confusingly resemble small shells (Fig.1, Fig.2), but the difference can be seen when inspecting the aperture of the test: shells always have a large aperture while foraminifers never have one. The aperture is either small (Fig.3 , Fig.4) or instead of an aperture there are only a few pores or slots to allow the plasma to leave the test. Foraminifers which build their tests by incorporating sand for example, are very difficult to identify as foraminifers - this can only be done only through experience.
How to improve experience
A beginner should not immediately try to determine the species found! It is much better to make a collection of PLUMMER cells first and to enjoy the abundance of different forms of objects. Later join a group of specialists. You can find these groups on the internet.
Sooner or later you have to buy a more powerful stereo microscope. The optical quality of the device is important, but also a good "ergonomic design" so that working without stress is possible. An (expensive) trinocular tube is recommended to always have a digital camera at hand.
One more tip may be added: Magnificent pictures of foraminifers are obtained by using a dark-field reflected light microscope. Such devices are very expensive - perhaps it is possible to get access to such a device by contacting a geological institute.
Finally, here is a remark concerning the SEM images of foraminifers of this site: To study foraminifers a scanning electron microscope is not required, it is even a disadvantage, since you can see the objects only from outside and you cannot move them into any direction (which is very important for their identification!). A visual examination under a stereo microscope is not only cheaper but even more informative! Only in case of photographic representation the SEM is more powerful because of its extraordinary depth of field and the possibility of digital post-processing.