Slim Pickings

Today’s entry is by student employee Tait Earney.  Tait has been spending considerable time picking for microfossils.  This is not a straightforward process where a sediment sample is dumped under a microscope and small fossils are removed randomly.  In order to properly assess the amount of sediment picked and to maintain a statistically accurate sample, a very specific protocol is followed which Tait outlines.  Note the attention that even our students pay to accurate documentation of samples.

“The samples that I have worked on were collected in 1994 from various formations in the Chesapeake Bay area. They are from the Miocene epoch, ranging in age from about 23 to 5 million years old. The focus of my efforts has been rather simple; pick through the sediment and identify/catalog all identifiable fossils. This may sound easy, but after spending a few hours looking through a microscope at individual grains of sediment only a few hundred microns wide, believe me when I say that both your head and eyes will begin to hurt. Before any of this begins, however, there is some prep work to be done.

As soon as we receive a new sample, before we begin any work, it is extremely important to properly document and record any field notes or information associated with the sample. This includes recording the sample number, weight of the unwashed fraction, weight of the washed fraction, whether or not there has been any prior picking, whether the sample was wet or dry sieved [screen washed under water or dry], as well as any locality information pertaining to where the sample was collected (nearby geographic features, formation, member, etc.). This information not only helps us in our analysis, but will also benefit others down the road should they need the same sample for their own research needs.

Once the sample has been properly documented, it is time to prep the sample for analysis. First, we weigh the unwashed fraction of sediment that will be analyzed for microfossils and record the value. We then put the same unwashed fraction through the splitter, sieving out anything larger than 2 millimeters at the same time. The splitter is a device that splits the sample into two bins of equal weight. We repeat this process until we get a fraction of the original sample that weighs around 100 grams.

The splitter, used to accurately divide samples into equal portions.
The splitter, used to accurately divide samples into equal portions.

The rest of the unwashed fraction is set aside, and not used in the rest of our analysis. Then, we proceed to wash the 100 gram fraction of sediment in a 63 micron sieve. This breaks up any remaining sediment chunks, and removes the smallest particles which would be too difficult to analyze under our microscopes. Once the sediment has dried, we take a 2 gram sample and break it down into fractions of 500 microns, 250 microns, and 125 microns. These fractions are then what we analyze under the microscope and pick for microfossils. This whole process takes about 30 minutes to complete, not including the amount of time it takes for the sample to dry after it has been washed.”

Thank you for reading and Happy Holidays!


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