Plant remains from ancient sediments

During the weeks before Christmas I was busy at the microscope looking through sample after sample to select plant remains for radiocarbon dating. Radiocarbon dates provide us with an age for our sediment sequences, and to obtain good and valid ages, it is important to select the right type of organic material and to work in a clean environment to avoid any type of contamination. Radiocarbon dating is expensive, but without many dates, it is not possible to establish a good chronology. And only a well-dated sequence allows for comparisons and correlations to other well-dated sequences.

Before I could sit at the microscope, all our sediment cores had to be sampled and each sample had to be sieved, so that the fine sediment particles disappeared. What was left in the sieve, was what I could examine under the microscope. It is fascinating to go through sample after sample and to see how the composition of the organic material changes through time. Leaf fragments, seeds, flower buds, insect remains, chironomid head capsules, shell fragments, ostracodes, wood and twigs are just a few of all the material that can be observed.

Samples selected for radiocarbon dating will only be composed of terrestrial plant remains, which use atmospheric carbon dioxide, to avoid any bias connected with plants that would take up carbon from the lake water.

Since the tiny plant remains are so beautiful, I post a few pictures here. Too bad the scale disappeared, but imagine that these small, fragile things are not larger than 1-2 mm! Those shown below are about 14,000-16,000 years old and belong to arctic plants that once grew in southern Sweden.

Late Glacial plant remains

Late Glacial plant remains

Late Glacial plant remains

The following pictures are seeds and leaves, and shells from our tropical lake Nong Thale Pron. These are also between 10,000 and 16,000 years old and tiny!

Leaf fragments

Leaf fragments

Najas seeds

Shell

Seeds and leaf fragments

Seeds

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