Diatom Microfossils in Archaeological Settings

Abstract

The full potential of diatom microfossils in archeology has yet to be realized. Here were present a review of the use of diatoms in archeological settings. Included in this, we explain what diatoms are, the important components of their morphology, how they can be recovered from a range of materials, and how to distinguish these microfossils from other siliceous fossils with which they might be confused. We discuss their ability to provide robust environmental information from sites within and adjacent to archeological sites, along with specific examples from case studies that have used diatoms. We also recommend ways to avoid potential interpretive biases.

Description of the Plates

The following selection of plates is meant to showcase a wide range of diatom images to give readers enough examples to be able to distinguish diatoms from other microfossils. For a more complete collection of diatom images that could be used for genus or species level identification, we recommend visiting online guides representative of regional flora, such as Diatoms of the US (Spaulding et al. 2019) or Freshwater Diatom Flora of Britain and Ireland (Jüttner et al. 2018).

The following images have been arranged into broad groups, starting with “centric” diatoms. Centric diatoms have symmetry around one or more points (see, e.g., Plate 1). Most centric diatoms live either as solitary planktonic organisms, representing open water (Plate 1, Figs. a–d, f–k, n–r) or filamentous colonies representing environments ranging from open water (Plate 1, Figs. t–v), to flowing water (Plate 1, Figs. e, w), to aerophylic habitats (Plate 1, Fig. l, m, s).

The remaining images represent “pennate” diatoms, which are characterized by symmetry around one or more planes (see Plates 2–7). Pennate taxa can be further grouped by the absence/presence of their raphe structure on one or both valves, the type of raphe present, and the type of valve symmetry typically expressed. Most araphid pennate diatoms (Plate 2) are colonial (see Plate 2, Figs. i, s) and may represent either shallow or deep water environments. In contrast, most diatoms with one or more valve with a raphe structure present (Plates 3–7) typically represent aquatic environments where benthic substrates are sunlit.

All images in the plates were collected using a light microscope outfitted with differential interference contrast, collected at 1000× magnification. All images for the plates are identically scaled; all scale bars shown in Plates 1–7 are 10 μm in length.