Life in a Devonian marine lagoon

The article presents an overview of marine environments that existed in the area of present-day Poland around 380–360 million years ago, during the Devonian period, when this region was covered by an extensive shallow and warm sea. This sea was oversaturated with calcium, a component of the common biomineral calcite. Specific environmental conditions—elevated calcium concentrations, fluctuating salinity, and microbial activity—favoured the fossilization of microorganisms that normally are not preserved in the fossil record. Devonian marine sediments of southern Poland are thus a “taphonomic window” providing insight into ancient microorganisms that typically do not produce calcareous skeletons.

Illustration: Calcispheres (a kind of calcareous microfossils) from Sosnowiec IG-1 core with preserved organic matter. A–B. Volvocacean calcispheres with preserved cells forming a colony; C–D. Radiospherid (spinose) calcispheres with highly mineralized mucous envelopes around single-celled algae. Scale A the same for B and D. The central chamber of the calcisphere is typically between 30 and 50 µm.