THE EFFECTS OF SPRING LEVEL ON STROMATOLITE LAMINATION AND MORPHOLOGY, YELLOWSTONE NATIONAL PARK

Siliceous stromatolites were collected from a hot spring in Yellowstone National Park in order to investigate environmental effects on stromatolite morphogenesis. Light-dark couplets comprised of weakly mineralized cyanobacterial filaments constitute the main body of the stromatolite. A less common style of lamination drapes the entire structure, contains coccoidal and filamentous forms and diatoms, and is well-cemented. During stromatolite growth, the main body style and the drape style lamination alternated.

In situ growth experiments coupled with micro-stratigraphic investigation of existing stromatolites suggest that the light-dark couplets are linked to rising water levels, whereas formation of the drape represents falling water levels/emergence. Overall, the structures grow a few cm per year. ¹⁴C analysis produced anomalously old ages versus the growth experiments, where the main body consistently contained lower Δ¹⁴C versus the drape fabric. When used as a tracer rather than an indication of age, the ¹⁴C data are consistent with the observations from the in situ growth experiments: as CO₂ from the hydrothermal vent waters is likely radio-carbon dead, the main body formed deeper in the spring, resulting in a greater influence from spring derived CO₂ during photosynthetic CO₂ uptake, and the drape formed when the structure was emergent or nearly emergent, resulting in a greater incorporation of atmospheric CO₂. ¹⁴C may be a particularly useful tracer for the uptake of CO₂ from different sources in this, and perhaps other similar systems.

Several environmental factors may influence stromatolite growth in the spring. Hourly temperature logs from Obsidian Pool Prime record near-diurnal variability but also seasonal trends and storm-events which cool pool waters by >15°C enhancing SiO2 supersaturation. It is possible that the changing spring levels record larger-scale climatic and geologic processes in Yellowstone National Park.