Benthic response to the strong Silurian climatic fluctuations – implications from Gotland (Sweden)

Climatically the Silurian was a most unstable period, as it is shows several strong d 13C excursion, with the Lau excursion being the strongest short-lived positive d 13C excursion of the entire Phanerozoic. The causes of these excursions are still debated. In order to determine how benthic communities responded to these climatic perturbations, a microfacies analysis of carbonate rocks from the Silurian (Late Telychian to the uppermost Ludfordian) of the Gotland was carried out. Reef development was strongly enhanced during periods with carbon isotope excursions, compared to time intervals without. In times of very high d 13C values (≥ 3‰) bryozoans and microbes become more abundant and, in some areas, form reefs (Bryostromatolites), while corals and stromatoporoids were the main reef builders in periods of lower isotope ratios (0–3‰). In addition, a significant increase of phosphatic components, gypsum pseudomorphs and the microproblematicum Palaeomicrocodium is observed in times of increased isotope ratios. A model is proposed explaining the changes in the benthic communities over time. It is based on previously published models which assume climatic shifts from humid to arid climate but adds phosphorous in sea water as an important factor for the development of the benthic communities