Gypsum evaporites in the Ludlovian of Gotland

Abstract

Gypsum crystals in fine-grained limestone in a Ludlovian stromatoporoid biostrome on Gotland are believed to be the first evaporites described from Gotland. The haphazardly orientated and well formed crystals were found in sediment adhering to a stromatoporoid coenosteum, but not in contact with the stromatoporoid skeleton. Crystals cut across laminations in the sediment without displacement, thus indicating growth during post-lithification diagenesis. Therefore there is no implication of hypersaline conditions during the life of the biostrome's biota. Occasional dolomite rhombohedra also occur in the sediment near the gypsum. Although several processes may have produced the gypsum, its presence suggests that evaporative conditions may have existed in these beds and should be searched for elsewhere on Gotland.

Key Words:

• Gypsum
• evaporites
• Ludlovian
• Silurian
• Gotland