Deposition and diagenesis of a reef-like limestone of the wenlockian slite beds on gotland, Sweden

A 100 m Iong and 12 m high section named Spillings 3 cuts vertically through the marginal part of a subcircular reef-like limestone body in the uppcrmost Slite Beds (upper Wenlockian). The limestone is massive, abounds in Iarge sedentary fossils, and directly rests on stratified limestone. The rocks in the upper part of the section contain a higher proportion of large fossils than the rocks in the lower part. Stromatoporoids form a frame- work, 10 m across, in the marginal part within the reef-like body. In thin sections, the matrix limestone is micritic and the common fossil components are echinodcrms, bryozo- ans, and calcareous algae. The limestone was exposed and mechanically fraetured in a subaerial environment. Fracture cavities were filled with stratified crinoidal limestone, dark grey micritic calcarenite, and stromatolitic sediment. The subaerial exposure is indi- cated by the occurrence of vadose cement protruding downward from echinoderm grains. The investigated section contains various kinds of sedentary organisms, such as stromatoporoids, favositids, halysitids and rugose corals. The reef-like strueture is less mature than the Ludlovian reef limestones formed mainly by stromatoporoids. □ Gotland, upper M'en- lockian, reef limestone, quanlitative analysis, fracture, subaerial exposure, cathodolumin- escence, Slite Beds.