En silurisk transgressiv karbonatlagerföljd vid S:t Olofsholms stenbrott, Gotland

Sammanfattning: An investigation of carbonate sediments from the upper part of the Slite Beds on Gotland shows that the deposition has occurred in a shallow oxidated marine environments. The sediments in S:t Olofsholms Quarry consist of six different lithologies: 1) Coarse-grained crinoid rudstone, 2) Fine-grained crinoid rudstone, 3) Coarse-grained crinoid grainstone, 4) Fine-grained crinoid grainstone, 5) Floatstone 6) Boundstone The sediments consist for the most part of crinoid fragments of sand to gravel size and were deposited during high energy conditions close to a reef. A high frequency of detrital, overturned stromatoporoids indicate that storms were important. High energy environments are reflected by erosional surfaces, low-angle cross-bedding, shell lags and large-scale wave ripples. The lithologies and sedimentary structures indicate shoreface deposition. The upwards fining grain size and the decreasing frequency of redeposited stromatoporoids point towards a gradually decreasing energy, which can be related to a known relative sea-level rise. The sandy and silty sediments with small solitarian biostroms (floatstone and boundstone) at the top of the succession can be interpretated as deposited few metres below sea level, were nutrient and energy conditions were suitable for the formation of patch reefs. Fine sediments (floatstone) only occur trapped in biostrome cavities.