Climate influenced deposition on a low latitude Sheinwoodian carbonate ramp, Gotland, Sweden

Sammanfattning: The Sheinwoodian succession of Gotland comprises the Högklint, Tofta and Hangvar Formations and most of the Slite Group. The succession consists of hierarchically ordered shallow marine depositional cycles, produced by orbitally forced climate changes. During warmer and wetter intervals (climate maxima) more carbonate was produced than during the cooler and dryer climate minima. Higher carbonate production was the outcome of an overall higher water turbulence (waves, storms and currents), higher temperatures and therefore higher sea-levels during climate maxima. As a consequence of lower temperatures during climate maxima, weaker winds and lower sea-levels resulted in lower turbulence levels which in turn resulted in lower carbonate production. Based on the climate-deposition model presented herein a local sea-level curve was derived which harmonises with the global standard sea-level curve. The only significant relative sea-level change for the study area is a shallowing upward trend throughout the entire succession. Cyclic changes in tempestite thickness and frequency are interpreted as mainly dependent on variations in storm frequency and magnitude. The studied succession was deposited during low-amplitude sea-level changes, mainly due to thermal expansion, and probably without the impact of melting and waxing polar ice caps. A sequence stratigraphic interpretation is presented where outcrops and cores were linked. The nine long eccentricity cycles (413 ka) detected may correspond to fourth order sequences and the two superimposed longer fluctuations (2 Ma) may correspond to two third order sequences.