The Burgsvik Beds, an Upper Silurian storm generated sand ridge complex in southern Gotland, Sweden

Abstract

The abundance of hummocky cross stratification in fine and very fine grained calcareous, micaceous, quartz arenites in the Ludfordian Burgsvik Beds of southern Gotland, Sweden, indicates that this sequence formed in a storm influenced environment as a detached shoreface bar. Oolitic to pisolitic strata within and at the top of the formation, formed in response to oscillating currents which swept the bar tops in water depths of less than 10 m. While there is possible evidence for local emergence in the form of rill marks, most of the sequence was developed below storm wave base. Wrinkle marks, developed on the top of hummocky cross-stratified sands were produced by wave induced fabric collapse. Similarly large scale loadcasts were produced by repetitive wave shock and not by seismic activity.

Key Words:

• Ludlovian
• Gotland
• hummocky cross-stratification
• wrinkle marks
• load structures
• fabric collapse
• storm deposits
• detached shoreface bars
• liquefaction
• wave shock