Wackestone petrography and bipolar orientation of cephalopods as indicators of littoral sedimentation in the Ludlovian of Gotland

Abstract

The orientations of the apical end of orthoconic nautiloids that occur in abundance on the bedding planes of a sequence of wackestones in the Hemse Beds show two subequal opposing maxima, giving a bipolar orientation pattern. The petrography of the wackestones indicates an early lithification. It is concluded that the rocks represent littoral deposition in a lagoonal environment, and that the nautiloid shell accumulations were caused by stranding in connection with ephemeral incidents. The inferred bathymetry contradicts earlier opinions based exclusively on palaeontological criteria.

Key Words:

• Limestone petrography
• early lithification
• orientation of cephalopods
• bipolar orientation
• littoral sedimentation
• ephemeral sedimentation
• bathymetry
• Hemse Beds
• Ludlovian
• Silurian
• Gotland
• Sweden
• N5726 N5727 E1854 E1853