Abstract

The vertical orientations of shells of Rhynchorthoceras in Lower Ordovician limestone at Satatorp, Vastergotland, Sweden indicate that these shells stranded in unconsolidated carbonate sediment in shallow water. The mean position for the siphuncle, which takes up 1/6 of the diameter of the shell, is at 267 degrees (almost directly in the bottom location) with an angular deviation of 27 degrees . It is suggested, that the shells have remained undisturbed by swash action sufficiently long to become securely fastened in the sediment. This suggests the possibility of using the orientation of the siphuncle of suitable orthoconic nautiloids as an indicator of rolling action by swash currents after stranding.

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