Original Article

Polychaete palaeoecology in an early Late Ordovician marine astrobleme of Sweden

MATS E. ERIKSSON^a1 c1 and ÅSA M. FRISK^a2

^a1 Department of Earth and Ecosystem Sciences, Division of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden

^a2 Department of Earth Sciences, Palaeobiology, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden

Abstract

The post-impact Dalby Limestone (Kukruse; Upper Ordovician) of the Tvären crater, southeastern Sweden, has been analysed with regards to polychaetes, as represented by scolecodonts. A palaeoecological succession is observed in the Tvären-2 drill core sequence, as the vacant ecospace was successively filled by a range of benthonic, nektonic and planktonic organisms. Scolecodonts belong to the first non-planktonic groups to appear and constitute one of the most abundant fossil elements. The polychaete assemblage recorded has an overall composition characteristic of that of the Upper Ordovician of Baltoscandia. Oenonites, Vistulella, Mochtyella and the enigmatic ‘Xanioprion’ represent the most common genera, whereas Pteropelta, Protarabellites?, Atraktoprion and Xanioprion are considerably more rare. The assemblage differs from coeval ones particularly in its poorly represented ramphoprionid fauna and the relatively high frequency of ‘Xanioprion’. A taxonomic succession and changes in abundance and relative frequency of different taxa is observed from the deepest part of the crater and upwards towards more shallow water environments. The initial post-impact assemblage does not, however, necessarily represent a benthonic colonization of the crater floor. Instead it seems to be a taphocoenosis, as indicated by its taxonomic correspondence to the rim facies fauna recovered from Dalby Limestone erratics of the Ringsön island. The Tvären succession has yielded considerably richer scolecodont assemblages than hitherto recorded from the approximately coeval Lockne crater, possibly as a consequence of shallower water settings in the former area.

(Received October 07 2009)

(Accepted May 27 2010)

(Online publication August 04 2010)

Keywords:

• palaeoecology;
• scolecodonts;
• polychaetes;
• impacts;
• Kukruse;
• Upper Ordovician;
• Tvären Bay;
• Sweden

Correspondence:

^c1 Author for correspondence: Mats.Eriksson@geol.lu.se