Furongian (Cambrian) agnostoids of Scandinavia and their implications for intercontinental correlation

Abstract

AbstractOut of the 14 agnostoid species/subspecies so far recorded from the Furongian of Scandinavia, seven are excellent biostratigraphical indices and important for correlation between Baltica and other palaeocontinents.Glyptagnostus reticulatus,Aspidagnostus lunulosusandAgnostus(Homagnostus)obesusfirst appear at the base of theG.reticulatusZone, allowing a precise correlation of the base of the Paibian Stage into Scandinavia.Tomagnostella orientalisandPseudagnostus cyclopygeappear near the base of theParabolina brevispinaZone, suggesting a correlation with the uppermost Paibian through the lowermost Jiangshanian stages.Lotagnostus americanus andPseudagnostus rugosushave an intercontinental distribution and their first appearance in Scandinavia allows for a correlation with one of the most favourable levels for defining the base of Cambrian provisional Stage 10. In the Furongian of Scandinavia, agnostoids are conspicuously assembled in three different intervals: the lowerGlyptagnostus reticulatusZone, the lowerPseudagnostus cyclopygeZone and theLotagnostusamericanusthrough lowerTrilobagnostus holmizones. The agnostoid-barren and largely unfossiliferous succession separating the lower and middle agnostoid-bearing intervals can be explained by means of subsequent dissolution of the calcareous fauna and/or a hostile environment. The middle agnostoid-bearing interval is succeeded by an anomalous succession dominated by the orthide brachiopodOrusia lenticularis, reflecting a regressive event coupled with increasing levels of oxygen at the sediment/water interface. This shallowing evidently resulted in unfavourable conditions for agnostoids.