Dispersed spore assemblages from the Lower Devonian Rañeces - La Vid groups of Northern Spain: Palaeogeographical implications

Abstract

Dispersed spore assemblages are described from the Early Devonian (late Lochkovian-late Emsian) Rañeces Group (Asturias) and equivalent La Vid Group (Leon) of Northern Spain. The lower part of both groups consists predominantly of limestone and yields only impoverished palynological assemblages. However, the upper parts contain more clastic sediments and yield rich assemblages of well preserved palynomorphs. These are dominated by marine forms but also include abundant spores. Sixty-two spore taxa are reported from the Valporquero Formation (Leon). These all belong to a single assemblage that can be equated with the lindlarensis-sextantii Assemblage Zone (mid-early late Emsian age) erected in northern Gondwana. The sequences are independently age constrained by conodont and invertebrate macrofossil evidence and the ages derived from these studies are concordant with the assigned spore zones. The Spanish spore assemblages are from deposits that accumulated around the Armorican Terrane Assemblage (ATA), a group of islands that lay between the continents of Laurussia and Gondwana. Jacaard Index analysis indicates that the Valporquero Formation spore assemblage is endemic, and not closely related to those previously described from Laurussia or Gondwana, although it has more in common with the latter. This suggests that the Armorican Terrane Assemblage was widely separated from both Laurussia and Gondwana, but was located closer to and had more connectivity with Northern Gondwana.