Reassessment of Viséan miospore biostratigraphy in the Amazon Basin, northern Brazil

A late Visean age within the late Holkerian–early Brigantian time span (TC–VF zonal range) is proposed for the highest, shalier, transgressive part of the Faro Formation in well 2-LF-1-AM and equivalent sections of other Amazon Basin boreholes, which in some cases have been misattributed to the underlying Oriximina Formation. Late Tournaisian–middle Visean microfloras (CM–TS zonal succession) are now regarded as absent in at least the Amazonian regions of northern Brazil. This supports the hypothesis of a regional unconformity separating the late Visean sequence from the latest Famennian/early late Tournaisian sequence in those areas. Palaeoenvironmental factors of uncertain nature seem to have controlled the presence or absence of miospore index-species (either of Euramerican or Gondwanan affinities) in the Amazon Basin. Such erratic nonoccurrences have led to miscorrelations of local miospore successions. Early to middle Visean sections are either missing or highly condensed in northern Brazil, and a similar situation may occur in North Africa and adjacent regions.