Miospore biostratigraphy of the type Barreirinha Formation (Curua Group, Upper Devonian) in the Tapajos River area, Amazon Basin, North Brazil

The miospore biostratigraphy of the Barreirinha Formation in its type area (Tapajos River near Itaituba town, Para State, North Brazil) has been assessed in terms of the two most used miospore zonal schemes for the Old Red Sandstone Continent and adjacent regions. The present study is based on the palynological investigation of 375 core samples from the Caima PH-2 shallow borehole. This section, altogether ca. 137 metres thick, encompasses the whole Barreirinha Formation, plus the lower part of the overlying Curiri Formation, and perhaps the top of the underlying Erere Formation. The lowest 35 metres of radioactive black shales in this borehole make up the lower part of the Barreirinha Formation, and are demonstrated to correspond to a rather condensed section comprising possibly the entire Frasnian and much of the Famennian despite the absence of Early and Middle Famennian diagnostic miospores. In contrast, the upper three-quarters of the studied section, not less than 96 metres in thickness, display the same Late Famennian (pre-'Strunian') age. This younger section includes the less radioactive shares and the siltstones of the upper Barreirinha and lower Curiri units. Comparisons are made with the miospore assemblages of other correlative Sections previously studied in the subsurface of the Amazon Basin.