Silurian-Devonian chitinozoan biostratigraphy along the Urubu, Uatumã and Abacate rivers in the western part of the Amazonas Basin, Northern Brazil

Outcrops along the Urubu, Uatumã and Abacate rivers in the western part of the Amazonas Basin, northern Brazil, have been investigated for chitinozoans. Diverse and abundant chitinozoan assemblages of Late Silurian (late Ludlow and early Pridoli) age occur together with early Lochkovian, early Givetian and Frasnian assemblages. The lower part of the Manacapuru Formation crops out extensively in the area, and can be as old as late Ludlow, which indicates that the base of this formation is diachronous. Other rock units less commonly exposed in this region include the upper Manacapuru (early Lochkovian), upper Ererê (early Givetian) and lower Barreirinha formations (Frasnian). Of the 54 species encountered (some for the first time in Brazil), 29 are left in open nomenclature, and three are newly described: Armigutta urubuense, Ramochitina bjornsundquisti and Saharochitina gomphos.