The record of marine ingression in western Gondwana from Devonian conodonts in the Amazonas and Solimões basins, Brazil

During the Devonian, the Gondwana supercontinent was in a paleogeographic position in high-latitudes, close to the South Pole. The arrangement of continents, tectonic activity, climate fluctuations, and the evolution of marine life played an important role in the marine ecosystems during this period. Conodont occurrences in high-latitudes are scarce. In the Upper Devonian (Frasnian/Famenian) of western Gondwana, conodonts have been found in anoxic black-shale deposits associated with maximum flooding surface (MFS) of a distal platform, in the Barreirinha Formation of the Amazonas Basin and Jandiatuba Formation of the Solimões Basin, in northern Brazil. The fauna is characterized by low diversity and well-preserved platform and ramiform elements of Mehlina gradata, Ozarkodina sp. aff. O. sannemanni, Cryptotaxis sp. and Polygnathus sp. in the Amazonas Basin and Cryptotaxis sp., Parapolygnathus sp., Pandorinellina sp., and Hibbardella sp. in the Solimões Basin. The conodont faunal association and sedimentary succession suggest a marine ingression in cool water conditions to the Devonian sea of the Amazonian region.