The Morrowania Tokan Bounoary in the Amazonas Basin, base on Conodont investigation

Abstract

In the Amazonas and Solimões basins the Carboniferous sequence is represented by Monte Alegre and Itaituba formations, and at least, the lower portion of Nova Olinda Formation. Within the interval comprised by the aforementioned formations it was possible to identify the Morrowan/Atokan boundary in wells 2-CA-1-AM and 1UI- 1-AM situated in the middle portion of the Itaituba Formation. Two zones of conodont association were established: the first zone comprising the Monte Alegre Formation and the lower portion of the Itaituba Formation, has been designated Neognathodus symmetricus/Rachistognathus muricatus, and the second zone recognized in the middle-and upper portions of the Itaituba Formation was designated Diplognathodus orphanus/ Diplognathodus coloradoensis. The first zone presents typical elements of the Morrowan, and lhe second zone shows forms attributed to the Atokan. The interval comprised by the two zones is the most enriched with conodonts within the basin, test ifying the presence of normal marine environments developed during longer time spans during each of the cycles lhat characterize the Carboniferous sedimentation ot the Amazonas Basin.