New sedimentological and palynological data from surface Miocene strata in the central Amazonas Basin areaNew sedimentological and palynological data from surface Miocene strata in the central Amazonas Basin area

Abstract

The scarcity of stratigraphic data has hindered the demarcationof the outcropping area of Miocene deposits of the AmazonBasin, represented informally by the Novo Remanso Formation.Moreover, this unit is characterized by a sparse and irregular geographicdistribution due to its sedimentological features and rare fossilcontent. Miocene deposits cropping out in central Amazonas Basinarea were described in sedimentological terms and analyzed palynologically.All analyses were undertaken in samples collected at theUatumaRiver banks (Itapiranga and Sao Sebastiao do Uatuma cities).Lithostratigraphic data shows that Novo Remanso Formation consistsof sandstones, with subordinate conglomerates and pelites, characteristicof a meandering fluvial paleosystem, with fluvial channel, pointbar, floodplain and crevasse splay facies. The palynoflora retrieved fromfive samples consists exclusively of continental-origin palynomorphsdominated by angiosperms species. Trilete spores are well represented,while gymnosperms pollen grains are minor components. The presenceof Psilastephanoporites tesseroporus, Syncolporites poricostatus, Jandufouriaseamrogiformis and Polypodiaceoisporites potoniei ensure these depositsfits into the Grimsdalea magnaclavata palynozone (Regali et al.1974a, b), and the Grimsdalea magnaclavata/Crassoretitriletes vanraadshoovenipalynozones of Jaramillo et al. (2011) considered MiddleMiocene age. This age is confirmed by the zonation of Jaramillo et al.(2011), based on the LADs of Bombacacidites baumfalki (11.57Ma)and Crototricolpites annemariae (12.91Ma); and the FAD of Psilastephanoporitestesseroporus (14.00Ma). With these new data presentedherein, it is possible to assume that the Miocene strata represented bythe Novo Remanso Formation covers a larger area in the basin thanpreviously considered, and that it may be extended for about 300 kmuntil the Manacapuru village, indicating a Miocene subsidence phase.