Diversidade e composição ecológica do conteúdo palinológico de depósitos neogênicos (formação solimões) e holocênicos da bacia do Solimões

Abstract

The present study have by its principal objectives to answer bioestratigraphic and paleoecologic questions about the western Amazon paleoflora of the Neogene period (23 million years Before Present ) through the study of palinogical content present in a core (1A-15-AM) collected from Solimões Formation (AM), Brasil (Neogene) and also the study of the palynological content from recent sediments (Holocene) collected in different deposition subambients of Solimões Basin. It was counted a number of 300 spores and grains of pollen per sample and parallelly other palynomorphs present in the slides (dinoflagellate cists, algae cellule, acritarchs, foraminifers). 51 samples were analyzed (30 from the 1AS-15-AM profile and 21 of the holocenic material). After the taxonomic analyses and the count of the material were tabulated datas of FAD (First Appearance Datum) and LAD (Last Appearance Datum) for the palynomorphs present in the profile 1AS-15-AM aiming to date the sediments by the graphic correlation method. The taxa were classified according to its ecology and also was made use of statistical indices to characterize the palynomorph diversity. A total of 284 pollen types were found in the 30 analyzed samples of the fossil palinoflora from the 1-AS-15-AM core (234 of angiosperms and 50 of pteridophytes). In the 21 analyzed samples of the recent material, 231 pollen types were found (202 of angiosperms and 29 of pteridophytes). A total of 46 new species are described for fossil material, 10 new species of spores and 36 new species of pollen and through graphical correlation is attributed the final age of late early Miocene to early late Miocene (16.1 to 7.1 Ma) to sediments of core 1-AS-15-AM. The predominant types in the fossil palinoflora were M. franciscoi and Poaceae and types associated with lowland floodplains and undifferentiated lowland amazonian environments for Holocene palinoflora. The statistical indices evidenced a lack of difference of the fossil and holocene palinofloras in relation to diversity, but a great difference in relation to the composition. It was possible to conclude with the work that the vegetation of the Northwest of the Amazon Basin underwent great changes from the Neogene period (23 Ma) to the present, reflecting the presence of the system of large lakes (Early-middle Miocene ) its extinction (Late Miocene) and establishment of an erosive fluvial system (Pliocene until current period). On the other hand, its vegetation has always been that of a typically tropical forest as we know it today.