Re-investigating Miocene age control and paleoenvironmental reconstructions in western Amazonia (northwestern Solimoes Basin, Brazil)

Autor(es)

Kern, Andrea K. ^[1] ; Gross, Martin ^[2] ; Galeazzi, Cristiano P. ^[1] ; Pupim, Fabiano N. ^{[1, 3]} ; Sawakuchi, Andre O. ^[1] ; Almeida, Renato P. ^[1] ; Piller, Werner E. ^[4] ; Kuhlmann, Gabriel G. ^[1] ; Basei, Miguel A. S. ^[1]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Geociencias, Sao Paulo, SP - Brazil

^[2] Univ Joanneum, Dept Geol & Palaeontol, Graz - Austria

^[3] Univ Fed Sao Paulo, Dept Ciencias Ambientais, Diadema, SP - Brazil

^[4] Karl Franzens Univ Graz, Inst Earth Sci, NAWI Graz Geocetr, Graz - Austria

• Tipo de documento: Artigo Científico
• Fonte: PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY; v. 545, MAY 1 2020.
• Citações Web of Science: 1

Resumo

The modern Amazonian rainforest has a great fascination and global significance, but our knowledge of past landscape changes is still limited due to sparse data and the lack of radiometric age constrains. Precise dating in records older than the late Pleistocene are difficult to obtain and often regionally confined, therefore biostratigraphic correlations are used to estimate depositional ages across sedimentary basins. Aiming for a better understanding of the Neogene changes in western Brazil, we studied palynology and ostracod assemblages from the Solimoes Formation, a key site for paleoenvironmental models to discuss the biotic changes in Amazonia. Further, we compare the biostratigraphic information of both groups with radiometric maximum deposition ages constrained by U/Pb measurements on detrital zircon grains. Down to the depth of similar to 95 m, zircon populations show a maximum deposition age of 11.42 +/- 0.66 Ma documenting Tortonian (late Miocene) or younger ages for the top of the Solimoes Formation. Palynological biostratigraphy show the Psilatricolporites caribbiensis zone (latest Miocene-Pliocene) down to a depth of 181.8 m, where the Grimsdalea magnaclavata zone suggests a late middle Miocene to early late Miocene age. In comparison, ostracod biostratigraphy indicates the Cyprideis cyrtoma zone (late Miocene) down to 176.0 m and the Cyprideis minipunctata (late middle to late Miocene) for the bottom of the section. Thus, both biostratigraphic concepts suggest ages close to the maximum ages indicated by the detrital zircons. This comparison of the biozonations with U/Pb maximum deposition ages represents the first independent calibration of these widely used methods for age determination in the Solimoes Basin. Palynological and ostracod data illustrate dynamic environments varying from fluvial settings with wetland forests and swamps to lakes and/or abandoned channels with temporary slightly saline conditions. Instead of a slow evolution of Neogene Amazonian environments, our results show migrating rivers and waterbodies surrounded by rainforest during the period recorded by the base and top of the studied core material, separated by a phase of more extensive lakes and swamps (core depth 90-120 m). Indicators for slightly elevated salinity are found until the topmost sample and thus persisted during the late Miocene. This highlights the importance of new age control to improve the regional biostratigraphic timescale and reconstructed environmental changes. (AU)

• Processo FAPESP: 17/06874-3 - Dinâmica fluvial e depósitos sedimentares no Rio Amazonas: providenciando ferramentas para decifrar a evolução paleogeográfica da Amazônia e depósitos de grandes rios no registro rochoso
• Beneficiário: Cristiano Padalino Galeazzi
• Modalidade de apoio: Bolsas no Brasil - Doutorado
• Processo FAPESP: 14/23334-4 - Reconstrução de mudanças no sistema fluvial da Amazônia durante o Cenozoico tardio (<5 Ma) por meio da integração de análises por luminescência opticamente estimulada (OSL) e nuclídeos cosmogênicos (TCN).
• Beneficiário: Fabiano Do Nascimento Pupim
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 14/05582-0 - Estruturação e evolução da biota amazônica e seu ambiente: paleobotânica e palinologia da Bacia Amazônica
• Beneficiário: Andrea Kern
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 12/50260-6 - Estruturação e evolução da biota amazônica e seu ambiente: uma abordagem integrativa
• Beneficiário: Lúcia Garcez Lohmann
• Modalidade de apoio: Auxílio à Pesquisa - Programa BIOTA - Temático