The timing of continental-scale marine flooding events in Western Amazonia during the Neogene is still an unsolved question. Despite broad proxy-based evidence of such events, the pathways and duration of late Miocene marine incursions remain controversial. We provide coupled calcareous and organic microfossil and geochemical data from six onshore cores from Neogene sequences of the Solimões Basin, Brazil. Our records support minor marine influence in the early Miocene (23.0, 21.1, 18.6, and 16.3 Ma), middle Miocene (14.9, 13.7, and 12.9 Ma) and early Pliocene (4.7, 4.2–4.1, and 3.8 Ma), and conspicuous marine incursions in the late Miocene (11.1–8.8 Ma) suggested by the consistent presence of salinity-indicative microfossils and geochemical data. Our findings challenge the view of major marine incursions in the early and middle Miocene in the studied area. We propose for the first time a new late Miocene incursion (LMI) event as the main marine flooding event in Western Amazonia during the Neogene. These onshore records are compared with three offshore cores from the Atlantic and Pacific Oceans. The similarity between microfossil assemblages of the Solimões Basin and the Caribbean Sea, and evidence of increased runoff from the Orinoco river drainage system, strongly suggest the Caribbean Sea as the primary source area of the marine incursions, supporting a Venezuelan seaway. We further show for the first time the potential linkage between Neogene marine incursions (mainly the LMI) into the Solimões Basin and major disturbances in the global carbon cycle.
This study reports a set of primeval marine incursions identified in the two drill cores (1PS-06-CE and 1PS-10-CE) recovering the Barbalha Formation, Araripe Basin, Brazil. Based on multi-proxy approach involving stratigraphy, microbiofacies, ichnofossils, and microfossils found in the Barbalha Formation, three short-lived marine incursions were identified, designated Araripe Marine Incursions (AMI). The AMI-1 and AMI-2, which occur within the shaly Batateira Beds (lower part of the Barbalha Formation), were identified through the occurrence of benthic foraminifera, calcareous nannofossils, dinocysts, and a mass mortality event of non-marine ostracods. The AMI-3 is recorded in the upper part of the Barbalha Formation and its identification was based on occurrence of ichnofossils and planktic foraminifers. The presence of planktic foraminifera genus Leupoldina suggests, for the first time in the basin, an early Aptian/early late Aptian age for the deposits and allows correlation of this unit with global foraminifera biozonation. Our findings have implications for the breakup of the Gondwana Supercontinent, as these incursions represent the earliest marine-derived flooding in the inland basins of Northeastern Brazil.
Additional information on geological settings; materials and methods; references; supplemental Figures S1–S5; a summary of samples processed and analyzed in this study by site and technique; and full age-calibrated microfossil and geochemical data sets.
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