Evidences for a Paleocene marine incursion in Southern Amazonia (Madre de Dios Sub-Andean Zone, Peru) (vol 414, pg 451, 2014)

M. Louterbach (1) , M. Roddaz (1) , J. Bailleul (2) , Pierre Olivier Antoine (3) , Sylvain Adnet (3) , J. H. Kim (4) , E. van Soelen (4) , F. Parra (1) , J. Gerard , Y. Calderon , C. Gagnaison (2) , J. S. Sinninghe Damste (4) , P. Baby (1)

1 GET - Géosciences Environnement Toulouse
2 Institut Polytechnique LaSalle Beauvais
3 UMR ISEM - Institut des Sciences de l'Evolution de Montpellier
4 NIOZ - Royal Netherlands Institute for Sea Research

This article presents new biostratigraphic dating, facies analysis, organic geochemical data and Nd–Sr isotopic provenance from five outcrops of southern Amazonia (MD-85, MD-177 MD-184, MD-255 and MD-256) to document for the first time the presence of a shallow marine ingression in the Paleocene of southern Amazonia basin. The co-occurrence of a selachian assemblage encompassing Potobatis sp., Ouledia sp., and Pristidae indet. with the ostracod Protobuntonia sp. and the charophytes Peckichara cf. varians meridionalis, Platychara perlata, and Feistiella cf. gildemeisteri suggests a Paleocene age for the studied deposits (most likely Thanetian but potentially Danian). Fifteen facies have been recognized and have been grouped into three facies assemblages. Facies association A corresponds to the sedimentary filling of a tide-influenced meandering channel formed in the fluvial–tidal transition zone. Facies association B is related to more distal tidal-flats, little channelized tidal inlets and saltmarsh deposits. Facies association C corresponds to a stressed shallow marine environment such as a bay or a lagoon. The δ13CTOC value (− 23.4‰) of MD-184 is enriched in 13C compared to the other samples suggesting the presence of substantial amounts of marine organic matter in MD-184. The δ13CTOC values of samples from other outcrops (− 27.3 to − 29.8‰) indicate a mixed organic matter origin, from terrestrial to brackish environments. The analyzed sediments have similar Nd–Sr isotopic compositions as those of the Cenozoic sediments of the Altiplano (εNd(0) values from − 6.2 to − 10.7 and 87Sr/86Sr compositions from 0.712024 to 0.719026) indicating a similar volcanic source. This multidisciplinary dataset documents the presence of a tide-dominated estuary sourced by the proto-Western Cordillera debouching into a shallow marine bay during Paleocene times. This transgression might be explained by subsidence created in response to the proto-Western Cordillera loading. Similar to Miocene marine incursions affecting the Pebas megawetland, Paleogene marine incursions in the Amazonian foreland basin associated with Andean uplift may have played a role in the Neotropical biodiversity dynamics in favoring biogeographical isolation and promoting allopatric speciation for terrestrial organisms.

Domaines: Paléontologie

M. Louterbach, M. Roddaz, J. Bailleul, Pierre Olivier Antoine, Sylvain Adnet, et al.. Evidences for a Paleocene marine incursion in Southern Amazonia (Madre de Dios Sub-Andean Zone, Peru) (vol 414, pg 451, 2014). Palaeogeography, Palaeoclimatology, Palaeoecology, 2015, 418, pp.386-386. ⟨10.1016/j.palaeo.2014.11.023⟩. ⟨hal-01255171⟩