Evidences for a Paleocene marine incursion in southern Amazonia (Madre de Dios Sub-Andean Zone, Peru)

M. Louterbach, M. Roddaz, J. Bailleul, P. O. Antoine, S. Adnet, J. H. Kim, E. van Soelen, F. Parra, J. Gérard, Y. Calderon, C. Gagnaison, J. S. Sinninghe Damsté, P. Baby

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Abstract

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 δ 13 C TOC value (-23.4‰) of MD-184 is enriched in 13 C compared to the other samples suggesting the presence of substantial amounts of marine organic matter in MD-184. The δ 13 C TOC 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 87 Sr/ 86 Sr 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.

Original languageEnglish
Pages (from-to)451-471
Number of pages21
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume414
DOIs
StatePublished - 5 Nov 2014
Externally publishedYes

Keywords

  • Amazonian foreland basin
  • Madre de Dios basin
  • Marine incursion
  • Paleogene
  • Peru
  • Tidal deposits

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