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

Abstract

This article presents new biostratigraphic dating, facies analysis, organic geochemical data and Nd-Sr isotopic provenance from five outcrops of southern Amazonia 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 fluvialtidal transition zone. Facies association B is related to more distal tidal-flats, little channelized tidal inlets and saltmarshes 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 favouring biogeographical isolation and promoting allopatric speciation for terrestrial organisms. Highlights:The presence of agglutinated benthic foraminifer Karreriella conversa, ostracod Protobuntonia and charophyte Peckichara cf. varians meridionalis suggest a Paleogene age for the studied deposits.We define three facies associations related to a tide-dominated estuary debouching into a shallow-marine bay or lagoon.

A 60-million-year Cenozoic history of western Amazonian ecosystems in Contamana, eastern Peru

“…1A), leading to the recognition of an early middle Miocene mammal assemblage ("Colloncuran" SALMA; Antoine et al, 2013), as well as an early Miocene mammalian faunule that is noteworthy for producing the earliest crown platyrrhine known so far (MD-61, "Pinturan" age; Marivaux et al, 2012), and an early middle Miocene mammal assemblage ("Colloncuran" SALMA; Antoine et al, 2013). Microfossils (foraminiferans), macrofossils (oysters and selachians), geochemical, and sedimentological evidence from the area document the occurrence of a (late) Paleocene marine incursion in the Southern Peruvian Foreland Basin (SPFB; Louterbach et al, 2014). A large early Eocene xenungulate mammal, of both Patagonian and eastern Brazilian affinities, was recently recovered in northwestern coastal Peru, further indicating that South American subaerial areas formed a single biogeographic realm in early Paleogene times (Máncora locality, Fig.…”

“…Sphaerochara huaroensis and Platychara cf. perlata have early Paleocene LADs (Jaillard et al, 1993(Jaillard et al, , 1994Louterbach et al, 2014). Accordingly, the "Sphaerochara Zone" as defined in the Peruvian Andes is early Paleocene in age (Jaillard et al, 1993(Jaillard et al, , 1994, which further supports a Danian age for CTA-54.…”

“…Accordingly, marine deposits are recorded in the NPFB (Lundberg et al, 1998), SPFB (based on selachian ichthyofauna; Louterbach et al, 2014), and Ucayali basin (Kummel, 1948). It seems that this shallow seaway withdrew around the Cretaceous/Paleogene transition (Lundberg et al, 1998), which is supported by the early Paleocene record of the Contamana area (Huchpayacu Fm., base; Fig.…”

“…A marine corridor bordered the eastern flank of the Proto-Andes during the late Cretaceous, as shown extensively from Argentina to Colombia (e.g., Lundberg et al, 1998;Hoorn et al, 2010a;Louterbach et al, 2014). Accordingly, marine deposits are recorded in the NPFB (Lundberg et al, 1998), SPFB (based on selachian ichthyofauna; Louterbach et al, 2014), and Ucayali basin (Kummel, 1948).…”

“…All measurements are given in millimeters, except where noted otherwise. The nomenclature of Cenozoic formations from the Contamana area mostly follows that proposed in the seminal monograph by Kummel (1948) and subsequent works (e.g., Christophoul et al, 2002;Hermoza et al, 2005;Roddaz et al, 2010 and references therein;Louterbach et al, 2014).…”