A tropical palynoflora in the K-Pg Vilacapujio section, southwestern Bolivia

PRÁMPARO, M.B.; NARVÁEZ, P.L; MAMANI QUISPE, B.; ANDRADE FLORES, R.; ANTOINE, P.-O.; MARIVAUX, L.; PUJOS, F.

Salvador

Congreso; XIV International Palynological Congress - X International Organisation of Palaeobotany Conference; 2016

Universidade Estadual de Feira Santana

Palynological productive samples from El Molino Formation were collected at the Vilcapujio locality, Eastern Cordillera, SW Bolivia. The present study is part of a multi-proxy approach (gathering palynomorphs and vertebrates), which will play a pivotal role for better understanding the settlement of early Cenozoic ecosystems in South America. The studied unit is mainly composed of marls and mudstones, with subordinated limestones and sandstones. Several depositional environments are recognized throughout the concerned interval: outer shelf, oolite barriers, inner shelf, mouthbar deposits, supratidal to intertidal zones, and continental domain. The El Molino Fm. yields an abundant palynoflora dominated in all assemblages by freshwater chlorophycean algae, but a few brackish/marine peridinioid dinocysts were also identified. The statistical results indicate percentages of 80% of algae of the total, at the base of the section represented by: Botryococcus, Pediastrum, Ovoidites, Lecaniella, and Scenedesmus. The terrestrial association is characterized by tropical to subtropical key species such as Buttinia andreevi Boltenhagen, Crassitricolporites brasiliensis Herngreen (a thick wall taxon endemic from northern South America), Aquilapollenites sp., Zlivisporis blanensis Pacltova, and abundant granulate periporate species similar to Psilastephanoporites brasiliensis Regali, Uesugui, Silva-Santos. Ephedripites (2-3%) is the most represented gymnosperm. Going up in the section the key taxa disappear and monocolpate palmae-type pollen increase in abundance (Retimonocolpites, Longapertites, and Arecipites) with percentages of nearly 30%. Large amounts of water ferns (spores and massulae) characterize the uppermost part of the section mainly represented by Gabonisporis vigourouxii Boltenhagen and Azolla boliviensis Vajda and McLoughlin. Cretaceous Bolivian palynofloras are included in the Palmae Province on the criteria outlined by Herngreen, which probably reflect warm, ever-wet conditions. The co-occurrence of the key palynomorphs (B. adreevi, C. brasiliensis, and G. vigourouxii) and of the sawfish Pucapristis cf. branisi Schaeffer, which all become extinct at the K-Pg boundary, corroborates the Maastrichtian age for the El Molino Fm. at Vilcapujio. The depositional environment was probably lagoonal with some marine influence, as indicated by the mixed character of the palynomorph-vertebrate association recovered. Two younger vertebrate faunas from the same section, Danian and Thanetian in age are under study (Santa Lucia and Cayara formations). The unexpected palynomorph diversity of this K-Pg locality, their exceptional preservation, and the co-occurrence of vertebrate-bearing levels in the same section, will provide relevant information on the evolution of floras and faunas during the crucial period of the K-Pg boundary in this region.