A tropical palinoflora in the K-Pg Vilcapujio section, southwestern Bolivia

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

Salvador

Congreso; XIV International Palynological Congress-XInternational Organisation of Paleobotanical Conference; 2016

Palynological productive samples from El Molino Formation were collected at the Vilcapujio locality, Eastern Cordillera, SW Bolivia. The present study is part of a multidisciplinary approach (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 the assemblages by freshwater chlorophycean algae, but a few brakish/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 Buttinia andreevi Boltenhagen, Crassitricolporites brasiliensis Herngreen (a thick wall taxon endemic in 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, Arecipites) with percentages of nearly 30%. Large amounts of water ferns (spores and massulae) characterize de uppermost part of the section mainly represented by Gabonisporis vigourouxii Boltenhagen 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 presence of the key palynomorphs (B. adreevi, C. brasiliensis and G. vigourouxii) and of the sawfish Pucapristis cf. branisi Schaeffer, which all go extinct at the K-Pg boundary, corroborate 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 association recovered. Two successive Paleocene 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-yielding levels in the same section, will provide relevant information on the evolution of flora and fauna during the crucial period of the K-Pg boundary, in the region.