An integrated palynological and Paleontological study of the K-Pg Vilcapujop section, southwestern Bolivia

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

San Francisco

Encuentro; 46º Annual Meeting of The Palynological Society; 2013

The Palynological Society

The present study is based on samples collected in the Vilcapujio locality, located in the Eastern Cordillera of the Oruro Department, SW Bolivia. Field exploration resulted in the location of eight palynological productive samples in association with scarce vertebrates of marine/brackish affinities in the late Cretaceous El Molino Fm. (e.g., the sawfish Pucapristis cf. branisai Schaeffer), and diverse vertebrate remains in the overlying Paleocene Santa Lucia and Cayara Fms. In the studied section, the El Molino Fm. (Late Campanian-Maastrichtian) lies over the Chaunaca Fm. (not investigated here). The former 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 some marine dinocysts were also recovered. At the base of the section, the tropical to subtropical key species Buttinia andreevi Boltenhagen, Crassitricolporites brasiliensis Hergreen, and Zlivisporis blanensis Pacltová occur in association with abundant Botryococcus, Pediastrum sp. aff. P. boryanum, Ovoidites, Lecaniella, and Scenedesmus. Gymnosperms are represented by several species of Ephedripites. The upper part of the section is characterized by abundant Gabonisporis vigourouxii Boltenhagen in association with psilate trilete spores (Deltoidospora spp), masulae of the water fern Azolla boliviensis Vajda and McLoughlin, Pandanus pollen type, Pediastrum, and few dinocysts (Senegalinium spp., ?Lingulodinium sp.). The depositional environment was probably lagoonal with some marine influence as indicated by the mixed character of the palynomorph association recovered. Upward in the section, the Santa Lucia and overlying Cayara Fms. were barren of palynomorphs. However, two diverse vertebrate assemblages were collected from the middle part of the Santa Lucia Fm. and the base of the overlying Cayara Fm., respectively. Both faunas are characterized by the abundance of turtles, crocodiles, and fishes (mostly Actinopterygii). The lower one yielded the Danian stingray Potobatis cf. semperei of marine/brackish affinities, while the upper one yielded freshwater lungfishes (Dipnoi). No mammal remain was recovered from the Santa Lucia Fm., while mammals are documented by dozens of isolated teeth of large and small native ungulates (the Xenungulata Carodnia and Notoungulata) and marsupials in the Cayara Fm., Thanetian in age. The unexpected palynomorph diversity of this K-Pg locality, their exceptional preservation, and the co-occurrence of vertebrate-yielding levels in the same section, provide relevant information on the evolution of flora and fauna during the crucial period of the K-Pg boundary, in SW Bolivia. The presence of the key palynomorphs (B. adreevi, C. brasiliensis and G. vigourouxii) and of the sawfish Pucapristis cf. branisi, which all go extinct at the K-Pg boundary, corroborate the Maastrichtian age for the El Molino Fm. at Vilcapujio. Two successive Paleocene vertebrate faunas from the same section, Danian and Thanetian in age, will play a pivotal role for better understanding the settlement of early Cenozoic ecosystems in South America.