First record of Lagenicula mixta (Winslow) Wellman et al. in Bolivia: biostratigraphic and paleobiogeographic significance

DI PASQUO, M.M.

La Plata

Simposio; XVI Simposio Argentino de Paleobotánica y Palinología; 2015

universidad nacional de La Plata y Museo

The megaspore Lagenicula mixta (Lepidocarpaceae) is documented for the first time in South America, in core samples from the Pando X-1 and Manuripi X-1, northern Bolivia. From the latter, the lowest sample analysed bearing this megaspore is at a depth of 1535-36 m (5 m above TD), and it is well represented at 1521 m. In the Pando X-1 (drilled to the metamorphic basement at 1981 m), the megaspore first appears at a depth of 1355 m, close to the D/C boundary. The palynoassemblages bearing this megaspore are similar in composition and preservation, and yielded a mixture of low-to-abundant indigenous palynomorphs (trilete spores, megaspores, algal remains) and more abundant reworked ones (spores, acritarchs, chitinozoans, scolecodonts). This megaspore has a single published occurrence from the mid-Tournaisian (Early Mississippian) of Ohio, USA. This age is given for both palynoassemblages supported by spore species Mississippian in age: Vallatisporites ciliaris, Granulatisporites granulatus, Reticulatisporites waloweekii, Dibolisporites setigerus, Crassispora scrupulosa, Cristatisporites echinatus. A terrestrial link between North America and northern South America is indicated by the mutual occurrence of the megaspore Lagenicula mixta and several microspores (e.g., Vallatisporites ciliaris, Cristatisporites echinatus, Reticulatisporites waloweekii). This scenario is supported by the end of the Rheic Ocean, triggered by tectonic changes in the paleoequatorial zone of the early Mississippian. The global sea level decreased (Mississippian glaciations) and new land regions in western Gondwana and USA were exposed, widening the inroads for the Tournaisian flora.