Palaeoevironmental reconstruction based on palynomorphs from the upper Oligocene San Gregorio Formation (core LB1), in a semiarid coastal marine setting, Baja California Sur, Mexico

Terrestrial and marine palynomorph assemblages from a total of 42 productive samples from San Gregorio Formation core LB1 were analysed. Marine palynomorphs, such as dinocysts, acritarchs, copepod eggs, among others, dominated the associations. With regard to terrestrial palynomorphs, dicotyledonae (e.g. Anacardiaceae type, Chenopodipollis spp., Brossipollis spp., Euphorbiaceae type, Fabaceae type, Quercoidites sp., Polygonaceae type and Sterculiaceae type) were more abundant than monocotyledonae (e.g. Liliacidites spp. and Graminidites sp.). The recovered palynoflora gave evidence of two temperate highland communities: Pinus forest and cloud forest. Furthermore, representatives of the local semiarid vegetation (Brossipollis, Chenopodipollis, Ephedripites and Graminidites), growing throughout a palaeoaltitudinal gradient from the uplands down to the shoreline, such as chaparral, tropical deciduous forest, coastal grassland and coastal dune also occurred. Terrestrial taxa richness varied between 5 and 57, the diversity index ranged between 1.2 and 3, and evenness oscillated between 0.4 and 1. As for marine palynomorphs, the dominant dinoflagellate cysts were Cleistosphaeridium sp., Cordosphaeridium sp., Chiropteridium lobospinosum, Homotryblium sp., Hystrichokolpoma rigaudiae, Lingulodinium machaerophorum, Operculodinium centrocarpum, Polysphaeridium sp. and Spiniferites spp., suggesting that San Gregorio Formation core LB1 was deposited in a neritic marine environment. The dinocysts Chiropteridium lobospinosum and Tuberculodinium vancampoae support a late Oligocene age for the San Gregorio Formation at LB1. Marine taxa richness oscillated between 5 and 18, the diversity index ranged from 0.2 to 2.4 and evenness fluctuated between 0.1 and 0.9. CONISS statistical analysis of the terrestrial and marine palynomorphs allowed us to group the SGF assemblages into four palynozones.Fil: Ramírez Arriaga, Elia. Universidad Nacional Autónoma de México; MéxicoFil: Pramparo, Mercedes Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Martínez Hernández, Enrique. Universidad Nacional Autónoma de México; MéxicoFil: Helenes Escamilla, Javier. Consejo Nacional de Ciencia y Tecnologia de Mexico. Centro de Investigacion Cientifica y de Educacion Superior de Ensenada Baja California.; Méxic