Palaeoevironmental reconstruction based on palynomorphs from the upper Oligocene San Gregorio Formation (core LB1), in a semiarid coastal marine setting, Baja California Sur, Mexico
Por:
Ramirez-Arriaga, Elia, Pramparo, Mercedes B., Martinez-Hernandez, Enrique, Helenes-Escamilla, Javier
Publicada:
1 ago 2021
Resumen:
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 Tuber-culodinium 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.
Filiaciones:
Ramirez-Arriaga, Elia:
Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria Coyoacán 04510, D.F., Mexico
Univ Nacl Autonoma Mexico, Inst Geol, Dept Paleontol, Ciudad Univ Coyoacan, Mexico City 04510, DF, Mexico
Pramparo, Mercedes B.:
IANIGLA-CCT CONICET, Avenida Adrian Ruiz Leal s/n, Parque Gral. San Martin, Mendoza, Argentina
IANIGLA CCT CONICET, Ave Adrian Ruiz Leal S-N,Parque Gral San Martin, Mendoza, Argentina
Martinez-Hernandez, Enrique:
Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria Coyoacán 04510, D.F., Mexico
Univ Nacl Autonoma Mexico, Inst Geol, Dept Paleontol, Ciudad Univ Coyoacan, Mexico City 04510, DF, Mexico
Helenes-Escamilla, Javier:
Departamento de Geología, Centro de Investigaciones Científicas y de Educación Superior de Ensenada (CICESE), Carretera Ensenada-Tijuana Km. 107, Ensenada, Baja California 22830, Mexico
Ctr Invest Cient & Educ Super Ensenada CICESE, Dept Geol, Carretera Ensenada Tijuana Km 107, Ensenada 22830, Baja California, Mexico
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