INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Late Oligocene-Early Miocene palynoflora from San Gregorio Formation, Baja California Sur, Mexico
RAMIREZ-ARRIAGA, E.; HELENES-ESCAMILLA, J.; PRAMPARO, M.B.; VALIENTE-BAUNET, A.; CARREÑO, A.
Simposio; AASP-TPS 46th Annual Meeting; 2013
San Gregorio Formation was deposited when Baja California was attached to the Mexican mainland (Hausback, 1984). The Late Oligocene ? Early Miocene San Gregorio Formation age is supported by radiometric dating, micro and macrofossils information (Gastil et al., 1979; Hausback, 1984; Applegate, 1986; Helenes and Carreño, 1999). The aim of the present research is to analyse the well preserved palynological assemblages recovered from LB-A borehole belonging to San Gregorio Formation, with particular emphasis in continental microfossils. Pollen and spores assemblages reflect the composition of plant communities evolved near the depositional area as well as regional vegetation. Besides, continental and marine palynomorphs provide information about paleoclimatic conditions and biostratigraphic data that will be important for future correlations. This study was supported by PAPIT-IN105411-DGAPA project of Universidad Nacional Autónoma de México (UNAM). LB-A borehole of 148.5 meters from San Gregorio Formation was analysed. A total of 116 samples were collected and chemically processed at Laboratorio de Paleopalinología, Instituto de Geología, UNAM in order to recover palynomorphs, 60 samples of them yielded marine and continental palynomorphs. Although marine elements are dominant (n=107,013 total count ?TC?), the pollen assemblage is very diverse; Dicotyledoneae dominate (n=2,219 TC) over the Monocotyledoneae (n = 232 TC). The most abundant Monocotyledoneae are Graminidites (n=179) and Liliacidites spp. (n=33 TC), meanwhile the most abundant Dicotyledoneae taxa are related to the following families: Amaranthaceae-Chenopodiaceae (n=1,255 TC), Juglandaceae (n=41 TC), Moraceae (n=24 TC), Polemoniaceae (n=19 TC), Polygonaceae (n=84 TC), Fagaceae (n=30 TC), Rosaceae (21 TC), Sterculiaceae (n=119 TC) and Ulmaceae (n=53 TC). Besides, gymnosperms (n=889 TC) are also well represented, such as Pinuspollenites (n=622 TC) and Ephedripites spp. (n=263). Pollen assemblages give evidence of regional temperate vegetation of Pinus and cloud forest (Momipites group), as well as local semiarid conditions that allowed the development of grassland with Chenopodiaceae?Amaranthaceae (Chenopodipollis spp.), Gramineae(Graminidites), and Ephedra (Ephedripites). Moreover, the tropical deciduous forest is proposed as local community. On the other hand, dinocyst (n=50,184 TC) are important in the marine assemblages. The most abundant dinocysts were Achomosphaera (1,080 TC), Chiropteridium lobospinosum (n=7,700 TC), Histrichokolpoma rigaudiae (n=4,683 TC), Operculodinium centrocarpum (n=11,085 TC), and Spiniferites (n=10,559 TC). Other abundant marine elements were copepod eggs (n=17,37 TC9).