First report of the Eocene palynoflora recovered from the Mequitongo Formation, Oaxaca, Mexico

RAMIREZ-ARRIAGA, E.; VALIENTE -BAUNET, A.; PRAMPARO, M. B.; NIETO-SAMANIEGO, A.F.; DAVALOS-ALVAREZ, O.G.

San Francisco

Simposio; 46th AASP-TPS Annual Meeting; 2013

AASP-TPS-NAMS

Mequitongo Formation had been included in the Tehuacán Formation (Centeno, 1988), widely distributed in Tehuacán-Cuicatlán Valley. Recently, Dávalos et al. (2007) divided the Tehuacan Formation in: a) Mequitongo Formation (Eocene) and b) Tehuacán Formation (Upper Oligocene- Middle Miocene). The isotopic dating gave 50.2 Ma for the bottom of the Mequitongo Formation (Dávalos, 2006; Dávalos et al., 2007). Lithologically, lodolites and sandstones with intercalations of gypsum characterize the Mequitongo Formation. The principal aim of this study is to document for the first time the microflora yielded from Mequitongo Formation as well as to suggest the plant communities that were developing in the Tehuacán-Cuicatlán Valley during the Eocene time. The present study was supported by PAPIIT-IN105411-DGAPA project of ?Universidad Nacional Autónoma de México?. A total of 31 samples from five outcrops located in San Juan de los Cues, Oaxaca State, Mexico, were processed by standard methods, and 24 samples of them contain palynomorphs with excellent preservation. Permanent slides of all samples were included in the Playnological collection of Institute of Geology, Universidad Nacional Autónoma de México. In general, most positive samples contain low species richness. The palynoflora present in Mequitongo Formation was developed after the early Eocene climatic optimum (EECO). It is well documented that the EECO was followed by a trend to cooler conditions (Zachos et al., 2001). Preliminary palynological assemblages from three sections (21 samples) give information about regional flora such as Pinus forest Pinuspollenites spp, Quercus forest (Quercoidites spp.) as well as cloud forest of Momipites sp., Caryapollenites, Juglanspollenites, between others. Gallery forest is also registered with dominance of Alnuspollenites spp. and by the presence of Fraxinuspollenites, Cupressacites and Salix type. The tropical deciduous forest was probably the local vegetation with taxa related to Burseraceae, Bombacaceae, Cesalpiniaceae, Euphorbiaceae, and Anacardiaceae families. Finally, it is important to mention that Tehuacán Formation assemblages (Middle Miocene) that have been recently studied in the Tehuacán-Cuicatlán Valley (Ramírez-Arriaga et al., in press) have more diverse and abundant palynomorphs than Mequitongo Formation (Eocene). Besides, the Tehuacán Formation is characterized by more diverse semiarid pollen grains. Key words: Eocene palynoflora, Mequitongo Formation, Tehuacán-Cuicatlán Valley, Oaxaca, Mexico.