The palynostratigraphy of red-bed and salt units of the Mexican Petroleum Sub-Basins of the Gulf of Mexico

Since 1975 Mexican Mesozoic red-bed and salt sequences were dated using the palynostratigraphical method developed at the Mexican Petroleum Institute by Rueda-Gaxiola. They represent the beginning of the Mesozoic marine transgression, which eventually formed the petroleum systems of the region. The palynostratigraphical method is based on a macro- and microscopic analysis of all the components in palynological residues and of the glycerinated alcohol in which they are preserved. This analysis allows the identification of litho-, bio-, and stratigraphic data, which can be related to tectonosedimentary and diagenetic processes. The Cahuasas and the Rosario formations (in the Tampico-Misantla subbasin), the Todos Santos Formation (in the southeastern subbasins and in the western Veracruz subbasin), the La Boca Alloformation (in the Huayacocotla-El Alamar Basin), Consuelo Group (in the Tlaxiaco Basin), and some salt units (in the southeastern subbasins) have been dated (J. Rueda-Gaxiola, 1972; J. Rueda-Gaxiola, 1976; L. Gutiérrez-Galicia, 1984; Herrera et al., 1990; J. Rueda-Gaxiola et al., 1993-1996; J. Rueda-Gaxiola; and J. JiménezRentería, 2002). These data were integrated with those obtained by Kirkland and Gerhard from the cap rock of the Challenger Knoll in the center of the Gulf of Mexico. They have helped understand the sedimentary and tectonic evolutions of the early Gulf of Mexico. These data indicate the existence of an unconformity between the basement and the Middle Jurassic red beds (La Joya and Todos Santos formations) in the Sabinas and southeastern subbasins of the Gulf of Mexico. This unconformity is also found between the Liassic rocks (La Boca Alloformation and Huayacocotla Formation) and the Middle Jurassic red beds (La Joya and Cahuasas formations) in the Huayacocotla-El Alamar Basin. However, in the marginal Sabinas, Tampico-Misantla, and southwestern subbasins, this unconformity is overlain by Middle Jurassic red beds, which is slightly older than the evaporitic rocks deposited in the center of the Gulf of Mexico. However, some localities of the Tlaxiaco Basin and in the northern part of the TampicoMisantla Basin, the Liassic Rosario Formation red beds gradually change to the Cualac and Cahuasas formations, which are the basis of the transgressive marine Upper JurassicMiddle Cretaceous sequence.