MICROFACIES, PALEOENVIRONMENTS, AND DIAGENESIS OF THE TLAYUA FORMATION (ALBIAN, LOWER CRETACEOUS), PUEBLA, CENTRAL MEXICO: NEW CONTRIBUTIONS

The Tlayúa Formation in central Mexico is one of the most important units of Albian (Early Cretaceous) age worldwide. However, its conditions of deposition are still on debate. This work provides additional data to unravel the conditions in which this unit was deposited. Two sections that include rocks of the Lower and Middle Members of the unit served as the basis for a microfacies analysis that includes both, field and laboratory data from outcrops that have not been hitherto studied. Both sections are close to the Tlayúa Quarry, 60 km to the southeast of Puebla City.

The analysis in both sections showed that the Lower Member consists of biopelsparites with benthonic foraminifera, ostracods, and mollusk fragments. Biocalcirudites with rudists fragments are also common in this member, indicating the nearby development of reefal facies, fact that was suggested in previous works.

Microscopic and field data allowed the recognition of a 6m-package of hybrid textures, representing the gradual transition between the Lower and Middle Members, and thought to be the result of excessive bioturbation and filamentous deposits of possible algal origin.

Finally, pelmicritic facies and abundant stromatolitic structures characterize laminated limestones of the Middle Member.

The microfacies types recognized herein suggest sedimentary conditions typical of a semi-restricted lagoon within a shallow carbonate platform. Moreover, through the sections it is evident an alternation of levels with abundant benthonic foraminifera, mainly miliolids, with horizons that record reductions of benthic production, indicating periods of stress conditions in the sediment/water inter-phase.

Additionally, this study yielded signs of alteration associated to diagenetic environments in which dolomitization processes are common. Mixed textures, neomorfism, syntaxial overgrowth in echinoids and silification of calcareous bioclasts are some of these diagenetic signs.

Thus, the variety of textures and fossil contents, the presence of stromatolitic structures, and the textural diagenetic products observed in this study, confirm previous ideas of a restricted lagoon-type environment for the deposition of the Tlayúa Formation, in opposition to recent hypotheses that suggest an open marine deeper environment.