Zircon U-Pb age of the cretaceous tlayúa fossil-lagerstätte in central Mexico

The Cretaceous Tlayúa Lagerstätte is a major conservation deposit of marine paleobiota located in Puebla, Central Mexico. It is a composite sequence of approximately 30 m thick consisting of fossil-bearing platy limestones with a predominance of exceptionally preserved fish assemblage. The previous age estimates for this sequence have significant discrepancies. In this study, we de-termined the maximum depositional age of Tlayúa based on detrital zircon U-Pb geochronology. Detrital zircon grains were isolated from clay horizons that are interbedded episodically with the platy limestones. U-Pb dating results in two central zircon populations indicated a depositional age of 110 ± 1 Ma in the Early Albian stage. A very nearly single modal age was observed in zircon populations with probability age peaks at ~110 Ma, with small U Pb age variations. Exceptionally, one zircon population shows ages in two peaks at ~110 and ~116 Ma. However, they remarkably belong to the same age interval between 119–101 Ma, with weighted crystallization age at 110 ± 1 Ma; this strongly suggests a restricted early Albian source, probably volcaniclastic. Accordingly, the remobilization of volcaniclastic sediments into a shallow marine basin by transgressions should be considered the most significant clay source in Tlayúa. Marine transgressions were recurrent events in the Late Cretaceous of North America. Episodes of potential transgression are consistent with paleoenvironmental scenar-ios known independently from previous studies, such as monsoon events of heavy seasonal storms in an ocean basin, the occasional deposition of paleosols in a nearshore tidal flat environment, the seawater-like signals in an ocean environment and periodical contributions of freshwater and terrige-nous sediments to an ocean basin.