MINERALOGY AND GEOCHEMISTRY OF THE SAN FELIPE FORMATION (UPPER CRETACEOUS) IN THE PEDRO CARRIZALES LOCALITY (RAYONES, NUEVO LEÓN), NORTHEASTERN MÉXICO

The San Felipe Formation has been described as a sedimentary sequence, representing the Santonian-Campanian period in the Sierra Madre Oriental stratigraphic column. This lithological unit is mainly constituted by argillaceous limestone strata evolving to thin shale beds, intercalated with greenish volcanic ash layers. In this work, we report an initial conceptual petrologic model for the San Felipe Formation, based on mineralogical and geochemical (major and trace-elements) features from the Pedro Carrizales section (total thickness ~200 m; Rayones, Nuevo Leon). The microfacies analysis on carbonate rocks shows that the predominant texture consists of pelagic wackestone. Nevertheless, there is a textural variation pattern: at the base of the sequence packstone-wackestone and towards the top mudstone. A relative Coniacian - Maastrichtian age is supported by the presence of abundant planktonic foraminifera [Hedbergella amabilis, Loeblich & Tappan, 1961; Heterohelix reussi, (Cushman, 1938); Globigerinelloides bollii, (Pessagno, 1967); and Globotruncana fornicata, Plumer, 1931]. According to its textural and micropaleontological content, it is determined a deep shelf margin facies, which indicates that the deposit occurred under low energy conditions in a calm and warm water environment. For the shale strata, several geochemical ratios indicate a felsic igneous source, probably linked to the basement and pre-Cretaceous continental arc rocks of the Mexican western margin. According to mineralogical and geochemical features, the volcanic tuff layers display an intermediate to acidic composition, being related to the Upper Cretaceous Laramidic continental arc. Volcanic ashes were quickly transported and deposited in a deep shelf margin. Diagenesis caused the alteration of glass and non-resistant minerals to illite and chlorite. Finally, the San Felipe Formation represents the transition from a calcareous sedimentation regime to a siliciclastic one related to a regional marine regression event, also influenced by an arc volcanism, during the Upper Cretaceous.