Stratigraphy and microfacies of the southern part of La Boca canyon, Santiago, Nuevo León, Mexico

Abstract

The cretaceous stratigraphic sequence cropping out of the at the South part of the La Boca Canyon is presented herein. This canyon cuts the Sierra San Juan Bautista, which belongs to the Sierra Madre Oriental, in Santiago, Nuevo León, Mexico. The transect studied herein was measured and oriented using the method of the open polygonal. Based on the polygonal, a structural profile and the local stratigraphic column were elaborated. Samples of limestones were thin-sectioned, and shales disaggregrated with the hydrogen peroxide method to separate the microfossils. Identification of microfossils and microfacies determination served as the basis to infer the geologic ages and sedimentary environments.

Five stratigraphic units are recognized: 1) stratified limestones, 0.20 to more than 3 meters in thickness, assigned to the Cupido Formation, with a determined age spanning from late Hauterivian to early Aptian, and assigned to a platform paleoenvironment; 2) limestones with strata thickness of 0.10 to more than 1 m attributed to the Tamaulipas Superior Formation, and assigned to an upper slope paleoenvironment that spanned from early to middle Albian; 3) an alternation of 0.10 to 0.4 m-thick limestone strata, and shales less than 0.03 m thick, that corresponds to the Cuesta del Cura Formation, with a middle Albian to Cenomanian age, and a suggested slope paleoenvironment; 4) argillaceous limestones and shales are attributed to the Agua Nueva Formation, with a late Cenomanian to Turonian age, and representing a basin paleoenvironment; 5) an alternation of predominantly shales and limestones were considered as part of the San Felipe Formation, with an early Coniacian age and a basin paleoenvironment interpretation. The whole stratigraphic sequence was analised through 2,078 m at the southern part of the Canyon.