Discordancia entre el Jurásico y Cretácico en Huizachal, Tamaulipas, México: Su posible correlación con un límite de secuencia global
In Huizachal, Tamaulipas, at the western end of the Rumbo Nuevo tunnel, clear stratigraphic relationships between the La Casita and the Taraises formations are well exposed. The contact between the formations is marked by a paraconformity, represented by an erosional surface overlain by an abrupt lithologic change. In the upper part of the La Casita Formation, fine-grained sandstone and siliciclastic mudstone are interbedded with conglomerates, and the top of the formation is truncated by a bedding-parallel erosional surface. The sandy matrix of the uppermost conglomerate contains Suarites sp. (Durangites Zone) and Crassicollaria sp. (with curved collar morphology), which indicate deposition during the late Tithonian (A2 or Crassicollaria brevis zone). The Taraises Formation overlies the conglomerate and consists of lime mudstone beds with Calpionella elliptica – C. alpina (small), which indicate deposition during latest-early Berriasian. The absence of distinctive fossils from the top of the latest Tithonian (A3 or Crassicollaria colomi Zone) and the earliest Berriasian (start Calpionella alpina Acme, isometric variety) suggests non-deposition or erosion between the La Casita and the Taraises formations. Up-section in the Taraises Formation, a rapid transition from mudstone to bioclastic wackestone beds is observed, marked by a succession of Calpionella alpina – C. elliptica, followed by Calpionellopsis simplex and Calpionellopsis oblonga, with a large form of Tintinnopsella longa and T. Carpathica, at the top Calpionellites. This lithologic and paleontologic succession suggests a stratigraphic continuity and change in age from the middle Berriasian to early Valanginian.The stratigraphic position of the paraconformity described in this study correlates with a regressive event. This may correspond to a sequence boundary of second order that separates Jurassic and Cretaceous strata on continental margins in other regions of Mexico and worldwide.