A wave to tidal influenced deltaic coastline in a carbonate environment: The Late Jurassic to Early Cretaceous La Casita Formation, northeastern Mexico

Abstract

In this study, we track the evolution of a clastic shoreline before carbonate deposition takes over. The Late Jurassic to Early Cretaceous La Casita Formation in northeastern Mexico serves as an excellent example for such a shoreline. The work includes a re-interpretation of the tectono-sedimentary environment. The La Casita Formation includes nine facies associations related to river, wave, storm, and tidal processes along a deltaic coastline. Systems influenced by rivers develop more muddy successions with sedimentary structures characteristic of these systems (e.g., normal gradation, parallel lamination, and ripples). In comparison, the systems influenced by waves/storms and tides develop more sandy successions with the development of structures generated by oscillatory flows (ripples and hummocky cross-stratification) and bidirectional ripples and dunes with mud-drapes on their stoss side, respectively. The distribution of sub-environments (e.g., interdistributary bay and shoreface) was controlled by waves and tides. Paleocurrent directions indicate that the coastline was oriented NNW-SSE. The wave- and storm-dominated sedimentary environments contain a large diversity of trace fossils (BI ∼4) related to colonizing organisms in well-oxygenized environments with abundant food, normal salinity, and high temperature. The river- and tide-influenced settings are governed by a low trace fossil diversity (BI ∼2), indicating highly stressful conditions generated by the incursions of hypopycnal plumes.Allocyclic processes were associated with the reactivation of basement faults that controlled the exposure and distribution area of the basement rocks (e.g., the nearby Coahuila block and Tamaulipas Arch). In conclusion, the revision of the environmental evolution of the La Casita Formation has implications for the marine incursion of the Gulf of Mexico and its relationship with the pacific margin and the strike-slip basin development.