Geochemistry and Petrography of Sandstones from the Huizachal and La Joya Formations (Upper Triassic–Lower Jurassic), NE of México

The basis of the stratigraphic column of the Sierra Madre Oriental consists of "red beds" of the Huizachal and La Joya formations (Upper Triassic - Lower Jurassic), as a result of movements of the initial opening of the Gulf of Mexico. In the area of Lomas de San Paulo Tranquitas (20 Km. South from Galeana, Nuevo Leon, Mexico) outcrops of both formations are found.

In the study area it was possible to divide the Formation Huizachal into two units. The lower unit is characterized by fining upward cycles, deposited in a continental environment, and later intruded by dikes and sills of basic composition. The upper unit consists of a complete fining upward cycle, starting with conglomeratic sandstones in the base and siltstones at the top. La Joya Formation begins with an angular unconformity marking the basis of the marine transgression widespread in the NE of Mexico.

The results of the petrographic and geochemical analysis indicate: a) the existence of metamorphic, metasedimentary, and intermediate igneous sources; b) a change in the source area towards the second unit of the Huizachal Formation, and c) a higher degree of transportation and recycling in the upper unit and La Joya Formation.

Supporting a "rift" model in the study area, four stages of the initial development of the basin can be observed: ₁₎ first extension movements reported by fining upward cycles at the base of the Huizachal Formation, ₂₎ Dikes and sills intrusions, ₃₎ Sedimentation of the upper unit, partialy derived from the recycling of the lower unit during stagnation in extension, and ₄₎ reactivationl of the rift with the onset of La Joya Formation.