Stratigraphy, sedimentology and tectonic model for the origin of the Late Cretaceous El Tuli Formation in northern Sonora, Mexico
El Tuli Formation is a Late Cretaceous, 2 km-thick, volcanosedimentary sequence located in the Rancho San Antonio area, 40 km south of Cananea, north-central Sonora, Mexico. This unit consists of dusky or medium red, poorly sorted, polymictic conglomerate and breccia, sandstone, siltstone, and porphyritic to aphanitic andesite, and includes Lower Cretaceous, limestone blocks, slabs, and olistoliths. Reconnaissance surveys north of the study area suggests that El Tuli may be 5 km thick, or even more. ^ A distinctive feature of El Tuli Formation is the presence of large limestone blocks in its conglomeratic parts. Most of them are boulders and blocks, in minor proportion, although the most spectacular are slabs and monoliths which can be more than 2 km long. ^ The age of El Tuli Formation is 76 Ma (Late Campanian). Paleobotanical studies of fossil plants in the Rancho Téguachi area and near Huépac, also indicate that El Tuli was probably deposited during Late Cretaceous time. Interpretation of facies groups and individual facies in El Tuli revealed that transport mechanisms of sediments were mainly debris flows in alluvial slopes, and secondly, lower flow regimes or tranquil flows in paleochannels that dissected medial and distal parts of alluvial fans. ^ Petrography of sixteen sandstones of members I and II of El Tuli revealed that a recycled orogen and a magmatic arc were the dominant tectonic settings under which sandstones originated. A minor influence were a craton interior and a transitional continental frameworks. ^ El Tuli Formation is interpreted as an association of volcaniclastic, alluvial-fluvial facies deposited at the foot of a prominent topographic feature called the Cananea High. The Late Cretaceous El Tuli sequence is a synchronous sedimentary sequence of mixed origin deposited in a large basin called the Sonora Basin. This basin was part of an intra arc setting. The El Tuli thick volcaniclastic sequence may have originated in the eastern portion of the Cretaceous Cordilleran magmatic arc, or the eastern prolongation of the Jurassic-Cretaceous Alisitos magmatic arc identified in parts of northeastern Baja California and adjacent regions. ^
Garcia y Barragan, Juan Carlos, "Stratigraphy, sedimentology and tectonic model for the origin of the Late Cretaceous El Tuli Formation in northern Sonora, Mexico" (2003). ETD Collection for University of Texas, El Paso. AAI3146480.