The La Boca Formation is a geological formation in Tamaulipas state, northeast Mexico. It was originally thought to date back to the Early Jurassic , concretely the Pliensbachian stage epoch of 193-184 Ma . Later studies found that while the unit itself was likely deposited during the earliest Pliensbachian, as proven by zircon dating 189.0 ± 0.2 Ma, the local vulcanism (related to the aperture of the Atlantic Ocean and the several Rift Events) continued until the Bajocian .
13-593: However, the lower section of the fossil taxa deposited on the rocks above the La Boca Formation is likely of Late Pliensbachian-Lower Toarcian age, and the upper section of Late Toarcian-Late Aalenian age. Due to successions of Aalenian depositional systems on the upper layers of the Huizachal Canyon , has been delimited the formation to the Toarcian stage, being the regional equivalent of
26-583: A "Burrowing diapsid representing a heretofore unknown clade", was later found to have a compact skull similar to that of Dibamidae and Amphisbaenia by convergent evolution. Toarcian The Toarcian is, in the ICS ' geologic timescale , an age and stage in the Early or Lower Jurassic . It spans the time between 184.2 Ma (million years ago) and 174.7 ±0.8 Ma. It follows the Pliensbachian and
39-511: A basin formed between the Nazas Volcanic Arc center and the so-called Huizachal-Peregrina Anticlinorium , giving the basin layers whose origin is linked with braided river deposits with different flooding levels, channels fills, and channel belts filling valleys. In locations such as Aramberri , the development of fluvial channels and the flooding of surfaces was restricted due to the presence of flanking volcanic activity, as well
52-575: Is controversial. The Toarcian takes its name from the city of Thouars , just south of Saumur in the Loire Valley of France . The stage was introduced by French palaeontologist Alcide d'Orbigny in 1842, after examining rock strata of this age in a quarry near Thouars. In Europe this period is represented by the upper part of the Lias . The base of the Toarcian is defined as the place in
65-618: Is followed by the Aalenian . The Toarcian Age began with the Toarcian Oceanic Anoxic Event , a major anoxic event associated with marine extinctions and increased global temperatures that sets its fossil faunas apart from the previous Pliensbachian age. It is believed to have ended with a global cooling event known as the Comptum Cooling Event, although whether it represented a worldwide event
78-602: Is genetically related to the Nazas volcanic Arc of the same age (Pliensbachian-Aalenian, ~189.5–171.6 Ma), which was created when Mexico evolved in a convergent plate margin, with the Gulf of Mexico remaining as a restricted basin and a passive margin. The influence of this arc is seen on the continental units such as Todos Santos Formation , which deposited volcanic materials in both nonmarine strata and marginal marine red beds of eastern Mexico. La Boca Formation left its sediments on
91-732: The Moroccan Azilal Formation . Deposits of Late Triassic Age referred to this unit have been reclassified in a new formation, El Alamar Formation . In North America, La Boca Formation was found to be a regional equivalent of the Eagle Mills redbeds of southern United States , the Todos Santos Formation of southern Mexico and the Barracas Group of the Sonora desert region. La Boca Formation
104-464: The fossils were not buried in situ, as most of the smaller specimens show disarticulation. All data trends suggest a highly unusual debris-flow environment in which local fluvial alluvial bodies were not big enough to sustain large freshwater biota such as fishes, and most of the preserved specimens were fast-buried near the place of death. Mermia Locomotion trace Domichnia & Fodinichnia Densely looped grooves or ridges. Taxon linked with
117-526: The increased force of the younger flows. The rock fragments moved by the currents are bigger in upper layers. In the southernmost outcrop, in Miquihuana the sheet sands show greater flooding events than on any other location. In the main fossiliferous level of the Huizachal Canyon , in which more than 8000 specimens have been found, the preservation of delicate specimens such as Pterosaurs suggests an environment with little transportation and reworking. Yet
130-403: The local Paleozoic basement highs. In this outcrop the fluvial system evolved in several ways. Towards the north, it meanders from braided to ephemeral sandy, with the presence of common laminated sands sheets. The latter are likely a local indicator of unconfined flash floods across floodplains, with some sections recovering periods of desiccation thanks to the presence of mudcracks . Towards
143-1197: The major Early Jurassic flooding of the Huizachal Valley , developed locally mostly on a gravel-bed braided fluvial style with paleocurrents oriented west-northwest Scoyenia Burrows Domichnia & Fodinichnia Burrow fossils in lacustrine or fluvial environments, probably made by arthropods Bocaconodon B. tamaulipensis Jim's Joy, Huizachal Canyon Lower Part Teeth A basal Mammaliaform Bocatherium B. mexicanum Huizachal Canyon Lower Part IGM 3492, Skull A Tritylodontid Huasteconodon H. wiblei Huizachal Canyon Lower Part Teeth A Gobiconodont Victoriaconodon V. inaequalis Rene's Roost, Huizachal Canyon Lower Part Teeth A Triconodontid Unnamed Mammaliaforms (IGM 6622,IGM 6855, and IGM 6856) Indeterminate Lower Part IGM 6855, partial right dentary; IGM 6856, left dentary; IGM 6622, partial right dentary Tamaulipasaurus T. morenoi Dinosaur National Monument South, Huizachal Canyon Lower Part A strange burrowing Lepidosauromorph, probably related with Ardeosauridae . Described originally as
SECTION 10
#1732793103230156-516: The south, in localities such as El Olmo Canyon , the layers show gravelly braided rivers, oriented east-west, which then evolve into high-sinuosity single-thread meandering rivers. Other southern localities, such as the Caballeros Canyon and Huizachal Canyon , have layers that record gravel-bed braided rivers over a floodplain with high-energy flows: an element recorded on the local stratigraphy as older layers which were highly degraded by
169-581: The stratigraphic record where the ammonite genus Eodactylites first appears. A global reference profile (a GSSP ) for the base is located at Peniche, Portugal . The top of the stage is at the first appearance of ammonite genus Leioceras . In the Tethys domain , the Toarcian contains the following ammonite biozones : Scoyenia Scoyenia is an ichnogenus found in paleozoic - mesozoic strata in North America . It appears to be
#229770