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Jorge O. Calvo, Cynthia Rivera & Laura Avila (2021)
An overview of Upper Cretaceous dinosaur tracks and other trace fossils from the Barreales lake area, NeuquÃn Province, Patagonia, Argentina.
Journal of South American Earth Sciences 103375
doi:
https://doi.org/10.1016/j.jsames.2021.103375Â
Highlights
Upper Cretaceous dinosaur tracks from Barreales Lake, NeuquÃn, Argentina.
Dinosaur tracks from Barreales Lake, NeuquÃn, Argentina.
Barreales Lake, Dinosaur Tracks, Argentina.
An overview on dinosaur tracks from Barreales lake, Argentina.
Cretaceous Dinosaur tracks, Barreales Lake, Argentina.
Abstract
Upper Cretaceous (TuronianâSantonian) tracksites at Barreales Lake, NeuquÃn Province, Argentina are described. Tracksites studied for the last 20 years on the northern and northeastern coasts of the lake mainly contain theropod and sauropod tracks preserved as either natural molds, concave epireliefs, concave hyporeliefs, or convex hyporeliefs. Sauropod tracks and trackways represent taxa that exhibited wide-gauge locomotor styles. Based on their morphology and evidence from body fossils, they are interpreted as having been produced by titanosaurs. Theropod tracks are represented by tridactyl prints with claw impressions. Some of the theropod tracks are inferred as having been made by megaraptorids. The dinosaur track record of the Barreales Lake region spans several formations: the Portezuelo Formation yielded theropod tracks at the Baal, Punta Motorhome, Aguas Claras, and South Loma de la Lata sites; the Plottier Formation preserves sauropod and ornithopod tracks at the Proyecto Dino and Middle Loma de la Lata sites, respectively; and the Bajo de la Carpa Formation yielded sauropod and theropod tracks at the QuerubÃn site. Here we describe all these dinosaur tracksites and make inferences regarding their paleoenvironments. A brief description of some invertebrate traces from the QuerubÃn tracksite is also provided. The description of these tracks and trackways adds to knowledge of Late Cretaceous continental paleoecosystems of southern South America.
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Sedimentary processes in a microbial flat, developed in a progradational environment and trampled by vertebrates, were monitored under varying energy conditions. A vertebrate footprint made on the sedimentary surface was selected and was kept under observation for two years visited on nine field trips. Thus, this contribution provides a detailed analysis of the evolution of a microbial tidal flat with high-sediment-flux events and contributes to a better understanding of the sedimentary processes involved in the preservation of a true track. This study demonstrates that the formation of biolaminites (sequence of microbial mats interbedded with sand layers) in the coastal environment is caused by episodic pulses in the hydrodynamic regime of the area. Through the detailed inspection of a cross section of a sedimentary block containing the vertebrate footprint, the sedimentation history since the footprint creation is unravelled in relation to hydrodynamic records. Water energy was inferred using the measurements of a water-level sensor located on the tidal flat recording continuously every 10 minutes. The results indicate that the seawater enters into the zone by floods that occur during storm surges, reaching up to 70 cm height in the water column, and transporting abundant sediment, which produces the deposition of flat sand layers or sand ripples on the microbial mats. A sedimentation rate of 0.32 to 0.41 cm per year was calculated along the two-years monitoring. The study recognizes the plastic behavior of the microbial mat, one of their most important rheological properties, as a response to the registration of a vertebrate footprint. Petrographic analysis of microbial-mat layers reveals the precipitation of thin carbonate laminae during periods of seawater evaporation, which may enhance the preservation of sediments. Episodic sediment transport, in addition to the presence of a microbial-mat, creates the perfect conditions for formation, early burial, and preservation of the footprint in siliciclastic sediments.
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Sedimentary facies show transition from aeolian to fluvio-lacustrine ecosystem.
Semi-aquatic herbaceous plant fragments and petrified trees suggest wet conditions.
Lava-fed deltas formed as subaerial lava flows entered lakes with ~10-m-deep waters.
Sediment deformation by the earliest pillow lavas is evidence for no stratigraphic gap.
Climate in southern Gondwana was consistent with global Pliensbachian climate trend.
Abstract
Palaeoenvironmental changes during continental flood basalt volcanism in large igneous provinces are increasingly linked to global environmental perturbations. Whilst the geology of the Karoo-Ferrar continental flood basalts, including their eruption history, mode of emplacement, timing, geochemistry, palaeomagnetism, has been described, and the causal link of this massive volcanic event to global climate trends and the mass extinction as well as oceanic anoxia near the PliensbachianâToarcian boundary is established, little is known about the dynamics of the southern African palaeoenvironment and palaeoclimate at that time. This study is focused on a field investigation of the uppermost Karoo Supergroup, which accumulated in the changing Early Jurassic palaeo-landscapes of southern Gondwana. Using well-exposed successions in southwestern Lesotho, we document evidence of a humid phase at the onset of Karoo volcanism in the central part of the main Karoo Basin. The studied interval encompasses the conformable contact of the Sinemurian-Pliensbachian Clarens Formation and the Pliensbachian-Toarcian flood basalts in the lower Drakensberg Group. Facies changes in the succession provide evidence for shifts in the ancient landscape and in the associated subaerial and subaqueous conditions. Specifically, the facies suggest a climatic change from a dry desert setting with large, down-wind migrating sand dunes to a wetter desert ecosystem in the Late Pliensbachian. The latter sustained a fairly diverse biota of land-dwelling organisms, which included herbaceous and wooded areas where the diametre of gymnospermous tree trunks was in excess of 50âcm. The earliest flood basalts comprise massive basalt lava flows and up to ~10-m-thick foreset-bedded pillow lavas. These show that during the initial outpouring of the Karoo continental flood basalts, the land surface was locally covered by streams and lakes into which the earliest basaltic lavas flowed forming lava-fed deltas in the Late Pliensbachian.