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U-Pb ages for Laotian Late Triassic continental deposits

A new article online:

Blanchard, S., Rossignol, C., Bourquin, S., Dabard, M.-P., Hallot, E., Nalpas, T., Poujol, M., Battail, B., Jalil, N.-E., Steyer, J.-S., Vacant, R., Véran, M., Bercovici, A., Diez, J. B., Paquette, J.-L., Khenthavong, B. and Vongphamany, S. 2013. Late Triassic volcanic activity in South-East Asia: new stratigraphical, geochronological and paleontological evidence from the Luang Prabang Basin (Laos).
Journal of Asian Earth Sciences 70-71: 8–26.


In South-East Asia, sedimentary basins displaying continental Permian and Triassic deposits have been poorly studied. Among these, the Luang Prabang Basin (North Laos) represents a potential key target to constrain the stratigraphic and structural evolutions of South-East Asia. A combined approach involving sedimentology, palaeontology, geochronology and structural analysis, was thus implemented to study the basin. It resulted in a new geological map, in defining new formations, and in proposing a complete revision of the Late Permian to Triassic stratigraphic succession as well as of the structural organization of the basin. Radiometric ages are used to discuss the synchronism of volcanic activity and sedimentation.

The Luang Prabang Basin consists of an asymmetric NE-SW syncline with NE-SW thrusts, located at the contact between Late Permian and Late Triassic deposits. The potential stratigraphic gap at the Permian–Triassic boundary is therefore masked by deformation in the basin. The Late Triassic volcaniclastic continental deposits are representative of alluvial plain and fluvial environments. The basin was fed by several sources, varying from volcanic, carbonated to silicic (non-volcanic). U–Pb dating of euhedral zircon grains provided maximum sedimentation ages. The stratigraphic vertical succession of these ages, from ca. 225, ca. 220 to ca. 216 Ma, indicates that a long lasting volcanism was active during sedimentation and illustrates significant variations in sediment preservation rates in continental environments (from ∼100 m/Ma to ∼3 m/Ma). Anhedral inherited zircon grains gave older ages. A large number of them, at ca. 1870 Ma, imply the reworking of a Proterozoic basement and/or of sediments containing fragments of such a basement. In addition, the Late Triassic (Carnian to Norian) sediments yielded to a new dicynodont skull, attributed to the Kannemeyeriiform group family, from layers dated in between ∼225 and ∼221 Ma (Carnian).


As a sidenote, the reference ISC used in this paper is outdated. In fact, the dated strata are now ALL Norian in age. It should have been corrected before publication, but, well...


Le 20/05/2013 23:32, Ben Creisler a écrit :
From: Ben Creisler

A new online article:

S. Lautenschlager & T. Hübner (2013)
Ontogenetic trajectories in the ornithischian endocranium.
Journal of Evolutionary Biology (advance online publication)
DOI: 10.1111/jeb.12181

Understanding ontogenetic and developmental patterns is critical for
reconstructing the life history of fossil vertebrates. In dinosaurs,
ontogenetic studies have nearly exclusively focused on changes in the
cranial and post-cranial skeleton, whereas ontogenetic changes in the
endocranium have received little attention. Here, we present digital
reconstructions of the brain and inner ear anatomy of two ontogenetic
stages of the Jurassic ornithischian dinosaur Dysalotosaurus
lettowvorbecki. Results show that the endocranial anatomy underwent
considerable changes during growth, including a rostrocaudal
elongation of the olfactory apparatus, a reduction in the cephalic and
pontine flexure and an increase in cerebellum size. Functional
elements, such as the cerebral hemispheres and the inner ear, were
already well developed in early ontogenetic stages, indicating a large
degree of precociality. The anisotropic pattern of size and shape
changes in the endocranium further indicates that ontogenetic
trajectories may be controlled by functional and environmental demands
in the different growth stages in Dysalotosaurus lettowvorbecki. The
occurrence of similar ontogenetic patterns in the endocranial anatomy
of derived ornithopod dinosaurs suggests a more widespread
distribution of this growth trajectory.

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"As a Professor of Science, I assure you we did in fact evolve from filthy monkey men." Hubert J. Farnworth.