| 1. |
- Blanchard, Sebastien, et al.
(författare)
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Late Triassic volcanic activity in South-East Asia: New stratigraphical, geochronological and paleontological evidence from the Luang Prabang Basin (Laos)
- 2013
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Ingår i: Journal of Asian Earth Sciences. - : Elsevier BV. - 1367-9120. ; 70-71, s. 8-26
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Tidskriftsartikel (refereegranskat)abstract
- 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 similar to 100 m/Ma to similar 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 similar to 225 and similar to 221 Ma (Carnian). (C) 2013 Elsevier Ltd. All rights reserved.
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| 2. |
- Vajda, Vivi, et al.
(författare)
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A snapshot into the terrestrial ecosystem of an exceptionally well preserved dinosaur (Hadrosauridae) from the Upper Cretaceous of North Dakota, USA
- 2013
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Ingår i: Cretaceous research (Print). - Elsevier : Elsevier BV. - 0195-6671 .- 1095-998X. ; 46, s. 114-122
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Tidskriftsartikel (refereegranskat)abstract
- A palynological investigation of sedimentary rocks enclosing an exceptionally well-preserved fossil dinosaur (Hadrosauridae) discovered in the upper part of the Hell Creek Formation in south western North Dakota was conducted in order to document the immediate paleoenvironment of this dinosaur. The specimen, an Edmontosaurus annectens is remarkable in having exceptional three-dimensional preservation of soft tissue around the skeleton, indicating rapid burial. A well-preserved palynological assemblage dominated by fern and bryophyte spores, with lesser gymnosperm and angiosperm pollen was recovered. Sparse fresh-water algae and marine dinoflagellate cysts were also recorded. The palynofacies is dominated by wood fragments, including charcoal, with little amorphous organic matter. The presence of some typical pollen taxa of the Wodehouseia spinata Assemblage Zone including Striatellipollis striatellus, Tricolpites microreticulatus, Leptopecopites pocockii as well as a diverse suite of Aquilapollenites, is fully consistent with a Late Cretaceous (late Maastrichtian) age. The palynoflora indicates a local vegetation composed of a canopy of conifers dominated by Pinaceae and a minor sub-canopy of Taxodium and cycads, as well as an understory of hydrophilous ferns, mosses and herbaceous angiosperms, indicative of a warm and humid climate e an environment where this specific hadrosaur roamed over 66 million years ago.
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