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Laos Expedition 2007

A View on Pangaea

A Franco-Laotian team has recently finished investigating a 255 million-year-old sedimentary basin on the right bank of the Mekong River. The researchers' objective is to reconstruct the landscape and better understand this regional biotope as it was during the Permian period.


pangaea

© M. Boulay et S. Lorrain/Hox.fr/ADAGP Paris

The Luang Prabang site. It was probably a large swamp at the time.



There are scorpions, huge centipedes and the biggest poisonous snake in the world–the king cobra. When this fearsome predator rears up, ready to attack, it can easily reach a height of 1.50 meters. And as it’s not too keen on intruders coming into its hunting territory, even if you cut and run, it’ll come after you.” Luckily, Jean-Sébastien Steyer and Sylvie Bourquin, co-leaders of the expedition in Laos’ Luang Prabang region, didn’t cross paths with any of these unpleasant creatures. Steyer is a young specialist in ancient tetrapods at the Paris Paleobiodiversity and Paleoenvironments laboratory,1 and Bourquin is a stratigrapher2 and sedimentologist at the Rennes Geosciences laboratory.3 They set off to the right bank of the Mekong River, a superb landscape of sparsely wooded red hills, to investigate a 20 km2 sedimentary basin and to get a better understanding of what this part of the planet looked like 255 million years ago.
At the time, this area was part of the supercontinent Pangaea–a single land mass formed by nearly all the world’s continents. Pangaea started to break up at the beginning of the Triassic (between 253 and 199.6 million years ago) as the plates started to move apart, driven by plate tectonics–the same force that is still today pulling Eurasia and Africa from the Americas.
What makes the Luang Prabang province so fascinating is that the region (well known to paleontologists) has already revealed extremely interesting fauna and flora from the Permian period (299 to 251 million years ago). Among other finds, earlier expeditions had discovered the skull of a carnivorous amphibian with a crocodile-like head, apparently endemic, as well as a number of skeletal components from mammal-like reptiles called dicynodonts4. “These cosmopolitan herbivorous quadrupeds, which are found in many Permian deposits in Pangaea, were 1 to 2 meters long,” Steyer explains. “They were equipped with two prominent canines probably used for sexual recognition and for digging up bulbs and other tough plants they fed on.” The flora the researchers discovered mainly consisted of leaf debris and petrified tree stumps belonging to the Dadoxylon genus. For Bourquin, “these conifer-like plants point to well-drained environments in Luang Prabang in the Permian.”
Yet major questions still remain unanswered. For instance, in what climate–doubtless hot and humid–and in which environments did the local flora and fauna live in the Upper Permian? What connections were there between the Indochina and Eurasian plates? Do the Luang Prabang fauna and flora show any resemblance to those discovered in other Permian sites in France, Niger, Morocco, and other countries? More generally, what was Pangaea like, and how did life on Earth function just before the mass extinction crisis at the end of the Permian, which led to the disappearance of around 85% of the marine fauna and 95% of the terrestrial flora? These questions are what brought together, for the first time in Luang Prabang, paleozoologists, paleobotanists, and geologists. By carrying out stratigraphic cross-sections and surveys, the geologists hope to find answers to some very precise questions. For example, are the deposits fluvial, and if so, were the rivers that gave rise to them connected to a lake (either shallow or deep), or to the sea?
The ultimate goal is to reconstruct as accurately as possible the environment of the region’s flora and fauna in Permian times. “We are not only studying known outcrops, but also others that have never been explored or investigated. Our objective is to understand how these sediments formed over 250 million years ago, and in what kind of environment,” Bourquin explains. At the same time, paleozoologists and paleobotanists have been scouring the area, searching for the remains of skeletons and samples of flora. “The Permian site in Luang Prabang offers an extremely valuable glimpse into the world of Pangaea,” says Steyer, who is delighted that the mission has strengthened scientific ties between France and Laos.

Philippe Testard-Vaillant

Notes :

1. CNRS / Muséum national d'histoire naturelle / Université Paris-VI.
2. Stratigraphers determine the geological history of strata.
3. CNRS / Université Rennes-I.
4. Reptiles with mammal-like features, especially with regard to their teeth.

Contacts :

Jean-Sébastien Steyer,
Paléobiodiversité et Paléoenvironnements, Paris.
steyer@mnhn.fr
Sylvie Bourquin,
Laboratoire Géosciences, Rennes.
sylvie.bourquin@univ-rennes1.fr


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