Secrets of Permian vegetation in Inner Mongolia

Scientists from the Nanjing Institute of Geology and Palaeontology and the University of Pennsylvania have uncovered a forest buried under volcanic ash in Inner Mongolia during the Permian period, some 300 million years ago.

In a report published in the Proceedings of the National Academy of Sciences in the US, Jun Wang and Hermann W Pfefferkorn with two colleagues say that early Permian floras are of particular importance because they represent a time of oscillating climatic changes during transitions between icehouse and greenhouse times that might serve as an analogue for modern global vegetation change.

The scientists say plant communities of the geologic past can be reconstructed with high fidelity only if they were preserved in place in an instant in time. They found just such communities of floras in Inner Mongolia during a time and in an area where the information being uncovered is filling a large gap of knowledge.

“These catastrophically preserved floras, which capture the composition of vegetation in a specific area and at a moment in time, can be generated by various types of volcanic action or flooding, of which volcanic air-fall tuffs produce the most reliable representation of the existing vegetation.”

Excavation of the forest is taking place on the Wuda coal field, on the northwest margin of the Helanshan mountain chain.

The peat-forming forest was preserved in a manner similar to the towns of Pompeii and Herculaneum by a smothering volcanic ash. This buried and killed the plants, broke off twigs and leaves, toppled trees and preserved the forest remains within the ash layer.

The layer is now 66 centimetres thick after compaction and lithification. The report says the thickness of the layer is relatively consistent over the area of current exposure, which has a north-south extension of more than 10 kilometres. From the data, the researchers say it appears the volcanic eruption was quite large and the area covered with tuff was extensive.

“The vegetation preserved in the tuff grew on the peat that later formed coal. The tuff is of early Permian age, based on the floral composition [and] during Permian times, Wuda was located on the northwest part of the North China Block, which appeared as a large island or micro-continent in the tropical zone in the paleo-Tethys Ocean.”

“About 1,000 square metres of forest growing on peat could be reconstructed based on the actual location of individual plants. Tree ferns formed a lower canopy and either a coniferophyte or a lycopsid were present as taller trees.

“An enigmatic and extinct spore-bearing plant group of small trees is represented by three species that have been found as nearly complete specimens and are presented in reconstructions in their plant community.”

Wang and Pfefferkorn say the Permian floras demonstrate similarities and differences to those of the same age in Europe and North America. Therefore, this flora will serve as a baseline for the study of other fossil floras in East Asia and the early Permian globally that will be needed for a better understanding of paleoclimate evolution through time.

“The understanding of paleoecosystems in Earth's deep past ideally requires the reconstruction of actual sites of ancient plant communities.

“Only vegetation buried in growth position in a geological instant can offer such an unbiased window into the composition and ecology of ancient vegetation, which in turn enhances larger scale paleoecological and paleoclimatic interpretations.”