Geoscience

Rising of Gangdese Mountains: Much Earlier Than Himalayas

Recent study revealed the Gangdese Mountains had been uplifted to 4,500 m at least before 55 Ma, earlier than the Himalaya Mountains that obtained such elevation. A Tibetan group, lead by Prof. Ding Lin from the Institute of Tibetan Plateau Research, CAS, designed this research topic in the Linzhou Basin, north of the Lhasa City. The Linzhou Basin partly filled by the laustrine and fluvial Nianbo and Pana formations with paleosols and Ostracode fossils bearing during 60-47 Ma. The ostracodes shell measured by the Nano-SIMS show seasonal variations of the oxygen isotope have still being kept, identifying that the oxygen isotope of the carbonates from the Nianbo and Pana formations did not undergo late-stage diagenetic reset. On this basis, the authors used the oxygen isotope and a thermodynamic model to reconstruct the paleoelevations of the Linzhou basin being 4,500 m at 55 Ma. This result further revealed that the Gangdese magmatic arc, stood at southern margin of the Lhasa terrain, was characterized by Andean-type Mountains before India-Asia collision. With the previous paleoelevations, they gave a novel perspective for the Eocene topography of the Tibetan Plateau, that a low-lying Nima-Lunpola basin was bounded by the Qiangtang and Gangdese mountain belts to the north and south, respectively. The finding would “force us to rethink the evolution of Asian monsoons”, says Prof. Dupont-Nivet from France, and “is critical for understanding- and modeling- what drove monsoon cycle in the past and how they will change in the future”. This research was published in Earth and Planetary Science Letters, an international journal for earth sciences, and immediately promoted comprehensive discussions.

Iconic Ediacara Fossils Discovered in China

Recently, multi-types of iconic Ediacara fossils were found in the carbonate succession in the Three Gorges area, China, the general topography of which can be compared with those areas in Namibia, Australia and elsewhere of the world by Profs. Chen Zhe, Zhou Chuanming, etc. More important was that the Ediacara fossils were found in the marine carbonate succession, while Ediacara fossils found in other areas are more preserved as cast or mold in siliciclastic rocks. The new discovery demonstrates that the Ediacara fossils have not only wider geographical and stratigraphic distribution, but the living space of the Ediacara organisms was also extended to the whole ocean. The evidence further proves that those Ediacara organisms are typical marine organisms, and thus denied the terrestrial Ediacara hypothesis. The new discovery has also provided a new opportunity to study a series of important issues concerned with the Ediacara organisms, such as their trophic strategies, eco-space and substrate competition, etc. Their study was published on Scientific Reports (4, 4180; DOI:10.1038/srep04180) entitled New Ediacara fossils preserved in marine limestone and their ecological implications.