North Qiangtang Block is located at the northwestern part of China's Tibet Autonomous Region, between the Longmuco-Shuanghu and Xijinwulan-Jinshajiang suture zones. Among these regions, the Paleozoic strata in Ngari Prefecture of North Tibet are widespread and relatively complete.
The paleogeographic evolution of North Qiangtang Block in Tibet is a hot topic in recent years, particularly concerning the location and affiliation of the North Qiangtang Block and adjacent terranes.
During the field trip supported by the Second Tibetan Plateau Scientific Expedition Program, researchers from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS) carried out comprehensive geological investigations and found typical mound-shaped patch reefs besides the Shouxinghu lake.
Their findings were published in Palaeoworld on Feb. 28.
The researchers collected the quadrats of three most prominent reefs in the Lazhuglung-Bangdagco region and prepared a total of 10,85 thin sections.
They studied the reef structure and components, and found that the patch reefs were constructed mainly by 10 species of corals and stromatoporoids, forming rigid and stable reefs by a combination of framestone and coverstone. Complex biotic interactions among the reef organisms were also found, which fit the features of mesophotic coral ecosystems.
Previous studies have controversial opinions in the affiliation of the Lazhuglung-Bangdagco region. While in this study, the researchers found that the main reef builders, two species of stromatoporoid Gerronostromaria, possessing closely spaced laminae and pillars, co-occurred in the Lazhuglung-Bangdagco region, Changdu and South China and distributed only among the three terranes.
"Therefore, our study provides new evidence to prove the close paleobiogeographic affinity between Lazhuglung-Bangdagco region, Changdu and South China," said LIANG Kun, corresponding author of the study.
In addition, according to the assemblages of tabulate corals and stromatoporoids, the reefs belong to Middle Devonian Givetian in age. Therefore, the Devonian strata in Lazhuglung-Bangdagco region extends at least to the Middle Devonian, which enhances our understanding on the stratigraphic distribution features of the regions.
This study was supported by the grants from the Second Tibetan Plateau Scientific Expedition and Research Program, Chinese Academy of Sciences, and the National Science Foundation of China.
Fig. 1 Field photo of Shouxinghu and an overview of Middle Devonian patch reefs in the Lazhuglung-Bangdagco region (Image by NIGPAS)
Fig. 2 Reef components and the major reef builders tabulate coral Alveolites and stromatoporoid Gerronostromaria in the patch reefs (Image by NIGPAS)
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