Staff from INGG SB RAS together with colleagues from the Nanjing Institute of Geology and Paleontology, CANS proposed an updated correlation scheme between Upper Jurassic (163.5 million years – 145 million years ago) and Lower Cretaceous (145 million years – 100.5 million years ago) deposits in the Sikhote Alin and China. Specialists expect to conduct similar work in the Transbaikalia – according to scientists, these studies have important fundamental and applied value.
Igor Nikolaevich Kosenko, Scientific Secretary of INGG SB RAS, PhD in Geology and Mineralogy, told about some of the results and further plans. He is also a postdoctoral researcher at the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences.
- Why are you interested in Sikhote-Alin?
- This is a very interesting mountainous region on the border with China, which is geologically different from the rest of China. About 130 million years ago, in the late Jurassic and early Cretaceous, there was the sea on the territory of Sikhote-Alin. The territory of modern southwestern Sikhote-Alin was the place from where in the Late Jurassic and Cretaceous period sea transgressions took place onto the territory of modern China, i.e. sea water was flooded. And just at the expense of it in the areas of China bordering Russia from time to time accumulated marine deposits with marine fossils, allowing correlation not only with the border territories of Russia, but also with the international stratigraphic scale, based on the distribution of just marine fossils. This, in turn, makes it possible to specify the age of the deposits.
However, at the end of the Early Cretaceous, the situation on Sikhote-Alin changed. At that time, the territory of Sikhote Alin was located in the subduction zone, the place where the ancient oceanic plate was pushed under the continental plate. At the end of the Early Cretaceous the character of subduction changed, and the formation of the East Sikhote-Alin volcanic belt began. Gold and other ore deposits are connected with it.
At the same time, in the border areas of China the situation was quite different, and markers for correlation between them and Sikhote-Alin are quite difficult to find. However, we have already solved the first tasks of correlating the Upper Jurassic and Lower Cretaceous, building the basis for future paleogeographic reconstructions.
- What exactly did you do in the process?
- We summarized and revised the available biostratigraphic data – that is, information about the distribution of fossils in this region. We studied all the isotopic dating and compiled a single table. Finally, we identified the sedimentological and tectonic boundaries of the development of this area. The data we collected can be used for geological surveying and other works.
This year, together with our co-authors Professor Sha from Nanjing University and Boris Nikolayevich Shurygin, Corresponding Member of the Russian Academy of Sciences, we reported our results in the highly rated journal Cretaceous Research. A second article is expected to be published soon in the same scientific journal. Now we want to expeditions to support the information obtained in the process of theoretical research.
- What field work are you planning as part of the project?
- This summer, in August, we are planning an expedition to Transbaikalia. We will study the Lower Cretaceous continental deposits, which should be very similar to those in China. There is a practical aspect here, because oil and coal reserves are associated with similar sediments in China.
In addition, we hope to find new fossil remains related to the Jehol biota. Traces of this ancient fauna are found over a large area – from the southeast of Transbaikalia in the north to the Chinese province of Liaoning in the south. Therefore, in the paleobiological aspect, future studies are also very interesting.
Again, in Russia, less attention is paid to the study of fossil biota from continental Lower Cretaceous sediments than in China. And some groups of fauna, which are very important just for correlation, for example, freshwater crustaceans conchostracans, have not been studied for a very long time. In the future expedition, we will collect new samples of fossil fauna in order to update our ideas about the correlation of the Lower Cretaceous of Transbaikalia and northeastern China and about the paleogeographic distribution of Jehol biota.