Paleolimnology Study: Taking Huadian Fault Basin as an example

Key words: 
• fault basin

Abstract: Paleolimnology is a science to study the historical evolution of lake systems, which belongs to highly comprehensive geosciences. This paper presents a review on the definitions, research status and commonlyused research methods in paleolimnology, and takes the Paleogene oil shale bearing lake in Huadian basin, Jilin Province, as a case study. Huadian Basin is a smallscale halfgraben basin, and F1 fault in the southern margin of the basin controls the Palaogene lake evolution. Huadian Basin that is rich in oil shale resources has unique advantages for paleolimnological studies. Huadian oil shale shows characteristics of doublelayered structure, which consists of alternatively white and black thin layers. The organic and terrestrial mineral detritus layers rhythmically alternate each other  the organic layers show black or brown, while the other ones of quartz, feldspar and clay minerals show white. According to the vertical variations of TOC content, we interpret that the paleoproductivity of Huadian Basin varies as Middle Member(oilbearing) > Upper Member (coalbearing) > Lower Member (pyritebearing). Such a variation indicates that paleoproductivity was the highest when the oil shale was forming. From the petrography and mineral features of oil shale, the ratios of V/V＋N, Sr/Ba and B/Ga, we conclude that the paleowater characterizes as alternatively variation of fresh to brackishsaline water, which was a preferment environment for the lake stratified. The organism was well preserved because of the stratifyingcaused anoxic in the bottom water. With the development of paleolimnology, it is acting as an important role in the fields of hydrocarbon exploration and the studies for global environment and climate changes. However, challenges in theories and methods show up in front of paleolimnologists which are waiting for continuous endeavor and exploration.