Abstract:

Utilizing comprehensive ways of field outcrops, mineral assemblages, organic petrology and element geochemistry analysis, we study the oil shale features and origins of coal-oil shale bearing and oil shale bearing sections in Dalianhe Formation, Yilan basin. Organic matter type of oil shale organisms in coal-oil shale bearing sections is II₁ and II₁-II₂ in oil shale bearing sections. Oil shale not only in coal-oil shale bearing sections, but also in oil shale bearing sections, are all characterized by weak oxidized-reduced, and with different origins.Oil shale of coal-oil shale bearing sections was generated in lacustrine-swamp systems and was located on the former swamps when the base level was rising. Because the hydrodynamic was relatively weak and oxygen can hardly be renewed, large quantities of plants and animals died and be well buried forming into organismrich oil shale. Oil shale of oil shale bearing sections was generated in deep and semi deep lacustrine systems, in which the gravity flows took place very often. Gravity flows can not only bring terrigenous clastics, but also induce oxygen into the deep and semi deep lacustrine systems. In this environment, organism was poorly preserved. As a result, the organisms in oil shale bearing sections are characterized by mixed ones (II₁-II₂) and weak oxidized-reduced.

Key words: Yilan basin, Dalianhe Formation, oil shale, gravity flow