E. А. Deliu

Geological structure of the Lower Jurassic deposits in the Vilyuy Syneclise

Abstract. Discovery of the Vilyuy Syneclise gas deposits in anticlinal traps, with gas observed at shallow depth, dates back to the 1960s. High reservoir properties are characteristic of the Kyzyl-Syr Formation reservoirs that wells in the study area encountered. The author used geophysical data to correlate the Lower Jurassic stratigraphic section within the study area: layer-by-layer and detailed intra-layer correlation, with sedimentological analysis data from the new well core included. The findings support unconformity between the Kyzyl-Syr and Suntar formations at the top of the Lower Jurassic deposits in the Khapchagai region of the Lena-Aldan structural-facies zone in the Vilyuy Syneclise. The author traced four consecutive cycles of deposit formation in the J1-1 bed and newly mapped the deposit erosion boundary in the last cycle; previous researchers had only assumed its presence. The author identified coastline location in the western part of the study area, as well as the sources position and direction of sedimentary material in the Early Jurassic period.

Keywords: Vilyuy Syneclise, Lower Jurassic deposits, Kyzyl-Syr Formation, unconformity, core