DEPOSITIONAL CONDITIONS OF THE UPPER PART OF THE LOWER CRETACEOUS DEPOSITS IN THE SOUTHEAST OF THE WESTERN SIBERIA

I. A. Melnik

Innovative method of well logging data interpretation from 130 wells in the Tomsk Region enabled measuring of the boron content in sandy Cretaceous deposits. Average boron content normalized to clay content in sandstones (which characterizes paleosalinity) of the lower member of the Pokur Formation was correlated with a number of coal layers in the studied member, which revealed eight linear regressions (well groups) caused by three-factor influence of depositional conditions on the studied parameters. These factors include paleorelief surface gradient, frequency of tectonic bulging-up cycles, and relative supply of fresh water to sedimentary basin. Each factor is characterized by increasing or decreasing impact. The authors have calculated coefficients of impact of these three factors on paleosalinity and quantity of coal intervals in the studied member. The boron content, foremost, depends on paleosalinity, and then on the above three factors, and the quantity of coal intervals exceptionally on the factors. Any group (regression) is controlled by the unique facies environment, which helps to assign the studied member to a definite group and reveal a paleofacies based on correlation of the normalized boron content and the number of coal layers.

Key words: well logging data interpretation, paleosalinity, boron content, Cretaceous deposits, depositional conditions, facies analysis.

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