抄録
In Tenpoku district, petroleum exploration has been continued from 1914, but only 6 oil and 1 gas pools have been discovered, and their main producing horizon is neogene Mapsuporo formation.
Considering the variation of lithofacies and thickness of neogene tertiary formation of this district, it can be distinguished that the geological condition during the deposition of these formations undergo considerble transformation and fluctuation. The writer can explain these phenomena more clearly for Masuporo and Wakkanai formations, because at those stages more geological data are available.
At Masuporo stage, it is recognized that there were several uplift parts such as Masuporo, Matsuozawa, Kiyokawa and Chikubetsu, and depression areas such as Magaribuchi, Utakoshibetsu and Sarakitomanai.
The nature of these uplift and depression areas are different in their genesis and development. From the earlier stage of Magaribuchi, Soya, and Onishibetsu, some parts of these differences had been succeeded.
But later Wakkanai stage, the configuration of the sedimentary basin is widely changed and simplified.
The center of sinking is clearly distinguished along Wakkanai-Sarakitomanai trend, and the west and east margins of the basin are graduary made clear of their presence.
The writer presents a hyposesis to explain the mode of occurence of petroleum in Tenpoku district.
