(1) In petroleum geology, a deposit of oil or gas bounded along the strike by strata of petroleum-impermeable rocks.
Three types of screened deposits are distinguished: tectonic screened deposits, where the stratum containing the oil or gas deposit is bounded by a disjunctive tectonic displacement (normal fault, slip-strike fault); lithological screened deposits, which are characterized by an abrupt alteration in the lithological composition of the collector rocks by impermeable rocks; and strati-graphic screened deposits, in which the collector strata are cut off by the surface of a stratigraphic unconformity above which are petroleum-impermeable rocks.
Tectonic screened deposits are widespread in petroleum and gas provinces that are associated with regions of subsidence of mountain ranges, intermontane depressions, and foredeeps characterized by various types of large-scale faulting. In platform conditions such deposits are usually found in areas of tectonic salt structures. Accumulations of oil in lithological screened deposits occur widely in both platform regions and folded areas.
Stratigraphic screened deposits are rare in the USSR; they contain small quantities of petroleum. They are widespread on the North American Platform in the United States.
The term “screened deposit” of oil or gas was first proposed in 1937 by the Soviet geologist I. O. Brod.
(2) In mining geology, screened deposits of mineral products are ore bodies occurring beneath water-impermeable rock strata from ascending ore-bearing hydrothermal solutions. They are common in layered strata, especially among carbonate rocks alternating with clay shales, which form the screen that blocks the movement of the ore-bearing solutions.
REFERENCESBrod, I. O. “O klassifikatsii neftianykh zalezhei po ikh formam.” In Trudy 17-oi sessii Mezhdunarodnogo geologicheskogo kongressa, vol. 4. Moscow, 1940.
Khel’kvist, G. A. Geologicheskoe stroenie zonal’nykh zalezhei nefti. Moscow-Leningrad, 1946.
Smirnov, V. I. Geologiia poleznykh iskopaemykh, 3rd ed. Moscow, 1976.
L. M. BOGDANOVA