Use of heavy minerals in lithostratigraphic correlation, with examples from Brent sandstones of the northern North Sea

Abstract

In the Middle Jurassic Brent Group of the northern North Sea, there were major variations in both the depositional environment and the diagenetic history. Thus, the use of heavy minerals for correlation purposes is potentially unreliable. However, there are several lines of evidence for changes in provenance within the Brent sequence of the Oseberg Field that provide a mineralogical basis for correlation across the field. These are: 1) changes of apatite:tourmaline and zircon:rutile ratios; 2) variations in tourmaline colours; and, most definitively, 3) changes in detrital garnet compositions. Garnet geochemistry also provides a basis for well-to-well correlation of individual channel sandstones in the Ness Formation. The data indicate that, in one well, the top Etive Formation has been eroded and replaced by Ness channel sandstones. This feature is not readily identifiable by other means. The implications of such erosion on sand volumes and distribution can be incorporated in reservoir volume calculations and in numerical simulation of recoverable reserves. -from Authors