Rb-Sr and K-Ar Investigations Used to Reconstruct Diagenetic Evolution of Sedimentary Basins
Norbert Clauer, Nicole Liewig, Jean Remi Mossman, Sam Chaudhuri
The Rb-Sr and K-Ar isotopic methods allow workers to evaluate the crystallization time of well-characterized, authigenic, potassium-enriched clay minerals. When the formation of these minerals is directly related to fluid migrations, oil trapping, or a combination of both, the age of ore deposition or oil emplacement can be estimated. The period and conditions of oil migrations into reservoirs may be deduced from combined microthermometric investigations on fluid inclusions and isotopic dating on associated authigenic illite-type clays. Furthermore, strontium isotopic determinations combined with elemental chemistry on reservoir brines may provide information about their origin and the extent of their interaction with the host rocks.
However, these methods need careful preliminary petrographic and mineralogic investigations by optical, scanning, and transmission electron microscopy and x-ray diffractometry, to characterize the mineral and separate types precisely. Special sample preparation also must be considered to minimize the overcrushing effect on detrital components, especially in sandstones where they might contaminate the authigenic clay fractions that must be separated and purified.
Various aspects of this combined mineralogical, geochemical, and isotopic approach will be described for oil and geothermal reservoirs of the Jurassic Brent Formation in the North Sea, the Triassic sandstones in the Paris basin and Rhine graben (France), and the Mississippian carbonates in Kansas (U.S.).
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.