Effects of Smectite-Illite Reactions in Shales
on Sandstone Diagensis,
Park, Anthony J.1 (1) Sienna
Geodynamics & Consulting Inc,
Shales and mudrocks
are volumetrically dominant components in many sedimentary basins, and smectite is the most abundant of minerals composing them.
However, smectite is a highly unstable mineral and
readily undergoes thermal decomposition with increasing temperature, resulting
in precipitation of illite and export of other
solutes, such as Na, Ca, Fe, Mg, and Si. Sillica released from smectite-illite
reactions are assumed to contribute significantly to quartz overgrowth.
Observed temperature-dependent smectite-illite
reaction trends can be effectively described using simple empirical rate laws.
Because of the volumetric abundance of shales, it is also easy to see that total masses of various
chemical elements associated with smectite-illite
reactions are significantly greater than the mass of elements involved in
sandstone diagenesis. Thus, one can expect that
sandstone diagenesis should be therefore strongly
influenced by smectite-illite reactions.
To test the soundness of this expectation
Balance diagenesis simulator was used to assess how smectite-illite reactions affect sandstone pore water
chemistry, and thus diagenetic processes of
sandstones. Published petrographic and water
chemistry data of
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California