The ‘oil-filling’ model

The ‘oil-filling’ model
This is our preferred model for the depth-d18O
correlation. Kaolin recrystallisation could only be affected
gradationally by hydrocarbon emplacement if recrystallisation
and hydrocarbon filling were synchronous. It is difficult
to directly date the timing of oil filling in Cormorant IV,
however, as it has been proposed that authigenic illite in the
Brent Group grew at the time of trap filling (Hamilton et al.,
1992), the K–Ar dating of illite provides a possible solution.
Unfortunately, only a single illite age of 60.3 ^ 2.0 Ma has
been obtained from Cormorant IV, from an oil-filled zone.
In the adjacent, structurally higher, areas of the Cormorant
field (designated Cormorant I–III), illite has been dated as
35 ^ 1 and 41 ^ 1 Ma within a water-filled zone (Hamilton
et al., 1992). Here, detrital contamination was identified as a
potential problem, so that the true age of the illite may be
younger than the analytical result.