Rr. Hillis et al., QUANTIFICATION OF TERTIARY EROSION IN THE INNER MORAY FIRTH USING SONIC VELOCITY DATA FROM THE CHALK AND THE KIMMERIDGE-CLAY, Marine and petroleum geology, 11(3), 1994, pp. 283-293
Sonic velocities for the Chalk and Kimmeridge Clay were analysed to de
termine the importance and magnitude of Tertiary erosion for 26 wells
in the Inner Moray Firth. Apparent erosion (height above maximum buria
l depth) was derived by the displacement, along the depth axis, of a g
iven velocity-depth trend from the normal (undisturbed) trend. The sim
ilarity in apparent erosion results derived from the Cretaceous Chalk
and Late Jurassic Kimmeridge Clay successions of the Inner Moray Firth
suggests that burial beyond present depths caused the observed overco
mpaction rather than any sedimentological and/or diagenetic process. R
esultant apparent erosion estimates are variable across the Inner Mora
y Firth. Such values reach approximately 1 km in the western part of t
he basin and decrease progressively to zero in the eastern Inner Moray
Firth. However, the actual magnitude of erosion (equal to the sum of
apparent erosion and post-erosional Tertiary burial) was approximately
1 km throughout the whole Inner Moray Firth area, indicating that Ear
ly Tertiary erosion was regional and not simply restricted to the inve
rted basin margins. However, a well defined mechanism sufficient to ha
ve generated the regional event is still sought.