The Voreppe Thrust

The Voreppe Thrust is one of the frontal structures of the Chartreuse.  In its type area it carries Jurassic limestones onto Miocene molasse. You will find structural data at the bottom of this page.

The molasse in its footwall includes conglomerates.  These are locally strongly pitted implying a strong degree of compaction.  Of all the various rock types within the conglomerate it is the limestone clasts that are the most pitted, while the clasts of basement hardly show any effects. 
Why do you think these conglomerates are strongly pitted and why is it that the limestones are most affected?

Pitted limestone pebbles in the Miocene conglomerates in the footwall to the Voreppe Thrust.

The following table contains structural data along the Voreppe Thrust.