The only thing I can think of is the amount of nitrogen compounds present in the must effect the yeast. For example, in '04, I made a Cab Franc from grapes grown in the Niagara Peninsula and I used a yeast strain that required a high amount of nitrogen. I was supposed to supplement the nitrogen content by using yeast nutrient, but failed to do so, as I was unfamiliar with the yeast strain recommended to me. As a result, the yeast, being nitrogen starved, went through a reduction reaction and produced mercaptans, very foul smelling aromatics. I have no idea how this relates to geology, but there is a connection between nitrogen and winemaking. Perhaps the same grapes from a different terroir would have had enough nitrogen, but adding the yeast nutrient or using a less nitrogen dependent yeast strain would have also solved my problem.