Two different mechanisms have been proposed to be important for the formation of extreme total ozone events in mid-latitudes, so-called miniholes: (A) far-range meridional transport of air masses from regions with different climatological ozone mixing ratios, and (B) (local) adiabatic vertical displacement of isentropes. Here, the relative importance of these two mechanisms is studied using two different ozone profile reconstruction techniques for all miniholes and minihighs (events with anomalously high ozone) during the time period 1980--1989 over Switzerland. Composites for the two types of events of their vertical potential vorticity (PV) reveal a vertical dipole structure of PV anomalies in the lower and middle stratosphere. They, in agreement with the profile reconstructions, highlight the importance of fast far-range transport (mechanism A). Dynamically consistent with this PV structure is a relatively weak vertical displacement of isentropes between the PV dipole, that provides an additional but less important contribution (mechanism B).