The idea of disc dark matter is highly speculative, and requires a subdominant dark matter candidate with significant self-interactions (We know that most of the dark matter is in a roughly spherically symmetric halo).

Also, the correspondence between disc crossings and cratering looks tenuous at best...someone should check my work, but I plotted the tabulated impact pulses that the author associates with extinction events as a function of phase (assuming period = 30 Myr, t0 = now) at http://imgur.com/dfTkNEW . Running a Rayleigh statistic shows no evidence for non-uniformity (Rayleigh=0.16, N=13) and the mean phase is close to pi/2 too.