When a crack accelerates beyond the material shear-wave speed, shear-waves pile up into a shock front, a striking Doppler-induced signature of supershear fractures. While supershear fracture is best known from dynamic rupture in strike-slip earthquakes, it has recently been observed and modeled in snow slab avalanches triggered by the failure of a weak layer beneath cohesive slabs. These slabs are typically stratified, with layers of distinct mechanical properties that strongly influence wave propagation. Here, we combine numerical simulations with a long snow-fracture experiment to identify Mach cones associated with supershear crack propagation in layered snow slabs. We show that slab layering alters both the crack propagation speed and Mach cone geometry, and that curvature of the cone can be explained by wave refraction at layer interfaces. These findings advance our understanding of avalanche release and supershear fracture dynamics and provide a framework for detecting and interpreting Mach cones in snow-fracture experiments.