In the vicinity of the Town of Gaspé, the relationships between the Silurian–Devonian sedimentary succession of the Gaspé Belt and the Humber and the Dunnage zones are complex. To unravel these relationships, we used high-resolution aeromagnetic data and regional gravimetric data coupled with field tectonostratigraphic information. The magnetic vertical derivative located several magnetic anomalies associated with near-surface features in the Silurian–Devonian cover sequence. In particular, a conglomerate with magnetic fragments that overlies the Late Silurian Salinic Unconformity is clearly recognizable. Large ovoid anomalies of significant intensity located in the Silurian–Devonian sedimentary cover area cannot be associated with any known geological feature. The interpretation of the high-pass and low-pass filtered aeromagnetic survey indicates that the ovoid anomalies originate below the Silurian–Devonian cover sequence. The most significant of the ovoid anomalies is associated with a gravimetric anomaly. It is proposed that these geophysical anomalies are probably associated with ultramafic and (or) volcanic rocks correlative in the subsurface with outcrops of the Cambrian–Ordovician lithologies of the Lady Step Complex and (or) the Shickshock Group.