Abstract

The Devonian clastic succession of eastern Gaspe is a coarsening upward mega-sequence resting conformably on shallow marine Lower Devonian limestone. It commences with shallow marine sandstones of the York River Formation (Lower Devonian) which are transitional upward into the lower Battery Point Formation (Lower Devonian: Petit-Gaspe and Cap-aux-Os Members). These members comprise an alternation of distal alluvium (with both low and high sinuosity channels) and coastal plain/tidal channel deposits. The paleoslope was northward, with axial drainage westward towards the sea.

The upper Battery Point (Ft. Prevel Member, Lower to Middle Devonian) and Malbaie Formations (Middle Devonian) record a change to more proximal braided alluvium and switching of the axial drainage towards the east. The northward paleoslope was maintained, and cobbles in the Malbaie Formation were transported on a proximal braidplain, whereas the eastward axial flow transported sand in sheetfloods and low sinuosity channels.

This succession and its paleogeographic changes resulted from plate motions that caused the Acadian Orogeny. Oblique convergence between the Avalon exotic terrane and North America generated a major mountain belt and dextral shearing along the continental margin. Convergence was diachronous; its initial impact in the Gulf of St. Lawrence raised that area and initiated westward axial drainage in Gaspe. As the impact zone migrated southwestward it progressively raised the source terrane, causing axial drainage to switch to the east. This model provides an explanation for the nature of the Devonian succession in eastern Gaspe and also the decreasing age of deformation and resultant clastic wedges southwestward along the Acadian Orogen.