Marine geology of Baie des Chaleurs

Abstract

Baie des Chaleurs is the fourth largest estuary in eastern Canada. The bay is a broad and shallow basin, filled with up to 50m of unconsolidated Quaternary sediment. The distribution of this sedimentary mass is in part controlled by a Cenozoic (Tertiary or Quaternary) drainage system that follows the main structural elements of the underlying Paleozoic sedimentary bedrock. Ice-contact Pleistocene sediment, including till, is generally thin or absent. However, in the central and outer bay the Cenozoic channels contain linear morainal accumulations up to 30m thick. These deposits may indicate the terminal position of the Gaspe ice dome. Six large but separate glacimarine fans mark the position of major discharge outlets that operated during the retreat phase of the regional ice sheets. These Pleistocene deposits were partly eroded by glacifluvial drainage channels during a low sea level stand (-90m) circa 9000 yrs BP. Subsequently, during the early to middle Holocene marine transgression, the glacigenic sediments were subjected to wave erosion. These deposits thus thin towards shallower water and are marked by shore-parallel terraces and surface lags along the margins of the bay. By 7000 yrs BP, a sandur complex located in the shallower inner bay was also transgressed by the rising sea. Modern oceanographic conditions become established circa 5000 years ago. -from Author