A DELTAIC REGIME RECORDED BY THE LOWER DEVONIAN COMPTON FORMATION IN SOUTHERN QUEBEC: REGIONAL IMPLICATIONS

The Lower Devonian Compton Formation is the uppermost unit of the St. Francis Group in the Connecticut Valley - Gaspé synclinorium of southern Quebec. The Compton Formation is composed of three informal members for which a deep marine origin has been largely proposed over the years. Five distinct sedimentary facies have been recognized in the lower two members of the Compton Formation. High-energy, shallow marine and channel sand deposits dominate the Milan member. The overlying Lac Drolet member consists of below wave base mud and silt deposits with abundant turbidite sand interbeds. The Milan member is interpreted to represent deposits of river-dominated delta front to delta plain environments, whereas the Lac Drolet member is suggestive of below wave base pro-delta to deeper shelf deposits. The transition from the Milan to the Lac Drolet members is correlated with the deepening event recognized in coeval succession in the Gaspé peninsula and known as the T2 event. There, the coeval Indian Point Formation is interpreted to represent pro-delta sediments. In Maine, the slightly younger Matagamon Sandstone is interpreted as representing deposits of delta front - plain environments. The coeval Frontenac Formation in southern Quebec is preliminary interpreted to represent a facies correlative with the Matagamon Sandstone. The new paleogeographic maps for the Lochkovian illustrates the development of deltaic lobes from northern Gaspé to southern Quebec. In late Lochkovian-early Pragian, a major deltaic regime was established in southern Quebec - northern Maine whereas the successions further north-east (Gaspé Peninsula - New Brunswick) were experiencing significant synsedimentary tectonic collapse.