Paleogeography and tectono-sedimentary history at the margin of Laurentia during silurian to earliest Devonian time: The Gaspe Belt, Quebec

The Silurian-Lower Devonian sequence of the Gaspe Belt at the Laurentia mar gin south of the Quebec reentrant and St. Lawrence promontory was deposited during the period between the two main orogenies that created the northern Appalachians: the Late Ordovician Taconian and the Middle Devonian Acadian orogenies, Although this sequence is traditionally considered to have been deposited during a period of quiescence between both orogenies, significan t tectonic activity attributed to the Salinic disturbance began during late Llandoverian (Telychian) time and persisted until the Acadian orogeny, Thi s tectonic activity has profoundly influenced the composition and distribut ion of the Silurian-earliest Devonian sedimentary facies, The shelf and shelf edge history at the Laurentia margin along the Quebec r eentrant-St. Lawrence promontory is summarized according to four broad phas es. Phase 1 is a Llandoverian-Wenlockian regressive phase (R1) related to p ost-Taconian successor basin filling, that culminated with extensive carbon ate platform development. Phase 2 is a late Wenlockian-Ludlovian transgress ive phase (T1), Phase 3 corresponds to a later Ludlovian-Pridolian second r egressive phase (R2), Phases 2 and 3 were accompanied by extensional tecton ics that produced shelf faulting and block tilting, on top of which block r eefs and reef complexes settled and built a reef tract all the way along th e Gaspe-Temiscouata shelf. Phase 4 is an Early Devonian phase of accelerate d subsidence (transgression T2) affecting the northwestern part of the segm ent (Quebec reentrant area), while the southeastern part (St, Lawrence prom ontory area) was already uplifted due to the ongoing collision between Laur entia and the western margin of Gondwana-related terranes to the south. Composition and distribution of sedimentary facies were controlled by the i nteraction of tectonics, sediment influx, and sea-level fluctuations. Const ruction of a post-Taconian-pre-Acadian palinspastic map to plot facies has proven to be basic to obtaining a realistic picture of the paleogeography o f the shelf and shelf edge of the Gaspe-Temiscouata segment at the margin o f the Laurentia craton during the Silurian-earliest Devonian time interval.