Donna Kirkwood

Paleogeography and tectono-sedimentary history at the margin of Laurentia during Silurian to earliest Devonian time: The Gaspé Belt, Québec

The Silurian–Lower Devonian sequence of the Gaspe Belt at the Laurentia margin 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, significant tectonic activity attributed to the Salinic disturbance began during late Llandoverian (Telychian) time and persisted until the Acadian orogeny. This tectonic activity has profoundly influenced the composition and distribution of the Silurian–earliest Devonian sedimentary facies. The shelf and shelf edge history at the Laurentia margin along the Quebec reentrant–St. Lawrence promontory is summarized according to four broad phases. Phase 1 is a Llandoverian–Wenlockian regressive phase (R1) related to post-Taconian successor basin filling, that culminated with extensive carbonate platform development. Phase 2 is a late Wenlockian–Ludlovian transgressive phase (T1). Phase 3 corresponds to a later Ludlovian–Pridolian second regressive phase (R2). Phases 2 and 3 were accompanied by extensional tectonics that produced shelf faulting and block tilting, on top of which block reefs and reef complexes settled and built a reef tract all the way along the Gaspe-Temiscouata shelf. Phase 4 is an Early Devonian phase of accelerated subsidence (transgression T2) affecting the northwestern part of the segment (Quebec reentrant area), while the southeastern part (St. Lawrence promontory area) was already uplifted due to the ongoing collision between Laurentia and the western margin of Gondwana-related terranes to the south. Composition and distribution of sedimentary facies were controlled by the interaction of tectonics, sediment influx, and sea-level fluctuations. Construction of a post-Taconian–pre-Acadian palinspastic map to plot facies has proven to be basic to obtaining a realistic picture of the paleogeography of the shelf and shelf edge of the Gaspe-Temiscouata segment at the margin of the Laurentia craton during the Silurian–earliest Devonian time interval.

Vertical and fold-axis parallel extension within a slate belt in a transpressive setting, northern Appalachians

Abstract An incremental and finite strain study of a Mid-Paleozoic slate belt in a transpressive setting in Gaspe, Canadian Appalachians, has been undertaken using syntectonic fibers from pyrite-type pressure shadows. Regionally, strain estimates are quite consistent and reflect only slightly higher strain in the central part of the anticlinorial structure defining the slate belt. Extensions of up to 160% vertically and 110% parallel to the fold axis were recorded in the slate belt combined with an estimated overall regional shortening of 80%. The fibers first rotated toward the final position of the cleavage within a vertical section normal to the cleavage, and then rotated from a vertical to a horizontal orientation. This change in fiber orientation observed in cleavage-parallel sections indicates an abrupt change in the incremental stretching direction from sub-vertical to sub-horizontal (fold-axis parallel). The vertical extension is related to folding and cleavage development during coaxial flattening. The horizontal extension reflects the strain imposed on the rocks during regional simple shear which produced strike-slip faulting and further tightening of the folds. Folding, cleavage development, fold-axis parallel extension and faulting are all related to oblique convergence during the Middle Devonian Acadian orogeny in this part of the Canadian Appalachians and clearly indicate an overall transition from a pure shortening deformation to a simple shear dominant deformation in an overall transpressive setting.

Moose Mountain Virtual Explorer: A learning and ground-truthing tool to explore high-resolution remote sensing and geoscience data in mountainous area

The objective of the Moose Mountain Virtual Explorer system (MMVE http://www.cgq-qgc.ca/geoide/) is to provide access, through an efficient web interface, to a geologically-rich digital library to remote sensing and geoscience researchers, resource explorationists and students. Data sets are all geographically located within a rugged area of the Rocky Mountain Foothills of Alberta. The library collection was acquired through field campaigns, and airborne and satellite acquisitions, over the course of a 3-year canadian GEOIDE Network of Excellence project (Moose Mountain project, Lebel et al. 2001). High-resolution aerial orthoimages, oblique aerial and terrestrial photographs, radar imagery, geological data, maps and cross-sections constitute the database content. The project is nearing completion and aims to promote the integration of geoscientific, photogrammetric and remote sensing data as a guide for oil and gas exploration in mountain fold and thrust belts. Moose Mountain was selected because it represents a surface analogue of complexly faulted carbonate rock formations that host a gas field at depth. MMVE can thus be used to explore the complex relationships that exist between rock properties and hydrocarbon reservoir favourability within the context of small and subtle gas plays that are being explored in the deep subsurface of the Canadian Cordilleran Foothills.