Nicolas Pinet

Far-field effects of Appalachian orogenesis: A view from the craton

The sedimentary cover of the North American craton preserved little evidence of the Paleozoic tectonic events that shaped the Appalachian orogen on its eastern side. A notable exception is the NNW-trending Hudson Bay central high, which corresponds to a normal-fault array extending for a minimum length of 500 km. A working hypothesis is proposed in which stresses applied to the continental margin during the Silurian–earliest Devonian Salinian orogeny were transmitted over a distance of >1400 km in the continental interior, where they induced the normal-fault reactivation of older structural discontinuities. The shutdown of tectonic activity along the Hudson Bay central high during the latest Early Devonian to earliest Middle Devonian is interpreted as resulting from a change in the direction of plate convergence during the Acadian orogeny.

The Paleozoic Hudson Bay Basin in northern Canada: New insights into hydrocarbon potential of a frontier intracratonic basin

The Hudson Bay Basin is the largest intracratonic basin in North America, although it is the only one without any proven hydrocarbon reserves. The stratigraphic succession that fills the basin consists mainly of Paleozoic strata, with a maximum preserved thickness of about 2500 m (8202 ft). The Paleozoic succession includes Ordovician to Devonian shallow marine carbonates, reefs, and shales with locally thick Devonian evaporites. The Paleozoic strata are locally unconformably overlain by a thin Mesozoic and Cenozoic cover of nonmarine and marine strata. From 1964 to 1985, over 46,000 line-km (28,600 mi) of seismic reflection data were acquired, and four onshore and five offshore exploration wells were drilled. The data acquired at that time led to pessimistic conclusions on source rocks and the thermal rank of the basin and resulted in the stoppage of exploration activities. However, hydrocarbon shows or indicators were identified in well log data and seismic reflection profiles. The likelihood of an active petroleum system has also been recently supported by recognition of pockmarks on the seafloor and possible marine oil slicks identified on satellite images. New studies of geological, geophysical, and biostratigraphic data reveal that the Hudson Bay Basin had an irregular subsidence and uplift history. Syntectonic deposition occurred during the Late Ordovician(?) to Early Devonian and sag-basin deposition during the Middle to Late Devonian. The basin contains four unconformity-bounded sequences, with significant depocenter migration over time. Analyses of petroleum-system data indicate the Hudson Bay Basin has higher petroleum potential than previously considered. Porous platform limestones, reefs, hydrothermal dolomites, and siliciclastics form potential hydrocarbon reservoirs. Upper Ordovician organic-rich shales with type II-S organic matter are recognized at several locations in the basin. Newly acquired organic matter reflectance and Rock-Eval data indicate Ordovician–Silurian strata locally reached the oil window. Basin modeling demonstrates significant potential for oil generation and expulsion from Ordovician source rocks. Five petroleum play types are identified in the Hudson Bay Basin, including an untested fault-sag or hydrothermal dolomite play. The synthesis of the petroleum system information indicates that the Hudson Bay Basin is, at least locally, prospective for oil accumulations.

The St Lawrence Platform and Appalachian deformation front in the St Lawrence Estuary and adjacent areas (Quebec, Canada): structural complexity revealed by magnetic and seismic imaging

New magnetic and seismic datasets offer a unique opportunity to document the geometry of the Appalachian front in a poorly studied segment of the orogen. Interpretation of high-resolution magnetic data allows, for the first time, the documentation of the contact between the autochthonous St Lawrence Platform and the Appalachians and highlights the regional significance of previously poorly documented ENE faults that experienced post-Ordovician strike-slip motion. Seismic data reveal tectonic slices in the foreland domain underlying the Appalachians and show that the depth of the decollement at the base of the Appalachian tectonic wedge varies significantly. Taken together, geological, magnetic and seismic data suggest that the geometry of the Appalachian front exhibits significant variations in map and cross-section views and recorded a polyphased structural history.

Hinterland-directed transtensional faulting at an orogen structural front: The example of the Cap-Chat mélange, Quebec Appalachians

The Cap-Chat melange is a regional-scale dismembered unit that occurs close to the Quebec Appalachian front. The melange records early (D 1 , Taconian) and late (D 3 , Acadian) regional deformations. The greater degree of disruption of the melange compared with surrounding units is due to the superimposition of D 2 structures that are rare outside the melange. D 2 structures include both layer-extensional features such as block disruption along shear zones and faults and layer-contractional features such as folds that record the transtensional collapse of the Taconian orogenic wedge along a rheologically weak deformation zone. The Cap-Chat melange is interpreted as the westernmost remnant of a zone of mechanical decoupling in the upper crust, which allows normal or transtensional faulting in the inner parts of the orogen. This paper presents evidence that beyond the general complexity of melange units, geological observations may still contribute to unraveling their tectonic history and that transtensional reactivation of original thrust faults is a viable mechanism in the frontal parts of orogens.

Partly-filled U-shaped morphology of the Laurentian Channel, St Lawrence Estuary, Canada

The geomorphology of the St Lawrence Estuary seafloor is dominated by post-glacial landforms and processes. However, some segments of the estuary are still characterized by a U-shaped morphology, inherited from one or more glacial episodes, that is only partially modified by postglacial sedimentation. Marine-geophysical data on the morphology and stratigraphy of the estuary are used to describe and interpret this partly sediment-filled submarine environment. The Laurentian Channel is a long and continuous trough >300 m deep that extends 1500 km from the mouth of the Saguenay River in the St Lawrence Estuary to the edge of the continental shelf in the Atlantic Ocean (Fig. 1). It is a clear physiographic feature, whose U-shaped morphology in cross-section, including steep bounding escarpments, is particularly well developed at its upstream (western) extent (Fig. 1a). Fig. 1. Multibeam bathymetry, high-resolution seismic and schematic geometry of the U-shaped segment of the Laurentian Channel in the St Lawrence Estuary. ( a ) Sun-illuminated multibeam-bathymetric image showing the U-shaped portion of the Laurentian Channel (LC). Acquisition system Kongsberg EM1000 (before 2005) and Kongsberg EM1002 (2005 and 2006 surveys). Frequency 95 kHz. Grid-cell size 10 m. ( b ) Perspective view from the NE. VE ×15. ( c ) Perspective view from the east …