Maturation thermique, potentiel roche mère des roches ordoviciennes à dévoniennes du nord-ouest du Nouveau-Brunswick
Authors: Bertrand R , Malo M 
Published: November 2010

Introduction: A study of organic matter petrography and geochemistry is carried out on 160 samples from lower and middle Paleozoic rocks in northwestem New Brunswick. The study aims to document potential hydrocarbon source rocks and thermal maturity of these
successions. Geological context: The successions form part of a successor basin that unconf ormably overlies Cambrian-Ordovician basement rocks of the Appalachians Dunnage and Gander zones. The successions crop out in three structural elements - from south to north : the Chaleurs Bay synclinorium,
the Aroostook-Percé anticlinorium and the Gaspé-Connecticut Valley synclinorium. These elements are bordered by major faults and other faults divide these elements into distinct tectonic blocks. Two folding episodes are recognized. The successor basin comprises seven lithostratigraphic
groups mostly dominated by siliciclastic sediments which cover the Upper Ordovician to Middle Devonian interval : the Grog Brook, Matapédia, Chaleurs, Perham, Dalhousie, Gaspé Sandstones and Fortin groups. Source rock potential: The hydrocarbon source rock potential ofthese successions is
evaluated on the results of the Total Organic Carbon, the programmed pyrolysis(Rock Eval) and the petrographic characteristics oftheir kerogens. The Middle Ordovician Popelogan Formation of the underlying Dunnage zone and the Ritchie Brook Member of the upper part of the Boland Brook Formation
(Upper Ordovician Grog Brook Group) are the best hydrocarbon source rocks of the area and have generated significant amounts of liquid and gas hydrocarbons. Sorne coal beds found at the top of the volcano-sedimentary pile (Val d' Amour and Campbellton formations) are also potential source rocks.
However, these are immature and no hydrocarbons have been generated from these coals. Thermal maturation - nature-intensity-correlation with tectonic events: The thermal maturation of the rock succession in northwestem New Brunswick covers a wide range of equivalent vitrinite reflectance values
(0.36% to 8.9%). This range encompasses the immature hydrocarbon zone to the metamorphic greenschist facies. Even if sedimentary burial plays a critical role in the thermal maturation of the succession, this burial is highly variable from one area to the other. Therefore, most of the
sedimentary units cover a wide range of thermal ran1cs regardless of their position in the sedimentary pile. Two areas are favourable for the preservation of liquid hydrocarbons. Of these, the Restigouche syncline, which is limited by the Sellarsville and Black Lake faults, is the best documented.
The second one is restricted to a tectonic block limited by the Jacket River Pointe Arleau Brook fault to the west and by an unnamed fault to the east. With the exception of these two latter cases, all successions that crop out to the west of the tectonic blocks limited by the major strike-slip
faults (Restigouche, McKenzie Gulch, Rocky Brook-Millstream, Jacket River-Pointe Arleau Brook faults) are in the dry gas zone. The successions to the east of these blocks are usually in the overmature to metamorphic domains. The thermal maturation post-dates the first NW-SE folding phase, but is
more or less coeval with the second NE-SW folding phase. The thermal maturation post-dates the Silurian