Basin evolution in western Newfoundland: New insights from hydrocarbon exploration

The Humber zone is the most external zone of the Appalachian orogen in west ern Newfoundland. It records multiphase deformation of the Cambrian-Ordovic ian passive margin and of the Ordovician to Devonian foreland basins by the Taconian, Salinian, and Acadian orogenic events. The recent phase of exploration drilling has provided new evidence for stru ctural, stratigraphic, reservoir, and source rock maturation models of west ern Newfoundland. The first well, Port au Port 1, supported the hypothesis that the Round Head thrust had an earlier extensional history prior to the Acadian compressional inversion that created the present-day structural hig h of the Port au Port Peninsula. The well tested a small anticline formed i n a footwall shortcut fault of the Round Head thrust. The second well, Long Point M-16, was drilled at the northern tip of Long Point to test a triang le zone identified by previous workers. This well demonstrates that the fro ntal monocline at the western edge of the triangle zone is elevated by a st ack of imbricate thrusts composed of rocks of the Taconian allochthon and c ompressional basement-involved faults that have uplifted the Cambrian-Ordov ician carbonate platform. The structural model developed in the Port au Port area with the aid of the se wells has been extended throughout the Humber zone in western Newfoundla nd. Changes in structural style illustrated by regional cross sections sugg est that prospective trap geometries are only developed in the southern and central parts of the region. The reservoir model proposed invokes exposure and karsting of the footwalls of extensional faults formed as the carbonate platform collapsed during a Middle Ordovician hiatus, the St. George unconformity. Structural relief be came more pronounced as extensional collapse continued through the Middle O rdovician. These structurally high fault footwalls became the foci for dolo mitizing and mineralizing fluids that used major faults as fluid conduits d uring the Devonian. Fluids deposited sulphide ores and created zebra and sp arry dolomite and some sucrosic hydrothermal dolomites in the St. George Gr oup and the Table Point Formation. The reservoir model, maturity and source rock data, and the structural mode ls have been combined with seismic and onshore surface geology. This enable s the prospectivity of the western Newfoundland Cambrian-Ordovician play tr end to be evaluated for further exploration.