The Deer Lake Basin, Newfoundland: structural constraints from new seismic data

摘要

The Deer Lake Basin in western Newfoundland is of Late Devonian to Permian (?) age and was formed by localized transtension, associated with dextral strike slip along the Cabot Fault zone. The basin infill is dominated by clastic sediments deposited in an alluvial to lacustrine environment. The stratigraphy and architecture of the basin have been studied extensively by surface mapping, though the absence of seismic data has limited interpretation of the depth structure. There is current interest in re-evaluating the petroleum potential of the Deer Lake Basin as part of a study of Palaeozoic sediments bordering and underlying the Gulf of St. Lawrence. Most of the activity in the Deer Lake Basin has focused on the northwest portion where the Lower Carboniferous (Visean) sediments of the Deer Lake Group outcrop. The Deer Lake Group forms a gentle synform, whose axis trends roughly northeasterly, paralleling the trend of the Cabot Fault. The depth extent of the Deer Lake Group sediments has been inferred from geological mapping and gravity and magnetics, though the sparse data sets have called these interpretations into question. The Centre for Earth Resources Research, in cooperation with Vinland Petroleum, acquired and processed seismic data along two test lines in the northwest portion of the basin. The objectives of the surveys were threefold: ⅰ) to determine appropriate acquisition parameters for high resolution seismic surveying in this region; ⅱ) to determine the thickness and structure of the Deer Lake Group; and ⅲ) to determine the nature of the "basement" to the Deer Lake Group in this part of the basin. The first line (line 1) was a short (～2 km) test along the axis of the synform near Reidville. Although successful in imaging the internal structure and thickness of the Deer Lake Group, it was too short to reveal any lateral structure and had insufficient source energy to image the deeper sediments in the basin. The second line (line 2 - ～12 km) along Paddy's Reef Road traversed the east limb of the synform. This line provided good images of the Deer Lake Group and underlying structures. There are several significant features seen in the data. There is a clear change in the reflective character of the sediments on both lines at about 0.7 s - 0.9 s two-way time (TWT). This is interpreted as the base of the Deer Lake Group. The syn-formal structure of the basin is well imaged at the southwest end of line 2. A number of high-angle faults, both normal and reverse, intersect the Upper Carboniferous sediments. Many of these faults are associated with an intensely faulted zone at the base of the Deer Lake Group. This zone is directly along strike from the Fisher Hills block of Anguille Group (Tournaisian and older) exposed to the southwest of line 2 and is interpreted as a flower structure developed in Late Devonian to Early Carboniferous time with subsequent burial in the Late Carboniferous, though with evidence of continuing fault activity throughout the whole Carboniferous period. The flower structure and its associated faults provide numerous opportunities both for migration and entrapment of petroleum. Thermal maturation indicators and geothermal modelling indicate that the lower Deer Lake Group experienced maximum paleotemperatures of 125℃ and is well within the oil generation window.%Le bassin sédimentaire de Deer Lake de la partie ouest de Terre-Neuve est d'âge du Dévonien tardif à Permien (?) et il a été formé par une transtension localisée, se rapportant à un rejet horizontal de faille dextre le long de la zone de la faille de la région de Cabot.