| Summary: | The North Brook Formation in the Deer Lake Basin of western Newfoundland consists of red to grey, pebble to boulder conglomerates and arkosic sandstones, and less common muds tones and limestones. These rocks represent deposition in alluvial fans, associated downfan braided and meandering (?) systems, and small, carbonate-precipitating lakes. The upper part of the North Brook Formation is believed to intertongue with the mostly lacustrine Rocky Brook Formation of Viséan age. Deposition of these nonmarine fades occurred mostly in two lateral basins, which flank elongate flower structures containing strata of the Devonian (?) - Tournaisian Anguille Group. The flower structures were squeezed up as a result of dextral transpression along the Cabot Fault Zone. West of the flower structures there is no evidence that strike-slip faulting directly created the western lateral basin. This is based mainly on the distribution of carbonate clasts in North Brook conglomerates which matches the distribution of carbonate rocks in the adjoining basement. The western lateral basin is interpreted to have formed by a combination of gravity faulting and thermal sagging. One area, however, in a topographically low position in one of the flower structures contains about 7 km of North Brook sediment This stratigraphic thickness is thought to be much greater than the vertical depth to basement, an inference based on gravity measurements, which do not show an anomalously strong gravity low. This discrepancy in thickness vs. depth is interpreted in terms of a pull-apart basin, in which deposited sediment is shunted along the extension direction. The pull-apart area is believed to represent the initial deposition of North Brook sediment, when dextral motion was still in progress along this stretch of the Cabot Fault Zone. Lessening of strike-slip movements, probably in the Viséan, was accompanied by more pronounced gravity faulting and North Brook deposition in lateral basins. RÉSUMÉ La Formation de ...
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