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CSPG Special Publications

Abstract


Sedimentary Basins and Basin-Forming Mechanisms — Memoir 12, 1987
Pages 45-69
Extensional Basins

Thermal and Subsidence History of the Labrador and West Greenland Continental Margins

Dale R. Issler, Christopher Beaumont

Abstract

The first order subsidence and thermal characteristics of the Labrador continental margin, the northern Labrador Sea and the central West Greenland margin along Davis Strait are investigated using a one-dimensional, finite element model, calibrated with measured thermal properties of sediments from borehole samples. The model is a variation of the McKenzie stretching model, which allows differing amounts of extension in the upper and lower lithosphere, and it assumes that heat transport is by thermal conduction. Model predictions are tested using bottom-hole temperature, and geochemical and paleoenvironmental data from 27 industry wells.

An instantaneous, depth-dependent extension model is generally consistent with the observed geological constraints. Predicted heat flow ranges from 40 to 50mW/m2 for the Labrador Shelf and 50 to 60mW/m2 for the northern Labrador Sea-Davis Strait region. For most of the wells, the model predicts maximum water depths during the Paleocene and Eocene, in qualitative agreement with interpreted paleobathymetry. Crustal extension, β, ranges from 1.20 to 2.15 for the Labrador Shelf-northern Labrador Sea wells, and from approximately 1.6 to 1.9 for the central West Greenland margin. Subcrustal lithospheric extension, δ, varies from approximately 1 to 3 times the amount of crustal thinning in most of the wells, β estimates are biased by the presence of basement topography and reflect local changes in crustal thickness rather than true crustal extension. Thermal predictions appear to depend most strongly on estimates of δ which, in turn, depend on the quality and resolution of paleobathymetry data.

Profiles across the Labrador Shelf and in the northern Labrador Sea are used to study variations in the timing and position of the petroleum generation zone and are related to specific hydrocarbon occurrences. This zone varies temporally and spatially along the margin, but its present-day thickness is predicted to increase seaward from the Labrador coastline, with progressively younger sediments becoming mature toward the shelf edge. Calculations for the northern Labrador Sea imply that gas and condensate have been locally generated from organic-rich Paleocene shales since Late Miocene time. Potential oil source rocks of Eocene age are predicted to occur within the oil window beneath the outer part of the Labrador Shelf. Mature Upper Cretaceous to Paleocene mudstones with oil and gas potential were encountered in two wells on the West Greenland margin, and should be at the threshold for peak hydrocarbon generation in deeper parts of the basin.


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