Abstract
Many of the Earth’s sedimentary basins are affected by glaciations. Repeated glaciations over millions of years may have had a significant effect on the physical conditions in sedimentary basins and on basin structuring. This paper presents some of the major effects that ice sheets might have on sedimentary basins, and includes examples of quantifications of their significance. Among the most important effects are movements of the solid Earth caused by glacial loading and unloading, and the related flexural stresses. The driving factor of these movements is isostasy. Most of the production licenses on the Norwegian Continental Shelf are located inside the margin of the former Last Glacial Maximum (LGM) ice sheet. Isostatic modeling shows that sedimentary basins near the former ice margin can be tilted as much as 3 m/km which might significantly alter pathways of hydrocarbon migration. In an example from the SW Barents Sea we show that flexural stresses related to the isostatic uplift after LGM deglaciation can produce stress changes large enough to result in increased fracture-related permeability in the sedimentary basin, and lead to potential spillage of hydrocarbons out of potential reservoirs. The results demonstrate that future basin modeling should consider including the loading effect of glaciations when dealing with petroleum potential in former glaciated areas.
Highlights
It is commonly accepted that major changes in Earth’s climate started in Gelasian (~2.6 million years ago), and initiated the growth of ice sheets in the Northern Hemisphere (e.g., [1])
In an example from the SW Barents Sea we show that flexural stresses related to the isostatic uplift after Last Glacial Maximum (LGM) deglaciation can produce stress changes large enough to result in increased fracture-related permeability in the sedimentary basin, and lead to potential spillage of hydrocarbons out of potential reservoirs
Assessment of the flexural stresses induced by the lithospheric flexure related to glacial isostasy and tilt, and their effect on faults during glaciations and interglacials, here illustrated by an example from the SW Barents Sea where the stress modelling is limited to the flexural stress effects of deglaciation after LGM
Summary
It is commonly accepted that major changes in Earth’s climate started in Gelasian (~2.6 million years ago), and initiated the growth of ice sheets in the Northern Hemisphere (e.g., [1]). Differential vertical movement of the lithosphere related to glacial isostasy lead to repeated tilting of sedimentary formations and potential petroleum reservoirs therein, which may have greatly affected hydrocarbon migration pathways in the former glaciated areas [5]. Stress changes induced by glaciations are related to two main effects: 1) direct load introduced by the weight of the ice on the surface and 2) flexural load caused by the subsidence and uplift of the lithosphere due to glacial isostasy [10,28]. Assessment of the flexural stresses induced by the lithospheric flexure related to glacial isostasy and tilt, and their effect on faults during glaciations and interglacials, here illustrated by an example from the SW Barents Sea where the stress modelling is limited to the flexural stress effects of deglaciation after LGM. The stress effects of vertical ice load and related stress migration are not calculated here
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