Dynamic topography and evolving drainage patterns on a rift flank: an Arctic analogue of the Nile

Continental break-up is typified by the development of intracontinental rift systems that undergo multiple phases of extension, eventually progressing to seafloor spreading. On the passive margins bordering these oceans, clastic sediments deposited during the pre-drift phase are commonly the most important reservoir units. Locating sediment input points to the former rift, and understanding the tectonic controls on sediment input, are therefore a key concern of the hydrocarbon geologist. However, with the focus on sediment entering the rift, it is easy to overlook one important consequence of rift geometry, namely that most of the sediment eroded from the rift flanks may not enter the rift basin. This pattern of sediment supply arises because a typical intracontinental rift consists of a narrow central graben system flanked by broad regions sloping away from the rift zone. This back-tilting of the rift flanks results from footwall uplift along the graben-bounding faults, which in some cases may be superimposed on longer-wavelength dynamic uplift associated with anomalously hot asthenosphere below the rift. The consequence of this geometry is that river systems draining away from the rift zone have catchment areas commonly an order of magnitude greater than rivers draining directly into the rift. The bulk of the sediment generated by erosion of the rift flanks is therefore likely to end up in a depocentre which may be many 1000s of kilometres from the rift zone. Clearly, these successions can provide important information about the nature and timing of tectonic events that affected the rift system.

The best present-day example of such a drainage system is the Nile: the headwaters drain the flank of the East African rift system, while the lower course flows west of the Red Sea rift at the base of the rift flank. Most of the sediment eroded from the rift flanks is deposited in and around the delta on the margin of the Mediterranean Sea, a depocentre outside the main rift zone. Here we consider the tectonic controls on the evolution of a Mesozoic drainage system analogous in scale and setting to the Nile, which drained the western flanks of the North Atlantic rift system, disgorging northwards into the Sverdrup Basin in Arctic Canada. The delta size and sediment yields suggest a catchment area the size of Greenland. A clear link exists between tectonic events in the Atlantic rift and changes of sediment flux to the delta. Of particular significance is that transient dynamic uplift associated with mantle plumes can be shown to cause major changes to drainage patterns. These plume-driven drainage modifications are genetically linked to important Jurassic and Cretaceous reservoir facies in the North Atlantic region.