Valley Incision in a Tectonically Active Basin, Onshore West Greenland
Gregers Dam, Lotte M. Larsen, Martin Sonderholm, and Asger
In latest Maastrichtian - Early Paleocene time the Nuussuaq Basin, onshore West Greenland was subjected to two, possibly three extensional tectonic episodes, each followed by uplift. Fault displacements of several hundred meters have been recorded from each of these episodes, resulting in a pronounced structural relief. The uplift periods were associated with a sudden fall in base-level and incision of two major valley systems on the south-coast of Nuussuaq. Most of the paleovalleys are associated with and are cross-cutting the faults, suggesting that the faults were governing not only the establishment but also the trend of the valleys. All the valleys were filled in response to rising base levels, and thus belong to the transgressive systems tract. Filling of the uppermst valley system was characterized by a balance between a rapidly rising base-level, high river discharge and high sedimentation rates. This led to extremely uniform facies successions of the valley fills which constitute the Quikavsak Member. The sea-level rise during this transgressional phase was in the order of 800 m. It was followed by the extrusion of voluminous volcanic rocks which formed thick hyaloclastite deposits in a marine basin. The dramatic sea-level rise and the formation of the volcanic rocks probably had a common cause in a major extensional episode leading to crustal thinning and sagging, and to mantle upwelling with ensuing decompression melting. The extension was related to the onset of sea-floor spreading in the Labrador Sea - Baffin Bay region.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California