Abstract: Sedimentological Evolution of an Incised Valley System, Lower Paleocene Quikavsak Member, Nuussuaq, West Greenland

Gregers Dam, Martin Sonderholm

An extensive Early Paleocene incised valley system is exposed on the south coast of Nuussuaq, West Greenland. The valley system includes six time-synchronous valleys that are 1-2 km wide and up to 160 m deep. The valleys were incised during a major relative sea level fall and were cut into Cretaceous and earliest Paleocene deltaic and shelf sandstones, mudstones and paraconglomerates. The sedimentary valley fill represents a transgressive systems tract starting with a uniform unit of fluvial sandstones without any sequential repetition of facies. This was probably due to a delicate balance between relative sea level rise, river discharge and sedimentation, and probably bears witness of a very rapid rise in relative sea level. In valleys where the relative sea level rise was so rapid t at the increased accommodation space was greater than the supply of fluvial sediment, the fluvial valleys became the site of estuaries. A mudstone separating the fluvial and estuarine units was probably deposited in the underlying mid-estuary funnel between the fluvial and estuary-mouth sands. The sharp boundary between the estuary-mouth sands and the mid-estuary funnel mudstone probably formed as the ebb-tidal delta migrated back into the estuary, and hence it reflects a transgressive erosional surface. The fluvial and estuarine valley-fill sandstones and funnel mudstone are succeeded abruptly by shelf mudstones, indicating that the final stage of valley filling was coincident with a major landward shift in facies.

The Upper Cretaceous to lowest Paleocene sediments below the Quikavsak Member include shelf and valley-fill and provide evidence of a period of faulting prior to incision of the Quikavsak Member valleys. The relative role of eustacy versus tectonics on valley incision in this area can thus be discussed.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994