High to Low Frequency Baselevel Fluctuations, Resulting Primarily from Climate Change, Develop Grossly Different Architectures in the Fluvial Statfjord Formation, Northern North Sea

M. Dalrymple, D. J. Prosser, B. P. J. Williams

Sequence stratigraphic models developed thus far typically lack a comprehensive understanding of the relative roles that allocyclic controls, namely climate, tectonism and eustasy, play in the development of upstream, coastline distal, fluvial systems. In the lower Statfjord Formation sediments resulting from a 12 Ma. depositional period developed as a result of high frequency baselevel fluctuations whereas an essentially low frequency baselevel drop resulted in deposition of the upper Statfjord Formation. The two different scales of baselevel fluctuation developed distinct stratal architectures, an understanding of which are of paramount importance in the production of hydrocarbons.

The Cormorant/Lunde Formations underlying the Statfjord Formation are interpreted to have been deposited in semi-arid intra-continental areas, possibly as terminal fluvial systems. As the Laurasian/Gondwanan plate system moved northwards the area of Statfjord Formation deposition evolved into a more humid environment. The much neglected climatic allocyclic mechanism for baselevel change is proposed to be the main control on the variation in architecture through the Statfjord Formation. Subsequent marine transgression results in deposition of the Nansen and Dunlin Formations. The relative roles of tectonism and climate, in developing fluvial sequences, decrease downstream as the role of relative sea level increases. This is reflected in the preservation styles of the finer grained sedi ent types, as well as changes in bedform and channel morphologies.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995