The Lillehammer Submarine Fan Complex

Abstract

Abstract

The Lillehammer Submarine Fan Complex is a mixed mud/sand rich turbidite fan system. The fan complex was deposited in the Neoproterozoic Hedmark rift basin from west towards east extending at least 50 km from the basin margin.

A detailed sedimentary study of outcrops in the Lillehammer area is performed with the aim of analyzing the depositional environment as an analogue for subsurface turbidite systems. Seven sedimentary logs cover a nearly 1000 meter thick stratigraphic section. Seven facies have been organized into seven facies associations, representing architectural elements including basin plain-thin bedded turbidites, basin plain-hemipelagic shale, lobe, lobe-channel, basin floor channel infill, major channel and channel-levee. The Lillehammer Submarine Fan Complex represents two or three fan systems, separated by hemipelagic black shale or thick unit of homogenous shale that may indicate rise in relative sea level. The overall system is progradational and represents an outer and middle to inner fan environment. The main factors controlling the development of the Lillehammer Submarine Fan Complex are thought to be tectonic activity at the basin margin and sediment influx. Comparison of the Lillehammer Submarine Fan Complex with the Upper Cretaceous fans in the Vøring Basin reveals a good geometrical resemblance despite large differences in sandstone petrography and clay matrix content. The petrographic more impure and clay-rich sandstones of the Lillehammer Submarine Fan Complex, as compared with those in the Vøring Basin, is interpreted to be related to differences in provenance and basin structure.

Synthetic seismograms were performed for a 400 meter thick logged section to discuss the differences in seismic resolution under 1500 meter of overload and 3500 meter of overload. Only half of the seismic events are shown in the deepest model compared to the shallow model. Reflections associated with most interfaces are recognizable, but difficult to distinguish from each other. The shallow model reveals good seismic resolution of two fans separated by a thick layer of homogenous shale. The same model under a thicker overload does not have the same obvious trends, but is recognizable when you know what to expect.