Long-Wavelength Compressive Related Deformation Causes Large Relative Sea Levels Shift Along the Inner Mid Norwegian Passive Margin

Abstract

Massive compressive stress formed regionally distributed inversion domes along the North Atlantic margins during mid and late Miocene. The stress was reduced during the Miocene-Pliocene boundary. Here we study long wavelength tectonic response of compressive stress-release along the inner Mid Norwegian margin on seismic data. The aim of the study is to quantify the relative sea level rise along an inner passive margin upon release of massive compressive stress. The positions of late Cenozoic coasts, related relative sea level changes and tectonic events are still poorly understood along large parts of the North Atlantic margin due to severe glacial erosion and inconclusive biostratigraphic ages. Here we show the first 3D seismic images of a transgressive coastal delta (lower Molo Formation) that constrains the late Cenozoic evolution. Regional 2D seismic sections and a 990 km2 3D survey are used to investigate parts of the up to 60 km-wide and 600 km long coast-parallel Molo Formation. We propose a further subdivision of the Molo Formation into a lower and an upper unit. The up to 120 ms thick lower unit we interpret as a coastal delta characterized by a sand-rich parasequence that exhibits a progradational motif during a regional transgression of the margin. It records a short still stand during a rapid 400 m+ rise in relative sea level. It deposited during the Miocene to Pliocene transition and coincides with the termination of both the North Atlantic Miocene compressive stress period and the global Miocene tectonic event. The upper Molo Formation, which corresponds to the previously described Molo Formation, a fluvial-dominated, wave-influenced progradational delta, deposited after additional 300 m of relative sea level rise. A 2D seismic section, possibly located near the mouth of a paleo river, shows delta trajectories from the first 100 m of this 300m relative sea level rise. We reconstruct the geological evolution and assign a Pliocene age to the Molo Formation, postdating the Kai Formation and predating the Naust Formation.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017