Mesozoic-Cenozoic exhumation events in the eastern North Sea Basin: a multi-disciplinary study based on palaeothermal, palaeoburial, stratigraphic and seismic data

摘要

Four Mesozoic-Cenozoic palaeothermal episodes related to deeper burial and subsequent exhumation and one reflecting climate change during the Eocene have been identified in a study of new apatite fission-track analysis (AFTA((R))) and vitrinite reflectance data in eight Danish wells. The study combined thermal-history reconstruction with exhumation studies based on palaeoburial data (sonic velocities) and stratigraphic and seismic data. Mid-Jurassic exhumation (ca. 175 Ma) was caused by regional doming of the North Sea area, broadly contemporaneous with deep exhumation in Scandinavia. A palaeogeothermal gradient of 45 degrees C km(-1) at that time may be related to a mantle plume rising before rifting in the North Sea. Mid-Cretaceous exhumation affecting the Sorgenfrei-Tornquist Zone is probably related to late Albian tectonic movements (ca. 100 Ma). The Sole Pit axis in the southern North Sea experienced similar inversion and this suggests a plate-scale response along crustal weakness zones across NW Europe. Mid-Cenozoic exhumation affected the eastern North Sea Basin and the onset of this event correlates with a latest Oligocene unconformity (ca. 24 Ma), which indicates a major Scandinavian uplift phase. The deeper burial that caused the late Oligocene thermal event recognized in the AFTA data reflect progradation of lower Oligocene wedges derived from the uplifting Scandinavian landmass. The onset of Scandinavian uplift is represented by an earliest Oligocene unconformity (ca. 33 Ma). Late Neogene exhumation affected the eastern (and western) North Sea Basin including Scandinavia. The sedimentation pattern in the central North Sea Basin shows that this phase began in the early Pliocene (ca. 4 Ma), in good agreement with the AFTA data. These three phases of Cenozoic uplift of Scandinavia also affected the NE Atlantic margin, whereas an intra-Miocene unconformity (ca. 15 Ma) on the NE Atlantic margin reflects tectonic movements of only minor amplitude in that area. The study demonstrates that only by considering episodic exhumation as an inherent aspect of the sedimentary record can the tectonic evolution be accurately reconstructed.