Late Cenozoic submarine slope failures in the southern North Sea - Evolution and controlling factors

During the Late Miocene to early Pleistocene sedimentation in the southern North Sea Basin was dominated by a westward prograding depositional system. Progradation is evidenced by a series of large-scale, westward dipping clinoforms with amplitudes of up to 400 m. The clinoforms are related to a shelf-slope-basin physiography during deposition and their development and growth reflects the basinward migration of the Late Cenozoic shelf margin through time. Numerous submarine slope failures occurred on the shelf margin during this time, recognized as kilometer-scale mass-transport deposits (MTDs). Comparatively little is known about the earliest slope failures on this prograding shelf margin, yet their role is important in developing a coherent understanding of the origins of the instability of the margin as a whole. In this study we present detailed analyses of the first MTDs occurring on this Late Cenozoic shelf margin. Based on interpretation of 2D seismic reflection profiles, borehole data and integration of new chronostratigraphic datings the development and causes of slope instabilities are reconstructed. Three MTDs are distinguished within the German part of the southern North Sea, one (MTD1) that has been displaced in the Late Tortonian and two (MTD 2/3) in the Piacenzian. MTD 1 was triggered by salt-induced seismicity, as evident from salt-related faulting of the Late Cenozoic succession in its headwall domain. Pore pressure build up due to fluid migration from deeper levels in combination with loading imposed to the basin by the prograding shelf prism are the main factors controlling the initiation of MTDs 2 and 3.Subsequent slope failures occurring during shelf progradation within the Dutch North Sea are much more frequent compared to the earliest slope failures. The development from a relatively stable shelf margin towards a margin affected by repeated slope failures coincides approximately with the intensification of Northern Hemisphere Glaciations during Pleistocene times. The development and deposition of the MTDs in the Dutch North Sea is clearly linked to climate-driven environmental changes, whereas prior to the Pleistocene failure mechanisms are preferably limited to those independent of glaciations and associated sea level changes and therefore fewer failures have occurred

Late Cenozoic submarine slope failures in the southern North Sea - Evolution and controlling factors

During the Late Miocene to early Pleistocene sedimentation in the southern North Sea Basin was dominated by a westward prograding depositional system. Progradation is evidenced by a series of large-scale, westward dipping clinoforms with amplitudes of up to 400 m. The clinoforms are related to a shelf-slope-basin physiography during deposition and their development and growth reflects the basinward migration of the Late Cenozoic shelf margin through time. Numerous submarine slope failures occurred on the shelf margin during this time, recognized as kilometer-scale mass-transport deposits (MTDs). Comparatively little is known about the earliest slope failures on this prograding shelf margin, yet their role is important in developing a coherent understanding of the origins of the instability of the margin as a whole. In this study we present detailed analyses of the first MTDs occurring on this Late Cenozoic shelf margin. Based on interpretation of 2D seismic reflection profiles, borehole data and integration of new chronostratigraphic datings the development and causes of slope instabilities are reconstructed. Three MTDs are distinguished within the German part of the southern North Sea, one (MTD1) that has been displaced in the Late Tortonian and two (MTD 2/3) in the Piacenzian. MTD 1 was triggered by salt-induced seismicity, as evident from salt-related faulting of the Late Cenozoic succession in its headwall domain. Pore pressure build up due to fluid migration from deeper levels in combination with loading imposed to the basin by the prograding shelf prism are the main factors controlling the initiation of MTDs 2 and 3.Subsequent slope failures occurring during shelf progradation within the Dutch North Sea are much more frequent compared to the earliest slope failures. The development from a relatively stable shelf margin towards a margin affected by repeated slope failures coincides approximately with the intensification of Northern Hemisphere Glaciations during Pleistocene times. The development and deposition of the MTDs in the Dutch North Sea is clearly linked to climate-driven environmental changes, whereas prior to the Pleistocene failure mechanisms are preferably limited to those independent of glaciations and associated sea level changes and therefore fewer failures have occurred

Using high‐resolution XRF analyses as a sequence stratigraphic tool in a mudstone‐dominated succession (Early Cretaceous, Lower Saxony Basin, Northern Germany)

Delineation of stratigraphic sequences and their component systems tracts in mudstone‐dominated successions is challenging due to the relatively homogenous, fine‐grained nature of the strata. High‐resolution elemental intensity data from X‐ray fluorescence core scanning is used in order to develop a sequence stratigraphic framework for the Lower Cretaceous monotonous mudstone succession in the eastern Lower Saxony Basin. The study is based on four drill cores covering the Berriasian to Aptian interval. In addition, carbon isotope (δ13Corg), grain size and CaCO3 analyses were carried out on discrete samples. The studied cores represent both proximal and distal basinal environments of the eastern Lower Saxony Basin and can be reliably correlated by utilizing variations in selected X‐ray flourescence elemental ratios, K/Ti data have proven to be particularly suitable in this regard. The core correlation shows that chemostratigraphic variability within the studied succession is laterally reproducible in the eastern Lower Saxony Basin, and can be used to establish a sequence stratigraphic framework. Further, Si/Al and Ca/Ti ratios have been applied to characterize the cores in terms of variation in grain size and CaCO3 content, respectively. Vertical grading trends inferred from Si/Al changes were used to identify transgressive and regressive systems tracts within the studied succession. An important regression in the uppermost lower Valanginian coincides with the onset of the Valanginian Weissert Event, as indicated by the well‐known positive δ13C shift, and, thus, supports the idea that the initial interval of this event corresponds to enhanced supply of terrigenous material. The results of this study are also in agreement with previously recognized transgressive–regressive trends in the Lower Saxony Basin and adjacent areas. This clearly shows that systematic geochemical variations recorded in mudstone‐dominated basinal settings are suitable to establish sequence stratigraphic frameworks

Jurassic to Lower Cretaceous tectonostratigraphy of the German Central Graben, southern North Sea

The Central Graben is a Mesozoic sedimentary basin that is significantly influenced by rift and salt tectonics. Its southern part is located in the German and Dutch sectors of the North Sea. Even though studies exist on the tectonic and stratigraphic development of the Danish and Dutch Central Graben, the German Central Graben as an important link is less investigated. We aim to fill this gap and to investigate the sedimentary development from the Latest Triassic to the Early Cretaceous, the relative influence of salt and rift tectonics on subsidence and how our results fit into the existing studies of the Danish and Dutch Central Graben. Knowledge of the development of the graben and its sedimentation is critical for any possible economic use like hydrocarbon exploitation or carbon capture and storage. Therefore, we mapped nine laterally traceable horizons on 2D and 3D reflection seismic data from the Lower Jurassic to the Lower Cretaceous within the German Central Graben and adjacent Danish Salt Dome Province as well as the northern Dutch Central Graben. These horizons include the base horizons of four tectonostratigraphic mega-sequences of the southern Central Graben adopted from the current Dutch tectonostratigraphic concept. Based on the mapping results, we constructed subsidence, thickness and erosion maps of the tectonostratigraphic mega-sequences and their subdivisions. The tectonostratigraphic mega-sequences were then correlated with well logs to determine the lithology. The results show that the structural and stratigraphic architecture of the German Central Graben was consecutively dominated by either subsidence controlled by rifting, salt tectonics or by thermal uplift and subsidence. We suggest that the German Central Graben is divided by a large strike-slip fault zone, the Mid Central Graben Transverse Zone, into a northern part that geologically rather belongs to the Danish and a southern part that rather belongs to the Dutch Central Graben. We discuss how this division and the tectonics influenced the regional lithology

X-ray fluorescence data obtained from sediment core Frielingen 9 (1 cm resolution)

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