[1] Spatial patterns of soil often do not reflect those of topographic controls. We attempted to identify possible causes of this by comparing observed and simulated soil horizon depths. Observed depths of E, Bt, BC, C1, and C2 horizons in loess-derived soils in Belgium showed a weak to absent relation to terrain attributes in a sloping area. We applied the soil genesis model SoilGen2.16 onto 108 1 × 1 m2 locations in a 1329 ha area to find possible causes. Two scenarios were simulated. Model 1 simulated soil development under undisturbed conditions, taking slope, aspect, and loess thickness as the only sources of variations. Model 2 additionally included a stochastic submodel to generate tree-uprooting events based on the exposure of trees to the wind. Outputs of both models were converted to depths of transitions between horizons, using an algorithm calibrated to horizon depths observed in the field. Model 1 showed strong correlations between terrain attributes and depths for all horizons, although surprisingly, regression kriging was not able to model all variations. Model 2 showed a weak to absent correlation for the upper horizons but still a strong correlation for the deeper horizons BC, C1, and C2. For the upper horizons the spatial variation strongly resembled that of the measurements. This is a strong indication that bioturbation in the course of soil formation due to treefalls influences spatial patterns of horizon depths.
The glauconitic sands in the upper part of the lower‐middle Miocene Berchem Formation are subdivided into the Kiel and Antwerpen Members. Although lithological differences between both members are well known from temporary outcrops in the Antwerp city area, they are difficult to distinguish in boreholes, which hinders regional mapping of these units. In this study, we investigate whether both members can be distinguished on cone penetration tests (CPTs). For this purpose, we correlated multiple outcrops—in which the Kiel and/or Antwerpen Members have been identified—with nearby CPTs. On the CPTs, the boundary between the Kiel and Antwerpen Members is clearly identifiable as it coincides with an abrupt upwards decrease in cone resistance ( q c ). The lower q c of the basal part of the Antwerpen Member is probably related to the finer grain size with more clayey admixture compared to the underlying Kiel Member. This change to a finer grain size is caused by a decrease in depositional energy and sedimentation rates as the region was transgressed during the eustatic sea‐level rise at the start of the Mid‐Miocene Climatic Optimum. On the CPTs, several spikes in q c values were observed within the Antwerpen and Kiel Members. These spikes could be correlated to shell beds, three horizons with sandstones and possibly a hardground. The sandstones appear to be discontinuous, whereas some of the shell beds could be traced across the entire study area. Most shell beds probably represent storm deposits within an otherwise relatively low energetic sedimentary environment. A phosphatic shell bed above the base of the Antwerpen Member is interpreted as the maximum flooding surface, lying in a zone with the lowest q c values for the Antwerpen Member, which might reflect maximum fining. The shell beds and interlayered sands of the Antwerpen Member thin in a southern direction, indicating reduced accommodation space in this direction.
Recently published multidisciplinary studies discussed the glauconiferous sand units of the Berchem and Diest formations in large temporary outcrops near the Antwerp International Airport, east of the City of Antwerp, northern Belgium. At this location, the upper Miocene Diest Formation was subdivided into an upper Deurne Member and a lower, recently introduced, Borsbeek Member. In the current study, Cone Penetration Tests performed near the outcrops were used to geotechnically characterize the exposed units for regional correlations. For the Kiel and Antwerpen members of the middle Miocene Berchem Formation, the geotechnical expressions are nearly identical to those recently described further west in the City of Antwerp area. Contrary to the latter area, however, the upper part of the Antwerpen Member is missing, due to erosion below the Borsbeek Member. This erosion reached up to the level of a regionally occurring, compact shell bed in the middle of the Antwerpen Member, which may have protected the underlying sand from further erosion. Throughout the study area, the Borsbeek and Deurne members each show a consistent geotechnical facies, allowing for them to be distinguished on electric CPTs and thus for more reliable predictions of their areas of occurrence.
A temporary outcrop near the “Rubenshuis” in the centre of Antwerp (northern Belgium) facilitated the study of the Neogene glauconitic sand of the Berchem and Kattendijk formations, west and south of their respective stratotype sections. In contrast to the latter sections, the exposed Kiel Member of the Berchem Formation contains a relatively silty interval in its upper part, which is also reflected in Cone Penetration Tests. This silty interval is rich in molluscs, including the subspecies Glossus lunulatus cf. lunulatus and Ennucula haesendoncki haesendoncki, previously unknown from this member. Dinoflagellate cysts indicate that the main body of the Kiel Member was deposited during the middle Burdigalian, while only the upper part was deposited during the late Burdigalian. The Kiel Member is covered by the shell-rich, silty sand of the Langhian Antwerpen Member (Berchem Formation). Both members display soft-sediment deformation structures, probably caused by differences in silt content between and within these units. The Antwerpen Member is incised by the Lower Pliocene Kattendijk Formation, which reduced the thickness of the former to only 1.1 m, compared to 7 m in northeastern Antwerp. As a result, the basal gravel of the Kattendijk Formation contains many fossils reworked from the Antwerpen Member, in addition to autochthonous molluscs and Ditrupa. The Zanclean fauna resembles associations known from the highest part of the Kattendijk Formation in the former Oosterweel outcrop north of Antwerp, while it differs from the fauna of the lowermost Kattendijk Formation near Doel and Kallo. Hence, the palaeontological observations corroborate the regional depositional model of this unit, suggesting that only the youngest gully sequence of the Kattendijk Formation was deposited across the city of Antwerp.
The combined use of newly interpreted well data and reprocessed 2D seismic data provides new insights in the Early to Middle Paleocene tectonic evolution of the south-eastern part of the Campine Basin. A late Danian fundamental change in the intra-plate stress-field of Europe changed the deformation style in several southern North Sea basins, including the Campine Basin and neighboring Roer Valley Graben. In the south-eastern part of the Campine Basin, this stress change ended an early to middle Danian tectonic quiet phase with calcarenite deposition and started a late Danian to middle Selandian phase of differential subsidence and restricted deposition of continental to shallow marine siliciclastics. Onlap patterns and associated thickness variations in the siliciclastics indicate that the south-eastern part of the Campine Basin experienced flexural subsidence in the direction of the downthrown Roer Valley Graben. Simultaneously, in the footwall to the Roer Valley Graben border fault system, the Bree Uplift was deformed by subtle (re)activation of faults, possibly in strike-slip mode. After the middle Selandian, former dynamics diminished throughout the region.
Abstract The late Maastrichtian to Late Paleocene seismostratigraphic record of the Roer Valley Graben provides new data on the timing and dynamics of stress changes related to the intra-plate deformation of northwestern Europe. During the deposition of late Maastrichtian to middle Danian limestones, no severe tectonic movements occurred in the southern part of the Roer Valley Graben. Around the late Danian, a known fundamental change in the European intra-plate stress field initiated an increase in subsidence of the southern part of the Roer Valley Graben. Subsidence along the graben border zone enabled relatively thick accumulations of the latest Danian to mid-Selandian siliciclastics in the intra-graben zone. Subsidence was not bounded by large offsets along faults, but rather by flexuring within and along the borders of the Roer Valley Graben. The intensity of these dynamics diminished after the middle Selandian. Most likely due to inherited intra-basinal structural differences, the northern and southern part of the Roer Valley Graben experienced distinctly different late Maastrichtian to Late Paleocene tectonics.
Correlations between bio‐ and/or lithostratigraphically analysed boreholes provide new insights on the late‐early to early‐late Miocene depositional evolution of the central Roer Valley Rift System (RVRS) as part of the southern North Sea Basin. This evolution started with a major regression that occurred in two steps, one during the late Burdigalian and another during the earliest Langhian. Each step coincides with a coarsening of the grain size, reduction in the content of glauconite and increase in the lignite content. The amount of open marine dinocysts also showed a strong decrease. Regression continued up to the middle Langhian as a large delta system builded out in the central RVRS. The main phase of regression ended in the late Langhian. Around the Langhian/Serravallian boundary, a major marine ingression drowned the former delta system. Transgression was evidenced by an increase in the content of glauconite and open marine dinocysts and a decrease in the lignite content. Maximum flooding occurred in the middle/late Serravallian and was followed by another regression. This regression ended in a regional latest Serravallian‐earliest Tortonian hiatus with locally deep erosion. During the early Tortonian, the whole region was transgressed again which was expressed by an increase in the content of glauconite and open marine dinocysts and decrease in the lignite content in the central RVRS. The late‐early to early‐late Miocene depositional evolution of the southern North Sea Basin corresponds very well with that previously described for the eastern and central (Danish) part of the North Sea Basin, but not with the global sea‐level curves, which show mainly the opposite trends. These mismatches could be explained by tectonics and/or changes in sedimentation rates.
