Michiel Dusar

Palynostratigraphy of the Tournaisian (Hastarian) rocks in the Namur Synclinorium, West Flanders, Belgium

Abstract The first detailed palynostratigraphy of the Hastarian in Belgium is described. The Hastarian is the lower subdivision of the Belgian Tournaisian and spans the Tn1b and Tn2 lithostratigraphical units. A succession of well to moderately well preserved miospore assemblages has been obtained from this stratigraphical interval in five boreholes located in the western part of the Namur Synclinorium, where the Hastarian succession is represented by a mixed sequence of marine clastic and carbonate rocks. These miospore assemblages are assigned to four biozones (VI, HD, BP, and PC) of the miospore zonation scheme established for the Tournaisian rocks of southern Ireland. Detailed sampling in the lower part of the Hastarian succession in the Namur boreholes has allowed a finer resolution of the Kraeselisporites hibernicus—Umbonatisporites distintus (HD) Miospore Biozone, based on the successive first appearances of the two zonal species. Correlation of the miospore biozones with conodont faunas obtained from the same boreholes indicates that the HD Miospore Biozone equates with the Siphonodella sandbergi and lower S. crenulata Conodont Zones, the BP Miospore Biozone spans the boundary between the lower and upper S. crenulata Conodont Zones, and the base of the PC Miospore Biozone occurs within the upper S. crenulata Conodont Zone.

Diagenetic control on secondary porosity in flood plain deposits: an example of the Lower Triassic of northeastern Belgium

Abstract The Lower Triassic sandstones of northeastern Belgium were deposited in channels and by sheet floods. Introduction of clays, formation of iron oxides and alteration of feldspars in these sediments occurred at near-surface conditions. Subsequent calcite precipitation and the replacement of feldspars and quartz occurred at low temperatures (21°–26°C) in meteoric waters with a δ 18 O ≈ − 5.8‰ SMOW. Characteristic is the bleaching of the originally red-coloured sediments. Red coloration was caused by iron oxide pigments in clay coatings around quartz grains. The bleaching is the result of the reduction of these iron oxides, most likely by organic acids. The oxidation-reduction reaction produced carbon dioxide and protons, which altered the feldspars. The underlying Upper Carboniferous strata are a potential source for organic acids released by thermocatalytic degradation of its kerogen. The bleaching took place before a period of important authigenic quartz growth, which occurred after compaction. Feldspars, quartz and calcites have been replaced by dolomite and ankerite. These carbonates could have formed from meteoric waters at relatively low temperatures (e.g. 50°C) as well as from brines at higher temperatures (e.g. 120°C). Following dolomite/ankerite cementation, an intensive dissolution of feldspar took place. The secondary pores have been filled with kaolinite, barite and illite. Primary and secondary porosity is now significantly lower in clay-rich sandstones than in pure sandstones. Early diagenetic replacive calcites have a negative effect on late diagenetic porosity creation. Feldspar grains, which have been replaced by calcites were either slightly or not affected by late diagenetic dissolution.

Overview of the influence of syn-sedimentary tectonics and palaeo-fluvial systems on coal seam and sand body characteristics in the Westphalian C strata, Campine Basin, Belgium

Abstract The Westphalian C strata found in the northeastern part of the former Belgian coal district (Campine Basin), which is part of an extensive northwest European paralic coal basin, are considered. The thickness and lateral continuity of the Westphalian C coal seams vary considerably stratigraphically and areally. Sedimentological facies analysis of borehole cores indicates that the deposition of Westphalian C coal-bearing strata was controlled by fluvial depositional systems whose architectures were ruled by local subsidence rates. The local subsidence rates may be related to major faults, which were intermittently reactivated during deposition. Lateral changes in coal seam groups are also reflected by marked variations of their seismic signatures. Westphalian C fluvial depositional systems include moderate to low sinuosity braided and anastomosed river systems. Stable tectonic conditions on upthrown, fault-bounded platforms favoured deposition by braided rivers and the associated development of relatively thick, laterally continuous coal seams in raised mires. In contrast, rapidly subsiding downthrown fault blocks favoured aggradation, probably by anastomosed rivers and the development of relatively thin, highly discontinuous coal seams in topogenous mires.

Burial history and thermal evolution of Westphalian coal-bearing strata in the Campine Basin (NE Belgium)

A 1D-modelling program has been applied to reconstruct the burial and thermal histories of two exploration boreholes, KB172 and KB174, located in the Campine Basin. The results show differences in geological histories. The coalification of the Westphalian A and B strata in KB174 (0.66–0.98% Ro) was pre-Permian. Calculated maximum temperatures, based on borehole data and vitrinite reflectance, regional thicknesses and a heat flow of 84 mW/m2 during the Late Westphalian, range from 110 °C at the top to 175 °C at the bottom of the Westphalian cored in this borehole. The high coalification (0.85–1.30% Ro) of the Westphalian C and D strata in KB172 could be the result of the deposition of ∼2500 m of Upper Permian to Middle Jurassic sediments in combination with elevated heat flows (71–80 mW/m2). Two coalification periods, i.e. Late Westphalian and Middle Jurassic, are suggested for this borehole. The simulated maximum temperatures range from 130 °C at the top to 175 °C at the bottom of the investigated Westphalian C and D. The differences in the burial and thermal histories of both boreholes can be related to the activity of the transversal Donderslag Fault, a major structural element in the Campine coalfield, and the Roer Valley Graben.

Geomorphosites: Function and Geoheritage Preservation in Belgium

This chapter opens with stressing the need for geomorphosite recognition, and situating the concept of geomorphosite in the broader context of geosites and the relations between geodiversity and biodiversity. Then, after mentioning the measures taken at the national level, notably with the creation in 1835 of the Royal Commission for Monuments, whose responsibilities were extended to sites in the first half of the twentieth century, it reviews the separate legislative evolution for site protection in Wallonia and Flanders after the competence had been transferred to the regional level in the 1980s. In parallel, the sites with a major geomorphic component listed as protected exceptional heritage in Wallonia are briefly reviewed and other sites so far unlisted but worth of interest are also pointed. A similar list of protected geosites is presented for Flanders, where the situation is however very different. Flat landscapes and densely populated areas make geosites far less spectacular there. The number of protected sites with a geologic or geomorphic component is nevertheless similar in Flanders and Wallonia, in each case about 20. Flanders promotes initiatives taken to arouse public interest for geosites by, e.g. integrating them in hiking or cycling trails. Recently, local groups of mixed lay people and geoscientists are also highly active in attempts to create geoparks, which in some cases gather all conditions required by UNESCO for a nomination as Global Geopark.

Halloysite occurrence at the karstified contact of Oligocene sands and Cretaceous calcarenites in Hinnisdael quarries, Vechmaal (NE of Belgium)

1. Introduction Halloysite is a dioctahedral 1:1 clay mineral of the kaolinite group frequently discussed in literature because of its potential for nanotechnological applications (Keeling, 2015; Yuan et al., 2015; Yuan et al., 2016). Its geological occurrence has been primarily linked to soil and weathering environments, by the weathering and alteration of volcanic rocks (Vaughan et al., 2002; Velde & Meunier, 2008), the alteration of clay minerals like montmorillonite or biotite (Hill, 2000; Papoulis et al., 2009) or weathering of feldspars (Sheets & Tettenhorst, 1997; Adamo et al., 2001). Halloysite is also a common mineral constituent in karst and paleokarst environments as a result of acid weathering (Polyak & Guven, 2000; Joussein et al., 2005). In Belgium, halloysite was reported in over 30 localities, almost all with a very similar geological setting, i.e. karstified carbonate substrates filled up by Cenozoic sand deposits (Buurman & Van der Plas, 1968; Dupuis & Ertus, 1995; Goemaere & Hanson, 1997; Nicaise, 1998; Kloprogge & Frost, 1999; De Putter et al. 2002; Bruyere, 2004). A similar geological setting is found inside the underground quarries of Hinnisdael, locally known as “mergelgrotten” (“marl caves”), located in Vechmaal, Limburg province, Belgium (Fig. 1). In two of the Hinnisdael underground quarries, dolines filled with marine sand were intersected and an irregular white clay layer occurs at the contact between the karstified top of the Cretaceous calcareni