Rieko Adriaens

Clay mineralogical constraints on weathering in response to early Eocene hyperthermal events in the Bighorn Basin, Wyoming (Western Interior, USA)

Series of transient greenhouse warming intervals in the early Eocene provide an opportunity to study the response of rock weathering and erosion to changes in temperature and precipitation. During greenhouse warming, chemical weathering is thought to increase the uptake of carbon from the atmosphere, while physical weathering and erosion control sediment supply. A large ancient greenhouse warming event is the Paleocene-Eocene Thermal Maximum at 56 Ma. In many coastal sites, an increase in the abundance of kaolinite clay during the Paleocene-Eocene Thermal Maximum is interpreted as the result of reworking from terrestrial strata due to enhanced runoff caused by increased seasonal precipitation and storminess during a time of decreased vegetation cover. In the continental interior of North America, Paleocene-Eocene Thermal Maximum paleosols show more intense pedogenesis and drying, which are indicated by deeply weathered and strongly oxidized soil profiles. The weathering and oxidation could be related to temperature and precipitation changes, but also to increased time available for weathering and increased soil permeability in coarser sediment. Here, we provide evidence for enhanced climate seasonality, increased erosion of proximal laterites and intrabasinal floodplain soils, and a potential slight increase in chemical weathering during the smaller early Eocene hyperthermals (Eocene Thermal Maximum 2, including H1 and H2) postdating the Paleocene-Eocene Thermal Maximum, for which no previous clay mineral data were available. Hyperthermal soil formation at the site of floodplain deposition causes a similar, insignificant clay mineralogical change as occurred during the background climates of the early Eocene by showing small increases in smectite and decreases in illite-smectite and illite. Remarkably, the detrital sediments during the hyperthermals show a similar pedogenic-like increase of smectite and decreases of mixed-layer illite-smectite and illite, while the kaolinite and chlorite proportions remained low and unchanged. Since sedimentation rates and provenance were similar during the events, enhanced smectite neoformation during soil formation in more proximal settings, and associated reworking, is the likely process causing this clay mineralogical change. The hundreds to thousands of year time scales at which individual paleosols were formed were probably too short for significant alteration of the rocks by in situ chemical weathering despite changing climates during the two post−Paleocene-Eocene Thermal Maximum greenhouse warming episodes. The relatively small signal, however, raises the question of whether increased chemical weathering can indeed be a strong negative feedback mechanism to enhanced greenhouse gas warming over the time scales at which these processes act.

Natural clay-sized glauconite in the Neogene deposits of the Campine Basin (Belgium)

Natural clay-sized glauconite has the same mineralogical composition as sand-sized glauconite pellets but occurs in <2 μm clay fractions. This particular glauconite habit has been described previously from soil environments resulting from pelletal weathering but is rarely reported in higher-energy sedimentary environments. In the present study, clay-sized glauconite was identified as a common constituent in transgressive Neogene glauconite pellet-rich deposits of the southern North Sea in Belgium. X-ray diffraction results revealed that the characteristics of the clay-sized glauconite are very similar to the associated glauconite pellets in sand deposits. Both glauconite types consisted of two glauconite-smectite R1 phases with generally small percentages of expandable layers (<30%) with d060 values ranging between 1.513 Å and 1.519 Å. Clay-sized glauconite was not neoformed but formed by the disintegration of sand-sized glauconite pellets which were abraded or broken up during short-distance transport within the sedimentary basin or over the hinterland. Even in an environment where authigenic glauconite pellets occur, minimal transport over transgressive surfaces is sufficient to produce clay-sized glauconite. Furthermore, clay-sized glauconite can be eroded from marine deposits and subsequently resedimented in estuarine deposits. Clay-sized glauconite is, therefore, a proxy for the transport intensity of pelletal glauconite in energetic depositional environments and, moreover, indicates reworking in such deposits which lack pelletal glauconite.

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

Better Understanding Shales by Accurate Qualitative and Quantitative Mineralogy

A thorough characterization of the mineralogy and detailed clay mineralogy is an important tool in scientific research and industrial applications of shales. It helps to understand the geological history of the deposits and significantly contributes to solving specific geological problems. In three separate examples, it is demonstrated how the clay mineralogy of fine-grained deposits during different stages of diagenesis is characterized in detail. In a first example, clay minerals are used as provenance indicators in recent muds of the Belgian North Sea. A second example handles on the detailed clay mineralogy of early diagenetic Ypresian clays which are currently being researched as possible host rock for radioactive waste disposal. A third example involves the mineralogical characterization of a later diagenetic potential shale gas play in Belgium.