Delineation of stratigraphic sequences and their component systems tracts in mud-stone-dominated successions is challenging due to the relatively homogenous, finegrained 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 (δ 13 C org ), grain size and CaCO 3 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 CaCO 3 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 δ 13 C 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. K E Y W O R D SLower Cretaceous, Lower Saxony Basin, mudstones, sequence stratigraphy, Weissert Event, X-ray fluorescence core scanning | 237 THÖLE ET aL.
Goethite (α-FeOOH) is one of the most abundant minerals on the Earth surface, occurring in temperate, tropical and equatorial climates. Fe in goethite can be substituted by many cations such as Al, Ni for instance. A large amount of research has been conducted on the effect of varying elemental compositions (mainly Al-content) on the spectral features of goethites with most of the studies based on materials synthesized with different elemental ratios. The different elemental ratios, however, may not only affect the composition of the products but also their crystallinity and/or particle size and shape. Both parameters are known to affect results of both X-ray diffraction (XRD) and infrared spectroscopy (IR). These methods are predominantely used to characterize goethites. In the present study, therefore, a significant set of natural goethites was considered in order to investigate the effect of elemental composition on XRD and IR results. The focus was on crystallised samples which had a limited chemical variability but artefacts caused by the presence of admixtures could be excluded in most cases. First of all Rietveld refinement was optimized based on varying different parameters. A fairly good correlation of Rietveld derived crystallite sizes and specific surface area determined by N2-adsorption (SSA) was found which proves the importance of considering the crystallite size parameters for Rietveld refinement and at the same times proves the quality of it. Using IR spectroscopy yet published relations of band position and Al-content could be confirmed despite the fact that the range of Al-contents was small. However, the band position of the Fe–O stretching, previously used as proxy for crystallinity assessment, was found to be least variable hence contradicting yet published results. Controversial results were also published for the effect of the Al-content on the position of the asymmetric FeOH stretching band at 450 cm−1. The goethites investigated in the present study indicate that the crystallite size determines the band position rather than the Al-content which is at least valid for the limited range of Al-contents. The results of the present study indicate that using synthetic sample sets bears the problem that more than one parameter might show systematic differences (e.g. crystallite size in a set of chemically varied goethites). The paper, therefore, provides IR reference data based on a set of natural well crystallised goethites.
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