Detlev K. Richter

Nature and Nurture: Environmental Isotope Story of the River Rhine

The total dissolved load of the Rhine river increases downstream due to the combined impact of natural and pollution loads. The natural background, controlled by geology, is soon swamped by pollution, particularly from salt and coal mining activities in Alsace and the Ruhr area. The Rhine is also a net source of CO2 from oxidation of excess organic productivity that is fuelled by nutrient pollution, a problem even more serious for some of its tributaries.

LOW LIMIT OF MN2+-ACTIVATED CATHODOLUMINESCENCE OF CALCITE : STATE OF THE ART

In the literature, the lower limit for Mn2+-activated cathodoluminescence (CL) of calcite is variously reputed to over a very wide range of values above 10 ppm Mn. Our spectroscopic investigations of the CL response in natural calcite reveal that below 10 ppm manganese content Mn2+-activation is also present. Using the Quantitative High Resolution Spectral analysis of CL (QHRS-CL) an activation by Mn2+ in the range of 700 ppb is proved, which cannot be determined visually. So, if not quenched, the minimum Mn2+ content for Mn2+-activation is one atom in the irradiated calcite crystal lattice volume. As the intrinsic (background blue) luminescence is used to determine non-altered biogenic calcite, the limit of Mn2+-activation plays an important role in the interpretation of diagenetic processes. Our results of spectroscopic analyses require a revision of current opinions about the diagenesis of calcite as revealed by CL investigation.

Sub-Milankovitch climatic cycles in Holocene stalagmites from Sauerland, Germany

Calcitic stalagmites from caves in the Sauerland, Germany, prove the existence of sub-Milankovitch cycles in precipitation during the last 6000 yr. The δ18O record dated with Th/U is interpreted as an indicator of paleohumidity. Spectral analysis of δ18O from 6000 a BP up to the recent top of a stalagmite from the Atta cave yields statistically significant peaks at 1450, 117, 64 and 57 a. Additionally we find a good correlation of the stalagmite’s δ18O and Δ14C from European tree rings. The 1450 a cycle in the stalagmite probably is analogous to the pervasive millennial scale climate cycle described by Bond et al. [Science 278 (1997) 1257–1266; 294 (2001) 2130–2136] derived from the amount of ice rafted debris in deep sediments from the North Atlantic. Our results suggest that the centennial to millennial shifts observed in the North Atlantic are accompanied by synchronous shifts of the climate in Northern and Central Europe, which most probably can be attributed to solar irradiation variations.

REE-activated cathodoluminescence of calcite and dolomite: high-resolution spectrometric analysis of CL emission (HRS-CL)

Abstract Cathodoluminescence (CL) investigations of Phanerozoic marine limestones, sinter calcites and saddle dolomites of hydrothermal veins indicate that in contrast to previous knowledge rare earth element (REE)-activated CL in sediments is common. The methods of high-resolution spectrometric analysis of CL emission (HRS-CL) combined with ‘hot-cathode’ CL microscopy are able to prove qualitatively some REE below the detection limits of electron microprobe and proton-induced X-ray emission analysis (PIXE). Our investigations document Sm3+, Dy3+, Tb3+ and probably Ho3+-activated CL in calcite and Eu3+-activated CL in a saddle dolomite of hydrothermal veins. Sometimes the REE-activated CL is hidden by dominant Mn 2+ emission. In such cases the REE emission spectrum may be obtained by subtracting a spectrum of luminescence produced only by Mn2+. The occurrence of only one REE in natural samples is uncommon. In all observed samples REE are present in groups.

Bunker Cave stalagmites: an archive for central European Holocene climate variability

Holocene climate was characterised by variability on multi-centennial to multi-decadal time scales. In central Europe, these fluctuations were most pronounced during winter. Here we present a record of past winter climate variability for the last 10.8 ka based on four speleothems from Bunker Cave, western Germany. Due to its central European location, the cave site is particularly well suited to record changes in precipitation and temperature in response to changes in the North Atlantic realm. We present highresolution records of δ18O, δ13C values and Mg/Ca ratios. Changes in the Mg/Ca ratio are attributed to past meteoric precipitation variability. The stable C isotope composition of the speleothems most likely reflects changes in vegetation and precipitation, and variations in the δ18O signal are interpreted as variations in meteoric precipitation and temperature. We found cold and dry periods between 8 and 7 ka, 6.5 and 5.5 ka, 4 and 3 ka as well as between 0.7 and 0.2 ka. The proxy signals in the Bunker Cave stalagmites compare well with other isotope records and, thus, seem representative for central European Holocene climate variability. The prominent 8.2 ka event and the Little Ice Age cold events are both recorded in the Bunker Cave record. However, these events show a contrasting relationship between climate and δ18O, which is explained by different causes underlying the two climate anomalies. Whereas the Little Ice Age is attributed to a pronounced negative phase of the North Atlantic Oscillation, the 8.2 ka event was triggered by cooler conditions in the North Atlantic due to a slowdown of the thermohaline circulation.

Quantitative High Resolution Spectral Analysis of Mn2+ in Sedimentary Calcite

Cathodoluminescence (CL) is used to detect trace element distribution in minerals. Thus, a possible quantitative analysis of activator elements based on their CL intensity has served as the incentive for numerous investigations. There is general agreement in the literature about the role of Mn2+ as the most important activator element, and of Fe2+, as the most efficient quencher element in calcites and dolomites (e.g. Richter and Zinkernagel 1975, 1981; Pierson 1981; Frank et al. 1982; Fairchild 1983; Grover and Read 1983; Machel 1985; Meyers and Lohmann 1985; ten Have and Heijnen 1985; Mason 1987; Walker et al. 1989; Mason and Mariano 1990; Machel et al. 1991). But the correlation of CL intensity and Mn concentration is controversial discussed. Frank et al. (1982) reported that CL intensity is controlled by the Fe/Mn ratio only. A much more complex correlation was revealed by Mason (1987) and Hemming et al. (1989), in which CL intensity is predominantly controlled by the absolute Mn content and the efficiency of Fe quenching, which increases with increasing Mn concentration. Fairchild (1983) and Pierson (1981), however, pointed out that Fe quenching is not affected by increasing Mn concentrations. Savard et al. (1995) suggested an “erratic” Mn2+activated CL behavior for Mn concentrations below 225 ppm in calcite.

Cathodoluminescence microscopy and spectroscopy of plagioclases from lunar soil

Abstract Cathodoluminescence (CL) microscopy and spectroscopy of single plagioclase grains from lunar soil show that plagioclases from Luna 20 (highland) have more or less homogeneous CL with both blue or green colors, whereas plagioclase grains sampled by Luna 24 (mare) luminesce dominantly green with partially distinct oscillatory zoning. The three main emission bands in the blue (~450 nm), green (~560 nm), and red-IR (~690 nm), mimic the most common emission bands in terrestrial feldspars. Mn2+ is the most important activator element in lunar plagioclases. Variations in the amount of structurally incorporated Mn2+ cause variations in the intensity of the green emission band at 560 nm, in some cases resulting in zoning of the CL intensity within single crystals. Calculations by a combination of quantitative spectral analysis of CL emission and PIXE measurements yield Mn concentrations of 7-47 ppm. The intense intrinsic emission band at 450 nm (probably an Al-O--Al center), which was especially prominent in Luna 20 plagioclases, causes their blue CL color. The occurrence of a CL emission band at ~690 nm in plagioclases from Luna 24 samples confirms that Fe3+-activated CL is common in these grains. The results indicate that at least some of the Fe in Luna 24 plagioclases is Fe3+, whereas all Luna 20 plagioclases have Fe3+-near the CL detection limit of about 0.1 ppm.

Cement stratigraphy in Triassic and Jurassic limestones of the Weserbergland (northwestern Germany)

Abstract Cement stratigraphy of the Korallenoolith (Oxfordian) and Trochitenkalk (Upper Muschelkalk) Formations, southern Lower Saxony Hills of Germany, is based on investigation of 232 carbonate samples by cathodoluminescence (CL). This enables subdivision of cements into four main generations: Generation 1, consisting of fine columnar, equant and syntaxial cements with blotchy CL and/or microdolomite inclusions, that is interpreted as originally submarine Mg calcitic precipitate. Generation 2, found in Jurassic samples only. These cements show intrinsic to non-luminescent CL with thin bright orange subzones and they are interpreted as meteoric phreatic calcites. Generation 3.1, characterized by zoned calcites with variable CL colours. These cements precipitated under shallow burial conditions, in a phreatic environment during an incipient stage of late diagenesis. Generation 3.2, with relatively uniform orange CL, indicative of precipitation in a stable chemical environment. This cement generation is interpreted as late diagenetic deep burial calcites. Generation 3.3, partially strongly zoned and with a characteristically intense CL contrast. It has been identified in only 17 of the 82 Trochitenkalk samples. Deformation twins end within this generation, indicating a post-tectonic genesis for the subsequent younger cement zones. The cements were probably precipitated in a near-surface environment characterized by reducing or variable Eh conditions. Generation 4, consisting of calcites that show intrinsic CL with bright orange subzones comparable to generation 2, but lacking deformation twins. These cements are interpreted as post-tectonic late diagenetic products of a meteoric phreatic environment. Based on detailed CL petrography, fifteen diagenetic events (three calcite cements, three dolomite generations, three fissure generations, two stages of dedolomitization, aragonite dissolution, matrix recrystallization and two stages of HMC → LMC transformation) can be distinguished and timed relative to cement zonation. The progressively decreasing δ18O values for cement generations 1 to 3.2 likely reflect increasing temperatures caused by burial. The low δ18C values of cement generation 4 are probably a reflection of a meteoric diagenetic environment. A time—burial—cementation pathway can be modelled combining CL patterns, cement isotopic data and the subsidence history of the study area. The main features of this model are: 1. (1) Generation 1 cements are submarine precipitates and their age therefore coincides with sedimentation. 2. (2) Cement generation 3.1 of the Trochitenkalk commenced precipitation at a depth of about 120 m, reached during Late Triassic time. In case this minimum depth is also the formation depth of generation 3.1 in the Korallenoolith Formation, then precipitation of these cements started during Late Jurassic time. 3. (3) Cement generation 3.2 of both the Trochitenkalk and the Korallenoolith Formation, precipitated at assumed depths > 1000 m, reached during the Doggerian and at the time of Jurassic/Cretaceous transition, respectively. 4. (4) Cement generation 4 precipitated after the sediments had undergone telogenesis, and must thus be younger than the Intra-Senonian (Sub-Hercynian) tectonic phase and possibly even younger than the Paleocene tectonic pulse (Laramian Phase).

Diagenetic history of sedimentary carbonates: Constraints from combined cathodoluminescence and trace element analyses by micro-PIXE

Abstract Trace element data for a succession of cements can contribute to the reconstruction of the diagenetic history of sediments. In the case of carbonate cements, cathodoluminescence (CL) microscopy has been successfully utilized for qualitative description of different cementation environments. In order to interpret correctly CL colour, trace element data other than Mn and Fe are often required. Due to frequent microscale zonation of trace elements in natural calcites and due to their low threshold concentration for CL activation, microsampling techniques with high spatial resolution and low detection limits are required. In this case study, trace element concentrations have been correlated with the CL behaviour of carbonate cements using the Bochum proton microprobe (PIXE) and a hot cathode luminescence device. The CL patterns, including the fine zonation, correlate well with the trace element distribution.

Micro-PIXE and quantitative cathodoluminescence spectroscopy: Combined high resolution trace element analyses in minerals

Abstract We combined high resolution Cathodoluminescence (CL)-spectroscopy and micro-PIXE to study the correlation of the activator concentration and the CL-intensity. Based on these results the Quantitative High Resolution Spectral analysis of Cathodoluminescence (QHRS-CL) is developed. Micro-PIXE and the new method (QHRS-CL) have been used to investigate trace elements in minerals. Using micro-PIXE and related methods the crystal lattice site and charge state of the analysed elements cannot be determined. This can be analysed exactly by using QHRS-CL. So the combination of micro-PIXE and QHRS-CL is a powerful tool for analysing trace element concentration above 100 ppb, the charge state and the lattice site of these elements in crystal structures.