Diagenetic conditions controlling authigenic formation of anatase and in situ LA-ICP-MS U–Pb isotope dating of this phase are studied in Upper Rotliegend II sandstones from two wells in NW-Germany. Anatase grew after breakdown of detrital Ti-phases (e.g. ilmenite) although local scale Ti transport and mobilization from detrital clay-hematite coats or condensed hydrocarbons cannot be ruled out. The anatase-forming reaction marks the change from a regime of reducing conditions imposed by first hydrocarbon generation to oxidizing conditions, probably caused by influx of a fluid from evaporitic Zechstein rocks. This change in fluid influx is interpreted as response to enhanced normal faulting and halokinesis during accelerated burial in Triassic times. Isotope data of U and Pb indicate incorporation of crustal common Pb from Mesozoic pore fluids but precisely mark diagenetic growth of anatase at 224.3 + 5.1/− 5.6 Ma in a Tera-Wasserburg plot. Locally, U–Pb isotope signatures are consistent with either additional incorporation of U and Pb from detrital precursor phases or with uptake of uranogenic Pb from hydrocarbons generated prior to 224 Ma. Anatase is shown to be a valuable authigenic phase suitable for U–Pb chronometry of diagenetic events, which appears to be unaffected by protracted burial and temperatures exceeding temperatures of crystallization.

Basalts and other mafic rocks are frequently used for road construction. The aggregates have to provide intrinsic mechanical strength and skid resistance. However, smectite contents stemming from alteration processes may deteriorate these mechanical properties considerably because of the resulting contrast in hardness. Quantitative relationships between smectite content, kind of distribution, and aggregate stability are rare except for a recent study by Kauthold et al. (2012). In this work thirteen basalt and andesite samples from German quarries were analysed by X-ray diffraction (XRD) for their mineral contents (including clay minerals), their cation exchange capacities (CEC) and their resistance against disaggregation in dimethyl sulfoxide. Smectite contents from XRD exceeded those calculated from the CEC regardless of the kind of occurrence of smectite observed in thin sections. The hypothesis that rocks with smectites occurring mostly in patches should differ in terms of CEC and mechanical properties from those rocks where smectites are more disseminated could not be confirmed. However, the amounts of smectite accessible to cation exchange correlated with the DMSO losses. Therefore, the fast CEC determination with Cu-Trien exchange can be substituted for the time-consuming DMSO test.