New information on the thermal history of the southwestern Lower Saxony Basin, northern Germany, based on fission track analysis

The southwestern part of the Lower Saxony Basin (LSB) is characterized by gravity and magnetic anomalies and by an extremely high thermal maturity of organic matter. This was for many years attributed to a Late Cretaceous intrusion, but actually deep burial is being debated. The complex thermal history of the area has been studied by fission track analysis. Zircon data provide evidence for widespread (hydro)thermal activity during the Permian and Upper Jurassic/Lower Cretaceous. Apatite ages indicate a major cooling event in the mid Cretaceous (∼89–72 Ma) reflecting the time of inversion of the LSB. During the Cretaceous, the cooling of the basin centre was rapid compared to the basin margins. Apatite fission track ages from borehole samples which are recently within the upper part of the APAZ indicate a young heating of the sedimentary sequences until present.     

Proterozoic ministromatolites with radial-fibrous fabric

Small digitate stromatolites with diameters in the range of 0·2–20 mm (ministromatolites) are common in Early and Middle Proterozoic carbonate sequences, and extend stratigraphically from the Archaean to the Holocene. An occurrence of columnar and stratiform types exhibiting a primary or early diagenetic radial-fibrous fabric and microscopically crinkled (microcrenate) lamination is described from the ? 1·9 Gyr old Belcher Supergroup (McLeary Formation) in southeastern Hudson Bay, Canada. The structures, which can be considered to be a variety of tufa, are unusually well preserved because of early diagenetic silicification. Columnar types are referable to Pseudogymnosolen (Asperia), and are morphologically similar to other occurrences of these taxa in coeval dolostones in northwestern and eastern Canada, where the fabric is normally preserved by a secondary mosaic of dolomite. The textural evidence of angulate cross-sections and rectilinear divergent patterns indicates that the radial-fibrous fabric represents primary or very early diagenetic precipitation, and that pseudogymnosolenids with mosaic dolomite originally also had radial-fibrous structure. The precipitation may have been within, or on, microbial mats.     

An idealized model of the one-dimensional carbon dioxide rectifier effect

The net flux of carbon dioxide (CO₂) from the land surface into the atmospheric boundary layer has a diurnal cycle. Drawdown of CO₂ occurs during daytime photosynthesis, and return of CO₂ to the atmosphere occurs during night. Even when the net diurnal-average surface flux vanishes, the diurnal-average profile of atmospheric CO₂ mixing ratio is usually not vertically uniform. This is because of the diurnal rectifier effect, by which atmospheric vertical transport and the surface flux conspire to produce a surplus of CO₂ near the ground and a deficit aloft.
This paper constructs an idealized, 1-D, eddy-diffusivity model of the rectifier effect and provides an analytic series solution. When non-dimensionalized, the intensity of the rectifier effect is related solely to a single 'rectifier parameter'. Given this model's governing equation and boundary conditions, we prove that the existence of the rectifier effect is related to the correlation of CO₂ gradient and transport, and also to the day–night symmetry of transport.
The rectifier-induced near-surface CO₂ surplus ought to be included in inverse calculations that use near-surface CO₂ mixing ratio to infer land–surface sources and sinks of carbon. Such inverse modeling is facilitated by our model's simplicity. To illustrate, we use a 1-D inverse calculation to infer the amplitude of diurnal CO₂ surface flux.