Fractured bedrock and saprolite hydrogeologic controls on groundwater/surface-water interaction: a conceptual model (Australia)

Hydrologic conceptual models of groundwater/surface-water interaction in a saprolite-fractured bedrock geological setting often assume that the saprolite zone is hydraulically more active than the deeper bedrock system and ignore the contribution of deeper groundwater from the fractured bedrock aquifer. A hydraulic, hydrochemical, and tracer-based study was conducted at Scott Creek, Mount Lofty Ranges, South Australia, to explore the importance of both the deeper fractured bedrock aquifer system and the shallow saprolite layer on groundwater/surface-water interaction. The results of this study suggest that groundwater flow in the deeper fractured bedrock zone is highly dynamic and is an important groundwater flow pathway along the hillslope. Deep groundwater is therefore a contributing component in streamflow generation at Scott Creek. The findings of this study suggest that hydrologic conceptual models, which treat the saprolite-fractured bedrock interface as a no-flow boundary and do not consider the deeper fractured bedrock in hydrologic analyses, may be overly simplistic and inherently misleading in some groundwater/surface-water interaction analyses. The results emphasise the need to understand the relative importance of subsurface flow activity in both of these shallow saprolite and deeper bedrock compartments as a basis for developing reliable conceptual hydrologic models of these systems.     

Revealing the “fingerprints” of the magnetic precursor of C-shocks

We present the first C-shock and radiative transfer model that calculates the evolution of the line profiles of neutral and ion species like SiO, H¹³CO⁺ and HN¹³C for different flow times along the propagation of the shock through the unperturbed gas. We find that the line profiles of SiO characteristic of the magnetic precursor stage have very narrow linewidths and are centered at velocities close to the ambient cloud velocity, as observed toward the young shocks in the L1448-mm outflow. Consistently with previous works, our model also reproduces the broad SiO emission detected in the high velocity gas in this outflow, for the downstream postshock gas in the shock. This implies that the different velocity components observed in L1448-mm are due to the coexistence of different shocks at different evolutionary stages.     

Hydrocarbon biomarkers of Neoproterozoic to Lower Cambrian oils from eastern Siberia

The Neoproterozoic Era is of widespread geobiological interest because it marks the critical transition from a world of microbes to one where animals become an established feature of the landscape. Much research into this time period has focused on the ventilation of the oceans, as this is widely considered a primary factor driving the diversification of complex, multicellular life. In this study, Proterozoic to Cambrian aged oils from eastern Siberia were analyzed for their hydrocarbon biomarker contents and compound specific carbon isotopes in order to further our understanding of the prevailing environment and its microbial and metazoan communities. Geochemically, these oils are broadly comparable to those of the Ediacaran-Cambrian sedimentary rocks and oils of the South Oman Salt Basin. Organic matter in the source sedimentary rocks included significant contributions from green algae, demosponges and bacteria including cyanobacteria and methanotrophic proteobacteria. Although the ages of the Siberian oils and putative parent source rock intervals are poorly constrained, the geochemical similarities between the Ediacaran Oman Huqf and Nepa-Botuoba-Katanga family of Siberian oil samples are impressive, leading to the inference that their source rocks are coeval. On the other hand, oils from the Baykit High are distinctive, likely older and possibly of Cryogenian age.     

Chemistry ahead of Herbig-Haro objects

There is now compelling evidence that dark molecular clouds are clumpy. Much of the clumpiness is unresolved by single-dish telescopes but is apparent in the data from array telescopes. Molecular clumps may also be observed close to Herbig-Haro (HH) objects. These clumps are easily observable because they are `illuminated' due to the UV radiation from the shock front of the HH jet. A detailed observational and theoretical study of one HH clump has been performed and it indicates that this clump must be transient and has a similar density and temperature to those clumps detected in the cloud interior. Thus, HH clumps may be used as an independent method of determining physical parameters of the clumpiness of molecular clouds.     

A highly reflective low cost backscattering target

A low cost biplanar reflector target has been developed and used in a system performance test of a near surface omnidirectional source and receiver. The target was constructed from sheets of closed cell plastic bubble sheeting. Theoretically, this material should have very high reflectance characteristics, and this was demonstrated by the experiment. The strongly reflecting target was located at the sea surface, and allowed the interpretation of data as the ship passed through a range of azimuthal angles. The higher than expected backscatter from the target was presumed to be due to the bubble sheeting behaving as a coherent reflector, like a thin layer of air, rather than an ensemble of individually resonating bubbles. This was verified by the data analysis. Lloyd's mirror effects were strong, because practically all of the return signals from the 10-ms continuous wave pulses were overlapping. The target strength (TS) of the reflector was strongly reduced at ranges over 100 m. The experiment shows that studies of the statistical distribution of fish school TS must consider the effects of Lloyd's mirror