A new model for the formation of microbial polygons in a coastal sabkha setting

The stratigraphic record of microbially induced sedimentary structures spans most of the depositional record. Today, microbes continue to generate, bind and modify sediments in a vast range of depositional environments. One of the most cited of these settings is the coastal microbial mat system of the Persian/Arabian Gulf. In this setting, an extensive zone of microbial mat polygons has previously been interpreted as resulting from desiccation‐related contraction during episodic drying. This study employs 15 years of field‐based monitoring of the interaction between environmental factors and the development and evolution of polygon morphologies to test the desiccation model in this setting. On the basis of these observations, a new model is proposed that accounts for the genesis and development of microbial polygons without the need for desiccation‐induced shrinkage. Conversely, the formation, development and erosion of microbial polygons is a direct result of the production of large amounts of organic matter in a healthy, yet spatially limited, microbial community. The recognition of microbial polygons has previously been applied as a diagnostic tool for the reconstruction of ancient depositional environments. The present study calls these interpretations into doubt. It is inferred that preservation of the microbial polygons as a recognizable form would be rare. Biological degradation and compaction will reduce polygons to produce the ‘wispy’ laminae that are a common feature of ancient sabkha lithofacies

Geomechanical properties of coal macerals; measurements applicable to modelling swelling of coal seams during CO2 sequestration

Understanding the mechanical response of coal to CO2 injection is necessary to determine the suitability of a seam for carbon capture and underground storage (CCUS). The bulk elastic properties of a coal or shale, which determine its mechanical response, are controlled by the elastic properties of its individual components, i.e. macerals and minerals. The elastic properties of minerals are relatively well understood, and attempts have been made previously to acquire maceral elastic properties (Young's modulus) by means of nanoindentation. However, due to the resolution of a nanoindent and small size of macerals, the response is likely to be from a combination of macerals composition and minerals. Here atomic force microscopy is used for the first time to give a unique understanding of the local Youngs modulus of individual macerals, with a precision of 10 nm in both immature and mature coals/shale. Alginite, cutinite, inertinite and sporinite macerals are analysed from a samples of cannel coal (rich in cutinite), paper coal (enriched in sporinite), Northumberland coal (higher rank coal, rich in vitrinite and inertinite) and alginite rich New Albany Shale. Initial findings on the New Albany Shale indicate that kerogen isolation is not a suitable preparation technique for atomic force microscopy and as such, no alginite maceral moduli are accurately reported. Therefore results of the coal derived macerals (cutinite, inertinite and sporinite) are included in this study. The results at this length scale indicate that the mean and modal Young's modulus values in all coal macerals is less than 10 GPa. This range is similar to Young's modulus values acquired by nanoindentation within previous studies. A major difference is that the modal modulus values obtained here are significantly lower than the modal values obtained within previous studies. Thermally immature liptinite macerals (cutinite/sporinite) have a lower modal modulus (1.35–2.97GPa) than the inertinites (1.44–3.42 GPa) from the same coal. The modulus response is also non-normally distributed and most likely conforms to a gamma distribution with shape parameter between 1.5 and 2.5. The modal Young's modulus of all macerals increases with maturity, but not at the same rate, whereby the liptinite macerals become stiffer than the inertinites by the dry gas window (1.56 % Ro in Northumberland Coal). Modelling of volumetric strain under CO2 injection indicates an inversely proportionate relationship to Young's modulus, which suggests that differential swelling is more likely to occur in immature coals. It is therefore preferable to target mature coals for CCUS, as the reaction of macerals at higher maturities is more predictable across an entire coal seam

A record of spontaneous subduction initiation in the Izu–Bonin–Mariana arc

The initiation of tectonic plate subduction into the mantle is poorly understood. If subduction is induced by the push of a distant mid-ocean ridge or subducted slab pull, we expect compression and uplift of the overriding plate. In contrast, spontaneous subduction initiation, driven by subsidence of dense lithosphere along faults adjacent to buoyant lithosphere, would result in extension and magmatism. The rock record of subduction initiation is typically obscured by younger deposits, so evaluating these possibilities has proved elusive. Here we analyse the geochemical characteristics of igneous basement rocks and overlying sediments, sampled from the Amami Sankaku Basin in the northwest Philippine Sea. The uppermost basement rocks are areally widespread and supplied via dykes. They are similar in composition and age—as constrained by the biostratigraphy of the overlying sediments—to the 52–48-million-year-old basalts in the adjacent Izu–Bonin–Mariana fore-arc. The geochemical characteristics of the basement lavas indicate that a component of subducted lithosphere was involved in their genesis, and the lavas were derived from mantle source rocks that were more melt-depleted than those tapped at mid-ocean ridges. We propose that the basement lavas formed during the inception of Izu–Bonin–Mariana subduction in a mode consistent with the spontaneous initiation of subduction

Microscope observation of cracks of clay

Clay has wide application in engineered barriers. However, it is prone to crack if moisture content decreases at most circumstances. This research aimed to microscopically study drying shrinkage and associated cracking of two different clays: kaolin and sodium-based bentonite, using optical microscope-Leica DM2700 M, under controlled condition. The samples used were cylindrical with 20mm in diameter and 1mm in depth. During the observation, microscopic images were captured and saved. These images were used to analyse the cracking behaviour due to drying. The testing results showed that cracks initially occur in the middle of the sample and then propagate to the sample boundary. The length and width of the crack was increased as moisture decreased

Supplementary Materials

Figures, diagrams and extra data items that did not fit into the main manuscript of " Characterising the internal structural complexity of the Southern North Sea Zechstein Supergroup Evaporites"  Items include objects refrenced in the above paper - word document detailing the velocity model process - Residuals generated from the velocity model - Extra figures relating to the scientific paper and refrenced in text - Further well information (salt structures)</p