Sedimentary stylolite networks and connectivity in Limestone: Large-scale field observations and implications for structure evolution

International audienceStylolites are rough surfaces, formed by localized rock dissolution, and prevalent in carbonates and other sedimentary rocks. Their impact on porosity and permeability, and capacity to accommodate compactive strain, are well documented. This paper presents a meso-scale field study on sedimentary stylolites in carbonates, characterizing large-scale distributions of stylolites, including measurements conducted on longer than kilometer-long stylolites. Our field study suggests that on large-scales connections between stylolites become important. Since connectivity, and also lack of connectivity, are expected to play a significant role in strain accommodation and hydraulic rock properties, we suggest that large-scale analysis may require a new characterization scheme for "stylolites populations", based on their connectivity. We therefore divide sedimentary stylolite populations into three end-member types, which are correlated with the three possibilities for percolation of such systems: isolated stylolites (with zero percolation/connectivity), long-parallel stylolites (with 2-dimensional percolation/connectivity), and interconnected stylolite networks (with 3-dimensional percolation/connectivity). New statistical parameters and measures are devised and used to quantitatively characterize the different population types. Schematic mechanistic models are then offered to explain the evolution of the three end-member connectivity-classes. In addition we discuss the effect on fluid flow of the different population types

Microbial and Chemical Characterization of Underwater Fresh Water Springs in the Dead Sea

Due to its extreme salinity and high Mg concentration the Dead Sea is characterized by a very low density of cells most of which are Archaea. We discovered several underwater fresh to brackish water springs in the Dead Sea harboring dense microbial communities. We provide the first characterization of these communities, discuss their possible origin, hydrochemical environment, energetic resources and the putative biogeochemical pathways they are mediating. Pyrosequencing of the 16S rRNA gene and community fingerprinting methods showed that the spring community originates from the Dead Sea sediments and not from the aquifer. Furthermore, it suggested that there is a dense Archaeal community in the shoreline pore water of the lake. Sequences of bacterial sulfate reducers, nitrifiers iron oxidizers and iron reducers were identified as well. Analysis of white and green biofilms suggested that sulfide oxidation through chemolitotrophy and phototrophy is highly significant. Hyperspectral analysis showed a tight association between abundant green sulfur bacteria and cyanobacteria in the green biofilms. Together, our findings show that the Dead Sea floor harbors diverse microbial communities, part of which is not known from other hypersaline environments. Analysis of the water’s chemistry shows evidence of microbial activity along the path and suggests that the springs supply nitrogen, phosphorus and organic matter to the microbial communities in the Dead Sea. The underwater springs are a newly recognized water source for the Dead Sea. Their input of microorganisms and nutrients needs to be considered in the assessment of possible impact of dilution events of the lake surface waters, such as those that will occur in the future due to the intended establishment of the Red Sea−Dead Sea water conduit

The Life and Death of Stylolites: stylolite roughness as indicator for the duration and amount of dissolution

International audienceStylolites are rough surfaces formed by localized dissolution, mostly in carbonates and sandstones. They often account for a large degree of dissolution, and their impact on porosity and permeability is well recognized. Understanding their formation mechanism can advance our ability to predict their occurrence and effect on flow, which has appreciable geological and economical implications. Still, many fundamental issues concerning their structure and evolution are still unresolved. This manuscript studies the roughening of long parallel stylolites, which are one of three types of stylolite populations identified by us in a separate paper. Here we report measurements of stylolite surface roughness at a scale larger than ever measured before (10-2-101m). Measurements were performed using ground-based-LIDAR on 6 naturally-exposed surfaces of >km long stylolites in Northern Israel. The outcome of these measurements is a topography model of the surfaces, on which different techniques for calculating their roughness characteristics were used. Our results show that up to scales of ~10cm, the average deviation of the surfaces from a planar surface is related to the scale by a power-law with an exponent H. The surfaces are thus defined as self-affine only up to ~10cm with H~0.7. Above this scale H decreases almost to zero. This observed upper-bound of self-affine roughness measured here for the first time has been predicted by theory [1, 2, 2bis]. Our measurements support these theoretical models and together with them present a scenario in which stylolites evolve from preferential dissolution along an existing surface that was initially smooth and progressively roughened with time. Such a mechanism of stylolites growth is different from previously suggested mechanisms for other classes of stylolite which might propagate sideways from an initial defect. Based on the theoretical roughening model that we adopted, the upper limit to fractality for this class of stylolites may be used as a measure of the amount of dissolution on stylolites. Indeed, the amount of dissolution of the stylolites in our field site which we calculated from the upper limit to fractality is comparable to our estimates of dissolution from two additional independent techniques