Michael J. Duane

Microbial-Activated Sediment Traps Associated with Oncolite Formation Along a Peritidal Beach, Northern Arabian (Persian) Gulf, Kuwait

Identification of microbial communities within shoreline sediments and sediment precipitates from the Tigris-Euphrates delta (northern Kuwait) were determined by microscopic/nanoscopic studies, and by molecular analysis. Oncolites are syn-diagenetic carbonate precipitates that are surviving in a shallow subtidal to intertidal siliciclastic environment with periodically excessive hydraulic energy, extreme salinity (up to 47 per mil), and high concentrations of organic matter. X-ray diffraction techniques reveal that oncolite cortices are predominantly composed of calcite, quartz, halite and dolomite, associated with minor fractions of clay minerals. Quantitative analysis of the Corey Shape Factor reveals distinct morphological populations but with local overlap. A plot of the Equivalent Diameter vs. Corey Shape Factor provided the best indicator of the morphological relationships within the total oncolite population, indicating a hydrodynamically controlled morphological distribution defining intertidal and subtidal oncolite classes. Direct microscopic examination of the samples indicates that diatoms are the most abundant eukaryotic algae in subtidal sediments and within actively precipitating carbonate cements, especially the genus Navicula. In contrast, filamentous cyanobacteria from the genus Anabaena are most abundant in the intertidal zone sediments. The PCR-DGGE of the 16SrRNA gene of the cyanobacteria shows a higher diversity for this genus of bacteria in all sediment samples and that the cyanobacterial population in the diagenetically precipitating oncolites are closely related to the population found in the subtidal sediments. Dunaliella viridis dominates the culturable algae obtained from the four tidal zones. Our results indicate that a range of microbial populations are actively contributing to the formation of microbially-induced sedimentary structures in the extreme conditions of the southern Tigris-Euphrates delta.

Biomineralization and phytokarst development on cavernous Quaternary carbonate terraces, Mohammedia, northwest Morocco

Subaerial Quaternary limestones exposed on raised beach terraces on the Atlantic coastline north of Casablanca, Morocco, are undergoing rapid denudation by fungal and cyanobacterial destructive processes. Erosion is accomplished by penetration of the substrate by mycelia, including dissolution of carbonate substrate which subsequently becomes trapped in the biofilms in the photic zone along the terraces. The cyanobacteria cause biophysical disintegration, redistribution and biosynthesis of mineral components. Invasion of the pore space created by cyanobacteria is followed by microbially mediated carbonate cementation, beginning with the precipitation of several generations of crystallographically diverse carbonate cements. The micro-caves exhibit a range of features dominated by speleothemic calcite, microborings, algal filaments, hyphae, and calcite spherulites, which support the role of micro-organisms in the bioerosion and subsequent cementation of carbonate rocks in the terrestrial environment.

Fungal biomineralization in a surficial vadose setting, Temara district (Saibles D’Or), northwest Morocco

The mineralogy and ecology of the crystals that occur at the microbe-mineral interface, and the evolution of minerals around calcified filaments in a calcretized calcarenite from Temara (Rabat south, Morocco) are the focus of this study. From X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) studies, it is apparent that complexity of the interface between mineral-microbe can be investigated at the nanometre scale. Previous workers proposed a model for the evolution of the fungal filament biomineralization that describes the episodic modification of weddellite into whewellite, a phase absent from the present study. The common association of carbonate phases with microorganisms suggests that the organisms enhance conditions suitable for the growth of morphologically diverse crystal forms. A nanocrystalline calcium carbonate phase maybe a transient precursor phase of calcite mediated by the lichen Xanthoria parietina. Despite extensive studies on biomineralization, little is known about the causes of polymorph selection during fungal oxalate mineralization in nature.

Mud volcanoes and evaporite seismites in a tidal flat of northern Kuwait—implications for fluid flow in sabkhas of the Persian (Arabian) Gulf

This paper reports the first interpretative field map and stable isotope geochemistry of an exhumed Miocene inlier with conical mud volcanoes in a Persian (Arabian) Gulf salt flat (sabkha). In Kuwait, the siliciclastic low-heat flow margin of the northern gulf sector produced sedimentary conditions with numerous multilayered, unstable density gradients that were highly susceptible to recording liquefaction effects. The geotechnical characteristics of the sabkhas and the effects of local seismic activity resulted in ideal conditions in marginal sediments of Kuwait Bay, well suited for the development of deformation features. Three-dimensional, pseudo-biohermal exposures exhibit ellipsoidal pillows with craters separated by fluidized channels of chaotic orientation. The size and morphology of these structures together with co-genetic mud volcanoes are strongly influenced by sedimentary factors such as density gradients and tectonic events such as localized seismic activity, which caused mixing of fluids. Diapirs emerged concurrently with syn-sedimentary deformation, and the mud injection responded to episodic seismic activity. Interpretation based on previously published reflux models such as evaporative pumping and seawater flooding of coastal sabkhas is not applicable in this case. Rather, a model of focused ascent of brine initiated by episodic seismicity is proposed. Swarms of mud volcanoes represent new abiotic sedimentary features in sabkhas, but the per-ascensum nature of the fluid offers some comparisons to siliceous hot-water vents in south-eastern Brazil.

Geochemistry and modification of oilfield brines in surface pits in Northern Kuwait

Oilfield brines (produced water) are produced as a waste product daily at the gathering centers (GCs) in Kuwait oilfields. The geochemical evolution of the water produced at the GC (fresh brine) to stagnant pit water (evaporate) has been investigated in the northern fields of Kuwait, and a model is presented showing time-dependent variations. Kuwait oilfield brines are globally similar to others in other large sedimentary basins (USA, Canada), but modifications have occurred due to seawater injection practices performed episodically during the oil extraction process. Brine water chemistry changes from generally average brine chemistry (based on cations and anions) to saturated mixture of seawater, oilfield brine, and anthropogenic chemical pollutants. The objective of this study was to harmonize the database of brine waters in terms of regional identity by comparison with oilfield brines elsewhere, identify water–rock interaction, and statistically treat daily recordings from the pits in order to identify injection peaks and troughs. Laboratory analysis of major and minor cations and anions from the Rawdatayn samples gave the following concentration ranges in parts per million (ppm): (Na+, 11,698–203,977), (Ca2+, 2,216–98,514), (Mg2+, 1,602–28,885), (K+, 1,528–16,573), (Sr2+, 70–502), (Ba2+, 0.01–18.04), (Fe2+, 0.01–8.93), (Li+, 0.09–6.48), (Si2+, 0.00–13.18), (B3+, 0.05–37.45), (SO42+, 330–3100). For the Sabriyah oilfield samples, the major and minor cations and anions concentration ranges in ppm are: (Na+, 9,807–274,947), (Ca2+, 2,555–77,992), (Mg2+, 1,415–28,183), (K+, 764–19,201), (Sr2+, 77.84–641), (Ba2+, 0.15–6.76), (Fe2+, 0.016–38.88), (Li+, 0.05–6.83), (Si2+, 0.0195–16.84), (B3+, 7.17–55.33), (SO42+, 44,812–135,264). The stable isotopic analysis of five samples indicates normal trends in oxygen and hydrogen isotopes that classify the waters as “connate” which follow an evaporation trend. Carbon isotopic signatures are normal for hydrocarbon fields and average out around GC15, δ18O‰ = 1.4, δD‰ = −10, δ13C‰ = −3.6; while for GC23, δ18O‰ = 2.3, δD‰ = −4, δ13C‰ = −2.5; for GC25, δ18O‰ = −2.0, δD‰ = −14, δ13C‰ = −4.6; for pit1, δ18O‰ = 2.3, δD‰ = −5, δ13C‰ = −18.3; and for pit 2, δ18O‰ = 2.5, δD‰ = −4, δ13C‰ = −17.8. Carbon isotope average values for all brine samples from the GCs is = −56 which falls within normal hydrocarbon formation water category. Data spikes coincide with injection periods at the following times (A: May–Jun, 2006), (B: Sep–Oct, 2006), (C: Jan–Feb, 2007), (D: Mar, 2007), (E: May–Jun, 2007), (F: Feb, 2006), (G: Mar–Apr, 2006) and, subsequently the decay to “normal” brine occurs over a period of several weeks. The database was large enough to apply a principal component statistical analysis (PCA). PCA and geo-statistical techniques reveal several distinct population groups. The main chemical groups in the data are as follows: plateau, spike groups, and pit evaporation group. The spike periods correlate closely with seawater injection periods (Jan–Feb, Mar–Apr, May–Jun, and Sep–Oct). The pit chemistry reveals exceptionally high evaporation processes coinciding with summer peak temperature. PCA results show distinct groupings centered around the major elements reminiscent of other oilfields, but with the added evaporation trend strongly enhanced.

Pelagosite and coniatolite crusts associated with zones of sea spray on coastal terraces, Mohammedia (Northwest Morocco)

Clusters of finely laminated, pelagosite and micro-pelagosite occur on exposed terraces on the Atlantic coastline of Morocco. These structures occupy a substrate of potholed, calcareous Quaternary sandstone, which is receding rapidly due to biogenic and mechanical erosion processes. Sandstone overhangs that are weathered into craggy prominences in the tidal zone are preferential sites of carbonate precipitation. These restricted environments at times become supersaturated with carbonate. Crusts are strongly indurated and exhibit a variety of structures, the most common of which are laterally linked spheroidal aragonite crusts reminiscent of biogenic hemispheroids (LLH), and stacked hemispheroids (SH). They encrust a variety of vertical substrate irregularities occasionally forming dripstone coniatolite. Vertical relief of the spheroids varies from 10–200 μm and all forms are characterized by branching bundles of crystals with concentrical layers of radial fibrous aragonite. The vertical cliff faces provide a modern example of palagonite formed by cement precipitation facilitated by sea spray on variable microtopography. Although many of these aragonitic crusts resemble lithified algal stromatolites, their dripstone morphologies, nanostructures and lack of desiccation cracks, strongly suggest that they are formed by physico-chemical precipitation from seawater. The vertical distribution of aragonite is controlled by CO2 entrapment and release, sea-spray Ca, and the pH of the surrounding areas.