Open-system chemical behavior in deep Wilcox Group mudstones,Texas Gulf Coast,USA

Wilcox Group mudstones have been mechanically and geochemically transformed over a temperature range of 20–200 °C. Our research controlled for provenance and age by sampling from five wells, parallel to the paleodepositional axis, all within the Houston delta system. Across the sampled depths, mudstone porosity has been reduced from ∼25 to <10% and bulk mineralogical change as documented by quantitative X-ray diffraction includes decreases in quartz, K-feldspar and kaolinite content whereas illite + illite − smectite, chlorite, and plagioclase increase. These mineral transformations transfer elements at a scale of less than 1 mm from one mineralogical form to another, however, X-ray fluorescence data suggest that among major elements only Al₂O₃ and TiO₂ are fully conserved within the system (trace-element ZrO₂ is also conserved). K₂O has been added to and SiO₂ released from the Wilcox Group mudstones. Cathodoluminescence and secondary electron imaging did not find this SiO₂ locally precipitated. We, therefore, document an open-system geochemical behavior.     

Generation of Hydrogen Gas as a Result of Drilling Within the Saturated Zone

Hydrogen gas was discovered within the steel casing above standing water in a percussion-drilled borehole on the Hanlord Site in south-central Washington state. In situ measurements of the borehole fluids indicated anoxic, low-Eh (<-400 mV) conditions. Ground water sampled from adjacent wells in the same formation indicated that the ground water was oxygenated. H₂ was generated during percussion drilling, due to the decomposition of borehole waters as a result of aqueous reactions with drilled sediment and steel from the drilling tools or casing. The generation of H₂ within percussion-drilled boreholes that extend below the water table may be more common than previously realized. The ambient concentration of H₂ produced during drilling was limited by microbial activity within the casing-resident fluids. H₂ was generated abiotically in the laboratory, whereby sterilized borehole slurry samples produced 100 times more H₂ than unsterilizcd samples. It appears that H₂ is metabolized by microorganisms and concentrations might be significantly greater if not for microbial metabolism.     

Vital and mortal staining of algae in the presence of chlorine-produced oxidants

Evans blue and neutral red were tested as mortal and vital stains respectively for eight estuarine algal species which had been exposed to chlorine-produced oxidants in a continuous-flow system. The effect of CPO on staining with Evans blue was negligible. High concentrations of CPO affected staining with neutral red in several instances; this is probably due to CPO-induced mortality of test organisms during the exposure or staining period. Neutral red leached fromSkeletonema costatum andOlisthodiscus luteus before the end of the staining period. Staining ofDunaliella tertiolecta with neutral red proceeded more slowly. Evens blue, which was incorporated quickly and remained in the cells, is recommended for live-dead determinations for all species examined exceptNitzschia closterium, for which neutral red should be used. Neither stain was effective onMychonastes ruminatus (Simpson and Van Valkenburg 1978).     

Reprint of: Diagenetic controls on evolution of porosity and permeability in lower Tertiary Wilcox sandstones from shallow to ultradeep (200–6700 m) burial,Gulf of Mexico Basin,U.S.A.

Reservoir quality is a critical risk factor in deep to ultradeep reservoirs at depths >4.5 km. Analysis of Paleogene Wilcox sandstones on the upper Texas Gulf Coast provides insight into the evolution of reservoir quality during shallow to ultradeep burial diagenesis. Reduction of porosity and permeability with burial in Wilcox sandstones was evaluated using subsurface samples from 200 to 6700 m, at temperatures of 25–230 °C. Diagenesis and petrophysical properties were interpreted from petrographic data and core analyses. Wilcox sandstones are mostly lithic arkoses and feldspathic litharenites having an average composition of Q₅₉F₂₂R₁₉. Provenance did not change significantly during Wilcox deposition in this area, nor does average sandstone composition vary among lower, middle, and upper Wilcox sandstones. However, composition does vary with sequence-stratigraphic position; lowstand slope-fan deposits contain more rock fragments than do deposits from highstand or transgressive systems tracts. Given observations from this onshore dataset, Wilcox sandstones deposited in deepwater environments in the Gulf of Mexico are likely to contain more rock fragments than their linked highstand equivalents.     

Consistent global responses of marine ecosystems to future climate change across the IPCC AR5 earth system models

Climate Dynamics - We analyze for the first time all 16 Coupled Model Intercomparison Project Phase 5 models with explicit marine ecological modules to identify the common mechanisms involved in...