Robert G. Maliva

Secular change in the Precambrian silica cycle: Insights from chert petrology

Chert deposits preserve a record of secular change in the oceanic silica cycle. The evolutionary radiation of silica-secreting organisms resulted in a transition from abiological silica deposition, characteristic of the Archean and Proterozoic eons, to the predominantly biologically controlled silica deposition of the Phanerozoic. Comparative petrography of Phanerozoic and Precambrian cherts indicates that an earlier change in chert deposition occurred toward the end of the Paleoproterozoic era (ca. 1.8 Ga). In Neoproterozoic and Mesoproterozoic strata, early diagenetic chertification is largely restricted to peritidal environments. These early diagenetic cherts typically occur as nodules or discontinuous beds within carbonate deposits that have similar depositional textures. The cherts formed primarily by carbonate replacement with subsidiary direct silica precipitation. Some of the Paleoproterozoic cherts associated with iron formations, however, are distinctly different from younger cherts and appear to have formed largely by direct silica precipitation at or just below the seabed. These primary cherts lack ghosts or inclusions of carbonate precursors, have fine-scale grain fracturing (possibly from syneresis), exhibit low grain-packing densities, and are not associated with unsilicified carbonate deposits of similar depositional composition. Cherts in some Paleoproterozoic iron formations (e.g., the Gunflint Formation, northwestern Lake Superior region) are composed of silica types similar to those in Phanerozoic sinters (e.g., the Devonian Rhynie and Windyfield cherts, Scotland). Such cherts may provide evidence that basinal, and perhaps global, oceanic silica concentrations were higher during the Paleoproterozoic era than at later times.

Arid lands water evaluation and management

From the Contents: Aridity and Drought.- Geology of Arid Lands.- Aquifer Concepts in Arid Lands.- Introduction to Aquifer Hydraulics.- Water Budget.- Precipitation and Evapotranspiration.- Recharge Concepts and Settings.- Sustainability and Safe Yield.- Assessment of Groundwater Resources.- Recharge Measurement in Arid and Semiarid Regions.- Environmental Isotopes.- Wadi Recharge Evaluation.- Microgravity.- Compaction and Land Subsidence.- Surface and Airborne Geophysics.- Borehole Geophysical Techniques.- Remote Sensing.- Geographic Information Systems.- Groundwater Flow and Solute-Transport Modeling.- Ancient Water Management.- Rainwater, Stormwater, and Fog Harvesting.- Managed Aquifer Recharge.

Unusual calcite stromatolites and pisoids from a landfill leachate collection system

Low-magnesium calcite stromatolites and pisoids were found to have precipitated within the leachate collection system piping of a Palm Beach County, Florida, landfill. The stromatolites and pisoids formed in an aphotic and anoxic environment that was at times greatly supersaturated with calcite. The stromatolites are composed of branching cylindrical bundles of concentrically laminated radial fibrous crystals. The pisoids consist of concentric layers of radial fibrous and microcrystalline calcite. Bacteria, likely sulfate reducing, appear to have acted as catalysts for calcite crystal nucleation, and thus the formation of the stromatolites and pisoids. The leachate system stromatolites provide a recent example of stromatolites that formed largely by cement precipitation. By acting as catalysts for calcite nucleation, bacteria may cause more rapid cementation than would have occurred under purely abiotic conditions. Rapid calcite precipitation catalyzed by bacteria has interfered with the operation of the Palm Beach County landfill leachate collection by obstructing pipes and may be an unrecognized problem at other landfill sites.

Use of beach galleries as an intake for future seawater desalination facilities in Florida and globally similar areas

AbstractDesalination of seawater using the reverse osmosis process can be made less costly by the use of subsurface intake systems. Use of conventional open-ocean intakes requires the addition of a number of pretreatment processes to protect the primary RO process. Despite using the best designs possible for the pretreatment, seawater RO membranes tend to biofoul because of the naturally-occurring organic material and small bacteria present in seawater. These materials are not completely removed by the pretreatment system and they pass through the cartridge filters into the membranes, thereby causing frequent and expensive cleaning of the membranes. Quality of the raw water can be greatly improved by the use of subsurface intakes which can substantially reduce the overall treatment cost. There are a number of possible subsurface designs that can be used including conventional vertical wells, horizontal wells, collector wells, beach galleries, and seabed filters. The key selection criteria for the type of ...

Restoration of Wadi Aquifers by Artificial Recharge with Treated Waste Water

Fresh water resources within the Kingdom of Saudi Arabia are a rare and precious commodity that must be managed within a context of integrated water management. Wadi aquifers contain a high percentage of the naturally occurring fresh groundwater in the Kingdom. This resource is currently overused and has become depleted or contaminated at many locations. One resource that could be used to restore or enhance the fresh water resources within wadi aquifers is treated municipal waste water (reclaimed water). Each year about 80 percent of the countrys treated municipal waste water is discharged to waste without any beneficial use. These discharges not only represent a lost water resource, but also create a number of adverse environmental impacts, such as damage to sensitive nearshore marine environments and creation of high-salinity interior surface water areas. An investigation of the hydrogeology of wadi aquifers in Saudi Arabia revealed that these aquifers can be used to develop aquifer recharge and recovery (ARR) systems that will be able to treat the impaired-quality water, store it until needed, and allow recovery of the water for transmittal to areas in demand. Full-engineered ARR systems can be designed at high capacities within wadi aquifer systems that can operate in concert with the natural role of wadis, while providing the required functions of additional treatment, storage and recovery of reclaimed water, while reducing the need to develop additional, energy-intensive desalination to meet new water supply demands.

Skeletal aragonite neomorphism in Plio-Pleistocene sandy limestones and sandstones, Hollywood, Florida, USA

Abstract The basic mechanics of the neomorphism of aragonitic shells to calcite are generally understood, but fundamental questions remain concerning the details of the process. Completely and partially neomorphosed aragonitic skeletal fragments recovered in cores of Plio-Pleistocene limestones and sandstones from Hollywood, Florida, provide some insights into the process. Skeletal aragonite neomorphism occurred in a volume for volume manner across solution films, which resulted in the preservation of ghosts of fine-scale microstructures. Neomorphic calcite crystals that replaced skeletal aragonite in at least some instances inherited their crystallographic orientation from adjoining calcite cement crystals rather than from the host shell microstructure. Some neomorphic calcite crystals inherited the optical orientation of nearby echinoderm ossicles. However, host shell microstructure commonly controlled the direction of migration of the neomorphic replacement front. Anisotropies in shell solubility influenced the directional rates of growth of neomorphic calcite crystals, as evidenced by the strong tendency for the boundaries between neomorphic calcite and aragonite to parallel or coinicide with shell microstructural features. No examples were observed where neomorphic calcite replaced aragonite along euhedral crystal faces, such as commonly occurs during dolomitization and the replacement of limestone by megaquartz.

Displacive Calcite Syntaxial Overgrowths in Open Marine Limestones

Some calcite syntaxial overgrowths in the Upper Greensand (Cretaceous) of southern England and the Onondaga Limestone (Devonian) of New York State had a displacive mode of formation. Precipitation of the overgrowths in both of these open shelf marine limestones occurred in a phreatic environment. Two displacive crystal growth patterns are recognized by cathodoluminescence: (1) unimpeded displacive precipitation, in which obstructions, such as adjacent grains and matrix, offer little resistance to crystal growth, and (2) impeded displacive precipitation, in which obstructions significantly decrease the calcite precipitation rate at overgrowth-obstruction contacts. Impeded displacive precipitation can be recognized by an irregular luminescence zonation, reflecting precipitation perpendicular to overgrowth-obstruction contacts rather than along rational crystal faces.

Aquifer recharge and recovery: groundwater recharge systems for treatment, storage, and water reclamation.

Aquifer recharge and recovery (ARR) is a means to costeffectively treat reclaimed water to a quality standard wherein it can be used safely for either irrigation or indirect potable reuse. ARR is well suited to save energy and costs in developed countries. It could also be used in developing countries with limited resources to implement conventional water treatment. Reclaimed water is a valuable resource that should no longer be wasted while providing a solution to meet the global United Nations Millennium Development Goal for providing safe water to the more than one billion people now without. Over much of the world, waste water from domestic sources is being treated and discharged to tidal waters, rivers, and ephemeral streams with little benefit. For most developed countries, treated waste water effluent is commonly viewed only as a nuisance and a disposal issue and, at best, is used for irrigation during dry periods and simply discharged during wet or other periods of reduced demand. In the United States, approximately 135 GL/day of treated or partially treated waste water is discharged with less than 8% being reused. Globally, the reuse percentage is even lower. Using aquifers for treatment is not a new concept. Riverbank filtration (RBF) and dune filtration systems have been used effectively in Europe for the past century and the United States for the past 50 years. RBF systems decrease concentrations of suspended solids, dissolved metals, biological contaminants (bacteria, viruses, Cryptosporidium, Giardia, etc.), organic matter, and trace organic contaminants (pesticides, industrial and household chemicals, personal care products) occurring in most river systems. Extensive research has examined the effectiveness of RBF on water used for public supplies in both the European Union and the United States. Most potable water supply systems in Europe that use RBF as a part of drinking treatment do not use any disinfection in the treatment of

Managed Aquifer Recharge

Water scarcity can be caused primarily by a shortage in the total amount of water available, or to temporal imbalances between supply and demand. In many areas of the world, periodic water shortages can be alleviated by storing water available during rainy periods (or other times of excess supply) for later use during dry periods. The storage and recovery cycle could be seasonal or inter-year with water stored in years with higher than normal rainfall for use during subsequent dry years. Even in arid lands, where the average annual total supply of water is inadequate to meet all demands, seasonal or inter-year storage of water may still be of value by capturing water that would otherwise not be available for beneficial use. Mutiso (2003) observed that in most arid and semiarid lands, the quest for water does not depend on the absolute amount of precipitation, but on the fraction retained.

Advanced aquifer characterization for optimization of managed aquifer recharge

Managed aquifer recharge (MAR) will play an increasingly important role in solving water scarcity. The performance of MAR systems depends primarily upon local hydrogeology. Greatest opportunities for improvement in the implementation of MAR systems lie in the targeted application of conventional and advanced technologies to improve aquifer characterization. Surface geophysics (e.g., VES, TDEM, and seismic reflection and refraction) generally provide low resolution, but areal extensive data on subsurface hydrogeology. Times series of relative microgravity measurements have been used to map changes in both vadose and phreatic zone storage and to augment monitoring well systems. Surface nuclear magnetic resonance (NMR) has the potential to provide quantitative data on water-filled porosity and pore size distribution and, in turn, an estimate of hydraulic conductivity. Standard borehole geophysical logging techniques can provide coarse-scale data on aquifer heterogeneity. Advanced borehole logging techniques, such as NMR, microresistivity imaging, and gamma ray spectroscopy, have been used in MAR projects in the USA and UAE to provide fine-scale petrophysical data (e.g., porosity, porosity-types, and pore-size distribution). Groundwater modeling is used in MAR investigations to evaluate system feasibility and to optimize system design and operation. Opportunities to improve groundwater modeling exist through the application of advanced reservoir simulation platforms that allow for the processing and integration of available lithological, geophysical, and aquifer testing data and their subsequent incorporation into groundwater flow models. Advanced groundwater modeling programs are available that allow for the simulation of complex aquifers such as dual-porosity systems and variable density.