Peter T. Kolesar

Continuous 500,000-Year Climate Record from Vein Calcite in Devils Hole, Nevada

Oxygen-18 (δ18O) variations in a 36-centimeter-long core (DH-11) of vein calcite from Devils Hole, Nevada, yield an uninterrupted 500,000-year paleotemperature record that closely mimics all major features in the Vostok (Antarctica) paleotemperature and marine δ18O ice-volume records. The chronology for this continental record is based on 21 replicated mass-spectrometric uranium-series dates. Between the middle and latest Pleistocene, the duration of the last four glacial cycles recorded in the calcite increased from 80,000 to 130,000 years; this variation suggests that major climate changes were aperiodic. The timing of specific climatic events indicates that orbitally controlled variations in solar insolation were not a major factor in triggering deglaciations. Interglacial climates lasted about 20,000 years. Collectively, these observations are inconsistent with the Milankovitch hypothesis for the origin of the Pleistocene glacial cycles but they are consistent with the thesis that these cycles originated from internal nonlinear feedbacks within the atmosphere-ice sheet-ocean system.

Analysis of CO 2 Leakage through 'Low-Permeability' Faults from Natural Reservoirs in the Colorado Plateau, East-Central Utah

Abstract The numerous CO2 reservoirs in the Colorado Plateau region of the United States are natural analogues for potential geological CO2 sequestration repositories. To understand better the risk of leakage from reservoirs used for long-term underground CO2 storage, we examine evidence for CO2 migration along two normal faults that cut a reservoir in east-central Utah. CO2-charged springs, geysers, and a hydrocarbon seep are localized along these faults. These include natural springs that have been active for long periods of time, and springs that were induced by recent drilling. The CO2-charged spring waters have deposited travertine mounds and carbonate veins. The faults cut siltstones, shales, and sandstones and the fault rocks are fine-grained, clay-rich gouge, generally thought to be barriers to fluid flow. The geological and geochemical data are consistent with these faults being conduits for CO2 moving to the surface. Consequently, the injection of CO2 into faulted geological reservoirs, including faults with clay gouge, must be carefully designed and monitored to avoid slow seepage or fast rupture to the biosphere.

Two-million-year record of deuterium depletion in great basin ground waters.

Fluid inclusions in uranium series-dated calcitic veins from the southern Great Basin record a reduction of 40 per mil in the deuterium content of ground-water recharge during the Pleistocene. This variation is tentatively attributed to major uplift of the Sierra Nevada Range and the Transverse Ranges during this epoch with attendant increasing orographic depletion of deuterium from inland-bound Pacific storms.

Natural Leaking CO 2 -Charged Systems as Analogs for Failed Geologic Storage Reservoirs

Publisher Summary This chapter presents a variety of geologic data sets and methodologies to examine the sources, travel paths, and fate of CO2 from a subsurface reservoir to the Earths surface. The geological and structural analysis shows that the three-dimensional structure of the system consists of an open, north-plunging anticline cut by northwest-trending normal faults. These faults cut a Mesozoic section of clastic rocks that range from high-porosity and permeability eolian and fluvial sandstones, which are the dominant aquifers of the area, and low-permeability shales that appear to form effective top seals to a series of stacked CO2-charged reservoirs. Although the faults provide a barrier to cross fault flow, the footwall reservoir has leaked for > 150 years through the fault-related fractures in the damage zone. Typically in these types of rocks, analyses of fault seal capacity would predict that these faults would be barriers for cross-fault flow. In contrast, fractures in the damage zone associated with the faults appear to provide a conduit for CO2 leakage through the cap rock units. The sealing characteristics of faults are therefore a key to understanding the storage capacity in these settings, more recent leakage is focused around abandoned oil wells and water wells.

A Field and Chemical Study of Serpentinization—Stonyford, California: Chemical Flux and Mass Balance

Serpentinized harzburgites and dunites in the Coast Range ophiolite near Stonyford, California, form massive, decameter- to kilometer-scale blocks in serpentinite schist; together these form serpentinite broken formation that grades into mélange where exotic blocks have been incorporated into the serpeninite schist. Whole rock geochemical data and modal reconstruction of protolith compositions show that serpentinization here proceeded essentially isochemically for Si, Mg, and Fe, whereas other elements (Ca, Al, Cr) were lost to an aqueous flux. Mass balance calculations based on actual primary and secondary mineral compositions show that significant Fe, Al, and Cr may be accommodated in serpentine. The transformation of orthopyroxene to serpentine (bastite) releases significant amounts of silica, which forms additional serpentine when it reacts with MgO released by the serpentinization olivine; this reaction suppressed brucite formation and accounts in part for the conservation of silica and magnesia documented by whole rock geochemistry. For normal harzburgites (20-25% modal orthopyroxene), approximately half of the potential brucite was suppressed. Volume expansion was considerable: 25-30% for pseudomorphic replacement of orthopyroxene, 50-60% for replacement of olivine. The increase in volume resulted primarily from the addition of water to hydrate the primary silicate assemblage; loss of Al and Ca to aqueous solutions results in a slight loss of mass. Expansion is accommodated by orthogonal fractures at both the microscopic and macroscopic scales. Subsequent movement along the macroscopic serpentinized fractures led to the formation of serpentinite broken formation, with a matrix of sheared and foliated serpentinite, and relict blocks of massive, less serpentinized peridotite. This movement may have resulted in part from the volume expansion of the peridotite, as rigid, less serpentinized blocks were forced to adjust to increased volumes in their totally serpentinized selvages by differential movements that forced the blocks to move in the direction of least principal stress.

Hydrogeochemical Characterization of Leaking, Carbon Dioxide-Charged Fault Zones in East-Central Utah, With Implications for Geologic Carbon Storage

We examined a natural, CO 2 -charged subsurface system located near two fault zones in East-Central Utah that is analogous to engineered sequestration sites. Geologic information and geochemical and isotopic data from water and gas samples were used to develop a conceptual model of the flow system. This flow-system description indicates that CO 2 from a depth >800 m migrates upward through a system of shallower, stacked aquifers. The geologic structure in the area serves to focus the CO 2 -rich waters at the location of a faulted, anticlinal trap. The faults in the area impede horizontal flow but allow vertical leakage through thick, low-permeability formations. An important implication from this CO 2 -sequestration analog is that leakages occur along discrete flow paths in the subsurface; thus, in sequestration scenarios, detailed understanding of discrete flow paths will be necessary. Another implication is that groundwater can transport a significant amount of CO 2 , and thus, sampling groundwater chemistries from wells may be a better way to identify leakages than using monitoring techniques at the surface. Finally, even though mineralization occurs during CO 2 leakage to the surface, self-sealing has not occurred at this natural analog and may not occur at engineered sequestration sites.

Influence Of Depositional Environment On Devil's Hole Calcite Morphology And Petrology

Devils Hole, a steeply dipping (δ80°) tectonically formed planar fissure >165 m deep (Riggs et al., 1994), has been accumulating calcite speleothems that contain at least two different paleoclimate records. Below water table deposits contain a 560,000 year paleoclimate isotopic record (Winograd et al., 1992), while above water table deposits record 120,000 years of changing water table elevation (Szabo et al., 1994). The different depositional environments in Devils Hole control the form of the speleothems.

A comparison of the silica and Na-K-Ca geothermometers for thermal springs in Utah

Abstract The silica and Na-K-Ca chemical geothermometers do not always agree (within 25°C) when applied to hot springs in Utah. Some of the differences can be explained by mixing of hot and cold ground waters. However, the geology of the areas in which the springs arise must also be taken into account.

Energetics of Chemical Alteration in Fault Zones and its Relationship to the Seismic Cycle

We examine the composition of small and medium-displacement faults in the western San Bernardino Mountains, southern California, in order to determine the nature and degree of alteration in faults, and to relate this alteration to the heat generated by earthquakes. The development of clay-rich fault gouge in the faults is clearly syntectonic, and the reactions that produced the fault gouge are endothermic. We suggest and test the hypothesis that a primary source of energy to drive these reactions is the heat produced by earthquakes. We use standard thermodynamic values for enthalpies of formation to estimate the energy required to drive syntectonic alteration reactions. We use the Eastwood fault, a ∼ 7 km long fault with a clay-rich fault core 3-10 cm thick and a damage zone 20-40 m thick, as a model and show that these reactions could consume approximately 20 % of the energy available from the repeated earthquakes that slipped along the fault. Many of the reactions that take place in and around faults to produce clay and mica minerals are endothermic, suggesting that chemical reactions can be a significant sink of energy produced in earthquake ruptures in faults in the upper 10 km of the crust. Consumption of heat by chemical reactions in and around faults would also result in a reduced heat flow anomaly associated with the fault.