Fracture‐focused fluid flow in an acid and redox‐influenced system: diagenetic controls on cement mineralogy and geomorphology in the <scp>N</scp>avajo <scp>S</scp>andstone

Bell, Julianne H.; Bowen, Brenda B.

doi:10.1111/gfl.12075

Cited by 4 publications

(12 citation statements)

References 29 publications

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“…Similarities in the mineral assemblages (including the presence of arsenic) and the association with bleaching at a significant outcrop of jarosite-cemented Entrada Sandstone in the Grand Staircase-Escalante National Monument (Bell and Bowen 2014) suggest that the observations made in our study may have a larger regional relevance. Our identification of a pyrite mineralization event provides a possible identification of the ''unidentified sulphide'' at their site.…”

Section: Discussionsupporting

confidence: 68%

“…Of particular note is the presence of jarosite (KFe 3 (SO 4 ) 2 (H 2 O) 6 ). Jarosite formation occurs in Fe 3þ -rich, acidic (pH , 3), high-Eh (oxic) environments (Stoffregen et al 2000;Zolotov and Shock 2005;Smith et al 2006), and is most commonly found as a product of the oxidative alteration of sulfide minerals (Bladh 1982;Long et al 1992 ;Bigham and Nordstrom 2000;Bell and Bowen 2014).…”

Section: Pyrite Formation and Pyrite Oxidationmentioning

confidence: 99%

“…Jarosite forms under conditions of low pH and high Eh, and is commonly associated with the surface oxidation (weathering) of pyrite in the presence of aluminosilicates (Long et al 1992;Bingham and Nordstrom 2000). Its presence is an indicator of the earlier presence of sulfide minerals (Bladh 1982;Long et al 1992;Bigham and Nordstrom 2000;Bell and Bowen 2014). As fragments of the jarosite-bearing iron mineralization assemblage are enclosed within gypsum-cemented fractures (Fig.…”

Section: Jarositementioning

confidence: 99%

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Red-bed bleaching in a CO2 storage analogue: Insights from Entrada Sandstone fracture-hosted mineralization

Rushton

Wagner

Pearce

et al. 2020

Journal of Sedimentary Research

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Improving our ability to predict the interactions between CO2 and reservoir rocks at geological time scales is of key importance if carbon capture and storage (CCS) is to have a role in climate-change mitigation, particularly in the light of likely regulatory requirements. Understanding and identifying the relevant geological processes over long time scales can be obtained only at natural-analogue sites. At one such site, in the Salt Wash Graben area of Utah, USA, widespread bleaching affects the Middle Jurassic red-bed “wet dune” Entrada Sandstone. Previous work has proposed a genetic link between the bleaching and spatially concomitant recent and modern CO2-rich fluids. The results presented here challenge some of the previous models and come from a detailed petrographic examination of mineralized fractures in the Entrada Sandstone that are centered in vertical extensions to the bleaching. These fractures typically contain complex mineralization assemblages. Pyrite was a paragenetically early phase, identifiable from common pseudomorphs of mixed iron oxides and oxyhydroxides that rarely contain relict pyrite. The pyrite contains up to 3 wt% arsenic. The volume of fracture-adjacent bleached sandstone is sufficient to have been the source of iron for the pyrite originally present in the fracture. The pyrite pseudomorphs occur at the center of fracture- and pore-filling cements that comprise intergrowths of hematite–goethite–jarosite–gypsum, an assemblage that suggests that their formation resulted from the oxidative alteration of pyrite, a genetic link supported by the arsenic present in the iron-bearing minerals. The presence of jarosite and proximal removal of earlier, sandstone-hosted carbonates are consistent with, and indicative of, the low-pH conditions associated with pyrite oxidation reactions. Calcite- and gypsum-cemented fractures crosscut, and contain fragments of, the pyrite-pseudomorphic and -oxidation assemblages, proving that they postdate pyrite formation and its subsequent oxidation, and that pyrite oxidation was not a result of modern weathering reactions. In outcrop, some calcite- and gypsum-cemented fractures link with travertine deposits associated with the modern and recent CO2-rich fluids. The mineral assemblages observed here, and the paragenetic sequence that we have inferred, suggest that the fracture-associated bleaching patterns result from the fracture-fed movement of sulfur-bearing reducing fluids, with hydrogen sulfide the most likely bleaching agent. We conclude that bleaching adjacent to fractures is not genetically related to modern CO2-bearing fluids despite the spatial relationship. The bleaching was already present when the modern fluids utilized the same fracture-based fluid pathways. We suggest that the more widespread regional bleaching formed contemporaneously with the fracture bleaching and followed similar mechanisms. This study highlights the complexity of interpreting analogue sites and the importance of using field and petrographic observations to unravel textures and events that are juxtaposed spatially but not temporally.

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Section: Discussionsupporting

confidence: 68%

Section: Pyrite Formation and Pyrite Oxidationmentioning

confidence: 99%

Section: Jarositementioning

confidence: 99%

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Red-bed bleaching in a CO2 storage analogue: Insights from Entrada Sandstone fracture-hosted mineralization

Rushton

Wagner

Pearce

et al. 2020

Journal of Sedimentary Research

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“…Fluid fl ow and solute transport are important in some natural fracture systems (Evans, 1995;Eichhubl et al, 2004;Fischer et al, 2009;Bell and Bowen, 2014). The spatial distribution of quartz cement in fractures, however, appears to be inconsistent with the solutes being derived primarily by large-scale advection through the fracture network.…”

Section: Silica Sourcementioning

confidence: 99%

Insights into rates of fracture growth and sealing from a model for quartz cementation in fractured sandstones

Lander¹,

Laubach

2014

Geological Society of America Bulletin

173

194

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A new model accounts for crystal growth patterns and internal textures in quartz cement in sandstone fractures, including massive sealing deposits, thin rinds or veneers that line open fracture surfaces, and bridge structures that span otherwise open fractures. High-resolution cathodoluminescence imaging of bridge structures and massive sealing deposits indicates that they form in association with repeated micron-scale fracturing of growing quartz crystals, whereas thin rinds do not. Model results indicate that the three morphology types develop in response to (1) the ratio of the rates of quartz growth to fracture opening and (2) the substantially faster growth rate that occurs on noneuhedral surfaces in certain crystallographic orientations compared to euhedral crystal faces. Rind morphologies develop when the fracture opening rate exceeds two times the fastest rate of quartz growth (along the c axis on noneuhedral surfaces) because growing crystals develop slow-growing euhedral faces. Massive sealing, on the other hand, develops where the net rate of fracture opening is less than twice the rate of quartz growth on euhedral faces because all quartz growth surfaces along the fracture wall seal the fracture between fracturing events. Bridge structures form at fracture opening rates that are intermediate between the massive sealing and rind cases and are associated with crystallographic orientations that allow growth to span the fracture between fracturing events. Subsequent fractures break the spanned crystal, introducing new, fastgrowing noneuhedral growth surfaces where quartz grows more rapidly compared to the euhedral faces of nonspanning crystals. As the ratio of fracture opening to quartz growth rate increases, the proportion of overgrowths that span the fracture decreases, and the range in c-axis orientations for these crystals comes progressively closer to perpendicular to the fracture wall until the maximum spanning limit is reached. Simulation results also reproduce "stretched crystal," "radiator structure," and "elongate blocky" textures in metamorphic quartz veins.The model replicates a well-characterized quartz bridge from the Cretaceous Travis Peak Formation as well as quartz cement abundances, internal textures, and morphologies in the sandstone host rock and fracture zone using the same kinetic parameters while honoring fl uid-inclusion and thermal-history constraints. The same fundamental driving forces, in both in the host rock and fracture system, are responsible for quartz cementation, with the only signifi cant difference within the fracture zone being the creation of new pore space as well as new noneuhedral surfaces for cases where overgrowths span fractures between fracturing events. Rates of fracture growth and sealing may be inferred from fracture cement textures using model results.

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“…Owing to the potential usefulness of jarosite and alunite as indicators of past aqueous conditions on Mars, considerable study of these minerals in terrestrial analog sites has been conducted in recent years; for example, in [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ] and many others. On Earth, large deposits of alunite and jarosite are most commonly found in volcanic acid-sulfate systems—where they usually precipitate by alteration of feldspar and other silicates—or in acid mine drainages such as Rio Tinto, where they precipitate by oxidation of pyrite and other metal sulfide minerals in massive sulfide deposits [ 20 , 31 , 32 ].…”

Section: Introductionmentioning

confidence: 99%

Jarosite and Alunite in Ancient Terrestrial Sedimentary Rocks: Reinterpreting Martian Depositional and Diagenetic Environmental Conditions

Potter-McIntyre

McCollom

2018

Life

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Members of the alunite group are precipitated at low pH (<1 to ~4) in oxidizing environments, are unstable in circumneutral conditions, and are widespread on Mars. At Mollies Nipple in Kane County, Utah, USA, jarosite and alunite are abundant as diagenetic cements in Jurassic sandstones. This research characterizes the jarosite and alunite cements with the goal of determining their origin, and tests the hypothesis that jarosite and alunite may be more stable than the current understanding indicates is possible. Previous studies have placed the jarosite- and alunite-bearing caprock at Mollies Nipple in the Navajo Sandstone, but the presence of water-lain deposits, volcanic ash, volcanic clasts, and peloids show that it is one of the overlying Middle Jurassic units that records sea level transgressions and regressions. A paragenetic timing, established from petrographic methods, shows that much of the cement was precipitated early in a marginal marine to coastal dune depositional environment with a fluctuating groundwater table that drove ferrolysis and evolved the groundwater to a low pH. Microbial interaction was likely a large contributor to the evolution of this acidity. Jarosite and alunite are clearly more stable in natural environments than is predicted by laboratory experiments, and therefore, the Martian environments that have been interpreted as largely acidic and/or dry over geologic time may have been more habitable than previously thought.

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Fracture‐focused fluid flow in an acid and redox‐influenced system: diagenetic controls on cement mineralogy and geomorphology in the Navajo Sandstone

Cited by 4 publications

References 29 publications

Red-bed bleaching in a CO2 storage analogue: Insights from Entrada Sandstone fracture-hosted mineralization

Red-bed bleaching in a CO2 storage analogue: Insights from Entrada Sandstone fracture-hosted mineralization

Insights into rates of fracture growth and sealing from a model for quartz cementation in fractured sandstones

Jarosite and Alunite in Ancient Terrestrial Sedimentary Rocks: Reinterpreting Martian Depositional and Diagenetic Environmental Conditions

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