Jurassic Lake T'oo'dichi': A large alkaline, saline lake, Morrison Formation, eastern Colorado Plateau

Turner, Christine E.; Fishman, Neil S.

doi:10.1130/0016-7606(1991)103<0538:jltoda>2.3.co;2

Cited by 145 publications

(114 citation statements)

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“…Based on studies of the diagenesis of PaleogeneNeogene deposits of the Gulf Coast, the presence of illite could indicate temperatures of 100 °C or more (Boles and Franks, 1979;Bourdelle et al, 2013). However, Turner and Fishman (1991) found that pore-water chemistry can be more important than temperature in illite formation and that illite can form at near-surface temperatures in saline alkaline lakes similar to the McDermitt caldera setting.…”

Section: Mineralizationmentioning

confidence: 99%

Geology and evolution of the McDermitt caldera, northern Nevada and southeastern Oregon, western USA

et al. 2017

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The McDermitt caldera (western USA) is commonly considered the point of origin of the Yellowstone hotspot, yet until now no geologic map existed of the caldera and its geology and development were incompletely documented. We developed a comprehensive geologic framework through detailed and re connaissance geologic mapping, extensive petrographic and chemical analy sis, and highprecision Eruption of the McDermitt Tuff generated the irregularly keyholeshaped, 40 × 30-22 km McDermitt caldera. Collapse occurred mostly along a narrow ringfault zone of discrete faults with variable downwarp into the caldera be tween faults. Minor parallel faults locally widen the zone to as much as 6 km. We find no evidence that the McDermitt caldera consists of multiple nested calderas, as previously postulated. Total collapse was no more than ~1 km, and total erupted volume was ~1000 km 3 , of which 50%-85% is intracaldera tuff. Uncertainties in these estimates arise because an intracaldera tuff section is exposed only along the western edge of the caldera, and outflow tuff is not completely mapped. Megabreccia and mesobreccia are common in intracal dera tuff in the complete section. Intracaldera tuff is strongly rheomorphic, scrambling the compositional zoning, which is locally better preserved in out flow sections. However, outflow tuff is also strongly rheomorphic where it was deposited over steep topography.The caldera underwent postcollapse resurgent uplift driven by intrusion of icelandite magma, which also erupted from two major vents and as wide spread lavas. Major igneous activity around the McDermitt caldera lasted from before 16.7 to 16.1 Ma, although minor highalumina olivine tholeiite lavas were emplaced ca. 14.9 Ma in the youngest recognized igneous activity.Tuffaceous sediments as much as 210 m thick filled the caldera, although whether deposition preceded, followed, or spanned resurgence is unresolved. Although formed during regional extension, the caldera is cut only at its west ern and eastern margins by much younger, highangle normal faults that re sulted in gentle (~10°) eastward tilting of the caldera.Numerous hydrothermal systems probably related to caldera magmatism and focused along caldera structures produced Hg, Zrrich U (some along the western caldera ring fracture dated as 16.3 Ma), Ga, and minor Au mineral ization. Lithium deposits formed throughout the intracaldera tuffaceous sedi ments, probably ca. 14.9 Ma.Silicic central Snake River Plain, which also erupted voluminous rhyolitic tuffs. How ever, the Snake River Plain ignimbrites are metaluminous and homogeneous in bulk chemistry, with plagioclase, sanidine, and minor quartz as common phenocrysts, and rarely contain pumice or lithics.

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Section: Mineralizationmentioning

confidence: 99%

Geology and evolution of the McDermitt caldera, northern Nevada and southeastern Oregon, western USA

et al. 2017

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“…Such Mg-rich assemblages were attributed to initial formation of mixed-layer trioctahedral corrensite or chlorite soon after deposition in hypersaline sediments by either neoformation or transformation of detrital minerals (e.g., Turner and Fishman, 1991;Hillier, 1993 and references therein). However, there is no direct evidence from modern evaporative settings for early precipitation of corrensite or chlorite (e.g., Bodine and Madsen, 1987).…”

Section: Implications For Burial Diagenesismentioning

confidence: 99%

“…The Mg-rich trioctahedral mixed-layer smectitechlorite, corrensite, and chlorite clay mineral assemblages, commonly observed in sediments, are interpreted as forming in ancient hypersaline marine or lacustrine environments (Droste, 1963;Dyni, 1976;Bodine and Standaert, 1977;Tettenhorst and Moore, 1978;Eberl et al, 1982;Khoury et al, 1982;Bodine and Madsen, 1987;Fisher, 1988;Turner and Fishman, 1991;Andreason, 1992;Hillier, 1993). Such Mg-rich assemblages were attributed to initial formation of mixed-layer trioctahedral corrensite or chlorite soon after deposition in hypersaline sediments by either neoformation or transformation of detrital minerals (e.g., Turner and Fishman, 1991;Hillier, 1993 and references therein).…”

Section: Implications For Burial Diagenesismentioning

confidence: 99%

Mg-Smectite Authigenesis in a Marine Evaporative Environment, Salina Ometepec, Baja California

Hover

Walter

Peacor

et al. 1999

Clays and clay miner.

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Abstract--Formation of authigenic trioctahedral Mg-rich smectite is common in evaporative lake sediments, hut was not described previously in modern marine evaporative environments. This study documents formation of au~higenic K-rich, Mg-smectite during very early diagenesis in the dominantly siliciclastic Salina Ometepec (Baja California), a large supratidal evaporative sabkha complex near the mouth of the Colorado Rivet. Here, sediment pore waters are exceptionally Mg2+-rich relative to other marine evaporative environments due to suppressed sulfate reduction which limits production of carbonate alkalinity and, hence, carbonate (particularly dolomite) precipitation. Sediment cores were obtained along a five km transect seaward across the hypersaline mud flat to evaluate how these atypical geochemical conditions would affect the clay mineral compositions.Scanning transmission electron microscopy (STEM) observations show that the smectite from the marine Inlet, near the sediment source, consists of grains of irregular shape that give selected area diffraction (SAED) patterns reflecting dominant turbostratic stacking. Analytical electron microscopy (AEM) analyses indicate that K + is the dominant interlayer cation; the mean composition is approximately Ko.7(A13.:~Fe(III)0.3Mg05)(A105Si7s)O20(OH) 4. Such smectite is implied to be detrital in part because it is similar to smectite known to be deposited by the Colorado River.Smectite from the hypersaline mud flat occurs as aggregates of small subhedral pseudohexagonal plate or lath-shaped crystals <~250 nm in diameter; with thicknesses varying between three and ten layers. The SAED patterns reflect substantial turbostratic stacking, but with a greater frequency of interlayer coherency as compared with detrital smectite. Crystals from greater sediment depths are larger and more nearly euhedral. This smectite is dominantly trioctahedral, with mean composition approximately I~w(A107Fe(III)0sMg4.45)(All 2Si~8)Oz0(OH)4 (saponitic). This smectite is inferred to be dominantly authigenic in origin.The X-ray diffraction (XRD) and STEM/AEM data collectively imply that detrital aluminous dioctahedral smectite reacts to form authigenic Mg-rich trioctahedral smectite, driven in part by the high Mg2+/ Ca 2' ratio of pore waters. Such early-formed Mg-rich smectite may be the precursor for the trioctahedral mixed-layer smectite, corrensite, and chlorite assemblages found in ancient marine evaporative sequences. These results also add to the accumulating evidence that interlayer K" in marine smectite is fixed during the earliest stages of marine diagenesis near the sediment water interface.

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“…A better explanation for clay mineral reactions involves the Ostwald step rule, which states that a system in a state of metastable equilibrium will proceed via steps toward a state which has minimum free energy, i.e., the system will move toward a state of stable equilibrium (Ostwald 1897, van Santen 1983, May et al 1986. The evolution of clay minerals in diagenetic and low grade metamorphic sequences may be interpreted in terms of Ostwaldian steps, whereas equilibrium relations have yet to be demonstrated for most clay minerals during diagenesis.…”

Section: The Basis Of Clay Mineral Thermometrymentioning

confidence: 99%

Clay Mineral Thermometry—A Critical Perspective

Essene

Peacor

1995

Clays and clay miner.

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129

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Abstract--Diagenetic clay minerals usually occur as heterogeneous assemblages of submicroscopic layers consisting of different structure types such as illite, smectite and chlorite, with variable composition within a given structure type, and with highly variable concentrations of imperfections. The dimensions of mixed-layering, the semi-coherent to coherent nature of the structures across the layering, and compositional heterogeneity occur at a scale well below that of an individual thermodynamic phase. These relations imply that most clays are not distinct minerals or phases, and that assemblages of clays in shales and mudstones are incompatible with the phase rule. Such relations are better evaluated in terms of the formation of metastable materials with each small unit having unique chemical properties, rather than as a small number of stable homogeneous phases. Consequently, treatment of most clay minerals in terms of equilibrium stability with either a thermodynamic or experimental approach is subject to error.Chemical reactions involving most clay minerals are best understood with kinetic models. These involve a great variety of parameters such as time, fluid/rock ratio, deformation history, nature of starting materials and transformation mechanisms, as well as the variables, such as temperature, pressure and composition, that are commonly used to define equilibrium. Solubility experiments on the stabilities of clay minerals are unlikely to attain equilibrium at low temperatures. Moreover, the activity of soluble species may be controlled by surface equilibria, or by absorbed or exchangeable cations. Interpretations of available experiments on the solubility of illite vs. other mineral assemblages are in violation of Schreinemakers' rules and indicate lack of equilibrium.Predictable sequences of clay minerals as a function of temperature are best understood through the Ostwald step rule, in which clay mineral assemblages undergo reactions in response to kinetic factors that represent reaction progress rather than an approach to equilibrium. Currently used clay mineral thermometers (illite crystallinity, smectite/illite reaction, chlorite composition) are not based on equilibrium reactions. Such systems are not accurate thermometers and therefore have questionable utility.

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Jurassic Lake T'oo'dichi': A large alkaline, saline lake, Morrison Formation, eastern Colorado Plateau

Cited by 145 publications

References 0 publications

Geology and evolution of the McDermitt caldera, northern Nevada and southeastern Oregon, western USA

Geology and evolution of the McDermitt caldera, northern Nevada and southeastern Oregon, western USA

Mg-Smectite Authigenesis in a Marine Evaporative Environment, Salina Ometepec, Baja California

Clay Mineral Thermometry—A Critical Perspective

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