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Title: Origin and timing of Dauphiné twins in quartz cement in fractured sandstones from diagenetic environments: Insight from fluid inclusions

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Journal Article: Publisher's Accepted Manuscript
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Journal Volume: 687; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-10-04 21:08:02; Journal ID: ISSN 0040-1951
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Fall, András, Ukar, Estibalitz, and Laubach, Stephen E. Origin and timing of Dauphiné twins in quartz cement in fractured sandstones from diagenetic environments: Insight from fluid inclusions. Netherlands: N. p., 2016. Web. doi:10.1016/j.tecto.2016.08.014.
Fall, András, Ukar, Estibalitz, & Laubach, Stephen E. Origin and timing of Dauphiné twins in quartz cement in fractured sandstones from diagenetic environments: Insight from fluid inclusions. Netherlands. doi:10.1016/j.tecto.2016.08.014.
Fall, András, Ukar, Estibalitz, and Laubach, Stephen E. 2016. "Origin and timing of Dauphiné twins in quartz cement in fractured sandstones from diagenetic environments: Insight from fluid inclusions". Netherlands. doi:10.1016/j.tecto.2016.08.014.
title = {Origin and timing of Dauphiné twins in quartz cement in fractured sandstones from diagenetic environments: Insight from fluid inclusions},
author = {Fall, András and Ukar, Estibalitz and Laubach, Stephen E.},
abstractNote = {},
doi = {10.1016/j.tecto.2016.08.014},
journal = {Tectonophysics},
number = C,
volume = 687,
place = {Netherlands},
year = 2016,
month = 9

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Publisher's Version of Record at 10.1016/j.tecto.2016.08.014

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  • Recent studies of fluid inclusions in quartz overgrowths have shown quartz cementation to have taken place at temperatures within the range 60--145 C in several sandstones from the North Sea and offshore mid-Norway (Malley et al. 1986; Konnerup-Madsen and Dypvik 1988; Burley et al. 1989; Walderhaug 1990; Ehrenberg 1990; Saigal et al. 1992; Nedkvitne et al. 1993). This study aims at determining whether these results are typical for quartz cementation of sandstones by presenting homogenization temperatures for 274 aqueous and 366 hydrocarbon inclusions in quartz overgrowths from Jurassic reservoir sandstones on the Norwegian continental shelf, and by reviewing previously publishedmore » fluid-inclusion data. Possible explanations for different ranges of homogenization temperatures in different sandstones are also discussed, and possible sources of quartz cement and the effect of hydrocarbon emplacement on quartz cementation are considered.« less
  • Precipitation rates for quartz cement in quartz-rich Jurassic sandstones from the Norwegian shelf have been determined by combining petrographic data, fluid-inclusion data, and temperature-history modeling. Thin-section petrography enables the number of moles of quartz cement precipitated in a sample and the surface area available for precipitation to be determined. Measurement of homogenization temperatures for fluid inclusions located at the boundaries between quartz clasts and quartz overgrowths permits the temperature of initial quartz cementation to be found, and this temperature may be translated to date by constructing a temperature-history curve for each sandstone. Since quartz cementation has continued up to themore » present in the studied sandstones, precipitation rates for quartz cement per unit time and surface area can be calculated. The calculated precipitation rates enable an equation giving quartz precipitation rate as a function of temperature to be defined. Quartz cementation, and consequently also porosity evolution, in deeply buried quartz-rich sandstones can therefore be predicted quantitatively.« less
  • This study was initiated to investigate if coals on the Norwegian offshore continental shelf (NOCS) expel petroleum and in which form. The results revealed that equally isotopically light methane (C{sub 1}) was released from fluid inclusions in sandstones and from adjacent coal (-60.9 to -72.7 parts per thousand). The analyzed samples were collected from cored northern North Sea and mid-Norwegian shelf wells in the depth interval 3924-5095 m. The vitrinite reflectance (R{sub o}) values of the coals range between 0.53 and 1.12%, with most values between 0.8 and 1.0%. The light C{sub 1} isotope values released both from the coalsmore » and from the fluid inclusions in the adjacent sandstones suggest that the origin of the gas is the coal, and that no isotope fractionation occurs during release of the gas in nature. Traditional isotope interpretation schemes suggest the C{sub 1} to have a biogenic origin, whereas recently published data also show the possibility for an early mature thermogenic origin. The isotope values represent averages of the total gas released from all the individual disintegrated fluid inclusions in each sample. These did not form simultaneously, but during multiple events potentially covering several million years. We speculate that significant volumes of isotopically light C{sub 1} have been expelled from the analyzed coals over time. The expelled isotopically light C{sub 1}, may mix with mature thermogenically produced gas and skew the overall methane isotope values of gas accumulations toward lighter values, thus explaining the isotopically lighter-than-expected gas accumulations on the NOCS (e.g., Troll, Frigg, and Draugen fields).« less
  • Fluid evolution during neo-alpine metamorphism during late stages of the continental collision between Europe and Africa was studied by analyzing fluid inclusions in alpine fissure quartz collected in forty-nine localities along a geotraverse through the Central Alps, Switzerland. The methods employed include microthermometry, micro-Raman spectroscopy, K/Na thermometry, and stable isotope analysis. Early fluid inclusions provide evidence of close to peak metamorphic temperatures of the late Tertiary or neo-alpine metamorphic event. Fluid composition evolved along the geotraverse from north to south as follows: higher hydrocarbons were dominant in the low- and medium-grade diagenetic zones, methane was the main volatile in themore » high-grade diagenetic and low-grade anchizone, water dominated in the high-grade anchizone and low-grade epizone, with CO[sub 2] > 10 mol% in the high-grade epizone and in the mesozone. Higher hydrocarbons and CH[sub 4] were the products of kerogen maturation and cracking of preexisting petroleum. Large water supplies originated from the dehydration of cooler metasedimentary rocks that were overthrust by crystalline basements of the Lepontines, Aar, and Gotthard massifs. Carbon isotope analyses suggest that the CO[sub 2] component was derived from oxidation of graphitic matter, especially in the vicinity of sulfate-bearing metasediments and from decarbonation reactions. In the Aar and Gotthard massifs as well as in the Helvetic Axen nappe and its underlying North Helvetic flysch, high fluid pressures prevailed and favored nappe transport. By contrast, in the southern Lepontine area, very low early fluid pressures were probably related to dry rocks and scarce metasediments, and to high geothermal gradients that resulted from intense uplift and erosion between 26 and 18 Ma.« less
  • The compositions of individual synthetic fluid inclusions in the systems NaCl-KCl, NaCl-CaCl{sub 2} and NaCl-KCl-CaCl{sub 2} have been semi-quantitatively determined by energy dispersive analysis of precipitates produced during thermal decrepitation. Inclusions containing known mixtures of 20 wt.% total salinity were synthesized by healing fractures in natural quartz at 600-700{degree}C and 5-7 kbars for 7-10 days. The two-phase, daughter-free inclusions homogenized at 170-250{degree}C, began to decrepitate after about 100{degree} of overheating and by 360-420{degree}C a significant number of decrepitates had formed on the polished surface. Peak heights generated by EDA (raster mode) of these decrepitates were standardized using both single andmore » mixed salt standards evaporated to dryness in a vacuum. Although the mixed salt standards better approximated the decrepitate compositions, difficulties were encountered in producing micron-scale homogeneity and the single salts yielded more reliable results.« less