Provenance of Triassic Feldspathic Sandstones in the Iberian Range (Spain): Significance of Quartz Types (original) (raw)
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Minerals
Within the Upper Triassic successions in the Iberian Basin (Spain), the occurrence of both idiomorphic bipyramidal quartz crystals as well as pseudohexagonal aragonite crystals are related to mudstone and evaporite bearing sequences. Bipyramidal-euhedral quartz crystals occur commonly at widespread locations and similar idiomorphic crystals have been described in other formations and ages from Europe, America, Pakistan, and Africa. Similarly, pseudohexagonal aragonite crystals are located at three main sites in the Iberian Range and are common constituents of deposits of this age in France, Italy, and Morocco. This study presents a detailed description of the geochemical and mineralogical characteristics of the bipyramidal quartz crystals to decipher their time of formation in relation to the diagenetic evolution of the sedimentary succession in which they formed. Petrographic and scanning electron microscopy (SEM) analyses permit the separation of an inner part of quartz crystals w...
Sedimentology, 1995
The Middle Muschelkalk [Middle Triassic) of the Catalan Coastal Range (north-east Spain) comprises sandstone, mudstone, anhydrite and minor carbonate layers. Interbedded sandstones and mudstones which are dominant in the northeastern parts of the basin are terminal alluvial fan deposits. South-westward in the basin, the rocks become dominated by interbedded evaporites and mudstones deposited in sabkha/mudflat environments. The diagenetic and pore water evolution patterns of the Middle Muschelkalk suggest a strong facies control. During eodiagenesis, formation of microdolomite, anhydrite, baryte, magnesite, K-feldspar and mixed-layer chlorite/smectite was favoured within and adjacent to the sabkha/mudflat facies, whereas calcite, haematite, mixed-layer illite/smectite and quartz formed mainly in the alluvial facies. Low 6180sMow values for microdolomite (+ 2 3. 7 to +28.4%0) and K-feldspar overgrowths (+ 1 7. 3 to +17.7%0) suggest either low-temperature, isotopic disequilibrium or precipitation from low-l80 porewaters. Low-~'O waters might have developed, at least in part, during low-temperature alteration of volcanic rock fragments. During mesodiagenesis, precipitation of quartz overgrowths and coarse dolomite occurred in the alluvial sandstones, whereas recrystallization of microdolomite was dominant in the sabkha/mudflat facies. The isotopic compositions of these mesogenetic phases reflect increasing temperature during burial. Upon uplift and erosion, telogenetic calcite and trace haematite precipitated in fractures and replaced dolomite. The isotopic composition of the calcite (6180sM0w=+21.5 to +25.6%0; 613C=-7.7 to-5.6%0) and presence of haematite indicate infiltration of meteoric waters.
Sedimentary Geology, 1996
The deposits of the Upper Triassic of the Subbetic Zone (Betic Cordillera) offer an example of semi-arid fluvial deposits passing into shallow-water facies through a mud-flat environment. From the study of the vertical changes in facies, a sequence model is proposed for the Upper Triassic succession, relating, for each systems tract, the changes in sea level, the accommodation space and the evolution of the facies within a coastal-plain depositional system. The lowstand depositional system is made up of a package of thick, amalgamated sandstone strata limited below by an erosive surface with little incision. These are sheet-flood deposits and channel fills which form part of an extensive alluvial system in which wide but shallow water courses appear, with the development of extensive sand bars. These sandbodies from the lowstand phase often contain mudrock intraclasts, plant remains and erosive surfaces. The accommodation space being extremely limited, the preservation of the floodplain or mud-flat deposits and palaeosols is practically nil. The result is an amalgamation of extensive sandbodies with fine intercalated claystone levels. The transgressive depositional systems consist mainly of a red claystone series, although the first sediments of these systems are composed of sandstone with major claystone intercalations. These lower sandy levels of the transgressive phase do not exceed 50 cm in thickness and usually contain burrows and small-scale sedimentary structures. In the intermediate part of the red claystone series of this transgressive episode of saline mud-fiat facies, there are sandstone levels of a little-developed fluvial system with channels which migrate laterally due to the rise of the base level. In addition, the predominance and the great development of the red claystone facies reflect the increase in the accommodation space, which permitted a greater accumulation of sediments during a transgressive phase than during the lowstand phase. In the upper part of the transgressive depositional systems, beds of calcrete and carniolar limestone are common, indicating a decreased sedimentation rate. The generation of accommodation space begins to slow down, leading to the enlargement of sandbodies corresponding to terminal-fan deposits (Friend, 1978). These developed over a fiat topography where the flow scattered and expanded laterally. In the highstand phase, the accommodation space reduced even more and the sedimentation rate is lower, favouring a great development of pedogenic carbonates. Furthermore, sand deposition was reduced or nil and the gradient of the slope was low, so that marine floods over the coastal plain were more frequent, permitting the precipitation of carbonates and sulphates in coastal salt pans.
HAL (Le Centre pour la Communication Scientifique Directe), 2019
Extensive areas of the Variscan granitic basement in NE Spain display profiles of red-stained albitized facies characterized by albitization of Ca-plagioclase, chloritization of biotite and microclinization of orthoclase, along with the alteration of igneous quartz to secondary CL-dark quartz. These profiles have a geopetal structure beneath the Triassic unconformity, with a very intense and pervasive alteration in the upper part that progressively decreases with depth to 150-200 m where the alteration is restricted to the walls of fractures. The red albitized facies contains secondary maghemite and hematite that indicate oxidizing conditions. Dating of microclinized orthoclase and secondary monazite that have formed in the red-stained albitized facies yielded K-Ar and U-Th-Pb total ages of 240 and 250 Ma, respectively, suggesting that the alteration developed during the Permian-Triassic period. The geopetal disposition of the red albitized profile with respect to the Triassic unconformity, its large regional extent, and the fracture-controlled alteration in the lower part of the profile indicate groundwater interaction. The δ 18 O values of albitized plagioclase (+ 11‰), microclinized orthoclase (+ 13‰), and secondary CL-dark quartz (+ 12‰) suggest that the alteration temperature was about 55 °C. This "low" temperature suggests that the alteration occurred during interaction of the granitic rocks with Na-rich fluids below a surficial weathering mantle on the Permian-Triassic palaeosurface. The latter is possibly related to Triassic evaporitic environments in long-lasting, stable landscapes in which Na-rich solutions infiltrated deep regional groundwaters.
Journal of Sedimentary Research, 1998
Petrographical and geochemical analysis of altered tuffaceous rocks of the Middle Triassic from the Iberian Range in Central Spain shows that pedogenic processes and subsequent diagenesis have strongly modified the original mineralogy and textures. These rocks are related to a magmatic episode that occurred at the Buntsandstein-Muschelkalk unconformity in this region, during the evolution of the Iberian Trough. The tuffaceous rocks accumulated in saline ponds in an open and terminal flood-plain setting. Their alteration is typified by neoformation of K-feldspar and illite. Precipitation of chert and carbonate cements and replacements were also important processes, resulting in intercalated chert beds and nodules. Much of the silica appears to be derived from extensive devitrification and weathering of glassy volcanic ash. X-ray diffraction analysis, microscopic observations, and EDX microanalysis reveal that the chert consists of various types of chalcedony, tridymite, micro and megaquartz, illite, K-feldspar, and small amounts of albite. In some of the nodules dolomite-ankerite is also common, enclosing anhydrite and barite relicts, which are partially silicified. Different levels of ammonium enrichment have been found in each petrofacies type: tuffs and tuffaceous rocks contain from 27 to 326 ppm (mean ؍ 139) of NH 4 ؉. Underlying arkosic sandstones with authigenic K-feldspar contain NH 4 ؉ ranging from 48 ppm to 191 ppm (mean ؍ 124). The NH 4 ؉ was probably derived from decay of organic matter in the evaporitic environment of deposition and its incorporation into feldspar and illite as they formed from unstable volcanic glass, sanidine, plagioclase, and vitric volcanic fragments. This transformation could have occurred via the intermediate phases of smectite and zeolites. The tuffaceous rocks also have a high content of B, ranging from 61 ppm to 170 ppm (mean ؍ 101). However, high levels of B are not positively correlated with high levels of NH 4 ؉ in the samples. Both B and NH 4 ؉ can be contained in either K-feldspar or illite, but it is not possible to know how much is present in each mineral without separating the minerals. Comparison of spidergrams of the tuffaceous rocks with those in the underlying arkosic sandstones indicates similar patterns with positive anomalies in La, Sm, and Y, and negative in Nb, P, Ti, and Yb, although the tuffaceous rocks are slightly richer in total REE. These data suggest that the distribution of REE must also be controlled by weathering and diagenetic reactions, and cannot be used for discrimination between volcanic and nonvolcanic sandstones.
International Journal of Earth Sciences
Extensive areas of the Variscan granitic basement in NE Spain display profiles of red-stained albitized facies characterized by albitization of Ca-plagioclase, chloritization of biotite and microclinization of orthoclase, along with the alteration of igneous quartz to secondary CL-dark quartz. These profiles have a geopetal structure beneath the Triassic unconformity, with a very intense and pervasive alteration in the upper part that progressively decreases with depth to 150-200 m where the alteration is restricted to the walls of fractures. The red albitized facies contains secondary maghemite and hematite that indicate oxidizing conditions. Dating of microclinized orthoclase and secondary monazite that have formed in the red-stained albitized facies yielded K-Ar and U-Th-Pb total ages of 240 and 250 Ma, respectively, suggesting that the alteration developed during the Permian-Triassic period. The geopetal disposition of the red albitized profile with respect to the Triassic unconformity, its large regional extent, and the fracture-controlled alteration in the lower part of the profile indicate groundwater interaction. The δ 18 O values of albitized plagioclase (+11‰), microclinized orthoclase (+13‰), and secondary CL-dark quartz (+12‰), suggest that the alteration temperature was about 55ºC. This "low" temperature suggests that the alteration occurred during interaction of the granitic rocks with Na-rich fluids below a surficial weathering mantle on the Permian-Triassic palaeosurface. The latter is possibly related to Triassic evaporitic environments in long-lasting, stable landscapes in which Na-rich solutions infiltrated deep regional groundwaters.