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Conditions of kaolin illitization in the Permo-Triassic sandstones from the SE Iberian Ranges, Spain
Journal of Geochemical Exploration 89 (2006) 263 – 266 www.elsevier.com/locate/jgeoexp
Conditions of kaolin illitization in the Permo-Triassic sandstones from the SE Iberian Ranges, Spain J.D. Martín-Martín
a,⁎
, D. Gómez-Gras b , T. Sanfeliu c , A. Permanyer d , J.A. Núñez b , D. Parcerisa e
a
b
Department of Earth Sciences, Uppsala University, 75-236 Uppsala, Sweden Unitat de Petrologia i Geoquímica, Dpt. Geologia, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain c Dpt. Ciències Experimentals, Universitat Jaume I, 12080 Castelló, Spain d Dpt. Geoquímica, Petrologia i Prospecció Geològica, Universitat de Barcelona, 08028 Barcelona, Spain e Centre d'informatique géologique, Ecole des Mines de Paris, 77305 Fontainebleau cedex, France Received 15 August 2005; accepted 16 November 2005 Available online 10 March 2006
Abstract Kaolin is a widespread authigenic clay mineral in the Permo-Triassic sandstones from the marginal areas of the SE Iberian Basin. However, relatively more extensive illitization of kaolin occurs in the SW basin margin compared with the slight occurrence in the NE margin. SEM analysis of sandstones reveals that illite replaced small kaolinite crystals while blocky dickite remained unaltered. Kaolin illitization is suggested to take place in relation to the maximum burial depth reached during Late Cretaceous post-rift stage. Vitrinite reflectance data denotes a maximum burial temperature of 118 °C and 144 °C in the NE basin margin and in the SW basin margin, respectively. Thus, the extent of illitization in the SW margin is attributed to the higher Tpeak reached by the Permo-Triassic succession. Regarding the lack of K-feldspars observed in the sandstones and interbedded mudrocks, the source of K+ is mainly related to the alteration of detrital mica. © 2006 Elsevier B.V. All rights reserved. Keywords: Authigenic illite; Kaolin; Sandstones; Permo-Triassic
1. Introduction Authigenic clay minerals in the Permo-Triassic sandstones from the marginal areas of the SE Iberian Basin (NE Spain) are widely dominated by kaolin, whereas very low-grade metamorphic conditions resulted in the complete transformation of kaolin into pyrophillite in the depocenter of the basin (Martín⁎ Corresponding author. E-mail address: [email protected] (J.D. Martín-Martín). 0375-6742/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.gexplo.2005.11.061
Martín, 2004). XRD, ATD-TG and SEM analysis of four clay size fractions (b1, b2, b6.3 and b20 μm) from sandstone samples reveal extensive diagenetic transformation of kaolinite into dickite in both SW and NE basin margins. According to Martín-Martín (2004), the progressive improvement of the structural order of kaolin and the increase in the dickite/kaolinite ratio as clay size fraction increases suggest that the kaolinite-todickite transformation is concomitant with an increase in the crystal size. Thus, kaolinite occurs as fine crystal aggregates, whereas dickite forms coarser blocky crystals. Contrary to dickitization, petrographic data
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indicate slight extent of kaolin illitization in sandstones from the NE margin compared to sandstones from the SW margin. Kaolin illitization has been reported in the Permian and Triassic sandstones from the NW Iberian Ranges and related to the alteration of K-feldspars and mica (Marfil et al., 1996a,b). The aim of this work is to compare the timing and temperature of illite formation in both basin margins, to investigate the relation between illitization and the presence of kaolin polytypes, and to discuss the origin of the fluids involved in the process. 2. Geological setting The Iberian Basin developed between Late Permian and Late Cretaceous in two major stages of rifting followed by two thermal post-rift stages (Salas and Casas, 1993). The basin was structurally inverted during the Paleogene, which resulted in the Iberian Ranges fold-thrust belt (Fig. 1). The continental Permian and Triassic (Permo-Triassic) cover the post-Hercynian unconformity and form a succession of red-beds divided into three main formations that range in age from Thüringian (Late Permian) to Anisian (Middle Triassic) (Arche and López-Gómez, 1996). These formations are referred to herein informally as the lower, middle and upper units. The lower unit consists of red mudrocks and sandstones deposited in meandering fluvial environments. The bottom of the lower unit is a conglomerate deposited as alluvial fans. The middle unit, which is composed of pink to red colored sandstones with minor
conglomerates, is interpreted as a braided river deposit. The upper unit consists on red mudrocks and sandstones deposited also in a meandering environment. The overlaying Triassic marine carbonates (Muschelkalk facies) are composed mainly of grey dolostones. The studied outcrops are located presently in the southeastern part of the Iberian Ranges (E Spain) (Fig. 1), and represent marginal areas of the Permo-Triassic Iberian Basin (Arche and López-Gómez, 1996; Martín-Martín, 2004). In the NE margin of the basin (Desert de les Palmes area), a Permo-Triassic succession up to ∼490m thick is recorded, whereas in the SW margin (Xelva area) the succession is only ∼313m thick. Upper unit is not recorded in the SW margin and is ∼25m thick in the NE margin. Sandstones from the lower and middle units are sublitharenites that evolve upwards to quartzarenites (Gómez-Gras, 1993). Quartz is the dominant component ranging between 60% and 70% of the sandstone. Other important components include metamorphic rock fragments (b 8%) and chert (b2%), while minor amounts of intrabasinal fragments (mud intraclasts), muscovite and heavy minerals occur too. Feldspars, which are dominated by plagioclases, are rare and mostly altered. 3. Samples and methods Sandstones and conglomerates (13), interbedded mudrocks (29) and coal (3) samples have been collected from the lower and middle units of the Permo-Triassic succession outcropping in both basin margins. Bulk rock and clay mineral (b2μm) composition was performed by X-ray diffraction (XRD) in randomly oriented powders and oriented preparations (air-dried, glycolated and heated), respectively, in a Phillips PW 1710 diffractometer. Authigenic illite in sandstones and conglomerates was examined using a Leo 440i scanning electron microscope (SEM) equipped with a Link-Oxford energy dispersive Xray spectrometer (EDX). Vitrinite reflectance (Ro) analysis of polished coal chips was performed using a Leitz-Leica reflected-light microscope equipped with a MPV C2 photometry tube (photometer and photomultiplier). 4. Results
Fig. 1. Location map showing the Iberian Chain (Spain) and both basin margins.
Mineralogical XRD analyses of sandstones and interbedded mudrocks denote a homogeneous bulk rock composition along the Permo-Triassic section dominated by quartz, phyllosilicates and hematite. Minor components (b 5%) include feldspars, dolomite and calcite. Clay mineralogy shows a predominant illite + kaolin assemblage in both sandstones and mudrocks (Table 1). Minor chlorite and mixed-layer illite-smectite
J.D. Martín-Martín et al. / Journal of Geochemical Exploration 89 (2006) 263–266 Table 1 Synthesized XRD data for the b2μm size-fraction of sandstones and mudstones in the lower and middle units from both basin margins Lithology
Unit
Il Mudrocks
SW margin
NE margin
Xelva area
Desert de les Palmes area
K Chl I–S
Middle 65 5 Lower 96 2 Sandstones Middle 100 – Lower 35 65
– – – Σ
– 2 – –
Il
K Chl I–S C–S
66 53 35 52
34 41 63 42
– 1 2 5
Σ 5 – 1
265
whereas a gradient of ∼25 °C/km is deduced for the SW margin. According to Worden and Morad (2003), illitization of kaolin becomes pervasive at temperatures N130 °C.
– Σ – –
Il: illite; K: kaolin minerals; Chl: Chlorite; I–S: interstratified mineral illite–smectite; I–S: interstratified mineral chlorite–smectite; Σ: exist.
(I–S) and chlorite–smectite (C–S) minerals are also found in the lower unit. SEM examination revealed that authigenic illite occurs as lath or flake-like crystals that cover kaolin aggregates (Fig. 2). Illite typically replaces fine crystalline kaolin (kaolinite), as evidenced by the etched plates, whereas booklets composed of coarse and/or thick kaolin crystals (dickite) have not been illitized. Petrographic data suggest minor kaolin illitization in sandstones and conglomerates from the NE margin. Conversely, kaolin illitization in the SW margin was extensive, particularly in relation with the thick conglomeratic deposit located in the bottom of the lower unit. In these conglomerates, authigenic illite completely covers the fine crystalline kaolinite aggregates (Fig. 2C). Vitrinite reflectance (Ro%) results obtained from coal samples located within the lower unit have been converted to temperatures using the empirical calibrations proposed by Baker and Pawlewicz (1994). Conversion revealed maximum burial temperatures (Tpeak) of 115–120 °C (average 118°C) in the NE margin and 144 °C in the SW margin. 5. Discussion and conclusions Petrographic observations suggest that kaolin illitization postdates the kaolinite to dickite conversion, and thus is probably related to the maximum burial depth reached by the Permo-Triassic succession during the Late Cretaceous post-rift stage (Salas and Casas, 1993). The maximum thickness of the sedimentary pile over the post-Hercynian unconformity is estimated to have been ∼2000m in the NE margin (Roca et al., 1994) and ∼5000 m in the SW margin (Martín-Martín, 2004). Consequently, a paleogeothermal gradient of ∼49 °C/km is inferred for the NE margin, assuming a surface temperature of 20 °C,
Fig. 2. SEM micrographs illustrating the occurrence of authigenic illite in the NE margin (A and B) and SW margin (C). (A) Fine kaolinite crystals showing etched borders and replaced by illite. (B) Lath-shape illite crystals covering blocky habit dickite. (C) Detailed view of flakelike illite replacing fine kaolin crystals. White arrows indicate blocky kaolin crystals (dickite) without signal of alteration.
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Hence, the extent of kaolin illitization in the SW margin compared to the NE margin is attributed to the higher Tpeak (144 °C) reached by the Permo-Triassic succession. Due to the lack of detrital K-feldspars in the studied sandstones and mudrocks, the source of K+ is mainly related to the alteration of detrital mica, rock fragments and mud intraclasts (Marfil et al., 1996a,b). Alternatively, an external source of K+ could also be suggested in the SW margin, which includes dissolution of the laterally connected Muschelkalk and Keuper evaporitic deposits (Gaup et al., 1993). Despite the high maximum burial temperature reached by the Permo-Triassic sandstones and conglomerates in the SW basin margin, blocky dickite crystals remain unaltered whereas small kaolinite crystals appear mostly illitized. Results confirm the assumption that kaolinite is preferentially replaced into illite compared to dickite, which have been related to the higher degree of crystal structure disorder of kaolinite by Morad et al. (1994).
Acknowledgements J.D. Martín thanks Generalitat Valenciana (Spain) for a post-doc scholarship at Uppsala University (grant CTBPDC/2004/069). The research was partially supported by the Spanish Ministry of Education and Science (Grants CGL2005-07445-C03-01/BTE and BTE2003-06915) and DURSI from Catalonia Government (2001SGR00075, “Grup de Geologia Sedimentària”). R. Salas (Barcelona University) is acknowledged for discussions about the SE Iberian Basin. Critical review by S. Morad and two anonymous referees was of great help in improving the manuscript.
References Arche, A., López-Gómez, J., 1996. Origin of the Permian–Triassic Iberian Basin, central-eastern Spain. Tectonophysics 266, 443–464. Baker, C.E., Pawlewicz, M.J., 1994. Calculation of vitrinite reflectance from the thermal histories and peak temperatures. In: Mukhopadhyay, P.K., Dow, W.G. (Eds.), Reevaluation of Vitrinite Reflectance, vol. 570. American Chemical Society, pp. 216–229. Gaup, R., Matter, A., Platt, J., Ramseyer, K., Walzebuck, J., 1993. Diagenesis and fluid evolution of deeply buried Permian (Rotliegende) gas reservoirs, northwest Germany. AAPG Bulletin 77, 1111–1128. Gómez-Gras, D., 1993. El Permotrías de las Baleares y de la vertiente mediterránea de la Cordillera Ibérica y del Maestrat: Facies y Petrología Sedimentaria (Parte II). Boletín Geológico y Minero 104 (5), 467–515. Marfil, R., Bonhomme, M.G., De la Peña, J.A., Penha dos Santos, R., Sell, I., 1996a. La edad de las illitas en areniscas pérmicas y triásicas de la Cordillera Ibérica mediante el método K/Ar: implicaciones en la historia diagenética y evolución de la cuenca. Cuadernos de Geología Ibérica 20, 61–83. Marfil, R., Scherer, M., Turmero, M.J., 1996b. Diagenetic processes influencing porosity in sandstones from the Triassic Buntsandstein of the Iberian Range, Spain. Sedimentary Geology 105, 203–219. Martín-Martín, J.D., 2004. Los minerales de la arcilla del PermoTriásico de la Cordillera Ibérica oriental: Procedencia y evolución diagenética. Ph. D. Thesis. Univ. Jaume I, Spain. (189 p.). Morad, S., Ben Ismail, H.N., De Ros, L.F., Al-aasm, I.S., Serrhini, N.-E., 1994. Diagenesis and formation water chemistry of Triassic reservoir sandstones from southern Tunisia. Sedimentology 41, 1253–1272. Roca, E., Guimerà, J., Salas, R., 1994. Mesozoic extensional tectonics in the southeast Iberian Chain. Geological Magazine 131 (2), 155–168. Salas, R., Casas, A., 1993. Mesozoic extensional tectonics, stratigraphy and crystal evolution during the Alpine cycle of the eastern Iberian basin. Tectonohysics 228, 33–55. Worden, R.H., Morad, S., 2003. Clay minerals in sandstones: controls on formation, distribution and evolution. In: Worden, R.H., Morad, S. (Eds.), Clay Mineral Cements in Sandstones. International Association of Sedimentologists Special Publication, vol. 34. Blackwell Publishing, Oxford, pp. 3–41.
Conditions of kaolin illitization in the Permo-Triassic sandstones from the SE Iberian Ranges, Spain J.D. Martín-Martín
a,⁎
, D. Gómez-Gras b , T. Sanfeliu c , A. Permanyer d , J.A. Núñez b , D. Parcerisa e
a
b
Department of Earth Sciences, Uppsala University, 75-236 Uppsala, Sweden Unitat de Petrologia i Geoquímica, Dpt. Geologia, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain c Dpt. Ciències Experimentals, Universitat Jaume I, 12080 Castelló, Spain d Dpt. Geoquímica, Petrologia i Prospecció Geològica, Universitat de Barcelona, 08028 Barcelona, Spain e Centre d'informatique géologique, Ecole des Mines de Paris, 77305 Fontainebleau cedex, France Received 15 August 2005; accepted 16 November 2005 Available online 10 March 2006
Abstract Kaolin is a widespread authigenic clay mineral in the Permo-Triassic sandstones from the marginal areas of the SE Iberian Basin. However, relatively more extensive illitization of kaolin occurs in the SW basin margin compared with the slight occurrence in the NE margin. SEM analysis of sandstones reveals that illite replaced small kaolinite crystals while blocky dickite remained unaltered. Kaolin illitization is suggested to take place in relation to the maximum burial depth reached during Late Cretaceous post-rift stage. Vitrinite reflectance data denotes a maximum burial temperature of 118 °C and 144 °C in the NE basin margin and in the SW basin margin, respectively. Thus, the extent of illitization in the SW margin is attributed to the higher Tpeak reached by the Permo-Triassic succession. Regarding the lack of K-feldspars observed in the sandstones and interbedded mudrocks, the source of K+ is mainly related to the alteration of detrital mica. © 2006 Elsevier B.V. All rights reserved. Keywords: Authigenic illite; Kaolin; Sandstones; Permo-Triassic
1. Introduction Authigenic clay minerals in the Permo-Triassic sandstones from the marginal areas of the SE Iberian Basin (NE Spain) are widely dominated by kaolin, whereas very low-grade metamorphic conditions resulted in the complete transformation of kaolin into pyrophillite in the depocenter of the basin (Martín⁎ Corresponding author. E-mail address: [email protected] (J.D. Martín-Martín). 0375-6742/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.gexplo.2005.11.061
Martín, 2004). XRD, ATD-TG and SEM analysis of four clay size fractions (b1, b2, b6.3 and b20 μm) from sandstone samples reveal extensive diagenetic transformation of kaolinite into dickite in both SW and NE basin margins. According to Martín-Martín (2004), the progressive improvement of the structural order of kaolin and the increase in the dickite/kaolinite ratio as clay size fraction increases suggest that the kaolinite-todickite transformation is concomitant with an increase in the crystal size. Thus, kaolinite occurs as fine crystal aggregates, whereas dickite forms coarser blocky crystals. Contrary to dickitization, petrographic data
264
J.D. Martín-Martín et al. / Journal of Geochemical Exploration 89 (2006) 263–266
indicate slight extent of kaolin illitization in sandstones from the NE margin compared to sandstones from the SW margin. Kaolin illitization has been reported in the Permian and Triassic sandstones from the NW Iberian Ranges and related to the alteration of K-feldspars and mica (Marfil et al., 1996a,b). The aim of this work is to compare the timing and temperature of illite formation in both basin margins, to investigate the relation between illitization and the presence of kaolin polytypes, and to discuss the origin of the fluids involved in the process. 2. Geological setting The Iberian Basin developed between Late Permian and Late Cretaceous in two major stages of rifting followed by two thermal post-rift stages (Salas and Casas, 1993). The basin was structurally inverted during the Paleogene, which resulted in the Iberian Ranges fold-thrust belt (Fig. 1). The continental Permian and Triassic (Permo-Triassic) cover the post-Hercynian unconformity and form a succession of red-beds divided into three main formations that range in age from Thüringian (Late Permian) to Anisian (Middle Triassic) (Arche and López-Gómez, 1996). These formations are referred to herein informally as the lower, middle and upper units. The lower unit consists of red mudrocks and sandstones deposited in meandering fluvial environments. The bottom of the lower unit is a conglomerate deposited as alluvial fans. The middle unit, which is composed of pink to red colored sandstones with minor
conglomerates, is interpreted as a braided river deposit. The upper unit consists on red mudrocks and sandstones deposited also in a meandering environment. The overlaying Triassic marine carbonates (Muschelkalk facies) are composed mainly of grey dolostones. The studied outcrops are located presently in the southeastern part of the Iberian Ranges (E Spain) (Fig. 1), and represent marginal areas of the Permo-Triassic Iberian Basin (Arche and López-Gómez, 1996; Martín-Martín, 2004). In the NE margin of the basin (Desert de les Palmes area), a Permo-Triassic succession up to ∼490m thick is recorded, whereas in the SW margin (Xelva area) the succession is only ∼313m thick. Upper unit is not recorded in the SW margin and is ∼25m thick in the NE margin. Sandstones from the lower and middle units are sublitharenites that evolve upwards to quartzarenites (Gómez-Gras, 1993). Quartz is the dominant component ranging between 60% and 70% of the sandstone. Other important components include metamorphic rock fragments (b 8%) and chert (b2%), while minor amounts of intrabasinal fragments (mud intraclasts), muscovite and heavy minerals occur too. Feldspars, which are dominated by plagioclases, are rare and mostly altered. 3. Samples and methods Sandstones and conglomerates (13), interbedded mudrocks (29) and coal (3) samples have been collected from the lower and middle units of the Permo-Triassic succession outcropping in both basin margins. Bulk rock and clay mineral (b2μm) composition was performed by X-ray diffraction (XRD) in randomly oriented powders and oriented preparations (air-dried, glycolated and heated), respectively, in a Phillips PW 1710 diffractometer. Authigenic illite in sandstones and conglomerates was examined using a Leo 440i scanning electron microscope (SEM) equipped with a Link-Oxford energy dispersive Xray spectrometer (EDX). Vitrinite reflectance (Ro) analysis of polished coal chips was performed using a Leitz-Leica reflected-light microscope equipped with a MPV C2 photometry tube (photometer and photomultiplier). 4. Results
Fig. 1. Location map showing the Iberian Chain (Spain) and both basin margins.
Mineralogical XRD analyses of sandstones and interbedded mudrocks denote a homogeneous bulk rock composition along the Permo-Triassic section dominated by quartz, phyllosilicates and hematite. Minor components (b 5%) include feldspars, dolomite and calcite. Clay mineralogy shows a predominant illite + kaolin assemblage in both sandstones and mudrocks (Table 1). Minor chlorite and mixed-layer illite-smectite
J.D. Martín-Martín et al. / Journal of Geochemical Exploration 89 (2006) 263–266 Table 1 Synthesized XRD data for the b2μm size-fraction of sandstones and mudstones in the lower and middle units from both basin margins Lithology
Unit
Il Mudrocks
SW margin
NE margin
Xelva area
Desert de les Palmes area
K Chl I–S
Middle 65 5 Lower 96 2 Sandstones Middle 100 – Lower 35 65
– – – Σ
– 2 – –
Il
K Chl I–S C–S
66 53 35 52
34 41 63 42
– 1 2 5
Σ 5 – 1
265
whereas a gradient of ∼25 °C/km is deduced for the SW margin. According to Worden and Morad (2003), illitization of kaolin becomes pervasive at temperatures N130 °C.
– Σ – –
Il: illite; K: kaolin minerals; Chl: Chlorite; I–S: interstratified mineral illite–smectite; I–S: interstratified mineral chlorite–smectite; Σ: exist.
(I–S) and chlorite–smectite (C–S) minerals are also found in the lower unit. SEM examination revealed that authigenic illite occurs as lath or flake-like crystals that cover kaolin aggregates (Fig. 2). Illite typically replaces fine crystalline kaolin (kaolinite), as evidenced by the etched plates, whereas booklets composed of coarse and/or thick kaolin crystals (dickite) have not been illitized. Petrographic data suggest minor kaolin illitization in sandstones and conglomerates from the NE margin. Conversely, kaolin illitization in the SW margin was extensive, particularly in relation with the thick conglomeratic deposit located in the bottom of the lower unit. In these conglomerates, authigenic illite completely covers the fine crystalline kaolinite aggregates (Fig. 2C). Vitrinite reflectance (Ro%) results obtained from coal samples located within the lower unit have been converted to temperatures using the empirical calibrations proposed by Baker and Pawlewicz (1994). Conversion revealed maximum burial temperatures (Tpeak) of 115–120 °C (average 118°C) in the NE margin and 144 °C in the SW margin. 5. Discussion and conclusions Petrographic observations suggest that kaolin illitization postdates the kaolinite to dickite conversion, and thus is probably related to the maximum burial depth reached by the Permo-Triassic succession during the Late Cretaceous post-rift stage (Salas and Casas, 1993). The maximum thickness of the sedimentary pile over the post-Hercynian unconformity is estimated to have been ∼2000m in the NE margin (Roca et al., 1994) and ∼5000 m in the SW margin (Martín-Martín, 2004). Consequently, a paleogeothermal gradient of ∼49 °C/km is inferred for the NE margin, assuming a surface temperature of 20 °C,
Fig. 2. SEM micrographs illustrating the occurrence of authigenic illite in the NE margin (A and B) and SW margin (C). (A) Fine kaolinite crystals showing etched borders and replaced by illite. (B) Lath-shape illite crystals covering blocky habit dickite. (C) Detailed view of flakelike illite replacing fine kaolin crystals. White arrows indicate blocky kaolin crystals (dickite) without signal of alteration.
266
J.D. Martín-Martín et al. / Journal of Geochemical Exploration 89 (2006) 263–266
Hence, the extent of kaolin illitization in the SW margin compared to the NE margin is attributed to the higher Tpeak (144 °C) reached by the Permo-Triassic succession. Due to the lack of detrital K-feldspars in the studied sandstones and mudrocks, the source of K+ is mainly related to the alteration of detrital mica, rock fragments and mud intraclasts (Marfil et al., 1996a,b). Alternatively, an external source of K+ could also be suggested in the SW margin, which includes dissolution of the laterally connected Muschelkalk and Keuper evaporitic deposits (Gaup et al., 1993). Despite the high maximum burial temperature reached by the Permo-Triassic sandstones and conglomerates in the SW basin margin, blocky dickite crystals remain unaltered whereas small kaolinite crystals appear mostly illitized. Results confirm the assumption that kaolinite is preferentially replaced into illite compared to dickite, which have been related to the higher degree of crystal structure disorder of kaolinite by Morad et al. (1994).
Acknowledgements J.D. Martín thanks Generalitat Valenciana (Spain) for a post-doc scholarship at Uppsala University (grant CTBPDC/2004/069). The research was partially supported by the Spanish Ministry of Education and Science (Grants CGL2005-07445-C03-01/BTE and BTE2003-06915) and DURSI from Catalonia Government (2001SGR00075, “Grup de Geologia Sedimentària”). R. Salas (Barcelona University) is acknowledged for discussions about the SE Iberian Basin. Critical review by S. Morad and two anonymous referees was of great help in improving the manuscript.
References Arche, A., López-Gómez, J., 1996. Origin of the Permian–Triassic Iberian Basin, central-eastern Spain. Tectonophysics 266, 443–464. Baker, C.E., Pawlewicz, M.J., 1994. Calculation of vitrinite reflectance from the thermal histories and peak temperatures. In: Mukhopadhyay, P.K., Dow, W.G. (Eds.), Reevaluation of Vitrinite Reflectance, vol. 570. American Chemical Society, pp. 216–229. Gaup, R., Matter, A., Platt, J., Ramseyer, K., Walzebuck, J., 1993. Diagenesis and fluid evolution of deeply buried Permian (Rotliegende) gas reservoirs, northwest Germany. AAPG Bulletin 77, 1111–1128. Gómez-Gras, D., 1993. El Permotrías de las Baleares y de la vertiente mediterránea de la Cordillera Ibérica y del Maestrat: Facies y Petrología Sedimentaria (Parte II). Boletín Geológico y Minero 104 (5), 467–515. Marfil, R., Bonhomme, M.G., De la Peña, J.A., Penha dos Santos, R., Sell, I., 1996a. La edad de las illitas en areniscas pérmicas y triásicas de la Cordillera Ibérica mediante el método K/Ar: implicaciones en la historia diagenética y evolución de la cuenca. Cuadernos de Geología Ibérica 20, 61–83. Marfil, R., Scherer, M., Turmero, M.J., 1996b. Diagenetic processes influencing porosity in sandstones from the Triassic Buntsandstein of the Iberian Range, Spain. Sedimentary Geology 105, 203–219. Martín-Martín, J.D., 2004. Los minerales de la arcilla del PermoTriásico de la Cordillera Ibérica oriental: Procedencia y evolución diagenética. Ph. D. Thesis. Univ. Jaume I, Spain. (189 p.). Morad, S., Ben Ismail, H.N., De Ros, L.F., Al-aasm, I.S., Serrhini, N.-E., 1994. Diagenesis and formation water chemistry of Triassic reservoir sandstones from southern Tunisia. Sedimentology 41, 1253–1272. Roca, E., Guimerà, J., Salas, R., 1994. Mesozoic extensional tectonics in the southeast Iberian Chain. Geological Magazine 131 (2), 155–168. Salas, R., Casas, A., 1993. Mesozoic extensional tectonics, stratigraphy and crystal evolution during the Alpine cycle of the eastern Iberian basin. Tectonohysics 228, 33–55. Worden, R.H., Morad, S., 2003. Clay minerals in sandstones: controls on formation, distribution and evolution. In: Worden, R.H., Morad, S. (Eds.), Clay Mineral Cements in Sandstones. International Association of Sedimentologists Special Publication, vol. 34. Blackwell Publishing, Oxford, pp. 3–41.