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Stable isotope and mineralogical investigations on clays from the Late Cretaceous sequences, Haţeg Basin, Romania
Applied Clay Science 45 (2009) 155–163
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Applied Clay Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c l a y
Stable isotope and mineralogical investigations on clays from the Late Cretaceous sequences, Haţeg Basin, Romania Ana-Voica Bojar a,⁎, Franz Ottner b, Hans-Peter Bojar c, Dan Grigorescu d, Aurel Perşoiu e a
Institute of Earth Sciences, Geology and Palaeontology, Karl-Franzens University, Heinrichstrasse 26, A-8010 Graz, Austria Institute for Applied Geology, Peter Jordan Strasse 70, A-1190 Wien, Austria Landesmuseum Joanneum, Department of Mineralogy, Raubergasse 10, A-8010 Graz, Austria d Department of Geology and Geophysics, Bucharest University, Bd. Bălcescu 1, R-010041 Bucharest, Romania e Department of Geology, University of South Florida, 4202 E. Fowler Ave., SCA 528, Tampa, FL, USA b c
a r t i c l e
i n f o
Article history: Received 18 November 2008 Received in revised form 1 April 2009 Accepted 4 April 2009 Available online 14 April 2009 Keywords: Stable isotopes Smectites Precipitations Paleosols Maastrichtian Haţeg Basin
a b s t r a c t In the Haţeg basin, South Carpathians, a thick continental sequence accumulated during the Maastrichtian. The alluvial sequences are characterized by the formation of paleosol horizons developed on the alluvial plain. In order to investigate the environmental signal stable isotope and mineralogical investigations have been carried out on smectites from paleosol. The RX as well as the FTIR spectra of the fraction b 2 µm indicate that the main clay mineral is smectite. Based on XRF analysis, the smectite is a montmorillonite with the formula {Na0.67 Ca0.1}[Al1.19 Mg0.62 Fe3+0.19] (Si3.78 Al0.22 O10) (OH)2. FTIR data show that interlayer water from smectite is liberated after ~24 h heating at 200 °C. Stable isotopic composition of precipitations have been monitored in the Hateg basin and in a neighbored area situated in the Apuseni mountains. The results show the same meteoric water line (LMWL) with the equation δD = 7.9 ⁎ δ18O + 8.14 for both sites. Stable isotope data on clay fraction less than 2 µm show that the structural water from smectites formed under different environmental conditions during the Maastrichtian have re-equilibrated isotopically with the present meteoric water. © 2009 Elsevier B.V. All rights reserved.
1. Introduction In the Haţeg basin, the research activity on Upper Cretaceous continental sediments and their rich faunal assemblages has a long and interesting tradition. This began with the work of baron Franz von Nopcsa who published in four different languages several papers concerning the deposits and their dinosaur, pterosaur, turtle and crocodilian assemblages (Nopcsa, 1900, 1914, 1923, 1926). Systematic research was restarted in the nineteen-eighties when the lithostratigraphy and chronostratigraphy of the deposits have been updated. At present, a rich vertebrate fauna with saurischians, ornithischians, ornithopods, pteropods, anurians, crocodilians and multituberculates has been described (Grigorescu, 1984; Grigorescu et al., 1985; Radulescu and Samson, 1986; Grigorescu and Hahn, 1987; Grigorescu, 1992; Csiki and Grigorescu, 1998; Grigorescu et al., 1999; Csiki and Grigorescu, 2000; Buffetaut et al., 2002; Codrea et al., 2002; Smith et al., 2002; Venczel and Csiki, 2003; Weishampel et al., 2003; Van Itterbeeck et al., 2004). Bojar et al. (2005) investigated facies and palaeosols from this area in order to get information about the conditions that controlled their
⁎ Corresponding author. E-mail address: [email protected] (A.-V. Bojar). 0169-1317/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2009.04.005
formation and to have a better understanding of the continental Upper Cretaceous in which dinosaur lived. According to this study, the observed changes in palaeosol features along Sibişel valley (in the NE sector of the basin) have been interpreted as the result of progressive cooling and enhanced tectonic activity during the Maastrichtian. In the present study we investigate the environmental record in the clay minerals from the Haţeg basin. For this purpose mineralogical (XRD, RX, FTIR analysis on clays) as well as stable isotope investigations have been carried out. The stable isotope investigations were done both on precipitations collected from the region as well as on clay minerals. 2. Geology of the region The south-western Southern Carpathians are mainly composed of basement nappes as the Getic and the Danubian nappes, separated by the ophiolitic Severin unit. In the Haţeg region, the oldest deposits overlying the Getic basement are Lower Jurassic continental clastic sediments, which gradually shift in Middle Jurassic to marine limestones and marls. Between the Upper Jurassic and the Aptian, reef and fore-reef limestones were deposited (Stilla, 1985). A major inversion took place during the end of the Aptian and beginning of the Albian, when the whole area was exhumed and eroded, as indicated by the bauxite deposits accumulated within the dolines developed on top of the exposed limestones. Facies changes and erosion were
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Fig. 1. A) Geological map of the study area; B) Haţeg basin: the distribution of the sampling points is shown.
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Fig. 2. A) RDX and B) FTIR spectra of smectites separated from the fraction less than 2 µm from Tuştea and Sibişel Valley.
related to closure of the Severin ocean, collision and stacking of the Supragetic units on the top of the Getic tectonic units. This event was also documented by K–Ar, 40Ar–39Ar, fission-track dating as well as sedimentological investigations (Grünfelder et al., 1983; Bojar et al., 1998; Dallmeyer et al., 1998; Willingshofer et al., 2001). During the late Albian to Campanian, coarse to fine grained clastics were deposited on shelf to outer slope environments (Melinte and Bojar, 2006 and references therein). The deposition of Maastrichtian continental deposits correlates with the stacking of the Getic nappe on the top of the Danubian realm, as well as uplift of the surrounding areas and orogenic collapse (Bojar et al., 1998; Willingshofer et al., 2001; Iancu et al., 2005).
Within the Haţeg basin, from Maastrichtian to early Paleogene two different continental formations are known: the Densuş-Ciula and the Sânpetru Formations, both represented by continental deposits. The Densuş Ciula Formation crops out in the north-western and central part of the basin and it is divided into three sub-formations, with a total thickness of around 2 km (Anastasiu and Csobuka, 1989; Grigorescu et al., 1990a,b). The Lower Densuş Ciula Sub-formation contains lacustrine marls with volcanoclasts, lying discordantly on the uppermost Campanian flysch deposits (Grigorescu and Melinte, 2001). The Middle Densuş Ciula Sub-formation is represented by matrix supported conglomerates, cross-bedded sandstones and massive red mudstones. The Palaeogene sediments of the Upper
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Table 1 Mineralogical composition of the clay fraction b2 µm. Location
Sample
Smectite
Illite
Chlorite
Kaolinite
Mixed layer
Tuştea
m 01 m 4.2.1 m 4.2.3 m 4.4.1 74 70 70a 92 94 96 85
89 91 94 86 43 57 40 68 55 54 46
7 7 4 10 34 30 37 16 20 15 24
– – – Traces 23 9 14 16 25 31 30
4 2 2 4 – 4 9 – – – –
– – – – Traces Traces – – – – –
Bărbat V.
Location 6 Sibişel Location 5 Sibişel Location 3 Sibişel
Densuş-Ciula Sub-formation are devoided of volcanoclastic material, as well as of dinosaur remains. The Sânpetru Formation crops out mainly along Râul Mare and Sibişel valleys. The Maastrichtian age for the Middle Densuş Ciula Subformation and Sânpetru Formation is indicated by fresh water gastropod assemblages including Bauxia bulimoides, Gastrobulimus munieri, Rognacia abreviata, Ajkaia cf. gregaria, and a palynological assemblage, dominated by spores with secondary gymnosperms and angiosperms (Antonescu et al., 1983; Pana et al., 2002; Bojar et al., 2005; Van Itterbeeck et al., 2005). Facies distribution of the Sânpetru Formation was investigated by Grigorescu et al., 1990a,b; Bojar et al., 2005; Therrien, 2005. The dinosaur assemblage includes Magyarosaurus dacus, Zalmoxes robustus, Zalmoxes shqiperorim, Telmatosaurus transsylvanicus, Euronychodon (Grigorescu and Csiki, 2002; Weishampel et al., 2003). Preliminary magnetostratigraphy for the Sânpetru Formation, suggests that the beginning of sedimentation started at the end of chron C32n (probably b 72 Ma) (Panaiotu and Panaiotu, 2002). All the other palaeomagnetic sites distributed upstream in younger deposits have only reversed polarity and the corresponding time interval is probably chron 31. The mean palaeolatitude of Haţeg Basin is best estimated from palaeomagnetic results obtained from contemporaneous magmatic activity: 27° N ± 5° (Patraşcu et al., 1992; Panaiotu, 1998). In the Haţeg basin, burial of the Maastrichtian strata by younger Paleogene and Neogene deposits was limited to a few hundred meters. 3. Analytical methods and materials 3.1. Clay separation and mineralogy Sample preparation generally followed the methods described by Whitting (1965) and Tributh (1991). Dispersion of clay particles and destruction of organic matter was achieved by treatment with dilute hydrogen peroxide. Separation of the clay fraction was carried out by centrifugation. The exchange complex of each sample (b2 µm) was saturated with Mg and K using chloride solutions by shaking. Similar to the methods of Kinter and Diamond (1956), the preferential orientation of the clay minerals was obtained by suction through a porous ceramic plate. The samples were studied by means of X-ray diffraction (XRD) using a Philips 1710 diffractometer with an automatic divergent slit, 0.1° receiving slit, Cu LFF tube 45 kV, 40 mA, and a single-crystal graphite monochromator. The measuring time was 1 s in step-scan mode and step size of 0.02°. Bulk samples as well as the clay fractions b2 µm were analyzed. To avoid disturbance of the orientation during drying, the samples were equilibrated over 7 days in saturated NH4NO3 solution. Next, expansion tests were made, using ethylenglycol, glycerol and DMSO, as well as contraction tests by heating the samples up to 550 °C. After each step, the samples were run from an angle of 2 to 40°. The clay minerals were identified and quantified according to Schulz (1964), Thorez (1975), Riedmüller (1978), Brindley and Brown (1980), Moore and Reynolds (1997), and Wilson (1989). FTIR (Fourier Transform Infrared Spectroscopy) was done on a Perkin Elmer Paragon 500 instrument. The sample (1 mg)
was powdered with 200 mg KBr. This mixture was pressed to a disk of 10 mm diameter. The sample chamber was purged with dried N2. The analyses were performed between 400 and 4000 cm− 1. The resolution of the measurements is 2 cm− 1. The XRF analysis were run at Austrian Research Center, Seibersdorf, using a Philips PW2400. The sample powder was mixed with 1:5 with di-Lithiumtetraborat (Spectromelt) and melt in Pt recipients to form a disk. 3.2. Stable isotope measurements The measurements of oxygen and hydrogen stable isotopes on clays were done in the Stable Isotopic Laboratory of the University of New Mexico, Albuquerque. All the measurements were done in duplicate. Oxygen stable isotope measurements were performed using a silicate line with Ni bombs. The samples were first heated at 200°C under vacuum for 1 day and then fluorinated with BrF5 at 550 °C for ~1 day. The oxygen was cryogenically cleaned and stable isotopes measured on a Finnigan MAT XP Mass Spectrometer. For the deuterium isotopic measurements the samples were also heated under vacuum one day at 200 °C, and than measured on a TC/EA apparatus in continuous flow (Sharp et al., 2001). Standard deviation is better than 2‰ for δD and 2‰ for δ18O. The collection of rain water has been done following the recommendation of Clark and Fritz (2000). We started to collect rain water in August 2005 and ended in August 2006. For each collected rain sample, temperatures were measured as well. For the Apuseni Mountains, collection of rain water started in December 2004 and ended in August 2006 (Perşoiu et al., 2007). The isotopic measurements of water were done at the Stable Isotope Laboratory, Joanneum Research, Graz. Deuterium was measured using an elemental analyzer (EA) configured with a Cr packed reactor held isothermally at 1050 °C. Oxygen was measured with a fully automated device for the classical CO2–water equilibration technique coupled to a Finnigan DELTA Plus mass spectrometer working in dual inlet mode. Results are reported in ‰ versus SMOW. Standard deviation is better than 1‰ and 0.2‰ for δD and δ18O, respectively. 4. Maastrichtian deposits in the Haţeg Basin The clays investigated in this study are from several outcrops indicated on Fig. 1 and described by Bojar et al. (2005). The Middle Densuş-Ciula Sub-formation is well represented at Tuştea quarry, situated at the northern border of the basin. Here a 10 m vertical escarpment comprises two levels of massive red mudstones intercalated with conglomerates and cross-stratified sandstones. The channel bodies show laterally crosscutting and alternating sandstones and conglomerates indicating unstable channelized flow with discharge fluctuations. The inter-channel areas, starved of coarse sediment supply, were site of pedogenesis. The palaeosols show a red mud horizon with blocky structure characterized by the presence of well developed vertical roots and burrows and a horizon with calcareous concretions. The thickness and distribution of the calcrete levels indicate multiply buried, moderate to strongly developed soils (Retallack, 2001), most probably formed on a stable terrace, close to the basin border. The described paleosols can be classified as calcisols (Mack and James,1994). These palaeosols contain fossil dinosaur eggs, bones, teeth, mollusc shells and plants. Associated with some of the concretion layers, just above them, dinosaurs nesting sites together with embryonic/hatchling skeletal relicts were found. Based on these remains, the eggs are thought to belong to a hadrosaurid, namely Telmatosaurus transsylvanicus (Grigorescu et al., 1994). XRD analysis show that in the fraction b2 µm, smectite dominates with up to 94 mass percent (Fig. 2A). Other clay minerals present in very small amounts are: illite, in the range of 4 to 10 mass percent, and kaolinite, 2 to 4 mass percent. Chlorite could be detected in traces only in one sample.
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Fig. 3. A) Isotopic composition of precipitations from Haţeg; B) Local meteoric water lines (LMWL) from Haţeg and Apuseni mountains; measured and calculated compositions of dehydrated smectites.
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The section along Bărbat Valley, south of the Pui locality, displays parallel laminated mudstones with numerous levels of concretions. Along Bărbat Valley, the strata dip with a few degrees toward the south, a 22 m thick vertical profile being opened along the valley. The facies are represented by coarse sandstones to conglomerates and alluvial plain deposits with palaeosols. For the paleosols, characteristic are the presence of a red horizon with drab-haloed traces, a level with parallel lamination and a level with calcareous concretions. The presence of calcrete levels up to 40 cm in thickness indicates high maturity of the soil and a distal position in report with the active channels. The pedofacies varies from cumulic to buried soil profiles. The sequences along Bărbat Valley were deposited at the margin of an
alluvial plain or on the distal part of a fan. Smectite is again the most frequent clay mineral, in the range of 40 to 57 mass %. Illite becomes more frequent than at Tuştea, and shows values up to 37 mass %. Chlorite is also present in the clay fraction (9-23 mass %), while the amount of kaolinite is low (Table 1). The Sânpetru Formation crops out mainly along Sibişel and Valea Mare Valleys. The Sânpetru facies is dominated by fluvial deposits, as described along the Sibişel Valley. Detailed mapping and description of the sequences and the facies are given in Bojar et al. (2005). The type of palaeosols from location 6 (Fig. 1) is dominated by calcisols, while vertisols without a calcic horizon are present only sporadically. Smectite is the most frequent clay mineral, with 55 to 68 mass %,
Fig. 4. A) Infrared spectra during stepwise heating of clays showing dehydrations. B) RDX of stepwise heated smectites.
A.-V. Bojar et al. / Applied Clay Science 45 (2009) 155–163 Table 2 Stable isotope composition of precipitation in the Haţeg basin and the calculated isotopic composition of smectites. Month
08.2005 08.2005 09.2005 09.2005 10.2005 11.2005 11.2005 12.2005 01.2006 01.2006 02.2006 02.2006 03.2006 04.2006 04.2006 05.2006 05.2006 06.2006 06.2006 07.2006 07.2006
δD
− 25.2 − 49.4 − 35.2 − 84.0 − 56.4 − 124.5 − 104.6 − 111.3 − 148.0 − 106.4 − 150.9 − 120.1 − 146.9 − 49.0 − 50.,2 − 72.7 − 51.9 − 51.1 − 20.6 − 21.1 − 16.8
δ18O
− 3.8 − 3.8 − 7.6 − 11.6 − 9.2 − 17.2 − 14.1 − 14.3 − 19.6 − 14.4 − 20.4 − 16.2 − 19.1 − 7.7 − 7.5 − 9.4 − 6.7 − 7.8 − 3.3 − 4.0 − 3.0
Air temperature
Calculated smectite
Calculated smectite
(°C)
δD
δ18O
20 19 16 14 5 0 3 2 −1 −6 2 −3 0 2 12 10 20 15 20 19 23 Mean calculated values of smectite
− 67.06 − 91.5 − 78.0 − 127.2 − 101.9 − 171.3 − 150.6 − 157.6 − 195.0 − 154.8 − 197.1 − 168.4 − 193.6 − 95.2 − 93.9 − 116.9 − 93.7 − 94.1 − 62.5 − 63.1 − 58.0 − 120.5
22.2 18.5 21.1 15.6 20.2 13.3 15.7 15.8 11.2 17.7 9.7 15.2 11.4 22.4 20.2 18.7 19.3 19.3 22.6 22.1 22.3 17.8
subordinately chlorite and illite being also present (Fig. 2). Progressively, toward location 5, the predominant type of paleosol changes from calcisols to vertisols. At location 5 and 3, the palaeosols display the following horizons, from top to bottom: organic rich grey-green mudstones, mudstones, calcrete underlined again by grey-green mudstones. Variations from this type of soil occur as the organic rich or the calcrete layer are sometimes missing. At location 3, the amount of chlorite and illite exceeds that of smectite (Table 1). 5. Stable isotope composition and mineralogy of smectites The distribution of the O and H stable isotopes in the rain water from Haţeg area as well as the monthly variation across the years are given in Table 1 and Fig. 3a. The slope of the regression line for the δ18O-T relationship is 0.52 (Fig. 3a), which is similar with the slope calculated by Rozanski et al. (1993) for continental interiors. In Fig. 3b the precipitation data from the Haţeg basin are shown together with data from the Apuseni Mountains (Perşoiu et al., 2007). The data from both sites show similar LMWL which are δD = 7.94⁎δ18O + 8.14 for the Haţeg basin and δD = 7.87⁎δ18O + 8.14 for the Apuseni Mountains (Fig. 3b). The calculated formula of montmorillonite based on XRF-analysis is: {Na0.67 Ca0.1}[Al1.19 Mg0.62 Fe3+0.19] (Si3.78 Al0.22 O10) (OH)2. The FTIR spectra of the fraction b2 µm have in the OH-stretching vibration region a band at 3622 cm− 1 (Fig. 2b). The bands at 3435 cm− 1 and 3637 cm− 1 are related to stretching and bending vibration of H2O-molecule. These
Table 3 δD isotopic values in various phases. Phase
δD
− 74‰ (measured isotopic composition of cumulated absorption, interlayer, and structural water) Smectite heated previously − 142‰ (measured isotopic at 200 °C for 24 h composition of structural water) Absorption and interlayer − 36‰ (calculated value for water for not heated smectite absorption and interlayer water)
Smectite not heated
Air moisture
− 130‰ (measured)
14 weight% water total
5 weight% water 9 weight% water (calculated) 12% humidity
161
bands confirm that the main clay mineral is smectite. In the lower wave number region Si–O stretching appears at 1031 cm− 1. The aluminous character of smectite is underlined by the band at 915 cm− 1 (AlAlOH). Small shoulders at 817 and 1417 cm− 1 are related to traces of carbonate minerals and at 795 cm− 1 to quartz. The assignment of the bands follows Farmer (1974); Van der Marel and Beutelspacher (1976) and Burzu (2007). In order to measure the stable isotopic composition of hydrogen from the hydroxyl and oxygen from the hydroxyl and SiO4 positions in the smectites, absorption and interlayer water were removed. It is known that adsorbed and interlayer water of clays exchange rapidly with atmospheric vapor at ambient temperatures (Moum and Rosenqvist, 1958; Savin and Epstein, 1970). Tests for removing nonstructural water were done on a STX1 smectite. The samples were heated to 200 °C and after each heating step an infrared spectrum and X-ray diffraction were performed. Infrared spectra show that only after 24 h of heating all the interlayer water is removed, 12 h heating being is insufficient (Fig. 4a). X-ray diffraction of heated STX 1 standard shows the collapse of the (001) layer (Fig. 4b) due to removing of the interlayer water. Unheated smectite shows a (001) dspacing of about 14.7 Å. After 3.5 h at 200 °C the d-spacing is 10.4 Å, heating longer than 24 h does not change the layer distance. One smectite sample was not heated previously and its deuterium isotopic composition was measured. The δD value is −74‰, being different from the value of the same sample (− 142‰) heated under vaacum at 200 °C for 24 h (Table 3). In the same day, the δD value of the air moisture at the site were the sample was measured (Albuquerque, New Mexico) was − 130‰ (Mel Strong, personal communication). Using the measured value and the water content in the non heated and heated smectite, the isotopic composition of the absorption and interlayer water were calculated. The isotopic compositions of various phases are shown in Table 2. Using the equations of Yeh and Savin (1977) and Yeh (1980) we calculated the δ18O and δD values of smectites in equilibrium with the rain water (Table 2). For the calculation of each value, we used the monthly measured stable isotopic values of rain. The calculated values define a line parallel with the present meteoric water line. The measured isotope compositions of smectites from the Haţeg basin, dehydrated at 200 °C are given in Table 4 and plotted in Fig. 3b. 6. Discussions and conclusions The profiles from Tuştea, Bărbat Valley and bottom part of the sequence along the Sibişel valley show similar types of paleosols. The red coloration of the mudstone intercalations as well as the presence of this type of soil are indicative of a semi-arid climate with wet and dry seasons, and rainfall-evaporation interplay. The progressive decrease of the soil maturity from Bărbat to Sibişel is related to different sedimentation rates at the two sites and to the more distal position of Bărbat Valley outcrops relative to the channel belt. Besides Table 4 Measured stable isotopic compositions of smectites from the Hateg basin. sample smectite
δD
δ18O
m0.1, Tuştea m4.2.1, Tuştea m4.2.3, Tuştea m4.4.1, Tuştea avrom 70, Bărbat Valley avrom 70a, Bărbat Valley avrom 73, Bărbat Valley avrom 92, location 6, Sânpetru avrom 94, location 6, Sânpetru avrom 96, location 5, Sânpetru avrom 98, location 5, Sânpetru avrom 85, location 3, Sânpetru Mean measured smectite:
− 143.4 − 145.8 − 155.1 − 166.2 − 165.3 − 154.7 − 103.2 − 111.6 − 118.7 − 109.2 − 113.5 − 99.4 − 132.2
19.9 18.7 20.7 19.9 17.6 16.5 16.8 14.9 15.3 15.8 17.8 14.6 17.4
Valley Valley Valley Valley Valley
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the difference in maturity between the two already mentioned sites, there are also changes in the type of paleosol along Sibişel valley from a generally well drained, periodically water logged soils, towards soils indicating rather stagnant water conditions. Based also on the stable isotope composition of calcretes, this was interpreted by Bojar et al. (2005) as the result of a climatic shift towards cooler and/or wetter conditions. Unstable tectonic conditions toward the top of the sequence accumulated along the Sibişel Valley are supported by the presence of massive channel conglomerates at location 3, changes from smectite to illite-chlorite dominated clay mineralogy (Chamley, 1989) as well as by increase in minerals indicating erosion from a crystalline substrates as quartz and feldspar. In conclusion, the general trend towards younger Maastrichtian deposits indicate both a climatic change as well as a shift from relative stable tectonic conditions towards more unstable ones (Bojar et al., 2005; Therrien, 2006). The smectites listed in Table 4 were collected from Maastrichtian sequences deposited under different environmental conditions. The FTIR data show that all the investigated smectites, separated from the fraction less than 2 µm are montmorillonite. The measured isotopic compositions of smectites in Fig. 3b, are distributed along the calculated line for smectites in equilibrium with the recent meteoric water. Moreover, mean oxygen and hydrogen isotopic compositions, for calculated and measured values are close each other (Tables 2, 3 and Fig. 3b). We interpret this trend as reflecting the re-equilibration of structural water from smectite with the recent meteoric waters. A similar interpretation was given by Savin and Epstein (1970) and Lawrence and Taylor (1971) for kaolinites and montmorillonites formed at different latitudes. The values from Table 3 show that the fractionation of hydrogen between absorption and interlayer water in smectite and vapor is 94‰ at room temperature (ca. 20 °C). This is even larger than the hydrogen fractionation between liquid and vapor which is ~80‰ at 20 °C (Horita and Wesolowski, 1994; Halas, 2008) but less than the fractionation between ice and vapor which is ~120 °C (Merlivat and Nief, 1967). This indicates that the structure of the interlayer and absorption water is similar with the water in ice phase. It also suggests that the hydrogen from the structural water is not in equilibrium with the hydrogen form the water vapors. Acknowledgements FWF P16258-N06 to Ana-Voica Bojar is acknowledged for founding this work. Zachary D. Sharp and Viorel Atudorei (University of New Mexico) are acknowledged for assistance during isotope measurements. The paper benefit from the constructive comments of the journal editor and an anonymous reviewer, which are kindly acknowledged. References Anastasiu, N., Csobuka, D., 1989. Non-marine Uppermost cretaceous deposits from the Stei-Densuş Region (Haţeg Basin): sketch for a Facies model. Revue de Geologie Academia Romana 35, 45–53. Antonescu, E., Lupu, D., Lupu, M., 1983. Correlation palynologique du Cretace terminal du sud-est des Monts Metaliferi et de depression de Haţeg et de Rusca Montana. Annales de L'Institut de Geologie et de Geophysique, Bucharest, vol. 59, pp. 71–77. Bojar, A.-V., Neubauer, F., Fritz, H., 1998. Cretaceous to Cenozoic thermal evolution of the south-western South Carpathians: evidence from fission-track thermochronology. Tectonophysics 297, 229–249. Bojar, A.-V., Grigorescu, D., Ottner, F., Csiki, Z., 2005. Paleoenvironmental interpretation of dinosaur- and mammal-bearing continental Maastrichtian deposits, Haţeg basin, Romania. Geological Quarterly 49, 205–222. Brindley, G.W., Brown, G., 1980. Crystal structures of clay minerals and their X-ray identification. Mineralogical Society of London. 495 pp. Buffetaut, E., Grigorescu, D., Csiki, Z., 2002. A new giant pterosaur with a robust skull from the Latest Cretaceous of Romania. Naturwissenschaften 89, 180–184. Burzu, E., 2007. Magnetic Properties of Non-Metallic Inorganic Compounds Based on Transition Elements Phyllosilicates Subvolume I5α. Springer. 537 pp. Chamley, H., 1989. Clay Mineralogy. Springer. 623 pp. Clark, I., Fritz, P., 2000. Environmental Isotopes in Hydrogeology. Lewis Publishers. 328 pp.
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A new method for preparation and treatment of oriented aggregate samples of soil clays for X-ray diffraction analysis. Soil Science 81, 111–120. Lawrence, J.R., Taylor Jr., H.P., 1971. Deuterium and oxygen-18 correlation: clay minerals and hydroxides in Quaternary soils compared to meteoric waters. Geochimica et Cosmochimica Acta 35, 993–1003. Mack, G.H., James, C.W., 1994. Paleoclimate and the global distribution of paleosols. Journal of Geology 102, 360–366. Melinte, M., Bojar, A.-V., 2006. Upper Cretaceous marine red beds in the Haţeg area (SW Romania). Mesozoic and Cenozoic vertebrates and Paleoenvironments. Editura Ars Docendi, Bucharest 167–174. Merlivat, L., Nief, G., 1967. Fractionnement isotopique lors des changements detats solide-vapeur et liquide-vapeur de l’eau a des temperatures inferieures a 0 Degrees C. Tellus 19, 122–127. Moore, D.M., Reynolds Jr., R.C., 1997. X – Ray Diffraction and the Identification and Analysis of Clay Minerals. Oxford Univ. 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Paleo-ecological significance of the continental gastropod assemblages from the Maastrichtian dinosaur beds of the Haţeg Basin. Acta Paleontologica Romaniae 3, 337–343. Panaiotu, C., 1998. Paleomagnetic constraints on the geodynamic history of Romania. In: Sledzinski, J. (Ed.) Monograph of Southern Carpathians. Reports on Geodesy, vol. 7. pp. 205–216.
A.-V. Bojar et al. / Applied Clay Science 45 (2009) 155–163 Panaiotu, C., Panaiotu, C., 2002. Palaeomagnetic studies. In: The 7th European Workshop of vertebrate palaeontology. Abstract Volume Excursion Field Guide, vol. 59. Patraşcu, S., Bleahu, M., Panaiotu, C., 1992. The paleomagnetism of the Upper Cretaceous magmatic rocks in the Banat area of the South Carpathians: tectonic implications. Tectonophysics 213, 314–352. Perşoiu, A., Bojar, A.-V., Onac, B.P., 2007. Stable isotopes in cave ice: what do they tell us?, Studia Universitatis Babeş-Bolyai. Geologia 52 (1), 59–62. Radulescu, C., Samson, P.-M., 1986. Precisions sur les affinities des multitubercules (Mammalia) du Cretace superieur de Romanie. Comptes Rendus de l'Academie des Sciences Paris II/304, 1825–1830. Retallack, G.J., 2001. Soils of the past. An introduction to palaeopedology. Blackwell Science. 404 pp. Riedmüller, G., 1978. Neoformations and transformations of clay minerals in Tectonic shear zones. Tschermaks Mineralogische Petrographische Mitteilungen 25, 219–242. Rozanski, K., Araguas-Araguas, L., Gonfiantini, R., 1993. Isotopic patterns in modern global precipitation. In: Swart, P.K., Lohmann, K.C., McKenzie, J., Savin, S. (Eds.), Continental Isotope Indicators of climate. American Geophysical Union Monograph, vol. 78, pp. 1–37. Savin, S.M., Epstein, S., 1970. The oxygen and hydrogen isotope geochemistry of clay minerals. Geochimica and Cosmochimica Acta 34, 35–42. Schulz, L.G., 1964. Quantitative interpretation of mineralogical composition from X-ray and chemical data of the Pierre Shales. Geological Survey Professional Paper 391C, 1–31. Sharp, Z.D., Atudorei, V., Durakiewicz, T., 2001. A rapid method of hydrogen and oxygen isotope ratios from water and hydrous minerals. Chemical Geology 178, 197–210. Smith, T., Codrea, V.A., Sasaran, E., Van Iterbeeck, J., Bultynck, P., Csiki, Z., Dica, P., Farcas, C., Garcia, G., Godefroit, P., 2002. A new exceptional vertebrate site from the Late Cretaceous of Haţeg Basin (Romania). Studia Universitas Babes-Bolyai, Geologia, Special Volume, vol. 1, pp. 321–330. Stilla, A., 1985. Geologie de la region de Haţeg-Cioclovina-Pui-Banita (Carpathes Meridionales). Anuarul Institutului de Geologie si Geofizica 66, 92–197. Therrien, F., 2005. Paleoenvironments of the latest Cretaceous (Maastrichtian) dinosaurs of Romania: insights from fluvial deposits and palaeosols of the Transylvanian and Haţeg basins. Paleogeography, Paleoclimatology, Paleoecology 218, 15–56.
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Applied Clay Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c l a y
Stable isotope and mineralogical investigations on clays from the Late Cretaceous sequences, Haţeg Basin, Romania Ana-Voica Bojar a,⁎, Franz Ottner b, Hans-Peter Bojar c, Dan Grigorescu d, Aurel Perşoiu e a
Institute of Earth Sciences, Geology and Palaeontology, Karl-Franzens University, Heinrichstrasse 26, A-8010 Graz, Austria Institute for Applied Geology, Peter Jordan Strasse 70, A-1190 Wien, Austria Landesmuseum Joanneum, Department of Mineralogy, Raubergasse 10, A-8010 Graz, Austria d Department of Geology and Geophysics, Bucharest University, Bd. Bălcescu 1, R-010041 Bucharest, Romania e Department of Geology, University of South Florida, 4202 E. Fowler Ave., SCA 528, Tampa, FL, USA b c
a r t i c l e
i n f o
Article history: Received 18 November 2008 Received in revised form 1 April 2009 Accepted 4 April 2009 Available online 14 April 2009 Keywords: Stable isotopes Smectites Precipitations Paleosols Maastrichtian Haţeg Basin
a b s t r a c t In the Haţeg basin, South Carpathians, a thick continental sequence accumulated during the Maastrichtian. The alluvial sequences are characterized by the formation of paleosol horizons developed on the alluvial plain. In order to investigate the environmental signal stable isotope and mineralogical investigations have been carried out on smectites from paleosol. The RX as well as the FTIR spectra of the fraction b 2 µm indicate that the main clay mineral is smectite. Based on XRF analysis, the smectite is a montmorillonite with the formula {Na0.67 Ca0.1}[Al1.19 Mg0.62 Fe3+0.19] (Si3.78 Al0.22 O10) (OH)2. FTIR data show that interlayer water from smectite is liberated after ~24 h heating at 200 °C. Stable isotopic composition of precipitations have been monitored in the Hateg basin and in a neighbored area situated in the Apuseni mountains. The results show the same meteoric water line (LMWL) with the equation δD = 7.9 ⁎ δ18O + 8.14 for both sites. Stable isotope data on clay fraction less than 2 µm show that the structural water from smectites formed under different environmental conditions during the Maastrichtian have re-equilibrated isotopically with the present meteoric water. © 2009 Elsevier B.V. All rights reserved.
1. Introduction In the Haţeg basin, the research activity on Upper Cretaceous continental sediments and their rich faunal assemblages has a long and interesting tradition. This began with the work of baron Franz von Nopcsa who published in four different languages several papers concerning the deposits and their dinosaur, pterosaur, turtle and crocodilian assemblages (Nopcsa, 1900, 1914, 1923, 1926). Systematic research was restarted in the nineteen-eighties when the lithostratigraphy and chronostratigraphy of the deposits have been updated. At present, a rich vertebrate fauna with saurischians, ornithischians, ornithopods, pteropods, anurians, crocodilians and multituberculates has been described (Grigorescu, 1984; Grigorescu et al., 1985; Radulescu and Samson, 1986; Grigorescu and Hahn, 1987; Grigorescu, 1992; Csiki and Grigorescu, 1998; Grigorescu et al., 1999; Csiki and Grigorescu, 2000; Buffetaut et al., 2002; Codrea et al., 2002; Smith et al., 2002; Venczel and Csiki, 2003; Weishampel et al., 2003; Van Itterbeeck et al., 2004). Bojar et al. (2005) investigated facies and palaeosols from this area in order to get information about the conditions that controlled their
⁎ Corresponding author. E-mail address: [email protected] (A.-V. Bojar). 0169-1317/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2009.04.005
formation and to have a better understanding of the continental Upper Cretaceous in which dinosaur lived. According to this study, the observed changes in palaeosol features along Sibişel valley (in the NE sector of the basin) have been interpreted as the result of progressive cooling and enhanced tectonic activity during the Maastrichtian. In the present study we investigate the environmental record in the clay minerals from the Haţeg basin. For this purpose mineralogical (XRD, RX, FTIR analysis on clays) as well as stable isotope investigations have been carried out. The stable isotope investigations were done both on precipitations collected from the region as well as on clay minerals. 2. Geology of the region The south-western Southern Carpathians are mainly composed of basement nappes as the Getic and the Danubian nappes, separated by the ophiolitic Severin unit. In the Haţeg region, the oldest deposits overlying the Getic basement are Lower Jurassic continental clastic sediments, which gradually shift in Middle Jurassic to marine limestones and marls. Between the Upper Jurassic and the Aptian, reef and fore-reef limestones were deposited (Stilla, 1985). A major inversion took place during the end of the Aptian and beginning of the Albian, when the whole area was exhumed and eroded, as indicated by the bauxite deposits accumulated within the dolines developed on top of the exposed limestones. Facies changes and erosion were
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Fig. 1. A) Geological map of the study area; B) Haţeg basin: the distribution of the sampling points is shown.
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Fig. 2. A) RDX and B) FTIR spectra of smectites separated from the fraction less than 2 µm from Tuştea and Sibişel Valley.
related to closure of the Severin ocean, collision and stacking of the Supragetic units on the top of the Getic tectonic units. This event was also documented by K–Ar, 40Ar–39Ar, fission-track dating as well as sedimentological investigations (Grünfelder et al., 1983; Bojar et al., 1998; Dallmeyer et al., 1998; Willingshofer et al., 2001). During the late Albian to Campanian, coarse to fine grained clastics were deposited on shelf to outer slope environments (Melinte and Bojar, 2006 and references therein). The deposition of Maastrichtian continental deposits correlates with the stacking of the Getic nappe on the top of the Danubian realm, as well as uplift of the surrounding areas and orogenic collapse (Bojar et al., 1998; Willingshofer et al., 2001; Iancu et al., 2005).
Within the Haţeg basin, from Maastrichtian to early Paleogene two different continental formations are known: the Densuş-Ciula and the Sânpetru Formations, both represented by continental deposits. The Densuş Ciula Formation crops out in the north-western and central part of the basin and it is divided into three sub-formations, with a total thickness of around 2 km (Anastasiu and Csobuka, 1989; Grigorescu et al., 1990a,b). The Lower Densuş Ciula Sub-formation contains lacustrine marls with volcanoclasts, lying discordantly on the uppermost Campanian flysch deposits (Grigorescu and Melinte, 2001). The Middle Densuş Ciula Sub-formation is represented by matrix supported conglomerates, cross-bedded sandstones and massive red mudstones. The Palaeogene sediments of the Upper
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Table 1 Mineralogical composition of the clay fraction b2 µm. Location
Sample
Smectite
Illite
Chlorite
Kaolinite
Mixed layer
Tuştea
m 01 m 4.2.1 m 4.2.3 m 4.4.1 74 70 70a 92 94 96 85
89 91 94 86 43 57 40 68 55 54 46
7 7 4 10 34 30 37 16 20 15 24
– – – Traces 23 9 14 16 25 31 30
4 2 2 4 – 4 9 – – – –
– – – – Traces Traces – – – – –
Bărbat V.
Location 6 Sibişel Location 5 Sibişel Location 3 Sibişel
Densuş-Ciula Sub-formation are devoided of volcanoclastic material, as well as of dinosaur remains. The Sânpetru Formation crops out mainly along Râul Mare and Sibişel valleys. The Maastrichtian age for the Middle Densuş Ciula Subformation and Sânpetru Formation is indicated by fresh water gastropod assemblages including Bauxia bulimoides, Gastrobulimus munieri, Rognacia abreviata, Ajkaia cf. gregaria, and a palynological assemblage, dominated by spores with secondary gymnosperms and angiosperms (Antonescu et al., 1983; Pana et al., 2002; Bojar et al., 2005; Van Itterbeeck et al., 2005). Facies distribution of the Sânpetru Formation was investigated by Grigorescu et al., 1990a,b; Bojar et al., 2005; Therrien, 2005. The dinosaur assemblage includes Magyarosaurus dacus, Zalmoxes robustus, Zalmoxes shqiperorim, Telmatosaurus transsylvanicus, Euronychodon (Grigorescu and Csiki, 2002; Weishampel et al., 2003). Preliminary magnetostratigraphy for the Sânpetru Formation, suggests that the beginning of sedimentation started at the end of chron C32n (probably b 72 Ma) (Panaiotu and Panaiotu, 2002). All the other palaeomagnetic sites distributed upstream in younger deposits have only reversed polarity and the corresponding time interval is probably chron 31. The mean palaeolatitude of Haţeg Basin is best estimated from palaeomagnetic results obtained from contemporaneous magmatic activity: 27° N ± 5° (Patraşcu et al., 1992; Panaiotu, 1998). In the Haţeg basin, burial of the Maastrichtian strata by younger Paleogene and Neogene deposits was limited to a few hundred meters. 3. Analytical methods and materials 3.1. Clay separation and mineralogy Sample preparation generally followed the methods described by Whitting (1965) and Tributh (1991). Dispersion of clay particles and destruction of organic matter was achieved by treatment with dilute hydrogen peroxide. Separation of the clay fraction was carried out by centrifugation. The exchange complex of each sample (b2 µm) was saturated with Mg and K using chloride solutions by shaking. Similar to the methods of Kinter and Diamond (1956), the preferential orientation of the clay minerals was obtained by suction through a porous ceramic plate. The samples were studied by means of X-ray diffraction (XRD) using a Philips 1710 diffractometer with an automatic divergent slit, 0.1° receiving slit, Cu LFF tube 45 kV, 40 mA, and a single-crystal graphite monochromator. The measuring time was 1 s in step-scan mode and step size of 0.02°. Bulk samples as well as the clay fractions b2 µm were analyzed. To avoid disturbance of the orientation during drying, the samples were equilibrated over 7 days in saturated NH4NO3 solution. Next, expansion tests were made, using ethylenglycol, glycerol and DMSO, as well as contraction tests by heating the samples up to 550 °C. After each step, the samples were run from an angle of 2 to 40°. The clay minerals were identified and quantified according to Schulz (1964), Thorez (1975), Riedmüller (1978), Brindley and Brown (1980), Moore and Reynolds (1997), and Wilson (1989). FTIR (Fourier Transform Infrared Spectroscopy) was done on a Perkin Elmer Paragon 500 instrument. The sample (1 mg)
was powdered with 200 mg KBr. This mixture was pressed to a disk of 10 mm diameter. The sample chamber was purged with dried N2. The analyses were performed between 400 and 4000 cm− 1. The resolution of the measurements is 2 cm− 1. The XRF analysis were run at Austrian Research Center, Seibersdorf, using a Philips PW2400. The sample powder was mixed with 1:5 with di-Lithiumtetraborat (Spectromelt) and melt in Pt recipients to form a disk. 3.2. Stable isotope measurements The measurements of oxygen and hydrogen stable isotopes on clays were done in the Stable Isotopic Laboratory of the University of New Mexico, Albuquerque. All the measurements were done in duplicate. Oxygen stable isotope measurements were performed using a silicate line with Ni bombs. The samples were first heated at 200°C under vacuum for 1 day and then fluorinated with BrF5 at 550 °C for ~1 day. The oxygen was cryogenically cleaned and stable isotopes measured on a Finnigan MAT XP Mass Spectrometer. For the deuterium isotopic measurements the samples were also heated under vacuum one day at 200 °C, and than measured on a TC/EA apparatus in continuous flow (Sharp et al., 2001). Standard deviation is better than 2‰ for δD and 2‰ for δ18O. The collection of rain water has been done following the recommendation of Clark and Fritz (2000). We started to collect rain water in August 2005 and ended in August 2006. For each collected rain sample, temperatures were measured as well. For the Apuseni Mountains, collection of rain water started in December 2004 and ended in August 2006 (Perşoiu et al., 2007). The isotopic measurements of water were done at the Stable Isotope Laboratory, Joanneum Research, Graz. Deuterium was measured using an elemental analyzer (EA) configured with a Cr packed reactor held isothermally at 1050 °C. Oxygen was measured with a fully automated device for the classical CO2–water equilibration technique coupled to a Finnigan DELTA Plus mass spectrometer working in dual inlet mode. Results are reported in ‰ versus SMOW. Standard deviation is better than 1‰ and 0.2‰ for δD and δ18O, respectively. 4. Maastrichtian deposits in the Haţeg Basin The clays investigated in this study are from several outcrops indicated on Fig. 1 and described by Bojar et al. (2005). The Middle Densuş-Ciula Sub-formation is well represented at Tuştea quarry, situated at the northern border of the basin. Here a 10 m vertical escarpment comprises two levels of massive red mudstones intercalated with conglomerates and cross-stratified sandstones. The channel bodies show laterally crosscutting and alternating sandstones and conglomerates indicating unstable channelized flow with discharge fluctuations. The inter-channel areas, starved of coarse sediment supply, were site of pedogenesis. The palaeosols show a red mud horizon with blocky structure characterized by the presence of well developed vertical roots and burrows and a horizon with calcareous concretions. The thickness and distribution of the calcrete levels indicate multiply buried, moderate to strongly developed soils (Retallack, 2001), most probably formed on a stable terrace, close to the basin border. The described paleosols can be classified as calcisols (Mack and James,1994). These palaeosols contain fossil dinosaur eggs, bones, teeth, mollusc shells and plants. Associated with some of the concretion layers, just above them, dinosaurs nesting sites together with embryonic/hatchling skeletal relicts were found. Based on these remains, the eggs are thought to belong to a hadrosaurid, namely Telmatosaurus transsylvanicus (Grigorescu et al., 1994). XRD analysis show that in the fraction b2 µm, smectite dominates with up to 94 mass percent (Fig. 2A). Other clay minerals present in very small amounts are: illite, in the range of 4 to 10 mass percent, and kaolinite, 2 to 4 mass percent. Chlorite could be detected in traces only in one sample.
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Fig. 3. A) Isotopic composition of precipitations from Haţeg; B) Local meteoric water lines (LMWL) from Haţeg and Apuseni mountains; measured and calculated compositions of dehydrated smectites.
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The section along Bărbat Valley, south of the Pui locality, displays parallel laminated mudstones with numerous levels of concretions. Along Bărbat Valley, the strata dip with a few degrees toward the south, a 22 m thick vertical profile being opened along the valley. The facies are represented by coarse sandstones to conglomerates and alluvial plain deposits with palaeosols. For the paleosols, characteristic are the presence of a red horizon with drab-haloed traces, a level with parallel lamination and a level with calcareous concretions. The presence of calcrete levels up to 40 cm in thickness indicates high maturity of the soil and a distal position in report with the active channels. The pedofacies varies from cumulic to buried soil profiles. The sequences along Bărbat Valley were deposited at the margin of an
alluvial plain or on the distal part of a fan. Smectite is again the most frequent clay mineral, in the range of 40 to 57 mass %. Illite becomes more frequent than at Tuştea, and shows values up to 37 mass %. Chlorite is also present in the clay fraction (9-23 mass %), while the amount of kaolinite is low (Table 1). The Sânpetru Formation crops out mainly along Sibişel and Valea Mare Valleys. The Sânpetru facies is dominated by fluvial deposits, as described along the Sibişel Valley. Detailed mapping and description of the sequences and the facies are given in Bojar et al. (2005). The type of palaeosols from location 6 (Fig. 1) is dominated by calcisols, while vertisols without a calcic horizon are present only sporadically. Smectite is the most frequent clay mineral, with 55 to 68 mass %,
Fig. 4. A) Infrared spectra during stepwise heating of clays showing dehydrations. B) RDX of stepwise heated smectites.
A.-V. Bojar et al. / Applied Clay Science 45 (2009) 155–163 Table 2 Stable isotope composition of precipitation in the Haţeg basin and the calculated isotopic composition of smectites. Month
08.2005 08.2005 09.2005 09.2005 10.2005 11.2005 11.2005 12.2005 01.2006 01.2006 02.2006 02.2006 03.2006 04.2006 04.2006 05.2006 05.2006 06.2006 06.2006 07.2006 07.2006
δD
− 25.2 − 49.4 − 35.2 − 84.0 − 56.4 − 124.5 − 104.6 − 111.3 − 148.0 − 106.4 − 150.9 − 120.1 − 146.9 − 49.0 − 50.,2 − 72.7 − 51.9 − 51.1 − 20.6 − 21.1 − 16.8
δ18O
− 3.8 − 3.8 − 7.6 − 11.6 − 9.2 − 17.2 − 14.1 − 14.3 − 19.6 − 14.4 − 20.4 − 16.2 − 19.1 − 7.7 − 7.5 − 9.4 − 6.7 − 7.8 − 3.3 − 4.0 − 3.0
Air temperature
Calculated smectite
Calculated smectite
(°C)
δD
δ18O
20 19 16 14 5 0 3 2 −1 −6 2 −3 0 2 12 10 20 15 20 19 23 Mean calculated values of smectite
− 67.06 − 91.5 − 78.0 − 127.2 − 101.9 − 171.3 − 150.6 − 157.6 − 195.0 − 154.8 − 197.1 − 168.4 − 193.6 − 95.2 − 93.9 − 116.9 − 93.7 − 94.1 − 62.5 − 63.1 − 58.0 − 120.5
22.2 18.5 21.1 15.6 20.2 13.3 15.7 15.8 11.2 17.7 9.7 15.2 11.4 22.4 20.2 18.7 19.3 19.3 22.6 22.1 22.3 17.8
subordinately chlorite and illite being also present (Fig. 2). Progressively, toward location 5, the predominant type of paleosol changes from calcisols to vertisols. At location 5 and 3, the palaeosols display the following horizons, from top to bottom: organic rich grey-green mudstones, mudstones, calcrete underlined again by grey-green mudstones. Variations from this type of soil occur as the organic rich or the calcrete layer are sometimes missing. At location 3, the amount of chlorite and illite exceeds that of smectite (Table 1). 5. Stable isotope composition and mineralogy of smectites The distribution of the O and H stable isotopes in the rain water from Haţeg area as well as the monthly variation across the years are given in Table 1 and Fig. 3a. The slope of the regression line for the δ18O-T relationship is 0.52 (Fig. 3a), which is similar with the slope calculated by Rozanski et al. (1993) for continental interiors. In Fig. 3b the precipitation data from the Haţeg basin are shown together with data from the Apuseni Mountains (Perşoiu et al., 2007). The data from both sites show similar LMWL which are δD = 7.94⁎δ18O + 8.14 for the Haţeg basin and δD = 7.87⁎δ18O + 8.14 for the Apuseni Mountains (Fig. 3b). The calculated formula of montmorillonite based on XRF-analysis is: {Na0.67 Ca0.1}[Al1.19 Mg0.62 Fe3+0.19] (Si3.78 Al0.22 O10) (OH)2. The FTIR spectra of the fraction b2 µm have in the OH-stretching vibration region a band at 3622 cm− 1 (Fig. 2b). The bands at 3435 cm− 1 and 3637 cm− 1 are related to stretching and bending vibration of H2O-molecule. These
Table 3 δD isotopic values in various phases. Phase
δD
− 74‰ (measured isotopic composition of cumulated absorption, interlayer, and structural water) Smectite heated previously − 142‰ (measured isotopic at 200 °C for 24 h composition of structural water) Absorption and interlayer − 36‰ (calculated value for water for not heated smectite absorption and interlayer water)
Smectite not heated
Air moisture
− 130‰ (measured)
14 weight% water total
5 weight% water 9 weight% water (calculated) 12% humidity
161
bands confirm that the main clay mineral is smectite. In the lower wave number region Si–O stretching appears at 1031 cm− 1. The aluminous character of smectite is underlined by the band at 915 cm− 1 (AlAlOH). Small shoulders at 817 and 1417 cm− 1 are related to traces of carbonate minerals and at 795 cm− 1 to quartz. The assignment of the bands follows Farmer (1974); Van der Marel and Beutelspacher (1976) and Burzu (2007). In order to measure the stable isotopic composition of hydrogen from the hydroxyl and oxygen from the hydroxyl and SiO4 positions in the smectites, absorption and interlayer water were removed. It is known that adsorbed and interlayer water of clays exchange rapidly with atmospheric vapor at ambient temperatures (Moum and Rosenqvist, 1958; Savin and Epstein, 1970). Tests for removing nonstructural water were done on a STX1 smectite. The samples were heated to 200 °C and after each heating step an infrared spectrum and X-ray diffraction were performed. Infrared spectra show that only after 24 h of heating all the interlayer water is removed, 12 h heating being is insufficient (Fig. 4a). X-ray diffraction of heated STX 1 standard shows the collapse of the (001) layer (Fig. 4b) due to removing of the interlayer water. Unheated smectite shows a (001) dspacing of about 14.7 Å. After 3.5 h at 200 °C the d-spacing is 10.4 Å, heating longer than 24 h does not change the layer distance. One smectite sample was not heated previously and its deuterium isotopic composition was measured. The δD value is −74‰, being different from the value of the same sample (− 142‰) heated under vaacum at 200 °C for 24 h (Table 3). In the same day, the δD value of the air moisture at the site were the sample was measured (Albuquerque, New Mexico) was − 130‰ (Mel Strong, personal communication). Using the measured value and the water content in the non heated and heated smectite, the isotopic composition of the absorption and interlayer water were calculated. The isotopic compositions of various phases are shown in Table 2. Using the equations of Yeh and Savin (1977) and Yeh (1980) we calculated the δ18O and δD values of smectites in equilibrium with the rain water (Table 2). For the calculation of each value, we used the monthly measured stable isotopic values of rain. The calculated values define a line parallel with the present meteoric water line. The measured isotope compositions of smectites from the Haţeg basin, dehydrated at 200 °C are given in Table 4 and plotted in Fig. 3b. 6. Discussions and conclusions The profiles from Tuştea, Bărbat Valley and bottom part of the sequence along the Sibişel valley show similar types of paleosols. The red coloration of the mudstone intercalations as well as the presence of this type of soil are indicative of a semi-arid climate with wet and dry seasons, and rainfall-evaporation interplay. The progressive decrease of the soil maturity from Bărbat to Sibişel is related to different sedimentation rates at the two sites and to the more distal position of Bărbat Valley outcrops relative to the channel belt. Besides Table 4 Measured stable isotopic compositions of smectites from the Hateg basin. sample smectite
δD
δ18O
m0.1, Tuştea m4.2.1, Tuştea m4.2.3, Tuştea m4.4.1, Tuştea avrom 70, Bărbat Valley avrom 70a, Bărbat Valley avrom 73, Bărbat Valley avrom 92, location 6, Sânpetru avrom 94, location 6, Sânpetru avrom 96, location 5, Sânpetru avrom 98, location 5, Sânpetru avrom 85, location 3, Sânpetru Mean measured smectite:
− 143.4 − 145.8 − 155.1 − 166.2 − 165.3 − 154.7 − 103.2 − 111.6 − 118.7 − 109.2 − 113.5 − 99.4 − 132.2
19.9 18.7 20.7 19.9 17.6 16.5 16.8 14.9 15.3 15.8 17.8 14.6 17.4
Valley Valley Valley Valley Valley
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the difference in maturity between the two already mentioned sites, there are also changes in the type of paleosol along Sibişel valley from a generally well drained, periodically water logged soils, towards soils indicating rather stagnant water conditions. Based also on the stable isotope composition of calcretes, this was interpreted by Bojar et al. (2005) as the result of a climatic shift towards cooler and/or wetter conditions. Unstable tectonic conditions toward the top of the sequence accumulated along the Sibişel Valley are supported by the presence of massive channel conglomerates at location 3, changes from smectite to illite-chlorite dominated clay mineralogy (Chamley, 1989) as well as by increase in minerals indicating erosion from a crystalline substrates as quartz and feldspar. In conclusion, the general trend towards younger Maastrichtian deposits indicate both a climatic change as well as a shift from relative stable tectonic conditions towards more unstable ones (Bojar et al., 2005; Therrien, 2006). The smectites listed in Table 4 were collected from Maastrichtian sequences deposited under different environmental conditions. The FTIR data show that all the investigated smectites, separated from the fraction less than 2 µm are montmorillonite. The measured isotopic compositions of smectites in Fig. 3b, are distributed along the calculated line for smectites in equilibrium with the recent meteoric water. Moreover, mean oxygen and hydrogen isotopic compositions, for calculated and measured values are close each other (Tables 2, 3 and Fig. 3b). We interpret this trend as reflecting the re-equilibration of structural water from smectite with the recent meteoric waters. A similar interpretation was given by Savin and Epstein (1970) and Lawrence and Taylor (1971) for kaolinites and montmorillonites formed at different latitudes. The values from Table 3 show that the fractionation of hydrogen between absorption and interlayer water in smectite and vapor is 94‰ at room temperature (ca. 20 °C). This is even larger than the hydrogen fractionation between liquid and vapor which is ~80‰ at 20 °C (Horita and Wesolowski, 1994; Halas, 2008) but less than the fractionation between ice and vapor which is ~120 °C (Merlivat and Nief, 1967). This indicates that the structure of the interlayer and absorption water is similar with the water in ice phase. It also suggests that the hydrogen from the structural water is not in equilibrium with the hydrogen form the water vapors. Acknowledgements FWF P16258-N06 to Ana-Voica Bojar is acknowledged for founding this work. Zachary D. Sharp and Viorel Atudorei (University of New Mexico) are acknowledged for assistance during isotope measurements. The paper benefit from the constructive comments of the journal editor and an anonymous reviewer, which are kindly acknowledged. References Anastasiu, N., Csobuka, D., 1989. Non-marine Uppermost cretaceous deposits from the Stei-Densuş Region (Haţeg Basin): sketch for a Facies model. Revue de Geologie Academia Romana 35, 45–53. Antonescu, E., Lupu, D., Lupu, M., 1983. Correlation palynologique du Cretace terminal du sud-est des Monts Metaliferi et de depression de Haţeg et de Rusca Montana. Annales de L'Institut de Geologie et de Geophysique, Bucharest, vol. 59, pp. 71–77. Bojar, A.-V., Neubauer, F., Fritz, H., 1998. Cretaceous to Cenozoic thermal evolution of the south-western South Carpathians: evidence from fission-track thermochronology. Tectonophysics 297, 229–249. Bojar, A.-V., Grigorescu, D., Ottner, F., Csiki, Z., 2005. Paleoenvironmental interpretation of dinosaur- and mammal-bearing continental Maastrichtian deposits, Haţeg basin, Romania. Geological Quarterly 49, 205–222. Brindley, G.W., Brown, G., 1980. Crystal structures of clay minerals and their X-ray identification. Mineralogical Society of London. 495 pp. Buffetaut, E., Grigorescu, D., Csiki, Z., 2002. A new giant pterosaur with a robust skull from the Latest Cretaceous of Romania. Naturwissenschaften 89, 180–184. Burzu, E., 2007. Magnetic Properties of Non-Metallic Inorganic Compounds Based on Transition Elements Phyllosilicates Subvolume I5α. Springer. 537 pp. Chamley, H., 1989. Clay Mineralogy. Springer. 623 pp. Clark, I., Fritz, P., 2000. Environmental Isotopes in Hydrogeology. Lewis Publishers. 328 pp.
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