Print version ISSN 1026-8774
Rev. mex. cienc. geol vol.25 no.2 México Aug. 2008
Carbon and oxygen isotope geochemistry of Neoproterozoic limestones of the Shahabad Formation, Bhima basin, Karnataka, southern India
Geoquímica de isótopos de carbono y oxígeno de calizas neoproterozoicas de la Formación Shahabad, cuenca de Bhima, Karnataka, sur de la India
Ramasamy Nagarajan1,2, Alcides N. Sial3, John S. ArmstrongAltrin4,*, Jayagopal Madhavaraju5, and Raghavendra Nagendra1
1 Department of Geology, Anna University, Chennai600 025, India.
2 Present Address: School of Civil Engineering, SASTRA University, Thirumalaisamudram, Thanjavur 613 402, India.
3 Núcleo de Estudos Geoquímicos Laboratório de Isótopos Estáveis (NEG LABISE), Departmento de Geologia, Universidade Federal de Pernambuco, C.P.7852, Recife, PE, 50670000 Brazil.
4 Universidad Autónoma del Estado de Hidalgo, Centro de Investigaciones en Ciencias de la Tierra, Ciudad Universitaria, Carretera PachucaTulancingo Km. 4.5, 42184 Pachuca, Hidalgo, México. * email@example.com
5 Estación Regional del Noroeste, Instituto de Geología, Universidad Nacional Autónoma de México, Apartado Postal 1039, 83000 Hermosillo, Sonora, México.
Manuscript received: March 17, 2007
Corrected manuscript received: January 25, 2008
Manuscript accepted: January 28, 2008
Petrography, major (including four trace elements), stable isotopes (carbon and oxygen), and 87Sr/86Sr geochemistry of limestones of the Shahabad Formation, Bhima basin, Karnataka, southern India are reported. These limestones show a narrow range of δ13C (1.341.96) and δ18O ( 6.04 to 7.61 ) values. The petrographic study reveals the presence of microsparite and micro and macrostylolites. The δ13C and 87Sr/86Sr values indicate that these limestones were deposited during the late Neoproterozoic age and the δ18 O values also are very similar to the average Proterozoic carbonate values. Mn and Sr concentrations and low Mn/Sr ratio (<1) together with the stable and radiogenic isotope data suggest that the studied samples are wellpreserved or scarcely altered limestones and probably have retained their primary isotopic signatures.
Key words: geochemistry, stable isotopes, delta oxygen, delta carbon, strontium isotopes, carbonate rocks, diagenesis, Bhima basin, India.
En este trabajo se reportan resultados de la geoquímica de isótopos estables (carbono y oxígeno) y de elementos mayores (incluyendo cuatro elementos traza) en las calizas de la Formación de Shahabad, cuenca de Bhima, Karnataka, en India meridional. Las calizas de la cuenca de Bhima muestran un estrecho intervalo de los valores de δ13C (1.34 a 1.96) y δ18O ( 6.04 a 7.61). El estudio petrográfico revela la presencia de dolomía, microesparita y calcita recristalizada con micro y macroestilolitos. Los valores de δ13C y 87Sr/86Sr revelan que estas calizas fueron depositadas durante el Neoproterozoico Tardío y los valores de δ18O son muy parecidos a los valores promedio de los carbonatos del Proterozoico. Las concentraciones de Mn y Sr y los valores bajos de Mn/Sr (< 1), junto con los datos de isótopos estables y radiogénicos, indican que estas calizas están bien preservadas o escasamente alteradas y probablemente han conservado su firma isotópica primaria.
Palabras clave: geoquímica, isótopos estables, delta oxígeno, delta carbono, isótopos de estroncio, rocas carbonatadas, diagénesis, cuenca de Bhima, India.
Chemical composition of sedimentary rocks is widely used to delineate specific units of carbonate and clastic strata (Primmer et al., 1990). In recent years, much work has been focused on constraining primary δ13C and δ18O signatures of Precambrian carbonate sequences to understand the depositional processes, the evolution of the oceanatmospheric system, and the interactions of biotic and abiotic processes during the Earth's history (Burdett et al., 1990; Veizer et al., 1992a, 1992b; Knoll et al., 1995). The temporal δ13C fluctuations of sedimentary carbonates represent secular variations of δ13C in ocean water. Strontium isotope stratigraphy is a reliable and precise tool for stratigraphic correlations and age determinations. If these carbonates precipitate in contact with seawater and remain relatively unaltered by postdepositional events during diagenesis, their strontium content should retain a seawater strontium isotope signature (Banner and Kaufman, 1994; Burke et al., 1982; DePaolo and Ingram, 1985). Although extensive isotopic data are available from different parts of the world for Proterozoic sedimentary rocks, only a few studies have been published on samples from the Bhima basin (Sathyanarayan et al., 1987; Kumar et al., 1997; Kumar et al., 1999; Nagarajan, 2003).
In this study, elemental and stable and radiogenic isotope data of limestones from the Malkhaid quarry (named after Malkhaid village) are presented. The quarry of the Malkhaid village (located near the Mulkod and Mudbol villages; Figure 1) belongs to the Shahabad Formation of the Bhima basin. The Malkhaid quarry section was selected for the present study because it is considered as the best exposed vertical section (60 m) in the Shahabad Formation. Our main aim was to test if these limestones have retained their original chemical and isotopic compositions without significant postdepositional changes.
Sedimentary formations of the Bhima basin are exposed as an array of narrow, EW stretching, sygmoidal strips arranged in an en echelon pattern, with a thickness of about 300 m, and extended over an area of 5,000 km2 (Figure 1). These sedimentary rocks mainly comprise an alternating sequence of clastic and carbonate rocks (Rao et al., 1975; Misra et al., 1987; Kale, 1990; Kale et al., 1990; Nagarajan, 2003). The Mesoproterozoic Kaladgi sugergroup and the Neoproterozoic Bhima group overlie the Archean granitegreenstone basement in Karnataka, southern India. The Archean granitegreenstone terrain mainly consists of TTG (tonalitetrondhjemitegranodiorite), popularly known as Peninsular gneisses (Dharwar greenstone belts). The sedimentary rocks of the Mesoproterozoic Kaladgi supergroup and Neoproterozoic Bhima group were deposited on the eroded edges of the Dharwar craton (Kumar and Srinivasan, 2002). The Kaladgi sedimentary basin is exposed EW for a length of 160 km, with a width varying from 40 to 65 km, and covers an area of about 8,000 km2 to the west of the Bhima basin. The Bhima group is younger than the Kaladgi supergroup, and the Bhima basin rocks have been affected by intense faulting. Major structural faults across the basin define the boundaries of the different sectors (Kale and Peshwa, 1995). As a result of EW trending faults, the limestones found in the middle part of the basin directly rest on the granitic rocks.
King (1872) coined the term Bhima Series and divided the sedimentary rocks into Muddebihal sandstones and Talikote limestone. Mahadevan (1947) proposed a new threefold classification: 1) Lower Bhima Series, 2) Middle Bhima Series, and 3) Upper Bhima Series. Later, Rao et al. (1975) assigned the Group status to the sedimentary rocks of the Bhima basin and divided them into five distinct formations: 1) Rabanpalli Formation, 2) Shahabad Formation, 3) Halkal Shale, 4) Katamedavarhalli Formation, and 5) Harwal Shale. Misra et al. (1987) subdivided the Bhima Group into Sedam Subgroup (Rabanpalli Formation and Shahabad Formation) and Andola Subgroup (Halkal Shale, Katamedavarhalli Formation, and HarwalGogi Shale). They identified a sedimentation break between the Sedam and Andola subgroups and interpreted it as a paraconformity. Later, Malur and Nagendra (1994) introduced a new name for Shahabad Formation as Kurkunta Formation. Recently, the clastic rocks of the Rabanpalli Formation were studied in detail by Nagarajan et al. (2007a, 2007b). The classification proposed by Rao et al. (1975) has been adopted for the present study. The five formations seem to represent two major cycles of sedimentation. The Rabanpalli and Shahabad Formations form the first cycle whereas the Halkal, Katamedavarhalli and Harwal Formations form the second cycle of sedimentation. Each cycle of sedimentation commenced with an arenaceous facies.
The limestone member is the dominant lithotype of the Bhima basin and is classified under Shahabad and Katamedavarhalli Formations. The Shahabad Formation is exposed in the central and eastern parts of the Bhima basin (16°15' to 17°35' Lat N; 76°15' to 77°30' Long E; Figure 1). The Shahabad limestones can be classified as (1) flaggy, pale blue limestone, (2) blocky, light grey limestone, (3) variegated, bluish green or pink/pale blue limestone, (4) massive, dark/bluish grey limestone, and (5) flaggy, dark grey/bluish grey argillaceous limestone (Rao et al., 1975; Malur and Nagendra, 1994). These limestones occupy an area of 2,000 km2 in the Bhima basin. According to Kale et al. (1990) the vertical thickness of Shahabad Formation is less than 75 m. Representative limestone samples of Malkhaid quarry (60 m depth) were used for this study. The limestone deposits of Malkhaid area (Figure 1) exhibit grey to dark grey and yellowish grey colour. Malkhaid limestones are well exposed near the villages Mulkod and Mudbol. These limestones are classified under the Shahabad Formation, Bhima basin (Figure 1). The wellexposed limestones are quarried by Zuari Cement (private company) for cement manufacturing. The samples were collected from the quarry section, which consists of six 10m high benches. The vertical profile of the limestone quarry (Figure 2) shows a black cotton soil as surface cover, which is underlain by limestone boulders mixed with yellowish and dark grey limestones. The whole limestone section is micritic in nature and varies in color at different depths. Macrostylolites are identified at certain places with increasing depth.
Twelve limestone samples of the Malkhaid quarry (collected perpendicular to the strike at the different stages; Figure 2) were analyzed for major and some trace elements in the XRF Laboratory, University of Kentucky. The XRF detection limits for RbSr and MnFe pairs were consistent with the systematic behavior suggested by Verma and Santoyo (2005). Carbon and oxygen isotope analyses were carried out at the Stable Isotope Laboratory (LABISE) of the Federal University of Pernambuco, Brazil.
For carbon and oxygen isotopic determinations, CO2 was extracted from powdered carbonates in a high vacuum line after reaction with orthophosphoric acid at 25°C, and cry ogenically cleaned, according to the method described by Craig (1957). CO2 gas released by this method was analyzed for carbon and oxygen isotopes in a double inlet, triple collector SIRA II mass spectrometer, using the reference gas BSC (Borborema Skarn Calcite), which calibrated against NBS18, NBS19, and NBS20 has a value of 11.28 ± 0.004 pdb for δ18O and 8.58 ± 0.02 PDB for δ13C. The results are expressed in the notation δ (per mil) in relation to international PDB scale.
Two representative samples were selected for Sr isotope analyses. Limestone samples were leached in 1 N ammonium acetate prior to acid digestion. Sr was separated in 2.5 M HCl using BioRad AG50W X8 200400 mesh cation exchange resin. Total procedure blank for Sr samples prepared with this method was <200 pg. For mass spectrometry, Sr samples were loaded onto single Ta filaments with 1 N phosphoric acid. Sr samples were analyzed on a VG Sector 5430 multiple collector mass spectrometer. A 87Sr intensity of 1V (1 x 1011 A) ± 10% was maintained and the 87Sr/86Sr ratio was corrected for mass fractionation using 87Sr/86Sr = 0.1194 and an exponential law. The VG Sector 5430 mass spectrometer was operated in the peakjumping mode with data collected as 15 blocks of 10 ratios. For this instrument, NIST SRM987 gave a value of 0.710260 ± 11 (1 SD, n = 17). To facilitate comparison of Sr isotopic data from different laboratories we have adjusted the 87Sr/86Sr values of our limestone samples to NIST SRM987 87Sr/86Sr of 0.710230, following the practice of the MaxPlanck Institute, Mainz, Germany (see e.g., the data repository in Verma, 2002).
The limestones of Shahabad Formation are micritic (calmicrite) in nature. Stylolites and pressure solution structures are present in the limestones. Some of the pressure solution structures are related to horizontal compressional forces (probably resulting from tectonism). Most of the stylolites have parallel features (Figure 3ac). The limestones also exhibit crosscutting stylolites and fractures filled by calcite and quartz. Few limestone samples from the top of the section exhibit small grains of saddle dolomite (Figure 3d), which are seen adjacent to stylolites. The limestones also exhibit some mineral grains, which occur along the stylolites (Figure 3e). Limestones of Shahabad Formation show pressure solution and chemical deposition of fibrous voidfilling calcite (Figure 3f) on free surfaces of individual crystals and polycrystalline aggregates. Terrigenous particles like quartz and feldspar occur as aggregates and lenses in the interlaminar areas.
The results of major (in wt. %), four trace elements (in ppm), strontium isotopes, and carbon and oxygen isotopes () for the Malkhaid quarry section limestones are presented in Table 1. We also report mean values for all elements in these limestone samples without testing if these data represent a normal population and if there are any discordant outliers present. Sample MK11 would probably represent a discordant outlier for SiO2 and sample MK2 would be for Rb if the method and critical values proposed by Verma and QuirozRuiz (2006a, 2006b) are used for this purpose. Proper handling of discordant outliers would have improved the veracity of mean and standard deviation values, particularly for those parameters that have outlying observations (Verma et al., 2008).
The major and trace element variations with depth are shown in Figure 4. The limestones show high content of CaO (41.046.4 wt.%; except MK11). The distribution of SiO2 is reverse to that of CaO (9.1814.4 wt.%). Other elements like Al2O3 (0.571.86 wt.%), K2O (0.160.41 wt.%), Fe2O3 (0.110.93 wt.%), and Na2O (0.030.04 wt.%) are much lower than the CaO and SiO2 contents. Na2O content is uniform throughout the quarry section (Figure 4). The aluminum concentration is a reasonably good measure of detrital flux (Veizer, 1983). Positive correlations of A12O3 with TiO2, MgO and Fe2O3 (linear correlation coefficient, r = 0.96, 0.87, and 0.81, respectively; number of samples n = 12) are statistically significant at 99% confidence level (for more details on significance levels and the corresponding critical values, see Verma, 2005) and indicate that these elements are associated with detrital phases. Slight differences in the major element concentrations of the sample MK4 (Table 1) compared to other samples may be due to the presence of clay minerals formed along the stylolitic seams. The limestone samples of this study show very low Mg/Ca ratio (0.0050.030; Table 1), even though some minor saddle dolomite grains are present in a few samples (Figure 3d). These low values indicate that the studied samples are not dolomitized, because dolomitization would necessarily cause a marked increase in the Mg/Ca ratio of the limestones (e.g., Kaufman et al., 1992).
Trace element analyses show that the Ba content (1275,700 ppm) in the samples is much higher than the Sr (112350 ppm), Mn (77125 ppm), and Rb (1180 ppm) contents. The enrichment of Ba is particularly noted in the samples MK11 (5,700 ppm) and MK9 (2,300 ppm), which show stylolites and veins filled with insoluble residues. The recent shallow marine carbonates have Sr concentrations between 8,000 and 10,000 ppm (Milliman, 1974). The Sr contents of samples in this study (112350 ppm) are also much lower than the average value given for lithosphere carbonates (Sr = 610 ppm; Turekian and Wedepohl, 1961). The abnormal enrichment of Rb in sample MK2 (180 ppm; Table 1) may be due to the influx of clay minerals.
The carbon and oxygen isotope values range from 1.34 to 1.96 and 6.04 to 7.61, respectively. Two samples (MK1 and MK8) were analyzed for 87Sr/86Sr (0.70684 and 0.70696, respectively; Table 1).
Identification of primary isotopic signatures
Many criteria have been emphasized to assess the degree of postdepositional alteration in carbonate rocks (Hudson, 1977; Veizer et al., 1992a; Derry et al., 1992; Kaufman and Knoll, 1995). The variations in trace elements have been used as a technique to identify diagenetic alteration (e.g., Brand and Veizer, 1980; Ditchfield et al., 1994; Jones et al., 1994a, 1994b; Price and Sellwood, 1997; Podlaha et al., 1998; Hesselbo et al., 2000; Price et al., 2000; Jenkyns et al., 2002; Grocke et al., 2003). These studies suggest that high concentrations of Fe and Mn are mainly associated with negative δ18O and δ13C values. During diagenetic alteration by meteoric fluids, Mn may be incorporated and Sr may be expelled from the carbonate system (Brand and Veizer, 1980; Veizer, 1983). Hence, the diagenetic alteration of lowMg calcite will decrease the Sr content and increase the Mn content (Veizer, 1983). However, such a trend is not observed in the limestones of the Shahabad Formation because the linear correlation coefficient (r) between Mn and Sr (r = 0.16; n=12) is not statistically significant (see Verma, 2005, for statistical significance of r values).
Due to the distinct behavior of Mn and Sr during diagenesis (marine and meteoric) of limestones, Mn/Sr ratio is generally considered as a reliable indicator of the degree of alteration (Jacobsen and Kaufman, 1999). Many studies (Derry et al., 1992; Kaufman et al., 1992, 1993; Kah et al., 1999) reveal that the limestones with Mn/Sr < 2 generally display unaltered isotopic signature. Furthermore, Jacobsen and Kaufman (1999) proposed a model on the basis of trace elements and stable isotopes, and concluded that the limestones with Mn/Sr <2, δ18O values from 5 to 10 %o and Sr concentrations between 150 and 2,500 ppm show primary isotopic signatures. In the present study, the Mn/Sr ratios (0.260.86), δ18O values (7.61 to 6.04), and Sr concentrations (112350 ppm), fall well within these ranges and indicate the preservation of primary isotopic signatures.
Many studies have shown that carbon isotopic signatures are well preserved in Proterozoic carbonates (Schildlowski et al., 1975; Knoll et al., 1986), because pore spaces are sealed soon after the deposition, which inhibit subsequent fluidrock interaction and isotopic resetting (Buick et al., 1995), but meteoric diagenesis can still alter the primary carbon isotope compositions (Veizer, 1983; Kaufman and Knoll, 1995). Similarly, δ18O values of carbonate rocks are sensitive diagenetic indicators because the later fluidrock interactions tend to decrease the primary δ18O values imparted by seawater (Veizer, 1983). The diagenetic alteration of the primary δ13C signatures can be identified by the covariance relationship between δ13C and δ18O values. A significant positive correlation between δ513C and δ18O values is an indicator of δ13C alteration (Brasier et al., 1996). The lack of a statistically significant positive correlation between δ13C and 518O values (r=0.34, n=12; see Verma, 2005 for more details) indicates that diagenetic modification of primary δ13C values can be excluded. Thus, geochemical parameters such as Mn, Sr and Mn/Sr ratio, and the relationship between δ13C and δ18O strongly support that the limestones of the Shahabad Formation (Bhima basin) retained the primary isotopic signature of Neoproterozoic seawater.
Carbon isotopic composition
δ13C excursions studied worldwide imply that the oceanic environment has affected the carbon reservoir in a basin or on a global scale. Variations in the carbon isotopes of limestones and cooccurring organic matter record secular changes in the burial rate of the carbon phases with increasing δ13C values (Hayes, 1993). Postdepositional thermal alteration of organic matter often preserves primary carbon isotopic signatures in carbonate phases (Kah et al., 1999). Therefore, ancient carbonates commonly retain their primary carbon isotopic compositions (Marshall, 1992; Buick et al., 1995; Kaufman and Knoll, 1995; Knoll et al., 1995). During transgression, a greater amount of organic matter is stored in the marginal areas, resulting in the enrichment of 13C, whereas during regressive phases of the sea, the stored organic matter is eroded and oxidized, resulting in 12C enrichment in the deep ocean (Broecker, 1982).
In an isotopic study of the limestones from the Sedam area of the Shahabad Formation (Figure 1), Kumar et al. (1999) reported δ13C values ranging from 0%o to 3.7. In another study, Kumar et al. (1997) obtained a range of δ13C values between 0.89 and 3.59 for the Shahabad Formation and pointed out that the majority of the δ13C values cluster around 2PDB, except in the basal unit of the Shahabad Formation with a mean value of 3.25PDB. In the present study, the limestone samples show a narrower range of δ13C values (1.341.96 %o) but within the ranges observed by the previous workers. These values are close to the plateau values (2; Kaufman and Knoll, 1995) and are similar to the values obtained for limestone sections in Namibia (Grotzinger et al., 1995; Saylor et al., 1998) and Canada (Narbonne et al., 1994). In this context it is also important to point out that after ca. 600 Ma the 13C values in carbonates remained high (+2 to +4) until the PrecambrianCambrian boundary (Knoll et al., 1986; Fairchild and Spiro, 1987; Lambert et al., 1987; Kaufman et al., 1991). Afterwords, the 13C values in lower Cambrian carbonates were close to about 1. These data therefore provide age constraints for limestones of the Shahabad Formation.
Oxygen isotopic composition
Oxygen isotope studies of carbonate rocks have provided insight into Precambrian seawater chemistry (Perry and Tan, 1972; Veizer et al., 1992b). Oxygen isotopic compositions of carbonates are much prone to alteration during diagenesis (Hudson, 1977; Veizer, 1983). The results of this study are plotted in a δ13C vs. δ18O (Figure 5) cross plot diagram (Hudson, 1977), in which the Shahabad limestone samples plot in the fields of late cements and marine limestones. The δ18O of a carbonate precipitated from water depends chiefly on the δ18O composition and temperature of the water. Increasing lighter (more negative) δ18O value is connected with decreasing salinity and increasing temperatures (Hudson, 1977). The range of moderately depleted δ18O values in most limestones is supportive of cementation under mainly burial and/or meteoric conditions rather than by synsedimentary marine cements as in many tropical carbonate deposits. The depletion in 18O observed in geologically older carbonates, commonly ascribed to postdepositional isotope exchange with meteoric waters (Clayton and Degens, 1959; Keith and Weber, 1964; Schidlowski et al., 1975), also holds in the case of many Proterozoic carbonate formations. Limestones of the present study show a narrow range of 6.04 to 7.6l, which is comparable to the 'best preserved' δ18O mean value (7.5 ± 2) reported for most of the ProterozoicEarly Cambrian limestones (Brasier et al., 1990; Burdett et al., 1990; Kaufman et al., 1991; Veizer et al., 1992a; Hall and Veizer, 1996).
Strontium isotopic composition
The 87Sr/86Sr composition of seawater has been considered as a powerful tool for making correlations and indirect age assignment, reconstruction of global tectonics, and tracing diagenetic processes (Burke et al., 1982; Veizer, 1989; Banner, 2004; Halverson et al., 2007). 87Sr/86Sr of the modern ocean (0.7092) generally indicates a combination of hydrothermal alteration of the oceanic crust (0.7035) and input from continental weathering (0.7120; Edmond, 1992). The problems in applying strontium isotope stratigraphy to the Cenozoic record become more important for older time periods (Burke et al., 1982) and are particularly acute for the Precambrian, where the geological record is less complete or incomplete. However, the limited availability of biostratigraphic inferences and meager radiometric dating on the Precambrian rocks require chemostratigraphic methods to correlate and integrate the incomplete stratigraphic records (Knoll and Walter, 1992; Knoll, 2000). Hence, the Srisotope stratigraphy is generally applied to the Proterozoic sedimentary rocks. Limestone samples at depths of 12m (MK1) and 32m (MK8) were analysed for 87Sr/86Sr isotope and yielded values of 0.70684 (MK1) and 0.70696 (MK8). These samples (MK1 and MK8) are very low in Mn/Sr ratio (0.31 and 0.37, respectively) and have positive δ13C values (1.75%oPDB and 1.85%oPDB respectively). Kumar et al. (2002) noticed that the Upper Vindhyan carbonates are characterized by positive δ13C values at low 87Sr/86Sr (0.7068 ± 0.0002), which represent a Neoproterozoic interval of deposition. In general, diagenesis tends to increase 87Sr/86Sr values. Therefore, a very low 87Sr/86Sr value from any horizon can be interpreted as a maximum estimate of original seawater composition (Knoll, 2000). The 87Sr/86Sr values of this study show little variation (0.706840.70696). Furthermore, Sr isotopic composition and δ13C values of the present study are comparable to that of the upper Vindhyan carbonates, which suggests that the limestones of the Shahabad Formation were deposited during the Neoproterozoic age. Finally, the low 87Sr/86Sr, less positive δ13C values, and low Mn/Sr ratio indicate that the studied samples can be considered as well preserved marine limestones that have retained their primary chemical and isotopic signatures.
A petrographic study showed the presence of microstylolites and siliclastic veins in limestones of the Shahabad Formation. On the basis of chemical and isotopic data, the studied limestone samples are considered as wellpreserved limestones.
The authors thank Dr. Hendry Francis for his assistance in major and trace elements analyses. This manuscript has been greatly improved from indepth reviews by Prof. Yong Il Lee, and Dr. Nallappa Reddy. Our special thanks to Prof. Surendra P. Verma for his innovative ideas and useful suggestions. JSA wishes to express his gratefulness to SEPPROMEP (Programa de Mejoramiento del Profesorado; Grant No: UAEHGOPTC280), CONACYT (Consejo Nacional de Ciencia y Tecnología; 52574), and PAI (Programa Anual de Investigación; 69B), Mexico, for financial assistance.
Banner, J.L., 2004, Radiogenic isotopes: systematics and applications to earth surface processes and chemical stratigraphy: Earth Science Reviews, 65(34), 141194. [ Links ]
Banner, J.L., Kaufman, J., 1994, The isotopic record of ocean chemistry and diagenesis preserved in nonluminescent brachiopods from Mississippian carbonate rocks, Illinois and Missouri: Geologial Society of America Bulletin, 106(8), 10741082. [ Links ]
Brand, U., Veizer, J., 1980, Chemical diagenesis of a multi component carbonate system: 1. Trace elements: Journal of Sedimentary Petrology, 50, 12191236. [ Links ]
Brasier, M.D., Magaritz, M., Corfield, R., Huilin, L., Xiche, W., Lin, O., Zhiwen, J., Hamadi, B., Tinggui, H., Frazier, A.G., 1990, The carbon and oxygen isotope record of the PrecambrianCambrian boundary interval in China and Iran and their correlation: Geological Magazine, 127 (4), 319332. [ Links ]
Brasier, M.D., Shields, G., Kuleshov, V.N., Zhegallo, L.A., 1996, Integrated chemoand biostratigraphic calibration of early animal evolution: Neoproterozoicearly Cambrian of southwest Mongolia: Geological Magazine, 133(4), 445485. [ Links ]
Broecker, W.S., 1982, Glacial to interglacial changes in ocean chemistry: Progress in Oceanography, 11(2), 151197. [ Links ]
Buick, R., Marais, D., Knoll, A.H., 1995, Stable isotopic compositions of carbonates from the Mesoproterozoic Bangemall Group, northwestern Australia: Chemical Geology, 123(14), 153171. [ Links ]
Burdett, J.W., Grotzinger, J.P., Arthur, M.A., 1990, Did major changes in the stable isotope composition of Proterozoic seawater occur?: Geology, 18(3), 227230. [ Links ]
Burke, W.H., Denison, R.E., Hetherington, E.A., Koepnick, R.B., Nelson, F.F., Otto, J.B., 1982, Variations of seawater 87Sr/86Sr throughout Phanerozoic time: Geology, 10(10), 516519. [ Links ]
Clayton, R.N., Degens, E.T., 1959, Use of carbon isotope analysis of carbonate for differentiating freshwater and marine sediments: Bulletin of the American Association of Petroleum Geologists, 43, 890897. [ Links ]
Craig, H., 1957, Isotope standard for carbon and oxygen and correction factors for mass spectrometry analysis of carbon dioxide: Geochimica et Cosmochimica Acta, 12(12), 133149. [ Links ]
DePaolo, D.J., Ingram, B.L., 1985, Highresolution stratigraphy with strontium isotopes: Science, 227(4689), 938941. [ Links ]
Derry, L.A., Kaufman, A.J., Jacobsen, S.B., 1992, Sedimentary cycling and environmental change in the Late Proterozoic: evidence from stable and radiogenic isotopes: Geochimica et Cosmochimica Acta, 56(3), 13171329. [ Links ]
Ditchfield, P.W., Marshall, J.D., Pirrie, D., 1994, High latitude palaeotemperature variations: New data from the Thithonian to Eocene of James Ross Island, Antarctica: Palaeogeography, Palaeoclimatology, Palaeoecology, 107(12), 79101. [ Links ]
Edmond, J., 1992, Himalayan tectonics, weathering processes, and strontium isotope record in marine limestones: Science, 258(5088), 15941597. [ Links ]
Fairchild, I.J., Spiro, B., 1987, Petrological and isotopic implications of some contrasting Late Precambrian carbonates, NE Spitsbergen: Sedimentology, 34(6), 973989. [ Links ]
Grocke, D.R., Price, G.D., Ruffell, A.H., Mutterlose, J., Baraboshkin, E., 2003, Isotopic evidence for Late JurassicEarly Cretaceous climate change: Palaeogeography, Palaeoclimatology, Palaeoecology, 202(12), 97118. [ Links ]
Grotzinger, J.P., Bowring, S.A., Saylor, B.Z., Kaufman, A.J., 1995, Biostratigraphic and geochronologic constraints on early animal evolution: Science, 270(5236), 598604. [ Links ]
Hall, S.M., Veizer, J., 1996, Geochemistry of Precambrian carbonates: VII. Belt Supergroup, Montana and Idaho, USA: Geochimica et Cosmochimica Acta, 60(4), 667677. [ Links ]
Halverson, G.P., Dudás, F.O., Maloof A.C., Bowring, S.A., 2007, Evolution of the 87Sr/86Sr composition of Neoproterozoic seawater: Palaeogeography, Palaeoclimatology, Palaeoecology, 256(34), 103129. [ Links ]
Hayes, J.M., 1993, Factors controlling 13C contents of sedimentary organic compounds: Principles and evidence: Marine Geology, 113(12), 111125. [ Links ]
Hesselbo, S.P., Meister, C., Grocke, D.r., 2000, A potential global stratotype for the SinemurianPliensbachian boundary (Lower Jurassic), Robin Hood's Bay, UK: ammonite faunas and isotope stratigraphy: Geological Magazine, 137(6), 601607. [ Links ]
Hudson, J.D., 1977, Stable isotopes and limestone lithification: Journal of the Geological Society of London, 133(6), 637660. [ Links ]
Jacobsen, S.B., Kaufman, A.J., 1999, The Sr, C and O isotopic evolution of Neoproterozoic seawater: Chemical Geology, 161(13), 3757. [ Links ]
Jenkyns, H.C., Jones, C.E., Grocke, D.R., Hesselbo, S.P., Parkinson, D.N., 2002, Chemostratigraphy of the Jurassic System: applications, limitations and implications for paleoceanography: Journal of the Geological Society of London, 159(4), 351378. [ Links ]
Jones, C.E., Jenkyns, H.C., Hesselbo, S.P., 1994a, Strontium isotopes in Early Jurassic Seawater: Geochimica et Cosmochimica Acta, 58(4), 12851301. [ Links ]
Jones, C.E., Jenkyns, H.C., Coe, A.L., Hesselbo, S.P., 1994b, Strontium isotopes in Jurassic and Cretaceous Seawater: Geochimica et Cosmochimica Acta, 58(14), 30613074. [ Links ]
Kah, L.C., Sherman, A.G., Narbonne, G.M., Knoll, A.H., Kaufman, A.J., 1999, 813C stratigraphy of the Proterozoic Bylot supergroup, Baffin Island, Canada: implications for regional lithostratigraphic correlations: Canadian Journal of Earth Sciences, 36(3), 313332. [ Links ]
Kale, V.S., 1990, Problems of the Purana Basins, in Tandon, S.K., Gupta, K.R. (eds.), Challenging Areas in Earth Sciences for the Nineties: Memoir Geological Society of India, 18, 7793. [ Links ]
Kale, V.S., Peshwa, V.V., 1995, Bhima Basin: Bangalore, Geological Society of India, 142 p. [ Links ]
Kale, V.S., Mudholkar, A.V., Phansalkar, V.G., Peshwa, V.V., 1990, Stratigraphy of the Bhima Group: Journal of the Palaeontological Society of India, 35, 91103. [ Links ]
Kaufman, A.J., Knoll, A.H., 1995, Neoproterozoic variations in the Cisotopic composition of seawater: stratigraphic and biogeochemical implications: Precambrian Research, 73(14), 2749. [ Links ]
Kaufman, A.J., Heyes, J.M., Knoll, A.H., Germs, G. J. B., 1991, Isotopic compositions of carbonates and organic carbon from upper Proterozoic successions in Namibia: stratigraphic variation and the effects of diagenesis and metamorphism: Precambrian Research, 49(34), 301327. [ Links ]
Kaufman, A.J., Knoll, A.H., Awramik, S.M., 1992, Biostratigraphic and chemostratigraphic correlation of Neoproterozoic sedimentary successions: Upper Tindir Group, northwestern Canada, as a test case: Geology, 20(2), 181185. [ Links ]
Kaufman, A.J., Jacobsen, S.B., Knoll, A.H., 1993, The Vendian record of Sr and C isotopic variations in seawater: Implications for tectonics and paleoclimate: Earth and Planetary Science Letters, 120(34), 409430. [ Links ]
Keith, M.L., Weber, J.N., 1964, Carbon and oxygen isotopic composition of selected limestones and fossils: Geochimica et Cosmochimica Acta, 28(1011), 17871816. [ Links ]
King, W., 1872, The Cuddapah and Kurnool formations in Madras Presidency. Memoir. Geological Survey of India, 8(1), 1346. [ Links ]
Knoll, A. H., 2000, Learning to tell Neoproterozoic time: Precambrian Research, 100(13), 320. [ Links ]
Knoll, A.H., Walter, M.R., 1992, Latest Proterozoic stratigraphy and Earth history: Nature, 356(6371), 673678. [ Links ]
Knoll, A.H., Hayes, J.M., Kaufman, A.J., Swett, K., Lambert, I.B., 1986, Secular variations in carbon isotope ratios from upper Proterozoic successions of Svalbard and East Greenland: Nature, 321(6073), 832838. [ Links ]
Knoll, A.H., Kaufman, A.J., Semikhatov, M.A., 1995, The carbon isotope composition of Proterozoic carbonates: Riphean successions from northwestern Siberia (Anabar Maasif, Turukhansk uplift): American Journal of Science, 295, 823850. [ Links ]
Kumar, B., Das Sharma, S., Shukla, M., Sharma, M., 1999, Chronostratigraphic implication of Carbon and Oxygen isotopic compositions of the Proterozoic Bhima carbonates, southern India: Journal of the Geological Society of India, 53, 593600. [ Links ]
Kumar, B., Das Sharma, S., Sreenivas, B., Dayal, A.M., Rao, M.N., Dubey, N., Chawla, B.R., 2002, Carbon, oxygen and strontium isotope geochemistry of Proterozoic carbonate rocks of the Vindhyan Basin, central India: Precambrian Research, 113(12), 4363. [ Links ]
Kumar, G., Shankar, R., Maithy, P.K., Mathur, V.K., Bhattacharya, S.K., Jain, R.A., 1997, Terminal ProterozoicCambrian sequences in India: A review with special reference to Precambrian Cambrian boundary: The Palaeobotonist, 2, 1931. [ Links ]
Kumar, P.S., Srinivasan, R., 2002, Fertility of Late Archaean basement granite in the vicinity of Umineralised Neoproterozoic Bhima basin, peninsular India: Current Science, 82(5), 571576. [ Links ]
Lambert, I.B., Walter, M.R., Wenlong, Z., Songnian, L., Guogan, M., 1987, Palaeoenvironment and carbon isotope stratigraphy of Upper Proterozoic carbonates of the Yangtze platform: Nature, 325(6100), 140142. [ Links ]
Mahadevan, C., 1947, The Bhima Series and other rocks of Gulbarga district. Jour. Hyderabad: Geological Survey, 5(1), 160. [ Links ]
Malur, M. N., Nagendra, R., 1994, Lithstratigraphy of the Bhima Basin (Central Part), Karnataka, Southern India: Journal of the Paleontological Society of India, 39, 5560. [ Links ]
Marshall, J.D., 1992, Climatic and oceanographic isotopic signals from the carbonate rock record and their preservation: Geological Magazine, 129(2), 143160. [ Links ]
Milliman, J.D., 1974, Marine Carbonates: New York, Springer Verlag, 375 p. [ Links ]
Misra, R.N., Jayaprakash, A.V., Hans, S.K., Sundaram, V., 1987, Bhima Group of Upper Proterozoic a stratigraphic puzzle: Memoir Geological Society of India, 6, 227 237. [ Links ]
Nagarajan, R., 2003, Geochemistry and depositional environment of Neoproterozoic sediments of Bhima basin, Karnataka, South India: Chennai, India, Anna University, Ph.D. Thesis, 292 p. [ Links ]
Nagarajan, R., ArmstrongAltrin, J.S., Nagendra, R., Madhavaraju, J., Moutte, J., 2007a, Petrography and geochemistry of terrigenous sedimentary rocks in the Neoproterozoic Rabanpalli Formation, Bhima Basin, southern India: Implications for paleoweathering condition, provenance, and source rock composition: Journal of the Geological Society of India, 70(2), 297312. [ Links ]
Nagarajan, R., Madhavaraju, J., Nagendra, R., ArmstrongAltrin, J.S., Moutte, J., 2007b, Geochemistry of Neoproterozoic shales of Rabanpalli Formation, Bhima Basin, Northern Karnataka, Southern India: Implications for provenance and paleoredox conditions: Revista Mexicana Ciencias Geológicas, 24(2), 150160. [ Links ]
Narbonne, G.M., Kaufman, A.J., Knoll, A.H., 1994, Integrated chemostratigraphy and biostratigraphy of the Windermere Super Group, northwestern Canada: implications for Neoproterozoic correlations and the early evolution of animals: Geological Society of America Bulletin, 106(10), 12811292. [ Links ]
Perry, E.C., Jr. Tan, F.C., 1972, Significance of oxygen and carbon isotope variation in Early Precambrian cherts and carbonate rocks of southern Africa: Geological Society of America Bulletin, 83(3), 647664. [ Links ]
Podlaha, O.G., Mutterlos, J., Veizer, J., 1998, Preservation of S18O and S13C in belemnite rostra from Jurassic/Early Cretaceous successions: American Journal of Science, 298(4), 324347. [ Links ]
Price, G.D., Sellwood, B.W., 1997, Warm palaeotemperatures from high Late Jurassic palaeolatitudes (Falkland Plateau): Ecological, environmental or diagenetic controls?: Palaeogeography, Palaeoclimatology, Palaeoecology, 129(34), 315327. [ Links ]
Price, G.D., Ruffell, A.H., Jones, C.E., Kalin, R.M., Mutterlose, J., 2000, Isotopic evidence for temperature variation during the early Cretaceous (late RyazanianmidHauterivian): Journal of the Geological Society of London, 157(2), 335343. [ Links ]
Primmer, T. J., Kerr, S. A., Myers, K. J., 1990, Feasibility of insitu elemental analysis in mudrocks evaluation: Geological Society of London, Special Publications, 148, 203210. [ Links ]
Rao, L.H.J., Rao, C.S., Ramakrishnan, T.L., 1975, Reclassification of the rocks of Bhima basin, Gulburga district, Mysore state: Geological Survey of India, Miscellaneous Publications, 23 (1), 177184. [ Links ]
Sathyanarayan, S., Arneth, J.D., Schidlowski, M., 1987, Stable isotope geochemistry of carbonates from the Proterozoic Kaladgi, Badami and Bhima Groups, Karnataka, India: Precambrian Research, 37(2), 147156. [ Links ]
Saylor, B.A., Kaufman, A.J., Grotzinger, J.P., Urban, F., 1998, A composite reference section for terminal Proterozoic strata of southern Namibia: Journal of Sedimentary Research, 68(6), 12231235. [ Links ]
Schidlowski, M., Eichmann, R., Junge, C.E., 1975, Precambrian sedimentary carbonates: carbon and oxygen isotope geochemistry and implications for the terrestrial oxygen budget: Precambrian Research, 2(1), 169. [ Links ]
Turekian, K.K., Wedepohl, K.H., 1961, Distribution of elements in some major units of earth's crust: Geological Society of America Bulletin, 72(2), 175192. [ Links ]
Veizer, J., 1983, Chemical diagenesis of carbonates; theory and application of trace element technique, in Arthur, M.A., Anderson, T.F., Kaplan, I.R., Veizer, J., Land, L.S. (eds.), Stable Isotopes in Sedimentary Geology: Society of Economic Palaeontologists and Mineralogists, 3100. [ Links ]
Veizer, J., 1989, Strontium isotopes in seawater through time: Annual Review of Earth and Planetary Sciences, 17, 141167. [ Links ]
Veizer, J., Clayton, R.N., Hinton, R.W., 1992a, Geochemistry of Precambrian carbonates, IV. Early Paleoproterozoic (2.25 ± 0.25Ga) seawater: Geochimica et Cosmochimica Acta, 56(3), 875885. [ Links ]
Veizer, J., Plumb, K.A., Clayton, R.N., Hinton, R.W., Grotzinger, J.P., 1992b, Geochemistry of Precambrian carbonates, V. Late Paleoproterozoic (1.8 ± 0.25 Ga) seawater: Geochimica et Cosmochimica Acta, 56(6), 24872501. [ Links ]
Verma, S.P., 2002, Absence of Cocos plate subductionrelated basic volcanism in southern Mexico: a unique case on Earth?: Geology, 30(12), 10951098. [ Links ]
Verma, S.P., 2005, Estadística Básica para el manejo de datos experimentales: Aplicación en la geoquímica (Geoquimiometría): México, D.F., Universidad Nacional Autónoma de México, 186 p. [ Links ]
Verma, S.P., QuirozRuiz, A., 2006a, Critical values for six Dixon tests for outliers in normal samples up to sizes 100, and applications in science and engineering: Revista Mexicana de Ciencias Geológicas, 23(2), 133161. [ Links ]
Verma, S.P., QuirozRuiz, A., 2006b, Critical values for 22 discordancy test variants for outliers in normal samples up to sizes 100, and applications in science and engineering: Revista Mexicana de Ciencias Geológicas, 23(3), 302319. [ Links ]
Verma, S.P., Santayo, E., 2005, Is oddeven effect reflected in detection limits?: Accreditation and Quality Assurance, 10(4), 144148. [ Links ]
Verma, S.P., QuirozRuiz, A., DíazGonzález, L., 2008, Critical values for 33 discordancy test variants for outliers in normal samples up to sizes 1000, and applications in quality control in Earth Sciences: Revista Mexicana de Ciencias Geológicas, 25(1), 8296. [ Links ]