Geochemistry of Neoproterozoic limestones of the Shahabad Formation, Bhima Basin, Karnataka, Southern India

Major, trace and rare earth element (REE) geochemistry of carbonate rocks of the Neoproterozoic Shahabad Formation, Southern India were studied in order to investigate the depositional environment and source for the REEs. The PAAS (Post Archaean Australian Shale) normalized REE + Y pattern of Shahabad limestones have consistent seawater-like pattern i.e., i) LREE depletion (average (Nd/Yb)SN = 0.64 ± 0.08), ii) negative Ce anomaly, iii) positive Gd anomaly (average GdSN/Gd* = 1.05 ± 0.16), iv) superchondritic Y/Ho ratio (average Y/Ho = 38.13 ± 21.35). The depletion of LREE and enrichment of HREE are clearly indicated by the (La/Yb)SN, (Dy/Yb)SN and (Nd/Yb)SN ratios, which suggest the retention of seawater characteristics in these limestones. The negative Ce anomaly reflects the incorporation of REE directly from seawater or from the pore water under oxic condition, and also reveals the mixing of two-component systems with terrigenous clay (detrital) in the marine sediments. The terrigenous input in these limestones is confirmed by positive correlation of ΣREE with Al2O3, negative correlation of ΣREE with CaO and differences in Y/Ho ratios. V, Cr, and Sc, are positively correlated with Ti, and strong positive correlation of ΣREE with Fe2O3, Ni, Cr, Sc, and Y also indicate the presence of terrigenous materials in the Shahabad limestones

Carbon, oxygen, and strontium isotope geochemistry of the Proterozoic carbonate rocks, Bhima basin, south India: Implication for diagenesis

A carbonate dominated shallow marine Proterozoic Bhima basin consists of carbonates and clastic rocks, and is widely distributed in the northern part of the Karnataka state, south India. Limestones of the Shahabad Formation have been selected for this study and secular variations in C, O, and Sr isotope compositions are reported. δ13C values are varying from +3.50 to -1.38‰PDB. Similarly, the δ18O values recorded a range between -5.76 and -12.93‰PDB 87Sr/86Sr ratio for these limestones is varying between 0.70699 and 0.7117. Higher burial rate of organic matter could have been responsible for the positive δ13C values, which is common in the Proterozoic carbonate rocks. The δ18O values in most of the samples are similar to the average value of the Proterozoic carbonate rocks. Albeit some of the samples are modified in their original isotopic signature, which shows high negative δ18O values 1.5 and a negative trend between δ18O and 87Sr/86Sr, suggesting that the δ18O and 87Sr/86Sr isotopic signatures of Bhima carbonates have been altered by diagenesis. The post depositional diagenetic alteration is also supported by the petrographic characters of these carbonates

Geochemistry of sands along the San Nicolás and San Carlos beaches, Gulf of California, Mexico: implications for provenance and tectonic setting

The weathering conditions, provenance, and tectonic setting of sands from the San Nicolás (SN) and San Carlos (SC) beaches along the Gulf of California, Mexico, have been studied using mineralogy, major element, and trace element data. The compositional similarity among 4 independent groups (each beach area consists of 2 grain-size groups, i.e. medium- and fine-grained sands) was tested statistically by the application of analysis of variance at the 99% confidence level to avoid misinterpretation. The X-ray diffraction and SEM-EDS data revealed that the fine-grained SN sands were abundant in rutile and zircon minerals. The higher SiO2/Al2O3 ratio of the SN sands than the medium- and fine-grained SC sands indicated that the compositional maturity was greatest for the SN sands (Fcalc = 366.756151 and (Fcrit)99% = 5.065158, where Fcalc > (Fcrit)99% indicates that the data populations are significantly different at 99% confidence level). The chemical index of alteration values for the SN (ca. 41–45) and SC (ca. 48–51) sands indicated low to moderate weathering intensity in the source region. The significant enrichment of the low rare earth element and the flat heavy rare earth element patterns of the SN sands indicated that the sources were largely felsic rocks. The low positive Eu anomaly in the SC sands was probably due to the contribution of sediments from intermediate rocks between felsic and mafic compositions. The comparison of rare earth element data of the sands with rocks located relatively close to the study areas revealed that the SN sands received a major contribution from felsic rocks and SC sands from intermediate rocks. The compositional difference between the SN and SC beach areas indicated that longshore currents played a less significant role. Discriminant function-based major element diagrams for the tectonic discrimination of siliciclastic sediments revealed a rift setting for the Gulf of California, which is consistent with the general geology of Mexico

Geochemistry of the Jurassic and Upper Cretaceous shales from the Molango Region, Hidalgo, eastern Mexico: Implications for source-area weathering, provenance, and tectonic setting

This study focuses on the Jurassic (Huayacocotla and Pimienta Formations) and Upper Cretaceous (Mendez Formation) shales from the Molango Region, Hidalgo, Mexico. In this article, we discuss the mineralogy, major, and trace element geochemistry of the Mesozoic shales of Mexico. The goal of this study is to constrain the provenance of the shales, which belong to two different periods of the Mesozoic Era and to understand the weathering conditions and tectonic environments of the source region

An integrated study of geochemistry and mineralogy of the Upper Tukau Formation, Borneo Island (East Malaysia): Sediment provenance, depositional setting and tectonic implications

An integrated study using bulk chemical composition, mineralogy and mineral chemistry of sedimentary rocks from the Tukau Formation of Borneo Island (Sarawak, Malaysia) is presented in order to understand the depositional and tectonic settings during the Neogene. Sedimentary rocks are chemically classified as shale, wacke, arkose, litharenite and quartz arenite and consist of quartz, illite, feldspar, rutile and anatase, zircon, tourmaline, chromite and monazite. All of them are highly matured and were derived from a moderate to intensively weathered source. Bulk and mineral chemistries suggest that these rocks were recycled from sedimentary to metasedimentary source regions with some input from granitoids and mafic-ultramafic rocks. The chondrite normalized REE signature indicates the presence of felsic rocks in the source region. Zircon geochronology shows that the samples were of Cretaceous and Triassic age. Comparable ages of zircon from the Tukau Formation sedimentary rocks, granitoids of the Schwaner Mountains (southern Borneo) and Tin Belt of the Malaysia Peninsular suggest that the principal provenance for the Rajang Group were further uplifted and eroded during the Neogene. Additionally, presence of chromian spinels and their chemistry indicate a minor influence of mafic and ultramafic rocks present in the Rajang Group. From a tectonic standpoint, the Tukau Formation sedimentary rocks were deposited in a passive margin with passive collisional and rift settings. Our key geochemical observation on tectonic setting is comparable to the regional geological setting of northwestern Borneo as described in the literature

Statistically coherent calibration of X-Ray Fluorescence Spectrometry for major elements in rocks in minerals.

We applied both the ordinary linear regression (OLR) and the new uncertainty weighted linear regression (UWLR) models for the calibration and comparison of a XRF machine through 59 geochemical reference materials (GRMs) and a procedure blank sample. )e mean concentration and uncertainty data for the GRMs used for the calibrations (Supplementary Materials) (available here) filewere achieved from an up-to-date compilation of chemical data and their processing from well-known discordancy and significance tests. )e drift-corrected XRF intensity and its uncertainty were determined from mostly duplicate pressed powder pellets. )e comparison of the OLR (linear correlation coefficient r∼0.9523–0.9964 and 0.9771–0.9999, respectively, for before and after matrix correction) and UWLR models (r∼0.9772–0.9976 and 0.9970–0.9999, respectively) clearly showed that the latter with generally higher values of r is preferable for routine calibrations of analytical procedures. Both calibrations were successfully applied to rock matrices, and the results were generally consistent with those obtained in other laboratories although the UWLR model showed mostly narrower confidence limits of the mean (slope and intercept) or lower uncertainties than the OLR. Similar sensitivity (∼2.69–46.17 kc·s1·%1 for the OLR and ∼2.78–59.69 kc·s1·%1 for the UWLR) also indicated that the UWLR could advantageously replace the OLR model. Another novel aspect is that the total uncertainty can be reported for individual chemical data. If the analytical instruments were routinely calibrated from the UWLR model, this action would make the science of geochemistry more quantitative than at present

The challenges and opportunities of addressing particle size effects in sediment source fingerprinting: A review

publisher: Elsevier articletitle: The challenges and opportunities of addressing particle size effects in sediment source fingerprinting: A review journaltitle: Earth-Science Reviews articlelink: http://dx.doi.org/10.1016/j.earscirev.2017.04.009 content_type: article copyright: © 2017 Elsevier B.V. All rights reserved

Provenance of sands from Cazones, Acapulco, and Bahía Kino beaches, México

La petrografia y geoquimica de elementos mayores, traza y de tierras raras de arenas de tres playas de Mexico (Cazones, Acapulco y Bahia Kino) fueron estudiadas para determinar su procedencia. El estudio textural revela que la proporcion del cuarzo en las arenas es mayor en Bahia Kino (~48.83 %) que en Cazones (~22.48 %) y en Acapulco (~20.48 %). La mayoria de las muestras de arenas son clasifi cadas como arenas felsicas de acuerdo con su contenido de SiO2. Las variaciones en el contenido de SiO2, Fe2O3, MgO, TiO2 y las relaciones Al2O3/TiO2, K2O/Na2O, SiO2/Al2O3 determinadas en las tres areas de estudio refl ejan diferencias en las caracteristicas de la roca fuente. Los bajos valores en el Indice de Alteracion Quimica (CIA: ~38.58) sugieren la prevalencia de condiciones de bajo intemperismo en las regiones de las rocas fuente. La estable tendencia de intemperismo identifi cada en el diagrama A-CN-K para las arenas de Acapulco y Cazones indica un levantamiento de la region de la fuente, por lo que se deduce que las arenas se derivaron de diversas fuentes. Una mayor variacion en los contenidos de �°REE es observada en las arenas de Acapulco (~22.390 ppm) que en Cazones (~49.83 ppm) y que en las arenas de Bahia Kino (~50�89 ppm), lo que se debe probablemente a diferencias en el fraccionamiento de minerales. Sin embargo, todas las muestras de arena presentan patrones similares REE con enriquecimiento de LREE, empobrecimiento de HREE y una anomalía negativa de Eu. La comparación de los datos de REE de las muestras con los obtenidos para la roca fuente, localizada relativamente cerca del área de estudio, sugiere que las arenas de Cazones y Acapulco fueron derivadas de rocas félsicas e intermedias, mientras que las arenas de Bahía Kino se derivaron sólo de rocas félsicas.Petrographic, major, trace, and rare-earth element geochemistry of sands from three beaches of Mexico (Cazones, Acapulco, and Bahia Kino) were studied to determine their provenance. The textural study reveals that the proportion of quartz is higher in Bahia Kino (~48.83 %) than in Cazones (~22.48 %) and Acapuclo (~20.48 %) sands. Most of the sand samples are classifi ed as felsic sands using SiO2 content. The variations in SiO2, Fe2O3, MgO, TiO2 contents and Al2O3/TiO2, K2O/Na2O, SiO2/Al2O3 ratios among the three study areas refl ect differences in source rock characteristics. The low Chemical Index of Alteration values (CIA: ~38.58) suggest the prevalence of week weathering conditions in the source regions. A steady weathering trend identifi ed in the A-CN-K diagram for Acapulco and Cazones sands is indicative of uplift along the source region and indicates that sands were derived from diverse sources. A major variation in �°REE content is observed in Acapulco sands (~22.390 ppm) than in Cazones (~49.83 ppm) and Bahia Kino sands (~50.89 ppm), and is likely due to differences in fractionation of minerals. However, all the sand samples show similar REE patterns with enriched LREE, depleted HREE and a negative Eu anomaly. The comparison of REE data of sands with those of source rocks located relatively close to the study areas suggest that Cazones and Acapulco sands were derived from felsic and intermediate rocks, whereas Bahia Kino sands were derived from felsic rocks