Coastal margins, especially the river-influenced coastal areas, are considered as active interfaces between the continental and oceanic environments, which have huge dispersal of detrital materials and heavy metal input. It is well determined that the fine-grained sediments are important reservoir for the accumulation of heavy metals. In this study, we analyzed the radiocarbon age, texture, organic matter, carbonate content, and geochemical compositions of two sediment cores (GM42 and GM44) retrieved in front of the Coatzacoalcos River mouth basin, southwestern Gulf of Mexico (∼864 and 845 m water depth, respectively). Our objective was to infer the sedimentation rate, intensity of weathering, provenance, and influence of anthropogenic activities on heavy metal contamination in sediments. The radiocarbon-age measurements of mixed planktonic foraminifera for core GM44 reveals an age of 21,289 ± 136 cal. years B.P., which fall within the Late Glacial Maximum (LGM; 21000 ± 2000 years B.P). The calculated sedimentation rate for core GM42 (~0.013 cm/year) is lower than in core GM44 (0.022 cm/year), which is probably due to the variations in detrital sediment input and/or seafloor topography. The weathering indices such as chemical index of alteration (CIA), chemical index of weathering (CIW), and plagioclase index of alteration (PIA) suggested that the source area experienced low to moderate intensity of chemical weathering under warm to humid climatic conditions. The SiO2/Al2O3, Al2O3/Na2O, and K2O/Al2O3 ratio values indicated moderate to high compositional maturity. The major and trace element concentrations suggested that the sediments were likely derived from intermediate source rocks. The heavy metal contents indicated that the sediments were not contaminated by the industrial waste disposals supplied by the Coatzacoalcos River. The redox proxy sensitive elements such as V, Cr, Cu, and Zn indicated an oxic depositional environment for the deep-sea sediment cores. The application of discrimination diagrams for the geochemistry data revealed a passive margin setting for the sediment cores. The compositional variations observed at the upper sections (<30 cm) between the two sediment cores revealed that the type of detrital sediments supplied by the Coatzacoalcos River to the deep sea area is not uniform, which is also revealed by the variation in sedimentation rate.

Geochemistry of deep-sea sediments in two cores retrieved at the mouth of the Coatzacoalcos River delta, western Gulf of Mexico, Mexico

Geochemistry and U–Pb geochronology of detrital zircons in the Brujas beach sands, Campeche, Southwestern Gulf of Mexico, Mexico

Geochemistry and Sm–Nd isotope systematics of mafic-ultramafic rocks from the Babina and Mauranipur greenstone belts, Bundelkhand Craton, India: Implications for tectonic setting and Paleoarchean mantle evolution

Geochemistry of komatiites and basalts from the Rio das Velhas and Pitangui greenstone belts, São Francisco Craton, Brazil: Implications for the origin, evolution, and tectonic setting

In order to establish the best statistical procedure for estimating improved compositional data in geochemical reference materials for quality control purposes, we evaluated the test performance criterion (πD|C) and swamping (πswamp) and masking (πmask) effects of 30 conventional and 32 new discordancy tests for normal distributions from central tendency slippage δ = 2-10, number of contaminants E = 1-4, and sample sizes n = 10, 20, 30, 40, 60, and 80. Critical values or percentage points required for 44 test variants were generated through precise and accurate Monte Carlo simulations for sample sizes nmin(1)100. The recursive tests showed overall the highest performance with the lowest swamping and masking effects. This performance was followed by Grubbs and robust discordancy tests; however, both types of tests have significant swamping and masking effects. The Dixon tests showed by far the lowest performance with the highest masking effects. These results have implications for the statistical analysis of experimental data in most science and engineering fields. As a novel approach, we show the application of three conventional and two new recursive tests to an international geochemical reference material (Hawaiian basalt BHVO-1) and report new improved concentration data whose quality is superior to all literature compositions proposed for this standard. The elements with improved compositional data include all 10 major elements from SiO2 to P2O5, 14 rare earth elements from La to Lu, and 42 (out of 45) other trace elements. Furthermore, the importance of larger sample sizes inferred from the simulations is clearly documented in the higher quality of compositional data for BHVO-1.

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Improved composition of Hawaiian basalt BHVO-1 from the application of two new and three conventional recursive discordancy tests

Multidimensional classification of magma types for altered igneous rocks and application to their tectonomagmatic discrimination and igneous provenance of siliciclastic sediments

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. The 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. The drift-corrected XRF intensity and its uncertainty were determined from mostly duplicate pressed powder pellets. The comparison of the OLR (linear correlation coefficient ∼0.9523–0.9964 and 0.9771–0.9999, respectively, for before and after matrix correction) and UWLR models ( ∼0.9772–0.9976 and 0.9970–0.9999, respectively) clearly showed that the latter with generally higher values of 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·s−1·%−1 for the OLR and ∼2.78–59.69 kc·s−1·%−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.

https://downloads.hindawi.com/journals/jspec/2018/5837214.pdf

Alejandra Amezcua-Valdez

Papers

Multidimensional classification of magma types for altered igneous rocks and application to their tectonomagmatic discrimination and igneous provenance of siliciclastic sediments

Statistically Coherent Calibration of X-Ray Fluorescence Spectrometry for Major Elements in Rocks and Minerals