• JOHN S ARMSTRONG-ALTRIN

      Articles written in Journal of Earth System Science

    • Provenance and palaeoenvironmental significance of microtextures in quartz and zircon grains from the Paseo del Mar and Bosque beaches, Gulf of Mexico

      MAYLA A RAMOS-VAZQUEZ JOHN S ARMSTRONG-ALTRIN

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      Microtextures of quartz and zircon grains from the Bosque and Paseo del Mar beaches in the Gulf of Mexico were examined using a Scanning Electron Microscopy (SEM), to infer their provenance and palaeoenvironment. A total of 16 microtextures from 200 grains were identified and were grouped into mechanical, chemical, and mechanical/chemical origin. Microtextures of mechanical origin represent parallel striations (ps), cracks due to collision (ck), conchoidal fractures (cf), v-shaped marks (vs), abrasion fatigue (af), meandering ridges (mr), chattermarks (ch), curved (cg) and straight grooves (sg), which are attributed to a high-energy fluvial and sub-aqueous marine environment. Solution pits (sp), crystal overgrowth (cro), and silica globules (sgl) of chemical origin indicated precipitation and dissolution in a silica saturated marine environment. Adhered particles (ap), elongated depressions (dp), and relief are grouped as mechanical/chemical origin, suggested a sub-aqueous nearshore marine environment. Although zircon is considered as a resistant mineral, the frequency of microtextures observed was higher in zircon than in quartz. The results of this study revealed that the Los Tuxtlas volcanic field, Chiapas Massif and Oaxacan Complexes in the SW Gulf of Mexico are the potential source areas, which supplied sediments to the Paseo del Mar and Bosque beach areas.

      $\bf{Highlights}$

      $\bullet$ Microtextures of quartz and zircon grains in the Bosque and Paseo del Mar beaches in the SW Gulf of Mexico were analyzed.

      $\bullet$ Frequency of microtextures are higher in zircon than in quartz grains revealed that microtextures are independent of grain hardness.

      $\bullet$ The dominance of microtextures of chemical origin in the Paseo del Mar beach suggested a low-energy environment with carbonate rich sediments.

      $\bullet$ Chiapas Massif and Oaxacan Complexes are identified as the potential source areas, which supplied sediments to the beach areas.

    • Heavy metal contamination and provenance of sediments recovered at the Grijalva River delta, southern Gulf of Mexico

      MARTHA PATRICIA AYALA-PEREZ JOHN S ARMSTRONG-ALTRIN MARIA LUISA MACHAIN-CASTILLO

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      This study examines textural characteristics, carbonate, organic carbon and chemical composition of sediment samples recovered in the nearshore region (${\sim}$ 3–19 m water depth) at the Grijalva River mouth, southern Gulf of Mexico. The aim of this study is to assess the heavy metal contamination and provenance variations in sediments between the dry and northers (rainy) seasons. The proportion of sand, carbonate, and organic carbon contents were abundant at sites located near to the Grijalva River mouth, principally in northers season. Silt content is dominant in the dry season, especially in the sites located away from the Grijalva River mouth. The Chemical Index (CIX) values obtained for the dry (${\sim}$ 76–84) and northers (${\sim}$ 75–87) seasons indicated a moderate to high intensity of weathering and a humid climate in the source area. The low K$_{2}$O/Al$_{2}$O$_{3}$ ratio values (<0.5) in the dry and northers seasons indicated a higher proportion of aluminosilicates than detrital minerals, due to moderate-to-high intensity of weathering. The correlation among elemental concentrations revealed the association of Cr, Nb, Zr, Hf, Y, and rare earth elements (REE) with detrital minerals rather than aluminosilicates. The major element concentrations, Th/Sc, La/Sc, Co/Th, and Cr/Ni elemental ratios indicated the derivation of sediments from intermediate and mafic igneous rocks. A similarity in the North American Shale Composite (NASC) normalized rare earth element (REE) patterns and Eu anomaly between the dry and northers seasons suggested that the variations in sediment input played a less significant role and the provenance of sediments remained constant. The enrichment factor (EF) showed moderate to severe enrichment for Cr, Ni, and Sb (EF = ${\sim}$ 2.63–7.57), highest in the northers season, especially at the Grijalva River mouth, although the index of geo-accumulation (I$_{geo}$) for these elements suggested as moderately polluted (I$_{geo}$ = 0.34–2.0). The slightly elevated EF values for Cr, Ni, and Sb during northers season were probably due to an increase in sediment discharge into the sea during the northers season. We inferred that the enrichment of Cr, Ni, and Sb in sediments was due to both lithogenic and anthropogenic origins. The sediments were influenced by the intermediate and basic igneous rocks of the Chiapas Massif Complex, and the waste generated by the urban areas located within the Grijalva River drainage basin.

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