METAL CONCENTRATIONS AND PROVENANCE STUDIES OF SEDIMENTS FROM PUEBLA RIVER BASIN, CENTRAL MEXICO: AN URBAN-VOLCANIC ZONE

Weathering process involves recycling of material upon the earth´s surface. Major and trace element geochemistry and mineralogy of siliciclastic sediments are affected by chemical weathering. 31 surface sediment samples were collected from three distinct zones of the river (the upstream Zahupan River, Atoyac River and downstream region) in the States of Puebla, Tlaxcala in Mexico. The metal concentrations were determined to know the enrichment pattern and geochemical processes occurring in the riverine sediments. Higher averages of Cu (56.27 mg kg-1), Pb (34 mg kg-1), and Zn (235.64 mg kg-1) in the downstream side indicates the influence of natural and external (anthropogenic) input. In order to determine the degree and extent of weathering, indices such as chemical index of alteration (CIA), chemical index of weathering (CIW) and plagioclase index of alteration (PIA) were applied and the mean values obtained were 59-75, 62-79 and 59-78 respectively indicating intermediate silicate weathering. Weathering proxies (ACNK, ACNK-FM & Al₂O₃-Zr-TiO₂) suggest that the river sediments are moderately weathered from the source rocks. All the provenance and weathering proxies of the present study reveal that the riverine sediments of Puebla have undergone intermediate chemical weathering process and are chemically immature referring to the dominance of physical weathering being subjected to tectonically active zone. Metal pollution indices studies infer that S (Class 4 & Class5), Pb (Class 4), Zn and Mo (Class 3), Cr (Class 2) are enriched in the river sediments (especially in downstream side) due to the natural (weathering and volcanic activity) and anthropogenic source. Ecological risk assessment studies indicate that Cr (10%), Ni (35%) and Zn (13%) could cause adverse biological effects in the riverine environment in near future.