Global climate forcing on late Miocene establishment of the Pampean aeolian system in South America.

Wind-blown dust from southern South America links the terrestrial, marine, atmospheric, and biological components of Earth's climate system. The Pampas of central Argentina (~33°-39° S) contain a Miocene to Holocene aeolian record that spans an important interval of global cooling. Upper Miocene sediment provenance based on n = 3299 detrital-zircon U-Pb ages is consistent with the provenance of Pleistocene-Holocene deposits, indicating the Pampas are the site of a long-lived fluvial-aeolian system that has been operating since the late Miocene. Here, we show the establishment of aeolian sedimentation in the Pampas coincided with late Miocene cooling. These findings, combined with those from the Chinese Loess Plateau (~33°-39° N) underscore: (1) the role of fluvial transport in the development and maintenance of temporally persistent mid-latitude loess provinces; and (2) a global-climate forcing mechanism behind the establishment of large mid-latitude loess provinces during the late Miocene.

Occurrence and distribution of high arsenic in sediments and groundwater of the Claromecó fluvial basin, southern Pampean plain (Argentina).

Occurrences of high arsenic (As) in sediments and groundwaters were investigated in the Claromecó fluvial basin, southern Pampean plain, Argentina. This investigation includes sedimentology, mineralogy, and hydrogeochemistry of the Neogene and Quaternary aquifers to determine possible sources and transport mechanisms for As in the Claromecó basin. Characterization of the sediments revealed homogeneous mineralogy in both Neogene highlands and Quaternary floodplains with abundant plagioclase, volcanic glass shards (VGS), K-feldspar, quartz, clay minerals and minor concentrations of clinopyroxenes, orthopyroxenes, hornblende, epidote, Fe-(oxy)hydroxides and fluorapatite. The sedimentary As concentrations ranged between 2.8 and 31 mg kg-1 in both aquifers. The average total dissolved As (dissolved AsT) concentrations was 47.2 ±â€¯30.8 µg L-1 (15.3-110 µg L-1) in groundwater in Neogene aquifer (GW1), while it was 97.1 ±â€¯30.6 µg L-1 (45-144 µg L-1) in Quaternary floodplain aquifer (GW2), with all samples exceeding WHO's guideline for dissolved AsT in safe drinking water of 10 µg L-1. Some GW1 (33%) and all GW2 samples contained high levels of fluoride (F-) ranging from 0.6 to 2.6 mg L-1 (1.37 ±â€¯0.59 mg L-1) in GW1 and 2 to 5 mg L-1 (3.2 ±â€¯0.9 mg L-1) in GW2 which also exceeded WHO's guideline for F- in safe drinking water of 1.5 mg L-1. Elevated concentrations of Na+, Cl- and SO42- in the Quaternary flood plain groundwater (GW2) could indicated some degree of sea water mixing as well as some contribution from inland processes (e.g. high evapotranspiration rates, long residence time and soil-water interactions). Dissolution of As bearing VGS or Fe-(oxy)hydroxides, alkaline desorption or competitive desorption with HCO3- from Fe-(oxy)hydroxides appear to be dominating processes of As mobilization, while desorption from fluorapatite elevate dissolved F- levels. This study provides valuable insights on As mobilization processes in Neogene and near coast Quaternary floodplain aquifer.