Where Does the Chilean Aconcagua River Come from? Use of Natural Tracers for Water Genesis Characterization in Glacial and Periglacial Environments

The Aconcagua river basin (Chile, 32 °S) has suffered the effects of the megadrought over the last decade. The severe snowfall deficiency drastically modified the water supply to the catchment headwaters. Despite the recognized snowmelt contribution to the basin, an unknown streamflow buffering effect is produced by glacial, periglacial and groundwater inputs, especially in dry periods. Hence, each type of water source was characterized and quantified for each season, through the combination of stable isotope and ionic analyses as natural water tracers. The δ18O and electric conductivity were identified as the key parameters for the differentiation of each water source. The use of these parameters in the stable isotope mixing “simmr” model revealed that snowmelt input accounted 52% in spring and only 22–36% during the rest of the year in the headwaters. While glacial supply contributed up to 34%, both groundwater and periglacial exhibited a remarkable contribution around 20% with some seasonal variations. Downstream, glacial contribution averaged 15–20%, groundwater seasonally increased up to 46%, and periglacial input was surprisingly high (i.e., 14–21%). The different water sources contribution quantification over time for the Aconcagua River reported in this work provides key information for water security in this territory.

New sedimentological, bio-magnetostratigraphic and palynologic data on the Upper Cretaceous of “Alan-Kyr” (Central Crimea)

In this article there are the results of sedimentological, palynological and paleomagnetic studies of upper Cretaceous in Alan-Kyr section (Central Crimea). The nomenclature of rocks was specified, and their deep-water genesis was justified. According to palynologic data, the age of sediments is estimated as late Campanian, in the lower part of the section palynomorphs were not found. In the lower part of the section there was established a reverse polarity magnetozone — probable analogue of C33r magnetic chron, which base should be desirable to use as a primary attribute to determine the lower border of Campanian stage in the section according to Wolfring’s recommendation [Wolfgring et al., 2018]. The received data found a significant divergence microfaunistic dating of the section, conducted before [Bragina et al., 2016].