Geochemical characteristics of pore waters from sediment cores of the Wagner Basin, Gulf of California. (February 2020)

• Record Type: Journal Article
• Authors: Batista Cruz, Ramón Yosvanis; Peiffer, Loïc; Weber, Bodo; Herguera, Juan Carlos; Liotta, Marcello; Fernández, Antonio González; Barragán Reyes, Rosa María; Kretzschmar, Thomas Gunter
• Is Part Of: Applied geochemistry. Volume 113(2020)
• Publication Date: 2020-02
• Subjects: Gulf of California -- Wagner basin -- Pore waters -- Stable isotopes -- 87Sr/86Sr -- DIC; Environmental geochemistry -- Periodicals; Water chemistry -- Periodicals; Geochemistry -- Social aspects -- Periodicals; Geochemistry -- Periodicals; 551.9
• DOI: 10.1016/j.apgeochem.2019.104467
• Languages: English
• ISSNs: 0883-2927

Abstract

Abstract: The Wagner Basin (WB) is a shallow basin (depth < 225 m) belonging to the northernmost section of the Gulf of California rift system. Hydrothermal activity and high heat fluxes prevail in some regions of the WB. For this contribution, we report the first dataset of chemical (major and some trace elements) and isotopic compositions (δ 18 O, δD, 87 Sr/ 86 Sr, δ 13 C) from pore water sampled at the bottom of the WB, in areas affected by hydrothermal activity. The goals of the study are to determine the origin of the fluids emanating from the anomalous heat flow zones and to characterize the physical and chemical processes controlling their composition. The 18 pore water samples are classified into two groups: low temperature (LT) and high temperature (HT) samples, according to the sampling temperature (from 16.4 to 25.6 °C, and 32.5–99.6 °C, respectively). LT samples have chemical and isotopic (δ 18 O and δD) compositions similar to those of present-day seawater. On the opposite, HT cores are typically more enriched in Cl (26, 100–37, 074 mg L −1 ) and other elements (Br, Na, K, Ca, B and Sr) than those of present-day seawater (Cl = 20, 284 mg L −1 ). HT samples are also strongly depleted in deuterium isotopes (up to −30.48‰). This characteristic could be related to the mixing between ancient evaporated seawater and Colorado river waters. Conceptually, the origin of a saline paleo-aquifer/reservoir can be related with the gradual marine flooding of shallow lagoons and depressions at the time Gulf of California was rifting (6–8 Ma) or during the Last Glacial Maximum (20–26 Ky). Additionally, it is not ruled out that some of the deuterium depletion observed in HT samples may be related to secondary processes (e.g., clays exchange, organic matter). Radiogenic 87 Sr/ 86 Sr signatures (0.70929–0.70997) of the HT samples likely reflect the leaching of radiogenic continental sediments from the Colorado River (filling the WB) and authigenic minerals (e.g., calcite or barite) precipitated from seawater. Solute geothermometry indicates that HT pore fluids underwent water-rock interactions at temperature of at least 220 °C. Finally high δ 13 C values (up to +10.5‰) in DIC from HT samples indicates partial equilibration of methane with DIC, or partial reduction of DIC. Highlights: We present the first dataset of chemical and isotopic compositions from pore water sampled in the Wagner Basin. Depleted in deuterium samples could be related to mixing between ancient evaporated seawater and Colorado river waters. Radiogenic 87 Sr/ 86 Sr signatures of the HT samples reflect the leaching of continental sediments and authigenic minerals. Anomalous heavy carbon suggest the partial equilibration of methane with DIC, or partial reduction of DIC.