Publication: Los isótopos de S en los yesos del Grupo Oncala: evidencia de influencia marina en los depósitos carbonático-evaporíticos berriasienses de la cuenca de Cameros
(La Rioja-Soria)
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Publication Date
2016
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Sociedad Geológica de España.
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Abstract
Discriminar si el origen de las salmueras en las que precipitaron numerosas sucesiones evaporíticas era marino o continental puede resultar complicado usando exclusivamente criterios sedimentológicos si no contienen fósiles diagnósticos. Éste es el caso de los depósitos carbonático-evaporíticos laminados del Gr. Oncala (Berriasiense, cuenca de Cameros oriental), formados en extensos cuerpos de agua someros. En este trabajo se busca determinar el origen de la salmuera en la que se formaron estos sedimentos mediante el análisis de las composiciones del δ34S de los yesos preservados en la unidad. Los valores de δ34S de entre +18,5‰V-CDT y +21,8‰V-CDT (media de +20,5‰V-CDT) de los yesos del Gr. Oncala coinciden con la signatura isotópica de los sulfatos precipitados a partir de agua marina de edad berriasiense de acuerdo con las curvas globales más recientes (≈ +17 - +20‰V-CDT), lo que sugiere que la principal fuente de sulfato en estos cuerpos de agua procedía de aportes de agua marina, en lugar del reciclaje de evaporitas triásicas como se había propuesto anteriormente. El reconocimiento de influencia marina en estos cuerpos de agua permite clasificarlos como salinas costeras.
Determining if the origin of the brine in which an evaporitic succession precipitated was marine or continental by analysing only sedimentological criteria may be difficult if it does not contain diagnostic fossils. This is the case of the laminated carbonate-evaporite deposits of the Oncala Gr (Berriasian, Cameros Basin), which were accumulated in shallow water bodies. The aim of this work is to interpret the origin of the brine in which these sediments were formed by analysing the δ34S compositions of the gypsum preserved in this unit. Gypsum δ34S values between +18,5‰V-CDT and +21,8‰V-CDT (mean value of +20,5‰V-CDT) in the Oncala Gr coincide with the isotopic signature of the sulphates precipitated in Berriasian seawater according to the most recent global curves (≈ +17 -+20‰V-CDT), which suggests that the main sulphate source in the water bodies was marine water, instead of the recycling of Triassic evaporites as previously interpreted. The recognition of marine influence in these water bodies allows us to classify them as coastal salinas.
Determining if the origin of the brine in which an evaporitic succession precipitated was marine or continental by analysing only sedimentological criteria may be difficult if it does not contain diagnostic fossils. This is the case of the laminated carbonate-evaporite deposits of the Oncala Gr (Berriasian, Cameros Basin), which were accumulated in shallow water bodies. The aim of this work is to interpret the origin of the brine in which these sediments were formed by analysing the δ34S compositions of the gypsum preserved in this unit. Gypsum δ34S values between +18,5‰V-CDT and +21,8‰V-CDT (mean value of +20,5‰V-CDT) in the Oncala Gr coincide with the isotopic signature of the sulphates precipitated in Berriasian seawater according to the most recent global curves (≈ +17 -+20‰V-CDT), which suggests that the main sulphate source in the water bodies was marine water, instead of the recycling of Triassic evaporites as previously interpreted. The recognition of marine influence in these water bodies allows us to classify them as coastal salinas.