Elsevier

Applied Geochemistry

Volume 15, Issue 1, January 2000, Pages 51-65
Applied Geochemistry

Geochemistry of the formation waters in the Po plain (Northern Italy): an overview.

https://doi.org/10.1016/S0883-2927(99)00016-5Get rights and content

Abstract

The Po Valley brines represent the base level of the Quaternary aquifer located in a thick clay-sands sedimentary sequence. Geochemistry indicates that these are marine waters, evaporated to the stage of gypsum precipitation and trapped at the bottom of the basin in the late Messinian. Most of the groundwater samples collected from different springs and wells in the plain result from a mixture of these Na–Cl brines and shallow groundwaters laterally recharged by the Alpine and Apennine chains.

Natural outflows of brackish waters are associated with major tectonic features. Mud volcanoes, located in the eastern sector of the Po plain, are constantly monitored as sudden chemical changes are significant precursors of seismic activity. In the western sector, calcite-filled veins isotopically record different degrees of water-rock interaction. These are outcropping fossil conduits, where mixing between shallow groundwaters and deep seated brines has occurred. The temporal continuity of the hydrological circuits allows the reconstruction of past and present groundwater circulation patterns.

This paper summarises and integrates the geochemical data produced over many years in order to obtain a regional picture of brine origins and the natural mechanisms of groundwater flow.

Section snippets

Introduction and geological background

The Po plain (Fig. 1) is located in Northern Italy and covers an area of approximately 46 000 km2. It is bound to the N by the Alps, to the SW by the Apennine chain and to the E by the Adriatic Sea. The basin formation is related to the early stages of the opening of the Atlantic Ocean, where the Mesozoic carbonate substratum was formed. Starting from late Cretaceous, the basin was progressively filled with sediments derived from the Alpine and Apennine chains. The stratigraphy includes gypsum

Major elements

Major cations plotted against Cl (Fig. 2) for the most concentrated brines show good agreement with the geochemical characteristics of a marine water evaporated to the stage of gypsum precipitation (Fontes and Matray, 1993). Most of the natural springs and wells sampled fall on a dilution curve between this end-member and shallow fresh waters. Discrepancies are greater for the most diluted terms, originating by lateral recharge of the aquifers from the Alps and the Apennines. Some cation

Natural outflows

Two sectors of the Po plain have been especially investigated in order to identify the natural mechanisms leading to the upward flow of the deep seated brines: the eastern border of the Northern Apennine chain, where mud volcanoes are found, and the western sector (Monferrato) where outcropping Messinian gypsum deposits may be found (Fig. 1).

Summary and conclusion

The Po Valley brines represent the base level of the Quaternary aquifer located in the thick clay-sand layer sedimentary sequence. Geochemistry indicates that these are marine waters, evaporated to the stage of gypsum precipitation, trapped at the bottom of the basin in late Messinian. The mobility of these brines is restricted because of their high density. Nevertheless, natural outflows of brackish waters are observed, especially in relationship with tectonic features, such as buried and

Acknowledgements

For the Monferrato region, we wish to acknowledge L. Turpin from the Centre des Faibles Radioactivités, Gif sur Yvette, France, for the Sr content and isotopic analysis of groundwaters and carbonates, and R. Polino from the Centro Studi sulla Dinamica delle Catene Collisionali (C.N.R.), Torino, Italy, for help in sampling and in outlining the regional geologic framework. Our gratitude goes to W. M. Edmunds for his support and his suggestions for text improvement. The manuscript also benefit

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