Isotopic evidence of paleowaters in the Po sedimentary basin (Northern Italy).

Abstract

Stable isotopic composition and radiometric age were measured for groundwaters in the Emilia area of the Po sedimentary basin (Northern Italy). Waters from uncontmned shallower aquifers, deep circulating continental waters and sodium chloride waters (relic waters) squeezed out from underlying marine forma tions during past geological events were considered. Waters from supposed confined aquifers (paleowaters) are usually depleted in 0-18 (61'0 < -10° o) and their 6180-6D relationships are not consistent with their belonging to the present hydrological cycle. Isotope data on sodium chloride waters suggest mixing of relic saline waters with deep circulating continental waters. Processes affecting stable isotope composition of groundwaters in unconsolidated sediments are discussed. Oxygen isotope chemistry is considered to be a rather conservative parameter at least at low temperatures, thus able to give paleoclimatic information. Some 14C age data on deep circulating groundwaters suggest permanence times within the aquifers greater than 15,000yrs in some cases. These data agree with paleoclimatological deductions in pointing out the presence of paleowaters in the Po sedimentary basin.

Geochemistry of shallow aquifers and soil gas surveys in a feasibility study at the Rivara natural gas storage site (Po Plain, Northern Italy)

“…7). Waters from the upper unconfined aquifer (Group A) have temperatures ranging from 10.8 and 15.2°C, very close to the annual mean of the surface air temperature of the study area (13.5°C, Gorgoni et al, 1982 and S. Felice sul Panaro meteorological station data available at: http://dexter-smr.arpa.emr.it) and show circum neutral pH between 6.7 and 7.5. TDS values are highly variable (from 512 to 3168 mg/L) while positive Eh values (with the exception of sample 16) denote oxidizing conditions in the leached strata.…”

“…As a whole, no hints of thermal anomalies have been detected in the studied aquifers, as occur elsewhere in the Po Plain in areas crossed by faults and/or fault systems as well as where structural highs have been recognised at depth (Chiaramonte and Novelli, 1985;Conti et al, 2000;Gorgoni et al, 1982;Federico et al, 2008). Indeed, starting from the annual mean of the surface air temperature, water temperatures are in general agreement with the vertical gradient measured in deep exploration wells or inferred in the area in/for the first 900 m depth from geological, geothermal and structural consideration, equals 3°C/100 m (Gorgoni et al, 1982).…”

Na-carbonate waters of extreme composition: Possible origin and evolution.

“…(continued) the Po plain, Italy (Gorgoni et al, 1982) not reported in Table 1. The few tritium data support a long-term circulation at depth (Gorgoni et al, 1982;Toscani et al, 2001). The waters reported in Table 1 may be distinguished into two main groups:…”

“…NaCW may have both high (e.g., Larderello geothermal field, central Italy: Duchi et al, 1992) and low temperature (e.g., Northern Apennines, Italy: Toscani et al, 2001; Po plain, Italy: Gorgoni et al, 1982) and salinity. Salinity may range from very low (e.g., some waters from the Gotthard Tunnels, Switzerland: Michard et al, 1966) up to some hundred of milliequivalent/L (mEqle/L) of total dissolved ions (Σions) (e.g., waters from Gambassi and Casciana, Central Italy: Bencini et al, 1977).…”

“…(5) The sodic character is due to ionic exchange involving Na-rich clay which releases Na and acquires Ca (and Mg) (e.g., London and Berkshire basins, UK: Elliot et al, 1999; northern Apennines and Po plain, Italy: Gorgoni et al, 1982;Venturelli et al, 2000).…”