How do turbidite systems behave from the hydrogeological point of view? New insights and open questions coming from an interdisciplinary work in southern Italy

Abstract

Turbidite successions can behave either as aquitards or aquifers depending on their lithological and hydraulic features. In particular, post-depositional processes can increase rock permeability due to fracture development in the competent layers. Thus, at a local scale, turbidite systems warrant further detailed investigations, aimed at reconstructing reliable hydrogeological models. The objective of this work was to investigate from the hydrogeological perspective a turbiditic aquifer located in southern Italy, where several perennial and seasonal springs were detected. Considering the complex hydrodynamics of these systems at the catchment scale, to reach an optimal characterization, a multidisciplinary approach was adopted. The conceptual framework employed microbial communities as groundwater tracers, together with the physicochemical features and isotopic signature of springs and streams from water samples. Meanwhile, geophysical investigations coupled with the geological survey provided the contextualization of the hydrogeological data into the detailed geological reconstruction of the study area. This modus operandi allowed us to typify several differences among the samples, allowing identification of sources and paths of surface water and groundwater, along with diffuse groundwater outflow along streams. As a final result, a hydrogeological conceptual model was reconstructed, underlining how at a very local scale the lithologic, hydraulic, and geomorphological heterogeneity of the studied relief can lead to an improved hydrogeological conceptual model compared to that of other turbidite systems. These results open new questions about the hydrogeological behavior of turbiditic aquifers, which could be pivotal in future research. In fact, these systems could support relevant ecosystems and anthropic activities, especially where climate change will force the research of new (and probably less hydrogeologically efficient) water sources.

Fig 1

Sketch map of the Southern Apennines (A), schematic geological map of the Agri Valley (B) and stratigraphic column of the Albidona and Gorgoglione Formations (C). After Prosser et al. [26], modified.

Fig 2. Albidona Formation outcrops recognized between Monte dell’Agresto and Contrada La Rossa.

(A) Alternating, dm-thick graded turbidite sandstones and clays (AAPD); (B) Regularly alternating, thin-bedded sandstones and clays (BARD); (C) Crudely bedded marls (MRN); (D) microconglomerates (BCMD).

Fig 3. Geological map, geophysical investigation, and monitored springs/streams.

After Prosser et al. [26], modified.

Fig 4. Comparison of recorded voltages (in mV) versus geometrical factor of the different datasets.

(A) MSS-1TX; (B) MSS-2TX; (C) MSS-4TX; (D) SP; (E) regression functions for the different datasets.

Fig 5. Mosaic of SPS (upper) and MSS (lower) ERT profiles.

Fig 6. Discharge measured at F001 (upstream) and F005 (downstream) along a single stream.

Fig 7. Examples of spring hydrographs (dates are given in month/day/year).

Fig 8. Comparison between thermal fluctuations in spring waters.

Dates are given in day/month/year.

Fig 9. Examples of EC fluctuations (red line) vs. discharge (blue line).

Graph A) represents spring P008 and graph B) in spring 153. Dates are given in month/year.

Fig 10. Plot of PCA1.

Acronyms are used for permanganate oxidation (Oss), NO₃^- (NO3), Cl^-(Cl), F^- (F), and SO₄^2- (SO4).

Fig 11. Plot of PCA2 (only spring water samples) according to sampling period.

Acronyms were used for permanganate oxidation (Oss), NO₃^- (NO3), Cl^-(Cl), F^- (F), and SO₄^2- (SO4).

Fig 12. Plot of PCA2 (only spring water samples) according to geological formation.

Acronyms are used for permanganate oxidation (Oss), NO₃^- (NO3), Cl^-(Cl), F^- (F), and SO₄^2- (SO4).

Fig 13. Relationship between δ²H and δ¹⁸O.

The red dots represent the investigated waters and the black dots symbolize the isotopic signature of local rainwater. The dashed black line shows the local meteoric water line.

Fig 14. Variation in the isotopic signature of spring waters over time.

Fig 15. Hydrogeological conceptual model.

Fig 16. Arable crops in the study area and watersheds of F001 and F005.

Base map and data from OpenStreetMap and OpenStreetMap Foundation.