The distribution of sedimentary deposits reflects processes acting within the depositional environment. Understanding the facies distribution as well as their hydraulic properties is essential for characterizing the behavior of aquifer systems. The Palatine Hill exhibits a complex stratigraphic architecture related to the Quaternary evolution of the Roman Basin, resulting from the interaction between tectonic uplift, volcanic activity and glacio-eustatic sea-level fluctuations (Milli, 1997; Mancini et al., 2018). The infill of Roman Basin is characterized by several depositional units constituting low rank depositional sequences (Middle Pleistocene PG3 to PG5 and Upper Pleistocene-Holocene PG9 sequences). The alternation of depositional and erosional phases determines the overlapping and/or lateral contact between different hydrofacies, which, on turn, brings variations in the confining conditions of aquifers, the inflow and recharge rates and the response to hydrological stresses. The ultimate objective of hydrofacies analysis is to capture the three-dimensional hydrogeological structure or architecture of aquifer systems and create realistic groundwater models, with a greater predictive capability. At first, sequences were detected by the well logs parametrization, and cross sections were built to form a fence diagram. Groundwater level oscillations were recorded every 1 hour in 5 monitoring wells (September 2011 - April 2012). Data were interpreted in the light of local stratigraphic architecture, and the multiple groundwater levels were associated to the corresponding sequences. Three groundwater circulations were detected: the deepest aquifer C (PG3, head about 10.5 m a.s.l.), with base level close to the valleys of Holocene tributaries shows a rapid and impulsive hydrological response to Tiber river flood, suggesting strong connection and high transmissivity; the shallow aquifer B (about 17 m a.s.l.) is hosted in sequences PG4 and PG5. The response to rainfall-floods are smoothed with respect to aquifer C, and occur with different magnitude in the two sequences. This suggests a weak connection with tributaries; differences in texture and porosity imply different storage coefficient for the two sequences; the subsurficial aquifer A (about 30 m a.s.l.) is hosted in the PG5; however, differently from aquifer B, it does not show any connection with river floods. Results show that the facies analysis and the sequence stratigraphy approach provide a better understanding of local groundwater flows, being very helpful in avoiding erroneous interpretations of piezometric data in complex geological contexts.
Evaluation of hydrofacies connectivity in the Palatine Hill (Rome) through sequence stratigraphy
2019
Abstract
The distribution of sedimentary deposits reflects processes acting within the depositional environment. Understanding the facies distribution as well as their hydraulic properties is essential for characterizing the behavior of aquifer systems. The Palatine Hill exhibits a complex stratigraphic architecture related to the Quaternary evolution of the Roman Basin, resulting from the interaction between tectonic uplift, volcanic activity and glacio-eustatic sea-level fluctuations (Milli, 1997; Mancini et al., 2018). The infill of Roman Basin is characterized by several depositional units constituting low rank depositional sequences (Middle Pleistocene PG3 to PG5 and Upper Pleistocene-Holocene PG9 sequences). The alternation of depositional and erosional phases determines the overlapping and/or lateral contact between different hydrofacies, which, on turn, brings variations in the confining conditions of aquifers, the inflow and recharge rates and the response to hydrological stresses. The ultimate objective of hydrofacies analysis is to capture the three-dimensional hydrogeological structure or architecture of aquifer systems and create realistic groundwater models, with a greater predictive capability. At first, sequences were detected by the well logs parametrization, and cross sections were built to form a fence diagram. Groundwater level oscillations were recorded every 1 hour in 5 monitoring wells (September 2011 - April 2012). Data were interpreted in the light of local stratigraphic architecture, and the multiple groundwater levels were associated to the corresponding sequences. Three groundwater circulations were detected: the deepest aquifer C (PG3, head about 10.5 m a.s.l.), with base level close to the valleys of Holocene tributaries shows a rapid and impulsive hydrological response to Tiber river flood, suggesting strong connection and high transmissivity; the shallow aquifer B (about 17 m a.s.l.) is hosted in sequences PG4 and PG5. The response to rainfall-floods are smoothed with respect to aquifer C, and occur with different magnitude in the two sequences. This suggests a weak connection with tributaries; differences in texture and porosity imply different storage coefficient for the two sequences; the subsurficial aquifer A (about 30 m a.s.l.) is hosted in the PG5; however, differently from aquifer B, it does not show any connection with river floods. Results show that the facies analysis and the sequence stratigraphy approach provide a better understanding of local groundwater flows, being very helpful in avoiding erroneous interpretations of piezometric data in complex geological contexts.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
