Realistic models of ground water circulation and transport in modern alluvial and coastal plains demand an accurate reconstruction of subsurface sedimentary architecture. In this study, we propose the characterization of a multilayered aquifer from the subsiding eastern Valdarno Basin, a strategic area far both water research and pollution issues, between the city of Pontedera and S. Croce. An integrated sedimentological, stratigraphic and micropaleontological study of six continuously cored boreholes allows the detailed reconstruction of Pliocene to Quaternary stratigraphy in the uppermost 100 m, and shows how a multidisciplinary approach may represent a successful tool to define three-dimensional facies relationships with in sedimentary bodies, and thus aquifer geometries. Moreover, AMS 14C dates associated to Sr isotope data prompt to place the identified stratigraphic units in a worthy chronostratigraphic framework, with a coherent depositional evolution in terms of space and time. The study area, oriented SW-NE along the Arno River course, is rimmed to the south and to the north by the Pisa and the Cerbaie Hills, respectively, both formed by Plio-Quaternary marine and continental deposits. A fault, located a long the southern margin of the Cerbaie Hills, causes the NNW-dipping, below the Arno-plain, of the Plio-Quaternary deposits cropping out o n the Pisa Hills. Stratigraphic architecture in the study area is varied. Except far the Holocene succession, consisting mainly of fine-grained alluvial-plain deposits lying onto transgressive swamp deposits and showing a homogenous spatial distribution, the pre-Holocene deposits exhibit noticeable distinct features west and east of Pontedera, respectively, due to the activity of a normal fault with an Apenninic orientation, causing the lowering of the west side of the study area. A thick Pleistocene alluvial succession, made up by a cyclic alternation of coarse-grained fluvial channel and fine-grained floodplain deposits, is recorded beneath Pontedera, whereas eastwards the stratigraphic sequence is characterized by Early-Middle Pliocene deposits, related to coastal-shallow marine sands with very subordinate alluvial facies. Given this structural setting, the reconstruction of stratigraphic architecture leads to the identification, in the uppermost 100 m, of a multilayered confined aquifer consisting of five aquifer systems (A-E) ranging in age between the Holocene and the Early-Middle Pliocene. Aquifer system A developed during the Holocene and exhibits a markedly lenticular geometry recording the recent dynamics of the Arno River. The underlying aquifer system (B), Lower-Middle Pleistocene-Holocene in age, consists of sands an d gravels of fluvial origin and is recorded only in the western sector of the examined area. The lower three aquifer systems (C-D-E), characterizing the eastern sector of the study area, mainly consist of sandy shallow-marine deposits, Early to Middle Pliocene in age, showing a cyclic arrangement. The Quaternary aquifer systems (A-B) exhibit a strongly lenticular shape, reflecting their fluvial origin, while the Early-Middle Pliocene aquifer systems (C-D-E) display a higher lateral continuity, as expected from sedimentary bodies deposited in coastal-littoral setting. The geological framework and the structural setting suggest the identification of water recharge areas in the Middle Pliocene sandy deposits cropping out on the Pisa Hills, taking into account their NNW dipping toward the Arno Plain .

Characterization of aquifer systems from high-resolution subsurface stratigraphy: the case of the eastern Valdarno basin (Tuscany, Italy)

SARTI, GIOVANNI;
2007-01-01

Abstract

Realistic models of ground water circulation and transport in modern alluvial and coastal plains demand an accurate reconstruction of subsurface sedimentary architecture. In this study, we propose the characterization of a multilayered aquifer from the subsiding eastern Valdarno Basin, a strategic area far both water research and pollution issues, between the city of Pontedera and S. Croce. An integrated sedimentological, stratigraphic and micropaleontological study of six continuously cored boreholes allows the detailed reconstruction of Pliocene to Quaternary stratigraphy in the uppermost 100 m, and shows how a multidisciplinary approach may represent a successful tool to define three-dimensional facies relationships with in sedimentary bodies, and thus aquifer geometries. Moreover, AMS 14C dates associated to Sr isotope data prompt to place the identified stratigraphic units in a worthy chronostratigraphic framework, with a coherent depositional evolution in terms of space and time. The study area, oriented SW-NE along the Arno River course, is rimmed to the south and to the north by the Pisa and the Cerbaie Hills, respectively, both formed by Plio-Quaternary marine and continental deposits. A fault, located a long the southern margin of the Cerbaie Hills, causes the NNW-dipping, below the Arno-plain, of the Plio-Quaternary deposits cropping out o n the Pisa Hills. Stratigraphic architecture in the study area is varied. Except far the Holocene succession, consisting mainly of fine-grained alluvial-plain deposits lying onto transgressive swamp deposits and showing a homogenous spatial distribution, the pre-Holocene deposits exhibit noticeable distinct features west and east of Pontedera, respectively, due to the activity of a normal fault with an Apenninic orientation, causing the lowering of the west side of the study area. A thick Pleistocene alluvial succession, made up by a cyclic alternation of coarse-grained fluvial channel and fine-grained floodplain deposits, is recorded beneath Pontedera, whereas eastwards the stratigraphic sequence is characterized by Early-Middle Pliocene deposits, related to coastal-shallow marine sands with very subordinate alluvial facies. Given this structural setting, the reconstruction of stratigraphic architecture leads to the identification, in the uppermost 100 m, of a multilayered confined aquifer consisting of five aquifer systems (A-E) ranging in age between the Holocene and the Early-Middle Pliocene. Aquifer system A developed during the Holocene and exhibits a markedly lenticular geometry recording the recent dynamics of the Arno River. The underlying aquifer system (B), Lower-Middle Pleistocene-Holocene in age, consists of sands an d gravels of fluvial origin and is recorded only in the western sector of the examined area. The lower three aquifer systems (C-D-E), characterizing the eastern sector of the study area, mainly consist of sandy shallow-marine deposits, Early to Middle Pliocene in age, showing a cyclic arrangement. The Quaternary aquifer systems (A-B) exhibit a strongly lenticular shape, reflecting their fluvial origin, while the Early-Middle Pliocene aquifer systems (C-D-E) display a higher lateral continuity, as expected from sedimentary bodies deposited in coastal-littoral setting. The geological framework and the structural setting suggest the identification of water recharge areas in the Middle Pliocene sandy deposits cropping out on the Pisa Hills, taking into account their NNW dipping toward the Arno Plain .
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/111170
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