GeoSed - Associazione Italiana per la Geologia del Sedimentario
Dipartimento di Scienze della Terra dell'Università di Siena
Via Laterina, 8
53100 Siena
segreteria@geosed.it
Username
Password
 


Table of Contents


Vol. 9 - 2010

Vol. 8 - 2009

Vol. 7 - 2008
SP 1 - 2008

Vol. 6 - 2007
Vol. 5 - 2006
Vol. 4 - 2005
Vol. 3 - 2004
Vol. 2 - 2003
Vol. 1 - 2001-2002

Notes for Authors
(PDF - 80 kb)



GeoActa Special Publication 1 2008


Acquisto online

GeoActa
an international Journal of Earth Sciences


Alessandro Amorosi
Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, Via Zamboni 67, 40127 Bologna, Italy. E-mail: amorosi@geomin.unibo.it

Delineating aquifer geometry within a sequence stratigraphic framework: Evidence from the Quaternary of the Po River Basin, Northern Italy



PDF (696 KB)
Abstract

Unravelling stratigraphic architecture and sediment-body geometries beneath modern alluvial and coastal plains represents a fundamental tool for interpreting spatial distribution of aquifers and aquifer systems. Specifically, the application of sequence-stratigraphic techniques to cyclic fluvial and coastal successions of Quaternary age can be used for delineating distribution of aquifer and aquitard sediments, and thus reservoir geometry.
Detailed stratigraphic analysis of middle-late Quaternary fluvial to shallow-marine deposits from the Po River Basin, in Northern Italy, reveals distinctive cyclic changes in lithofacies and channel stacking patterns, falling in the Milankovitch and sub-Milankovitch bands. The transgressive surfaces (TSs) represent readily identifiable features within the Po Basin fill. These surfaces allow stratigraphic subdivision of middle-late Quaternary deposits into vertically stacked, transgressive-regressive (T-R) sequences, 50-100 m thick, that accumulated over time spans of approximately 100 ka. The TSs, which exhibit peculiar downstream facies changes, have a distinctive pollen signature throughout the basin, and constitute basinwide stratigraphic markers that show greater extent and correlation potential than sequence boundaries or maximum flooding surfaces.
Base-level and palaeoclimatic fluctuations exerted a major control on stratigraphic architecture of T-R sequences. This is reflected, beneath the present coastal plain, by a characteristic cyclic pattern of nearshore and alluvial deposits, which is paralleled by the alternation of pollen diagnostic of interglacial and glacial conditions, respectively. The landward equivalents of T-R sequences record widespread floodplain aggradation at the onset of the interglacials, while increased channel clustering documents decreasing accommodation and increasing sediment supply with transition to glacial conditions. Tectonic subsidence played a fundamental role in generating accommodation, especially close to the basin axis. This led to the formation of thick fluvial reservoirs during phases of sea-level lowstand and, possibly, early stages of transgression.
This study suggests that sequence stratigraphy can be a powerful tool for delineating aquifer geometry and the vertical stacking of regional hydrostratigraphic units. Alluvial-fan gravel bodies at the basin margin, and sandy channel-belts close to the basin axis, form the most laterally extensive sediment bodies in the Southern Po Basin. These aquifers of fluvial origin, which accumulated around times of maximum regression close to the turnaround between glacial and interglacial conditions, invariably occur in the upper part of T-R sequences, their tops roughly corresponding to the TSs. Beneath the modern coastal plain, high-permeability sediment bodies include coastal sands that invariably overlie the TSs. These laterally extensive sand bodies, which are experiencing saltwater intrusion, are elongate parallel to the present shoreline and typically wedge out toward the alluvial plain.

Keywords: Sequence stratigraphy, Hydrostratigraphy, Aquifer, Po Plain, Quaternary.