Influence of glacial cycles and tectonics on natural subsidence in the Po Plain (Northern Italy): Insights from ¹⁴C ages

Abstract

[1] Samples rich in organic matter were collected from boreholes in the southern part of the Po Plain (Italy), a rapidly subsiding sedimentary basin. New 14 C dates, obtained from these samples, and 14 C data from the literature allowed for the evaluation of the rates of natural subsidence in the area. These range from 0 to 5 mm/yr. Most areas show rates around 1 and 2 mm/yr. The obtained subsidence rates are comparable with burial rates obtained from archaeological data. These data are interpreted in terms of long-term (related to tectonics and geodynamics) and short-term (glacial cycle) processes. It is concluded that approximately 50% of the subsidence rates are related to tectonics, geodynamics and sediment load/compaction while the other half is controlled by ice melting. The effects of the glacial cycle through time are discussed. It is shown that the southeastern Po Plain generally behaves as a far-field area in relation to the high-latitude ice caps. Deviations from this behavior observed in the northeastern part of the Po Plain are tentatively interpreted as the effects of ice formation and melting in the Alps during the last glacial cycle.Components: 6485 words, 7 figures, 1 table.

Glacio–isostatic Adjustment in the Po Plain and in the Northern Adriatic Region

“…This study extends previous results by CARMINATI and DI DONATO (1999) that only accounted for the effects of remote ice sheets and used a viscosity profile which is probably inappropriate for the Mediterranean region (LAMBECK and PURCELL, 2005). Our improved evaluation of the GIA effects in the study area may be useful for the interpretation of the total natural subsidence in the Po plain and for the assessment of the anthropogenic component of sea level rise during recent decades (CARMINATI et al, 2003).…”

“…In the bulk of the Mediterranean, this has been interpreted as mostly due to the effect of the isostatic disequilibrium induced by melt-water loading, while unloading from the Northern Hemisphere ice sheets may have affected the northern Adriatic region (LAMBECK and PURCELL, 2005;STOCCHI and SPADA, 2007). For the Po plain (northern Italy), it was suggested that approximately one half of the subsidence rates is related to tectonic processes and sediment loading or compaction, while glacio-isostatic adjustment (GIA) may account for the other half (CARMINATI et al, 2003). However, since the effects of GIA are sensitive to assumptions about mantle rheology and the time-history of ice sheets, providing upper and lower bounds even for a limited number of ice and rheological models may be more useful than giving point estimates as mostly done to date (e.g., CARMINATI and DI DONATO, 1999).…”

Estimation of Subsidence in Po Delta Area (Northern Italy) by Integration of GPS Data, High-Precision Leveling and Archival Orthometric Elevations

“…Long-term natural subsidence is mainly the result of deep tectonics, glacial cycles and geodynamic movements [14]- [19]. Carminati et al [14] indicated the downflexure of the Adria plate as one cause of movement, at a maximum rate of 2.5 mm/year.…”

“…Carminati et al [14] indicated the downflexure of the Adria plate as one cause of movement, at a maximum rate of 2.5 mm/year. The possible effects of tectonic activity along the northern Apennine thrust front buried under quaternary sediments was thoroughly discussed in [20].…”

“…Combined subsidence, due to natural and anthropogenic causes [55] [56] may lead to serious environmental problems with consequent economic and social implications, especially as regards the mean sea level increase caused by global climate variations [57]. The irregular lowering of the terrain also definitely modifies the drainage of the secondary hydraulic network, and increases the rise in the salt wedge for many kilometers: for these reasons, constant monitoring of plano-altimetric changes throughout the Po Delta is essential in implementing territorial defense systems against flooding [14] …”