Il Quaternario 
fta/ian Journal of Quaternary Sciences 

24, (Abstract AlGUA, Roma 02/2011), 114- 116 

Congresso AIQUA 
Il Quaternario Italiano: conoscenze e prospettive 

Roma 24 e 25 febbraio 2011 

CALIBRATION OF OSL DATA: MISMATCH BETWEEN STRATIGRAPHY ANO OSL CHRONOLOGY 
OF SEDIMENTS FROM THE PO PLAIN 

Laura Panzeri', lrene Zembo2
, Riccardo Bersezio2 & Marco Martini1 

1 Dipartimento di Scienza dei materiali, Università di Milano Bicocca, Milano 
2 Dipartimento di Scienze della Terra, Università degli studi di Milano, Milano 

Corresponding author: L. Panzeri <laura.panzeri@mater.unimib.it> 

ABSTRACT: Panzeri L. et al., Calibration of OSL data: mismatch between strat1ghraphy an d OSL chronology of 
sediments tram Po Plain. (IT ISSN 0394-3356, 2011) 
We present the results obtained with Optically Stimulated Luminescence (OSL) on alluvial sediments from Po Plain. 
The ages obtained are in good agreement with stratighraphic position and with radiocarbon ages for the younger 
samples (latest Pleistocene) while there is an underestimation for the oldest samples (middle Pleistocene). The cause 
of this behaviour is discussed. 

RIASSUNTO: Panzeri L. et al., Calibrazione di date ottenute mediante OSL: disaccordo tra la stratigrafia e la 
cronologia OSL di sedimenti della Pianura Padana. (IT ISSN 0394-3356, 2011) 
Vengono presentati i risultati ottenuti mediante Luminescenza Otticamente Stimolata (OSL) applicata a sedimenti 
alluvionali provenienti dalla Pianura Padana. Le età ottenute sono in accordo con la posizione stratigrafica e con i dati 
ottenuti mediante radiocarbonio per i campioni più giovani (Pieistocene Superiore) mentre sono sottostimate per i 
campioni appartenenti al Pleistocene Medio. Le possibili cause di tale comportamento sono discusse. 

Key words: alluvial sediments, OSL dating, P o p l ai n, Quaternary 

Parole chiave: sedimenti alluvionali, datazione OSL, Pianura Padana, Quaternario 

We applied OSL dating techniques to quartz 
samples from some outcrops in the alluvial 
Quaternary succession of the Po plain South of 
Milan, to assist the stratigraphic reconstruction. 
Luminescent dating is in fact used to determined 
burial ages of sediments that were exposed to 
sunlight prior to deposition (AITKEN, 1998). 
Prirnarily we aimed at obtaining new age 
determinations to tighten the chronological 
constraints that are traditionally applied to some 
crucial stratigraphic units, exposed at the so-called 
"Livello Fondamentale della Pianura 
(LFP)" (CASTIGLION! & PELLEGRINI, 2001 ). W e 
focused on three exposures, close to the southern 
end of the LFP, in different tectono-stratigraphic 
settings. From SW to NE we sampled: i) the Middle 
Pleistocene alluvial sediments in a quarry 
exposure at the northern flank of the san 
Colombano al Lambro isolated hill (DESIO, 1965), a 
spur of an Apenninic thrust front of the Western 
Emilia folds that was active during Middle and 
presumably Late Pleistocene (PELLEGRINI et al., 
2003), ii) the Middle Pleistocene alluvial sediments 
of the Casalpusterlengo relic relief ("Mindel" Auct., 
CREMASCHI, 1987), al the top of an Apenninic 
anticline, kinematically linked to the San 
Colombano structure (BERSEZIO et al., 2010), and 
iii) the top of the Late Pleistocene sediments of the 
LFP in the Lodi depocentre, just South of the 
interference zone between the Alpine and 
Apenninic thrust fronts. These deposits have been 
indicated on the various geologica! maps at scale 

1:100.000, but with a poorly defined age 
(CREMASCHI, 1987). 
Five samples were collected by hammering steel 
tubes into freshly cleaned exposures. The tubes 
were capped with aluminum sheets and sealed 
using black plastic bags. Samples GeMa1 and 
GeMa2 can be ascribed to the younger Cantù 
Alloformation (latest Pleistocene, STRINI, 2001 ), 
while samples GeSo1 and GeSo2 belong to the 
Casalpusterlengo relic relief ("Mindel" Auct., 
CREMASCHI, 1987). Sample GeBF was taken from 
the middle Pleistocene Cascina Parina Unit 
(PELLEGRINI et al., 2003) at the northern flank of 
the san Colombano al Lambro hill. Tab. 1 
summarises the stratigraphic position, the main 
sedimentological characteristics of the samples 
and their depositional environment. 
The quartz extraction was made following the 
conventional procedure (LANG et al., 1996). Ali the 
luminescence measurements were conducted on 
coarse quartz grains (75-120 ~m). The single­
aliquot regenerative-dose (SAR) protocol was used 
to determine the radiation dose absorbed by 
sediment grains since deposition (MURRAY & 
WINTLE, 2000). 
The OSL measurements were made using an 
automated luminescence system (Ris0 TLIOSL­
DA-15), equipped with a 90Sr/""v beta source 
delivering 0.14 Gy/s (±3%) to the sample position. 
The quartz OSL was stimulated by an array of blue 
LEDs (470±30 nm) for 100 s at 125'C with a 
constant stirnulation power of 54 mW/cm2

. The 



Calibration of OSL data: mismatch between stratighraphy .. 115 

Sampling 
Stratigraphic 

Dep. environment 
Si te Sample depth Description and pedological OSL age (ka) 

(cm) position interpretation 

Cantù Yellowish gray sandy silt and clay, 
Fluvial; pedogenic 

LFP Alloformation features indicate 
Mairago (Lodi). GeMa2 150 

(la test 
massive, with red mottling, day formalion of an 

19±2 

Pleistocene). 
coatings and Fe-Mn nodules. 

hydromorphic soil. 

Cantù 
Greyish brown, coarse-gra'1ned s'1lty 

Fluvial; pedogenic 
LFP Alloformation features indicate 
Mairago (Lodi). 

GeMa1 250 
(latest 

sand with grey to red mottling, clay 
formation of an 

16 ±2 

Pleistocene ). 
coatings and Fe-Mn nodules. 

hydromorphic soil. 

lsolated terraces 
Coarse to medium-grained, massive 

Alluvial; pedogenic 
Fluvial Formation features indicate 

Casalpusterlen 
(middle 

sand with norma! grading and mud 
formalion of go relic relief. GeSo2 420 

Pleistocene; 
chips at the bottom; red ferruginous 

polycyclic fersiallitic 
67 ± 6 

Costa Fagioli. 
Cremaschi, 

mott!ing, day coatings and Fe-Mn 
paleosol with alluvial 

1987). concretions. day horizon. 

lsolated terraces 

Casalpusterlen 
Fluvia! Formation Coarse lo medium-grained, normally 

(middle graded gray sand with cross-go relic relief. GeSo1 500 Alluvial. 107 ± 13 
Costa Fagioli. 

Pleistocene; lamination; ferruginous concretions at 
Cremaschi, the bottom. 

1987). 

Cascina Parina 

C.na 
Unit (middle Fine to coarse-graìned pebbly sands 

Belfuggito. GeBF 620 Pleistocene; with fine planar lamination and sofl Alluvial. 89 ± 9 
Pellegrini et al., sediment deformation. 

2003). 

T ab. 1. Stratigraphic constraints and OSL age determinations obtained al the sampling sites. 
Posizione stratigrafica, descrizione ed età OSL dei campioni. 

presence of feldspars was checked using an IR 
di ode array (830±1 O n m) with a stimulation power 
of 360 mW/cm2 Photons were detected by a 
bialkali photomultiplier tube (EMI 9235QB15) 
coupled lo a 7.5 mm Hoya U-340 filter. The 
preheat was al 180°C far 10 s far samples GeMa1 
and GeBF and 200°C far the other samples. To 
contrai the purity of the extracted quartz, the OSL­
IR-depletion ratio test (DULLER, 2003) was 
performed. IRSL signals were observed in ali 
samples. To reduce its presence another HF 
etching far 40 min was attempted and the test 
remade. Nevertheless, ali samples showed again a 
significant contribution due to feldspars. For this 
reason anomalous fading was tested using 
delayed Lx/T x measurements with delays of up lo 
1 month. 
The samples were initially tested using preheat 
plateau and dose recovery tests. 
In order lo calculate the annual dose, the Th and U 
concentrations of the sediments were measured 
with total alpha counting using ZnS scintillator 
discs (AITKEN, 1985), assuming a concentration 
ratio Th/U equal to 3. 4°K conteni was deduced 
from the total concentration of K that was 
measured with flame photometry. Attenuation of 
the beta dose was taken into account (BELL, 1979). 
The contribution of cosmic radiation was taken as 
0.15 mGy/a al depths of about 1 m. For greater 
depths attenuation factors were used (AITKEN, 
1985). The results of radioactivity measurements 
together with the corresponding dose rates are 

reported in Tab. 1. In calculating the dose-rates, il 
was assumed that the average water conteni over 
the entire burial period was about 20% for ali 
samples except for GeMa1 (30%). 
The OSL age obtained are listed in Tab.1. 
Samples GeMa1 and GeMa2 yielded OSL ages in 
good agreement with the stratigraphic position and 
calibration by radiocarbon ages (BERSEZIO et al., 
2004 ). Differently the OSL ages of the other 
samples do not fil the available stratigraphic 
constraints (late Pleistocene instead of the 
expected middle Pleistocene ). Different 
explanations can be claimed as indicated by recent 
literature: 1) the samples are too old lo be dated by 
OSL technique. Despite the samples haven't 
reached the saturation and have mel the standard ~ 
performance criteria set to test the reliability of the 
SAR protocol, they showed underestimation. 
(BUYLAERT et al., 2007; MURRAY et al. 2007; 
LOWICK et al., 201 O); 2) Some quartz has 
luminescence properties that make il problematic 
far dating application. In fact, despite the fact that 
quartz is nominally pure Si02, the minerai forms in 
several different geologica! settings. The 
luminescence properties of quartz are highly 
variable with geologica! source and vary even al a 
grain lo grain level within a sediment (GOTZE et al., 
2005; PREUSSER el al., 2009) 3) the samples 
belong to complex pedogenetic profiles. The role 
of weathering and water adsorption by quartz 
grains on OSL luminescence is stili poorly 
understood. 



116 

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Ms. received: January 14, 2011 
Testo ricevuto il 14 gennaio 2011