 |
| Titel |
A detrital thermochronological study on the late Messinian to Piacenzian sedimentary succession of the Valdesa basin, Northen Apennines, Italy: detecting tectonic and climatic signals |
| VerfasserIn |
Francesca Tangocci, Maria Laura Balestrieri, Marco Benvenuti, Sara Del Conte |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250032608
|
|
|
|
|
|
| Zusammenfassung |
| The aim of the study is to detect and discriminate signals of tectonic activity and climate
forcing in an intermontane basin of the northern Appennines, through a detrital
thermocronological study of the basin sedimentary succession coupled with a detailed
reconstruction of the paleogeography. Eighteen samples were collected from the sandy and
pebbly fluvial to shallow marine successions of the Valdelsa Basin, a NW-SE trending
depression bounded to the SW by the Mid Tuscan Ridge and to the NE and SE by the ridge
M. Albano- Monti del Chianti. Four samples come from the bedrock of the Macigno
Formation, a late Oligocene – early Miocene foredeep deposits. The apatite fission-track
(AFT) ages for the bedrock vary between 7.8±1.2 and 10.8±2.0 Ma and for the sediments
from 5.5±2.8 to 16.6±2.4 Ma. The AFT grain-age distributions of the sediment samples are
generally characterized by two components, one younger peak (P1) varying between
3.8±1.7 and 9.5±1.0 Ma and one older peak (P2) varying from 11.1±2.2 to 41.2±10
Ma. In orogenic setting, closure of low-temperature chronometers is commonly
associated with exhumation-related cooling caused by erosion or tectonic unloading. The
lag-time defined as the difference between the time of closure of a chronological
system in the source region and the time of the deposition in the basin can provides a
measure of the rate of exhumation. The average lag-time of the P1 component of the
Valdelsa Basin samples is ca. 4 Ma and a mean exhumation rate of 1.1-0.9 mm/yr
can be estimated. The curves, representing the variation of the lag time, for the
two components, show a general trend characterized by decreasing lag-time going
upwards in sedimentary succession. This implies increasing cooling rates in the source
region over time. Single variations of the lag-time curve correlate with recognised
tectonic pulses of the basin NE shoulder and in some cases with global sea-level
changes related to intense climatic fluctuation. In particular, four events, mainly
controlled by glacio-eustatic cycles, are recognized as being recorded in the lag-time
variation curve of component P1: (1) a significant transgression at Miocene – Pliocene
boundary, related to the re-establishing of the connection between Atlantic Ocean and
Mediterranean Sea after the Messinian salinity crisis; (2) in upper Zanclean (?)-Piacenzian
an eustatic level fall is caused by an important continental glaciation in Northern
Hemisphere at 3.5 Ma; (3) in the Piacenzian, an important rising in the sea-level,
associated with warm and possibly humid climate, overwhelm the tectonic signal;
(4) in upper Piacenzian – Gelasian a replacement, in the whole Valdelsa Basin,
of a fluvio-deltaic and marine-coastal environment with an alluvial environment
is probably caused by the rising of the north-eastern ridge of the basin and by a
significant drop in sea-level caused by an important cold period occurring around
2.6 Ma (now the base of Quaternary). In this case the tectonic and climatic signal
coupled. |
|
|
|
|
|
|