Variations du niveau marin relatif holocène dans l'ouest de la Bretagne (France): Reconstitution à partir des tourbes de base entre 7600 et 4000 cal. BP

TY - JOUR

T1 - Variations du niveau marin relatif holocène dans l'ouest de la Bretagne (France)

T2 - Reconstitution à partir des tourbes de base entre 7600 et 4000 cal. BP

AU - Goslin, Jérôme

AU - Van Vliet-Lanoë, Brigitte

AU - Stephan, Pierre

AU - Delacourt, Christophe

AU - Fernane, Assia

AU - Gandouin, Emmanuel

AU - Hénaff, Alain

AU - Penaud, Aurélie

AU - Suanez, Serge

PY - 2013

Y1 - 2013

N2 - With respect to others European oceanic facades, the Holocene relative sea-level (RSL) changes along the French Atlantic coasts have received relatively little attention. Even if it received some attention for geophysical modelling (Van de Plassche, 1991; Lambeck, 1997; Leorri et al., 2012), only two field-based studies really dealt with this subject in Western Brittany, agreeing on an oscillatory RSL pattern with a conspicuous pluri-metre negative variation occurring around 3000 BP (Morzadec-Kerfourn, 1974; Stephan, 2011). This paper is the first step on the way to update Western Brittany Holocène RSL data. It presents a new long-term Holocène RSL reconstruction based on basal peat deposits, compaction-free deposits that have been accumulated on top of the Pleistocene formations during the early-Holocene stages of the post-glacial transgression. Data used for the sea-level reconstruction are both new data and previously published datasets we have reassessed. New cores, extracted along the Finistère peninsula in the framework of a coastal risk assessment research program, allowed us to collect new stratigraphie data. Dates initially published on basal peat deposits in previous studies (Morzadec-Kerfourn, 1974) were re-assessed through the same process to allow their incorporation in a combined dataset. In the absence of microfossils in most of our deposits, an alternate approach was used to determine the salinity regime of the basal peat deposit environments through the use of stable carbon isotope ratios and the observation of macro-botanical remains: brackish peat deposits were used as sea-level index points, while freshwater ones provided only high-limiting constraints. Eight new radiocarbon datings were obtained. A total of six new sea-level index-points and six new limiting points allowed us to derivate the long-term (millennial) changes in RSL in Western Brittany. A comparison of these data with some foraminifera-based regional RSL data shows that both data sets closely match. Altogether, the combined data show the RSL bending ca. 7000 and 3000 cal. BP, indicating progressively decreasing rising rates. Further work is needed to fill the centennial to pluri-centennial gaps that remain to ascertain potential periods of stability or strong decrease in the rising rates of the RSL ca. 6200 ± 500 and 3000 ± 500 BP.

AB - With respect to others European oceanic facades, the Holocene relative sea-level (RSL) changes along the French Atlantic coasts have received relatively little attention. Even if it received some attention for geophysical modelling (Van de Plassche, 1991; Lambeck, 1997; Leorri et al., 2012), only two field-based studies really dealt with this subject in Western Brittany, agreeing on an oscillatory RSL pattern with a conspicuous pluri-metre negative variation occurring around 3000 BP (Morzadec-Kerfourn, 1974; Stephan, 2011). This paper is the first step on the way to update Western Brittany Holocène RSL data. It presents a new long-term Holocène RSL reconstruction based on basal peat deposits, compaction-free deposits that have been accumulated on top of the Pleistocene formations during the early-Holocene stages of the post-glacial transgression. Data used for the sea-level reconstruction are both new data and previously published datasets we have reassessed. New cores, extracted along the Finistère peninsula in the framework of a coastal risk assessment research program, allowed us to collect new stratigraphie data. Dates initially published on basal peat deposits in previous studies (Morzadec-Kerfourn, 1974) were re-assessed through the same process to allow their incorporation in a combined dataset. In the absence of microfossils in most of our deposits, an alternate approach was used to determine the salinity regime of the basal peat deposit environments through the use of stable carbon isotope ratios and the observation of macro-botanical remains: brackish peat deposits were used as sea-level index points, while freshwater ones provided only high-limiting constraints. Eight new radiocarbon datings were obtained. A total of six new sea-level index-points and six new limiting points allowed us to derivate the long-term (millennial) changes in RSL in Western Brittany. A comparison of these data with some foraminifera-based regional RSL data shows that both data sets closely match. Altogether, the combined data show the RSL bending ca. 7000 and 3000 cal. BP, indicating progressively decreasing rising rates. Further work is needed to fill the centennial to pluri-centennial gaps that remain to ascertain potential periods of stability or strong decrease in the rising rates of the RSL ca. 6200 ± 500 and 3000 ± 500 BP.

KW - Basal peats

KW - Brittany

KW - Holocene

KW - RSL

KW - Stable C isotopes

U2 - 10.4000/geomorphologie.10386

DO - 10.4000/geomorphologie.10386

M3 - Tidsskriftartikel

AN - SCOPUS:84893037417

SN - 1266-5304

SP - 425

EP - 444

JO - Geomorphologie. Relief, Processus, Environnement

JF - Geomorphologie. Relief, Processus, Environnement

IS - 4

ER -