Research Paper40Ar/39Ar temporal framework for the Alleret maar lacustrine sequence (French Massif-Central): Volcanological and paleoclimatic implications
Introduction
Multidisciplinary studies of lacustrine and paleo-lacustrine sequences (sedimentary, paleomagnetic, pollen sequence, stable isotope, radiochronology, bio-chronology) have shown their potential for describing paleoenvironmental evolutions at local and regional scales (e.g. Reille et al., 2000, Tzedakis et al., 1997, Tzedakis, 2005, Ammann et al., 2000, de Beaulieu et al., 2006, de Beaulieu et al., 2001, von Grafenstein, 2002). In the current context of studies of climate changes such data are extremely important because they help to understand the response times of vegetation changes to orbital forcing at different timescales. The vast majority of continuous paleoclimatic reconstructions extending from the Brunhes-Matuyama Boundary (BMB, c.a. 781 Ka, Singer et al., 2005; recalculated by Kuiper et al., 2008) to the present time are based on marine sediments and ice core archives. However, excluding marine sediments recovered near the continents and containing pollen (e.g. Roucoux et al., 2005, Desprat et al., 2005, Desprat et al., 2006, Shackleton et al., 2002, Shackleton et al., 2003) they do not allow detailed studies of the vegetation response to natural climate changes due to orbital forcing. In some cases, favorable geological conditions have led to the undisturbed accumulation of thick sedimentary lake sequences such as the Bouchet and Praclaux sequences in France (Reille et al., 2000, Roger et al., 1999, de Beaulieu et al., 2006), the Valle di Castiglione in Italia (Follieri et al., 1988, Magri and Tzedakis, 2000), the Ioannina and Tenaghi Philippon in Greece (Tzedakis, 2005, Tzedakis et al., 2006, Roucoux et al., 2008) (Fig. 1). These continental records combined with the marine pollen sequences have led to the emergence of a complete stratigraphical framework in Western Europe of changes in vegetation over the last 450 ka (Tzedakis, 2005, de Beaulieu et al., 2006). Unfortunately, excluding the Tenaghi Philippon sequence in Greece (Tzedakis et al., 2006), the sequence of the Vallo di Diano which (Russo and Cheddadi, 1997;Karner et al., 1999, see Fig. 1) and the Alleret maar (Pastre et al., 2007), lacustrine sequence that covers the interval ranging from 600 to 800 Ka (BMB to the MIS 15) are still extremely rare. It is critical because this period encompassed the Mid-Pleistocene Revolution (725–650 ka, Head and Gibbard, 2005) corresponding to the occurrence of the 100 ka cycle (Lisiecki and Raymo, 2007). Moreover, it also corresponds to the period of increase of sea-ice rafted debris in the northern seas starting around 650 ka (Helmke et al., 2005). The lack of data for this particular period is combined with the fact that a precise terrestrial time scale, for most of the Quaternary terrestrial records is still far from being sufficiently developed (Tzedakis, 2005, Tzedakis et al., 2006). Additional geochronological data from such records are crucial to provide meaningful phase comparisons or correlation with other archives. As a result, information constraining the timing of both terrestrial and marine changes is available only for the last two deglaciations (Tzedakis, 2005, Shackleton et al., 2002, Shackleton et al., 2003). In such general context, any new well-dated lacustrine sequence becomes crucial.
Few places in Europe can potentially provide Early to Middle Pleistocene lacustrine sequences with ash-falls that can be dated using radio-isotopic methods: the Piànico-Sèllere area, the Vallo di Diano basin (Pinti et al., 2001, Pinti et al., 2003, Brauer et al., 2007, Karner et al., 1999), the French Massif Central (FMC) (Roger et al., 1999, Reille et al., 2000, de Beaulieu et al., 2001, Pastre et al., 2007). In the latter, the Pleistocene explosive volcanic activity from the Velay region (FMC, Fig. 1) has generated numerous maar-type craters ranging in age from 2.5 Ma to 200 ka (Turner, 1998, Mergoil and Boivin, 1993). The younger and/or deeper craters are still occupied by lakes (e.g. Bouchet). Several of these maar lakes filling were studied over the last 20 years (e.g. de Beaulieu et al., 2006, Reille et al., 2000, Guiter et al., 2003, de Beaulieu et al., 1992) and they have yielded exceptional palynological and palaoclimatic sequences covering the last 450 ka (Reille et al., 2000, de Beaulieu et al., 2006). In this Maar, thick ash-falls from the Mont-Dore and Sancy volcanoes located only 60 km northwest (Fig. 1). Occurrences of K-rich feldspars such as sanidine make these ash-falls suitable for the laser fusion single grain 40Ar/39Ar method. The pioneer works in this region of Roger et al. (1999) in the Praclaux and Bouchet maars or more recently the study by Pastre et al. (2007) proved that such approach provides precise age control of the past climatic changes. To our knowledge, excluding the Alleret maar sequence (Fig. 1) (Pastre et al., 2007), no Early–Middle Pleistocene long lacustrine sequence is yet documented in France. The upper part of this sequence belongs to the MIS 15 (Pastre et al., 2007). In order to extend this unique record in time, a longer core (Al3) was obtained and sedimentary investigation revealed several thick ash-falls in the lower part of the filling (see core description below).
The aims of this paper are (1) to obtain a precise and accurate time framework for the Alleret maar lacustrine sequence and (2) to put in perspective this new sequence and associated ashes with the available western and south European pollen sequences, global paleoclimatic archives and regional volcanic history. Moreover, according to the investigated time range (e.g. Early Middle Pleistocene), the expected precision for the 40Ar/39Ar method is ≤1% (c.a. 6–7 ka); less than the duration of the onset of glacial inception and allowing important temporal constrains in the future to compare this continental paleoenvironmental records with other records.
Section snippets
Geological setting and the AL3 core
The Alleret maar (Saint-Privat du Dragon, Haut-Allier) is a sub-circular crater of about 1.0 km diameter located at the northwestern edge of the Devès volcanic plateau, 13 km SE from the town of Brioude (Fig. 1, Fig. 2). It is located at the contact zone between the Hercynian metamorphic basement (orthogneiss, sillimanite gneiss) and the basanites from the Devès plateau south of the small Oligocene graben of Paulhaguet and 60 km southeast of the Sancy volcano active from 900 to 250 ka (Cantagrel
40Ar/39Ar analytical method
All the samples were analyzed at the 40Ar/39Ar facility hosted at the LSCE (Gif-sur-Yvette, France). Pristine sanidine grains (160–250 μm) were handpicked from a K-feldspars concentration and slightly leached for 5 minutes in a 5% HF acid solution. A total of 25–30 grains for each sample were loaded in aluminum disks and irradiated 40 min (Irradiation 9) in the β1 tube of the OSIRIS reactor (CEA Saclay, France). The total neutron flux received by the samples ranges from 1.2 10+14 to 2.7 10+14 n/cm−2
40Ar/39Ar results
Full analytical details for individual grain experiments corrected for backgrounds, mass discrimination, and radioactive decay are given online (see online supplement Table T1). Age-probability density spectra with individual single crystal age (2σ) and inverse isochron are presented for each ash layer in Fig. 4. Detailed results for each tephra layer are now discussed:
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S223: A total of 19 crystals were analyzed for this tephra horizon. The age probability spectrum exhibits a unimodal
Discussion
Even if the ages we obtained are precise, the 40Ar/39Ar method accuracy is currently limited by uncertainties in ages of standards and radioactive decay rates reaching about 2.5% (Renne et al., 1998, Min et al., 2000). For this reason, radio-isotopic ages cannot be directly compared to astronomically calibrated ages. During the last decade, several attempts have been made to evaluate and to improve the accuracy of the 40Ar/39Ar method (Min et al., 2000, Kuiper et al., 2008). These works
Conclusions
We have dated, using single grain 40Ar/39Ar method, three new ash layers from the bottom part of the Alleret maar sedimentary filling. A total of four radio-isotopic ages are now available for this lacustrine sequence and suggest that the argillaceous filling represents more than 180 ka in duration MIS 18 (725 ka) to the beginning of the MIS 14 (550 ka). Radio-isotopic ages indicate that at least 6 major pyroclastic events occurred during the “Super-Besse cycle” (Sancy volcano) in only 40 ka with a
Acknowledgements
Hervé Guillou acknowledges the CEA and the CNRS INSU Mi-Lourd for the funding he obtained for the setup of the new LSCE 40Ar/39Ar facility. Authors would like to acknowledged the Bureau de Recherches Géologiques et Minières (BRGM, French Geological Survey) for the AL3 core realization. Comments by Dr. Wijbrans an anonymous reviewer and the editor P.R. Renne greatly improve the manuscript. This is LSCE contribution no. 4014.
Editorial handling by: P.R. Renne
References (50)
- et al.
Quantification of biotic responses to rapid climatic changes around the Younger Dryas – a synthesis
Palaeogeography, Palaeoclimatology, Palaeoecology
(2000) - et al.
Contribution of long pollen sequences to the knowledge of climatic variations in Pleistocene countrysides
Comptes Rendus Palevol
(2006) - et al.
An attempt at correlation between the Velay pollen sequence and the Middle Pleistocene stratigraphy from central Europe
Quaternary Science Reviews
(2001) - et al.
Is vegetation responsible for glacial insolation inception during periods of muted changes?
Quaternary Science Reviews
(2005) - et al.
Climatic variability of marine isotope stage 7: direct land-sea-ice correlation from a multiproxy analysis of a north-western Iberian margin deep-sea core
Quaternary Science Reviews
(2006) - et al.
Direct dating of Plio-Quaternary pumices by 40Ar/39Ar step-heating and single-grain laser fusion methods: the example of the Monts-Dore massif (Massif Central, France)
Journal of Volcanology and Geothermal Research
(1990) - et al.
The last climatic cycles in Western Europe: a comparison between long continuous lacustrine sequences from France and other terrestrial records
Quaternary International
(2003) - et al.
Changes in sedimentation patterns of the Nordic seas region across the mid-Pleistocene
Marine Geology
(2005) - et al.
A potential early middle Pleistocene tephrostratotype for the Mediterranean basin: the Vallo Di Diano, Campania, Italy
Global and Planetary Change
(1999) - et al.
Glacial and volcanic history of Icelandic table mountains from cosmogenic 3He exposure ages
Quaternary Sciences Review
(2007)
Plio-Pleistocene climate evolution: trends and transitions in glacial cycle dynamics
Quaternary Science Reviews
40Ar/39Ar step-heating and laser fusion dating of a Quaternary pumice from Neschers, Massif Central, France: the defeat of xenocrystic contamination
Chemical Geology
Orbital signatures and long-term vegetation patterns in the Mediterranean
Quaternary International
A test for systematic errors in 40Ar/39Ar geochronology through comparison with U–Pb analysis of a 1.1 Ga rhyolite
Geochimica et Cosmochimica Acta
Alder creek sanidine (ACs-2): a Quaternary 40Ar/39Ar dating standard tied to the Cobb Mountain geomagnetic event
Chemical Geology
The Alleret maar (Massif Central, France): a new lacustrine sequence of the early Middle Pleistocene in Western Europe
Comptes Rendus Geosciences
K-Ar dating of an early Middle Pleistocene distal tephra in the interglacial varved succession of Pianico-Sellere (Southern Alps, Italy)
Earth and Planetary Science Letters
40Ar/39Ar dating on tephra of the Velay maars (France); implications for the late Pleistocene proxy-climatic record
Earth and Planetary Science Letters
The response of NW Iberian vegetation to North Atlantic climate oscillations during the last 65 kyr
Quaternary Science Reviews
Vegetation history of the marine isotope stage 7 interglacial complex at Ioannina, NW Greece
Quaternary Science Reviews
Oldest human footprints dated by Ar/Ar
Earth and Planetary Science Letters
The classic marine isotope substage 5e
Quaternary Research
Marine isotope substage 5e and the Eemian interglacial
Global and Planetary Change
Subcommission on geochronology: convention on the use of decay constants in geo-and cosmochronology
Earth and Planetary Science Letters
Volcanic maars, long Quaternary sequences and the work of the INQUA Subcommission on European Quaternary stratigraphy
Quaternary International
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