Daniel Veres
email: daniel.veres@natgeo.su.se

Barbara Wohlfarth

Vale ´rie Andrieu

Linda Ampel

Jacques-Louis De Beaulieu

Siwan Davies

The lithostratigraphy of the Les Echets basin, France: tentative correlation between cores

 and de Beaulieu & Reille (1984a) provides a preliminary chronostratigraphic framework. Sedimentation during MIS3 started with accumulation of sands and silts and was followed by alternating gyttja and clayey gyttja silts. Exceptionally high sedimentation rates during MIS2 led to the infilling of the basin. Alternating organic-rich and minerogenicrich sediments appear to coincide with changes in pollen assemblages (de Beaulieu & Reille 1984a) and suggest that millennial-scale climatic changes controlled lake productivity and catchment stability during most of MIS3.

More than 20 years ago, de Beaulieu & Reille (1984a) presented in Boreas the first results of pollen stratigraphic investigations of a 56-m long lake sediment core obtained from the French site of Les Echets (Fig. 1A). This proved to be an important paper for defining the late Quaternary terrestrial stratigraphy of Europe (de Beaulieu & Reille 1984b, 1989;[START_REF] Guiot | A 140,000year continental climate reconstruction from two European pollen records[END_REF][START_REF] Pons | Recent contributions to the climatology of the last glacial Áinterglacial cycle based on French pollen sequences[END_REF][START_REF] Van Andel | Palaeolithic landscapes of Europe and environs, 150,000 Á25,000 years ago: an overview[END_REF][START_REF] Lowe | Reconstructing Quaternary Environments[END_REF][START_REF] Cheddadi | Was the climate of the Eemian stable? A quantitative climate reconstruction from seven European pollen records[END_REF][START_REF] Allen | Weichselian palynological records from southern Europe: correlation and chronology[END_REF][START_REF] Guiter | The last climatic cycles in western Europe: a comparison between long continuous lacustrine sequences from France and other terrestrial records[END_REF][START_REF] Klotz | Eemian to early Wu ¨rmian climate dynamics: history and pattern of changes in central Europe[END_REF]) and confirmed the successive vegetation communities identified by [START_REF] Woillard | Grande Pile peat bog: a continuous pollen record for the last 140,000 years[END_REF] within the La Grande Pile sequence.

Sediments started to accumulate in the lake basin of Les Echets during the penultimate termination, corresponding with the uppermost part of Marine Isotope Stage (MIS) 6. The series of successive forest episodes alternating with open vegetation were assigned to the climatic substages of MIS5 (de Beaulieu & Reille 1984a& Reille , 1989)). For the middle and upper part of the last glacial period, the pollen stratigraphic record indicated a dominance of cold-tolerant species but also a cyclic occurrence of intervals with high Pinus pollen percentages. Similar features have also been recognized in other long French sequences [START_REF] Reille | Pollen analysis of a long upper Pleistocene continental sequence in a Velay maar (Massif Central, France)[END_REF][START_REF] De Beaulieu | An attempt at correlation between the Velay pollen sequence and the Middle Pleistocene stratigraphy from central Europe[END_REF] and in the laminated lake record from Lago Grande di Monticchio in Italy [START_REF] Allen | Rapid environmental changes in southern Europe during the last glacial period[END_REF].

In addition, results from Lago Grande di Monticchio suggested that the palaeoenvironmental development during the last glacial period was closely linked with climatic changes in the North Atlantic region, where ice cores (e.g. [START_REF] Dansgaard | Evidence for general instability of past climate from a 250-kyr ice-core record[END_REF]North Greenland Ice Core Project Members 2004) and marine sediments (e.g. [START_REF] Bond | Correlations between climate records from North Atlantic sediments and Greenland ice[END_REF][START_REF] Rasmussen | Climatic instability, ice sheets and ocean dynamics at high northern latitudes during the last glacial period (58 Á10 KA BP)[END_REF]) indicate a period of severe climatic fluctuations, both in timing and amplitude. Abrupt shifts between stadial conditions and conditions similar to today's climate characterized this time, while extensive ice sheets covered North America and Europe [START_REF] Svendsen | Late Quaternary ice sheet history of northern Eurasia[END_REF]. These rapid shifts between cold and warm conditions have been termed DansgaardÁOeschger (D ÁO) stadials and interstadials, respectively. Most of the D ÁO interstadials started with an abrupt increase in temperature, thought to occur within a few decades, and some seem to coincide with ice-free conditions along the coast of Norway [START_REF] Raunholm | Weichselian interstadial sediments on Jaeren (SW Norway): paleoenvironments and implications for ice sheet configuration[END_REF]) and in northern Finland [START_REF] Helmens | The Last Interglacial ÁGlacial cycle in NE Fennoscandia: a nearly continuous record from Sokli (Finnish Lapland)[END_REF][START_REF] Sarala | The middle Weichselian interstadial: new OSL dates from southwestern Finnish Lapland[END_REF][START_REF] Ma ¨kinen | Quaternary Studies in the Northern and Arctic regions of Finland[END_REF]. Evidence for D ÁO events has been inferred from a number of different depositional environments in Europe, including marine sediments [START_REF] Rasmussen | Climatic instability, ice sheets and ocean dynamics at high northern latitudes during the last glacial period (58 Á10 KA BP)[END_REF][START_REF] Shackleton | Phase relationships between millennial-scale events 64,000 Á24,000 years ago[END_REF][START_REF] Sa ´nchez-Gon ˜i | Synchroneity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the Mediterranean region[END_REF], speleothems [START_REF] Spo ¨tl | Stalagmite from the Austrian Alps reveals Dansgaard-Oeschger events during isotope stage 3: implications for the absolute chronology of Greenland ice cores[END_REF][START_REF] Genty | Precise dating of Dansgaard-Oeschger climate oscillations in western Europe from stalagmite data[END_REF]) and lake sediments [START_REF] Allen | Rapid environmental changes in southern Europe during the last glacial period[END_REF][START_REF] Tzedakis | Ecological thresholds and patterns of millennial-scale climate variability: the response of vegetation in Greece during the last glacial period[END_REF]) (see also review by [START_REF] Voelker | Global distribution of centennial-scale records for Marine Isotope Stage (MIS) 3: a database[END_REF], suggesting a strong atmospheric teleconnection between marine and continental areas during the last glacial cycle.

In light of these findings from the North Atlantic region, a multiproxy study of the long lake sediment sequence at Les Echets seemed timely for a number of reasons. First, the site offers the potential for highresolution studies of MIS3 and MIS2 (de Beaulieu & Reille 1984a;[START_REF] Voelker | Global distribution of centennial-scale records for Marine Isotope Stage (MIS) 3: a database[END_REF]. Second, the landscape is open to the northwest, making it possible that the site records D ÁO events driven by changes in marine and atmospheric conditions in the North Atlantic region and that the signals would not be biased by orographic effects. Third, earlier investigations focused solely on pollen stratigraphy and a multiproxy investigation and detailed chronology were lacking, which prevented correlations with other records during parts of MIS4 and MIS3 (de Beaulieu & Reille 1984a;[START_REF] Allen | Weichselian palynological records from southern Europe: correlation and chronology[END_REF]. Finally, the timing and spatial extent of the Alpine ice sheet and glacial dynamics in the region during MIS4 to MIS2 are not well constrained chronologically [START_REF] Monjuvent | Glaciers quaternaires dans les Alpes franco-suisses et leur piedmont[END_REF][START_REF] Mandier | Le relief de la moyenne valle ´e du Rho ˆne au Tertiaire et au Quaternaire: essai de synthe `se pale ´oge ´ographique[END_REF][START_REF] Florineth | Alpine evidence for atmospheric circulation patterns in Europe during the Last Glacial Maximum[END_REF]. Given the location of the site in between the Alpine moraine belts [START_REF] De Beaulieu | Les E ´chets: un marais capital pour l'histoire climatique du Quaternaire Rhodanien[END_REF][START_REF] Mandier | Le marais des Echets: premiers enseignements pour l'histoire climato-stratigraphique du Quaternaire Lyonnais[END_REF], crucial information can potentially be extracted from the record of Les Echets by employing a multiproxy approach together with a detailed chronological framework. This record could also form an important link between the well-defined southern European pollen records [START_REF] Allen | Rapid environmental changes in southern Europe during the last glacial period[END_REF][START_REF] Tzedakis | Ecological thresholds and patterns of millennial-scale climate variability: the response of vegetation in Greece during the last glacial period[END_REF]) and north European pollen stratigraphies, which are still fragmentary [START_REF] De Beaulieu | An attempt at correlation between the Velay pollen sequence and the Middle Pleistocene stratigraphy from central Europe[END_REF] and thus difficult to correlate precisely [START_REF] Whittington | The Tolsta Interstadial, Scotland: correlation with D ÁO cycles GI Á8 to GIÁ5?[END_REF].

New sediment cores were obtained at Les Echets during a coring expedition in the autumn of 2001 (Fig. 1B), with the central aim of investigating whether and how the limnic and terrestrial ecosystem responded to the rapid climate variability during the last 140 kyr. This paper is the first in a series directed at a multiproxy re-investigation of the Les Echets sequence for MIS3 and MIS2. The project aimed to constrain the ages of the different temperate periods, earlier recognized in Les Echets during MIS3 and MIS2 (de Beaulieu & Reille 1984a, b), and provide a detailed reconstruction of the response of the terrestrial ecosystem to the abrupt changes observed in North Atlantic records. Here we present detailed lithostratigraphies of the two new sediment cores, including organic matter content and AMS 14 C measurements for the upper 30.06 m in core EC1 and 14.55 m in core EC3, which cover MIS3 and MIS2. We tentatively correlate these sequences with the previously recovered cores based on distinct lithological markers and radiocarbon ages. This correlation and re-investigation of the lithostratigraphy provides insight into the former depositional environment of this lake basin.

Site description

Les Echets is a mire (45854?N, 4856?E) located near the town of Lyon on the south-western part of the hilly Dombes Plateau, France (Fig. 1A,B). It is situated c. 4 km east of the westernmost moraine ridge of the Rissian external moraine complex at an altitude of 267 m a.s.l. [START_REF] De Beaulieu | Les E ´chets: un marais capital pour l'histoire climatique du Quaternaire Rhodanien[END_REF]) (Fig. 2). The mire itself extends over 13 km 2 inside a large glacial basin that covers an area of about 40 km 2 , and the basin rim reaches a maximum of just over 300 m on the moraine ridges. The glacial basin is thought to have been excavated during the penultimate glaciation by the Rho ˆne Glacier and dammed by the Rissian frontal moraines deposited a few kilometres to the west of the site [START_REF] De Beaulieu | Les E ´chets: un marais capital pour l'histoire climatique du Quaternaire Rhodanien[END_REF]. The hills around the basin are composed of Rissian glaciofluvial and Wu ¨rmian aeolian deposits, while the basin itself is filled up with c. 60 m of post-Rissian sediments (Fig. 2). Upper Pliocene and pre-Rissian glaciofluvial deposits are restricted to the southern and western edges of the plateau, while limestones and intrusive rocks outcrop to the west in the Sao ˆne valley. Geomorphological evidence indicates that alpine glaciers did not override the site during the Last Glacial Maximum but formed their terminal moraines (internal moraine belt in the Alpine area) approximately 15 km to the east. Extensive glaciofluvial deposits outcrop in the plains in front of the Wu ¨rmian terminal moraines. The former lake gradually filled-in at the end of the Wu ¨rmian and a large peat bog developed (120 Á130 ha) that today covers c. 10% of the former lake surface. Historical records mention that systematic drainage of the mire began as early as AD 1481 (de Beaulieu & Reille 1984a) and has continued up to the present day. The area receives average annual precipitations of 830 mm and mean annual temperatures are around 9.58C [START_REF] Guiot | A 140,000year continental climate reconstruction from two European pollen records[END_REF].

Earlier investigations at Les Echets

Investigations at Les Echets started several decades ago with a geological survey summarized by [START_REF] De Beaulieu | Les E ´chets: un marais capital pour l'histoire climatique du Quaternaire Rhodanien[END_REF] and [START_REF] Mandier | Le marais des Echets: premiers enseignements pour l'histoire climato-stratigraphique du Quaternaire Lyonnais[END_REF]. During the 1970s a series of drilling attempts resulted in the recovery of several cores (cores A ÁF; Fig. 1B) and the publication of the first composite pollen diagram by [START_REF] De Beaulieu | Les E ´chets: un marais capital pour l'histoire climatique du Quaternaire Rhodanien[END_REF]. Mechanized coring in 1979 in the middle of the palaeolake reached the Rissian till at a depth of 56 m (core G). Above a basal unit of glaciolacustrine, organic-poor laminated clays, the sediment became an intercalation of thick organic-rich gyttjas and marls overlain by a thick succession of clays and silts in the upper 30 m.

The pollen record (upper 39 m of sediment), starting with the Late Rissian pollen zone A, shows that important changes occurred in the structure of the vegetation, with alternating long-standing periods of closed woodlands, open woodland and tundra (de Beaulieu & Reille 1984a, b, 1989). Three important periods of forest development are correlated with the Eemian (pollen zone B), Saint Germain 1 (pollen zone D) and Saint Germain 2 (pollen zone F) and mark the middle part of the sequence overlying the late Rissian sediments. The palynostratigraphic record for this part of the sequence allows a secure comparison with other long lacustrine European records [START_REF] Woillard | Carbon-14 dates at Grande Pile: correlation of land and sea chronologies[END_REF][START_REF] Follieri | A 250 000-years pollen record from Valle di Castiglione (Roma)[END_REF][START_REF] Reille | Pollen analysis of a long upper Pleistocene continental sequence in a Velay maar (Massif Central, France)[END_REF][START_REF] Reille | Pollen analytical biostratigraphy of the last five climatic cycles from a long continental sequence from the Velay region (Massif Central, France)[END_REF][START_REF] De Beaulieu | An attempt at correlation between the Velay pollen sequence and the Middle Pleistocene stratigraphy from central Europe[END_REF][START_REF] Allen | Weichselian palynological records from southern Europe: correlation and chronology[END_REF]. Comparisons of palaeotemperature and precipitation estimates between Les Echets and La Grande Pile produced a highly similar trend for the two sequences [START_REF] Guiot | A 140,000year continental climate reconstruction from two European pollen records[END_REF].

The pollen stratigraphic record above Saint Germain 2 (pollen zones GÁP), however, is rather complex and its correlation with other sites is not as straightforward as the lower part of the sequence. The thick silty sediments yielded a pollen assemblage dominated by herbaceous taxa with sporadic peaks in Pinus pollen. de Beaulieu & Reille (1984a) cautiously interpreted this pollen assemblage as representing sudden and repeated changes in pollen production and delivery from a sparse vegetation cover under cold Átemperate and dry climates. Levels with high Pinus percentages and modest rises in Picea and mesophilous tree pollen may point to a minor expansion of nearby regional forest stands. These assemblages were considered minor interstadials (pollen zones H, J and L) by de Beaulieu & Reille (1984a). [START_REF] Allen | Weichselian palynological records from southern Europe: correlation and chronology[END_REF] noted that these pollen zones might correlate with pollen zones 11, 9 or 7 and 5b at Lago Grande di Monticchio, which would place them approximately between 50 and 26 kyr BP, but this correlation remained tentative given the lack of a good chronology for Les Echets.

Methods

A new coring expedition, undertaken in November 2001 by a joint Swedish ÁFrenchÁAmerican team, recovered two new long sediment cores from Les Echets, EC1 and EC3 (Fig. 1B). Core EC1 (44 m long) was drilled in the presumed middle of the palaeolake, approximately 1.15 km from the palaeoshore, with the intention of replicating core G of de Beaulieu & Reille (1984a), which had been cored c. 0.3 km to the southeast. Core EC3 (24.2 m long) was located c. 0.7 km south of EC1, closer to the former margin of the palaeolake (Fig. 1B). The cores were retrieved with a semi-automatic three-walled stationary piston corer (GEOBOR S 1500 mm) equipped with an outer wall that continuously cuts the sediment during the coring operation and allows the recovery of undisturbed sediment sections in 1.5-m long plastic PVC tubes with a diameter of 11 cm (G. Seret, pers. comm. 2006). A minor disadvantage of this device is that sediments may become compacted during coring and thus may expand when the cores are opened for investigation. The length of each subcore was measured immediately after drilling and after opening, and sediment decompression was estimated to have been minimal. With the exception of two large sediment gaps in the top and middle parts of core EC3 because of the loss of loose sands, sediment recovery was 98% of the drilled length. The cores were split in half in January 2002 and their lithostratigraphy was described in detail. Colour changes were assessed using the Munsell colour chart. One subset of cores was stored in the archive at IMEP, Aix-en-Provence (France), while the other half was transported to Stockholm University (Sweden) for further subsampling. Because of the large volume of work involved in studying such long sequences at high resolution, the work was divided between two teams within the 'Les Echets working group'. The top part of the sequences, corresponding to 30.06 m in core EC1 and 14.55 m in core EC3, which cover MIS3 and MIS2, were the object of the present study.

Volumetric samples for weight loss-on-ignition (LOI) analyses were taken in contiguous 2-cm increments, dried at 1058C for 12 h and subsequently ignited at 5508C for 4 h following the method of [START_REF] Heiri | Loss on ignition as a method for estimating organic and carbonate content in sediments: reproducibility and comparability of results[END_REF]. The weight loss during ignition at 5508C is regarded as the sediment organic matter content and is expressed as percentage loss (%) of the original weight. Samples for AMS 14 C measurements consisted of unidentified limnic and terrestrial plant material and Phragmites sp. These were dried at 1058C overnight in pre-cleaned glass vials before submitting them to the Poznan Radiocarbon Laboratory, Poland. Sample pretreatment included an acid Áalkali Áacid treatment. Radiocarbon ages are expressed as years before present (BP). The limnic plant remains could be affected by a hard water effect; however, the extent of this has to be evaluated by dating many more samples.

Lithostratigraphy of cores EC1 and EC3

Core EC1 (0 Á30.06 m)

The lowermost unit H (30.06Á27.48 m) is composed of dark-grey clayey gyttja silts and laminated clayey silt gyttjas, irregularly interbedded with centimetre-thick silts and sands (Fig. 3). The contact between the sandy horizons and the dominant sediment is very sharp and at times erosional. The organic matter content varies between 2% in the sandy horizons to more than 8% in the clayey silt gyttjas. Vivianite occurs mostly in the lower part of the unit.

A sharp contact between a silt layer and an olivegrey, silty algae gyttja marks the transition to unit G (27.48Á22.49 m), which is composed of alternating layers of highly compacted algae gyttjas, rich in organic matter and dark grey clayey gyttja silts with low organic matter content (Fig. 3). The sediments are occasionally laminated and very thin pale olive to pale yellow silt layers are present throughout. Vivianite occurs in the silty algae gyttjas and plant macrofossils (Phragmites sp.) are locally present in sediments with low organic content. The contact between the different layers is gradual. In the lower part of unit G, the organic matter content increases abruptly (over c. 20 cm of sediment) to /20%, fluctuates around these values for another 50 cm and sharply declines to low values again. These cycles are repeated several times, with each cycle covering more than 1 m of sediment. The last peak in organic matter content (c. 12%) in unit G coincides with blackish grey clayey gyttja silts and is centred around 22.70 m.

A sharp boundary separates unit G from the overlying unit F (22.49 Á18.55 m). This unit is composed of alternating clayey gyttja silts and faintly laminated clayey silt gyttjas and shows the same cyclic sedimentation pattern as the preceding unit (Fig. 3). However, the organic content is considerably lower, attaining around 6% in the clayey gyttja silts and around 12% in the clayey silt gyttjas. Millimetre-thick layers of clayey silt are occasionally observed. Distinct thin organicrich layers occur in the top part of the unit, while vivianite and FeS stains occur throughout.

The sharp decline in organic matter content at 18.55 m coincides with a distinct change in sedimentation at the onset of unit E (18.55 Á16.20 m). This unit is composed of a massive, faintly laminated dark grey clayey silt gyttja, which becomes slightly calcareous in the upper part. The organic content fluctuates around 8%. Distinct thin layers of beige clayey silt occur and coarse plant macrofossils are present. AMS radiocarbon dating of Phragmites macrofossils at 18.295 Á18.29 m depth gave an age of 23 8909/150 14 C BP (Poz-2493).

With the onset of unit D (16.20 Á11.55 m), the sediment becomes more minerogenic (Fig. 3). Dark grey partly oxidized and faintly laminated calcareous clayey gyttja silts make up the bulk of this unit. Vivianite occurs frequently. The organic matter content fluctuates around 6%, with values below 4% at the lower boundary of the unit. Thin horizons of clayey silt gyttjas are present around 14 m and at the transition to the overlying clayey gyttja silts of unit C. Although the lithology of the sediments in unit C (11.55Á5.91 m) is similar to unit D, the sediments appear to be more massive and are only discretely laminated and partly oxidized. This monotonous sedimentation is interrupted at 5.91 m by the appearance of sandy sediments rich in coarse organics that mark the onset of the overlying unit B (5.91 Á0.68 m). This unit is composed of grey clayey gyttja silts with frequent calcareous sandy layers, thin organic layers, sands and faintly laminated silty clays. This alternation of sediments produces an oscillating pattern in the organic matter content, varying between 2% and 10%. Root structures and FeS stains are visible in the upper part. Plant remains from an organic-rich layer between 5.69 m and 5.63 m depth gave an age of 17 0909/90 14 C BP (Poz-2492).

The sequence is capped by a 0.5-m thick black peat that is overlain by a peaty soil rich in clay lenses. The whole of this organic-rich horizon (peat and peaty soil) is distinguished as unit A (0.68 Á0 m). The upper peaty soil is probably disturbed by agriculture.

Core EC3 (0.3 Á15.80 m) Unit H comprises the sediment between 14.55 m and 13.00 m and has sharp lower and upper boundaries (Fig. 4). It starts with a 10-cm thick silty gyttja layer overlain by a clayey silt horizon that inversely grades upwards into massive sandy gyttja silts with occasional fine sand layers (Fig. 4). The contact at 14.55 m is probably erosional, and the majority of the underlying sand layer was lost during coring because of its loose nature.

Unit H is sharply overlain by an alternation of organic-rich gyttja horizons and thick gyttja silts that make up unit G (13.00 Á6.45 m). This unit can be separated into three subunits (Fig. 4): 13.00 Á11.00 m, 11.00 Á9.40 m and 9.40 Á6.45 m. The lower subunit between 13.00 m and 11.00 m consists of two silt gyttja layers separated by faintly laminated gyttja silts. The organic matter content rises abruptly to values around 25% in the silt gyttjas and oscillates around 5% in the gyttja silts. Between 11.00 m and 9.40 m, the sediment is made up of laminated sandy clayey gyttja silts alternating with thin layers of gyttja silts. FeS staining is frequent and coarse organic matter occurs throughout but is not abundant. The organic matter content is low but rises gradually towards the top of the subunit. Three minor peaks reaching around 9% occur in the middle of the subunit. A sudden change in lithology at 9.40 m marks the transition to 3 m of alternating darkgrey silt gyttjas and light-coloured gyttja silts. The organic matter trend follows these lithological changes, with five well-developed peaks of 10% or higher, alternating with low values of around 5%. Although the change in lithology is gradual, the rise to high organic matter values and the return to low values occur abruptly.

Unit F (6.45 Á4.90 m) starts with the appearance of massive FeS-stained slightly calcareous clayey gyttja silts, with a coarsening upwards trend (Fig. 4). Some coarse organic material occurs in the lower part of the unit and becomes abundant upwards. A few thin silt layers are observed in the top part. The organic matter content oscillates between 2% and 6%. A radiocarbon age of 23 6409/150 14 C BP (Poz-2494) was obtained on bulk sediment between 4.98 m and 4.88 m depth.

The overlying succession of faintly laminated clayey silts and clayey silt gyttjas, alternating with silty gyttja clays, that starts at 4.90 m is defined as unit E (4.90Á 3.60 m). The sediment is rich in calcareous clasts, coarse organic matter and vivianite. The contact between individual horizons is sharp and the organic matter content varies between 2% and 5%.

A sudden drop in the organic matter content between 3.60 m and 3.25 m depth to values below 2% marks a change in sediment type to grey sandy clayey silt (Fig. 4). Coarse organic material and carbonate clasts occur occasionally. This horizon is capped by a package of massive silty sands with low organic content (B/2%) but rich in carbonate clasts. The sediment between 2.10 m and 1.65 m was lost during coring. Above this gap, the sediment becomes coarser, massive and rich in plant macrofossils. The organic matter content fluctuates between 0% and 5%. The top 85 cm are made up of pebbly and gravelly silty gyttjas with fluctuating organic matter content (0 Á10%). This part of the sequence is probably disturbed by late agricultural activities. The whole of the sediment between 3.60 m and 0.3 m is grouped as unit DÁB.

Correlation between cores EC1 and EC3

Cores EC1 and EC3 were drilled in different parts of the former lake basin (Fig. 1B): EC1 was drilled close to the presumed centre of the basin and EC3 closer to the former shore. The different locations of the two profiles within the basin have certainly created different depositional environments, affecting sediment composition and deposition. We might expect more continuous deposition of fine-grained organic sediments in the deeper part of the basin, while clastic and coarser grained sediments accumulated around the margin of the basin. Also, the deeper site may have been less sensitive to changes in water levels compared with the marginal core, where lake level variations may have resulted in periods of non-deposition or reworking. Figure 5 shows a tentative correlation between cores EC1 and EC3, based on lithological markers, radiocarbon ages and trends in organic matter content but also taking into account the respective location of the cores and the resulting differences in sediment lithology and sedimentation rate.

The two sequences can be well correlated for the lowermost unit, H. This is the only interval in the two cores that shows abundant detrital sandy layers, suggesting that the sediments below 27.48 m in core EC1 might be contemporaneous with the sediments below 13.00 m in EC3. The well-sorted sandy layers are intercalated in clayey gyttja silts (EC1) and sandy gyttja silts (EC3) and may indicate oscillations in water level over shorter time intervals and/or periodical delivery of coarser sediments from the lake catchment.

Unit G is characterized by alternating layers of clayey gyttja silt, algae gyttja and clayey silt gyttja (EC1) and slightly more minerogenic sediments (clayey gyttja silt and clayey silt gyttja) in EC3 (Fig. 5). The alternation between more minerogenic and more organic sediments is clearly reflected in the organic matter content, which in this unit displays the most distinct variations in both sequences. We therefore assume that sediments between 27.48 m and 22.49 m in EC1 and between 13.00 m and 6.45 m in EC3 belong to the same sedimentary facies. Increased catchment erosion as a result of decreased vegetation cover during colder periods might have delivered more minerogenic sediments to the lake basin, while the algae gyttjas reflect higher aquatic productivity during more temperate intervals. Moreover, Phragmites macrofossils in layers with low organic matter content could indicate lower lake levels, while the algae gyttjas were probably deposited during periods with higher water levels. Sediments between 13.00 m and 9.50 m in core EC3 cannot be directly correlated with core EC1. The shape and amplitude of the organic matter peaks between 13.00 m and 11.00 m, as well as the interval with stable medium to high organic content between 11.00 m and 9.40 m, are features that are not recognizable in core EC1. Consequently, this would imply that either more sediment accumulated in the marginal part compared with the deeper part of the basin or the sediments in EC1, which are equivalent to the lower part of unit G in EC3, were eroded after their deposition. If dramatic lake-level changes took place, these could indeed have led to a partial erosion of older layers and could explain why the bottom part of unit G (between 13.00 m and 9.40 m) in core EC3 is missing in core EC1 (Fig. 5). However, as sediments are lacking in the deeper EC1 site, it would require erosion from bottom currents, perhaps as countercurrents to the dominating wind direction and focused on the deeper parts of the basin.

Based on the sediment lithology and organic matter curve, we assume that the clayey gyttja silt between 6.45 m and 4.90 m (unit F) in core EC3 could possibly correlate with the clayey silt gyttjas and gyttja silts encountered in core EC1 between 22.49 m and 18.55 m (Fig. 5). The sediments in unit E are made up of clayey silt gyttja, which in EC3 are overlain by gyttja silt/ gyttja clay, indicating slightly more minerogenic deposition in marginal areas. The age of 23 8909/150 14 C BP at 18.29 m in EC1 is close to the age of 23 6409/150 14 C BP obtained at 4.88 Á4.98 m in EC3, which supports the correlation. Additionally, the marked decline in organic matter content at the transition to unit D is a feature recognizable in both cores and may represent a synchronous event.

At 16.20 m the sediments in EC1 change to massive, faintly laminated clayey gyttja silts with no indications of hiatuses or erosional boundaries between the different layers that make up units D and C (Fig. 5). The low organic matter content may be a consequence of low aquatic productivity under cold climatic conditions and/or dilution of the organic fraction by high input of minerogenic particles (Meyers & Lallier-Verge `s 1999). High sedimentation rates for units D and C are indeed indicated by the radiocarbon ages of 23 8909/150 14 C BP and 17 0909/90 14 C BP obtained at 18.29 m and 5.69 Á5.63 m, respectively. The presence of vivianite coatings on macrofossils may also indicate that the organic matter was buried rapidly, probably under anaerobic conditions [START_REF] Fagel | Vivianite formation and distribution in Lake Baikal sediments[END_REF].

Anaerobic conditions would have prevented bioturbation of the sediment, which in turned would have favoured the preservation of sediment laminations in this part of the sequence.

Unit B (5.91 Á0.68 m) in core EC1 is composed of calcareous sediments with sand lenses, which may indicate sediment starvation and a low-energy sedimentary environment in this late stage of basin infilling. As a whole, units D ÁB may be interpreted as reflecting the gradual infilling of the basin. The package of sediments above unit E in both cores suggests that high and variable sedimentation rates for the distal units were associated with shoreward thinning and upward coarsening for the littoral areas (Figs 5,6). The coarse minerogenic sediments overlying unit E in EC3 cannot be further subdivided but probably indicate deposition in shallow water and may be synchronous with units D ÁB in EC1. The slopes adjacent to the mire are made up of unconsolidated and unsorted glaciofluvial deposits. During times of little vegetation cover (e.g. MIS2) and increased slope instability, these deposits could have provided the sediment for rapid infilling of the basin, which was probably achieved shortly after 17 0909/90 14 C BP (Poz-2492). Moreover, reworking of sediments from the littoral zone, as a result of changes in water level, might have been an important supplier of sediment to the middle of the lake. In addition, the occurrence of nearby aeolian sediments points to the fact that airborne particles may account for a large part of the sediments corresponding to MIS2 (de Beaulieu & Reille 1984a).

The uppermost unit A in core EC1 has no counterpart in EC3 and indicates that the marginal areas of the lake had already been filled in at the time of deposition of unit A in EC1.

Correlation of cores EC1 and EC3 to the earlier investigated sequences

Based on detailed pollen stratigraphy, de Beaulieu & Reille (1984a) attempted to correlate the littoral cores IVÁC, III ÁB and V ÁD of de [START_REF] De Beaulieu | Les E ´chets: un marais capital pour l'histoire climatique du Quaternaire Rhodanien[END_REF] and the centre core G (Figs 1B,6, Table 1). Their correlation showed that a number of hiatuses are evident in both sequences and that only parts of the pollen zones recognized in the central core G are present in the marginal cores III ÁV/B ÁD.

The sequence between 30 m and 36 m in core G is composed of alternating layers of gyttja and clayey silt (pollen zones B ÁF) and correlates with the interval between 17 m and 23 m in marginal cores III ÁV/B ÁD (Table 1) [START_REF] De Beaulieu | Les E ´chets: un marais capital pour l'histoire climatique du Quaternaire Rhodanien[END_REF]de Beaulieu & Reille 1984a). This succession has a pollen signal typical of vegetation development during the Eemian, Melisey 1, Saint Germain 1, Melisey 2 and Saint Germain 2 Reille (1984aReille ( , b, 1989) ) and are summarized in Table 1.

in France (de Beaulieu & Reille 1989;[START_REF] Reille | Pollen analysis of a long upper Pleistocene continental sequence in a Velay maar (Massif Central, France)[END_REF][START_REF] Reille | Pollen analytical biostratigraphy of the last five climatic cycles from a long continental sequence from the Velay region (Massif Central, France)[END_REF][START_REF] Pons | Recent contributions to the climatology of the last glacial Áinterglacial cycle based on French pollen sequences[END_REF] and in the Mediterranean region [START_REF] Allen | Weichselian palynological records from southern Europe: correlation and chronology[END_REF][START_REF] Tzedakis | Ecological thresholds and patterns of millennial-scale climate variability: the response of vegetation in Greece during the last glacial period[END_REF]. The sediment succession between 38 m and 31 m in core EC1 that overlays the glacial clays/silts can be correlated lithologically to core G and therefore attributed to the Eemian, Melisey 1, Saint Germain 1, Melisey 2 and Saint Germain 2.

Table 1. Pollen stratigraphic correlation between core G and the littoral cores (III ÁV/B ÁD) and summary of the main climatic events identified by [START_REF] De Beaulieu | Les E ´chets: un marais capital pour l'histoire climatique du Quaternaire Rhodanien[END_REF]) and de Beaulieu & Reille (1984a, b, 1989) Similarly, the sequence of layers between 24 m and 14 m in EC3 seems to be equivalent to the interval between 23 m and 18 m in cores III ÁV/BÁD (Fig. 6).

The pollen stratigraphies for the Middle and Upper Wu ¨rmian (B/30 m in core G and B/14 m in cores III Á V/B ÁD) were difficult to correlate [START_REF] De Beaulieu | Les E ´chets: un marais capital pour l'histoire climatique du Quaternaire Rhodanien[END_REF]de Beaulieu & Reille 1984a, b). It was tentatively suggested that pollen zones G ÁL in core G may be equivalent to zones VIIa ÁVIIefg in the marginal core and that pollen zones M ÁO may correspond to pollen zones VIIhij (Fig. 6, Table 1). Frequent hiatuses in the marginal sequence indicate periods of lake-level changes, which complicate a precise correlation with core G (de Beaulieu & Reille 1984a). Moreover, rapid infilling of the basin (pollen zones M ÁP) and/or low lake levels may have led to non-deposition in marginal areas. The sediments corresponding to pollen zones G ÁL in core G are composed of alternating layers of gyttja, gyttja silts and clayey silt and show an alternation between cold and dry woodless periods (pollen zones G, I and K) and periods with locally sparse wood stands (pollen zones H, J and L), with mainly Pinus but also some Picea (de Beaulieu & Reille 1984a). The pollen stratigraphic correlation between core G and cores III ÁV/B ÁD suggests hiatuses in the sediment record of the marginal cores corresponding to pollen zones H, I and K (Table 1). Although pollen zones M ÁP are mainly characterized by steppe elements, Pinus pollen values reach nearly 30% in zone N and show a number of abrupt and short peaks (de Beaulieu & Reille 1984a) that could indicate either long-distance transport of pollen or the presence of some pine trees in the region. Radiocarbon dates for pollen zones L ÁN obtained between 14.50 m and 24 m in core G give ages of between 18 000 and 24 500 14 C BP and infinite ages at around 24.50 m (Fig. 6).

Assuming that cold Ádry periods in our sequence are represented by more minerogenic sediments and low aquatic productivity, and warmer intervals by higher organic matter and higher aquatic productivity, the changes in lithology in cores EC1 and EC3 may be correlated with the vegetation succession and climatic inferences (cold Ádry vs. warm) suggested by de Beaulieu & Reille (1984a). Based on the lithology and organic matter values, we therefore tentatively correlate the sediment succession between 31.00 m and 27.48 m in EC1 and between 14.00 m and 13.00 m in EC3 with the interval comprising pollen zones G ÁI in core G and pollen zone VIIa in cores III ÁV/B ÁD, respectively (Fig. 6). Lithological units G ÁE in core EC1 (27.48 Á18.55 m) and EC3 (13.00Á3.60 m), which display marked variations in organic matter content and as such distinct changes in lake productivity, lake levels or erosion, very probably have a counterpart in pollen zones JÁN in core G and pollen zones VIIbcd Á VIIhij in cores III ÁV/B ÁD, where minor interstadials alternate with colder intervals. The predominantly clastic sediments with low organic matter in lithological units D ÁB document rapid infilling of the lake basin, possibly under cold and dry climatic conditions. These units may correspond with pollen zones O ÁP, for which steppe vegetation and extreme cold Ádry climates have been inferred (de Beaulieu & Reille 1984a). Moreover, radiocarbon dates of between 17 500 and 15 000 14 C BP in pollen zones O ÁP in core G indicate rapid sedimentation and compare well with the age of 17 010 14 C BP obtained for EC1 at 5.69 Á5.63 m.

The tentative correlation of cores EC1 and EC3 with the pollen stratigraphic record of cores G and III ÁV/ B ÁD shows that the sediments above 31 m in EC1 and above 14 m in EC3 were deposited during the middle and upper part of the last glacial, i.e. correspond with MIS3Á2. However, only the combination of pollen stratigraphy with other environmental proxy data and an independent chronology will allow a precise characterization of the different warmÁcold intervals that occurred during this time and their correlation with other archives. Still, our preliminary data show that the new sequence obtained at Les Echets will form an important contribution for a better understanding of the rapid climatic shifts that prevailed during the last glacial period and their impact on the terrestrial environment.

Conclusions

Two long sediment cores (EC1 and EC3) recently recovered from the Les Echets basin have been investigated and correlated based on detailed lithostratigraphy and fluctuations in organic matter content. A chronostratigraphic framework for the two sequences is based on AMS radiocarbon dates and an intrabasin correlation is proposed for the two new sediment cores and the lithostratigraphic data summarized by [START_REF] De Beaulieu | Les E ´chets: un marais capital pour l'histoire climatique du Quaternaire Rhodanien[END_REF]de Beaulieu &Reille (1984a). Based on these correlations, we conclude that the two new cores span MIS3 and MIS2, with three distinct periods of lake development evident during this time interval. Coarse sands and silts poor in organic matter accumulated at the onset of MIS3, while cyclic deposition of relatively organic-rich and organic-poor sediments characterize a large part of MIS3. Massive and rapid sedimentation of highly minerogenic sediments occurred during most of MIS2. The lake ultimately filled in during MIS2 and an extensive Holocene peat bog developed. We also note that there are substantial sedimentological differences between the proximal and distal areas of the former lake. The littoral areas support a more discontinuous, clastic sedimentation while the centre of the lake is more complete, rich in finer sediment and organic matter. Based on the intrabasin transect, we show that the sediment supply to the lake increased significantly during MIS3 and in the later stages of in-filling, providing an exceptional high-resolution terrestrial climatic record over MIS3 and MIS2. However, the most intriguing feature of the sequence is the cyclic alternation of relatively organic-rich and organic-poor sediments corresponding with the lithostratigraphic units G and E (MIS3). The organic-rich intervals are easily identifiable and the transitions to and from the minerogenic horizons are sharp but not erosional, indicating that important hydrological and geochemical changes occurred in the lake's regime at the time of their deposition. A close comparison with core G (de Beaulieu & Reille 1984a) indicates that the cyclic changes in the organic matter content coincide with recurring changes in pollen assemblages, suggesting that millennial-scale climatic changes controlled the lake's productivity and catchment stability during most of MIS3. A high-resolution dating effort as well as a multiproxy analytical investigation is currently in progress that will clarify the nature of these fluctuations and determine their relationship to D ÁO cycles.

Fig. 1 .

 1 Fig. 1. A. Location of the study area in Europe. B. Topographic map of the Les Echets basin. The new cores EC1 and EC3 are shown by black squares and previous coring locations by grey squares (de Beaulieu et al. 1980; de Beaulieu & Reille 1984a). The extent of the mire is approximately equivalent to the 275 m a.s.l. contour line. The shaded area to the west of the mire marks the Rissian external moraine belt.

Fig. 2 .

 2 Fig. 2. Simplified geological map of Les Echets area (adapted after J. Brulhet, pers. comm. 2006).

Fig. 3 .

 3 Fig. 3. Lithostratigraphy, radiocarbon ages and organic matter content (LOI) of Les Echets core EC1 (1.50 Á30.00 m) (see Fig. 5 for legend). The undulating horizontal lines mark erosional layer boundaries. The length of the individual subcores is shown by grey bars. Two intervals with contrasting lithologies are detailed in the expanded views to the right of the figure.

Fig. 3

 3 Fig.3(Continued)

Fig. 4 .

 4 Fig. 4. Lithostratigraphy, radiocarbon ages and organic matter content (LOI) of Les Echets core EC3 (0.30 Á14.55 m) (see Fig. 5 for legend). The undulating horizontal lines mark erosional layer boundaries. The length of the individual subcores is shown by grey bars.

Fig. 5 .

 5 Fig. 5. Lithostratigraphic correlation (dashed lines) between Les Echets cores EC1 and EC3 based on lithological markers and the organic matter content (LOI). The dotted line indicates where the correlation is uncertain. The undulating horizontal lines mark erosional layer boundaries.

Fig. 6 .

 6 Fig. 6. Stratigraphic transect (south to north) through the Les Echets basin (adapted from Mandier 1981) combining data from previous drillings (see Fig. 1B and Table 1) and the new cores EC1 and EC3. Details on the lithology and palaeoenvironmental interpretation of cores I, II ÁA, III ÁB, IV ÁC, V ÁD, E and F/G are given in de Beaulieu et al. (1980) and de Beaulieu &Reille (1984aReille ( , b, 1989) ) and are summarized in Table1.

  at Les Echets.

		Pollen zones core G
	Pollen zones cores III ÁV/B ÁD	(de Beaulieu &
	(de Beaulieu et al. 1980)	Reille 1984a)	Pollen stratigraphy/inferred vegetation
	Diagramme II	P	Pinus values decrease to c. 10%, Artemisia increases:
			steppe
			Start of Oldest Dryas
	VIIhij	O	Pinus values of 15 Á20%: steppe
		N*	Pinus values c. 30% with abrupt and short peaks
	End of Wu ¨rmian pleniglacial, cold and dry steppe
		M*	Pinus values B/10%
	VIIefg	L*	Very weak interstadial
		K*	Woodless, very dry phase
	VIIbcd	J*	Interstadial, minor tree expansion
		I*	Woodless immediate surroundings, sparse regional
			woodstands
		H*	Interstadial, locally sparse woodland
	Plant species during H, J and L require /108C mean July temperature
	Pollen zones G ÁL indicate cold and dry climate
	VIIa	G	Cold period
	VI	F7	Ognon 1
	V	F 6
	IVd	F5
	IVc	F4
	IVa reworked	Missing	Saint Germain 2
		F3
		F2
		F1
	?	E4	Melisey 2
	?	E3	Reworked sediments/pollen
	III	E2	Reworked sediments/pollen
	IIg	E1
	IIf	D11*
	Missing	D10
		D9
		D8
		D7
	IIe	D6	Saint Germain 1
	IId	D5
	Missing	D4
		D3
		Hiatus?
		D2
		D1	Lower part possibly reworked
	IIc2	C/reworked	Melisey 1
	IIc1 reworked		Reworked older sediments
	Missing	B9
	Missing	B8
	Missing	B7
	Missing	B6a, b	Eemian
	IIb	B5*
		Short hiatus
	IIa	B4
	Missing	B3	Reworking of older sediments or persistent aridity?
	Missing	B2
	Ib	B1
	Missing	A2a, b, c	End of Riss
	Ia	A1a, b*
	*Correlation uncertain.

Acknowledgements. Á We thank J. J. Lowe, an anonymous reviewer and the editor J. A. Piotrowski for their constructive comments and remarks. We are also grateful to T. Lacourse for editing and suggestions on an earlier draft of this paper. This is a contribution to the ESF EuroCores on EuroCLIMATE project RESOLuTION.


Etienne Valette

Bril El-Haouzi

Guillaume Demesure
email: guillaume.demesure@univ-lorraine.fr

Toward a Social Holonic Manufacturing Systems Architectures based on Industry 4.0 assets

Keywords: Industry of the future, MAS, HMS, CPS, IoT, Social approach, Human integration

For the last decade, the question of anthropocentric approaches has made its way through the research, and fully technocentered approaches have been questioned. The integration of social relationships between the components of systems has al-ready been identified as a crucial issue for the future development of reference architectures. However, the current research lacks a global approach based on both consideration of the human as an integrated agent of the system and the use of social concept to characterize inter-agents' relationships. The purpose of this paper is to bring an overview of these aspects' consideration in the manufacturing control architecture and to outline some guidelines allowing to revise the architecture of reference PROSA.

Introduction

Over twenty years have passed now since the proposition of the PROSA architecture for HMS [START_REF] Brussel | Reference architecture for holonic manufacturing systems: PROSA[END_REF]. Based on the constant evolutions of the market and of the technology (especially Information and Communication Technologies (ICT)), many agile, adaptative & reconfigurable architectures for HMS control have emerged [START_REF] Morel | Manufacturing Enterprise Control and Management System Engineering: paradigms and open issues[END_REF]- [START_REF] Jimenez | Pol-lux: a dynamic hybrid control architecture for flexible job shop systems[END_REF]. These architectures were using various approaches, like the centralized, decentralized, hybrid or product driven ones.

They have been classified by Cardin & al. [10] as "generic", "multi-agent oriented", "holonic architectures' extensions", "service & cloud oriented" or "dynamic". According to the authors, if Data have been established as well integrated into these, some issues appeared as maybe insufficiently challenged. Among them: ability to adapt to unplanned issues, sustainability, Data warehousing, and integration of the human in the loop. In short: these architectures are still mainly techno-centered.

Therefore, they are difficult to implement within actual industrial systems and their adaptation to future ones might stay uneasy.

Hence, future work should aim to answer the two following questions:

1. How to make today's reference architectures suitable for concrete implementation within concrete industrial systems?

2. How could these architectures take advantage from new concepts introduced by paradigms such as Industry 4.0?

Most of Intelligent Manufacturing System (IMS) community researchers agree on the lack of human aspects' consideration in manufacturing control architectures to answer these questions. Indeed, concrete industrial systems face with legacy systems, where multiple aspects of human factors need to be considered, e.g. cooperation support between either human or technological entities, development of human-inspired social interactions, integration of human on different decisional levels. Co-operation between human and technological entities has been widely studied, especially in air traffic, car/train driving and robotic applications domains. Concerning humanmachine cooperation, many efforts have been provided about balancing humanmachine interactions, improving human-machine communication, or under-standing human behaviour [START_REF] Flemisch | Shared control is the sharp end of cooperation: Towards a common framework of joint action, shared control and human machine cooperation[END_REF].

Anyway, human integration in manufacturing systems is a challenging issue [START_REF] Valette | Toward an anthropocen-tric approach for hybrid control architectures: case of a furniture factory[END_REF] Cooperation must be established between different kind entities/agents from different nature, such as intelligent products, intelligent resources, or humans. Because of these differences of nature, cooperation between agents could be achieved through different approaches. Our idea is, that a social approach for the description of relationships between a system's different agents (human or artefact) might ease the future design and implementation of human-adapted Holonic and Multi-Agent Systems (MAS) control architectures into real systems as well as their apprehension by human agents.

We believe that integrating the human back in the loop into industrial systems, along with other agents is at the heart of the initiative Industry 4.0. As a matter of fact, Industry 4.0 is today taken as background for almost all current research and publications concerning these systems' architectures design. For this reason, we have chosen to investigate an approach based on the notions of Cyber-Physical Systems (CPS) and Internet of Things (IoT), which are fundamentals in Industry 4.0, applied to Multi-Agent Systems. The Industry 4.0 [START_REF] Acatech | Securing the future of German manufacturing industry: Recom-mendations for implementing the strategic initiative INDUSTRIE 4.0 -Final re-port of the Industrie 4.0 Working Group[END_REF] has burst out in 2011 during Hanover Fair, forwarding the effort that Germany was doing to promote computerization in industry. In 2013, the Final Report of the Working Group Industrie 4.0 [START_REF] Acatech | Securing the future of German manufacturing industry: Recom-mendations for implementing the strategic initiative INDUSTRIE 4.0 -Final re-port of the Industrie 4.0 Working Group[END_REF] was submitted, identifying several keys for successful implementation. If the concept was born in Germany, many national initiatives are currently led across the world. We can especially mention the USA's "National Network for Manufacturing Innovation (NNMI)", the United Kingdom's "High Value Manufacturing Catapult (HVMC), the South Korean "Manufacturing Industry Innovation 3.0 Strategy", the French "Industry of the future" and the Chinese "Made in China 2025" [START_REF] Bidet-Mayer | L'industrie du futur à travers le monde[END_REF]. The innovative vision and concepts that all these initiatives brought have marked the beginning of what is now considered as the fourth industrial revolution, simply referred as "Industry 4.0". Today's literature is mainly focused on the technological aspects and developments that will be needed to support the transition to future industrial's systems. Artificial Intelligence and all its aspects (neural networks, Big Data, Data mining & refining, Deep Learning, etc.) might be the most wildly known ones. These new technologies have brought out the two new paradigms of Internet of Things (IoT) and of Cyber-Physical Systems (CPS). In what follows, we will focus on these two notions, that have already been widely studied for the last 15 years. Our focus will be on the integration of human factors that is at the heart of Industry 4.0's considerations.

CPS & IoT

The CPS paradigm is commonly recognized as the main pillar of Industry 4.0. Since the popularity of this concept is rather new in the scientific world (first enunciated by Lee in 2006 [START_REF] Lee | Cyber-Physical Systems -Are Computing Foundations Ade-quate?[END_REF]) and because of the wide range of its potential applications despite standardization attempts, its definition and limits are still fuzzy and unclear. In fact, the term of CPS is often associated with the one of Internet of Things (IoT), appeared in the 2000s [START_REF] Ashton | That "Internet of Things" Thing[END_REF]. Hence, IoT is the eldest concept, while the CPS term only appeared 7 years later.

For the Internet of Things, Madakan & al. [START_REF] Madakam | Internet of Things (IoT): A Literature Review[END_REF] gave the definition of: "an open and comprehensive network of intelligent objects that have the capacity to autoorganize, share information, data, resources, reacting and acting in face of situations and changes in the environment". In this definition, the IoT is clearly considered as a link between physical objects within a system. Cyber-Physical Systems were defined by Lee [START_REF] Lee | Cyber-Physical Systems -Are Computing Foundations Ade-quate?[END_REF] as "physical and engineered systems whose operations are monitored, coordinated, controlled and integrated by a computing and communication core. This intimate coupling between the cyber and physical will be manifested from the nano-world to large-scale wide-area systems of systems. And at multiple time-scales". Here, the CPS concept is related to the notion of "coupling" between physical and computational objects, and this is the definition we will be willing to stick to.

Considering the previous definitions, the Bagheri & Lee's conception seems adequate to represent CPS and IoT as we see them. IoT linking objects through horizontal connectivity / synchronization and CPS using cloud and sensors connection to link physical objects to their digital twin through vertical connectivity / synchronization (Fig. 1) [START_REF] Bagheri | Big future for cyber-physical manufacturing systems[END_REF].

Fig. 1. CPS & IoT [18]

El Haouzi [START_REF] Haouzi | Contribution à la conception et à l'évaluation des architec-tures de pilotage des systèmes de production adaptables : vers une approche anthropocentrée pour la simulation et le pilotage[END_REF] as well as Bordel & Alcarria [START_REF] Bordel | Cyber-physical systems: Ex-tending pervasive sensing from control theory to the Internet of Things[END_REF] stated that the definition and use of the terms CPS and IoT were differing depending on the scientific community (mechatronic engineering used to the CPS term) or to the geographical area considered (America: CPS; Europe & Asia: IoT). Hence, it is sometimes difficult to fully gets an author's purpose, for its comprehension and use of these terms might be unclear. For this reason, we will not do any dichotomy based on the previous elements between CPS and IoT in the subsection 2.3 and the section 3.

2.3

The Industrial aspect

In the previous subsection, we are presenting the CPS and the IoT as pillars of the Industry 4.0. However, their industrial application is not obvious. The concept of Industrial Internet of Things (IIoT), Industrial Internet (II) or Cyber-Physical Production Systems (CPPS) has emerged as an implementation of IoT and CPS within industrial contexts.

Schneider [START_REF] Schneider | The Industrial Internet of Things (IIoT): Applications and Tax-onomy[END_REF] have stated that the IoT could be seen as divided into two main subsets: The Consumer IoT and the Industrial IoT (respectively CIoT & IIoT). The CIoT would concern the connectivity of things around humans while IIoT would exclusively be concerning connectivity around industrial things. It is defined as "A system comprising networked smart objects, cyber-physical assets, associated generic information technologies and optional cloud or edge computing platforms, which enable real-time, intelligent, and autonomous access, collection, analysis, communications, and exchange of process, product and/or service information, within the industrial environment, so as to optimize overall production value". The IIoT is then considered as a fully techno-centered application of the IoT's concepts in the restricted area of an industrial system. In Boyes & al.'s publication [START_REF] Boyes | The industrial internet of things (IIoT): An analysis framework[END_REF], this approach is confirmed. The functions of the IIoT were there defined as "to monitor, collect, exchange, and analyse information so as to enable them to change their own behaviour, or else instruct other devices to do so, without human intervention".

Hence, authors like Schneider, Boyes & al or Gilchrist [START_REF] Schneider | The Industrial Internet of Things (IIoT): Applications and Tax-onomy[END_REF]- [START_REF] Gilchrist | IIoT Reference Architecture[END_REF] are putting forward a dichotomy between "humans" and "things" connectivity, humans being only considered as the "customers" of connected industrial things. These reasonings are differentiating the human operator from other agents and are accentuating the lack of hu-man-oriented considerations during the system's design. This leads to a system where human agents might face physical or mental overloads, lower their situational awareness, etc. perturbing the completion of their tasks and the global system itself. These issues are at the very basis of the "Magic human" phenomena [START_REF] Trentesaux | A Human-Centred Design to Break the Myth of the "Magic Human" in Intelligent Manufacturing Systems[END_REF] and are incompatible with Industry 4.0's considerations.

On the other side, Monostori's development of CPS [START_REF] Monostori | Cyber-physical Production Systems: Roots, Expectations and R&D Challenges[END_REF] presents the CPPS as an interconnection of cooperative elements and sub-systems "in situation dependent ways, on and across all levels of production, from processes through machines up to production and logistics networks" that would be the communication's enabler and support between "humans, machines and products alike". In this conception, human's integration into systems is implicit: human-machine symbiosis is even enunciated as one of the future R&D challenges for CPPS. Though, it has to be taken carefully, for a too strong dependence of the human on the system could raise important issues [START_REF] Pacaux-Lemoine | ETHICAL RISKS OF HUMAN-MACHINE SYMBIOSIS IN INDUSTRY 4.0[END_REF]. In the next section, we will study some of the main -approaches that have been initiated for human integration.

3

Human integration

Human's current consideration

A little while before the advent of Industrie 4.0, the lack of consideration of the human factors into the development of CPS led Wang [START_REF] Wang | The Emergence of Intelligent Enterprises: From CPS to CPSS[END_REF] to promote the concept of Cyber-Physical Social System (CPSS). With CPSSs, he assesses the importance of human factors' integration within systems. In order to achieve this integration, along with cyber and physical spaces, physiological, psychological, social and mental spaces are considered [START_REF] Liu | Cyber-Physical-Social Sys-tems for Command and Control[END_REF], [START_REF] Shi | Cyber Physical Socio Ecology[END_REF].

This concern has been shared by Schirner & al. [START_REF] Schirner | The Future of Human-in-the-Loop Cyber-Physical Systems[END_REF] and Pirvu & al. [START_REF] Pirvu | Engineering insights from an anthropocentric cyber-physical system: A case study for an assembly station[END_REF] who have respectively worked on the concepts of Human-In-The-Loop Cyber-Physical-Systems (HITL-CPS) and Anthropocentric Cyber-Physical-Systems (A-CPS). The later development of these being Cimini & al.'s Social Human-In-The-Loop Cyber-Physical Production System (Social-HITL-CPPS) [START_REF] Cimini | A human-in-the-loop manufac-turing control architecture for the next generation of production systems[END_REF]. HITL-CPS consists in an embedded system enhancing a human being's ability to interact with its physical environment and A-CPS is defined as a reference architecture integrating the three physical, computational/cyber and human components. The purpose of these works is the integration of human factors into systems (mainly but not exclusively industrial ones).

But even if the need to consider elements such as physiology, psychology, social and mental aspects is recognized, a neat distinction is made between humans and "things" constitutive of the system. The human is considered as a stranger needing to be integrated within a system through interfaces and then stays distinct from other agents. These approaches are forwarding technological development to link the human to the systems.

Concerning the Social HITL-CPPS, Cimini & al. [START_REF] Cimini | A human-in-the-loop manufac-turing control architecture for the next generation of production systems[END_REF] are defining humans as agents fully integrated to the system. The authors have identified the interpretation of hu-man agent's behaviour and their coordination with other agents as the two main challenges in the integration of humans into social environments (and not only manufacturing ones). To answer these challenges, a three-layer architecture has been proposed. This architecture is connecting, on one hand, human users to the cyber part through user interfaces, and on the over hand, physical parts (i.e. non-human agents & environment) to the cyber part through a network.

In all these approaches, human integration is achieved through human-machines or human-systems interfaces. Hence, these can be considered as techno-centered approaches for human integration. If the term "social" is here used as a keyword to mark the human-centered considerations of the authors, it can also refer to a completely different conception.

3.2

The social approach

In order to structure the IoT despite the growing number of objects composing it, Atzori & al. [START_REF] Atzori | SIoT: Giving a Social Structure to the Inter-net of Things[END_REF] have used the idea to cross Social Network Services (SNSs)' patterns to the IoT concept, initializing the concept of Social Internet of Things (SIoT). Inspired from the Social Web of Things (SWoT) [START_REF] Guinard | Sharing using social networks in a com-posable Web of Things[END_REF], the SIoT is built on the transposition to human's relationships into society to intelligent objects into Multi-Agent Systems (MAS). According to Mala [START_REF] Mala | Integrating the Internet of Things Into Software Engineering Practices[END_REF], this paradigm can be defined as a "social network of intelligent objects bounded by social relationships". From the work of Fiske [START_REF] Fiske | The Four Elementary Forms of Sociality: Framework for a Uni-fied Theory of Social Relations[END_REF], the five following relationships are established: Parental Object Relationship (POR), Ownership Object relationship (OOR), Co-Work Object Relationship (C-WOR), Social Object Relationship (SOR) and Co-Location Object Relationship (C-LOR) (Table 1). [START_REF] Atzori | SIoT: Giving a Social Structure to the Inter-net of Things[END_REF] In this vision, social relationships are established and exploited among things, but not among their owners. The supportive architecture enabling object-objects interac-tions, services and resources discovering in order to relieve human from any intervention is concretely excluding it. Nevertheless, social relationships are an interesting way to set up a better integration of the human holon into holonic architecture, and to facilitate the system's acceptance by human operators.

Table 1: Social Relationships

Then, we have detailed, in one hand, techno-centered approaches for human's integration within manufacturing systems, and in the other hand, social approaches for artefact agents' integration. Our idea consists in exploiting the social concepts enunciated by Atzori &al. [START_REF] Atzori | SIoT: Giving a Social Structure to the Inter-net of Things[END_REF] and to associate them to the holonic reference architectures PROSA for human-integration.

4

Future directions toward a social holonic systems Today, holonic architectures' relevance is commonly recognised into manufacturing systems. Based on their supporting literature, we would like to propose an evolution regarding what we presented in the previous parts. To do this, we will rely on a recognized reference architecture: PROSA reference architecture for holonic manufacturing systems, released by Van Brussel et al. in 1998 [37]. This was the first at-tempt to define a holonic control architecture dedicated to an industrial system. PROSA was conceived on a holonic modular basis, structured in a bottom-up aggregation, and based on three main interconnected basic holons plus an optional one: Resource, Product, Order and Staff Agent.

The holons are only coordinated by the sharing of different data sets: Process knowledges are shared between Product and Resource holons, Execution knowledges are shared between Order and Resource ones and Production knowledges are shared between Product and Order holons.

Some recent revisions of this architecture have emerged to try to better integrate human factors. This is especially the case for the works of Leuvennink, Kruger & Basson [START_REF] Leuvennink | Architectures for Human Worker Integration in Holonic Manufacturing Systems[END_REF]. In their considerations [START_REF] Leuvennink | Architectures for Human Worker Integration in Holonic Manufacturing Systems[END_REF], two approaches for human integration with HMS are detailed with the PROSA model as a basis. The first one, called Interface Holon Architecture (IHA) is considering the worker as outside of the holon. It is considered as an interchangeable tool used by the holon to perform various tasks. The second one, called Worker Holon Architecture (WHA), is considering the worker as part of the holon. But this integration is only relying on technical features (its interfacing with the system, the systems' protocols, etc.).

Another interpretation has been proposed by Valckenaers & Brussel [39] in the book Design for the Unexpected: From Holonic Manufacturing Systems towards a Humane Mechatronics Society [START_REF] Valckenaers | Design for the Unexpected: From Holonic Manufacturing Systems towards a Humane Mechatronics Society[END_REF], the authors show the importance of humans for the agility of future production systems and the shift from holonic production systems to a more human mechatronic society. Hence, they propose an extension of their ARTI holonic systems architecture [START_REF] Fiske | The Four Elementary Forms of Sociality: Framework for a Uni-fied Theory of Social Relations[END_REF] with a new holon called e-Person. This one would be an aggregation of the roles that can be played by the human in his environment and could either be a resource, a decision maker for an activity or for other resources, a part of an activity, etc

In our opinion, heading toward a social holonic system implies the exploration of 3 axes:

1) Consideration and integration of human holons along with artefact ones. Scientific locks concerning the way to model these holonshumans or artefact, the consideration of physical, energetic or Data transformations as well as the consideration of human factors (physiological, psychological, etc.) will then arise.

2)

Consideration of the relationships between these holons as more than data exchanges, but with other forms of relationships that will be able to govern this holarchy. For example, we can cite the service providing or customer -furnisher relationships that are usually found in Service Oriented Architectures (SOA) [START_REF] Indriago | H2CM: A ho-lonic architecture for flexible hybrid control systems[END_REF], symbiosis relationships, as proposed by Monostori & al. [25], or other forms of social organization like Fiske's Communal Sharing, Authority Ranking, Quality Matching & Market Pricing [START_REF] Fiske | The Four Elementary Forms of Sociality: Framework for a Uni-fied Theory of Social Relations[END_REF]. These will have to be defined and formalized in order to be tested onto experimental CPS-based platforms. The nature of the relationship would, for example, give in-formation about shared objectives, requirements, results, states, or actions.

3)

Consideration of a recursive aspect of the holonic structure that goes beyond the simple composition/decomposition of a holon into other ones, and that considers the notions of social relationships. The same holon can belong to several different holons depending on the nature of the social relationships between them (an operator can belong to the workshift X AND to the work-shop Y). This raises the issue of the formalization of these relationships with-in the framework of HMS and of the specification of their impact (for ex-ample on the nature of the information shared, trust, etc.).

Conclusion

In 40 years, industrial systems have significantly evolved. Research has focused on system's automation, integration, centralization, decentralization, human integration, socialization, etc. Considering the past research and industrial evolution, we believe that future development should be directed to the elaboration of hybrid holonic architecture based on social relationships allowing the human to be no more considered as a disturbance factor but as a fully integrated agent to the systems. For this reason, we will direct our future research on the notion of social relationships, their definition and characterization and their implementation into reference architectures. A lot of work is still to be done, starting with the exploitation of the three directives that we have presented below and their testing through simulation or real models on our research platforms.