Complementary dates from Chauvet.

[Jacques Cinq-Mars]

All,

Also from Comptes Rendus Palevol ( see HERE for another interesting paper published by the same journal), an interesting paper on the dating of the speleothem sequence that brackets some of the signs of palaeolithic human presence in Chauvet Cave.

Genty, Dominique, Bassam Ghaleb, Valérie Plagnes, Christiane Causse, HélèneValladas, Dominique Blamart, Marc Massault, Jean-Michel Geneste, and Jean Clottes. 2004. Datations U/Th (TIMS) et 14C (AMS) des stalagmites de la grotte Chauvet (Ardèche, France) : intérêt pour la chronologie des événements naturels et anthropiques de la grotte. C. R. Palevol 3: 629–642.

Abstract:

TIMS U/Th and 14C AMS ages of the Chauvet cave stalagmites: interest for the chronology of natural and human events of the cave. Eight stalagmites, two flowstones and several pieces of charcoal found trapped under the speleothems from the Chauvet cave (Vallon-Pont-d’Arc, Ardèche, France) have been dated by radiometric mass spectrometric methods (U/Th et 14C). Results give accurate ages for some geological features of the cave, and, for some of them, confirm the old ages of the prehistoric charcoal. They also indicate the timing of the climatic periods that were favourable to the stalagmites growth.

… and the Conclusion of the Abridged English version:

4. Conclusion TIMS U/Th dating of the Chauvet Cave stalagmites and flowstones brings the following results: • since 33 ka, several periods of stalagmite growth are observed and are coincident with climatic improvements; but it appears from this first set of analyses that no deposition occurred between 24.5 ± 0.5 ka and 15.5 ± 0.5 ka because the climate was too cold; • U/Th ages of the stalagmites that grew at the basis and at the top of the entrance collapse of the cave demonstrate that this collapse seems to have occurred before the end of the Younger Dryas, but more analyses on other stalagmites from the entrance collapse are necessary in order to confirm or not this hypothesis, especially because other ages obtained on archaeological remains indicate an older closing of the cave; • the 10-m-large collapse of the Hillaire Chamber occurred after 7.7 ka and the flowstone that seals the archaeological deposits of this part of the cave started to grow around 27.8 ± 1.9 ka; the comparison between speleothem U/Th and charcoals 14C ages demonstrates that the prehistoric charcoals are older than 30 ka, at least for the Croisillons Gallery and very likely for the Hillaire Chamber.

The dates presented and discussed in this paper appear to be in sync with the ones that were run earlier on the “cultural” material. In other words, there are no signs of chronometric bloopers and, in addition to providing a neat picture of the Chauvet karstic evolution (between 33ka and today), it reinforces the proposed human occupation/use chronology.

What I also find interesting, from a geomorphological and, by extension,  palaeoenvironmental point-of-view, is the discussion on the lack of speleothem development or deposition “between 24.5 ± 0.5 ka and 15.5 ± 0.5 ka because the climate was too cold”. As suggested by the following, it must have been cold indeed…

But the most important characteristic of these U/Th age results is the long period without any stalagmite deposition between 24.5 ± 1 and 15 ± 1 ka (Figs. 2 and 3). At the same time, the sea level is low [31] (Fig. 2), methane in the atmosphere, measured in ice core trapped air, is low [8], which demonstrates that, during this period, climate was extremely cold, at least at high and mid latitudes. In order to grow, speleothems need seepage water and vegetation above the cave in order to produce enough CO2 so that limestone dissolution is possible. Growth rates are mainly controlled by the seepage water [Ca] content, flow rate and temperature [16]. Consequently, speleothems do not grow during cold stages, especially at places where water or vegetation is not available. Frequency distribution of numerous U/Th ages of speleothems from northwestern Europe shows that speleothems are extremely rare around 20 ka [2,25]. In a southwestern France cave (Villars, Dordogne; at the same latitude as the Chauvet Cave) where many stalagmites have been dated with TIMS U/Th, no samples grew between 16 ± 1 and 32 ± 1 ka [23,24]. Thus, it appears that after 25 ka and before 16 ka, it is very likely that no stalagmites grew in the Chauvet caves.

… but certainly not enough, in my view, to turn much of western Europe (north of its Mediterranean face) into a dry, unvegetated “polar desert”, and this, for a period of 10,000 years. In other words, there must have been sufficient precipitations (rain and/or snow) to allow for the maintenance of some sort of arctic/subarctic-like vegetation cover. It is likely, then, that this lengthy LGM cold spell would have led to the development of extensive patches of (at the very least) discontinuous permafrost – not mentioned by the authors -- which would have made impossible the completion of the limestone dissolution process mentioned above, by neutralizing the essential “seepage” part of the equation. For some information on the importance of the role played by permafrost in this particular process, see:

Lauriol, B., D.C. Ford, J. Cinq-Mars, and W.A. Morris. 1997. The chronology of speleothem deposition in northern Yukon and its relationships to permafrost. Canadian Journal of Earth Sciences 34(7): 902-911.

Jacques Cinq-Mars

[Dale Hoogeveen]

Hi Jacques,

Did you mean to suggest permafrost in the French Riviera which would also likely mean at least seasonal harbor and bay ice on parts of the Mediterranean and perhaps in places even farther out into the open sea?

Dale

All,

Also from Comptes Rendus Palevol ( see HERE for another interesting paper published by the same journal), an interesting paper on the dating of the speleothem sequence that brackets some of the signs of palaeolithic human presence in Chauvet Cave.



… and the Conclusion of the Abridged English version:



The dates presented and discussed in this paper appear to be in sync with the ones that were run earlier on the “cultural” material. In other words, there are no signs of chronometric bloopers and, in addition to providing a neat picture of the Chauvet karstic evolution (between 33ka and today), it reinforces the proposed human occupation/use chronology.

What I also find interesting, from a geomorphological and, by extension,  palaeoenvironmental point-of-view, is the discussion on the lack of speleothem development or deposition “between 24.5 ± 0.5 ka and 15.5 ± 0.5 ka because the climate was too cold”. As suggested by the following, it must have been cold indeed…



… but certainly not enough, in my view, to turn much of western Europe (north of its Mediterranean face) into a dry, unvegetated “polar desert”, and this, for a period of 10,000 years. In other words, there must have been sufficient precipitations (rain and/or snow) to allow for the maintenance of some sort of arctic/subarctic-like vegetation cover. It is likely, then, that this lengthy LGM cold spell would have led to the development of extensive patches of (at the very least) discontinuous permafrost – not mentioned by the authors -- which would have made impossible the completion of the limestone dissolution process mentioned above, by neutralizing the essential “seepage” part of the equation. For some information on the importance of the role played by permafrost in this particular process, see:

Lauriol, B., D.C. Ford, J. Cinq-Mars, and W.A. Morris. 1997. The chronology of speleothem deposition in northern Yukon and its relationships to permafrost. Canadian Journal of Earth Sciences 34(7): 902-911.

Jacques Cinq-Mars

[Daryl Habel]

Hi Jacques,

Did you mean to suggest permafrost in the French Riviera which would also likely mean at least seasonal harbor and bay ice on parts of the Mediterranean and perhaps in places even farther out into the open sea?

Dale

I'd rather let Jacques answer that question whenever he catches up with us, but in the meantime I've been looking into the Last Glacial Maximum reconstructions for Western European climate, and found two excellent maps in Paul Mellars (1996) "The Neanderthal Legacy.  The first (Fig. 2.31) is a map reconstructing vegetation zones, ice sheets, and coastlines during the LGM ca. 18-20.  From this, it seems the Mediterranean coast was mostly forested except for a small area near present-day Monaco which is reconstructed here as "Parktundra".  So, I would reckon from this that on any given day during the LGM the temperature at Chauvet would be several degrees colder than at the Mediterranean coast.

I'll post the second attachment separately because of attachment size limits.

Dar

[Daryl Habel]

The caption for this attachment reads:

"Figure 2.32.  Estimated extent of glaciers in the Massif Central region of central France at the time of the last glacial maximum, ca. 18-20,000 BP (after Daugas & Raynal 1989).  The presence of these glaciers would inevitably have created much sharper east-west gradients in climatic and ecological conditions across the southwestern French region than at the present day."

I've added a star on the Ardeche River marking the location of Chauvet Cave.

Dar

[Jacques Cinq-Mars]

Hi Jacques,

Did you mean to suggest permafrost in the French Riviera which would also likely mean at least seasonal harbor and bay ice on parts of the Mediterranean and perhaps in places even farther out into the open sea?

Dale

No, not at all.

But first, a correction. My reference to "north of the Mediterranean face" was quite unclear, i.e., a bad choice of a poorly translated word. In French, I would have written “façade méditerranéenne” in reference to the coastal and near-coastal areas that border the sea, the Riviera. Chauvet Cave, while found in the eastern side of the Rhône drainage system, is located about 125 km (as the crow flies) from the present day northern shore of the Mediterranean, and in a somewhat rugged upland region (altitude ?) that is located just to the southeast of the Massif Central (and its LGM glaciers). Note also that, to the east/northeast, across the Rhône valley, you would have found, at that time, the more extensive glaciers of the Alps. In other words, the Chauvet Cave/Ardèche region, as well as all other areas located in the interior, directly to the south of the Massif Central – Alps glacial arc, would have likely been under a marked glacial “influence”. All things that have been clearly illustrated by Dar, in his earlier posts. Further to all this, find below, a (relief) map that points clearly (big red dot)to Chauvet’s relative proximity to the Massif Central.

As for having icebergs and ice pack decorating the near-shore areas of the French/Italian Riviera, well, I think you can forget it.  Here is a quote from Margherita Mussi’s excellent Earliest Italy:

Mussi, Margherita. 2001. Earliest Italy – An Overview of the Italian Palaeolithic and Mesolithic. New York, etc.: Kluwer Academic/Plenum Publishers

The general characteristics of the Mediterranean and of Italy, around the Glacial Maximum, are generally well known. (Newell et al. 1981; Thiede 1978; Thunell 1979). The surface temperature of the sea on the western coasts of Italy was between 13° and 19° C in winter (modern average 22-24° C).

.

Unfortunately, I do not have ready access to the references presented by Mussi, but I think that her brief statement, together with Dar’s judicious info, should put to rest your “cold” and “Mediterrarctic” speculations. In addition, if you look up something like “Late Glacial Mediterranean climate” on Google, not only will you come up with corrobating material, but also with information pointing to the existence of a rather steep temperature gradient between the coastal areas and the higher altitude hinterland.

Jacques

[Dale Hoogeveen]

Between your explanation and Dar's your meaning is quite clear and about what I thought initially.  I had not thought of the Rhone valley as a potential thoroughfare from Central Europe around the Alps to the Meditteranean, before; however.   Actually I hadn't even really noticed it before.

The Massif Central glaciers also appear to have been segmented more on the order of mountain top glaciers (of substantial magnitude, of course) than either an area wide ice sheet as come down from Scandinavia or the consolidated cap that appears to have been in place in the Alps.  

I would still question whether there was a consistant period of permafrost at Chavet over a long enough period at glacial maximum to produce the kind of permafrost cap you can describe in the Yukon.   I really doubt that permafrost accompanies essentially mountaintop glaciers anchored above the snowline in the same way that it might accompany the wider spread climatic changes that would accompany a general ice sheet.    

It really looks to me like at certain seasons of the year Mediterranean weather should sweep up the Rhone valley and with heights on either side, the funnel should be able to take a couple of hundred kilometers in stride.  That may very well not have moderated the harshness of winter upstream (when I would expect cold fronts to move south), but should have moderated summers (when I would expect Mediterranean weather with an African influence to dominate moving northward) enough that permafrost might not have been able to get a general enough foothold, even at the heights of Chavet.  I doubt that proximity to montaine glaciers is enough by itself to support extended periods of permafrost such as you suggested for long periods during the last glacial maximum,  not that far south in such exposed proximity to a very large body of southern water.   The determinant would not have been winter temperature dominated by the glacial north but rather how intense were the summer temperatures coming off the Mediterranean, whether they were enough to provide even a short growing season in earth with the frost out.

Just because there is a glacier at higher altitudes does not mean the lower valleys and river corredors or even adjacent mountain sides do not have open soil every summer, especially in those areas where there is exposure to milder climates that should operate most effectively in the summer.  In this case it should be summer maximums that would dominate, at least on the southfacing exposures.  That should also mean that the Mediterranean side of the Massif Central should have been substantially milder than the far side.  Chavet qualifies as the Mediterranean side, I think.

I suppose you can find evidence of permafrost but I if so I do not think you can assume any extended periods, such as you would need for a permafrost cap that could seal off the limestone caverns below from ground water containing enough organics to generate carbonic acid.

Eliminating shoreline icepack from less than 100 miles away makes extended periods of permafrost in areas directly exposed in that direction pretty hard to envision.  I have no problem at all, however, with the idea of permafrost for extended periods on the far side of the Massif Central, and for that matter even if no ice I expect that it snowed occasionally at the coast.

Dale

No, not at all.

But first, a correction. My reference to "north of the Mediterranean face" was quite unclear, i.e., a bad choice of a poorly translated word. In French, I would have written “façade méditerranéenne” in reference to the coastal and near-coastal areas that border the sea, the Riviera. Chauvet Cave, while found in the eastern side of the Rhône drainage system, is located about 125 km (as the crow flies) from the present day northern shore of the Mediterranean, and in a somewhat rugged upland region (altitude ?) that is located just to the southeast of the Massif Central (and its LGM glaciers). Note also that, to the east/northeast, across the Rhône valley, you would have found, at that time, the more extensive glaciers of the Alps. In other words, the Chauvet Cave/Ardèche region, as well as all other areas located in the interior, directly to the south of the Massif Central – Alps glacial arc, would have likely been under a marked glacial “influence”. All things that have been clearly illustrated by Dar, in his earlier posts. Further to all this, find below, a (relief) map that points clearly (big red dot)to Chauvet’s relative proximity to the Massif Central.

As for having icebergs and ice pack decorating the near-shore areas of the French/Italian Riviera, well, I think you can forget it.  Here is a quote from Margherita Mussi’s excellent Earliest Italy:


.

Unfortunately, I do not have ready access to the references presented by Mussi, but I think that her brief statement, together with Dar’s judicious info, should put to rest your “cold” and “Mediterrarctic” speculations. In addition, if you look up something like “Late Glacial Mediterranean climate” on Google, not only will you come up with corrobating material, but also with information pointing to the existence of a rather steep temperature gradient between the coastal areas and the higher altitude hinterland.

Jacques

[Jacques Cinq-Mars]

Dale,

Just view the following as a friendly, information addendum to what has already been said.

First, all I initially did was to suggest that permafrost should have been considered as a likely option. Contrary to what I said, the authors do mention permafrost, but only in passing, in a brief list of the main (palaeo)environmental conditions that are likely to bring to a stop the formation or growth of speleothems:

Au-delà d’un certain seuil, ils s’arrêtent de pousser, soit à cause d’un blocage de l’infiltration, lié à un pergélisol ou à une période sèche, soit à cause du manque de végétation qui empêche l’eau de se charger en CO2 et donc de dissoudre le calcaire encaissant.

However, they do seem to favour excessive aridity and lack of vegetation cover and this, only with references to rather long distance, global proxy data:

Mais le point essentiel qui ressort de ce premier ensemble d’âges est qu’il n’y a pas de croissance de stalagmite entre 25 et 16 ka environ, ce qui s’explique par des conditions climatiques rigoureuses. Ainsi, le niveau des mers est au plus bas entre 23 et 17 ka […]. Le méthane, qui caractérise l’activité biopédologique, mesuré dans les bulles d’air piégées dans les glaces de l’Antarctique et du Groenland montre aussi des valeurs très basses (~400 ppb) entre 26 et 17 ka, avant une augmentation brusque jusqu’à ~700 ppb à 14,8 ka […]. La fin de cet intervalle, autour de 16 ka, est particulièrement marquée dans nos échantillons, avec le début de croissance de plusieurs stalagmites […]. Elle correspond à la transition Pléniglaciaire/Bølling…

.

At any rate, I suppose I was just being picky, but then…

In Europe, at low altitude, permafrost extended in a discontinuous form over the Aquitaine (France, ca. 44° N), at about the same latitude as in the USA, as a consequence of the disappearance of the Gulf stream (a 10° C decline of the sea surface temperature) and a strong aridity (no snow cover protection), especially in the south of the Pyrenean belt. However, during the LMG, permafrost never reached the Po plain (Cremachi & Van Vliet-Lanoë, 1991). The ice wedge polygon boundary extended from Devon to the north of the Azov Sea, about 300 km to the north of the southern boundary of permafrost, traced by the extent of periglacial type of fragipan soils. In mid-altitude regions of the Massif Central, Spain, Yugoslavia (s.l.), Greece and Anatolia, mountain permafrost developed, as it has been particularly corroborated by fossil rock glaciers or large pattern grounds. The west coast of Iberia was devoid of permafrost, even in Galicia. In the eastern Pyrenean belt, it reached 800 m. In North Africa and in southern Spain mountain permafrost reached 1200 m in the Betic cordillera and 2000 m in the Atlas.

Petit-Maire, Nicole and Philippe Bouysse.1999. Map of the World Environments during the Last Two Climatic Extremes (CLIMEX). Explanatory Notes. Commission de la carte géologique du monde -  Commission for the geological map of the world.

Keeping in mind that the Chauvet Cave area happens to be located at 44.23°N; 4.26°E. and at an altitude of 240 m, it makes perfect sense to suggest that it could have been in an area where discontinuous or, at the very least, sporadic permafrost conditions prevailed at the height of the LGM.

For more information on the LGM conditions under discussion have a look at the attached map (original and reference to be found HERE); at Jonathan Adams’ maps [Global land environments since the last interglacial], HERE, and at a good summary of what permafrost is all about, HERE.

Jacques

PS Another map to follow.

[Jacques Cinq-Mars]

Find here-attached another informative map that uses a different set of proxy data. For access to the higher resolution original, click HERE

Enjoy,

Jacques

[Dale Hoogeveen]

Hi Jacques,

Thank-you for the maps and the links.  They are very informative

I can relate to both lattitude and altitude.  Minneapolis is almost exactly 45 degrees north.  I have spent all my adult life between there and my boyhood in Northwest Iowa at 43 degrees.  Minneapolis is about 250 meters above sealevel and Northwest Iowa something like 300 + with the highest point in Iowa just east of where I grew up at about 1000 feet.

What we do not have in either area is any obstruction for arctic cold air such as is found at Chavet from the entire body of the Massif Central, with Chavet sitting as it does in their southeast foothills.   (Most of Central plateau of the Massif Central runs at some 700 to 1000 meters above sealevel and is heavily supplied with volcanic activity as well;  so Chavet at 240 meters is actually quite a bit downslope and on the protected side as well. ) Nor do we have such a proximal presence of a moderating and moisture supplying southern body of water as is the Mediterranean. 

Without those influences I would agree with you that one should expect some permafrost at Chavet, but....

With Chavet downslope in the protected southeast foothills of the Massif Central opening directly onto the lower Rhone valley and its delta into the Mediterranean that suggestion seems to me to be a little harsh.  Chavet really looks more like a gateway into LGM refuge than an overly harsh and forbidding location.  I personally wouldn't expect that there was ever any permafrost in that area and except perhaps on the most unmoderated and heavily shaded NW slopes at the highest local altitudes, and then only temporarily in the worst years. 

I guess that I would not expect to find any general permafrost in the Chavet area and definitely no extended periods of it long enough to produce dramatic changes in speleological deposits.

General watertables may have lowered enough with the drop in sea levels and general aridity, however, to have effected moisture flow into some of those caverns, which would have had to have been ground level accessible at the time they were used by paleolithic humans, placing them in the upper levels of the contemporary local watertables .  Any lack of  necessary moisture may not have been so much related to ground level temperatures as to drops in the levels in those water tables.  I don't think that there is a 1 for 1 water table drop compared to sea level decline, but there should have been some such effect to some degree depending a lot on the local geology, of course.  I think that is more likely to be the cause for any gap in deposits than permafrost at least at Chavet, although I can understand how permafrost may have been a factor elsewhere.

Dale

Dale,

(snipped)

Just view the following as a friendly, information addendum to what has already been said.
...
Keeping in mind that the Chauvet Cave area happens to be located at 44.23°N; 4.26°E. and at an altitude of 240 m, it makes perfect sense to suggest that it could have been in an area where discontinuous or, at the very least, sporadic permafrost conditions prevailed at the height of the LGM.
...
Jacques

PS Another map to follow.

[Jacques Cinq-Mars]

<snipped>
Without those influences I would agree with you that one should expect some permafrost at Chavet, but....

With Chavet downslope in the protected southeast foothills of the Massif Central opening directly onto the lower Rhone valley and its delta into the Mediterranean that suggestion seems to me to be a little harsh.  Chavet really looks more like a gateway into LGM refuge than an overly harsh and forbidding location.  I personally wouldn't expect that there was ever any permafrost in that area and except perhaps on the most unmoderated and heavily shaded NW slopes at the highest local altitudes, and then only temporarily in the worst years.

I guess that I would not expect to find any general permafrost in the Chavet area and definitely no extended periods of it long enough to produce dramatic changes in speleological deposits.

General watertables may have lowered enough with the drop in sea levels and general aridity, however, to have effected moisture flow into some of those caverns, which would have had to have been ground level accessible at the time they were used by paleolithic humans, placing them in the upper levels of the contemporary local watertables .  Any lack of  necessary moisture may not have been so much related to ground level temperatures as to drops in the levels in those water tables.  I don't think that there is a 1 for 1 water table drop compared to sea level decline, but there should have been some such effect to some degree depending a lot on the local geology, of course.  I think that is more likely to be the cause for any gap in deposits than permafrost at least at Chavet, although I can understand how permafrost may have been a factor elsewhere.

Dale

Dale,

I almost decided to end the discussion with a polite “as you wish”, but thought better of it, if only because I admire your persistence and am fascinated by your constant and resourceful ability for lateral – if not “latitudinal” and “altitudinal” – thinking!

First, repeating myself, here, I didn’t say there was permafrost at Chauvet. I just noted that an explanation of the chronometrically demonstrated lack of speleothem formation, at the height of the LGM,  should take the role of permafrost into consideration. This is especially indicated when one realizes that the same general type of “hiatus” –- albeit variable in chronological amplitude -- has been found to occur over a very large area that encompasses karstic formations located at about the same latitude in the Southwest (Aquitaine basin, Dordogne valley – Genty & al. 2004, 631, 637). This said, it is clear that other climatically induced conditions (mentioned earlier, by Genty & al.) are likely to have played a (complementary) role in what had to have been the expression of a lengthy, complex and dynamic polygenetic process.

As for your “water table” argument, it is –- unless I misread you – somewhat irrelevant, to the extent that the entire process of speleothem formation occurs in a top-down fashion, in caves that have already been formed, shaped, and carved by underground fluvial activity and that sit, by definition, just at or well above the local aquifer.

Now, a few points in response to what I’ll call your “Mediterranean-Rhône valley” argument. At the time we are talking about, the Mediterranean was –- relatively speaking – a cold sea, surrounded, especially in its central and western portion by lands that were themselves quite affected in various ways by a lower (admittedly fluctuating) thermal regime of great duration. This is clearly shown by most, if not all, the marine and land climate/temperature proxy indicators that one can come up with. Note also that in those days no help from the Gulf Stream – - through (warm) water exchanges with the Atlantic – were to be expected. Heinrich events & al were playing havoc with the position and warm dedication of the former. As a matter of fact, I was just told a week or so ago that, for a while, the western Mediterranean shows inflow signals (?) that have been identified as coming from the Icelandic region of the North Atlantic.

In other words, the warming capabilities that you attribute to the Mediterranean with respect to the Chauvet area palaeoclimate at and around the LGM were, at the very best, greatly reduced and quite unlikely to have seriously affected the conditions that might have led to development of, at the very least, discontinuous or sporadic permafrost.

Also deserving of some attention are your views on the circulation of air masses that would have affected the overall (palaeo)climate situation around Chauvet and other similar areas located at about the same latitude(s). These happen to be found just below, and to the southwest, of a glaciated arc formed by the Massif Central and the Alps, a large area that straddles the Rhône valley, and where evidence of permafrost has been well documented. To be taken into consideration, here, is Dar’s mention (his earlier post) of “The presence of these glaciers would inevitably have created much sharper east-west gradients in climatic and ecological conditions across the southwestern French region than at the present day” and, more importantly, the unavoidable (k)catabatic wind regime that had to have emanated from the glaciated “arc” mentioned above and that, by definition, had to flow downhill, towards a cool (sensu palaeoclimate!) Mediterranean. Some sort of an exacerbated (palaeo)Mistral, as it were!

This said, I don’t know if there was ever permafrost, on top of Chauvet.

Jacques

PS  I suggest that given the tack taken by this discussion, and if it is to go on, we should move it where it belongs. i.e., in the Palaeoenvironmental Studies Board


 

[Dale Hoogeveen]

Hi Jacques,

Move the thread if you wish.

The core of the issue is the reason for the hiatus of speleological deposits in the caves at Chavet with the ancient art.    With the carbon datings at the limit of C14, defining the hiatus becomes important to verify those proposed dates.  Weather or not, that is still the core question.

I had a long look at your maps and did some other reading about the Massif Central both current and ancient.  I am not done with that yet.  

The maps are very interesting.  I think you have posted them before.  Thank-you again.  

Dale

PS I did landscaping and had a hardy perennial nursery here in Minnesota for some years.  Perhaps that caused some of my "lattitudinal" thinking.  In fact, it almost certainly did.

[Jacques Cinq-Mars]

Hi Jacques,

Move the thread if you wish.

The core of the issue is the reason for the hiatus of speleological deposits in the caves at Chavet with the ancient art.    With the carbon datings at the limit of C14, defining the hiatus becomes important to verify those proposed dates.  Weather or not, that is still the core question.

I had a long look at your maps and did some other reading about the Massif Central both current and ancient.  I am not done with that yet. 

The maps are very interesting.  I think you have posted them before.  Thank-you again. 

Dale

PS I did landscaping and had a hardy perennial nursery here in Minnesota for some years.  Perhaps that caused some of my "lattitudinal" thinking.  In fact, it almost certainly did.

Dale,

Well, actually – and to get back to the chronometric aspect of the problem under discussion, what may have caused the speleothem deposition/formation hiatus observed at Chauvet falls well within the range of 14C capabilities. On the basis of U/Th (TIMS) ages, the authors note:

… since 33 ka, several periods of stalagmite growth are observed and are coincident with climatic improvements; but it appears from this first set of analyses that no deposition occurred between 24.5 ± 0.5 ka and 15.5 ± 0.5 ka because the climate was too cold; (Genty at al., 2004. p. 631)

Jacques

PS   Reciprocally (on a more personal mode), I have spent well over thirty years of my life wallowing seasonally, at it were,  in permafrost(ed) environments. My bones keep reminding me all the time, with a vengeance.

[Dale Hoogeveen]

Hi Jacques,

15.5 to 24.5 kya would certainly be within C14 range, but they wouldn't be able to use C14 dating directly on the calcium deposits, would they?  IIRC the 33 kya date came from carbon from beneath them and was used to calbrate the limit of the dates on the deposits.  That date does approach the limits of C14.

Do you know how that correlated the points of hiatus in the deposits with external weather?

Dale

Dale,

Well, actually – and to get back to the chronometric aspect of the problem under discussion, what may have caused the speleothem deposition/formation hiatus observed at Chauvet falls well within the range of 14C capabilities. On the basis of U/Th (TIMS) ages, the authors note:

Quote:
… since 33 ka, several periods of stalagmite growth are observed and are coincident with climatic improvements; but it appears from this first set of analyses that no deposition occurred between 24.5 ± 0.5 ka and 15.5 ± 0.5 ka because the climate was too cold; (Genty at al., 2004. p. 631)

Jacques

PS   Reciprocally (on a more personal mode), I have spent well over thirty years of my life wallowing seasonally, at it were,  in permafrost(ed) environments. My bones keep reminding me all the time, with a vengeance.

I sympathize,  my father was crippled by rheumatoid arthritis.  So far I have little more than some stiffness in my finger joints, especially in weather like we are having now, being directly under a stationary Arctic high pressure system.  It could be better but at 56 I can't gripe too much.  But then I didn't catch fastpitch softball for almost 20 years like he did either;  so I didn't damage either my knees or my fingers to give it someplace to start.  

Or go grubbing in the permafrost like you.  

Around here we quit digging when the ground freezes.  (grin)

[Jacques Cinq-Mars]

Hi Jacques,

15.5 to 24.5 kya would certainly be within C14 range, but they wouldn't be able to use C14 dating directly on the calcium deposits, would they?

Until I read the Genty & al. paper, I was under the impression that the use of C14 for direct dating of speleothem was “iffy”, at the very best. In other words, what I thought was happening, in most instances, was as follows:

“… what is being sampled, in the body of a given speleothem, consists of organic contaminants of various types (e.g., humic acids, etc.). It can also be tried on pollen grains which should also be viewed as contaminants. In this case, the sample/signal one comes up with is likely to be rather biased/distorted to the extent that the constraints caused by the percolation of water through micro-fissures results in the filtering out of most large size pollen grains (e.g., in the size range of Pinus) (my notes, n.d.!).”

But science marches on and here is a bit of recent info from the paper itself (I hope you read French):

Pour le 14C (AMS), les prélèvements sur les stalagmites se font à la micro-perceuse (diamètre : 0,8 mm). Deux à quatre trous sont suffisants et peuvent être faits latéralement sur un même niveau de croissance, ce qui représente une durée de croissance variant de 1 à 5 ans. La méthode employée est détaillée dans [21,22]. Les incertitudes varient de 0,4 à 0,8 pMC (% modern carbon). Les âges issus des mesures de radiocarbone sur la calcite sont corrigés d’une proportion de carbone mort (carbone issu principalement de la dissolution du calcaire) et calibrés [21,22,33]. Cette proportion avait été estimée à 4% en comparant les âges U/Th et 14C de la stalagmite Chau-stm1, obtenus lors d’une précédente étude [21,22]. Seule la stalagmite Chau-stm4 a été datée uniquement par 14C, ainsi que le sommet de Chau-stm1.

Obviously a bit cryptic, unless one looks up some of the references in which case one finds out that the integrity/purity of the calcite crystal (micro)sample is obviously of utmost importance. Note, however, that few speleothem dates were obtained via radiocarbon (AMS in all instances).

IIRC the 33 kya date came from carbon from beneath them and was used to calibrate the limit of the dates on the deposits.  That date does approach the limits of C14.

I suppose that some “calibration” was attempted (in the case of those speleothems that have been subjected to both C14 and U/Th (TIMS) procedures, but from reading the paper, it might be better to talk about “comparisons”. In other words, radiocarbon dates can, at times, be “confronted”, as it were, with U/Th ones, but I wouldn’t refer to this “dialectic” exercise, at it were (again!) as one of calibration. Needless to say, I may be wrong.

As is true of radiocarbon dating procedures, U/Th dating ones are also profiting from the progress of science (i.e., TIMS, which is briefly described as follows:

De par la rareté du matériel, il était indispensable d’utiliser les méthodes de datation les plus précises possibles, comme la méthode U/Th par spectrométrie de masse par thermo-ionisation (TIMS). Celle-ci nécessite l’emploi de petits échantillons de calcite (0,3 à 2 g) et le fait de compter directement les isotopes de l’uranium et du thorium sur un spectromètre de masse augmente la précision analytique (entre 1 et 2% à 2 r pour des échantillons « propres »)

… and I don’t think that their validity/coherence relied on “calibration” input from the archaeological C14 date you are referring to. But, obviously, it is nice to see that there are no contradictions.

Finally – again, a question of scientific progress, most people who can be viewed as producers and/or consumers of C14 dates will tell you that the dating techniques now available allow one to go well beyond 34kya.

Do you know how that correlated the points of hiatus in the deposits with external weather?

This a big question! Much of the “external weather” that is being discussed in this and many other similar papers, is derived from data sets mostly obtained through the analysis of Greelandic and Antarctic “ice cores” and from oceanic ones (i.e, north Atlantic and Mediterranean) and that are then used by “modelers” to develop “palaeoclimate” models! As I said earlier, we are talking “global proxies” (i.e., models) which, in the words of some “modelers”, suffer from the lack of solid/coherent land derived equivalent or complementary data sets that could be plugged into the “models”. This is one of the main reasons why I questioned, in the first place, Genty & al.’s characterization of the Chauvet Cave climatic conditions during the LGM “hiatus”. Given the well know finnecky nature of land based nature (and its inhabitants), I tend to feel much more comfortable with local and/or regional information to fall back on, if only to compare and contrast.

Jacques

[Dale Hoogeveen]

Hi Jacques,

Very sorry but I do not read or speak French.  I will try to wade through the cognates and what translations I can find...

This may take a little while.

I think we are in a basic agreement that specific local climate conditions and the geographic features that influence them would need to be considered whether or not we agree with what those might be.