Interstratified palimpsests

Very nearly this time last year, I commented on a paper by Brad Gravina, Paul Mellars, and Christopher Bronk Ramsey concerning the stratigraphy of the Châtelperron type site. The paper documented evidence for an "interstratification" of the Châtelperronian and Aurignacian-type industries in the site stratigraphy. If these industries were interstratified, it provides evidence for the early appearance of Aurignacian peoples, and their possible influence on Neandertals who apparently manufactured the Châtelperronian.

Later, Mellars discussed the result in a commentary about the importance of new radiocarbon stratigraphies. Along with new radiocarbon dates from other sites, the Châtelperron evidence seemed to make clear the importance of new technologies and old-fashioned detective work in setting straight the course of events during the Upper Paleolithic in Europe.

Well, now a new paper by João Zilhão and colleagues has set out the reasons why the Châtelperron work was all wrong. It basically comes down to jumbled stratigraphy:

The Grotte de Fées at Châtelperron originally contained important Châtelperronian and Mousterian deposits. Both were palimpsests of remains left in the framework of repeated, short-term, nonresidential human occupations alternating with carnivore denning; scant Aurignacian and Solutrean objects testify to later, sporadic human visits. The presence in levels B4-5a of low percentages of edge-damaged and surface-weathered lithic objects indicates some syndepositional disturbance, perhaps in relation to flooding by the stream running 6 - 8 m below.
After its discovery, this very small site was intensively exploited with little concern for the stratigraphy, resulting in the accumulation of successive generations of disturbed deposits. Consideration of the totality of the evidence shows that, as at El Pendo, Le Piage, and Roc-de-Combe, the pattern of Aurignacian -- Châtelperronian interstratification only can be an artifact of postdepositional disturbance, whether that disturbance was caused by natural processes in the Pleistocene or by archeological excavation and fossil hunting in the 19th century (Zilhão et al. 2006:12648).

Should we believe it? Well, there is that small detail about the stream -- seems like the sort of thing that you shouldn't leave out if you are trying to establish whether 10 or so Aurignacian-type tools are part of a continuous sequence or not. There is also a fairly good picture of the stratigraphic profile, which certainly looks like a jumble in the crucial parts.

The paper also documents artifactual and faunal evidence for a jumbled stratigraphy -- most notably showing strong biases in artifact size and surface weathering among the crucial layers. They find that artifacts in the upper "B" levels of the site (B1-3) were likely left very sporadically when the cave was mainly occupied by carnivores, giving strong possibility for the intrusion of later material into the next lower layer, B4. The fact that a Solutrian-type artifact was found in these upper B levels would seem to confirm the long period over which they were accumulating artifacts.

So yes, I believe it -- it is a really good case study in why archaeologists have so much trouble with sites of this time period. And in this instance, all the signs point to the real possibility of stratigraphic confusion.

The paper critically discusses other evidence for pre-Châtelperronian Aurignacian in Western Europe:

The case for a precocious Aurignacian further rests on interstratifications with the Châtelperronian at El Pendo (Spain), Roc-de-Combe, Le Piage, and Grotte des Fées at Châtelperron (France), all of which are questionable. At El Pendo, the different levels of the sequence, a slope deposit at the base of a large uvala, feature a diverse mix of archeological materials (an Upper Paleolithic sagaie, for instance, was found 5 m below the purported interstratification, the overlying deposits containing hundreds of Mousterian-like flakes and cores). At Le Piage, a Châtelperronian lens interstratified in the Aurignacian was described for a small area that, in fact, corresponds to a slope deposit yielding a mix of Châtelperronian, Aurignacian, and surface-weathered Mousterian items throughout the entire sequence. At Roc-de-Combe, an Aurignacian lens interstratified in the Châtelperronian reportedly ex isted under the cave's overhang (the external area featured a single, Mousterian level, and the internal area featured a normal Aurignacian-over-Châtelperronian sequence), but this "level" was a post facto theoretical construct assembled from several true excavation units, all of which featured a mix of Gravettian, Aurignacian, Châtelperronian, and Mousterian pieces (Zilhão et al. 2006:12643, citations elided).

The lack of any good evidence for such interstratification at any other site is why the Grotte des Fées was assigned such importance by Gravina et al. (2005) and Mellars (2006), but it is illuminating to see this terse review. Zilhão and colleagues conclude that the most credible explanation for the total pattern of evidence is that the Châtelperronian preceded the Aurignacian in Western Europe. The paper takes this as support for an autochthonous origin of the Upper Paleolithic Châtelperronian in Western Europe, and for relative cognitive sophistication among the Neandertals.

References:

Gravina B, Mellars P, Ramsey CB. 2005. Radiocarbon dating of interstratified Neanderthal and early modern human occupations at the Chatelperronian type-site. Nature 438:51-56. DOI link

Mellars P. 2006. A new radiocarbon revolution and the dispersal of modern humans in Eurasia. Nature 439:931-935. Full text (subscription)

Zilhão J, d'Errico F, Bordes J-G, Lenoble A, Texier J-P, Rigaud J-P. 2006. Analysis of Aurignacian interstratification at the Châtelperronian-type site and implications for the behavioral modernity of Neandertals. Proc Nat Acad Sci USA 103:12643-12648. DOI link