1The study of past societies requires an understanding of their social organization. One way to do such study is to focus on mobility patterns and land use dynamics, which are only accessible at a high temporal resolution. While micro-chronological resolution (sub-annual to decennial) is accessible to ethnologists, it is generally not accessible to prehistorians, whose archaeological assemblages are unfortunately almost exclusively cumulative and mostly formed over long periods of time (fig. 1). The aim of this PhD thesis was to develop fuliginochronology (from fuliginous: sooty) as a technique to reach a high temporal resolution in archaeological settings. Fuliginochronology is the micro-chronological study of soot deposits, which are evidence of human occupations in caves, trapped in limestone crusts. The analysis of this geoarchaeological object thus consists of an anthropological study of past societies.

Fig. 1: Representation of the interlocking time scales with which the prehistorian works, the methods for accessing those scales, and the associated temporal resolutions. Fig. 1 : Représentation de l’imbrication des échelles de temps avec lesquelles travaille le préhistorien, des méthodes d’accès à ces échelles et des résolutions temporelles associées.

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Temporal resolutions may vary for archaeologists working on more recent periods, where texts, epigraphy, numismatics, etc. can provide a much better-defined framework for the Y studied period, as well as precise ante quem and post quem termini allowing to better circumscribe the duration during which human occupations succeeded one another. The durations here have blurred limits for the prehistorian, due to the low temporal resolution of radiometric dating for ancient periods. The central circle represents the window to access social time (non-uniform and non-homogeneous). The red box indicates the contributions of fuliginochronology.

S. Vandevelde

Les résolutions temporelles peuvent varier pour les archéologues travaillant sur des périodes plus récentes, où les textes, l’épigraphie, la numismatique, etc. peuvent fournir un cadre beaucoup mieux défini pour la période Y étudiée, de même que des terminus ante quem et post quem précis permettant de mieux circonscrire la durée pendant laquelle se sont succédées les occupations humaines. Les durées ont ici des limites floues pour le préhistorien, dues à la faible résolution temporelle des datations radiométriques pour les périodes anciennes. Le rond central représente la fenêtre d’accès sur le temps social (non uniforme et non homogène). L’encadré rouge indique les apports de la fuliginochronologie.

2Wall’s fragments covered with sooty carbonated crusts compose the study corpus. They have been collected in the twelve Pleistocene archaeological levels of the Grotte Mandrin site (Malataverne, Drôme, France), attributed to the Middle Palaeolithic and the transition between the Middle and Upper Palaeolithic periods, and in a thirteenth Holocene level that mainly contains remains of Neolithic cremations. The site is located on the left (east) bank of the middle Rhône valley and overlooks an ancient branch of the river at the level of a narrowing: the Donzère defile, giving the shelter a privileged position in the landscape, at the crossroads of different biotopes.

3Experimentations and additional analyses (U-Th dating at LSCE, Gif-sur-Yvette, France; ¹⁴C dating at RLAHA - University of Oxford, England; characterization of carbonated crusts by µLIBS at CEA, Saclay, France; characterization of soot by Raman spectroscopy and carbonates by FTIR - Fourier Transform InfraRed - spectroscopy at CERMA, Laval University, Quebec, Canada) were carried on. They demonstrated the dating potential of sooty speleothems and helped to better understand the genesis and post-depositional alterations affecting them. Moreover, they provided evidence demonstrating the annual nature of the calcite doublets that constitute them and are observable for most samples. Microscopic observation of thin, and/or polished, sections made in the speleothem growth axis reveals that what appears as a single black lamina to the naked eye generally resolves in a multitude of soot films a few micrometers thick, which resemble a barcode. These ‘barcodes’ can be inventoried and aligned to reconstruct longer sequences and the chronicle of human occupations in the shelter for each archaeological level. The joint study of soot films and calcite doublets allows us to set the chronicles on a micro-chronological time scale; the annual calendar of carbonate precipitation (fig. 2).

Fig. 2: An overview of fuliginochronology. Fig. 2 : Aperçu de la fuliginochronologie.

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(A) Formation process of the carbonated parietal crusts found on the Mandrin Cave’s clasts. (B) Microscopic observation of one of these coated clasts. A single soot film at low magnification resolves itself into a multitude of soot films under the microscope (x 100, LR). (C) Collecting of raw data using LnSeq module (Datawald platform, GL Conception). Barcode diagrams represent soot films’succession in carbonates. Plain lines: soot films. Dotted lines: probable soot films. Gray vertical bar: total speleothem thickness. (D) Photograph of a thin section (sample C-MAN34) where soot films are associated with both micritic (WPL) and sparitic (DCL) laminae. A combination of Reflected and Cross-Polarized Lights (RL+XPL) allows optimizing observation of both the soot (black films) and the crystalline fabric (opaque and whitish WPL, translucent DCL). It allows documenting the position of soot films in relation to calcite doublets. (E) Schematic representation of (D). On this simplified theoretical example, soot films are associated with both the WPLs and the end of DCLs but not exactly in the same way as in sample C-MAN34 (D). (F) Annual cycle of carbonates precipitation. Two seasons (wet and dry) can be recognized by observation of the crystal fabric. These two seasons may not have the same duration and are therefore of different sizes on this theoretical graph. WPL and DCL may not correspond to 6 months each but DCL + WPL = 1 year at Mandrin Cave. Human occupations (marked by soot deposits) are located as in (E). (G) Indexing occupations chronicle on the annual calendar of carbonates precipitation. In this theoretical example (derived from E and F) the soot films are always at the top of the micro-sparite laminae and sometimes in the micritic laminae. The parietal carbonated deposit records one to two occupations per year here.

S. Vandevelde

(A) Processus de formation des encroûtements carbonatés de paroi retrouvés sur les clastes de la Grotte Mandrin. (B) Observation microscopique de l’un de ces clastes encroûtés. Un seul film de suie observable à l’œil nu se résout en une multitude de films de suie au microscope (x 100, LR). (C) Collecte de données brutes à l'aide du module LnSeq (plateforme Datawald, GL Conception). La succession des films de suie dans les carbonates est représentée sous forme de diagramme en codes-barres. Lignes continues : films de suie. Pointillés : films de suie probables. Barre verticale grise : épaisseur totale du spéléothème (s.l). (D) Photographie d’une lame mince (échantillon C-MAN34) où des films de suie sont associés à la fois aux lamines micritiques (WPL) et sparitiques (DCL). Un éclairage combinant LR et LPA permet d’optimiser l’observation de la suie (films noirs) et de la fabrique cristalline (WPL opaque et blanche, DCL translucide). Il permet de documenter la position des films de suie par rapport aux doublets de calcite. (E) Représentation schématique de (D). Sur cet exemple théorique simplifié, les films de suie sont associés à la fois à la fin des DCL et aux WPL mais pas exactement de la même manière que pour l'échantillon C-MAN34 (D). (F) Cycle annuel de précipitation des carbonates. Deux saisons (humide et sèche) peuvent être reconnues par l'observation de la fabrique cristalline. Ces deux saisons peuvent ne pas avoir la même durée et sont donc de différentes tailles sur ce graphique théorique. WPL et DCL peuvent ne pas correspondre à 6 mois chacune mais DCL + WPL =  1 an à la Grotte Mandrin. Les occupations humaines (marquées par les dépôts de suie) sont localisées comme en (E). (G) Indexation de la chronique des occupations sur le calendrier annuel de précipitation des carbonates. Dans cet exemple théorique (dérivé de E et F) les films de suie se situent toujours au sommet des lamines micro-sparitiques et parfois dans les lamines micritiques. L’encroûtement pariétal enregistre ici une à deux occupations par an.

4Few studies have been carried out on this type of material. This work represents the first attempt to build the occupations chronicles across all archaeological levels in a rock shelter. Among the results, The Minimum Number of Occupations per archaeological level was determined, and occupation rhythms integrated into the annual cycle of nomadism or within multi-year cycles were identified at Mandrin Cave. This highlights that dynamics of the site’s occupation (and, to a certain degree, of the territory) are different between the archaeological levels. This finesse of perception, hitherto inaccessible for the study of ancient populations, also makes it possible to demonstrate that the succession between the last Neanderthals and the first regional Homo sapiens took place on this site in a very short time, a single year, indicating the contemporaneity of these two humanities on the same territory. The research applications of fuliginochronology are diverse. This micro-chronological method has a wide field of application both chronologically and geographically, since it can be applied anywhere in the world and for any period of time, as long as fires have been made in the vicinity of active speleothems.