The science of cupules (original) (raw)
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This paper describes a newly observed phenomenon, a rare form of lamina protecting petroglyphs from weathering, and it attempts an explanation of such features. These laminae are not precipitates but represent the floors of the original cupules that have become more resistant to erosion through conversion to tectonite. The process involves crystallization of the syntaxial quartz overgrowths on quartz grains that constitute the cement component of quartzite and silica-rich schist. It is attributed to the cumulative application of kinetic energy that derives from the tens of thousands of hammerstone blows that produced the cupule. The tribological process results in products similar to those formed in ductile shear zones when sandstone has been subjected to great kinetic stresses. In the cupules reported here, the re-metamorphosed lamina preserves their original surface and prevents the erosion of the protolith (parent rock) concealed by the modified layer. The thickness of the layer is a function of the cumulative amount of energy applied to the rock’s cement, and the process of alteration is defined as ‘kinetic energy metamorphosis’.
Relevance of site lithology and taphonomic logic to cupules
Most reports of cupules, and for that matter other petroglyphs, fail to provide adequate information on the lithology on which the rock art occurs. The relevance of such data is explained in terms of the taphonomy and technology of the cupules, of their dating and, ultimately, their interpretation. Similarly, the principles of taphonomic logic and their application to cupule research are briefly explained. It is shown that the patterns of cupule occurrence, in any period, environment or lithology, are largely determined by their taphonomy. This renders it impossible to determine the significance of variables relating to cupules, e.g. their apparent distribution or statistics, without first consulting their taphonomy. The principles of applying taphonomic logic to cupules are briefly presented.
In appraising the value of the etic interpretations of cupules, this wide-ranging review of the potential applications of forensic principles in their scientific study illustrates the huge credibility gap between impulsive etic explanations and a scientific approach. The interdependence of lithology, technology, morphology and taphonomy of cupules provides insights into some of the variables all petroglyph research must address. Replication studies have provided first sound data about cupule production and offer considerable potential for biomechanical enquiries, but also provide impetus for investigations into the production of cupules. Forensic studies focus on variables such as production technique and the tool types used. For instance such studies can discern between the traces of metal and stone implements, or even bone tools. They range from the investigation of tool traces to the tribochemical effects of tool application, and the surviving products of modification processes. Tectonite formation is a remarkable outcome of such mineral conversion, and after its recognition in cupules has been found to occur widely in geology. Rock art research is heavily indebted to the geological sciences, but this may be the first time that the former discipline has contributed to the latter by explaining unknown phenomena.
Discriminating between cupules and other rock markings
A number of natural processes are discussed that may result in phenomena archaeologists have found difficult to distinguish from cupules. In particular, erosion phenomena of several types are presented and their distinguishing characteristics are discussed in adequate detail to facilitate their identification in the field. Similarly, cupules on horizontal surfaces may resemble grinding hollows (mortars, querns, metates) and their discrimination is also discussed. The use of field microscopy is emphasised in discriminating cupules from natural or other artificial rock markings.
A short ethnography of cupules
Globally we have quite limited ethnographic information about petroglyphs, about their emic meaning or purpose. Such information is even more limited for cupules, amounting to just a few fragmentary and very isolated accounts. The currently known examples are cited, their scientific veracity is discussed, and it is demonstrated through them that the endeavours of archaeologists to determine the meanings or significance of cupules are generally misguided. Such etic interpretation is impossible, and where it is attempted it is scientifically irrelevant, except for the cognitive scientist in studying the cognition of the interpreter.
The dating of cupules presents the same challenges as does the dating of most petroglyphs, with the added difficulty that cupules, more than other petroglyphs, have often been subjected to reuse long after they were first created. This means that parts of their surface may derive from different periods, or all earlier surfaces may have been obliterated completely. Examples of this phenomenon are given, and a discussion of the currently available methods of estimating the antiquity of cupules is presented. It emerges that, since the dust created in making cupules or other petroglyphs is not realistically recoverable, the analytical possibilities in dating them are severely limited. One of the best options is not to date the rock art, but instead date the tools used in creating it. This has been successful in some cases. The use of field microscopy is shown to be indispensable in any analytical work with cupules.
THE ROLES OF TRIBOLOGY IN PALAEOART STUDY
Rock Art Research, 2020
Tribology, the science of interacting surfaces in relative motion, is at the basis of interpreting rock art and portable palaeoart by scientific means, and yet it has remained almost entirely ignored in that application. Tribological work conducted with palaeoart, but without involving its discipline, is briefly summarised, and examples are cited to illustrate the value of a scientific approach. In particular, the focus is on the contact mechanics of petroglyphs and the compressive-tensile principles involved. The tribology of rock art has also been invoked in the discrimination of anthropogenic from other rock markings.