A multi-technique characterization and provenance study of the pigments used in San rock art, South Africa

During the course of a conservation project at the rock shelter known as RSA TYN2 (Eastern Cape, South Africa), a sample of 33 painted fragments that had become detached from the wall were collected. They have been studied using a multi-technique approach (optical microscopy, SEM-EDS, Raman spectroscopy and FTIR), with the aim of achieving a better understanding of their paint stratigraphy, composition, and provenance. The paintings are on a Clarens Formation sandstone and are embedded in calcium sulphates and oxalates. The red pigments show two different ‘hues’, corresponding to two different compositions. The light red is a red ochre, possibly pure, which is probably a degradation product of the Clarens Formation sandstone. The dark red contains more iron oxides and may be a mixture between the red ochre and pure haematite. Because of the presence of crystals which may be identified as augite we suggest this haematite came from the basaltic upper part of the Drakensberg, at least 4 km away from the rock shelter. The black pigments have been identified as carbon black, that is to say, incomplete combustion products of organic compounds, and are radiocarbon dated to between 2120 and 1890 cal BP, making these samples the oldest directly dated South African rock art.     

Weathering of rock art at two sites in the KwaZulu-Natal Drakensberg,southern Africa

Sediments of the Karoo Basin in southern Africa represent one of the world's finest laboratories for investigating sandstone weathering. The natural breakdown of these sandstones, most notably in the Clarens Formation, is destroying much of the indigenous rock art heritage that exists there. In an attempt to elucidate the operative weathering processes, a range of micro-climatic, rock temperature, rock moisture, rock chemistry, and rock property data have been monitored over a 15 year period at two sites in the KwaZulu-Natal Drakensberg. Results suggest that rock moisture regimes and to a lesser extent, rock thermal regimes exert the most damaging influence on San paintings. It is argued that granular disintegration and the enlargement of existing sandstone pores and bedding planes close to the rock surface, facilitate an increasingly dynamic moisture regime, which leads to an accelerating rate of weathering. Recent technological advances in data collection suggest that a re-evaluation of environmental controls may be necessary before weathering, at a scale appropriate to the deterioration of rock art, can be fully understood. The continued existence of indigenous rock art in southern Africa depends on investigations aimed at the development of techniques for its preservation.     

贺兰口岩画附近典型危岩体稳定性分析

通过前期现场调查,分析了贺兰口岩画的主要病害,提出岩画附近的危岩体是其中威胁较大的一类地质病害。根据现场勘察将贺兰口岩画附近不同状态的危岩体分为坠落式、滑塌式和倾倒式三类失稳模式。经过室内试验得到了岩石矿物组成、密度、气孔率、吸水率、单轴抗压强度等物理性质,并且利用Hoek-Brown准则、贯通率法以及岩石表面回弹值估算了危岩体与主控结构面的强度参数,例如单轴抗拉和抗压强度、变形模量、内摩擦角和黏聚力,然后利用不同失稳模式的计算方法进行稳定性分析。结果表明部分危岩体处于不稳定状态中,需要进行加固。     

Minateda rock shelters (Albacete) and post-palaeolithic art of the Mediterranean Basin in Spain: pigments,surfaces and patinas

The inorganic and organic fractions of two microsamples of prehistoric paint from the same site, the Minateda rock shelters, are analysed here for the first time. The two samples correspond to two rock shelters of different styles (Levantine and schematic) – Abrigo Grande de Minateda (The Great Rock Shelter of Minateda) and Abrigo del Barranco de la Mortaja (Del Barranco de la Mortaja Rock Shelter). Since its discovery, historiographical tradition has emphasised the Abrigo Grande de Minateda, with its magnificence and complexity, as emblematic of the origin and evolution of rock art in the Mediterranean Basin of the Iberian Peninsula (a UNESCO World Heritage Site). Four complementary techniques –Microphotography, Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM-EDX), Raman Spectroscopy and Gas Chromatography–Mass Spectroscopy (GC–MS)– were combined to identify and characterise the physicochemical properties of the paint and of the surface. We present an interpretation of the results that leads us to define complex taphonomic alterations beyond the usual distinction of layers that include the surface, pigments and patinas.     

Palaeolithic engravings and sedimentary environments in the Côa River Valley (Portugal): implications for the detection,interpretation and dating of open-air rock art

The pre-Magdalenian phase of the Côa River Valley open-air rock art is mostly distributed at the boundary between the rocky valley slopes and the floodplain that correspond to the most favourable geomorphological setting for the preservation of pecked and deeply superposed engravings of the most famous artistic phase of the area. The natural vertical panels of the engraved art located at this geomorphological interface have suffered weathering during two cold events of the Lateglacial. They were buried by several colluvial and alluvial deposits. The reconstruction of the sedimentary and archaeological context of the CôaRiver Valley engraving permits a better assessment of the preservation processes and interpretation of Palaeolithic open-air rock art.