Red‐coated rocks on the seashore: The esthetics and geology of prehistoric rock art in Alta, Arctic Norway

Abstract

Research suggests that the World Heritage rock engravings in Alta, Northern Norway, were made along the seashore over a period of 5000 years. The postglacial rebound and consequent land uplift have caused a continuous displacement of the shoreline, now situating the earliest rock art panels up to 26 m above sea level. By examining the rock surfaces at Hjemmeluft and other sites, using field observations and geological analyses, we found that the pronounced red bedrock surfaces in the current seashore zone are composed of inorganic iron films related to a high content of magnetite in the native sandstone. Coupled with an interpretation of regional environmental history, we also found that it is highly likely that the rock art was originally carved on rocks with red iron films, rocks that are now generally gray. Due to the land uplift and subsequent covering of the rock art with lichen, moss, and turf, the red color has waned at the rock art sites. This knowledge may renew interpretation and understanding of the location of rock art in Alta and may have implications for conservation and management.

Mineralogical origin of the chromatic contrast enhancing the Mount Bego petroglyphs (Alpes‐Maritimes, France)

“…In a comparable context, Tansem and Storemyr (2021) recently demonstrated that the red iron film originally covering the outcrops displaying the prehistoric rock art in Alta fjord (Norway) has waned due to land uplift and subsequent biological colonization. In more drastic contexts, important quantities of Fe (hydr)oxides nanoparticles are discharged by glacier melt waters in Greenland (Bhatia et al, 2013; Graly et al, 2014; Hawkings et al, 2014) and the Arctic Ocean (Raiswell, 2013).…”

“…They occur as nanoparticles associated with the clay minerals composing the rock in the first few hundreds of micrometers as well as within the microcrack networks (Figure 4). Therefore, the Fe (hydr) oxides more likely originate from the superficial weathering of the minerals (Schindler & Dorn, 2017;Tansem & Storemyr, 2021).…”

“…They occur as nanoparticles associated with the clay minerals composing the rock in the first few hundreds of micrometers as well as within the microcrack networks (Figure 4). Therefore, the Fe (hydr)oxides more likely originate from the superficial weathering of the minerals (Schindler & Dorn, 2017; Tansem & Storemyr, 2021). Interestingly, the formation of Fe (hydr)oxides is combined with a slight decrease in the relative proportion of the phengite and ripidolite particles, as shown by XRD profile modeling (Figure 7).…”

“…Petroglyphs are created by incising, pecking, or carving rock surfaces. They are among the first marks in the history of hukind (Whitley, 2005) found in many culturally diverse regions of the world such as northern America (e.g., Mojave Desert, CA, USA, see Whitley et al, 2017), central Asia (e.g., Tamgaly, Kazahkstan, see Hermann, 2011), southern Africa (e.g., Twyfelfontein, Namibia, see Viereck & Rudner, 1957), Scandinavia (e.g., Alta fjord, Norway, see Tansem & Storemyr, 2021), and southern Europe (e.g., Valcamonica, Italy, see Anati, 2009). Despite the great variety of engraving techniques and geological outcrops throughout the world, petroglyphs are generally characterized by a chromatic contrast between the rock surfaces and the brighter engraved areas (Dorn, 1991; Tansem & Storemyr, 2021; Whitley, 2005).…”

“…Such coating is physically linked to the substrate but without a neogenetic relationship with it. Yet, the mobilization and oxidation of Fe present within the minerals composing a rock are also possible during its weathering (Meunier, 2010; Schindler & Dorn, 2017; Tansem & Storemyr, 2021). As such, newly formed particles of Fe (hydr)oxides are present in a wide variety of weathering products including soils (Theng & Yuan, 2008); river suspensions (Poulton & Raiswell, 2005); glacial sediments (Bhatia et al, 2013; Raiswell et al, 2006; Raiswell, 2013); and the surface of building stones (Pecchioni et al, 2016; Wedekind et al, 2018).…”