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Fluvial erosion of inscriptions and petroglyphs at Siega Verde, Spain
Abstract
Low-grade metamorphics such as slates and schists tend to be subjected to relatively rapid surface deterioration by both weathering and fluvial wear. If the rate at which such processes are effective on these relatively soft rocks could be calibrated through their effects on surfaces of known ages, this would provide a possibility of estimating the age of petroglyphs on similar facies and in similar environments. An attempt of quantifying these processes is presented, using the petroglyph site of Siega Verde in western Spain as an example. A series of dated inscriptions occurring at a site of zoomorphic petroglyphs provide the data to plot rock surface deterioration against time. The involvement of numerous variables prevents this method from providing much precision, but it is adequate to offer indications of order of magnitude of age. The zoomorphs at Siega Verde have been attributed to the Upper Palaeolithic, but this method suggests that most of the site's anthropic markings are under 200 years old. This finding is supported by several other factors, such as the degree of repatination of the supposedly Pleistocene petroglyphs, and the presence of a recent terrace predating these.
... The Olschewian of Vindija in Croatia has provided several fragmentary human remains interpreted as ''Neanderthals'', while that of the roughly contemporary occupation of nearby Velika Peć ina yielded a frontal fragment of a supposedly ''modern human'' (Karavanic, 1998). This illustrates the transitional nature of the Olschewian hominins again, being intermediate between Robusts and Graciles ( Bednarik, 2008a, Bednarik, 2011, Bednarik, 2020. Their technology has also been suggested to be related to the Szeletian and seems to be represented in the territory defined by Wierszchow and Mladeč in the north; Haligovce, Baia de Fier, Morowitza and Bacho-Kiro in the east; Lokve near Trieste in the south; and Wildhaus and Bockstein in the west (Fig. 7). ...
... BP) (Fladerer, 1997;Pacher and Stuart, 2009;Rabeder and Kavcik, 2013). We propose that the people responsible for the deposits were intermediate between robust and gracile Homo sapiens, but perhaps closer to the so-called Neanderthals than the so-called modern humans (Bednarik, 2011). This is a testable proposition, and we look forward to it being tested. ...
... There is virtually no possibility that the marks were not made by one or more pre-pubescent children. Moreover, as we need to assume that they belonged to the people of Olschewian tradition camped a few metres from the site, they were probably not fully gracile modern humans but were intermediate between robust and gracile Homo sapiens (Bednarik, 2008a(Bednarik, , 2008b(Bednarik, , 2011. It is assumed that robusts possessed thicker fingers than ''anatomically modern'' people (whatever that expression is intended to mean), which may further emphasise the low age of the fluter(s). ...
After well over a century of archaeological research in Drachenhöhle, the largest cave bear lair in the Alps, the first Pleistocene rock art in central Europe has been discovered deep in the cave. Two small panels of juvenile finger flutings occur together with cave bear claw marks at the only water source of the area. The site is within a few metres of the cave's large human occupation site, excavated in 1921. It is attributed to the Alpine Palaeolithic or Olschewian, a tradition of montane-adapted people of the Early Upper Palaeolithic of central Europe. The generic phenomena of finger fluting and moonmilk speleothems are discussed to provide a general context for the subject. The cave art is then described and analysed, and the previous claims for “Palaeolithic” age of other central European sites are briefly considered.
... Preservation would be significantly better in an arid or Arctic climate, where the four last-listed rock types might show minimal surface deterioration over ten millennia. Indeed, petroglyphs on granite surfaces in northern Karelia are relatively well preserved after 4000 years (Bednarik 1992), while historical, dated inscriptions on schist in the Côa valley of Portugal (Bednarik 1995) or Siega Verde in western Spain (Bednarik 2009a) are barely decipherable after a few centuries. In the arid Pilbara of north-western Australia, petroglyphs have survived for many millennia on gabbro, and for several tens of thousands of years on granite (Bednarik 2002a). ...
... Sklar and Dietrich 1998;Snyder et al. 2000). Again, the potential of such taphonomic processes has not been adequately explored so far, with only one published example addressing the quantification of fluvial erasure of petroglyphs (Bednarik 2009a). The common rock types perhaps most amenable to such studies are the low-grade metamorphics, such as schists, phyllites, slates and mudstones. ...
... The large site Siega Verde on the Río Agueda was selected for detailed study. Its schist panels are scoured by the very coarse sand (Bednarik 2009a: Fig. 15) consisting of 86.3% quartz, and the Degree of Erasure measured on engraved dates showed that most become unreadable after 100 to 200 years of exposure to the fluvial sand blasting (Fig. 16). The site's numerous petroglyphs occur in the same flood zone and on the same rocks, and they are of the same groove depths, therefore the quantified Degree of Erasure can be applied to them to estimate their ages. ...
One of the practical applications of research into the types and processes of rock weathering is in the field of rock art studies, where it plays a key role in two areas. First, it is among the most crucial indices in efforts of estimating the age of rock art, most especially that of petroglyphs. In this area, weathering is arguably the most promising variable in the 'direct dating' methodology that has been developed in recent years. The reasons for the failures of alternative dating methods are explored, leading to the proposition that weathering and related features offer the most reliable basis for future work in this field. Some of this new methodology is discussed within the overall context of the considerable difficulties generally experienced in rock art dating. The second role of weathering in rock art research is in the field of conservation and preservation. Here the various processes of weathering are of considerable consequences in developing appropriate strategies for the demands of cultural resource management practices.
... Since then, a tendency has developed to attribute any rock art zoomorph in south-western Europe to the Upper Palaeolithic period -particularly equine and bovine images (Bednarik 2009a). Many of these recent petroglyphs did in fact not even exist when Cartailhac (Fig. 4) wrote his famous mea culpa (Bednarik 2009b). Australia experienced a similar development: after strenuous rejection of Pleistocene antiquity, its eventual acceptance led to many excessive claims. ...
... This is reflected in the Degree of Erasure found on the petroglyphs affected. Based on the quantitative data from Siega Verde in western Spain (Bednarik 2009b), with a regime of much greater kinetic energy and far more effective abrasive, it can be estimated that the petroglyphs at the South Australian sites affected by fluvial erosion are very probably less than 3000 years old. ...
... What is particularly disturbing about these misapprehensions is that at some of these sites, e.g. in Spain and Portugal, dated historical inscriptions co-occur with the petroglyphs, and as they are subjected to the same regime of weathering they provide a good measure of rock marking ages. Such deterioration can even extend to fluvial erosion, which has now been quantified against time through such inscriptions, and even when it is thus demonstrated that petroglyphs of the same site are of the 20th century (Bednarik 2009b), some archaeologists continue to insist that they must be Palaeolithic. One more observation concerning the taphonomy of the Broken Hill -Flinders Ranges petroglyph sites, considered collectively, is that they tend to occur at sites where a stream broke through a rock barrier. ...
The recognition of the occurrence of Pleistocene rock art in Australia is reviewed in the context of historical developments as well as recent observations. The frequency of misinterpretations of reported data and their effects are discussed, with particular emphasis on the traditional heartland of the 'Panaramitee style', in NE South Australia. Despite the continuing paucity of credibly dated examples, it is apparent that most rock art of the earliest phase has survived as petroglyphs rather than pictograms, which is consistent with the evidence from the rest of the world. An attempt is made to characterise Australian petroglyphs that are probably of the Pleistocene, and to estimate their potential number. In comparing them with the Pleistocene rock art of other continents their close similarity with traditions elsewhere belonging to Mode 3 lithic industries is noted.
... Preservation would be significantly better in an arid or Arctic climate, where the four last-listed rock types might show minimal surface deterioration over ten millennia. Indeed, petroglyphs on granite surfaces in northern Karelia are relatively well preserved after 4000 years (Bednarik 1992), while historical, dated inscriptions on schist in the Côa valley of Portugal (Bednarik 1995) or Siega Verde in western Spain (Bednarik 2009a) are barely decipherable after a few centuries. In the arid Pilbara of north-western Australia, petroglyphs have survived for many millennia on gabbro, and for several tens of thousands of years on granite (Bednarik 2002a). ...
... Sklar and Dietrich 1998;Snyder et al. 2000). Again, the potential of such taphonomic processes has not been adequately explored so far, with only one published example addressing the quantification of fluvial erasure of petroglyphs (Bednarik 2009a). The common rock types perhaps most amenable to such studies are the low-grade metamorphics, such as schists, phyllites, slates and mudstones. ...
... The large site Siega Verde on the Río Agueda was selected for detailed study. Its schist panels are scoured by the very coarse sand (Bednarik 2009a: Fig. 15) consisting of 86.3% quartz, and the Degree of Erasure measured on engraved dates showed that most become unreadable after 100 to 200 years of exposure to the fluvial sand blasting (Fig. 16). The site's numerous petroglyphs occur in the same flood zone and on the same rocks, and they are of the same groove depths, therefore the quantified Degree of Erasure can be applied to them to estimate their ages. ...
Research into the types and processes of rock weathering plays a key role in two areas in the field of rock art studies. First, it is crucial to issues of conservation and preservation. This paper focuses on the second area of interest in weathering phenomena, in providing evidence supporting the efforts of estimating the age of rock art, most especially that of petroglyphs. In this area, weathering is arguably the most promising variable in the 'direct dating' methodology that has been developed in recent decades. The reasons for the failures of alternative dating methods are explored, leading to the proposition that weathering and related features offer the most reliable basis for future work in this field. Some of this new methodology is discussed within the overall context of the considerable difficulties generally experienced in rock art dating. Particular attention is given to the geometry of weathering, which is often most amenable to quantification, including that of the taphonomy of stone tools and rockshelters.
... This distortion is reflected in the listing of dozens of European sites of 'Ice Age rock art' on UNESCO's World Heritage List, where not a single such site from any other continent is listed. Some of these sites, such as those in the Côa valley of Portugal or Siega Verde in western Spain, are not even of the Pleistocene OPEN ACCESS (Bednarik 2009) [33]. All this feeds the illusion that 'art was invented in Europe', subconsciously reinforcing the European fantasy of cultural superiority. ...
... This distortion is reflected in the listing of dozens of European sites of 'Ice Age rock art' on UNESCO's World Heritage List, where not a single such site from any other continent is listed. Some of these sites, such as those in the Côa valley of Portugal or Siega Verde in western Spain, are not even of the Pleistocene OPEN ACCESS (Bednarik 2009) [33]. All this feeds the illusion that 'art was invented in Europe', subconsciously reinforcing the European fantasy of cultural superiority. ...
This comprehensive overview considers the currently known Pleistocene palaeoart of Asia on a common basis, which suggests that the available data are entirely inadequate to form any cohesive synthesis about this corpus. In comparison to the attention lavished on the corresponding record available from Eurasia’s small western appendage, Europe, it is evident that Pleistocene palaeoart from the rest of the world has been severely neglected. Southern Asia, in particular, holds great promise for the study of early cognitive development of hominins, and yet this potential has remained almost entirely unexplored. Asia is suggested to be the key continent in any global synthesis of ‘art’ origins, emphasising the need for a comprehensive pan-continental research program. This is not just to counter-balance the incredible imbalance in favour of Europe, but to examine the topic of Middle Pleistocene palaeoart development effectively.
... For instance, the petroglyphs of the western Spanish site Siega Verde, which "every single European Ice Age art specialist" has identified as Paleolithic (Bahn and Vertut 1997: 132) [12], are certainly of the same age range as the numerous dated inscriptions at the same site. Fluvial erosion indices have shown conclusively that the majority of the images are of the 20th century, centering on about 1925, but some of the "typically Paleolithic" zoomorphs are actually of the 1950s (Bednarik 2009) [34]. Much the same applies to a large series of sites in the nearby lower Côa valley of northern Portugal, where again most of the panels bearing recent petroglyphs only formed in the second half of the Holocene ( Figure 16). ...
... For instance, the petroglyphs of the western Spanish site Siega Verde, which "every single European Ice Age art specialist" has identified as Paleolithic (Bahn and Vertut 1997: 132) [12], are certainly of the same age range as the numerous dated inscriptions at the same site. Fluvial erosion indices have shown conclusively that the majority of the images are of the 20th century, centering on about 1925, but some of the "typically Paleolithic" zoomorphs are actually of the 1950s (Bednarik 2009) [34]. Much the same applies to a large series of sites in the nearby lower Côa valley of northern Portugal, where again most of the panels bearing recent petroglyphs only formed in the second half of the Holocene ( Figure 16). ...
As in Australia, Pleistocene rock art is relatively abundant in Europe, but it has so far received much more attention than the combined Ice Age paleoart of the rest of the world. Since archaeology initially rejected its authenticity for several decades, the cave art of France and Spain and the portable paleoart from various regions of Europe have been the subjects of thousands of studies. It is shown, however, that much of the published information is unreliable and subjective, and that fundamental trends in the evidence have been misunderstood. In particular, the data implies that the paleoart of the Early Upper Paleolithic, the work of robust humans such as Neanderthals, is considerably more sophisticated and developed that that of more recent times. Thus, the European paleoart demonstrates that the teleological model of cultural “evolution” is false, which is to be expected because evolution is purely dysteleological. This is confirmed by the extensive record of pre-Upper Paleolithic European paleoart, which is comprehensively reviewed in this paper.
... Some are fundamental in a methodological sense. For instance, analytical methods developed from the study of inscriptions of known ages can be directly applied to petroglyphs (Bednarik 2009a), as the present paper will attempt to show. Such methods may be concerned with deposition rates of accretions, weathering rates, lichen and other issues. ...
Rock inscriptions purportedly related to Dutch shipwrecks and other early exotic visitors on the west coast of Western Australia are examined. The question of authenticity is investigated by microscopic analysis of weathering phenomena, such as the retreat rate of carbonate cement in calcareous sandstone. Dated rock inscriptions are of great value in developing quantitative and repeatable methods of estimating the age of petroglyphs. In this context, they can be of considerable importance in scientific studies of rock art. Moreover, the study of rock art should not be arbitrarily divorced from the analysis of rock inscriptions, as similar scientific methods study the two forms of rock markings and can provide mutually complementary information. Introduction Rock inscriptions are not rock art, but we should also concern ourselves with inscriptions on rock to study rock art. There are several good reasons for this, one of which is eloquently discussed by Ahmed Achrati. He demonstrates what should have been evident to us all along, that in specific world regions, rock inscriptions can provide some of the most valuable ethnographic evidence about the meaning of rock art we can ever hope to glean (Achrati 2006). Since then, others have used this information source (Alzoubi et al. 2016; Bednarik 2017, 2021). However, as a discipline , we have left much of this potential untapped in the nascent state of this field of research. There are, however, various other reasons why rock art scientists need to concern themselves with ancient or even more recent scripts on rock surfaces. One of them relates to their frequent use in the calibration of methods of rock art age estimation (e.g.
... They drove its proponent, Marcelino Santiago Tomás Sanz de Sautuola, into a premature death. Over a century later, they took to declaring any rock art images of bulls and horses found in south-western Europe to be of the period they call the Palaeolithic, even if the images are less than 200 years old (Bednarik 2009a(Bednarik , 2009b(Bednarik , 2015. The 'cult of Palaeolithic art' completely ignored inconvenient details such as the far greater body of Pleistocene rock art elsewhere (e.g. in Australia; Bednarik 2010: 113-115) than that of Europe or that most of the world's surviving Pleistocene rock art was made by people of Mode 3 rather than Mode 4 technological traditions. ...
Among the many generic explanations offered over the past two centuries for rock art production, those involving several brain illnesses and shamanism are selected for detailed analysis. These proposals are reviewed in light of the aetiologies of the psychiatric conditions linked to rock art. Some are related to the assumption that palaeoart was introduced through shamanism. Although no simplistic link between shamanism and brain disorders has been demonstrated, relevant susceptibility alleles might be involved in some shamanic experiences. No connection between rock art and shamanism has been credibly demonstrated to date. Moreover, the assumption that neuropathologies and shamanism preceded the advent of palaeoart also appears to be mistaken. It derives from the belief that palaeoart was introduced by 'anatomically modern humans' and on the discredited replacement hypothesis. These interlinked issues are discussed.
... Proses tersebut dibagi menjadi dua, yaitu proses fisika dan proses kimia. Degradasi dengan proses fisika dapat terjadi akibat interaksi mekanik antara bahan dengan lingkungan, berupa gesekan dengan benda lain atau dengan aliran air (Bednarik, 2009). Salah satu contohnya yaitu erosi. ...
The Ayam Téas I inscription is one of the ancient inscriptions in Indonesia. Currently, the condition of the inscription has undergone natural degradation, causing the letters and the written message to become more difficult to read. Among the natural forms of degradation are corrosion and erosion. One method that can be used to address this problem is by utilizing image processing technology in the form of imageJ software. The analysis process involves capturing images using a camera and then processing the images using imageJ software. This software provides a mode that can remove unnecessary colors due to lighting, allowing some of the writings on the Ayam Téas I inscription to become more visible. Keywords: imageJ; prasasti; Ayam Téas I; histogram; grayscale
... Especially in Spain there seems to be an epidemic of wrong Palaeolithic determinations of rock art that is in many cases only centuries old. The prime example of this trend is Siega Verde, a schistose site of petroglyphs on the Agueda river that has been demonstrated to be mostly of the early 20th century (Bednarik 2009), but which all commenting archaeologists placed in the Upper Palaeolithic. ...
Most of the differences between humans and other animals still endorsed in the 20th century have now been refuted. Even theory of mind, self-awareness, recursion and metarepresentation are losing their eminence as exclusively human variables. This may leave us with just one distinguishing trait: the talent of creating and using memory traces external to the brain. Palaeoart is the principal empirical evidence of this ability from the human past, a corpus that has been misconstrued in various respects. For instance, the discussion of the dawn of art-like productions and the behavioural range they facilitate has been consistently marred by humanistic banalities and lapses. Among the most damaging are to treat such productions as art or as symbols, and to impose commensurate but false taxonomies. Another fatal shortcoming of this debate has been the rejection of exogrammatic evidence on the basis that it is not art. This presentation endeavours to correct some of these misunderstandings.
... Another example is the involvement of tribology in the age estimation of rock art. The underlying principles are exemplified by a study of the petroglyphs at Siega Verde in western Spain [26]. This rock art was the subject of a major controversy when some scholars pronounced it to be of the Pleistocene (as the basis of its submission to the UNESCO World Heritage List) while others proposed very recent antiquity. ...
It has long been appreciated that there are many applications of tribology in the geological sciences. These range in scale from microscopic levels to those of intercontinental tectonic processes. Some of the key aspects of geotribology are briefly discussed to illustrate the advantages of such an interdisciplinary approach, before exploring the even greater benefits of applying tribological methods to many aspects of archaeology. That discipline comprises a vast array of physical evidence that derives from tribological processes and cannot be credibly explained by traditional archaeology. Many of these processes are briefly described, and the methodology required to define and elucidate them is discussed. The paper concludes that, for the further development of archaeology and the study of rock art, it is essential to establish a sub-discipline of archaeotribology.
... The same author produced a new study in 2009, but this time in reference to Siega Verde. Using similar arguments, he proposed a sub-modern age for the engravings on the banks of the River Agueda (Bednarik 2009). ...
... However, in the Côa valley of western Iberia, results differed sharply from archaeological predictions, but matched those of radiocarbon and cosmogenic radiation analyses by three other archaeometrists (Bednarik 1995;Watchman 1995Watchman , 1996. Eventually is was shown conclusively that the supposedly Pleistocene petroglyphs of the nearby Siega Verde site could not be more than two centuries old (Bednarik 2009). The microerosion method has been applied most successfully in Saudi Arabia and China, where chronological frameworks of large petroglyph corpora based on almost one hundred results were derived largely from this method, supplemented by 14 C, OSL and Th/U analysis (Bednarik and Khan 2002, 2017Tang and Gao 2004;Tang and Mei 2008;Tang 2012;Tang et al. 2014Tang et al. , 2017Tang et al. , 2018. ...
This article presents the first attempts to secure direct dating of Brazilian rock art. Its results point to a sequence of petroglyph reuse and modification. On the basis of current evidence, petroglyph making in the studied area ranges from the middle of the Holocene up to the beginning of European colonisation of the region. The age estimates so far obtained by microerosion analyses are broadly in agreement with the relevant archaeological information from the sampled area, the Brazilian Northeast region. Its petroglyphs are generally found on exposures of granite, the rock type most suitable for microerosion studies.
... The zoomorphic petroglyphs are exposed to precisely the same gradual obliteration. At the lower level both are worn beyond recognition in well under 200 years (Bednarik, 2009a), and even the highest lying of the rock art cannot possibly be twice that age, judging from the corresponding inscriptions. In fact the majority of the Siega Verde zoomorphs date from around 1925, when the bridge was built, and up to the 1950s. ...
Rather than considering the myths supposedly depicted in the world’s rock art, this book examines the myths archaeologists and others have created about the meanings and significance of rock art. This vast body of opinions dominates our concepts of the principal surviving cultural manifestations of early worldviews. Here these constructs are subjected to detailed analysis and are found to consist largely of misinterpretations. From the misidentification of natural rock markings as rock art to mistaken interpretations, from sensationalist claims to pareidolic elucidations of iconographies, the book presents numerous examples of myths researchers have created about pre-Historic ‘art’. The claims about a connection between rock art and the neuropathologies of its producers are assessed, and the neuroscience of rock art interpretation is reviewed. The book presents a comprehensive catalogue of falsities claimed about palaeoart, and it endeavours to explain how these arose, and how they can be guarded against by recourse to basic principles of science. It therefore represents a key resource in the scientific study of rock art.
... The present imbalance is the result of misconceptions: the perceived value of Pleistocene rock art is determined by its great antiquity, yet archaeologists are largely unaware that rock art of similar or even greater age occurs widely outside of Europe. Most of the individual European rock art sites on the WHL, especially if the recently admitted seventeen Cantabrian sites are included, are listed for their Palaeolithic attribution -although, interestingly, the Côa valley sites and Siega Verde were included on the false assumption that they are of the Pleistocene (Bednarik 2009). The few non-Palaeolithic rock art sites of Europe on the WHL are the Valcamonica complex, the Levantine art sites in eastern Spain, and the Scandinavian sites of Alta and Tannum. ...
... Th ere is great controversy over what is and is not of that period (Bednarik 2009a) and of the almost 400 sites some include, perhaps only a quarter is solidly attributable to the Final Pleistocene; another is quite likely to be of that period but in need of more evidence supporting that contention; a third quarter needs to be much better researched before such attribution is credible; and propositions about the fi nal quarter range from the controversial to the absurd (e.g. Bednarik 2009b). ...
Although the largest known concentrations of cave art are those of southwestern Europe, southern Australia and northern Papua New Guinea, smaller corpora do exist elsewhere. In the first two regions mentioned, such cave art has been demonstrated to be of the Pleistocene and up to about 50,000 years old. Cave art has been studied most intensively in the famous caves of France and Spain. Due to the specific speleoclimates of caves, lithological conditions and often the delicate nature of the cave art itself, the preservation of this immensely valuable and irreplaceable cultural resource, its conservation and its management are more demanding than those of any other rock art. In France and Spain, such practices are particularly well developed, and in Australia, efforts to design uniform management and protection measures are currently being undertaken by the Australian Rock Art Research Association. Cultural use of caves is a global phenomenon, including their role as sacred sites, and some examples of such practices are recounted in this paper.
... In others, such animal figures occurring in conditions of high-kinetic fluviatile narrow valleys of very soft rock, subjected to rapid erasure by suspendedload quartz sands are attributed to the Pleistocene. This is despite their degree of erasure, calibrated by engraved dates, indicating a recent historical antiquity (Bednarik 2009). ...
In this broad overview the corpus of world rock art is defined and compared with the known distribution of Pleistocene rock art. The discrepancies are related to relative research efforts, to the taphonomy of rock art, and to issues relating to the age estimation of rock art. As each of these factors is examined, it becomes apparent that there have been significant distortions in the ways Pleistocene rock art has been characterised and defined. Most particularly, the taphonomic distortions remain inadequately understood and their effects are identified and explained. The first qualified attempt to quantify the world's surviving rock art was undertaken by Anati (1984), who arrived at the estimate that the existence of over 20 million motifs has been demonstrated worldwide, and that a grand total of 'well over 50 million' rock art figures can safely be postulated (Fig.
... Some of the "Palaeolithic" images were actually made of rock surfaces exposed by the bridge builders. Dated features, such as BEDNARIK R.G., "The Distribution of Franco-Cantabrian Rock Art" Congrès de l'IFRAO, septembre 2010 -Symposium : L'art pléistocène en Europe (Pré-Actes) IFRAO Congress, September 2010 -Symposium: Pleistocene art in Europe (Pre-Acts) 6 inscriptions (Fig. 5), were used in an attempt to calibrate the Degree of Erasure within the site's flood-zone relative to time, and the findings were then applied to the similarly affected petroglyphs (Bednarik 2009b). Accordingly some of the supposedly Upper Palaeolithic petroglyphs are of the middle and even late 20 th Century, and few if any should be assumed to be >200 years old. ...
In reviewing the geographical distribution of European rock art attributed to the Pleistocene, the " heartland " of the Franco-Cantabrian cave art can be contrasted with rock arts of numerous other regions of Europe. Most of the " external " sites are of percussion petroglyphs, and the attribution of many of them to the Pleistocene is controversial. This paper reviews all of the purported Pleistocene rock art sites listed by one specialist, and reviews each candidate. It emerges that nearly all the sites outside the traditional distribution of Franco-Cantabrian palaeoart have either been dated to the Holocene, or they remain controversial and the likelihood that they are of the Pleistocene is not very great. Therefore it is necessary to review all European attributions of rock art to the Ice Age.
... The zoomorphic petroglyphs are exposed to precisely the same gradual obliteration. At the lower level both are worn beyond recognition in well under 200 years (Bednarik, 2009a), and even the highest lying of the rock art cannot possibly be twice that age, judging from the corresponding inscriptions. In fact the majority of the Siega Verde zoomorphs date from around 1925, when the bridge was built, and up to the 1950s. ...
Rather than addressing the myths or cosmologies supposedly expressed in rock art, this paper explores some of the myths that have been and are still being created about rock art. We know from the study of the last rock art-producing peoples in the world that outsiders of their cultures cannot interpret their rock art correctly, or even understand their cosmologies adequately. This is not surprising, in view of the neuroscientific understanding of the underlying differences. In a sound hermeneutical system, the normative nature of interpretation must be recognized and accounted for. The record shows that little hermeneutical restraint has been exercised in rock art research, and that the discipline's credibility demands the expulsion of the extensive myths that have been created by it. Some of the most prominent of these falsities are presented to illustrate the point.
... In Asia, such claims for rock paintings appeared first in the 1970s, but have not been substantiated so far and it was petroglyphs that were first soundly attributed to the Pleistocene (Bednarik et al. 2005); in Africa, credible claims for Pleistocene rock art only date from recent years Bednarik 2010, 2013;Bednarik and Beaumont 2010;Huyge et al. 2011); and in the Americas, this issue remains to be resolved. In short, the discovery of Ice Age rock art has a history marred by rejections and false claims; for instance many of the Pleistocene attributions of European rock art are falsities (Bednarik 1995a(Bednarik , 2002(Bednarik , 2009. At least in that sense the situations in Europe and Australia match closely, in that archaeology seeks to dictate what are acceptable findings, but usually turns out to be wrong, and the sciences have to contend with its dogmas. ...
The numerous published claims concerning the depiction in Australian rock art of megafaunal species or their tracks are examined. Such proposals have appeared for a century now and they have involved both petroglyphs and pictograms. Patterns in the consideration of the evidence presented in their support are analysed and compared with patterns of similar contentions in other parts of the world. The rationales underpinning these various claims are examined and an attempt is presented to explain their apparent causes.
... Finally, Aubry et al. make no attempt to respond to the dozens of objections to a Palaeolithic age of the rock art or the occupation evidence at the base of the Côa valley. They need to respond to the evidence that most engraved motifs were made with metal implements (in one case the claim is that carbonised steel was used; Eastham 1999); that the distribution of Côa petroglyphs matches precisely the distribution of historical water mill structures; that the 'Palaeolithic' images are often much less weathered or patinated than engraved dates and inscriptions on the same or adjacent panels, that one of the horse pictures at Fariseu is shown wearing a bridle (Abreu and Bednarik 2000;Bednarik 2003: Fig. 2); that the petroglyphs within the annual flood-zone of the river bear very little or no fluvial wear; that their weathering and patina is no more than a few centuries old; that the schist hydrates and disintegrates rapidly; that all of the animals depicted in the valley occurred there in the most recent history; that there is a complete absence of the diagnostic form of Upper Palaeolithic rock art, the so-called signs; that the grooves of numerous purported Palaeolithic motifs dissect lichen thalli and must thus be younger than these thalli; that the style of most Côa images is not Palaeolithic, but Roman or later; that the specific motifs identified as the oldest are geometric and schematised zoomorphs, not remotely resembling any art of the Upper Palaeolithic; that the Vermelhosa figures are of the Iron Age ; that the Mazouco figures are not Palaeolithic (Baptista 1983); that all of the nearby and very similar Siega Verde petroglyphs must postdate the Roman period and have now been shown to be all under 200 years old, dating mostly from the 20th century (Bednarik 2009); that the local villagers at Siega Verde claim that the petroglyphs were made by shepherds and 'had a good laugh when archaeologists told them that the art was Palaeolithic' (Hansen 1997); that a 4-m-high and 2-km-long stone wall near Castro, in the same area as Siega Verde, bears literally hundreds of horse pictures like those at Siege Verde and Côa; that the Lascaux late phase, with which some Côa motifs were compared to show that they must be Pleistocene , is in fact of the Holocene (Bahn 1994(Bahn , 1995. In considering just one of these objections, the archaeozoologist Thomas Wyrwoll has examined all semi-naturalistic animal images in the Côa valley and has concluded that the idea that some of the Côa rock engravings would date to the Palaeolithic, as expressed by some Portuguese archaeologists because of the mere existence of ibex representations amongst them, is based on incorrect assumptions regarding the distributional history of this species. ...
... , accessed March 2012). The discovery of open -air Paleolithic art created quite a stir, and a range of techniques was used to validate the assessment of this art ' s signifi cance; conversely, science was invoked to contradict the conclusions that were initially founded on stylistic analyses and interpretations (see Batarda Fernandes 2009 ;Bednarik 2009 ). Archaeological excavation has since demonstrated that open -air occupation deposits date to in excess of 30,000 years, providing a secondary line of evidence for the signifi cant age of this rock art. ...
This Companion to Rock Art has been inspired by an effl orescence in rock art studies over the past decade. Advances in critical thinking, the explicit pursuit of methodo-logical rigor, and improved technological capacity in the digital age have seen rock art studies move to center stage in a number of archaeological and, indeed, broader social contexts. Our mandate for this volume has been to defi ne new research issues and directions and critique existing research paradigms, and we have explicitly sought theoretically pluralist approaches. It has been more than a decade since an edited volume has explored various theoretical approaches or focused on technical and scientifi c advances (e.g., Conkey et al. 1997 ; Chippindale and Ta ç on 1998 ; Helskog 2001 ; Whitley 2001). It is similarly some time since any anthology has explored particular rock art thematics, such as landscapes (David and Wilson 2002 ; Chippindale and Nash 2004) or gender (Gero and Conkey 1991 ; Casey et al. 1998). There have been more recent collected works that have focused on the rock art of specifi c regions or on a particular topic (e.g., Loendorf et al. 2005 ; Bahn 2010 ; Goldhahn et al. 2010), but none in the past decade that has aimed to provide a comprehensive overview of different approaches from around the world and from a range of theoretical perspectives. The resurgence in rock art research around the world has been spurred by national funding cycles, advances in technology, and, in many cases, the serendipitous coalition of different personalities and projects. For instance, in Australasia the Australian Research Council (ARC) has funded a number of major projects around the region
Parmi les zoomorphes proposés pour démontrer un âge pléistocène, le rhinocéros laineux a fait figure de favori pendant une bonne partie du XX e siècle. Un exemple récemment porté à notre attention est celui du site orné de Tayuan dans le District de Xinlin, Heilongjiang Province, dans la région chinoise de l'Amur, partie la plus au nord du pays. Ce site se trouve sur un tor granitique. Sur un côté, un petit panneau vertical, guère protégé de la pluie, comprend un anthropomorphe, deux possibles zoomorphes en position très inclinée et un couple de ABOUT WOOLLY RHINOS IN ROCK ART Among the zoomorphs in rock art that have been proposed to demonstrate Pleistocene age, the woolly rhinoceros has been a favourite for much of the 20th century. An example that came to attention only recently is from the Tayuan rock art site in the Xinlin District, Heilongjiang Province, in the Chinese Amur region, which is that coun-try's northernmost part. The site consists of a granite tor, on the side of which is a small vertical panel, barely protected from the rain, comprising an anthropomorph, two apparent zoomorphs shown in a steeply inclined position,
Siega Verde was the third open-air rock art site to be discovered in the Iberian Peninsula, even before Côa and the controversy that followed that discovery. Its practicable size and the study carried out without any publicity allowed the analysis of a new reality that would change the interpretation of Palaeolithic art. From the start of the research, stylistic criteria were used to date the art in the absence of archaeological excavations. Although this has often been criticized, it meant that Siega Verde and Côa could be dated from Leroi-Gourhan’s Style II onwards. Excavations at Fariseu, a site belonging to Côa in Portugal, have proved that hypothesis archaeologically, as well as supporting the applicability of Leroi-Gourhan’s styles. Siega Verde is a good representative of Palaeolithic art in the open, on rocks by a river-bank or on prominent hills, but it is not the only form that can be catalogued as open-air rock art, because there are intermediate forms. Th ese are found in cave entrances and in rock-shelters all over the Iberian Peninsula, especially in areas where little evidence of Palaeolithic art used to be known, such as on the southern Mediterranean coast and in Andalusia. This site possesses an exterior Upper Palaeolithic art ensemble, similar to the art found inside caves and of the same age,
but in a diff erent location. Formal relationships are usual inside and outside the caves and in both cases they represent a communicative code that did not need the dark and mystery to be expressed.
This paper reviews current developments in microerosion analysis, including the testing of a universal calibration curve based on regional precipitation. This enables the use of the method in regions that are unlikely to provide suitable calibration surfaces. The paper also considers the creation of the archive of the International Centre of Rock Art Dating, and the need for it to facilitate the testing of rock art age estimates.
In recent decades, numerous examples have been reported of open-air petroglyphs on schists and slates that were attributed to the Upper Palaeolithic period. In the majority of cases, these motifs are said to depict horses. In this paper, a rich concentration of equine petroglyphs on granite surfaces of approximately known ages is taken advantage of to add to understanding the rates of rock surface weathering. The general topic of mistaken Palaeolithic rock art across Eurasia is explored, leading to the appreciation of the difficulties in defining a rock art style. One of these problems is that so many non-Palaeolithic elements have been incorporated in this style that it cannot be regarded as reliable. Another complication arises from the emotive conviction that Pleistocene ‘art’ is more important than Holocene. That belief probably stems from the notion that the Franco-Cantabrian ‘art’ substantiates the paradigm of ‘civilisation’ initially arising in Europe.
This brief paper considers the submission to the UNESCO World Heritage List of the petroglyph site Siega Verde in western Spain. The justification of the submission, that the site features Pleistocene rock art, was unfounded and this had been published in the year before the site's inscription.
The tendency of many European and some asian archaeologists to pronounce rock art as being Palaeolithic in the absence of any evidence other than stylistic vibes is examined. numerous examples are presented and discussed, from central Europe, britain, France and especially from the Iberian Peninsula. The rest of the world is also briefly considered. All claims from outside the traditional main corpus, essentially in France and Spain, are shown to be tenuous and largely unsupported, and this applies to the entire region from Portugal to china. There are literally hundreds of false or very tenuous claims for Pleistocene rock art from Eurasia. This state is then compared with the situation in other continents, in an effort to understand the psychology of those making precipitate claims.
For a property to be inscribed on the World Heritage List it must be accepted by the World Heritage Committee as being of Outstanding Universal Value. The Operational Guidelines specify the key tests that the World Heritage Committee applies to decide whether a property is of Outstanding Universal Value:
*the Committee considers a property as having Outstanding Universal Value if the property meets one or more of the World Heritage criteria; and,
*to be deemed of Outstanding Universal Value, a property must also meet the conditions of integrity and/or authenticity, and must have an adequate protection and management system to ensure its safeguarding.
There is adequate existing research and data for the Dampier Archipelago to justify Criteria i, iii and iv as meeting the threshold for Outstanding Universal Value.
This report to the Australian Heritage Council identifies how this rock art provinces meets the defined OUV criteria and argues for its authenticity and integrity.
Using microerosion analysis, a calibration curve has been established for northern Portugal on the basis of data secured from historical engravings and two Roman bridges at Vila Real. The data collected are internally consistent but they indicate that the sampled surfaces have been subjected to subsequent damage. This is indicated by distinctive peaks in the micro-wane widths. The calibration curve is significantly below those from Grosio (Italy), Lake Onega (Russia) and Qinghai (China), but well above the values observed in the semi-arid Pilbara region (Australia).
The dating studies of the ‘modern rock-art scientists’, when critically examined, are found not to show that the Côa valley petroglyphs are of recent age. Their Upper Palaeolithic characteristics, and therefore their likely late Pleistocene age, are consistent with their archaeological context.
This paper presents the results of experiments testing the long-suggested possibility that colour gradations in the repatination of petroglyphs might be quantifiable for purposes of age estimation. Colorimetric readings from a series of engraved and repatinated dates found among major petroglyph concentrations in the Pilbara of Western Australia and from petroglyphs at Jabal Qara in southern Saudi Arabia are reported. They show fairly good consistency when plotted by age, raising the possibility of using this method for dating petroglyphs under favourable conditions. The method also has significant applications in rock art conservation and condition monitoring work.
Foram recentemente descobertas, ñas proximidades do Douro internacional, na freguesia de Mazouco (concelho de Freixo de Espada-à-Cinta, distrito de Bragança), gravuras rupestres cuja grande importancia reside no facto de serem, provavelmente, as primeiras gravuras de ar livre do Paleolítico superior portugués. Mazouco situa-se a cerca de 6 km. para NNE da sede do concelho e a cerca de 1.750 m. para NW do troço mais próximo do vale do Douro, num pequeño plateau inclinado, na margem direi ta da ribeira de Albagueira. Para chegar ao local das gravuras, é ne-cessario descer um íngreme estradâo, que corta formaçôes xisto-grauváquicas ante-ordovícicas, em direcçâo à referida ribeira de Albagueira, a qual corre num sentido aproximado norte-sul, para inflectir de-pots para SE, antes de desaguar no Douro. O sitio encontra-se na margem direita da ribeira, perto da confluencia (cuja morfologia se acha alterada devido à subida das aguas provocada por barragens), em frente e para oeste do «Picào do Navalho», na base do «Cabeço da Vigia», a urna cota aproximada de 210-220 m. As coordenadas geográficas de local sao as se-guintes (segundo a «Carta Militar de Portugal» na es-cala de 1/25.000, folha 132-Fornos): 41° 8' 17" Lat. N. 2 o 22' 15" Long. E. Lx. A estaçâo acha-se integrada em formaçôes do complexo xisto-grauváquico, «afectadas por metamor-fismo regional» (v, «Carta Geológica de Portugal» na esc. de 1/500.000, Serv. Geol. de Port., 4. a éd., 1972), numa área de contacto com granitos hercíni-cos, ante-vestefalianos (predominantemente alcalinos, de duas micas). A paisagem é extremamente alcanti-lada, com descidas abruptas para o Douro e seus afluentes, característica que, antes da construçâo das barragens, era obviamente ainda mais acentuada.
The simplicity and apparent mechanistic basis of the stream power river
incision law have led to its wide use in empirical and theoretical
studies. Here we identify constraints on its calibration and
application, and present a mechanistic theory for the effects of
sediment supply on incision rates which spotlights additional
limitations on the applicability of the stream power law. On channels
steeper than about 20%, incision is probably dominated by episodic
debris flows, and on sufficiently gentle slopes, sediment may bury the
bedrock and prevent erosion. These two limits bound the application of
the stream power law and strongly constrain the possible combination of
parameters in the law. In order to avoid infinite slopes at the drainage
divide in numerical models of river profiles using the stream power law
it is commonly assumed that the first grid cell is unchanneled. We show,
however, that the size of the grid may strongly influence the calculated
equilibrium relief. Analysis of slope-drainage area relationships for a
river network in a Northern California watershed using digital elevation
data and review of data previously reported by Hack reveal that
non-equilibrium profiles may produce well defined slope-area
relationships (as expected in equilibrium channels), but large
differences between tributaries may point to disequilibrium conditions.
To explore the role of variations in sediment supply and transport
capacity in bedrock incision we introduce a mechanistic model for
abrasion of bedrock by saltating bedload. The model predicts that
incision rates reach a maximum at intermediate levels of sediment supply
and transport capacity. Incision rates decline away from the maximum
with either decreasing supply (due to a shortage of tools) or increasing
supply (due to gradual bed alluviation), and with either decreasing
transport capacity (due to less energetic particle movement) or
increasing transport capacity (due less frequent particle impacts per
unit bed area). We use this model to predict longitudinal profiles under
varying boundary conditions and sediment supply rates and find that even
in actively downcutting rivers, the river slope needed to maintain
incision may be only slightly greater than the slope required to
transport the imposed load. Hence, the channel slope-drainage area
relationships of rivers actively cutting through bedrock may
predominately reflect the grain size and supply rate of sediment and
only secondarily the influence of bedrock resistance to erosion.
Until recently, published rates of incision of bedrock valleys came from indirect dating of incised surfaces. A small but growing literature based on direct measurement reports short-term bedrock lowering at geologically unsustainable rates. We report observations of bedrock lowering from erosion pins monitored over 1-7 yr in 10 valleys that cut indurated volcanic and sedimentary rocks in Washington, Oregon, California, and Taiwan. Most of these channels have historically been stripped of sediment. Their bedrock is exposed to bed-load abrasion, plucking, and seasonal wetting and drying that comminutes hard, intact rock into plates or equant fragments that are removed by higher flows. Consequent incision rates are proportional to the square of rock tensile strength, in agreement with experimental results of others. Measured rates up to centimeters per year far exceed regional long-term erosion-rate estimates, even for apparently minor sediment-transport rates. Cultural artifacts on adjoining strath terraces in Washington and Taiwan indicate at least several decades of lowering at these extreme rates. Lacking sediment cover, lithologies at these sites lower at rates that far exceed long-term rock-uplift rates. This rate disparity makes it unlikely that the long profiles of these rivers are directly adjusted to either bedrock hardness or rock-uplift rate in the manner predicted by the stream power law, despite the observation that their profiles are well fit by power-law plots of drainage area vs. slope. We hypothesize that the threshold of motion of a thin sediment mantle, rather than bedrock hardness or rock-uplift rate, controls channel slope in weak bedrock lithologies with tensile strengths below ∼3-5 MPa. To illustrate this hypothesis and to provide an alternative interpretation for power-law plots of area vs. slope, we combine Shields' threshold transport concept with measured hydraulic relationships and downstream fining rates. In contrast to fluvial reaches, none of the hundreds of erosion pins we installed in steep valleys recently scoured to bedrock by debris flows indicate any postevent fluvial lowering. These results are consistent with episodic debris flows as the primary agent of bedrock lowering in the steepest parts of the channel network above ∼0.03-0.10 slope.
The Côa rock art covers 17 km of the river valley and extends along the banks of the Douro, downstream of the confluence between the two rivers. A total of 194 different panels with Palaeolithic zoomorphic motifs have already been identified. Later prehistoric and historic periods, especially the Iron Age, are also represented. Settlement of the valley in Upper Palaeolithic times is documented by residential sites dating to the Gravettian, the Solutrean and the Magdalenian periods. Results of stylistic analysis, whose chronological predictions have been independently confirmed by superposition patterns derived from the figurative stratigraphies observed in the numerous palimpsests known, indicate that all these periods are also represented in the art. The outdoor location of the Palaeolithic art, the size of the territory, the number and aesthetic quality of the motifs represented and the almost uninterrupted continuity to the present of the artistic use of the region's rock faces concur to the uniqueness of this complex of sites. Accordingly, an Archaeological Park was established in the area, the construction of the dam that threatened to flood the rock art has been abandoned and the valley is to be included in UNESCO's World Heritage List.
German
Die Felszeichnungen erstrecken sich 17 km entlang des Côatals und dehnen sich weiter entlang der Ufer des Douro, flußabwärts des Zusammenflusses der beiden Flüsse, aus. 194 verschiedene Felsflächen mit paläolithisch-zoomorphen Darstellungen konnten bisher identifiziert werden. Spätere prähistorische und historische Perioden, insbesonders die Eisenzeit, sind auch vertreten. Im Tal wurde jungpaläolithische Siedlungsaktivität in Form von Lagerplätzen die ins Gravettien, Solutrean und Magdalénien datieren, nachgewiesen. Die Ergebnisse der Stilanalyse zeigen, daß alle diese Epochen auch in den Felsbildern repräsentiert sind. Die vermutete chronologische Abfolge der Zeichnungen fand zusätzlich unabhängige Unterstützung durch die Éberschreibmuster die anhand der Stratigraphien figuraler Motive in den zahlreichen schon bekannten Felskunstpalimpzesten beobachtet wurden. Die Lage der paläolithischen Kunst in der Landschaft, die Größe des Gebiets, die Anzahl und ästhetische Qualität der vorhandenen Motive sowie die fast ununterbrochene Kontinuität der künstlerischen Gestaltung der Felsoberflächen in der Region bis in die Gegenwart tragen zur Einmaligkeit dieses Komplexes beL Gemaß seiner Bedeutung wurde das Gebiet zum archäologischen Park erklärt. Das Bauvorhaben einer Staustufe, wodurch die Überflutung der Felszeichnungen gedroht hätte, wurde aufgegeben und das Tal wird nun in die Liste des Weltkulturerbes der UNESCO aufgenommen werden.
French
L'art rupestre s'étend sur 17 km. le long de la rivière qui coule dans la vallée de la Côa et continue sur les rives du Douro, en aval du confluent des deux rivières. On a déjà identifié 194 panneaux différents comportant des motifs zoomorphes du Paléolithique. Des périodes historiques et pré-historiques plus récentes, l'Âge de Fer en particulier, y sont aussi représentées. Des sites résidentiels datant de la période gravettienne, solutréenne et magdalénienne confirment que la vallée était habitée pendant le Paléolithique supérieur. Des résultats d'analyse stylistique, dont les prédictions chronologiques ont été confirmées de manière indépendante, à l'aide de modèles de superposition provenant de stratigraphies figuratives observées dans de nombreux palimpsestes déjà connus, indiquent que toutes ces périodes sont aussi représentées dans cet art. Le fait que cet art paléolithique se trouve sur un site à ciel ouvert, la taille du territoire qu'il occupe, le nombre et la qualité esthétique des motifs représentés, ainsi que la continuite jusqu'à présent quasi ininterrompue de l'utilisation artistique des parois rocheuses de la région, tout concourt au caractère unique de cet ensemble de sites. En consèquence, on a crèè un Pare Archèologique dans la règion et on a abandonnè la construction du barrage qui menaçait de submerger l'art rupestre. La vallèe de la Côa va aussi intègrer la Liste du Patrimoine Mondial.
A new calibrated method based on erosion phenomena is presented for the dating of petroglyphs (rock carvings and engravings) and geomorphic surfaces. In contrast to previous methods of petroglyph dating, which sought to determine the age of various mineral and organic deposits coating the art, microerosion analysis attempts to ascertain the time of mark production itself, by creating a geomorphologically based time frame. The method involves the establishment of calibration curves for the crucial variables to be considered. These are the rock type and climate of a particular region, microerosional indices and age. The theory, practical application, and prerequisites of the method are considered, and the paper concludes by defining the disadvantages and advantages of the method.
We use 10 Be to infer when, how fast, and why the Susquehanna River incised through bedrock along the U.S. Atlantic seaboard, one of the world's most prominent and ancient passive margins. Although the rate at which large rivers incise rock is a fundamental control on the development of landscapes, relatively few studies have directly measured how quickly such incision occurs either in tectonically active environments or along passive margins. Exposure ages of fluvially carved, bedrock strath terraces, preserved along the lower Susquehanna River, demonstrate that even along a passive margin, large rivers are capable of incising through rock for short periods of time at rates approaching those recorded in tectonically active regions, such as the Himalayas. Over eighty samples, collected along and between three prominent levels of strath terraces within Holtwood Gorge, indicate that the Susquehanna River incised more than 10 meters into the Appalachian Piedmont during the last glacial cycle. Beginning 36 ka, incision rates increased dramatically, and remained elevated until 14 ka. The northern half of the Susquehanna basin was glaciated during the late Wisconsinan; however, similar rates and timing of incision occurred in the unglaciated Potomac River basin immedi-ately to the south. The concurrence of incision periods on both rivers suggests that glaciation and associated meltwater were not the primary drivers of incision. Instead, it appears that changing climatic conditions during the late Pleistocene promoted an increase in the frequency and magnitude of flood events capable of exceeding thresholds for rock detachment and bedrock erosion, thus enabling a short-lived episode of rapid incision into rock. Although this study has constrained the timing and rate of bedrock incision along the largest river draining the Atlantic passive margin, the dates alone cannot explain fully why, or by what processes, this incision occurred. However, cosmogenic dating offers compelling evidence that episodes of rapid incision into bedrock are tied to glacial cycles and changes in global climate. These results, and the methods we employ, provide valuable insights into the nature of bedrock channel incision, not only along the Susquehanna River and passive margins, but also across a wide range of settings around the globe. Because river incision into bedrock transmits the effects of changing climate and tectonics through fluvial networks to hillslopes, comprehending when, where, and why rivers incise has important implications for the evolution of land-scapes.
Fluvial erosion of bedrock occurs during occasional flood events when boundary shear stress exceeds a critical threshold to initiate incision. Therefore efforts to model the evolution of topography over long timescales should include an erosion threshold and should be driven by a stochastic distribution of erosive events. However, most bedrock incision models ignore the threshold as a second-order detail. In addition, climate is poorly represented in most landscape evolution models, so the quantitative relationship between erosion rate and measurable climatic variables has been elusive. Here we show that the presence of an erosion threshold, when combined with a well-constrained, probabilistic model of storm and flood occurrence, has first-order implications for the dynamics of river incision in tectonically active areas. First, we make a direct calculation of the critical shear stress required to pluck bedrock blocks for a field site in New York. Second, we apply a recently proposed stochastic, threshold, bedrock incision model to a series of streams in California, with known tectonic and climatic forcing. Previous work in the area has identified a weak relationship between channel gradient or relief and rock uplift rate that is not easily explained by simpler detachment-limited models. The results with the stochastic threshold model show that even low erosion thresholds, which are exceeded in steep channels during high-frequency flood events, fundamentally affect the predicted relationship between gradient and uplift rate in steady state rivers, in a manner consistent with the observed topography. This correspondence between theory and data is, however, nonunique; models in which a thin alluvial cover may act to inhibit channel incision in the low uplift rate zone also provide plausible explanations for the observed topography. Third, we explore the broader implications of the stochastic threshold model to the development of fluvial topography in active tectonic settings. We suggest that continued field applications of geomorphic models, including physically meaningful thresholds and stochastic climate distributions, are required to advance our knowledge of interactions among surficial, climatic, and crustal processes.
Understanding and quantifying fluvial transport and bedrock abrasion process - es have become major concerns in modeling landform response to tectonic and cli- matic forcing. Recent theoretical and experimental investigations have in particular stressed the importance of sediment supply and size in controlling bedrock incision rate. Many studies on the downstream evolution of pebble size have focused on unrav- eling the respective roles of selective sorting and abrasion, without paying much atten- tion to sediment sources. In order to track sediment supply and characteristics from source to sink in an active tectonic setting, where long-term selective deposition can be excluded, we systematically measured sediment size and lithology on gravel bars along the Marsyandi River and its tributaries (Himalayas of central Nepal), and also in sediment source material from hillslopes (landslides, moraines, terrace deposits). The downstream evolution in lithological distribution is found to be in close agree- ment with common views on pebble abrasion and present views on denudation in the range: (1) pebbles from the more rapidly uplifted and eroded Higher Himalayan gneissic units are over-represented, due to their major contribution to sediment influx, (2) easily erodible lithologies such as schists, sandstones, and limestone are under-rep- resented relative to resistant rock types like quartzite. More surprisingly, we observe a general downstream coarsening of gravel bar material along the middle and lower Marsyandi River, whereas downstream sediment fining is typical of most river sys - tems. A simple integrative model that tracks pebbles from hillslope to the main stem of the river and includes abrasion coefficients for the different Himalayan lithologies and size distribution of hillslopes sediment supplies accounts for both changing litho- logic proportion along the Marsyandi and for the downstream coarsening of gravel bar material. This coarsening mainly results from differences in sediment sources along the Marsyandi Valley, in particular from differences in size distributions of landslide and moraine material. However, the median pebble size of subsurface mate- rial in gravel bars is coarser than median size of the blocky material in the source. The choice of the measurement methods and their potential bias are discussed but cannot explain this surprising feature displayed by our measurements. We suspect
El arte parietal de la Meseta española ha sido definido habitualmente como un fenómeno disperso e influenciado por las más numerosas manifestaciones de las áreas costeras. En este trabajo se analizan tanto las evidencias conocidas como los nuevos hallazgos, proponiéndose una cronología "corta", dentro de los estilos III/IV de Leroi-Gourhan.
It is over a decade since Palaeolithic parietal art was first spotted in Europe on exposed open-air surfaces—cave art without the caves. Now the major site in Portugal is threatened by the lake behind a river-dam under construction. Here is a report on what cave art outside the caves amounts to, and of the confrontations over the Côa site that were in the headlines early this year.
The topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock-channel incision. Quantitative field assessments of process-based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate. We evaluate and calibrate the shear stress (or similar unit stream-power) bedrock-incision model by studying stream profiles in a tectonically active mountain range. Previous work on emergent marine terraces in the Mendocino triple junction region of northern California provides spatial and temporal control on rock-uplift rates. Digital elevation models and field data are used to quantify differences in landscape morphology associated with along-strike northwest to southeast changes in tectonic and climatic conditions. Analysis of longitudinal profiles supports the hypothesis that the study-area channels are in equilibrium with current uplift and climatic conditions, consistent with theoritical calculations of system response time based on the shear-stress model. Within uncertainty, the profile concavity (θ) of the trunk streams is constant throughout the study area (θ ≈0.43), as predicted by the model. Channel steepness correlates with uplift rate. These data help constrain the two key unknown model parameters, the coefficient of erosion (K) and the exponent associated with channel gradient (n). This analysis shows that K cannot be treated as a constant throughout the study area, despite generally homogeneous substrate properties. For a reasonable range of slope-exponent values (n), best-fit values of K are positively correlated with uplift rate. This correlation has important implications for landscape-evolution models and likely reflects dynamic adjustment of K to tectonic changes, due to variations in orographic precipitation, and perhaps channel width, sediment load, and frequency of debris flows. The apparent variation in K makes a unique value of n impossible to constrain with present data.
Streams incise bed rock by cutting and quarrying rock exposed in the stream beds. The bed-rock-cutting mechanism is conceptually simple; except where solution or flow cavitation is acting, it must be abrasion by entrained sediment (Shepherd and Schumm, 1974). When a sediment particle strikes the bed, some of its kinetic energy may be expended in fracturing the bed material. Fractures from a severe enough impact, or coalescing fractures from a series of impacts, allow separation of a particle of bed material which is then carried away by the flow. The abrasion rate at a point will thus be proportional to the local sediment transport rate and will depend upon the details of the fluid flow. This paper describes a bed-load-abrasion, stream-incision model developed from engineering sandblast-abrasion theory. This model is not generally applicable to bed-rock incision because extensive bed-rock reaches in stream channels often develop complex morphologies which prevent hydraulic analysis at an appropriate scale. However, predominantly alluvial streams with short (compared to channel width) bed-rock reaches have relatively simple hydraulic geometry. The bed-rock reaches are local base levels, and they control incision; the alluvial reaches control channel geometry and sediment-transport rate. Model parameters can be evaluated in this case, which is common in streams incised into tilted, layered rocks of variable resistance to abrasion. Analysis of incision by a glacially diverted gravel-bed stream (Foley, 1980a, 1980b) is used to illustrate application of the model and to test the validity of the model.
Improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed. We present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion (e.g., plucking, abrasion, cavitation, solution) is a strong function of substrate lithology, and that joint spacing, fractures, and bedding planes exert the most direct control. The relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks, and their spatial distributions. We find that plucking dominates wherever rocks are well jointed on a submeter scale. Hydraulic wedging of small clasts into cracks, bashing and abrasion by bedload, and chemical and physical weathering all contribute to the loosening and removal of joint blocks. In more massive rocks, abrasion by suspended sand appears to be rate limiting in the systems studied here. Concentration of erosion on downstream sides of obstacles and tight coupling between fluid-flow patterns and fine-scale morphology of erosion forms testify to the importance of abrasion by suspended-load, rather than bedload, particles. Mechanical analyses indicate that erosion by suspended-load abrasion is considerably more nonlinear in shear stress than erosion by plucking. In addition, a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued. Cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive, unjointed rocks that is otherwise attributed to suspended-load abrasion. Direct field evidence of cavitation erosion is, however, lacking. In terms of the well-known shear-stress (or stream-power) erosion law, erosion by plucking is consistent with a slope exponent (n) of ~2/3 to 1, whereas erosion by suspended-load abrasion is more consistent with a slope exponent of ~5/3. Given that substrate lithology appears to dictate the dominant erosion process, this finding has important implications for long-term landscape evolution and the models used to study it.
The rates and patterns of bedrock channel incision significantly
influence landscape evolution and long-term interactions among climate,
tectonics, and erosion. Unfortunately, only sparse field data are
available to quantify the controls on river incision rates. We exploit
the diversion of the upper Ukak River by an ash flow in 1912 to measure
rates of incision along a newly formed bedrock channel. Minimum
estimates of the rate of incision into intact rock vary from 0.01 to
0.10 m · yr-1. This variation reflects differences in
channel slope, channel width, lithologic facies, and intensity of
jointing as well as the effects of upstream knickpoint migration. A
stream-power type incision model adequately explains the incision-rate
data, provided (1) variations in channel width are prescribed on the
basis of field measurements, (2) the slope exponent is significantly
less than unity (n = 0.4 ± 0.2), and (3)
observed downstream changes in lithologic facies and the intensity of
jointing account for the apparent twofold downstream decrease in the
coefficient of erosion. Despite the very rapid rate of incision,
calibrated stream-power erosion coefficients for the Ukak River
(K = 2.4 × 10-4 m0.2
· yr-1 to 9.0 × 10-4 m0.2
· yr-1) are within the range of previously published
estimates. Two plausible explanations for the low values of the slope
exponent n are that incision rate is limited by
either (1) a combination of physical weathering and hydrodynamic
joint-block extraction or (2) block fracture due to bedload impacts
modulated on steeper channel segments by suspension of a significant
fraction of the sediment load.
Field observations from western Washington and eastern Tibet indicate a strong lithologic influence on strath terrace formation and highlight the response of bedrock channel width to spatial gradients in bedrock erodibility and/or rock uplift rates. Measurements of local bedrock bed and bank erosion rates together with observations of the role of weathering processes on erosion of siltstones and sandstones illustrate a mechanism that underlies a conceptual model that predicts a strong lithological control on strath terrace formation. Direct measurements of bedrock erosion rates in lithologies susceptible to accelerated erosion upon sub-aerial exposure show that lateral rates of bedrock bank erosion can substantially exceed vertical incision below the perennial flow level due to an asymmetry in erodibility between perennially submerged rock and rock exposed to cyclic wetting and drying on bedrock channel walls. Under such conditions, the rapid, weathering-mediated lowering of bedrock exposed above baseflow promotes development of a beveled bedrock platform that could become a strath terrace upon abandonment. In contrast to previous studies, channel widths measured across a substantial gradient in lithology, slope, and long-term erosion rates in eastern Tibet do not follow conventional relations where channel width scales as a power law function of drainage area. Instead, as they flow across a zone of rapid uplift these channels systematically narrow relative to the predicted width extrapolated from traditional-power-law relations. Field studies from a wide range of geological settings and lithologies support the interpretation that, in general, strath terraces tend to be more extensive in rivers flowing over weak sedimentary rock and tend to be poorly developed and/or preserved where rivers flow over hard, erosion-resistant rock.
The temporal relationship between rapid climate shifts in the Northern and Southern Hemispheres at the end of the last glacial is crucial to understanding how the global climate system functions during periods of major transition. A detailed Southern Hemisphere mid-latitude pollen record from a climatically sensitive and well-dated upland site in New Zealand, unlike previous interpretations, shows clear evidence of late-glacial climate changes similar in structure to those in the Northern Hemisphere, including a cooling interval from ca. 11 600 to 10 700 14C yr B.P. Because the cooling interval occurred ca. 600 14C yr before the Younger Dryas chron, our record thus also suggests that some global climatic events during the last deglaciation may have registered earlier in the Southern Hemisphere The full paper was published in The Geological Society of Americas journal Geology
Measurements of fluvial bedrock incision were made with submillimeter precision in the East Central Range of Taiwan, where long-term exhumation rates and precipitation-driven river discharge are independently known. They indicate that valley lowering is driven by relatively frequent flows of moderate intensity, abrasion by suspended sediment is an important fluvial wear process, and channel bed geometry and the presence of widely spaced planes of weakness in the rock mass influence erosion rate and style.
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