Basalts

... Available online 12 March 2002. Abstract. The present contribution shows the results of tests on geological materials for determination of the rare-earth elements La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, as well as Y and Sc. ...

The impact that volcanic eruptions may have upon environments far from the volcanic source is conventionally assumed to depend on climatic modification by emitted gases. However, recent research has suggested that the damage caused by the direct impact of volcanic gases, mainly H 2SO 4, may be profound. This paper highlights the severity of this mechanism by reference to human sickness and death in France and contiguous with the eruption of the Laki fissure in Iceland in 1783. This work demonstrates the gains which may be made by interdisciplinary teams of researchers and illustrates the valuable knowledge that remains to be revealed by further research in the French historical record. To cite this article: J. Grattan et al., C. R. Geoscience 337 (2005).

The shrinkage of the Lisan Lake (LL) to form the recent Dead Sea (DS) was mainly a result of the reduction of the catchment area from around 157,000 km2 during Late Pleistocene to 43,000 km2 presently. The reduction in the catchment area resulted from the eruption and spread of the basalt flows of Jabal Arab-Druz (JAD), which together with the resulting deposition of thick rock debris and gravels occupied the drainage system. The filling of the pre-basalt drainage system, which used to feed the Dead Sea, with basalts and alluvial sediments blocked the inflows from reaching the Dead Sea. Local base levels along the basalt flow boarders such as Azraq Oasis, Sirhan Basin and Damascus Oasis, and numerous pools and mud flats were created.

The object of our research is Kazbegi basalt breccia. The deposit of this high quality facing and ornamental stone is located in headwaters of the river Devdoraki (the left tributary of the river Tergi) gorge, on the northern slope of the Main Range Zone of the Great Caucasus(one of the major tectonic units of Georgia)and is only partly exposed from under the glacier cover. The complicated ragged topography and lack of roads makes the primary deposit inaccessible for its exploitation. At present alluvial-glacial piles of basalt-breccia boulder blocks in the lower reaches of the river Devdorak is being quarried (total reserves 61300m 3). Kazbegi basalt-breccia is a green rock with breccia texture where large basaltic clasts are cemented by fine-grained epidote, calite and quartz mass resulted in formation of rather attractive decorative pattern of the rock and high demand on this rock as a raw material taking into account its good physical-mechanical properties[1] as well. It is though suggested that the Kazbegi basalt-breccia should be used more for lining of buildings' interiors and manufacturing of decorative items and mini-architectural artworks.As the similar type rock-formations are widespread in the region. The subject of precise recognition of the Kazbegi basalt-breccia textures and composition has become extremely essential. Thin section petrography of the breccia clasts and matrix, whole rock geochemistry and X-ray analysis have been conducted with the emphasis on alteration processes, mineralogical composition and textural features which stipulate special decorative pattern of basalt-breccia. According to previous data the rock was interpreted as epidote bearing breccia-like diabase or 'decorative diabase'. Based on our petrographic study the breccia-clasts (1-50cm.) have typical for basalts aphyric texture in contrast to diabase which is characterized by ophytic textures. This observation and chemical analyses results established that the rock corresponds to basalt; therefore the rock has been introduced as basalt-breccia [Fig.1].

A new category of large-scale volcanism, here termed Snake River (SR)-type volcanism, is defined with reference to a distinctive volcanic facies association displayed by Miocene rocks in the central Snake River Plain area of southern Idaho and northern Nevada, USA. The facies association contrasts with those typical of silicic volcanism elsewhere and records unusual, voluminous and particularly environmentally devastating styles of eruption that remain poorly understood. It includes: (1) large-volume, lithic-poor rhyolitic ignimbrites with scarce pumice lapilli; (2) extensive, parallel-laminated, medium to coarse-grained ashfall deposits with large cuspate shards, crystals and a paucity of pumice lapilli; many are fused to black vitrophyre; (3) unusually extensive, large-volume rhyolite lavas; (4) unusually intense welding, rheomorphism, and widespread development of lava-like facies in the ignimbrites; (5) extensive, fines-rich ash deposits with abundant ash aggregates (pellets and accretionary lapilli); (6) the ashfall layers and ignimbrites contain abundant clasts of dense obsidian and vitrophyre; (7) a bimodal association between the rhyolitic rocks and numerous, coalescing low-profile basalt lava shields; and (8) widespread evidence of emplacement in lacustrine-alluvial environments, as revealed by intercalated lake sediments, ignimbrite peperites, rhyolitic and basaltic hyaloclastites, basalt pillow-lava deltas, rhyolitic and basaltic phreatomagmatic tuffs, alluvial sands and palaeosols. Many rhyolitic eruptions were high mass-flux, large volume and explosive (VEI 6–8), and involved H2O-poor, low-δ18O, metaluminous rhyolite magmas with unusually low viscosities, partly due to high magmatic temperatures (900–1,050°C). SR-type volcanism contrasts with silicic volcanism at many other volcanic fields, where the fall deposits are typically Plinian with pumice lapilli, the ignimbrites are low to medium grade (non-welded to eutaxitic) with abundant pumice lapilli or fiamme, and the rhyolite extrusions are small volume silicic domes and coulées. SR-type volcanism seems to have occurred at numerous times in Earth history, because elements of the facies association occur within some other volcanic fields, including Trans-Pecos Texas, Etendeka-Paraná, Lebombo, the English Lake District, the Proterozoic Keewanawan volcanics of Minnesota and the Yardea Dacite of Australia.

Banded Iron Formations (BIFs), associated with Late Proterozoic metavolcanics, occur at Abu Marawat and Semna. As part of the BIFs occurrences in the Eastern Desert of Egypt, their nature arises much debate about their origin. The Precambrian rocks covering the study areas are, starting with the older units: (1) Serpentinite and related rocks, (2) Metavolcanics and BIF, (3) Arc granitoids, and (4) Molasse-type Hammamat sediments.The metavolcanics cover a large part of the area. They form a succession of intercalated metamorphosed volcaniclastics and volcanics. The volcaniclastics are lapilli tuffites, fine and coarse tuffites and agglomerates of basaltic to dacitic compositions. Lamination, cross bedding and graded bedding are reported. Smallscale syn-sedimentary faulting is observed. Clasts of the volcaniclastics are quartz, feldspar, volcanic rock fragments, jasper and iron oxides (derived from the associated BIF). The volcanic intercalations are represented by porphyritic amygdaloidal basalt and andesite.During this study a set of representative samples of the BIFs and the metavolcanics were collected for mineralogical and geochemical analyses. This involved semi-quantitative mineralogy using the X-ray diffraction technique (XRD) coupled with the matrix flushing technique, mineral chemistry analyses using Scanning Electron microscopy (SEM) and Energy Dispersive Spectrometry (EDS), bulk rock chemistry using X-ray Fluorescence Spectrometry (XRF), Inductively Coupled Plasma - Mass Spectrometry (ICP-MS), and ICP-Ms-4 acid digestion techniques. In addition, Small-scale experiments on upgrading the BIFs were carried out. These are mainly concerning with the ability to use the magnetic properties of the ore to separate the different minerals and upgrade the ore.The main minerals of the BIFs are magnetite, hematite, and quartz. Minor minerals are calcite, chlorite, siderite, dolomite, apatite, pyrite, chalcopyrite and pyrrhotite. Magnetite and quartz are more common in Semna BIF relative to those of Abu Marawat. Hematite and carbonates are relatively common in Abu Marawat. The abundance of chert and magnetite at Semna supports more distal and deeper environment compared to the shallower, more oxidant proximal deposition of the Abu Marawat BIF.Six types of BIF mesobands are described according to the dominant mineral assemblage. The mesobands are: (1) Jasper - magnetite mesobands, (2) Jasper - hematite - magnetite mesobands, (3) Jasper - magnetite - hematite mesobands, (4) Jasper - hematite mesobands, (5) Iron oxide - jasper mesobands, (6) Banded - oolitic mesobands.Primary textures and structures are observed, these includes lamination, banding, spherulitic, oolitic, microfaulting and slumping.SiO2 and Fe2O3 are the dominant constituents in the BIFs. The BIFs show significant enrichment in P and depletion in Ti. The BIFs show negative Ce anomalies, which suggest the existence of oxidizing conditions. The REE patterns of the BIF samples show a considerable depletion in LREE and a positive Eu anomaly. Such positive Eu anomalies are common in most Archean and Proterozoic BIFs and are considered to reflect the result of ocean hydrothermal input into an otherwise highly seawater-dominated system.The geochemistry of the metavolcanics of Abu Marawat and Semna indicates a strong depletion in Ni, Co, and Cr, which might exclude the mantle-derived origin. Semna metavolcanics show higher LREE/HREE ratio relative to those of Abu Marawat.The trace and REE distribution of Semna metavolcanics show many typical features basalts formed during plate convergence (arc basalt); includingnegative Ta and Nb anomalies, positive Th anomaly, enrichment of LILE relative to HFSE, enrichment of LREE relative to the HREE and slight negative Eu anomalies. Abu Marawat metavolcanics show relatively flat REE patterns which are similar to those reported for plume-enriched mid-ocean ridge basalts or back-arc basin basalts. Abu Marawat and Semna metavolcanics are believed to be deposited in island arc environs. Back-arc environment can be assumed for Abu Marawat metavolcanics.The Semna BIFs are relatively fine grained (usually < 0.1 mm in grain size) and hard cherty nature, the characteristics which constitute difficulty in the grindability and utilization of the ore. Abu Marawat is slightly coarser and less cherty and is more recommendable for crushing and grinding processes.The wet magnetic separation process was found suitable for enriching the Abu Marawat and Semna BIFs. Using the drum magnetic separator and Davis tube the ores of Abu Marawat and Semna can be upgraded from 50.27 Fe % up to 70.45 Fe % and from 52.33 Fe % to 71.01 respectively. Medium drum speed (60 revolutions per minute) give more enhanced separation compared to higher and lower drum speed. Roasting of the total ore at 750 - 800 °C followed by magnetic separation is found to be adequate. The optimal roasting time is 20 - 30 minutes.

Anthropological archaeologists have been investigating ancient human interaction for decades as interaction studies highlight how humans have communicated for 200,000 years at a variety of spatial and temporal scales. With the development of provenance studies and improved geochemical sourcing techniques, researchers can better document the movement of raw materials and formed artefacts from sources to habitation and ceremonial sites to understand economic, ideological, and sociopolitical interaction. In the Pacific, numerous researchers have documented how Oceanic people were highly mobile and adept at intra– and inter–island interaction across the great ‘sea of islands’ (Hauʻofa 1993). Within Polynesia, tracing interaction has mostly been accomplished through geochemical analyses of stone materials, especially basalt adzes. These findings uncovered regional voyaging and interaction spheres between numerous islands and archipelagos.

Rapa Nui (Easter Island) has been the subject of various scientific investigations. Much of this work has been dedicated to moai (statues) and ahu (platforms) and how these megalithic features venerated the island’s chiefly ancestors and supported sociopolitical organisation, ideological communication, economic (re)distribution, and elite management over the island’s ancient political economy. Although moai and ahu have been studied for centuries, archaeological investigation of the island’s many basalt sources and artefacts, including their geological provenance and geochemistry, has been minimal. Consequently, this lack of comprehensive geochemistry for basalt sources and artefacts has restricted the potential of ancient interaction studies on Rapa Nui.

To fill this gap in the archaeological literature, the “Rapa Nui Geochemical Project (RNGP)” was established in 2013. The main goals of the RNGP include: 1) to identify, geologically, the various types of basalt used archaeologically and document the stages of production for artefacts and construction stones; 2) to elucidate spatial and temporal patterns of basalt acquisition, transfer, and use; 3) to delineate economic, ideological, and sociopolitical interaction, including pathways that accompanied and facilitated stone exchange between members of the ancient Rapanui culture; 4) to highlight the attributes of Rapa Nui’s chiefly controlled ancient political economy through documenting the spatial and temporal distributions of archaeological basalt industries; 5) to evaluate economic and sociopolitical interpretations put forward by the ‘ecocide’ or ‘collapse’ narrative (Bahn and Flenley 1992; Diamond 1995, 2005); and 6) to create public archaeology and educational opportunities for the local Rapa Nui community.

Over six years, the RNGP collaborated with more than 30 individuals from 20 institutions from around the globe to conduct field archaeology (four campaigns from 2014–2018), geoarchaeological and material culture documentation (SLR camera and drone photos/videos and artefactual 3D scanning), geochemical analyses (inductively coupled plasma–mass spectrometry and portable x–ray fluorescence), radiometric dating (14C), artistic site reconstructions, and educational outreach.

RNGP results from six study areas reveal a diversity of operational sequences for basalt tool making which parallels the numerous economic, ideological and sociopolitical pathways used by the ancient Rapanui to acquire basalt for artefact and construction stone creation. The RNGP geochemically identified eight unique basalts during analysis and highlighted how quarries and sources at Ava oʻKiri and Pu Tokitoki provided most of the material used to manufacture the sample of basalt artefacts (adzes, picks, knives, and axes) analysed in this study.

Four pathways for the transfer of basalt were uncovered in this investigation, they included, opportunistic, communal, and confederation and elite (re)distribution. Thus, the complexity of interaction outlined in this Ph.D. thesis refutes economic and sociopolitical propositions put forward by the ‘collapse narrative’ for Rapa Nui’s pre–contact period. Instead, it establishes the common interaction and collaboration within and between mata (clans) and the two island confederations that existed during the island’s past, especially regarding the access to and use of culturally valuable stone such as basalt.

Rapa Nui is famous for its moai (statues) and ahu (platforms), yet research into the island's many basalt quarries, sources and workshops is limited. These geological and archaeological sites provided the raw materials for tools such as toki (adzes and picks), which facilitated the manufacture of Easter Island's iconic stonework. Other basaltic tools such as hoe (knives), ohio (axes) and mangai m¯ a'ea (stone fishhooks) served for subsistence practices. However, little is known about the sources of these artefacts, the sequence of their manufacture and their geochemical compositions. In this paper, we provide archaeological site descriptions and geochemistry of source material from the Rua Tokitoki quarry and a fine-grain basalt locality on Poike to contribute towards an understanding of prehistoric mining, social interaction and elite oversight on this isolated East Polynesian outpost. 

Rapa Nui est reconnue pour ses moai (statues) et ses ahu (plate-formes), mais la recherche sur lescarrì eres de basalte, les sources et les ateliers de lˆıle est limitée. Ces sites géologiques et archéologiques ont fourni lesmatì erespremì eres utilisées dans la confection d'outils comme le toki (herminettes et pioches), qui ont rendu possible la fabrication de la maçonnerie emblématique de l'Ile de Pâques. D'autres outils basaltiques, comme les hoe (couteaux), ohio (haches) et mangai m¯ a'ea (hameçons de pierre), servaient aussì a la survie. Toutefois, on sait peu de choses sur la source de ces artéfacts, la séquence de leur fabrication et leur composition géochimique. Ce papier présente des descriptions de sites archéologiques ainsi que la géochimie desmatì erespremì eres trouvées dans lacarrì ere de Rua Tokitoki et dans une région formée de basaltè a grain fin sur le Poike, pour contribuerà la compréhension de l'extractionminì ere préhistorique, des interactions sociales età la supervision d'´ elite de cet avant-poste isolé de la Polynésie de l'est.

ABSTRACT: The Non-destructive Structural-petrophysical analysis was applied with two main research methods: 1) Free water saturation method - consist seven fixed in the time specimens weightings in the process of water saturation; 2) Ultrasonic waves velocities (P- and S-waves (Vp, Vs)) determinations. By computer processing the following parameters was obtained: effective porosity (Pef), density(p); Poisson's ratio (μ); Young's modulus(E); Shear modulus(G), Debye temperature(θ) etc. The materials were selected from natural outcrops of Magellan (one sample), New Canton (2 samples), Clarion (6 samples) transform faults Central Pacific by dragging of 28th Mendeleev research vessel trip (1982). Petrographic characterization was made on the base of optical determinations. The results show that their physical properties vary in very large limits. This is a consequence of the very different rocks forming conditions. The better planning and special specimens collecting will Significantly improve the petrophysical marine investigations, which with their productivity, simplicity, low costs and highly informativity will help very much in better describing and understanding of ocean floor forming processes.

RÉSUMÉ: Dans l'útude est appliqúee l'analyse pútrophysique structurale non-destructive avec deux de ces múthodes: 1) La múthode de saturation libre en eau qui prevoit 7 pesúes, a des moments fixes, des úchantillons durant Ie temps de leur saturation en eau; 2) dútermination des vitesses des ondes ultrasoniques (P- et S- ondes, longitudinales et transversales; Vp et Vs). Par analyse mathúmatique avec ordinateur ont útú obtenu les resultats suivants: porositú effective (Pef); densitú (p); coefficient de Poisson (μ); module de Young (E); module de cisaillement (G); temperature de Debye (θ) etc. Les úchantillons útudiús sont en provenance des sites prus des failles transformantes du Pacifique: Magellan (1 úchantillon): Nouveau Canton (2 úchantillons): Clarion (6 úchantillonsl. Les' úchantiltons sont obtenus par dragage durant Ie 28-ume voyage du bateau scientifique Mendúlúiev en 1982. La caractúristlque pútrographlque des úchantillons est par microscopie optique. Les donnúes montrent une large variation de leures particularitús physiques. Cela est en consúquence des conditions diffúrentes de leur formation. Un meilleur úchantlllonage, planifiú et effectuú spúcialment, amúlieurera sensiblement les investigations marines dans Ie domaine de la pútrophysique, leur productivitú, simplicitú, les fera plus informatives et moins couteuses et de cette fason donnera une meilleure duscription et úlucidation des processus de fa formation de la croute oceanique.

ZUSAMMENFASSUNG: Die unzerstörbare strukturell-petrophysische Analyse mit zwei wissenschaftlichen Hauptmethoden wurde benutzt: 1) Freie Wasserbesatigung mit 7 in der Zeit fixierten Wagen der Muster wahrend der Besatigung; 2) Bestimmung der Geschwindingkeiten der Langs - und Querultraschallwellen (Vp, Vs). Durch Komputerberechnung sind folgende Parameter bestimmt: efektive Porositat (Pef), Dichte (p) Koeffizient von Poisson (μ), Modul von Young (E); Scherungsmodul (G); Temperatur von Debye (θ) u.a. Die analysierten Muster sind aus dem Boden des Zentralen Stillen Ozeans im Bereich der Magellan (1 Muster), Neue Canton (2 Muster), Clarion (6 Muster) TransforbrUche durch Dragieren, wahrend der 28 Farht des wissenschaftlichen Schiffes Mendeleev im 1982 gesammelt. Die petrographische Charakteristik der Gesteine ist mit der Hilfe der optischen Mikroskop gemacht. Die Ergebnissezeigen, dassdie physikalischen Eigenschaften der Gesteine in breiten Grenzen schwanken, und sie sind von den Bildungsbedingungen abhangig. Die bessere Planierung der Mustersammlung wird bessere Ergebnisse der petrophysikalischen Erforschung der Gesteine aus dem Ozeanboden geben. Mit ihren Produktivitat, Einfachkeit, niedrigen Preisen und hohen Informativitat können die petrophysikalische Erforschungen fuer die vollere Beschreibung und Verstandnis der Prozesse der Ozeansbodenbildung helfen.

INTRODUCTION

The materials collected by geologists of 28th Mendeleev research vessel trip (1982) at central Pacific (Melanholina et al. 1983, Peive 1981, Pushterovski & Melanholina, 1981) are investigated for their chemical and mineralogical composition. Thus our efforts are directed through petrophysical studies of the same materials for their physico-mechanical characterization.

It is out of doubt that the physical properties of rocks and other materials reflect every event in the history of their formation and transformation. In fact, they are the physical memory of every material and they include extremely important structure- genetic information which could be obtained by comprehensive experimental methods only. The main aim of this study is to fill the data gap of petrophysical properties of so rare and unique materials from the Central Pacific Ocean transform faults.

METHODS

The Structural petrophysical analysis (Starostin, 1979, Vladimirov, 1990) was applied with two main research methods: 1) Free water saturation method - consist seven fixed in the time specimens weightings in the process of water saturation; 2) Ultrasonic waves velocities (P- and S-waves) determinations. By computer processing the following parameters was obtained: effective porosity (Pef, the % of the total volume of the rock that consists of interconnecting voids)

Abstract[1] Crustal structure in Kenya and Ethiopia has been investigated using receiver function analysis of broadband seismic data to determine the extent to which the Cenozoic rifting and magmatism has modified the thickness and composition of the Proterozoic crust in which the East African rift system developed. Data for this study come from broadband seismic experiments conducted in Ethiopia between 2000 and 2002 and in Kenya between 2001 and 2002. Two methods have been used to analyze the receiver functions, the H-κ method, and direct stacks of the waveforms, yielding consistent results. Crustal thickness to the east of the Kenya rift varies between 39 and 42 km, and Poisson's ratios for the crust vary between 0.24 and 0.27. To the west of the Kenya rift, Moho depths vary between 37 and 38 km, and Poisson's ratios vary between 0.24 and 0.27. These findings support previous studies showing that crust away from the Kenya rift has not been modified extensively by Cenozoic rifting and magmatism. Beneath the Ethiopian Plateau on either side of the Main Ethiopian Rift, crustal thickness ranges from 33 to 44 km, and Poisson's ratios vary from 0.23 to 0.28. Within the Main Ethiopian Rift, Moho depths vary from 27 to 38 km, and Poisson's ratios range from 0.27 to 0.35. A crustal thickness of 25 km and a Poisson's ratio of 0.36 were obtained for a single station in the Afar Depression. These results indicate that the crust beneath the Ethiopian Plateau has not been modified significantly by the Cenozoic rifting and magmatism, even though up to a few kilometers of flood basalts have been added, and that the crust beneath the rifted regions in Ethiopia has been thinned in many places and extensively modified by the addition of mafic rock. The latter finding is consistent with models for rift evolution, suggesting that magmatic segments with the Main Ethiopian Rift, characterized by dike intrusion and Quaternary volcanism, act now as the locus of extension rather than the rift border faults.

The geological position and geochemistry of the basaltic sill and tuffs occurring within the Berriasian–?Albian pelagic limestones of the Czorsztyn Succession are described. The volcanic rock succession of the Velykyi (= Veliky) Kamenets’/Vilkhivchyk (= Vulkhovchik, Vulhovchik, Olkhivchyk) sites is related to intra-plate submarine volcanism, which took place at the southeastern termination of the Pieniny Klippen Belt. This volcanism was probably associated with the Early Cretaceous opening of the Magura/Fore-Magura basinal system, bounded by the Silesian/Marmarosh and Czorsztyn palaeoridges to the north and south respectively. The alkaline volcanic rocks from the Velykyi Kamenets’/Vilkhivchyk sites are geochemically similary to the basaltic block from Biała Woda (Małe Pieniny Mts., Poland), which is an olistolith a few metres across within the Jarmuta conglomerates (Maastrichtian/Paleocene). This basaltic block was eroded from the frontal part of the Czorsztyn Nappe and was deposited in the uppermost part of the Grajcarek Succession at the southeastern margin of the Magura Basin.

For the first time, white rusting/white coating of Silica on basaltic rocks has been observed at Lonar Crater Lake. Silica coating has been observed on basaltic rocks of Kilauea flow in Ka'u Desert on Hawaiian volcanic islands and has also been observed on the surface of Mars at Gusev Crater. The term white rusting/white coating of silica has been used for the same feature i.e., silica coating. White rusting /white coating phenomena observed on basaltic rocks of Lonar Crater Lake shows similarity to the silica coating observed on basaltic rocks of Kilauea flow in Ka'u Desert. Representative rock samples covered by white layer/white coating/white rusting were collected and after removal of the white-coated part were analyzed by XRF, showed that major oxide component was Silica (SiO₂) – 95-97 % mass of amorphous nature with minor quantities of SO₃, Fe₂O₃, Al₂O₃, CaO, and Cr₂O₃. The oxide content detected in white coating component at Lonar and that detected in silica coating on basaltic rocks of Kilauea flow in Ka'u Desert of Hawaiian volcanic islands shows good agreement which infers that similar processor unknown process may be operating at Lonar Crater Lake. From the studies carried by different researchers on silica coating on basaltic rocks of volcanic origin, it infers that the formation of white rusting at Lonar Crater Lake may be related to volcanic eruption or weathering conditions or physical changes due to climatic conditions existing at Lonar from the time the lake was formed. The white rusting is known to be a polymorph of silica in which SiO₂ value is found to be 95 – 97 mass %. This paper reports the first-hand information of observations and findings of white rusting/ white layer coating phenomena on basaltic rocks at Lonar Crater Lake on a preliminary basis and to put on record the works carried out regarding white coating phenomena with respect to silica coating on basaltic rocks of Kilauea flows in Ka'u Desert on Hawaiian volcanic islands. Phenomena with respect to silica coating on basaltic rocks of Kilauea flows in Ka'u Desert on Hawaiian volcanic islands.

ABSTRACT The Bois-de-Riquet archeological site (Lézignan-la-Cèbe, Hérault, France) provides significant paleontological and archeological data about the first occupations of Western Europe. Although only partially excavated, the site has already yielded an exceptionally rich paleontological assemblage as well as some stone artefacts. The archeostratigraphical unit “US2” is encased within a basalt flowstone radiometrically dated to 1.57 Ma. The sedimentary infill has preserved large and small mammal fossils, as well as coprolites. Biochronological interpretations suggest an age of around 1.3e1.1 Ma for the accumulation. A few basalt artefacts were exhumed alongside the fossil bones. Interpretation of the lithics has required the elaboration of a strict selection protocol based upon extensive knapping experiments with local basalt. This paper presents results from the interdisciplinary study of the Bois-de-Riquet site in the aim of contextualizing these discoveries. The microstratigraphical analysis of the deposits is presented with recent geological interpretations in order to contribute a better understanding of the main features of this assemblage, and its remarkable preservation within the thermal and textural boundary between a basalt flowstone&amp;#39;s base and its entablature.