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National Geographic recently published images taken during field work in the Cardamoms, where several burials have been found sheltered by high Jurassic sandstone walls. The scientific article appeard on Radiocarbon by archaeologists from University of Otago, NZ.

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This year the Cambodian Stone Project will continue thanks to a co-operation between several institutions, including the National Museum of Cambodia, the Metropolitan Museum of Art, the Freer and Sackler Galleries, among others.

 In one phase of the project, the research will focus on the stone materials used for the production of sculptures during the pre-Angkorian period, thanks to the co-operation of the researchers and conservators at the National Museum of Cambodia. Field work will also be organized to collect more information on specific sedimentary formations that might have been provided stone material for the outstanding pre-Angkorian sculptural production.

 In another phase, we are working together with Khmer and Australian archaeologists on the stone materials excavated from stone workshops in Angkor and Roluos. For more information on these excavations visit the article recently published on the Phnom Penh Post.

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It's hard to pull heavy loads, no matter where you are.

Colossal stone monuments have been providing material for ancient and modern myths in every culture. In Cambodia, at people’s eyes the temples of Angkor were the result of divine intervention, the work of the engineer of the world, who erected towers and modeled architectural detail from mud and water. In Egypt, similar feelings still arise while observing pyramids and colossal sculptures. Who could have done it? How they lifted such enormous blocks in position? When the challenge seems to transcend the human capability the myth thrives. In reality, the erection of Khmer, as well Egyptian or Roman monuments was accomplished by the collective work of thousands of people organized along an elaborate line of production.

Every year equipments and tools were produced and maintained, people were trained and moved across the empire, villages and communities were created, fed and clothed to the sole purpose of building the royal monuments (see D. Arnold, Building in Egypt, Oxford University Press, 1991).

Not everybody is enjoying the work.

Moving stone materials to the building site, whatever was the distance to cover, required a considerable amount of labor, lot of it provided by men. Numerous representations exist of Egyptian building scenes, such as the one in the tomb of Djehutihotep in Bersheh, where 172 men organized in four lines are pulling a colossal statue. Fewer and less detailed are the Khmer depictions of quarrying or building activity. Those from the inner and outer galleries of the Bayon are of poor quality and badly preserved, but definitely succeed in conveying the disappointment of the bunch of workers pulling and lifting stone blocks (see V. Roveda in Bayon. New Perspectives, River Book. 2007).

One of the most direct evidence of the activity behind the temple construction can be seen in what remains of the ancient Khmer quarries. There, many stepped surfaces of variable size, height and geometry, with traces of chisel marks, wedge holes, and channels, create a surreal garden of squared beauty. It is tempting to believe that those stone blocks rise from within the earth, growing with specific shapes to please the king’s desire, dressed to fit perfectly in the complex scheme of the sacred temples.

Pulling and lifting stone blocks in the building site.

The best known quarries are those located on the eastern foothill of Kulen Mountain, about 35 km E-NE of Angkor. Several quarry sites are known under different names, such as Phnom Bei, Trapeang Thmo Dap, O’ Thmo Dap, Poeng Preah Anglong, Toek Lick and O’Mealea.

During his survey in 1866, Garnier had the chance of studying the leftover blocks, chisel marks, and tools in this area, as well as asking locals about the ancient method of stone quarrying. He ended up with a partial reconstruction of it : […] “two parallel lines are traced at the end of the block; along them, a series of holes 2-3 cm wide and of similar depth are dig; the material in between them is removed using iron chisels with a four-face point and of length varying from 30 cm to 1 m , and the trenches perfected; finally, a new series of tranches about 10-15 cm wide are cut, that are pushed until the block is detached from the bedrock” (F. Garnier, Voyage d’exploration en Indo-Chine, II, 25-26, 1873).

What has been left by the Khmers is a rich and suggestive source of information, waiting to be fully unraveled. Take a look at what is left of the quarrying activity, and try to imagine how the work was accomplished.

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 The Commission d’Exploration du Mekong included Ernest Doudart de Lagrée (the Capitaine de Frégate), Francis Garnier (the second in command), Louis Delaporte (the draftsman), Eugène Joubert and Clovis Tuorel (physicians in charge of geological, anthropological and botanical observations), and Louis de Carné (the official of the French Ministry of Foreign Affairs). This group of six explorers entered the Mekong delta in 1866 to survey an immense area of land stretching north up to the Yangtze River, and located between the Tibetan plateau and the East China Sea.

A sandstone outcrop in the riverbed of the Mekong, north of Khemmarat, Thailand

The account of this adventurous trip was published in four volumes by Hachette in 1873, including atlases with several detailed maps of the whole field trip and architectural plans of the visited villages and temples, as well as one album picturesque which incorporated the drawings and pictures of Louis Delaporte.

The first volume includes the descriptive, historical and political treatises of the field trip, in the form of a travel diary written by Garnier himself. Along the Mekong River the explorative group took notes about flora and fauna, photographed the landscape and the native people, measured distances and heights of rivers, mountains as well as buildings, estimated ore volumes and calculated the discharge of the Mekong and its tributaries. Of course, great emphasis is given to the exploration of Angkor, which is narrated in detail in two richly illustrated chapters.

Of particular interest, at least for a geologist working on provenance of building stones, is the short essay dedicated to the stone materials used for the temple construction (pp.25-29). Garnier describes in these pages two types of stone. The first is called by the Khmers bai kriem (fried rice), because of its resemblance to a dark roasted, agglutinated mass of rice. It is also the Khmer word for laterite. The second, abundantly used in Angkor, is called thma phôc (mud stone), suggesting that all the buildings and temples have been shaped from a mixture of mud and water by Viśvákarma, the divine engineer of the world. Actually, this view is not very far from the truth, as one can say that this Jurassic sandstone formed by diagenesis of loose sand- and silt-sized sediment, after transport and deposition by water, and according to the directions of Nature.

Garnier guesses that this stone has been quarried close to Phnom Kulen, where at that time he could see traces of channeling and block splitting, as well as the abandoned iron chisels used for that purpose. These tools are described as having a four-face point, and a length varying from 30 cm to 1 m.

A section of the Mekong as drawn by Delaporte ca. February 1866 (left), compared to actual river imaged in December 2006 (center). According to the geological map (right), in this exact point the Mekong cuts throught sandstone belonging to the Sao Khua Formation (Khorat Group)

Positions and maps were determined and drawn after daily astronomical observations. As Garnier himself explains, the surveying group carried one theodolite, one repeating circle, one attitude indicator, one chronometer, and two measuring tapes.

The scientific observations made by the exploring committee are summarized in the second book. Here, the results of the geological and mineralogical investigations are presented and edited by Eugène Joubert, who also supervised most of the geological work in the field in search for valuable ores.

On February 13^th 1866, the group left the village of Khemmarat, on the Thai side of the Mekong, on six boats. This section of the river is characterized by a troubled riverbed with several sandstone outcrops which make the navigation difficult, especially in winter. These outcrops are dramatically pictured in the book, and carefully mapped all along the course of the Mekong. These maps, drawn by Delaporte, are quite accurate. If we compare the drawings made in 1866 to the geological map of Thailand, we understand that Garnier was leading the group through Cretaceous continental (at least for the most part) sandstone, now known in Thailand as Phu Phan Formation and Sao Khua Formation (Racey et al, 1996). In Cambodia, these formations of the Khorat Group are known under the name of Grès Supérieures Formation, introduced by French geologists to indicate those sub-horizontal continental sediments occupying the highlands of western and northern Cambodia.

Racey et al. 1996. Racey, A., Love. M.A., Canham, A.C., Goodall, J.G.S., Polachan, S., Jones, P.D., 1996. Stratigraphy and reservoir potential of the Mesozoic Khorat Group, NE Thailand. Journal of Petroleum Geology, 19-1, pp. 5-40, 1996

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Le Cambodge Occidental - Échelle, 1:3000000, from the seminal work of J. Gubler.

Gubler is a French geologist who extensively worked in western Cambodia under the direction of the Service Géologique de l’Indochine, at the same time when Edmond Saurin was surveying the eastern regions of the country, in 1935. This schematic geological map is the results of his work, as presented by Pierre Gourou in the Annales de Géographie, 1938, t. 47, n°268. pp. 405-407.

Enrolled by the Service Géologique de l’Indochine, Saurin worked hard with a team of young geologists to complete a geological map of Indochina, starting from January 1928. He was in charge of the southeastern portion of the peninsula. Geology was only one of many interests and passions he cultivated, and in his mind this science was tightly intertwined with archaeology, anthropology  and art history. Among his vast publications, including works on conchology and numismatics, there is the revealing paper about the sandstone of Angkor, Quelques remarques sur le grès d’Angkor, published on the Bulletin de l’École française d’Extrême-Orient in 1954 (Bulletin de l’École française d’Extrême-Orient, Volume 46, 2, 619 – 634). In this work, Saurin performed chemical, petrographic, physical and geotechnical analyses of several samples from temples, sculptures and quarries. His considerations involved weathering, conservation and provenance of the most common sandstones used by the Khmers. In summary, it was the most comprehensive study of that time, and still remains an invaluable source of information and data for scientist and conservators.

More information on life and production of Saurin can be found on Asian Perspectives, 1983 – Volume 23, Number 1 [11].

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The 1:2000000 geological map of Vietnam, Cambodia, and Laos edited by Jacques Fromaget in 1971

VoA Khmer, July 26, 2011 –  In Pasadena Museum, a Trove of Khmer Treasure

Phnom Penh Post, July 22, 2011 – Temple works have become a labour of love

Phnom Penh Post, July 6, 2011 – Rare maps on display at the CCF next month

The last news about the map exhibition at the French Cultural Center in Phom Penh reminded me of how much a geological map is a work of art, and not merely for its color attributes. Here an example, edited in 1971 by Jacques Fromaget, of a massive syntetic work published for the first time in 1937.

Besides writing about geology, stratigraphy and tectonic of the peninsula, Fromaget also published in 1932 one of the earliest petrographic study of the Angkor stone materials. His considerations about temples and geology of northern Cambodia appeared on the report of the French Académie des sciences.

The colors of this geological map are not the result of an arbitrary choice, as their use has been standardized various time to represent rocks of different age and type. If you want to know more about the history of colors and patterns in geology, you can read this introductory article, and visit the USGS website and the International Commission on Stratigraphy website.

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Some news in brief about artifacts returned to the National Museum of Cambodia since 2010

artdaily.org – United States Returns 7 Stolen Ancient Cambodian Sculptures – June 17, 2010

The Phnom Penh Post – Ancient bronze back in Kingdom- July 11, 2011

A lintel on view at the National Museum of Cambodia

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As a lot of people are looking for information about the geology of Cambodia, including geographic and geological maps, I post here a short excerpt from the article published on UDAYA – Journal of Khmer Studies in 2010. The paper reviews the existing knowledge about stone types and their use during the Khmer empire, and include a brief overview of the geology of Cambodia.

For more maps and information about the geology of Cambodia, visit also the website of the Ministry of Industry, Mines and Energy of Cambodia, as well as  http://www.cambodiaatlas.com/map.

A schematic geological map of the country, modified after the United Nation publication of 1993 (United Nations. Economic and Social Commission for Asia and the Pacific, Atlas of Mineral Resources of the Escap Region, Volume 10, Cambodia, Explanatory Brochure, 1993. New York: United Nation), is given in the post of July, 28 2010.

A riverbed outcrop of Triassic sandstone in Preah Vihear province

Cambodia occupies an area of about 177.000 square kilometers in the south-central Indochina Peninsula.  The country is dominated by the drainage systems of the Mekong and the Tonle Sap Rivers, which join near Phnom Penh before entering the broad Vietnamese delta system. The Great Lake occupies an extensive central plain characterized by alluvial deposits that spread to the foothills of the Dangrek Range, which marks a natural boundary between Cambodia and Thailand. Isolated residual buttes of variable extension and altitude rise from this plain as the result of erosion of the Mesozoic sedimentary units and igneous intrusions (Sotham 1997).

 Cambodia is part of the large crustal block known as Indosinia. Prevailing marine conditions persisted until the Carboniferous period, which resulted in Devono-Carboniferous cherts, shales, sandstones and conglomerates; predominantly Permian limestones; and sparsely fossiliferous clastic sequences during the Triassic period. Once consolidated, this large and mostly submerged tectonic unit remained essentially stable until strong folding related to the regional Indosinian Orogeny culminated during the middle-upper Triassic. Emergence of the underwater marine terrain occurred during this time (Tien 1991). Triassic sedimentary units are widespread in northern and southern Cambodia with both marine and continental sequences, the latter being particularly characteristic of the Upper Triassic. Undifferentiated marine sequences consist of basal conglomerates and breccias, compact sandstones with intercalated shales, marls, mudstones, and marly limestones. Starting from the Upper Triassic onwards, the area was characterized by erosion of the land surface and deposition of thick successions of Jurassic and Cretaceous continental conglomerates, sandstones and siltstones (Workman 1977).

In Cambodia, the main episode of the Indosinian Orogeny is marked by the important unconformity at the base of the Lower-Middle Jurassic sub-horizontal sedimentary unit known as Terrain Rouge. This sequence is widely distributed in Mondolokiri and Ratanakiri provinces and in northern Cambodia, while is absent in the south-central areas of the country. This sequence mostly occurs in isolated outcrops and comprises conglomerates, sandstones and siltstones of sub-continental origin. In northern Cambodia, this Jurassic unit is covered by thin, unconsolidated Quaternary deposits. As a consequence, this Jurassic sandstone is typically exposed in numerous riverbeds in Siem Reap and Preah Vihear provinces (Delvert 1963; Moriai 2001).

Overlying the Terrain Rouge, a thick continental sequence, called Grès supérieures, was deposited during Upper Jurassic and Lower Cretaceous periods. The Upper Jurassic-Cretaceous conglomerates and sandstones are widespread in northern and western Cambodia, and constitute the south margin of the Khorat Plateau, Phnom Kulen, Tbêng Mountain, and other isolated outcrops in Siem Reap and Preah Vihear provinces. This sequence is also broadly exposed in western Cambodia in the Cardamom Mountains. Medium to fine-grained, quartz-rich sandstones with some conglomerates are most common, while abundant fine volcanic rock fragments and pyroclasts are also found in stone exposed in Siem Reap province and in the central plain of the Tonle Sap River.

Upper Cretaceous and Tertiary rocks are not known in Cambodia. Pliocene sediments and plateau basalts are generally covered by loosely-consolidated Quaternary deposits and, when exposed, are strongly laterized.

Widespread Mid- to-Upper Triassic intermediate to acid volcanism and numerous syn-tectonic intrusions, mainly of granitic composition, are associated with the different thrusts of the Indonisian Orogeny. As a result, Triassic and older sedimentary units are folded and have undergone metamorphism of variable grade and type.

A quarry of Triassic sandstone in Kratie province

The building and sculptural material during the whole Khmer Empire are thought to have been provided mostly from the Jurassic to Cretaceous sedimentary units, although Triassic formations could have been also exploited for early statuary and building materials (Delvert 1963; Uchida et al. 1995; Baptiste et al. 2001; Douglas 2004), as well as for specific productions during the Angkor period.

References

Delvert, J., 1963, Recherches sur l’erosion des grès des monuments d’Angkor. Bulletin de l’École française d’Extrême-Orient51/2, 453-534.

Douglas, J. G., 2004, Stone materials used in Khmer sculpture from the National Museum of Cambodia. Udaya – Journal of Khmer Studies 5, 5-18.

Douglas J., Carò F., and Fischer C. Evidence of sandstone usage for sculpture during the Khmer Empire in Cambodia through petrographic analysis. UDAYA Journal of Khmer Studies 9, pp. 1-18, 2010.

Moriai, T., Matsumura, Y., Akama, Y., 2002, Geological Study on Angkor Monuments, Part 3. Memoirs of the Tohoku Institute of Technology. Science and Engineering 22, 23-39

Sotham, S., 1997, Geology of Cambodia. Coordinating Committee for Geoscience Programmes in East and Southeast Asia Technical Bulletin 26, 13-23.

Tien, P.C. (Ed.) et al., 1991, Geology of Cambodia, Laos and Vietnam. Explanatory note to the Geological map of Cambodia, Laos and Vietnam at 1:1000000 scale. Geological Survey of Vietnam 2^nd ed., Hanoi.

Uchida, E., Ogawa, Y., Hirari, K.,1995, Petrology. In: Nakagawa, T. (Ed.), Annual Report on the Technical Survey of Angkor Monuments. Japan International Cooperation Center, Japan, 353-362.

Workman, D.R., 1977, Geology of Laos, Cambodia, South Vietnam and the eastern part of Thailand, Overseas Geol. & Miner. Resour. 50, 1-33.

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Bakheng temple is built atop a hill northwest of Angkor Wat

After being in Cambodia for more than two weeks, on a Saturday morning we finally left our guesthouse towards the temples of Angkor. Of all the structures in the Angkor park, we decided to visit the temples of Bakheng, Pre Rup, The Bayon and Banteay Srei.

Each temple has its own special character and we easily could have written about each in a blog post . But here we would like to report about our late afternoon visit to Phnom Bakheng, a relatively early temple build at the end of the 9th century and dedicated to Shiva. Phnom Bakheng sits atop a small mountain about 1.5 km to the northwest of Angkor Wat. The temple was erected under Yashovarman I using the mountain as the core of the sandstone structure. Before laying the sandstone blocks, the mountaintop was reshaped to a five-tiered pyramid surrounded by a wide platform. Five towers in quincunx arrangement were built at the top of the pyramid to symbolize Mount Meru and the four holy mountain.

Stone debris layered along the slopes of Phnom Bakheng as the result of mountaintop levelling for temple construction

 

The most popular way to the temple and its famous sunset view runs along the north side with gentle slope, and offers a panoramic glimpse of the Western Baray and other amenities, such as the original laterite stairs to the top, now fallen in disuse. From the prospective of a geologist, the steep way used by the elephants to carry the most adventurous tourists is more interesting, as gives the chance of observing a cross section of the mountain, and reveals surprising details of the incredible work done to gouge the mountain. Along the path, at the base of Phnom Bakheng,  it is possible to observe conglomerate and breccias in their original place. According to the geological map these are volcano-sedimentary rocks. During the ascent, the bedrock gradually disappears under a thick cover of loose sediments, now mostly overgrown. A closer look to the road cuts reveal the unexpected truth:  the mountain slopes are covered by a layered debris of small, angular rock fragments. It is the artificial sediment accumulated during the leveling of the mountaintop, when the crushed rock was discarded and carefully redistributed around the construction site.

The bedrock has been shaped as a base for the temple

Looking down the steep stairs from the terrace

The bedrock, now a heavily fractured acid tuff, crops out again only at the very top of the mountain, where fallen sandstone blocks unveils the original, shaped core of the temple. The rock has vertical walls and narrow ledges that are cladded by sanstone blocks and crossed by incredibly steep stairs.

This characteristic is probably responsable for the famous view, open in every direction to Angkor Wat, the West Baray and its Mebon, Phnom Kulen and green jungle all the way to the horizon. This view makes Phnon Bakheng one of the most threatened temples at Angkor.  Numberless visitor come here every day to enjoy a romantic sunset.   On a given evening this time of year the number will be around 1000.

The sun is getting ready to set on our way down the steeper west path. Our descent is arduous, not because of the topography, but because all of humanity has arrived and is climbing the mountain to see the sunset.

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Early in the morning on Wednesday we left Rovieng for Svay Damnak for the last time. Workers were gathering along the main road, waiting for a truck that would take them to the fields or to the mines of Phnom Deik. While turning onto the dirt road to Svay Damnak with the rounded profile of Phnom Deik behind us, our expectations were running high.

The night before we decided to spend more time in the area, and follow the recommendation of a Kuy who told us about a stone quarry located 10 km north of the village. He was so resolute, even after he took a close look at the pictures of quarries we were carrying with us, that we were willing to take such a chance. Reaching the site the Kuy knew required in fact a two hours rocky ride on the back of a motorcycle. The early start would allow us to be back in Savy Damnak around noon and move on towards Ta Sang, where other sites needed to be surveyed before the end of the day.

For the first time during our trip, we decided to split paths. Federico moved north with the Kuy guide and the Khmer archaeologist in search of the quarry; Janet drove south towards the thick forest of Phnom Svay Damnak, where the French geologists mapped an extensive outcrop of Triassic rock. We each started our journey bidding each other success.

When we met again a few hours later, we exchanged bittersweet smiles. Janet walked about 4 kilometers into the forest without finding any rock outcrops. Federico, instead of sandstone quarry, found a small basalt hill with possible remains of iron mining.

A decorated palanquin in a traditional Buddhist ceremony in Svay Damnak

The braided and bumpy road to Ta Sang was rich in unexpected surprises, as we met families of local farmers, witnessed traditional ceremonies and other activities that have their roots in Angkorian times.

Along our way we offered to a ride to a family of five who were resting in the shade on the side of the road. With these five additional passengers, we reached Ta Seng a few hours later. We still had a couple of hours to survey outcrops in nearby areas. Aerial photographs taken by colleagues from the University of Sydney showed large outcrops of rock in a river bed located east of the village. At the end of the day we only found thinly bedded shale dipping vertically.  This shale is consistent with the Triassic sedimentary sequences mentioned in the geological reports, and can be found intercalated with sandstones and conglomerates.  This stone, however, is not suitable for producing sculpture due to its soft and friable nature.

To end our survey, in an athletic gesture Federico managed to fall into a pond dropping his GPS into the water. After picking up a couple of big clams, he was finally able to fish the indispensable device from the muddy bottom. Now we know the GPS really is waterproof.

At the end of the day, all of us enjoyed a fine rest at the guesthouse with some homemade palm wine and a night time cacophony of crowing roosters, yelping dogs and many vociferous pigs.