Khorat Basin Research Articles

Seroprevalence and risk factors associated with exposure of water buffalo (Bubalus bubalis) to Neospora caninum in northeast Thailand

Water buffalo are important draft animals for agriculture in resource-restricted areas worldwide. Water buffalo were shown to be experimentally susceptible to infection with Neospora caninum, potentially affected by neosporosis, and naturally exposed to the parasite in Asia. Although enzootic to Thailand, the distribution of N. caninum among Thai water buffalo is unclear. The objectives of this study were to determine the seroprevalence of N. caninum among water buffalo of northeast Thailand and to identify risk factors associated with their exposure to N. caninum. Sera from 628 water buffalo from 288 farms were tested with an indirect fluorescent antibody test (IFAT). A total of 57 samples from 48 herds contained antibodies to N. caninum, indicating overall seroprevalence of 9.1% and 16.7% among individual animals and herds, respectively. The overall seroprevalence was highest in provinces located in the Khorat Basin in the southern part of the region tested. Host age was also associated with seroprevalence, with the greatest seroprevalence (16.1%) among buffalo over 10 years of age, followed by 5–10 years of age (13.4%), 3–5 years (9.2%), and less than 3 years (1.2%). These results collectively suggested that horizontal transmission from canine definitive hosts was an important route of water buffalo exposure to N. caninum. These results also verified the importance of risk factor analysis for effective bovine neosporosis control strategies at the local level.

First SHRIMP U–Pb zircon ages of the potash-bearing Mengyejing Formation, Simao Basin, southwestern Yunnan, China

High temperatures and arid climates were extensive throughout the Tethyan domain during the mid-Cretaceous, and thus greatest volumes of evaporites were deposited and widely distributed. The Mengyejing Formation, which contains the only pre-Quaternary potash salt deposit in China, is thought to be genetically related to the Late Cretaceous Maha Sarakham Formation in the Khorat Basin. The age of the Mengyejing Formation has been a subject of debate and controversy and was previously interpreted as Paleocene in age mainly based on a few palynology and ostracoda fossils. In this paper, we report U–Pb sensitive high-resolution ion microprobe (SHRIMP) ages between 100 Ma to 110 Ma for the first time from the tuff beds interbedded with gypsum units and siltstones from the upper part of the Mengyejing Formation in the Simao Basin, southwestern Yunnan. This age indicates that the age of the Mengyejing Formation is likely Albian to Cenomanian providing precise geochronological constraint for the age of the Mengyejing Formation in the Simao Basin, which is consistent with the age of the Maha Sarakham Formation. Combined with marine origin of δ34S values for gypsum units in the Mengyejing Formation, the ages indicate that marine incursions from the Neo-Tethyan Ocean in the mid-Cretaceous were caused by global high sea level. However, the stratigraphic succession of the Mengyejing Formation cannot be well correlated with those of the Maha Sarakham Formation caused by marine incursion and tectonic inversion in the mid-Cretaceous.

Provenance and paleogeography of the Late Cretaceous Mengyejing Formation, Simao Basin, southeastern Tibetan Plateau: Whole-rock geochemistry, U–Pb geochronology, and Hf isotopic constraints

The Late Cretaceous Mengyejing Formation, which contains the only pre-Quaternary potash salt deposit in the Simao Basin, southeastern Tibet, is thought to be genetically related to the Maha Sarakham Formation in the Khorat Basin. The provenance and paleogeography of these two basins have been under debate, although little diagnostic evidence has been previously published. A combined analysis of whole rock geochemistry, zircon U–Pb chronology, and Hf isotopic compositions was performed to characterize the provenance of the Mengyejing Formation. These formation's sandstones are characterized by moderate chemical index of alteration (CIA) values. These values, together with plots of the Th/U–Th ratios, suggest that certain samples have undergone moderate weathering and sedimentary recycling. The major and trace elements (La/Th–Hf, Th/Sc–Zr/Sc, Eu/Eu*–Th/Sc, TiO2–Fe2O3T+MgO, Al2O3/SiO2–Fe2O3T+MgO, K2O/Na2O–SiO2) indicate that the sedimentary sources were felsic rocks from an active continental margin or continental arc with a minor amount of recycled sediment from a passive continental margin. The Mengyejing Formation contains detrital zircons primarily with U–Pb ages of 2.45–2.57Ga, 1.8–1.9Ga, 740–880Ma, 410–470Ma, and 215–300Ma. The results reveal that the pre-Devonian zircons are derived from the recycled sediments of the Yangtze block originating in the Qinling Orogenic Belt, and they share this provenance with the coeval sediments in the Khorat Basin. The magmatic rocks of the Ailaoshan and Lincang areas are responsible for supplying the Devonian to Triassic detrital zircons. These provenance data combined with published paleocurrent results suggest that the Simao Basin was situated on the western margin of the Khorat Basin during the Late Cretaceous. The basins were connected when marine incursion occurred. We propose that pre-Devonian materials from the southwestern Sichuan Basin first supplied detritus to the Simao Basin and subsequently to the Khorat Basin.

Petrography, mineralogy and geochemistry of Cretaceous sediment samples from western Khorat Plateau, Thailand, and considerations on their provenance

At Mo Hin Khao on the western flank of Khorat Plateau, Thailand, the Phra Wihan Formation reveals litharenite and sublitharenite with some subarkose and arkose. A cuesta in the eroded sedimentary sequence exhibits spectacular rock pillars of considerable geotourist potential. The rock sequence is high in silica (SiO2 67–98wt%) and contains quartz, mica, magnetite, chert fragments and accessory minerals such as zircon and tourmaline and amphibole species. These accessory minerals suggest felsic rocks, such as granite, granodiorite and pegmatite, were sources for the sandstones. Geochemical analyses of the sedimentary sequence suggest that source rocks may lie in the passive continental margin, before sediment transport and deposition in the Khorat Basin by rivers flowing across a large flood plain. Many depositional sequences/episodes formed thick beds of cross bedded clastic rocks. A high average maturity index (>5) indicates sedimentary reworking/recycling. Chemical Index of Alteration (CIA) values range from 47 to 98, suggesting variable chemical weathering within the source area rocks, largely representing moderate to high degrees of weathering. The average CIA value of these sediments (78) suggests that relatively extreme alteration factors were involved.

The Mineralogy of the Copper – Gold Ore Deposits at the Phu Kham, Mine, Laos

The Phu Kham Cu-Au deposit Porphyry-related skarn-type mineralization, Lao PDR is hosted by complexly deformed, schistose, quartz-sericite-pyrite altered Permo-Carboniferous volcanic, volcaniclastic and intrusive rocks. These rocks occupy the immediate hanging wall of a large NE-dipping thrust fault. Unmineralized, variably deformed red beds of the Mesozoic Khorat basin occur in the foot wall to the thrust. At Phu Kham the well defined foot wall and hanging wall sequences are separated by poorly-stratified quartz-rich conglomerate, breccia and lesser sandstone of uncertain affinities. In previous studies, the conglomerate package has both been included in the Khorat basin succession and interpreted tostratigraphically underlie the Permo-Carboniferous volcanics. Structural studies and additional U-P zircon geochronology were undertaken in 2009 to help clarify geological relations at Phu Kham. Improved constraints on thrust geometry and kinematics were also sought, enabling the deformation history at Phu Kham to be more confidently placed into a regional context. Results indicate the thrust was emplaced from the NE, and thus has greater affinity with deformation patterns in the NW-trending Truong Son fold belt.The conglomerate package is reinterpreted as a syn-orogenic molasse deposited ahead of the Advancing allochthon, but eventually overridden during the final stages of thrustemplacement. Unfortunately, definitive geochronological data supporting this conlusion were not obtained.

Identification of an anastomosing river system in the Early Cretaceous Khorat Basin, northeastern Thailand, using stratigraphy and paleosols

The Phu Kradung and Phra Wihan formations of the Early Cretaceous Khorat Group were investigated to characterize the depositional system and paleoclimate, based on stratigraphy, paleosol features, paleosol profiles, and reworked deposits. The sediments of both formations are classified into 12 facies on the basis of their primary depositional attributes, such as bedding, grain size, texture, and sedimentary structures. Furthermore, these facies are grouped into eight architectural elements based on stratigraphic relationships and outcrop-scale macroforms. The proportions of each architectural element indicate that the depositional system was that of an anastomosing river. The anastomosing river system in the studied section is characterized by a high rate of vertical floodplain aggradation and the development of a relatively stable crevasse channel. Paleosols are developed mainly in floodplain deposits, and are characterized by the development of calcretes. A semi-arid to sub-humid paleoclimate is deduced from the occurrence of the calcretes. In addition, their microstructures suggest that these calcretes were formed under several different conditions, with micritic carbonate precipitating under relatively arid climates, and alveolar septal structures under semi-arid to sub-humid conditions. Using the thicknesses of the calcrete horizons, we conclude that the difference in the amount of precipitation between the wet and dry periods was highly variable, without any order, during deposition of the studied section. The thicknesses of intervals between successive calcrete horizons indicate that the inflow of fine materials occurred randomly across the floodplain. Partly superimposed, multiple calcrete horizons were developed during periods of low sediment supply. A random deposition of floodplain sediments appears to characterize the anastomosing river system of the Khorat Basin.

Intrinsic variability of the mechanical properties of Maha Sarakham salt

Abstract Laboratory mechanical tests were carried out to study the intrinsic variability of rock salt specimens obtained from the Middle and Lower members of the Maha Sarakham formation in the Khorat basin. Prior to the mechanical tests, the types and amount of inclusions were identified by visual examination and after testing by X-ray diffraction and dissolution methods. The uniaxial compressive strength of the specimens linearly increases from 27 MPa to about 40 MPa as the anhydrite content (by weight) increases from 0% (pure halite) to 100% (pure anhydrite). The combined stiffness of the salt and the anhydrite causes an increase of specimen elasticity from 22 GPa (pure salt) to as high as 36 GPa (pure anhydrite). Tensile strengths increase with increasing anhydrite content, particularly when the content is above 60% by weight. Below this limit the anhydrite has an insignificant impact on the specimen tensile strength. The tensile strength of salt crystals can be as high as 2 MPa, whereas that of the inter-crystalline boundaries is 1 MPa. The visco-plasticity increases exponentially with crystal size, as dislocation glide mechanisms become predominant for the specimens comprising large crystals. Salt specimens with fine crystals deform by dislocation climb mechanisms, and hence reduce the specimen9s visco-plasticity. The true understanding of the impact of the inclusions on the mechanical properties of the salt is important for the design and stability analysis of underground mines and storage caverns.

Effect of soil surface salt on the density and distribution of the snail Bithynia siamensis goniomphalos in northeast Thailand

Opisthorchis viverrini infection is associated with human cholangiocarcinoma and northeast Thailand has the highest incidence of this disease in the world. Bithynia siamensis goniomphalos is the major freshwater snail intermediate host of O. viverrini in this area and an analysis based on geographical information systems was used to determine the effect of variation in soil surface salt on the density and distribution of this snail. A malacological survey was carried out in 56 water bodies in the Khorat basin, northeast Thailand at locations with various soil surface salt levels. Mollusk samples were collected from 10 ecologically representative water body sites with 10-20 sampling stations in each. The shoreline of clear, shallow water bodies was found to be the preferred B. s. goniomphalos habitat. The snails were exclusively found in water with salinity levels ranging between 0.05 and 22.11 parts per thousand (ppt), which supports the notion that B. s. goniomphalos prefers water with some saline content over pure, freshwater. The highest snail population densities were in rice fields, ponds, road-side ditches and canals within a water salinity range of 2.5-5.0 ppt. However, the presence of B. s. goniomphalos was negatively correlated with water salinity (P ≤0.05), both with regard to density and distribution. The areas with the highest density of B. s. goniomphalos were those with less than 1% soil surface salt (potential index = 0.314), while the lowest densities were found in areas exceeding 50% soil surface salt (potential index = 0.015).

Paleomagnetism of the Middle–Late Jurassic to Cretaceous red beds from the Peninsular Thailand: Implications for collision tectonics

Jurassic to Cretaceous red sandstones were sampled at 33 sites from the Khlong Min and Lam Thap formations of the Trang Syncline (7.6°N, 99.6°E), the Peninsular Thailand. Rock magnetic experiments generally revealed hematite as a carrier of natural remanent magnetization. Stepwise thermal demagnetization isolates remanent components with unblocking temperatures of 620–690 °C. An easterly deflected declination ( D = 31.1°, I = 12.2°, α 95 = 13.9°, N = 9, in stratigraphic coordinates) is observed as pre-folding remanent magnetization from North Trang Syncline, whereas westerly deflected declination ( D = 342.8°, I = 22.3°, α 95 = 12.7°, N = 13 in geographic coordinates) appears in the post-folding remanent magnetization from West Trang Syncline. These observations suggest an occurrence of two opposite tectonic rotations in the Trang area, which as a part of Thai–Malay Peninsula received clockwise rotation after Jurassic together with Shan-Thai and Indochina blocks. Between the Late Cretaceous and Middle Miocene, this area as a part of southern Sundaland Block experienced up to 24.5° ± 11.5° counter-clockwise rotation with respect to South China Block. This post-Cretaceous tectonic rotation in Trang area is considered as a part of large scale counter-clockwise rotation experienced by the southern Sundaland Block (including the Peninsular Malaysia, Borneo and south Sulawesi areas) as a result of Australian Plate collision with southeast Asia. Within the framework of Sundaland Block, the northern boundary of counter-clockwise rotated zone lies between the Trang area and the Khorat Basin.

‘Thailand was a desert' during the mid‐Cretaceous: Equatorward shift of the subtropical high‐pressure belt indicated by eolian deposits (Phu Thok Formation) in the Khorat Basin, northeastern Thailand

AbstractThe Tibetan Plateau is a key factor in controlling the present‐day climate and atmospheric circulation pattern in Asia. The pattern of atmospheric circulation after the uplift of the plateau is well known, whereas direct evidence is lacking regarding the nature of the circulation pattern prior to the uplift. The distribution of desert directly reflects the position of the subtropical high‐pressure belt, and the prevailing surface‐wind pattern recorded in desert deposits reveals the position of its divergence axis. Cretaceous eolian sandstone of the Phu Thok Formation is extensively exposed in the northern Khorat Basin, northeastern Thailand. We conducted a sedimentological study on this formation to reconstruct temporal changes in the latitude of the subtropical high‐pressure belt in low‐latitude Asia during the Cretaceous. Spatio‐temporal changes in the paleo‐wind directions recorded in the Phu Thok Formation reveal that the Khorat Basin mainly belonged to the northeast trade wind belt and subtropical high‐pressure belt was situated to the north of the Khorat Basin during the initial stages of deposition, shifted southward to immediately above the basin during the main phase of deposition, and then shifted northward again to the north of the basin during the final stages of deposition. The paleomagnetic polarity sequence obtained for the Phu Thok Formation comprises three zones of normal polarity and two of reversed polarity, correlating to chrons M1n to C34n of the geomagnetic polarity time scale. This result suggests that the Phu Thok Formation is mid‐Cretaceous in age (from c. 126 Ma to c. 99–93 Ma), similar to the age of eolian sandstone in the Sichuan Basin, southern China (the Jiaguan Formation). These results, in combination with paleo‐wind direction data, suggest the development of low‐latitude desert and an equatorward shift of the subtropical high‐pressure belt (relative to the present‐day) in Asia during the mid‐Cretaceous.

Palaeocene–early Eocene inversion of the Phuquoc–Kampot Som Basin: SE Asian deformation associated with the suturing of Luconia

Abstract: The little explored Cambodian and Vietnamese Phuquoc–Kampot Som Basin is a Late Jurassic to Early Cretaceous foreland basin developed in response to the build-up of a palaeo-Pacific magmatic arc. A combination of seismic data, well data and outcrop geology complemented by fission track and U/Pb analysis is used to unravel the basin history. This reveals a hitherto unknown earliest Palaeogene basin inversion associated with the Luconian suturing to SE Asia and the shutdown of palaeo-Pacific subduction underneath SE Asia. The Phuquoc–Kampot Som Basin and the Khorat Basin in Thailand constitute the erosional remnants of a larger basin that covered large parts of SE Asia in Late Mesozoic time, and subsequently became segregated during earliest Palaeogene inversion and erosion. Inversion was focused along the several hundred kilometres long Kampot and Khmer–Chanthaburi fold belts that confine the Phuquoc–Kampot Som Basin and merge with the Mae Ping and the Three Pagodas fault zones. These connections, together with local NW–SE-trending sinistral transpressional faults offshore, indicate a link between initial SE Asian left-lateral strike-slip faulting and the Luconian suturing. The separation between the once unbroken Khmer–Chanthaburi Fold Belt and the Phetchabun Fold Belt in Thailand suggests a 50–100 km Cenozoic left-lateral offset across the Mae Ping Fault Zone.

GEOCHEMISTRY OF SALT-AFFECTED AQUALFS IN NORTHEAST THAILAND

A geochemistry study was carried out on 248 samples from 28 pedons of salt-affected soils (Natraqualfs) formed on alluvial and wash deposits over salt-bearing rocks in five transects in the Khorat basin, Northeast Thailand, under tropical savanna climate to determine if salinization had affected the chemical properties of the soils. This project had the objective of providing the more detailed information needed to improve agricultural practices in the area. The soils were saline sodic, sodic, and acid saline sodic with halite in salt crusts and calcite in the lower part of some soil profiles. Smectite was a minor constituent of these kaolinitic soils and was more abundant in saline soils where it may have crystallized from soil solution or derived from underlying saline rocks. The chemical composition of the soils was highly diverse caused mostly by variation in texture of parent materials rather than the effects of salinity. Plots of geochemical factor scores and textural properties versus depth showed clear evidence of depositional layering in many profiles. Five main chemical affinity groups may be recognized; Group 1 consisted of elements associated with clay minerals and oxides: Al, Ga, Cs, Sr, Fe, U, Pb, Rb, V, Be, and Zn; Group 2 consisted of sand, Si, Mo, and Cr; Group 3 consisted of pH in water and pH in KCl; group 4 reflected biological activity and consisted of S, organic carbon, and N; and group 5, composed of electrical conductivity, Na, Cl, Br, and I, represented the only distinct effect of salinity on soil composition. The higher percentages that could be explained by the two factors of the low electrical conductivity and low exchangeable sodium percentage samples indicated well the difference between the salt-affected soils and the adjacent nonsalt-affected soils in the total set of samples. They also indicated that the geochemical diversity existing in these soils could at least partially be attributed to the effect of salt in the natural soil system.

Bayesian Mixture Modelling in Geochronology via Markov Chain Monte Carlo

In this paper we develop a generalized statistical methodology for characterizing geochronological data, represented by a distribution of single mineral ages. The main characteristics of such data are the heterogeneity and error associated with its collection. The former property means that mixture models are often appropriate for their analysis, in order to identify discrete age components in the overall distribution. We demonstrate that current methods (e.g., Sambridge and Compston, 1994) for analyzing such problems are not always suitable due to the restriction of the class of component densities that may be fitted to the data. This is of importance, when modelling geochronological data, as it is often the case that skewed and heavy tailed distributions will fit the data well. We concentrate on developing (Bayesian) mixture models with flexibility in the class of component densities, using Markov chain Monte Carlo (MCMC) methods to fit the models. Our method allows us to use any component density to fit the data, as well as returning a probability distribution for the number of components. Furthermore, rather than dealing with the observed ages, as in previous approaches, we make the inferences of components from the “true” ages, i.e., the ages had we been able to observe them without measurement error. We demonstrate our approach on two data sets: uranium-lead (U-Pb) zircon ages from the Khorat basin of northern Thailand and the Carrickalinga Head formation of southern Australia.

Discrepant Cretaceous paleomagnetic poles between Eastern China and Indochina: a consequence of the extrusion of Indochina

A paleomagnetic study of Cretaceous and Paleocene red-beds has been carried out in the Yunlong area (Yunnan province of China) of the Northern Indochina block. A high-temperature component with dual polarities was isolated from both Lower Cretaceous and Paleocene rocks, and of solely polarity for upper Early Cretaceous and lower Late Cretaceous rocks. Thirteen magnetic polarity zones are found along the Pijiang section. The primary nature of Cretaceous magnetic remanence is ascertained by positive and reversal fold tests. These results, combined with previous Cretaceous results from the Yunlong and Yongping areas of the Lanping basin, indicate that these areas behaved as a relatively rigid block, and rotated 37.2±17° clockwise relative to Eurasia since the Paleocene. Comparing available Early Cretaceous paleomagnetic results obtained both from Indochina and Eastern China, a statistically significant paleolatitude difference of 9.6±5.7° is inferred. This difference is consistent with an estimated 1000±400km extrusion of Indochina relative to South China, through a counter-clockwise rotation of 14° of Indochina around a finite rotation pole inferred from the stage poles of rotation derived from the magnetic isochrons in the South China Sea. The reconstruction is fully consistent between, the Cretaceous pole obtained from the Khorat basin of the stable core of the Indochina block and the coeval pole of Eastern China.

Combined detrital-zircon fission-track and U-Pb dating: A new approach to understanding hinterland evolution

For detrital-zircon provenance studies, we present a new methodology that combines low-temperature fission-track with high-temperature U-Pb single-grain dating methods. This approach removes single-technique-based bias which can lead to misinterpretation of source. By obtaining data from the same samples and/or grains, it is possible to identify both the underlying age structure of the source terrane and subsequent thermotectonic events. Using detrital zircons from sediments belonging to the Khorat Basin in Thailand, we show how a combined approach to zircon dating can be used to better understand the temporal association between source and depositional site—information that is integral to improving models of basin formation.

Clay-mineral assemblages from some levels of K-118 drill core of Maha Sarakham evaporites, northeastern Thailand

Clay-mineral assemblages in Middle Clastic, Middle Salt, Lower Clastic, Potash Zone, and Lower Salt, totalling 13 samples from K-118 drill core, in the Maha Sarakham Formation, Khorat Basin, northeastern Thailand were studied. The clay-size particles were separated from the water-soluble salt by water leaching. Then the samples were leached again in the EDTA solution and separated into clay-size particles by using the timing sedimentation. The EDTA-clay residues were divided and analyzed by using the XRD and XRF method. The XRD peaks show that the major-clay minerals are chlorite, illite, and mixed-layer corrensite including traces of rectorite? and paragonite? The other clay-size particles are quartz and potassium feldspar. The XRF results indicate Mg-rich values and moderate MgAl atom ratio values in those clay minerals. The variable Fe, Na, and K contents in the clay-mineral assemblages can explain the environment of deposition compared to the positions of the samples from the core. Hypothetically, mineralogy and the chemistry of the residual assemblages strongly indicate that severe alteration and Mg-enrichment of normal clay detritus occurred in the evaporite environment through brine-sediment interaction. The various Mg-enrichment varies along the various members reflecting whether sedimentation is near or far from the hypersaline brine.

Discussion on structural evolution of Mesozoic Peninsular Malaysia

C. S. Hutchison and S. P. Sivam write: Harbury et al ‘ s 1990 paper is a useful contribution to our knowledge of the Mesozoic Tembeling Formation. However, the generalizations on stratigraphy and orogenesis for the whole Peninsular Malaysia are based on inadequate literature research and a general unfamiliarity with the region. Accordingly we feel obliged to bring to your attention the most obvious shortcomings of the paper. The timing of the Indosinian Orogeny of Southeast Asia ( Belov et al. 1986 ) traditionally was based on the widespread elimination of marine sedimention and general uplift by early Jurassic time. The predominantly Carnian-Norian strata (collectively called Upper Triassic flysch), were followed by predominantly Jurassic-Cretaceous molasse: the characteristically red Tembeling Group (Malaysia) and the Terrain Rouge (Indochina), and the non-oxidized Gagau Group and Tebak Formation (Malaysia) and the Grès Supérieurs of Indochina. The critical locality in Peninsular Malaysia is at Jengka Pass, where the gently dipping marine Tembeling Formation is late Triassic to early Jurassic, unconformably underlain by vertically bedded Late Permian limestone, shale and sandstone ( Ichikawa et al. 1966 ). This situation is an analogue of the western margin of the Khorat Basin of NE Thailand, where the Upper Triassic to earliest Jurassic Huai Hin Lat Formation unconformably overlies late Permian Saraburi Limestone ( Kon’no & Asama 1973 ). Jurassic redbeds succeed the Huai Hin Lat Formation, and in Peninsular Malaysia the marine Jengka Pass sequence is succeeded eastwards by continental redbed facies. The information of the foregoing paragraph has been distorted by Harbury et

Distribution of Saline Soils in the Khorat Basin of Thailand

Distribution of Saline Soils in the Khorat Basin of Thailand