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Northeastern Part (northeastern + part)

Distribution by Scientific Domains

Earth and Environmental Science	66%
Life Sciences	22%

Selected Abstracts

Modeling of a Deep-Seated Geothermal System Near Tianjin, China

GROUND WATER, Issue 3 2001
Zhou Xun
A geothermal field is located in deep-seated basement aquifers in the northeastern part of the North China Plain near Tianjin, China. Carbonate rocks of Ordovician and Middle and Upper Proterozoic age on the Cangxian Uplift are capable of yielding 960 to 4200 m3/d of 57°C to 96°C water to wells from a depth of more than 1000 m. A three-dimensional nonisothermal numerical model was used to simulate and predict the spatial and temporal evolution of pressure and temperature in the geothermal system. The density of the geothermal water, which appears in the governing equations, can be expressed as a linear function of pressure, temperature, and total dissolved solids. A term describing the exchange of heat between water and rock is incorporated in the governing heat transport equation. Conductive heat flow from surrounding formations can be considered among the boundary conditions. Recent data of geothermal water production from the system were used for a first calibration of the numerical model. The calibrated model was used to predict the future changes in pressure and temperature of the geothermal water caused by two pumping schemes. The modeling results indicate that both pressure and temperature have a tendency to decrease with time and pumping. The current withdrawal rates and a pumping period of five months followed by a shut-off period of seven months are helpful in minimizing the degradation of the geothermal resource potential in the area. [source]

Variation of crustal thickness in the Philippine Sea deduced from three-dimensional gravity modeling

ISLAND ARC, Issue 3 2007
Takemi Ishihara
Abstract Crustal thickness of the northern to central Philippine Sea was gravimetrically determined on the simple assumption of four layers: seawater, sediments, crust and lithospheric mantle, with densities of 1030, 2300, 2800 and 3300 kg/m3, respectively. As for the correction of the regional gravity variation, a 15 km difference of the lithospheric thickness with a density difference of 50 kg/m3 against the asthenosphere below between both sides of the Kyushu-Palau Ridge was taken into consideration. Mantle Bouguer anomalies were calculated on the assumption of constant crustal thickness of 6 km, and then the crustal thickness was obtained by three-dimensional gravity inversion method. The results show occurrence of thin crust areas with a thickness of approximately 5 km in the southern part and at the western margin of the Shikoku Basin and also of thick crust areas in the northwestern and northeastern parts of the Parece Vela Basin. We suggest that these are because of the variation of magma supply at the time of sea floor spreading in the Shikoku and Parece Vela Basins, which is possibly related to the variation of spreading rate and enhanced magmatism near the past arc volcanic fronts. The results further show the occurrence of crust thinner than 5 km in the northeastern part of the West Philippine Basin, of crust thicker than 15 km in the Amami Plateau, the Daito and Oki-Daito Ridges, and also in the northern part of Kyushu-Palau Ridge, whereas the southern part of the Kyushu-Palau Ridge the crust is thicker than 10 km. It was also inferred that small basins in the Daito Ridge province have the thinnest oceanic crust of less than 5 km in the Kita-Daito Basin. [source]

Tectonic and stratigraphic significance of the Middle Ordovician carbonate breccias in the Ogcheon Belt, South Korea

ISLAND ARC, Issue 3 2002
In-Chang Ryu
Abstract Carbonate breccias occur sporadically in the Lower,Middle Ordovician Maggol Limestone exposed in the Taebacksan Basin in the northeastern part of the northeast,southwest-trending Ogcheon Belt, South Korea. These carbonate breccias have been previously interpreted as intraformational or fault-related breccias. Thus, little attention has been focused on tectonic and stratigraphic significance of these carbonate breccias. The present study, however, indicates that the majority of these carbonate breccias are solution,collapse breccias, which are causally linked to paleokarstification. Carbonate facies analysis in conjunction with conodont biostratigraphy suggests that an overall regression toward the top of the Maggol Limestone probably culminated in subaerial exposure of platform carbonates during the early Middle Ordovician (earliest Darriwilian). Extensive subaerial exposure of platform carbonates resulted in paleokarst-related solution,collapse breccias in the upper Maggol Limestone. This subaerial exposure event is manifested as a major paleokarst unconformity at the Sauk,Tippecanoe sequence boundary elsewhere beneath the Middle Ordovician succession and its equivalents, most notably North America and North China. Due to its global extent, this paleokarst unconformity has been viewed as a product of second- or third-order eustatic sealevel drop during the early Middle Ordovician. Although a paleokarst breccia zone is recognized beneath the Middle Ordovician succession in South Korea, the Sauk,Tippecanoe sequence boundary appears to be a conformable transgressive surface on the top of the paleokarst breccia zone in the upper Maggol Limestone. The paleokarst breccia zone beneath the conformable transgressive surface is represented by a thinning-upward stack of exposure-capped tidal flat-dominated cycles that are closely associated with multiple occurrences of paleokarst-related solution,collapse breccias. This paleokarst breccia zone was a likely consequence of repeated fourth- and fifth-order sealevel fluctuations. It suggests that second- and third-order eustatic sealevel drop may have been significantly tempered by substantial tectonic subsidence near the end of the Maggol deposition. The tectonic subsidence in the basin is also evidenced by the occurrence of coeval off-platform lowstand siliciclastic quartzite lenses as well as debris flow carbonate breccias (i.e. the Yemi Breccia). With the continued tectonic subsidence, subsequent rise in the eustatic cycle caused drowning and deep flooding of carbonate platform, forming a transgressive surface on the top of the paleokarst breccia zone. This tectonic implication contrasts notably with the slowly subsiding carbonate platform model for the basin as has been previously interpreted. Thus, it is proposed that the Taebacksan Basin in the northeastern part of the Ogcheon Belt evolved from a slowly subsiding carbonate platform to a rapidly subsiding intracontinental rift basin during the early Middle Ordovician. The proposed tectonic model in the basin gives much better insight to unravel the stratigraphic response to tectonic evolution of the Ogcheon Belt, which remains an enigmatic feature in formulating a tectonic framework of the Korean peninsula. The present study also provides a good example that the falling part of the eustatic sealevel cycle may not produce a significant event in a rapidly subsiding basin where the rate of eustatic fall always remained lower than the rate of subsidence. [source]

Metric and nonmetric dental variation and the population structure of the Ainu

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 2 2010
Tsunehiko Hanihara
Gene flow and genetic drift are important factors affecting geographic variations in human phenotypic traits. In the present study, the effects of gene flow from an outside source on the pattern of within- and among-group variation of the Ainu from Sakhalin Island and three local groups of Hokkaido are examined by applying an R-matrix approach to metric and nonmetric dental data. The comparative samples consist of their ancestral and neighboring populations, such as the Neolithic Jomon, the subsequent Epi-Jomon/Satsumon, the Okhotsk culture people who migrated from Northeast Asia to the northeastern part of Hokkaido during a period 1600,900 years B.P., and modern non-Ainu Japanese. The results obtained by using the census population sizes of the regional groups of the Ainu as an estimate of relative effective population size suggest the possibility of an admixture between the Okhotsk culture people and the indigenous inhabitants in Hokkaido, at least in the coastal region along the Sea of Okhotsk. Such gene flow from Northeast Asian continent may have exerted an effect on the genetic structure of the contemporary Ainu. The present findings indicate that the population structure, as represented by genetic drift and gene flow, tend to be obscured in the results obtained by standard statistical methods such as Mahalanobis' generalized distance and Smith's MMDs. The present extension of the R-matrix approach to metric and nonmetric dental data provide results that can be interpreted in terms of a genetically, archaeologically, and prehistorically suggested pattern of gene flow and isolation. Am. J. Hum. Biol., 2010. © 2009 Wiley-Liss, Inc. [source]

Granitoids and Their Magnetic Susceptibility in South Korea

RESOURCE GEOLOGY, Issue 3 2001
Myung, Shik JIN
Abstract: Magnetic susceptibility (MS) measurements were carried out for 1,120 samples in the Middle Proterozoic to Early Tertiary granitoids so far recognized in South Korea, and the lateral and spatial variation of their magnetic susceptibility, i.e., content of magnetite, is studied. The Middle Proterozoic two mica granitoids related to cassiterite (Sn) deposits in northeastern part of the Sobaegsan Massif show very low MS (less than 0.3 A- 10 -3 SI unit), and the Permo-Triassic tonalitic to granodioritic and monzonitic rocks which are barren in mineralization, distributed in the middle part of South Korea also show low MS (less than 1 A- 10 -3 SI unit). On the contrary the Late Triassic to Jurassic granitoids (= Daebo granitoids) which were evolved from tonalite through granodiorite to granite, and are most widely distributed in South Korea, show a wide variation on MS. Particularly in the Andong, Igsan, Gimcheon and Geochang areas, the granitoids which are barren in mineralization, are characterized by high MS (more than 10 A- 10 -3 SI unit). The Chuncheon, Jecheon, Namyang and Geumsan plutons related to molybdenite (Mo) and/or wolframite or scheelite (W), and fluorite (F) mineralizations show a little high MS (more than 3 A- 10 -3 SI unit). However, more than 60% of the Daebo granitoids show low MS (less than 3 A- 10 -3 SI unit) and the rest show a little high MS (more than 3 A- 10 -3 SI unit). Heterogeneous distribution of magnetite content in the Daebo granitoids is considered to reflect heterogeneity of redox state of the source materials for these granitoids. The Cretaceous to Early Tertiary granitoids (= Bulgugsa granitoids) in the Gyeongsang Basin had been generally evolved in the order of tonalite, diorite, granodiorite, granite and alkali-feldspar granites, which are closely related to base metal ore deposits, and mostly show higher MS (more than 3 A- 10 -3 SI unit) than other granitoids mentioned above, although some exceptions are recognized in highly evolved alkali-feldspar granites (SiO2 > 76%). In contrast, as most of the highly oxidized or evolved Cretaceous granitoids distributed in areas other than the Gyeongsang Basin show lower MS than those of the Gyeongsang Basin, and appear to be magnetite free, ilmenite-series granites, but they might be hematite bearing magnetite-series granitoids. Highly oxidized nature of the Bulgugsa granitoids may be due to high Fe2O3/FeO ratio of the source materials and also high level intrusion style of the granitic magma activities. Most of the granitic rocks of the Middle Proterozoic, Permo-Triassic and more than 60% of the Late Triassic to Jurassic (Daebo granitoids) belong to ilmenite,series, however less than 40% of the Daebo granitoids and most Cretaceous ones are magnetite,series. Thus, the granitic magma intruded in Korean Peninsula became oxidized while the intrusive ages become younger. [source]

Carbonate seismic stratigraphy of the Gulf of Papua mixed depositional system: Neogene stratigraphic signature and eustatic control

BASIN RESEARCH, Issue 2 2008
Evgueni N. Tcherepanov
ABSTRACT The Eocene,Miocene carbonate deposition in the Gulf of Papua (GoP) corresponds to the carbonate evolution phase of this continental margin mixed depositional system. Global sea-level (eustatic) fluctuations appear to have been the most important factor influencing the mixed depositional system development during its carbonate phase. Development of the major carbonate system in the Gulf was initiated during the Eocene. Subsequent to an early Oligocene hiatus, the carbonate system expanded its surface area, vertically aggraded, then systematically backstepped, and finally partially drowned during the late Oligocene,early part of the early Miocene. During the late early Miocene,early middle Miocene, the carbonate system continued its vertical growth in most platform areas, where it was able to keep up with sea-level rise. At the early middle/late middle Miocene (Langhian/Serravallian) boundary, carbonate deposition shifted downward during a long-term sea-level regression, exposing most of the early middle Miocene platform tops. Following this downward shift, active carbonate production became restricted during the late middle Miocene to only the northeastern part of the study area, and carbonate accumulation was characterized by four systematically prograding units. At the very beginning of the late Miocene, the platform tops were re-flooded. The carbonate system was partially drowned, systematically backstepped, and locally aggraded during part of the late Miocene, the early Pliocene, and the Quaternary. The overall organization of the carbonate sequence geometries, observed in the GoP, display a clear pattern, often referred to as the Oligocene,Neogene stratigraphic signature. This pattern is identical to contemporaneous sedimentary patterns observed in pure carbonate systems such as in the Maldives and in the Bahamas, and also in some siliciclastic systems. Because this pattern is observed in several globally distributed locations, the recognition of the Oligocene,Neogene stratigraphic signature in the GoP demonstrates that the depositional evolution during the late Oligocene,Miocene and the early Pliocene must have been dominantly controlled by eustatic fluctuations. [source]

Brazilian Tapir Density in the Pantanal: A Comparison of Systematic Camera-Trapping and Line-Transect Surveys

BIOTROPICA, Issue 2 2008
Mogens Trolle
ABSTRACT The density of Brazilian tapirs (Tapirus terrestris) was studied in the northeastern part of the Pantanal wetlands of Brazil using two simultaneous and independent methods: (1) systematic camera trapping combined with capture,recapture analysis, with camera traps spaced 1 km apart and distributed over 54 km2; and (2) line-transect sampling using an array of 12 linear transects, from 3.8 to 7.2 km long, covering the principal open and forest habitat types across the entire 1063 km2 SESC Pantanal Reserve. The two methods yielded conservative density estimates of 0.58 ± 0.11 tapirs/km2 (camera trapping) and 0.55 (95% CI 0.30,1.01) tapirs/km2 (line transects). The study suggests that certain Pantanal habitats and sites can sustain relatively high population densities of tapirs when these animals are protected from hunting. Further testing of the camera-trapping methodology as applied to tapirs is required, particularly focusing on extending the survey period. As it represents a relatively rapid method for estimating population density, in comparison to line-transect surveys, and as it generates information simultaneously on multiple species that are conservation priorities, we recommend that camera-trapping surveys be applied more widely across a variety of Pantanal habitats and land-use categories in order to confirm the value of the vast 140,000 km2 wilderness region for this vulnerable species. RESUMO A densidade de Tapirus terrestris foi avaliada na região Nordeste do Pantanal do Mato Grosso usando dois métodos simultâneos e independentes: 1) método sistemático com armadilhas fotográficas, combinado com análises de captura e recaptura, com câmaras fotográficas espaçadas 1 km entre si e distribuídas sobre uma área de 54 km2, dispostas em 4 grades contínuas, com 14 câmaras ativas por 9 dias consecutivos em cada grade; e 2) 12 transecções lineares variando em dimensões de 3,8,7,2 km de extensão, cobrindo os principais habitats abertos e fechados, sobre uma região de 1063 km2 da Reserva Particular do Patrimônio Natural SESC Pantanal. Os dois métodos resultaram em estimativas de densidade de 0.58 ± 0.11 antas/km2 (câmaras fotográficas) e 0.55 (95% intervalo de confiança 0.30,1.01) antas/km2 (transecções lineares). Os resultados sugerem que certos hábitats e áreas do Pantanal podem sustentar densidades relativamente elevadas de antas, quando protegidas da caça. A metodologia utilizando câmaras fotográficas em estudos sobre antas deve ser testada incrementando períodos de avaliação. Como o método representa uma forma rápida de avaliação das densidades populacionais, em comparação com transecções lineares, e gera informações simultâneas sobre múltiplas espécies que podem ser prioritárias para conservação, recomendamos que avaliações com armadilhas fotográficas sejam amplamente aplicadas para a espécie na variedade de hábitats do Pantanal, visando afirmar o valor dessa vasta e selvagem região de 140.000 km2. [source]

Ordovician Carbonate Reservoir Bed Characteristics and Reservoir-Forming Conditions in the Lungudong Region of the Tarim Basin

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2010
WANG Weili
Abstract: Basic characteristics of Ordovician carbonate reservoir beds in the Lungudong region of northeastern part of the Tarim Basin are described in detail and the reservoir-forming conditions of oil and gas are preliminarily discussed in this paper by collecting and sorting out a large amount of data. The carbonate reservoir beds are mainly developed in open-platform and platform marginal facies; the reservoir beds have large changes in and low average values of physical property; the main type is fractured reservoir beds with the fracture-porous type second. The reservoir bed development is chiefly controlled by the distribution of sedimentary facies, tectonic activity and karstification. Whereas the accumulation and distribution of hydrocarbons in the region are controlled by an advantageous structural location, a good reservoir-caprock combination and a favorable transporting system, with the distribution characterized by zones horizontally and belts vertically, the oil and gas are mainly concentrated in areas with structural uplift, densely developed fractures, and surface karst, a vertical vadose zone, and a horizontal undercurrent belt of palaeokarst. [source]