Journal of Southeast Asian earth sciences最新文献

During Devonian times South China lay to the north of the Palaeo-Tethyan ocean, the boundary being a passive continental margin. A shallow sea covered the southern parts of the continent while northern areas, forming the Huanan Landmass, were emergent. At the beginning of the Devonian most of South China was above sea level. Subsequent transgression from the south gave rise to an irregular coastline with the development of many fault-controlled gulfs. Further transgression led to the development of an epicontinental sea with reefs forming along the margins of the submerged gulfs and black shales deposited within them. By Emsian time a widespread carbonate platform was established, while anoxic deposition continued in the troughs. The marine transgression peaked in the Frasnian Stage. During Famennian time widespread regression occurred and much of South China became once more emergent. Peneplanation of the Huanan Landmass led to the partial infilling of many of the older fault-bounded depressions. Throughout the Devonian the local distribution of sediments was strongly controlled by NE-SW trending transtensional faults that bounded NW-SE trending normal faults. These structures continued to influence sedimentation in the Late Palaeozoic, the Mesozoic and possibly the Tertiary in the offshore Beibu Gulf Basin.

This paper describes and figures Mesozoic Radiolaria from cherts in Pulau Ungar, Tanimbar Islands, eastern Indonesia. Two assemblages of Radiolaria are recognised. The lower assemblage is indicative of upper Tithonian (uppermost Jurassic) to Berriasian (lowermost Cretaceous) and the upper assemblage is of upper Valanginian to Barremian age. These are the first precise ages obtained from the Ungar Formation, a unit including sandstones with apparently good petroleum reservoir characteristics.

A reconnaissance ground magnetic survey was conducted in the Baguio Mineral District in northern Luzon to investigate the geophysical signatures of the different lithologic units and areas of mineralization. The magnetic-intensity contours match the varying rock types. Magnetic lows were found to correspond to the sedimentary rocks. Magnetic highs coincide with presence of intrusive bodies and the skarn/porphyry-copper deposits. This is to be expected since igneous rocks are more magnetic than sedimentary rocks. Futhermore, the skarn/porphyry copper deposits consist of an ore assemblage of which magnetite is a component. An anomalouos zone, coincident with the sedimentary and igneous rock boundary, was defined from the magnetic survey results. This sedimentary and igneous rock boundary, inferred to be a zone of high permeability, is the probable host to mineable mineral deposits. The geophysically defined anomalous area, characterized by magnetic lows, is consistent with a previously defined prospective zone of mineralization.

Soft sediment deformation features are common in the Tertiary sedimentary succession of the Ombilin Basin, West Sumatra. A spectacularly large scale example of one of these features from fluvial sandstones and shales of the Sawahlunto Formation of the Ombilin Basin is illustrated and described. The structure is interpreted to be a sandstone load ball formed by syn-sedimentary liquefaction, the size of which merits description, since such large structures are rare in fluvial sequences and are more typically observed on a much smaller centimetre or millimetre scale or within marine, deep water sequences. The cause of the liquefaction is suggested to be from syn-sedimentary tectonic activity within the basin and/or along its margins, possibly related to movements on a precursor of the presently active Sumatran Fault System. Implications for palaeo-seismicity along the Sumatran Fault System and geology of the Ombilin Basin are discussed.

Late Cretaceous granitic rocks constitute an essential part of the pre-Tertiary Tananao metamorphic basement complex of Taiwan. They are dominantly of granodiorite to quartz monzonite composition. Most granitic rocks are peraluminous (A/CNK > 1.0 and normative corundum > 1%) and display moderately fractionated LREE and relatively unfractionated HREE patterns with negative Eu anomalies. On a primitive mantle-normalized trace-element diagram, they show a significant Nb depletion which is typical of the calc-alkaline magmatism from the subduction-zone environment. They fall within the volcanic arc field on the discrimination diagram of Pearce, Harris and Tindle (1984). The lack of systematic inter-element relationships suggests that the role of fractional crystallization is not significant and that these granitic rocks were derived from heterogeneous protoliths. Geochemical data suggest Taiwan granitic rocks are contaminated I-type and I-type granites related to the subduction of the Paleo-Pacific plate beneath the eastern margin of the Eurasia plate during late Mesozoic time.

The unusual rarity of Fusulinella species is one of the most interesting characteristics among the known Moscovian foraminiferal faunas in Thailand. Earlier an occurrence of Fusulinella bocki von Möller was documented in Northeast Thailand but with neither description nor illustration. For the first time, we have recently discovered a small foraminiferal fauna characterized by two Fusulinella species (F. bocki von Möller and F. praebocki Rauser-Chernoussova) from a limestone collected at Huai Luang, about 5 km east of Wang Saphung, Changwat Loei, Northeast Thailand, where the Fusulina pulchella fauna was reported previously. Geological evidence suggests that our foraminiferal fauna most certainly came from the strata referable to the Fusulina pulchella Zone although F. pulchella Gryzlova is absent from our fauna. The present discovery of a Fusulinella-bearing foraminiferal fauna from Huai Luang, indicative of a Late Moscovian age (most probably to the Myachkovsky Horizon in the Russian standard scheme), provides important data to clarify the faunal composition of the Fusulina pulchella Zone and to compare the Late Moscovian foraminiferal faunal affinity in the Loei-Wang Saphung area with those of the type and reference sections. In this paper, six species of fusulinaceans are described, and coexisting smaller foraminifers are listed and illustrated.

A gold-bearing hypogene mineralization from the Lucky Mill Mine in the Bau mining district, Sarawak, containing sarabauite and calcite as major constituents was investigated using a combination of optical microscopy, XRD and SEM + EDX. Sarabauite is the only Sb mineral of hypogene origin that is amenable to fluid inclusion studies in thin section under normal light. The ore mineralization may be subdivided into two different stages. During stage I at temperatures somewhat higher than 400°C, wollastonite, diopside and epidote evolved in the Bau Limestone that forms the wall rocks of the AuSb mineralization under study. In stage II, sarabauite developed together with gold at temperatures above 377°C, followed by calcite, stibnite and senarmontite, which formed in the T interval 377-194°C. The AuSb mineralization is of high temperature origin and characterized by Fe and S limitations. Both the temperature of formation and the chemical composition of the mineralizing fluids were responsible for the peculiar Sb-sulphide-oxides.

Radiolarians are abundant in mid-Paleozoic tuffs of the Kurosegawa terrane of southwest Japan. Well preserved Silurian radiolarian faunas recovered from several localities are described herein and include four new species: Ceratoikiscum kurosegum n. sp., Fusalfanus? konomoriensis n. sp., Futobari? jingamoriensis n. sp., and Futobari? tosaensis n. sp. The absence, within the same strata, of fossils belonging to other taxonomic groups has presented difficulties in determining the precise ages of the Kurosegawa radiolarian faunas. U/Pb SHRIMP ages of pyroclastic zircons from tuff units within the succession indicate Wenlockian [427.2 ± 7.6] and Pridolian [408.9 ± 7.6] ages and remove ambiguity regarding the Silurian age of tuffaceous rocks in the Kurosegawa sequence.

The greater Bandung area (West-Java, Indonesia) is a large intramontane basin surrounded by volcanic highlands. Geomorphological and sedimentological studies reveal that the morphology of the central basin and the Sunda-Tangkuban Perahu volcanic complex developed during the Middle-Late Quaternary, in particular since 125 kyr B.P. Tectonic subsidence, paroxysmal eruptions, volcanism-induced faulting/rifting, drainage system adaptations and intramontane lacustrine sedimentation (partly geomorphology-controlled) constitute the dominant landform-determining processes. A reconstruction of the regional morphological development is based on interpretation of morphological features and morphodynamic processes in the volcanic upland, in combination with analysis of the sedimentary record in the basin. A chronological framework is based on datings obtained from surficial sediments and deep drill cores.

Initially, long term patterns in volcanicity and tectonic effects determine regional sedimentation and relief development in the greater Bandung area. Fluvial sedimentation and weathering prevailed in the basin, while the southern and northern volcanic ranges gradually formed. Basin subsidence, with contemporaneous volcanism around 125 kyr B.P., resulted in the formation of an enclosed intramontane basin, and stimulated lacustrine sedimentation. From this time on, concentration of volcanicity in the northern Sunda-Tangkuban Perahu complex and the resulting morphostructural developments caused rapid (catastrophic) and localized morphological changes. Cataclysmic eruptions (around 105 kyr B.P. and 50-35 kyr B.P.) caused voluminous sediment inflow in the northwestern basin. These events mark the significance of the Sunda-Tangkuban Perahu volcanic centre during the Late Quaternary; the Sunda volcano collapsed into a caldera in which later the Tangkuban Perahu volcano developed. Moreover, these eruptions controlled regional sedimentation and determined landform development in the greater basin area. In the vicinity of the eruption centre, volcano-tectonic faulting formed the conspicuous E-W Lembang fault that controlled distribution of volcaniclastic sediments and the initiation of a new drainage system in the Lembang area. In the low-lying Bandung plain persistent (fluvio)lacustrine and volcaniclastic sedimentation, followed by basin subsidence and minor fluvial erosion characterised the younger phases of landform development.

This paper suggests for the first time that the Meso-Cenozoic process of continental convergence, dispersal and oceanic crustal renewal kinematically belongs to a spherical two-dimensional spiral movement and is a spherical-surface reflection of the three-dimensional spiral movement of the mantle circulation. The three-dimensional spiral movement of the mantle is genetically the results of coupling of the mantle meridional circulation with the rotation of the mantle currents around the Earth's axis, and is similar in kinematic nature to that of the Earth's atmospheric and oceanic circulations, both being genetically related with the Earth's rotation. The only difference between them is that the thermal energy of the atmospheric and oceanic thermal convections is derived from the solar radiation, while that of the mantle thermal convection comes from the Earth's interior. The present paper gives evidence for the close link between the thermodynamic process of mass movement of the Earth's spheres and the movement of the Earth as a celestial body, thus pinpointing a direction for studying the science of the Earth's system.