A record of Miocene carbon excursions in the South China Sea

High-resolution δ¹³C records are presented for the Miocene benthic foraminifersCibicidoides wuellerstorfi andC. kullenbergi (24-5 Ma) and the planktonic foraminiferGlobigerinoides sacculifer (18-5 Ma) from ODP Site 1148A (18° 50.17’N, 116° 33.93’E, water depth 3308.3 m), northern South China Sea. The general pattern of parallel benthic and planktonic δ¹³C shows a decrease trend of δ¹³C values from the early-middle Miocene to the middle-late Miocene. Two distinct δ¹³C positive excursions at 23.1-22.2 and 17.3-13.6 Ma, and two negative excursions at 10.2-9.4 and 6.9-6.2 Ma have been recognized. All these events are cosmopolitan, providing the good data for the stratigraphic correlation of the South China Sea with the global oceans as well as for studying the changes of the global carbon reservoir and its corresponding climate.     

Neogene oxygen isotopic stratigraphy, ODP Site 1148, northern South China Sea

A detailed stable isotopic study based on benthic foraminifera from 1165 samples of ODP Site 1148 (18° 50.17.3’N, 116° 33.93’E, water depth 3308.3 m), northern South China Sea, provides an excellent oxygen isotopic record with an average resolution of 30 ka. It contains the most continuous δ¹⁸O data with highest resolution for the whole Neogene sequence in the world. The δ¹⁸O curve shows a step-like increasing upwards and records 5 increases, 3 decreases and 2 stable stages during the Neogene, reflecting the general trend of global cooling. Among these events the δ¹⁸O decrease at 17.2–14.5 Ma, and two δ¹⁸O increases at 14.5-13.6 and 3.0-2.4 Ma are most marked and globally comparable. The intervals at 13.6-10.2 and 6.0-3.0 Ma with the lowest-amplitude and least fluctuation in δ¹⁸O represent the most stable bottom water periods for the South China Sea.     

Relocation and seismogenic structure of the 1998 Zhangbei-Shangyi earthquake sequence

Introduction The January 10, 1998 Zhangbei-Shangyi, Hebei Province, earthquake has been the third large event of magnitude 6.0 and greater since the 1976 great Tangshan earthquake of magnitude 7.8 in the northern China (33皛42癗, 110皛124癊). Before this event, there were only two events of magnitude 6.0 and greater occurred in or around the Tangshan area since 1976: the M=6.9 Ninghe, Tianjin, earthquake of November 15, 1976 and the M=6.2 Hangu, Tianjin, earthquake of May 12, 1977. The …     

Records of natural fire and climate history during the last three glacial-interglacial cycles around the South China Sea Charcoal record from the ODP 1144

The history of natural fire and its relationship to climate during the last three glacial-interglacial cycles in the Southern coast areas of China and the northern continental shelf of the South China Sea (SCS) are discussed based on the statistic study of charcoal particles and associated pollen data from ODP 1144 Site (20° 3′N, 117° 25’E, 2037 m in water depth). According to the results of the charcoal and pollen study, the sediments from the upper 225 m are divided into 8 zones (C1–C8), which might be correlated with the Marine Isotope Stage 1–8 (MIS1-8) respectively. Our study indicates that during the last glacial period (MIS2, 4), the influx of charcoal particle was much higher than that from the interglacial period, suggesting strong occurrence of natural fire and dry climate. During MIS 6 and MIS 8 (C6, C8), although the influx of fine charcoal particles was quite high, the influx of the coarse and medium charcoal particle were much low, which might be due to the smaller source area of fire probably resulting from the limited exposure of the continental shelf before MIS5. During the interglacial period (MIS1, 5, 7), the influxes of charcoal particles were much lower, implying dropping of intensity of the natural fire and then a humid climate. Another reason is that the continental shelf was submerged into the sea during the interglacial periods, and the source areas of fire were reduced then. Although the influx of the fine charcoal particles was much lower during MIS3, the influx of the coarse and medium charcoal particles were almost equal to those of MIS4 (C4), which suggests that the intensity of the natural fire remained quite high and the climate was considerably dry during that period.     

The paleoclimate change of Qaidam Basin during the last 2.85 Ma recorded by Gamma-ray logging

The geographical location of Qaidam Basin corresponds to N36°05’-38°10’ and E90°10’-98°05’. The thickness of the Quaternary deposits in the basin reaches 2000-3000 m. This paper deals mainly with the aspect of paleoclimate change of the basin. The approach used for the study consisted of (1) establishing the paleoclimate curve of the basin according to the climate indices, including the spore-pollen statistics, carbonate content and δ¹⁸O, obtained from the samples of the 760 m continuously-cored exploration holes sited in the basin, (2) comparing the paleoclimate curve with the natural gamma-logs of the same exploration holes, and (3) determining the paleoclimatic changes in the last 2.85 Ma on the basis of detailed geochronological calculations. These results are extremely important for comparison with the δ¹⁸O-based climate curve derived from the ODP659 in the Atlantic Ocean and with the cycles of paleosol in the Chinese loess.     

Potential volume for CO2 deep ocean sequestration: an assessment of the area located on western Pacific Ocean

Captured CO₂ could be deliberately injected into the ocean at great depth, where most of it would remain isolated from the atmosphere for centuries. CO₂ can be transported via pipeline or ship for release in the ocean or on the sea floor. In Taiwan, CO₂ release is preliminarily projected from 2010 to 2030 in an average amount of 6.957 Gt within this duration. If deep sea sequestration for CO₂ can be the possible option in Taiwan, it seems to exists possible potential area delimited between 122.0°E to 122.5°E and 21.8°N to 22.3°N for CO₂ sequestration on account of its isolated and flat topography. Apparently, the area to the southeast of Taiwan is found to reach a depth deeper than −3,000 m and can be taken as a testing area for pilot studies. This study searches the area using the contours from the depth of −4,554 to −5,500 m with 1-m interval; the area, topographic volume, maximum mean height (volume/area), and ocean volume are reported. If the emission rate is kept constantly, for 20-year storage it needs 3 m of thickness reaching the sea ridge at the depth −4,554 m using top-down style; for 100 years of storage it needs 12 m. On the other hand, if it accounts for the bottom the sea floor is taken as the reference and the accumulated CO₂ is stored from the depth at −4,900 m using bottom-up style, it requires about 37 m for the 20-year storage and 61 m for one decade.     

Long-term variations in the second sectorial Stokes harmonics on the basis of TOPEX/POSEIDON altimetry between 1993 and 2000

The long-term variations in the second degree sectorial Stokes parameters of the geopotential have been determined from TOPEX-POSEIDON (T/P) satellite altimeter data, covering the period of January 1, 1993 to January 3, 2001 (T/P cycles 11-305). It is the first attempt to determine the variations in the second sectorial harmonics in the Earth’s inertia tensor due to the ocean dynamics. The variations amount to about 1 × 10⁻¹⁰ (J ₂ ⁽²⁾ ≈ 1.6 × 10⁻⁶ and S ₂ ⁽²⁾ ≈ −0.9 × 10⁻⁶). The variations are about 5% of the tidal effect. This corresponds to variations in the directions of the equatorial axes of the Earth’s inertia ellipsoid of up to 10 arc-seconds. Consequently, the annual and semi-annual variations of the Earth’s equatorial flattening is about 10⁻⁹; i.e. it corresponds to a change of 8 units of its denominator of 91 030. (The equatorial flattening ≈ 1/91 030). Since the coverage of the Earth’s ocean surface is not worldwide, and the inclination of T/P is i = 66°, it is only 58.2% (min. depth of the ocean 2 000 m) of the Earth’s surface which is processed, the torque, resulting from the seasonal transfer of masses within a sea surface layer, is not zero. It amounts up to 10¹⁶ kg m²s⁻², which is comparable to the total indirect tidal torque due to the Moon and the Sun, ∼ 3.9 × 10¹⁶ kg m²s⁻². However, the above estimate strongly depends on the adopted thickness of the sea surface layer, ΔR = 50 m. For a larger thickness of ΔR = 100 m, the seasonal torque amounts to about ∼ 2.3 × 10¹⁶ kg m²s⁻².     

Evidence for natural fire and climate history since 37 ka BP in the northern part of the South China Sea

The history of natural fire since 37 kaBP and its relationship to climate for the northern part of the South China Sea are revealed from the statistic study of charcoal particles and associated pollen data from deep sea core 17940 (20° 07’N, 117° 23’E, 1 727 m in water depth). Our study indicates that, during the last glaciation, the concentration of charcoal and the ratio of con centration between charcoal and terrestrial pollen are much higher than that of the Holocene. This can be explained as the relatively high strength and frequency of natural fire during glaciation which is probably due to the drier climate; during the Last Glacial Maximum (LGM), the substantial rising of the concentration of large and medium charcoal particles probably suggests the local source area of the natural fires, i.e. the exposed continental shelf; moreover, the correlation between charcoal concentration with different size and pollen percentage may elucidate different transport dynamics. During the glacial time, almost all the peak concentrations of small particles correspond with the peak pollen percentage ofArtemisia, an indicator of comparatively dry climate, while for large particles, their concentrations always lag behind small particles and thus change with pollen percentage of montane conifers implying relatively cold and humid climate. So, it is possible to assume that small particles reflect regional emissions under drier climate and were brought over by strengthened winter monsoon. When the climate became relatively humid, the increasing precipitation carried the large particles accumulated on continental shelf before under arid condition to the studied area.     

Relocation of the 1998 Zhangbei-Shangyi earthquake sequence using the double difference earthquake location algorithm

Introduction On January 10, 1998, at 11h50min Beijing Time (03h50min UTC), an earthquake of ML=6.2 occurred in the border region between the Zhangbei County and Shangyi County of Hebei Province. In total 87 events with ML3.0 were recorded by Beijing Telemetry Seismic Network (BTSN) before March of 1999. Before relocation the preliminary hypocenters determined by BTSN showed an epicentral distribution of 25 km long and 25 km wide without any predominate orientation. The epicentral a…     

Inversion of gravity and topography data for the crust thickness of China and its adjacent region

Introduction Since the middle of the century, gravitational isostasy has been a fundamental hypothesis for inverting the gravity data to find the crust thickness. Geophysicists have done a lot of researches on using gravity data to investigate the depth of Moho discontinuity. Since 1980, the International Lithosphere Program emphasized the importance of investigating the Moho depth variation. Thereafter a lot of results have been published in the world (Braitenberg et al, 2000; Kaban et al,…     

Deep explosive focal depths during maar forming magmatic-hydrothermal eruption: Baccano Crater,Central Italy

We describe the eruptive activity of the Pleistocene composite Baccano maar crater in the Sabatini Volcanic Complex (Central Italy) combining stratigraphy, grain size/componentry and rare earth element and Yttrium (REY) composition of its eruptive products with the stratigraphy and geothermal data derived from deep wells drilled on the Baccano structural high. The main lithological characteristics of the basal Baccano maar pyroclastic deposit, composed of more than 60% wt of non-thermometamorphosed lithic clasts from the sedimentary basement, show that the first eruption was magmatic-hydrothermal in nature. The lithology of the sedimentary lithic clasts indicates that the fragmentation level was at a depth of −1,000 to −1,200 m, with fragment depth verified by deep well stratigraphy. The 15% wt juvenile non-vesicular glass components suggest that magma played a minor role in powering the eruption. Assuming that the high-salinity hot hydrothermal fluids (365<T<410°C and P∼25 MPa), hosted in the highly permeable and confined aquifer below the Baccano maar are representative of those at the time of the eruption, we propose that hydrofracturing would have triggered the eruption caused by overpressure at the top of the geothermal aquifer. REY analysis performed on pyroclastic fragments and basement rocks suggest that partial dissolution of the deeper limestones (>−1,400 m) by the aggressive hydrothermal fluids enriched in acid components (HF, HCl, and H2SO4) may have contributed to increased CO₂ partial pressure that helped to drive the hydrofracturing. This could have caused rapid vapour separation and pressure drop, allowing the almost simultaneous breaking of the aquifer cover and brecciation of the calcareous units down to −1,000 to −1,200 m depth. The relative abundance of calcareous lithics in the basal part of the first Baccano eruptive unit, representing about the upper 200 m of stratigraphy below the top of the Baccano structural high, reveals the descent of the piezometric surface during the eruption. Combining deep well information and maar product stratigraphy, using also REY data from maar pyroclastic fragments and the basement rocks we draw an interpretative model for the Baccano maar-forming eruption, concluding that a) magmatic-hydrothermal eruptions may originate deeper than previously thought, and b) hydrothermal fluids circulating in limestone aquifers may play an important role in triggering such eruptions.     

Geometric form of Haiyuan fault zone in the crustal interior and dynamics implications

The deep seismic reflection data on profile HY2 are reprocessed by the method of simultaneous inversion of velocity distribution and interface position. By the travel-time inversion with the data of the diving wave Pg and fault plane reflection wave, we determine the geometric form and velocity of Haiyuan fault zone interior and surrounding rock down to 10 km depth. The measured data show that the amplitudes have strong attenuation in the range of stake number 37–39 km, suggesting the fault zone has considerable width in the crustal interior. The results of this paper indicate that to the north of the fault zone the crystalline basement interface upheaves gradually from southwest to northeast and becomes shallow gradually towards northeast, and that to the south of the fault zone, within the basin between Xihua and Nanhua mountains, the folded basement becomes shallow gradually towards southwest. The obliquity of the fault zone is about 70° above the 3 km depth, about 60° in the range of the 3–10 km depths. From the results of this paper and other various citations, we believe that Haiyuan fault zone is in steep state from the Earth’s surface to the depth of 10 km. Foundation item: Joint Seismological Science Foundation of China (201001) and State Key Basic Research Development and Programming Project (95-13-02-02). Contribution No. RCEG200308, Exploration Geophysical Center, China Earthquake Administration.     

Tectonic model of Egypt based on magnetic analysis

The main target of this work was to study the dynamics of the Earth’s crust for Egypt based on the magnetic survey. High-resolution land magnetic data were analyzed, combined with the results of GPS and seismic stress analyses. The constructed tectonic map shows that the N35°-N45°W trend of the structure (related to the Red Sea and Gulf of Suez tectonics) predominates along the Gulf of Suez, Red Sea, covering wide parts of the study area. The N45°-N65°E tectonic trend (related to the Syrian Arc tectonics), prevailing in the northern part of Egypt, is of the second rank. The Aqaba (N15°-25°E) and E-W trends prevail in the northern part and along the transition zone of stable/unstable shelves. The depth to the basement rocks ranges from the surface along the Red Sea and southern parts of Egypt to more than 4 km below sea level at the northern part of the study area.     

Rupture process of the M L=4.1 earthquake in Huailai Basin on July 20, 1995

On July 20, 1995, an earthquake of M _L=4.1 occurred in Huailai basin, northwest of Beijing, with epicenter coordinates 40.326°N, 115.448°E and focal depth 5.5 km. Following the main shock, seismicity sharply increased in the basin. This earthquake sequence was recorded by Sino-European Cooperative Huailai Digital Seismograph Network (HDSN) and the hypocentres were precisely located. About 2 hours after the occurrence of the main shock, a smaller event of M _L=2.0 took place at 40.323°N, 115.447°E with a focal depth of 5.0 km, which is very close to the main shock. Using the M _L=2.0 earthquake as an empirical Green’s function, a regularization method was applied to retrieve the far-field source-time function (STF) of the main shock. Considering the records of HDSN are the type of velocity, to depress high frequency noise, we removed instrument response from the records of the two events, then integrated them to get displacement seismogram before applying the regularization method. From the 5 field stations, P phases in vertical direction which mostly are about 0.5 s in length were used. The STFs obtained from each seismic phases are in good agreement, showing that the M _L=4.1 earthquake consisted of two events. STFs from each station demonstrate an obvious “seismic Doppler effect”. Assuming the nodal plane striking 37° and dipping 40°, determined by using P wave first motion data and aftershock distribution, is the fault plane, through a trial and error method, the following results were drawn: Both of the events lasted about 0.1 s, the rupture length of the first one is 0.5 km, longer than the second one which is 0.3 km, and the rupture velocity of the first event is 5.0 km/s, larger than that of the second one which is about 3.0 km/s; the second event took place 0.06 s later than the first one; on the fault plane, the first event ruptured in the direction γ=140° measured clockwise from the strike of the fault, while the second event ruptured at γ=80°, the initial point of the second one locates at γ=−100° and 0.52 km from the beginning point of the first one. Using far-field ground displacement spectrum measurement method, the following source parameters about the M _L=4.1 earthquake were also reached: the scalar earthquake moment is 3.3×10¹³ N·m, stress drop 4.6 MPa, rupture radius 0.16 km. Contribution No. 99FE2022, Institute of Geophysics, China Seismological Bureau. This study is supported by the Chinese Joint Seismological Science Foundation (95-07-411).     

Thermal expansion-contraction and slope instability of a fumarole field inferred from geodetic measurements at Vulcano

Between 1987 and 1993, fumarole temperatures at the Fossa crater of Vulcano (Italy) were characterized by the highest values since the 1920’s, increasing from about 300°C in 1987 to 690°C in May 1993, before decreasing to 400°C by 1996–1997. During 1990, Vulcano’s Electronic Distance Measurement (EDM) network was expanded to provide more detailed coverage of the northern sector of the Fossa crater and, in particular, to monitor the movement of the northern flank the Fossa cone. Measurements, carried out between 1990 and 1994, showed shortening by about 6 to 7 cm along baselines measured to a small section of the northern rim. Over the following four years these baselines showed a slow extension by about 3 cm, to gradually recover part of the previous deformation. We believe that the shortening and lengthening of the EDM baselines was respectively due to the increasing and decreasing temperature of the rock body lying close to the deforming area. This caused thermal expansion, followed by contraction. The positive movement of the rim was not completely matched by a negative recovery, suggesting that a non-recoverable sliding movement was also responsible for some of the shortening of the baselines. We verified our hypothesis by calculating the expected dilatation of a rock body, as a function of the volume of rock heated and its thermal expansion coefficient, and compared the expected deformation to that observed. The geodetic investigation showed that the unstable portion affects a small length of the rim (about 100 m long) and involves a volume of about 0.8 × 10⁶ m³. However, this zone lies directly above a particularly unstable portion of the flank, as well as the main village and port on the island.     

MELIMEX,an experimental heavy metal pollution study: Vertical mixing in a large limno-corral

In a limno-corral (diameter 12 m, depth to sediments 10 m), located in Baldeggersee (Switzerland), vertical mixing has been measured during more than one year and compared to the conditions in the open lake (maximum depth 65 m, surface area 5.3 km²). The temperature method by McEwen and Hutchinson yields K_z values between 5×10⁻² cm²s⁻¹ at the upper boundary of the thermocline and 2×10⁻³ cm²s⁻¹ at the bottom, a value near the molecular diffusion of heat at 4°C (1.36×10⁻³ cm²s⁻¹). K_z calculated from profiles of excess radon-222 generally agree with those from the temperature data. Compared to the open lake, the corral has a more shallow epilimnion. However, during calm meteorological conditions, vertical mixing in the upper 10 m is similar outside and inside the corral. Supported by the Swiss National Science Foundation within the framework for its National Research Program on ‘Lake Currents.’     

Seismic microzonation of Dehradun City using geophysical and geotechnical characteristics in the upper 30 m of soil column

The understanding of geotechnical characteristics of near-surface material is of fundamental interest in seismic microzonation. Shear wave velocity (Vs), one of the most important soil properties for soil response modeling, has been evaluated through seismic profiling using the multichannel analysis of surface waves in the city of Dehradun situated along the foothills of northwest Himalaya. Fifty sites in the city have been investigated with survey lines between 72 and 96 m in length. Multiple 1-D and interpolated 2-D profiles have been generated up to a depth of 30–40 m. The Vs were used in the SHAKE2000 software in combination with seismic input motion of the recent Chamoli earthquake to obtain site response and amplification spectra. The estimated Vs are higher in the northern part of the study area (i.e., 200–700 m/s from the surface to a depth of about 30 m) as compared to the south and southwestern parts of the city (i.e., 180–400 m/s for the same depth range). The response spectra suggest that spectral acceleration values for two-story structures are three to eight times higher than peak ground acceleration at bedrock. The analysis also suggests peak amplification at 3–4, 2–2.5, and 1–1.5 Hz in the northern, central, and south-southwestern parts of the city, respectively. The spatial distributions of Vs and spectral accelerations provide valuable information for the seismic microzonation in different parts of the urban area of Dehradun.     

A simple smoothed velocity model of the uppermost Earth’s crust derived from joint inversion of Pg and Sg waves

The paper presents some results of seismic experiments carried out on the territory of northern Moravia and Silesia, roughly delimited by the coordinates 16°E–19°E and 49°N–51°N. The experiments were aimed at compiling a velocity model of the uppermost Earth’s crust using the database of arrival times of Pg and Sg waves recorded at a fairly large number of seismic stations, which enabled us to produce a simple 1D-layered velocity model of the region. The velocity model was computed using the traditional tomographic iterative process composed of consecutive solutions of linear equations. Based on the analysis of velocity distribution, it was found that the velocities of Pg and Sg waves increase from about 5.9 and 3.3 km/s at the surface, to about 6.1 and 3.5 km/s at a depth of 11 km, respectively.     

North American microtektites from the Caribbean Sea and their fission track age

Over 6000 microscopic glass spherules between 125 μm and 1 mm in diameter were found in a sediment core (RC9-58) from the Caribbean Sea. These glassy objects are mostly confined to a zone ～ 40 cm thick at a depth of ～ 250 cm. We believe that the microscopic glass objects are microtektites belonging to the North American strewnfield, based on their geographical location, appearance, physical properties, stratigraphic age (middle Upper Eocene), fission track age (～34.6 my) and major element compositions. The occurrence of North American microtektites in the Caribbean Sea indicates that the North American strewnfield is two to three times larger than previously indicated. An estimate on the abundance of microtektites in core RC9-58 indicates that the North American strewnfield may contain greater than 10¹⁷ g of tektite material.