Fine-grained Pleistocene deepwater turbidite channel system on the slope of Qiongdongnan Basin, northern South China Sea

Recently, as oil exploitation has become focused on deepwater slope areas, more multi-channel high resolution 2D and 3D seismic data were acquired in the deepwater part of the Qiongdongnan Basin, northern South China Sea. Based on 3D seismic data and coherence time slice, RMS and 3D visualization, a series of deepwater channels were recognized on the slope that probably developed in the late Quaternary period. These channels trend SW–NE to W–E and show bifurcations, levees, meander loops and avulsions. High Amplitude Reflections (HARs), typical for channel–levee complexes, are of only minor importance and were observed in one of the channel systems. Most of the detected channels are characterized by low-amplitude reflections, and so are different from the typical coarse-grained turbidite channels that had been discovered worldwide. The absence of well data in the study area made it difficult to determine the age and lithology of these channels. Using a neighboring drill hole and published data about such depositional systems worldwide, the lithology of these channels is likely to be dominated by mudstones with interbedded thin sandstones. These channels are formed by turbidity currents originated from the little scale mountain river of mid-Vietnam in SW direction and were probably accompanied by a relative sea level drop in the last glacial age. These channels discovered on the northern South China Sea slope are likely to be fine-grained, mud-dominant and low N:G deposits in a deepwater paleogeographic setting.     

Identification of fucans from four species of sea cucumber by high temperature 1H NMR

Acidic polysaccharide, which has various biological activities, is one of the most important components of sea cucumber. In the present study, crude polysaccharide was extracted from four species of sea cucumber from three different geographical zones, Pearsonothuria graeffei (Pg) from Indo-Pacific, Holothuria vagabunda (Hv) from Norwegian Coast, Stichopus tremulu (St) from Western Indian Ocean, and Isostichopus badionotu (Ib) from Western Atlantic. The polysaccharide extract was separated and purified with a cellulose DEAE anion-exchange column to obtain corresponding sea cucumber fucans (SC-Fucs). The chemical property of these SC-Fucs, including molecular weight, monosaccharide composition and sulfate content, was determined. Their structure was compared simply with fourier infrared spectrum analyzer and identified with high temperature ¹H nuclear magnetic resonance spectrum analyzer (NMR) and room temperature ¹³C NMR. The results indicated that Fuc-Pg obtained from the torrid zone mainly contained 2,4-O-disulfated and non-sulfated fucose residue, whereas Fuc-Ib from the temperate zone contained non-, 2-O- and 2,4-O-disulfated fucose residue; Fuc-St from the frigid zone and Fuc-Hv from the torrid zone contained mainly non-sulfated fucose residue. The proton of SC-Fucs was better resolved via high temperature ¹H NMR than via room temperature ¹H NMR. The fingerprint of sea cucumber in different sea regions was established based on the index of anomer hydrogen signal in SC-Fucs. Further work will help to understand whether there exists a close relationship between the geographical area of sea cucumber and the sulfation pattern of SC-Fucs.     

Tectonics in the Northwestern West Philippine Basin

The West Philippine basin (WPB) is a currently inactive marginal basin belonging to Philippine Sea plate, which has a complex formation history and various crust structures. Based on gravity, magnetic and seismic data, the tectonics in West Philippine basin is characterized by amagnma spreading stage and strike slip fractures. NNE trending Okinawa-Luzon fracture zone is a large fracture zone with apparent geomorphology and shows a right-handed movement. The results of joint gravity-magnetic-seismic inversion suggest that the Okinawa-Luzon fracture zone has intensive deformation and is a transform fault. Western existence of the NW trending fractures under Ryukyu Islands Arc is the main cause of the differences between south and north Okinawa Trough. The Urdaneta plateau is not a remained arc, but remnant of mantle plume although its lava chemistry is similar to oceanic island basalt (OIB).     

Seismic characteristics of a reef carbonate reservoir and implications for hydrocarbon exploration in deepwater of the Qiongdongnan Basin,northern South China Sea

Our analysis of approximately 40,000 km of multichannel 2-D seismic data, reef oil-field seismic data, and data from several boreholes led to the identification of two areas of reef carbonate reservoirs in deepwater areas (water depth ≥ 500 m) of the Qiongdongnan Basin (QDNB), northern South China Sea. High-resolution sequence stratigraphic analysis revealed that the transgressive and highstand system tracts of the mid-Miocene Meishan Formation in the Beijiao and Ledong–Lingshui Depressions developed reef carbonates. The seismic features of the reef carbonates in these two areas include chaotic bedding, intermittent internal reflections, chaotic or blank reflections, mounded reflections, and apparent amplitude anomalies, similar to the seismic characteristics of the LH11-1 reef reservoir in the Dongsha Uplift and Island Reef of the Salawati Basin, Indonesia, which house large oil fields. The impedance values of reefs in the Beijiao and Ledong–Lingshui Depressions are 8000–9000 g/cc × m/s. Impedance sections reveal that the impedance of the LH11-1 reef reservoir in the northern South China Sea is 8000–10000 g/cc × m/s, whereas that of pure limestone in BD23-1-1 is >10000 g/cc × m/s. The mid-Miocene paleogeography of the Beijiao Depression was dominated by offshore and neritic environments, with only part of the southern Beijiao uplift emergent at that time. The input of terrigenous sediments was relatively minor in this area, meaning that terrigenous source areas were insignificant in terms of the Beijiao Depression; reef carbonates were probably widely distributed throughout the depression, as with the Ledong–Lingshui Depression. The combined geological and geophysical data indicate that shelf margin atolls were well developed in the Beijiao Depression, as in the Ledong–Lingshui Depression where small-scale patch or pinnacle reefs developed. These reef carbonates are promising reservoirs, representing important targets for deepwater hydrocarbon exploration.     

Unit-pockmarks and their potential significance for predicting fluid flow

Unit-pockmarks were recognized as more-or-less insignificant features on the seafloor in the early 1980s. However, this investigation, at four different regions in Norwegian waters, suggests they are more significant for seep detection than previously believed. They occur as circular depressions in the seafloor (diameter < 5 m) either as singular features, as strings, or as clusters. One of our main conclusions is that they are widespread and represent the most recent and most active local seep locations. This is based on their areal density distribution, the finding of relatively high hydrocarbon concentrations inside sampled unit-pockmarks and at locations where they are abundant, and on theoretical considerations. When unit-pockmarks occur together with ‘normal-sized’ pockmarks, they often form to the side of the normal-pockmark centre. Our study also suggests that (1) the driving force behind seafloor hydraulic activity, i.e., the formation of unit-pockmarks, normal-pockmarks, and many other fluid flow features, is pockets of buried free gas, and (2) whereas unit-pockmarks likely manifest cyclic pore-water seepage, their larger related, normal-pockmarks, likely manifest periodic or intermittent gas bursts (eruptions), with extended intervening periods of slow, diffusive, and cyclic pore-water seepage. Our findings suggest that seep detection is most efficiently performed by mapping the seafloor with high-resolution bathymetry (at least 1 m × 1 m gridding), and acquiring geochemical samples where the density of unit-pockmarks is locally highest.     

南极普里兹湾1.5万年来气候演变的沉积记录

南极普里兹湾两沉积柱样代表了1.5万年来的沉积记录.其粒度特征、矿物成分、硅藻分布和地球化学等沉积特征表明,沉积记录对气候变化的反应十分敏感,尤其是发现14310aBP前后的Heinrich事件,据此将该区1.5万年来的古气候演化划分为8个阶段.     

An effective method for shear-wave velocity prediction in sandstones

Marine Geophysical Research - Shear-wave velocity is essential in various seismic exploration applications, including seismic modeling, amplitude variation with offset analysis, multicomponent...     

The assessment of submarine slope instability in Baiyun Sag using gray clustering method

It is a significant task to evaluate the seafloor stability for the exploitation of marine resources and the construction of marine structures. This paper analyzes the impact factors of submarine slope instability using geological and geophysical data of the Baiyun Sag in the Pearl River Mouth Basin and builds the evaluation index system of submarine slope instability. The weight of each index is calculated by analytic hierarchy process method to weaken subjective effect. Gray clustering method is applied to estimate the risk of submarine slope instability in Baiyun Sag qualitatively and quantitatively. The assessment standard is divided into five grades, and the whitening function of each gray cluster is determined by the assessment scheme. The gray evaluation weight vector of each indicator is calculated by the table-dispatching method. The gray assessment value is estimated by making the gray assessment weight vector single value, and the gray grade is determined according to the maximum principle. The evaluation results show quantitatively that the risk grade of submarine slope instability in the Baiyun Sag is medium, and the gray clustering method is reasonable and feasible.     

U37K与海水表层温度

Ｕ₃₇^Ｋ是指少数藻类生物所特有的一种分子化合物（长链不饱和酮）的不饱和指数。在现代海洋沉积物中，Ｕ₃₇^Ｋ与浮游有孔虫的¹⁸Ｏ值具有很好的相关性。在实验室培养的藻类生物体中、海洋悬浮颗粒物及海洋沉积柱样的表层样中均检测出长链不饱和酮，其Ｕ₃₇^Ｋ与生物生长环境的海水表层温度具有很好的线性关系。因此，在古气候研究中，Ｕ₃₇^Ｋ可作为一种有效的古温度指标，且在古气候研究中已得到应用。主要介绍了Ｕ₃₇^Ｋ作为海水表层温度指标的原理、定量公式及其研究现状和存在的问题。     

准噶尔盆地成藏动力学系统划分

本文在对成藏动力学系统的概念重新描述的基础上,选择经历了多旋回构造与沉积演化的准噶尔盆地进行成藏动力学系统划分。准噶尔盆地发育6套烃源岩、多套储集层、2套区域性盖层和数个局部盖层,它们构成6套生、储、盖组合。同时,钻井揭示盆地超压发育,结合测井与地震资料,将地层压力在垂向上划分为2个常压系统和3个超压系统。该盆地垂向通道众多,构造活动期流体上下连通性好,整体可划为一个复杂的成藏动力学系统。然而,断裂活动具幕式特征,相对盆地演化史,大部分时期处于静止封闭状态。因此,进一步将准噶尔盆地划分为6个成藏动力学子系统:①二叠系自源超压半封闭型成藏动力学子系统;②三叠系他源超压半封闭型成藏动力学子系统;③侏罗系混源超压半封闭型成藏动力学子系统;④白垩系—侏罗系混源常压开放型成藏动力学子系统;⑤古近系—白垩系混源超压封闭型成藏动力学子系统;⑥新近系他源常压开放型成藏动力学子系统。不同的子系统,成藏条件、成藏动力和成藏规律不同。