Holocene peat and carbon accumulation rates in the southern taiga of western Siberia

Although recent studies have recognized peatlands as a sink for atmospheric CO₂, little is known about the role of Siberian peatlands in the global carbon cycle. We have estimated the Holocene peat and carbon accumulation rate in the peatlands of the southern taiga and subtaiga zones of western Siberia. We explain the accumulation rates by calculating the average peat accumulation rate and the long-term apparent rate of carbon accumulation (LORCA) and by using the model of Clymo (1984, Philosophical Transactions of the Royal Society of London Series B 303, 605-654). At three key areas in the southern taiga and subtaiga zones we studied eight sites, at which the dry bulk density, ash content, and carbon content were measured every 10 cm. Age was established by radiocarbon dating. The average peat accumulation rate at the eight sites varied from 0.35 ± 0.03 to 1.13 ± 0.02 mm yr⁻¹ and the LORCA values of bogs and fens varied from 19.0 ± 1.1 to 69.0 ± 4.4 g C m⁻² yr⁻¹. The accumulation rates had different trends especially during the early Holocene, caused by variations in vegetation succession resulting in differences in peat and carbon accumulation rates. The indirect effects of climate change through local hydrology appeared to be more important than direct influences of changes in precipitation and temperature. River valley fens were more drained during wetter periods as a result of deeper river incision, while bogs became wetter. From our dry bulk density results and our age-depth profiles we conclude that compaction is negligible and decay was not a relevant factor for undrained peatlands. These results contribute to our understanding of the influence of peatlands on the global carbon cycle and their potential impact on global change.     

The use of heavy metal concentrations and dendrochronology in the reconstruction of sediment accumulation, Ma a Panew River Valley, southern Poland

Heavy metal concentrations were investigated in overbank sediments of the Mala Panew River, southern Poland. Samples were collected from seven vertical profiles located within channel infills of a 20th century floodplain at three sites, each up to 50 m wide. In each profile, 15–24 samples were collected and analysed for Ba, Cd, Cu, Pb, and Zn. Sequential extraction of these elements was carried out in the 0.063-mm fraction of selected samples. Additionally, the age of the oldest trees growing close to the profiles has been used to estimate the initiation of sediment accumulation there. Ba, Cu, and Pb, which occur mostly in less mobile, moderately reducible, and residual fractions, were used for sediment dating. Zn and Cd, which in 50–75% occur in the mobile exchangeable fraction, were not suitable for dating. Correlation of Ba, Cu, and Pb concentrations in vertical profiles with changes in the load of effluents discharged to the river showed abrupt changes in the thickness of the strongly polluted sediments across the floodplains. A comparison of the relative changes between heavy metal peaks in sediments of similar age in the different profiles suggests a variable rate of downward metal migration. In general, none of the heavy metals investigated seems to have been mobilised within the stratigraphic layers above the water table. In layers located at stratigraphically lower levels, the Zn and Cd peaks seem to migrate several centimetres to several decimetres down in the profile. In profiles inundated for several weeks every year, Zn and Cd, as well as the relatively less mobile Ba, Cu, and Pb, have migrated downward by several decimetres. The investigation shows that frequent fluctuations of the water table have blurred the original depositional metal patterns of metal concentrations within a period of less than 40 years.     

A precise monitoring of snow surface height in the region of Lambert Glacier basin-Amery Ice Shelf,East Antarctica

The net surface snow accumulation on the Antarctic ice sheet is determined by a combination of precipitation, sublimation and wind redistribution. We present a one-year record of hourly snow-height measurements at LGB69 (70°50'S, 77°04'E, 1850 m a.s.l.). east side of Lambert Glacier basin (LGB), and 4 year record at G3 (70°53'S, 69°52'E, 84 m a.s.l.), Amery Ice Shelf (AIS). The measurements were made with ultrasonic sensors mounted on automatic weather stations installed at two sites. The snow accumulation at LGB69 is approximately 70 cm. Throughout the winter, between April and September, there was little change in surface snow height (SSH) at the two sites. The negative SSH change is due to densification at LGB69, and is due to both ablation and densification at G3. The strongest accumulation at two sites occurred during the period between October and March (accounting for 101.6% at LGB69), with four episodic increasing events occurring during 2002 for LGB69, and eight events during 1999-2002 for G     

Characteristics of Energy Accumulation and Release of Seismogenic Tectonics and Seismic Risk Analysis in Some Areas in the Tianshan Mountains, Xinjiang1

INTRODUCTIONHowtocombinethestudyofseismogenictectonicswithearthquakepredictionisanurgentscientificdifficulty .Thereexistbiggapsbetweenstudymethodsandcurrentknowledgeonseismogenitectonics ,earthquakeprediction ,seismogenesisandthephysicsofearthquakeoccurre…     

The lateglacial Quercus expansion in the southern European Alps: rapid vegetation response to a late Allerød climate warming?

A pollen‐inferred vegetation shift, from pioneer birch–pine woodland to mixed pine–summergreen oak forests, in the southern Alpine forelands, is commonly attributed to a centennial‐scale warming that occurred between the Gerzensee Oscillation (GO) and the Younger Dryas. Two microtephra layers bracketing the Younger Dryas onset (the Laacher See Tephra and the Vedde Ash) improve the chronology at Lago Piccolo di Avigliana (northern Italy) and allowed accurate correlation with Central European records where the GO is clearly detected. We used pollen percentages, pollen accumulation rates (PARs) and plant macrofossils to assess the population dynamics of Quercus, and leaf‐cuticle analysis for a better taxonomic identification of Quercus. Our results indicate that the species that was locally present was probably Quercus robur. PARs suggest that the population expansion started as early as the Bølling and followed an exponential increase through time. We attribute this gradual shift to increasing summer temperatures and longer growing seasons which contrast with a gradually decreasing temperature trend as recorded in Greenland ice cores and in Central Europe. Breaks or set‐backs in the PAR record may indicate the biotic response to minor Lateglacial cooling events of different life‐history stages in the Quercus population. Copyright © 2011 John Wiley & Sons, Ltd.     

Multiple overpressure systems and their relationship with hydrocarbon accumulation in the Qikou Depression of the Bohai Bay Basin,China

Pressure measurements using drill stem tests and estimates from log data calculation indicate that three vertically stacked regional pressure compartments exist in the Qikou Depression of Bohai Bay Basin, N. China. The compartments comprise hydrostatic, upper weak, and lower overpressure systems. Laterally, overpressure (pressure coefficient > 1.2) occurs in the deeper areas and weakens gradually from the centre to the margin of the depression. The accumulation of oil and gas exhibits the interesting characteristics of oil‐bearing layers above gas‐bearing layers in the Qikou Depression. The pattern can be accounted for by the evolution of overpressure system, the maturity process of the source rock and the main fault activity. In the late Dongying Formation (Ed, 30 Ma), the lower overpressure system began to form shape, and the hydrocarbon sources generated a large volume of oil. However, because there was no migration pathway, the oil only accumulated in the original strata. In the late Guantao Formation (Ng, 12 Ma), the gas was generated, the upper overpressure system formed gradually, and the activity of the main fault gradually increased. Then, the overpressure pushed the early gathered oil to flow from the lower overpressure system into the upper overpressure system. Afterwards, the activity of the main fault decreased again and remains weak until now. Thus, later generated natural gas cannot keep migrating along the main fault and can only accumulate in the lower overpressure system. Copyright © 2014 John Wiley & Sons, Ltd.     

南美Oriente盆地北部海绿石砂岩油藏特征及成藏规律

南美厄瓜多尔Oriente盆地斜坡带发育的白垩系Napo组高伽马特征的UT海绿石砂岩段是成熟探区新发现的隐蔽含油层段。本文分析了海绿石砂岩储层的矿物组成、孔隙结构、成岩作用、物性特点,并结合烃源岩评价与石油空间分布探讨海绿石砂岩油藏的成藏特征。海绿石粘土矿物以颗粒形式存在,与石英共同构成海绿石砂岩的颗粒组分,海绿石砂岩的孔隙结构具有双峰特征,束缚水含量高,属于中-低孔、中-低渗储层类型,孔隙类型主要是剩余粒间孔。海绿石砂岩储层中石英次生加大属Ⅱ级,长石碎屑颗粒发生溶蚀作用,含铁碳酸盐类胶结物发育,结合泥岩低的I/S混层比和高的最高峰温值T_max,指示海绿石砂岩层段属于中成岩阶段A期的产物。与海绿石砂岩油藏紧邻的大面积分布的Ⅱ₁腐泥型成熟烃源岩就是缓翼斜坡带的生烃中心,大面积连续发育的海绿石砂岩与之构成优越的源储组合,有利于上生下储式成藏。海绿石砂岩油藏表现为近源性、成藏晚期性等特点,规模发育的海绿石砂岩储层得以成藏的主要运聚机制是体积流和扩散流运聚机制。这对盆地其它油区同类油藏的发现具有重要的借鉴意义。     

四川盆地海相碳酸盐岩的油气成藏条件

四川盆地位于亚洲大陆中南部,是我国最大的外流盆地。油气资源评价结果(2008)表明,四川盆地海相地层待发现资源量约为50111.84×108m~3,资源勘探潜力巨大。本文从地层的划分、层序格架及层序岩相古地理特征等方面,对四川盆地海相碳酸盐岩油气成藏条件做了进一步研究。认为研究区烃源岩包括下志留统、中二叠统、上二叠统龙潭组和上三叠统须家河组等4套岩石,及局部发育的上二叠统大隆组。储集层粉为构造成因类和沉积成因类,构造成因主要包括裂缝性储层;沉积成因类储层主要是礁滩储层、内幕白云岩储层和风化壳岩溶储层。中二叠统气藏主要为自生自储的裂缝性气藏和台内滩相气藏;茅口组顶部和雷口坡组顶部发育风化壳型气藏;吴家坪组、长兴组及飞仙关组地层含礁滩型气藏;嘉陵江组和雷口坡组地层含内幕白云岩型气藏。     

辽东湾坳陷东部地区走滑双重构造的发育特征 及其石油地质意义

在将构造发育特征与走滑双重构造理论模型进行类比分析的基础上,对辽东湾坳陷东部地区的走滑双重构造的发育特征进行了研究,并结合油气勘探实践成果,就其石油地质意义进行了探讨,研究结果表明:在受控于走滑与拉伸并存的多动力源区域地质背景下,辽东湾坳陷新生代构造演化体现了断陷与拗陷、拉张与走滑的叠加效应,NNE走向的辽中1号断裂、辽中2号断裂及辽东断裂的发育不仅控制了辽东湾坳陷东部地区的凸凹格局,其走滑侧接关系也导致了研究区走滑双重构造的发育;辽东凸起是由于辽中2号断裂、辽东断裂走滑弯曲、右行左阶侧接而形成的挤压走滑双重构造,而辽中凹陷在早期拉张断陷基础上,经历了后期走滑作用的改造,其断裂体系的发育体现了辽中1号断裂与辽中2号断裂的右旋右行侧列所产生的拉张走滑双重构造效应;在走滑双重构造的增压带,断裂侧向封堵性强,有利于形成有效的断层圈闭,是油气藏发育的有利区带。     

成岩作用与油气侵位对砂岩铀成矿的约束--以准南硫磺沟地区头屯河组砂岩铀成矿为例

为了解准噶尔盆地南缘硫磺沟地区中侏罗统头屯河组砂岩成岩-流体演化与铀成矿响应,进而客观评价其成矿潜力。通过光薄片鉴定、X衍射、扫描电镜分析得出:目的层主要为岩屑细砂岩,依次经历了浅埋藏、深埋藏和表生-热液成岩阶段,遭受较强的机械压实、胶结及溶蚀作用。其黏土矿物以高岭石为主,碳酸盐矿物有细亮晶和泥晶两类,硅质胶结微弱,局部见细晶黄铁矿及其褐铁矿氧化产物。成岩环境可能经历了由酸性到弱碱性再到酸性,由同生期氧化-浅埋期还原-短暂抬升期氧化还原过渡-缓慢沉降期还原增强-快速抬升期氧化的演化过程。砂岩中存在较多油气包裹体;酸解总烃为5.72~449.14 μL/kg,以CH₄为主;方解石脉δ13C_V-PDB为-25‰~-6.7‰,δ18O_V-SMOW为11.1‰~18.9‰;结合野外调查认为目的层存在一期中等偏弱的后生油气侵位,从而影响了砂体的Eh及pH值。以上成岩过程及烃类流体活动使得目的层早期形成了小型层间氧化带型铀矿并得以局部保存,晚期形成了一定规模的地表潜水氧化带型铀矿体。