Evaluation of Upper Triassic T3x5 Source Rocks (Western Sichuan Depression, Sichuan Basin) and their Hydrocarbon Generation and Expulsion Characteristics: Implication for Tight-Sand Gas and Shale Gas Accumulation Potential Assessment

An unconventional, continuous petroleum system consists of an accumulation of hydrocarbons that is found in low-matrix-permeability rocks and contain large amounts of hydrocarbons. Tight-sand gas in the Jurassic and shale gas within the fifth member of Xujiahe Formation (T₃x⁵) are currently regarded as the most prolific emerging unconventional gas plays in China. The conventional and systematical evaluation of T₃x⁵ source rocks was carried out for the first time in the western Sichuan basin (WSD). Hydrocarbon generation and expulsion characteristics (including intensity, efficiency, and amount) of T₃x⁵ source rocks were investigated. Results show that T₃x⁵ source rocks are thick (generally >200 m), have high total organic content (TOC, ranging from 2.5 to 4.5 wt%), and dominated by III-type kerogen. These favorable characteristics result in a great hydrocarbon generating potential under the high thermal evolution history (R _o > 1.2%) of the area. An improved hydrocarbon generation potential methodology was applied to well data from the area to unravel the hydrocarbon generation and expulsion characteristics of T₃x⁵ source rocks in the WSD. Results indicate that the source rocks reached hydrocarbon expulsion threshold at 1.06% R _o and the comprehensive hydrocarbon expulsion efficiency was about 60%. The amount of generation and expulsion from T₃x⁵ source rocks was 3.14 × 10¹⁰ and 1.86 × 10¹⁰ t, respectively, with a residual amount of 1.28 × 10¹⁰ t within the source rocks. Continuous-type tight-sand gas was predicted to develop in the Jurassic in the Chengdu Sag of the WSD because of the good source-reservoir configuration (i.e., the hydrocarbon generation and expulsion center was located in Chengdu Sag), the Jurassic sandstone reservoirs were tight, and the gas expelled from the T₃x⁵ source rocks migrated for very short distances vertically and horizontally. The amount of gas accumulation in the Jurassic reservoirs derived from T₃x⁵ source rocks is up to 9.3 × 10⁸ t. The T₃x⁵ gas shale has good accumulation potential compared with several active US shale-gas plays. Volumetrically, the geological resource of shale gas is up to 1.05 × 10¹⁰ t. Small differences between the amounts calculated by volumetric method compared with that by hydrocarbon generation potential methodology may be due to other gas accumulations present within interbedded sands associated with the gas shales.     

Relevance of Pentane- and Hexane-Utilizing Bacterial Indicators for Finding Hydrocarbon Microseepage: A Study from Jamnagar Sub-basin, Saurashtra, Gujarat, India

Mesozoic sediments are source rocks for nearly half the world’s hydrocarbon reserves. Hence, there is great interest in the oil industry to know the trap and sub-trappean sediment thickness and their extent in the trap covered regions of Jamnagar study area. The microbial prospecting method is applied in the Jamnagar sub-basin, Gujarat for evaluating the prospects for hydrocarbon exploration by investigating the anomalous abundance of n-pentane- and n-hexane-oxidizing bacteria of this area. A total of 150 near-surface soil samples were collected in Jamnagar sub-basin, Gujarat for the evaluation of hydrocarbon resource potential of the basin. In this study, bacterial counts for n-pentane-utilizing bacteria range between 1.09 × 10² and 9.89 × 10⁵ cfu/g and n-hexane-utilizing bacteria range between 1.09 × 10² and 9.29 × 10⁵ cfu/g. The adsorbed hydrocarbon gases consisting of ethane plus hydrocarbons (ΣC₂₊) of 1–977 ppb and n-pentane (nC₅) of 1–23 ppb. The integrated geomicrobial and adsorbed soil gas studies showed the anomalous hydrocarbon zones nearby Khandera, Haripur, and Laloi areas which could probably aid to assess the true potential of the basin. Integrated geophysical studies have shown that Jamnagar sub-basin of Saurashtra has significant sediment thickness below the Deccan Traps and can be considered for future hydrocarbon exploration.     

Distinction Between Oil Expulsion History and Gas Expulsion History

The process of organic matter transformation into oil and gas is also a balance process of hydrocarbon transformation. This article probes to distinguish the oil expulsion history from gas expulsion history based on the hydrocarbon generation, hydrocarbon residual, and hydrocarbon expulsion processes of the source rocks. In this method, the first step is to study the hydrocarbon expulsion rate by means of hydrocarbon generation potential method; the second step is to study the oil generation rate by means of the heating–pressuring experiment method; the third step is to study the oil residual rate by means of the mathematical method. The difference between the values of oil generation rate and oil residual rate is defined as the oil expulsion rate, while that between the values of hydrocarbon expulsion rate and the gas expulsion rate is defined as the gas expulsion rate. Then, combined with the geological parameters of source rocks, the oil and gas expulsion history can be obtained. This study on Es₁ Source rocks, Nanpu Sag, Bohai Bay Basin, China shows that the primary expulsion period of Es₁ source rocks is Guantao–Minghuazhen period.     

中国海洋油气资源开发与国家石油安全战略对策

石油是中国能源安全的核心问题,随着我国石油供应对外依赖程度的增大,石油安全问题越来越突出,将会成为我国21世纪经济、社会可持续发展面临的一个重要问题。我国是海洋油气资源丰富的国家,广阔的海域中分布着近100×10⁴km²的含油沉积盆地,近海石油资源量为240×10⁸t,天然气资源量为140×10¹²m³。海洋油气资源的开发利用,将能部分解决我国油气资源进口数量。本文讨论了解决石油安全的四种模式,对我国油气安全的国际和国内条件进行了分析,提出了解决我国油气安全的战略对策。     

柴达木低品位固体钾矿溶解转化率与品位关系

我国是缺钾大国,探明的可溶性钾盐十分有限,柴达木盆地是我国盐湖钾盐的聚集地,含水层骨架中含有数亿吨低品位固体钾矿,开发出这些低品位固体钾盐对增加国内钾肥供给,保障粮食安全具有重大意义。青海盐湖工业股份有限公司历经十年开发出低品位固体钾盐的浸泡式溶解转化方法,试验表明,固体钾盐的溶解转化率随固体钾品位的增加而增加,累计溶解转化率为56%～98%。该技术在柴达木多个盐湖得到推广应用,察尔汗盐湖保有固体钾盐达2.96×10~8 t,平均品位KCl为1.24%,根据试验数据回归分析溶解转化率77%,可溶解转化出钾盐(KCl)约2.28×10~8 t,柴达木盆地盐湖保有3.43×10~8 t固体钾盐,平均品位KCl为1.25%,溶解转化率78%,可溶解转化出钾盐(KCl)2.68×10~8 t,大幅度增加了钾盐储备量。     

The basic characteristics and spatial patterns of global cultivated land change since the 1980s

In this paper, we analyzed the spatial patterns of cultivated land change between 1982 and 2011 using global vector-based land use/land cover data. (1) Our analysis showed that the total global cultivated land area increased by 528.768×10⁴ km² with a rate of 7.920×10⁴ km²/a, although this increasing trend was not significant. The global cultivated land increased fastest in the 1980s. Since the 1980s, the cultivated land area in North America, South America and Oceania increased by 170.854×10⁴ km², 107.890×10⁴ km², and 186.492×10⁴ km², respectively. In contrast, that in Asia, Europe and Africa decreased by 23.769×10⁴ km², 4.035×10⁴ km² and 86.76×10⁴ km², respectively. Furthermore, the cultivated land area in North America, South America and Oceania exhibited significant increasing trends of 7.236× 10⁴ km²/a, 2.780×10⁴ km²/a and 3.758×10⁴ km²/a, respectively. On the other hand, that of Asia, Europe and Africa exhibited decreasing trend rates of–5.641×10⁴ km²/a,–0.831×10⁴ km²/a and–0.595×10⁴ km²/a, respectively. Moreover, the decreasing trend in Asia was significant. (2) Since the 1980s, the increase in global cultivated lands was mainly due to converted grasslands and woodlands, which accounted for 53.536% and 26.148% of the total increase, respectively. The increase was found in southern and central Africa, eastern and northern Australia, southeastern South America, central US and Alaska, central Canada, western Russia, northern Finland and northern Mongolia. Among them, Botswana in southern Africa experienced an 80%–90% increase, making it the country with the highest increase worldwide. (3) Since the 1980s, the total area of cultivated lands converted to other types of land was 1071.946×10⁴ km². The reduction was mainly converted to grasslands and woodlands, which accounted for 57.482% and 36.000%, respectively. The reduction occurred mainly in southern Sudan in central Africa, southern and central US, southern Russia, and southern European countries including Bulgaria, Romania, Serbia and Hungary. The greatest reduction occurred in southern Africa with a 60% reduction. (4) The cultivated lands in all the continents analyzed exhibited a trend of expansion to high latitudes. Additionally, most countries displayed an expansion of newly increased cultivated lands and the reduction of the original cultivated lands.     

Plio-Quaternary sediment budget between thrust belt erosion and foreland deposition in the central Andes, southern Bolivia

Estimates of the physical boundary conditions on sediment source and sink regions and the flux between them provide insights into the evolution of topography and associated sedimentary basins. We present a regional‐scale, Plio‐Quaternary to recent sediment budget analysis of the Grande, Parapeti and Pilcomayo drainages of the central Andean fold‐thrust belt and related deposits in the Chaco foreland of southern Bolivia (18–23°S). We constrain source‐sink dimensions, fluxes and their errors with topographic maps, satellite imagery, a hydrologically conditioned digital elevation model, reconstructions of the San Juan del Oro (SJDO) erosion surface, foreland sediment isopachs and estimated denudation rates. Modern drainages range from 7453 to 86 798 km² for a total source area of 153 632 km². Palaeo‐drainage areas range from 9336 to 52 620 km² and total 100 706 km², suggesting basin source area growth of ～50% since ～10 Ma. About 2.4–3.1 × 10⁴ km³ were excavated from below the SJDO surface since ～3 Ma. The modern foredeep is 132 080 km² with fluvial megafan areas and volumes ranging from 6142 to 22 511 km² and from 1511 to 3332 km³, respectively. Since Emborozú Formation deposition beginning 2.1 ± 0.2 Ma, the foreland has a fill of ～6.4 × 10⁴ km³. The volume and rate of deposition require that at least ～40–60% of additional sediment be supplied beyond that incised from below the SJDO. The data also place a lower limit of ≥0.2 mm year^?1 (perhaps ≥0.4 mm year^?1) on the time‐ and space‐averaged source area denudation rate since ～2–3 Ma. These rates are within the median range measured for the Neogene, but are up to 2 orders of magnitude higher than some observations, as well as analytic solutions for basin topography and stratigraphy using a two‐dimensional mathematical model of foreland basin evolution. Source‐to‐sink sediment budget analyses and associated interpretations must explicitly and quantitatively reconcile all available area, volume and rate observations because of their inherent imprecision and the potential for magnification when they are convolved.     

Reconstruction of cropland spatial patterns and its spatiotemporal changes over the 20th century on the Songnen Plain,Northeast China

We initially estimated the cropland area at county level using local historical documents for the Songnen Plain (SNP) in the 1910s and 1930s. We then allocated this cropland area to grid cells with a size of 1 km × 1 km, using a range of cultivation possibilities from high to low; this was based on topography and minimum distances to rivers, settlements, and traffic lines. Cropland areas for the 1950s were obtained from the Land Use Map of Northeast China, and map vectorization was performed with ArcGIS technology. Cropland areas for the 1970s, 1980s, 1990s, 2000s, and 2010s were retrieved from Landsat images. We found that the cropland areas were 4.92 × 10⁴ km² and 7.60 × 10⁴ km², accounting for 22.8% and 35.2% of the total area of the SNP in the 1910s and 1930s, respectively, which increased to 13.14 × 10⁴ km², accounting for 60.9% in the 2010s. The cropland increased at a rate of 1.18 × 10⁴ km² per decade from the 1910s to 1970s while it was merely 0.285 × 10⁴ km² per decade from the 1970s to 2010s. From the 1910s to 1930s, new cultivation mainly occurred in the central SNP while, from the 1930s to 1970s, it was mainly over the western and northern parts. This spatially explicit reconstruction could be offered as primary data for studying the effects of changes in human-induced land cover based on climate change over the last century.     

Cultivated land change in the Belt and Road Initiative region

The Belt and Road Initiative (BRI)–a development strategy proposed by China – provides unprecedented opportunities for multi-dimensional communication and cooperation across Asia, Africa and Europe. In this study, we analyse the spatio-temporal changes in cultivated land in the BRI countries (64 in total) to better understand the land use status of China along with its periphery for targeting specific collaboration. We apply FAO statistics and GlobeLand30 (the world’s finest land cover data at a 30-m resolution), and develop three indicator groups (namely quantity, conversion, and utilization degree) for the analysis. The results show that cultivated land area in the BRI region increased 3.73×10⁴ km² between 2000 and 2010. The increased cultivated land was mainly found in Central and Eastern Europe and Southeast Asia, while the decreased cultivated land was mostly concentrated in China. Russia ranks first with an increase of 1.59×10⁴ km² cultivated land area, followed by Hungary (0.66×10⁴ km²) and India (0.57×104 km2). China decreased 1.95×10⁴ km² cultivated land area, followed by Bangladesh (–0.22×10⁴ km²) and Thailand (–0.22×10⁴ km²). Cultivated land was mainly transferred to/from forest, grassland, artificial surfaces and bare land, and transfer types in different regions have different characteristics: while large amount of cultivated land in China was converted to artificial surfaces, considerable forest was converted to cultivated land in Southeast Asia. The increase of multi-cropping index dominated the region except the Central and Eastern Europe, while the increase of fragmentation index was prevailing in the region except for a few South Asian countries. Our results indicate that the negative consequence of cultivated land loss in China might be underestimated by the domestic- focused studies, as none of its close neighbours experienced such obvious cultivated land losses. Nevertheless, the increased cultivated land area in Southeast Asia and the extensive cultivated land use in Ukraine and Russia imply that the regional food production would be greatly improved if China’ “Go Out policy” would help those countries to intensify their cultivated land use.     

Groundwater Assessment for Current and Future Water Demand in the Daka Catchment,Northern Region,Ghana

The use of untreated surface water for domestic purposes has resulted in the infection of some people by guinea worm and other water borne diseases in the Northern Region of Ghana. The aim of this study is to assess the current groundwater quantity and quality conditions in the 7,820 km² Daka catchment and project the water demand in 2025. Results of groundwater analyses generally show good water quality for domestic use. Borehole analyses indicate that the catchment’s groundwater system can be characterized by a regolith aquifer underlain by a deeper fractured rock aquifer in some areas. The current per capita water demand is estimated at 40 l/day although 60 l/day is the desired amount, indicating that with the current population of 363,350, the projected water demand for the communities is 21,800 m³/day. With a projected population of 555,500 in 2025, an expected 33,300 m³/day of water is required. The estimated optimum potential groundwater available for use in the catchment is 154 × 10⁶ m³/year (4.24 × 10⁵ m³/day). However, the current total groundwater abstraction is only 8,876 m³/day or 2% of the optimum. In comparison, the projected total current and 2025 water demands are only 5 and 8%, respectively, of the optimum potential groundwater available for use in the catchment. In addition, only 1,780 m³/day (0.65 × 10⁶ m³/year) or 0.06% of the average annual flow of 1,016 × 10⁶ m³/year of the Daka River is treated for domestic use. These figures reveal that a significantly very large water resource potential exists for both surface and groundwater development in the Daka catchment. It is suggested that their development should proceed conjunctively.     

Reconstruction and Regional Significance of the Coire Breac Palaeoglacier,Glen Esk,Eastern Grampian Highlands,Scotland

We present a glaciological and climatic reconstruction of a former glacier in Coire Breac, an isolated cirque within the Eastern Grampian plateau of Scotland, 5 km from the Highland edge. Published glacier reconstructions of presumed Younger Dryas‐age glaciers in this area show that equilibrium line altitudes decreased steeply towards the east coast, implying a arctic maritime glacial environment. Extrapolation of the ELA trend surface implies that glaciers should have existed in suitable locations on the plateau, a landscape little modified by glaciation. In Coire Breac, a 0.35 km² cirque glacier existed with an equilibrium line altitude of 487 ± 15 m above present sea level. The equilibrium line altitude matches closely the extrapolated regional equilibrium line altitude trend surface for Younger Dryas Stadial glaciers. The mean glacier thickness of 24 m gives an ice volume of 7.8 × 10⁶ m³, and a maximum basal shear stress of c. 100 kPa^?1. Ablation gradient was c. –0.0055 m m^?1, with a mean July temperature at the equilibrium line altitude of c. 5.1°C. The reconstruction implies an arctic maritime climate of low precipitation with local accumulation enhanced by blown snow, which may explain the absence of other contemporary glaciers nearby. Reconstructed ice flow lines show zones of flow concentration around the lower ice margin which help to explain the distribution of depositional facies associated with a former debris cover which may have delayed eventual glacier retreat. No moraines in the area have been dated, so palaeoclimatic interpretations remain provisional, and a pre‐Lateglacial Interstadial age cannot be ruled out.     

Deep-Lacustrine Shale Heterogeneity and Its Impact on Hydrocarbon Generation,Expulsion, and Retention: A Case Study from the Upper Triassic Yanchang Formation,Ordos Basin,China

The Chang-7 shale of the Upper Triassic Yanchang Formation was deposited in a deep-lacustrine environment in the southwest part of the Ordos Basin. It is characterized by a strong lithological heterogeneity, consisting primarily of pure shale and sandy laminated shale. This study explored the impact of sandy laminae in the thick pure shale on hydrocarbon generation, retention, and expulsion, which were rarely considered in previous studies. Based on core observation, thin section, and geochemical analysis, the hydrocarbon generation, retention, and expulsion characteristics were obtained for both pure shale and sandy laminated shale. In general, the Chang-7 shale stays at low mature to mature thermal evolution stage and has good hydrocarbon generation potential. It contains mainly Type II kerogen with an average total organic carbon (TOC) of 2.9% and average (S₁?+?S₂) of 8.2 mg/g. Compared with sandy laminated shale, pure shale contains more retained liquid hydrocarbon and has a higher amount of asphaltene and nitrogen–sulfur–oxygen (NSO) polarized components, indicating a relatively weak hydrocarbon expulsion process. The middle part of a thick pure shale retains more liquid hydrocarbon and has higher percentages of asphaltene and NSO polarized components than that of the top and basal part of the shale where sandy laminae occur. The difference in hydrocarbon retention capacity is interpreted to have been primarily caused by the comparatively higher reservoir quality of the sandy laminated shale, having higher amount of brittle minerals and larger pores than the pure shale. Polymer dissolution and nanopore adsorption are also key factors in hydrocarbon retention and component partition. Based on this study, we suggest that sandy laminated shale, which receives most of the hydrocarbon from adjacent pure shale, should be the current favorable shale oil exploration targets. Even though pure shale contains high hydrocarbon potential, its development is still pending improved technologies, which could solve the challenges caused by complicated geological conditions.

     

中国西北水资源利用及生态环境安全

1 Introduction In the 21st century, water resources will become the international and strategic resource instead of petroleum (Kang et al., 1994a, b). At present, the freshwater resources crisis all over the world has made people aware that although water…     

Changes in the Geometry and Volume of Rabots glaciär,Sweden, 2003–2011: Recent Accelerated Volume Loss Linked to More Negative Summer Balances

Terminus geometry, ice margins, and surface elevations on Rabots glaciär were measured using differential GPS during summer 2011 and compared with those similarly measured in 2003. Glacier length over the eight years decreased by ～105 m corresponding to 13 m a^?1, a rate consistent with ice recession over the last several decades. Measured changes in surface elevations show that between 2003 and 2011 the glacier's volume decreased by ～27.6 ± 2.6 × 10⁶ m³, or 3.5 ± 0.3 × 10⁶ m³ a^?1. This compares favorably with an estimate of ?28.1 ± 2.6 × 10⁶ m³ based on a mass‐balance approach. The rate of volume loss appears, however, to have significantly increased after 2003, being substantially greater than rates determined for the intervals 1959–80, 1980–89, and 1989–2003. This increase corresponds to a sustained interval of more negative summer balances. Previous work suggests that as of 2003 Rabots glaciär had not yet completed its response to a ～1°C warming that occurred c. 1900, and thus the current marked increase rate of ice loss might reflect the effect of recent, or accelerated regional warming that occurred during the last decade superimposed on its continued response to that earlier warming.     

Sediment accumulation along a glacially impacted mountainous coastline: north-east Gulf of Alaska

Tectonically active coastal regions of the world recently have been suggested to supply the bulk of sediment from land to the oceans. Seabed sampling on the continental shelf and in coastal embayments of the north-east Gulf of Alaska (Alsek River to Prince William Sound) was performed to examine the temporal and spatial variability of sediment accumulation in a mountainous coastal setting. Cores of varying lengths (30–300 cm) were collected at 84 stations to provide information on sedimentary processes using radiochemical (²¹⁰Pb and ¹³⁷Cs) techniques. Four types of ²¹⁰Pb activity profiles were observed, dominantly reflecting steady-state sediment accumulation. However, nonsteady-state profiles also were measured, resulting in part from episodic deposition near glacier-fed rivers and on the Copper River Delta. Sediment accumulation rates in the eastern half of the study area are highest at midshelf depths (≈100 m) (≥10 mm yr^?1) and near rivers draining the Bering Glacier (≈20 mm yr^?1). On the Copper River Delta, sediment accumulation rates are highest for the delta front (> 20 mm yr^?1) and decrease westward along the sediment dispersal route. Total annual sediment accumulation is 90–140×10⁶ tons yr^?1 on the shelf in the study area. Annual sediment accumulation for the total marine environment in the study area (including Icy and Yakutat Bays) exceeds 250×10⁶ tons yr^?1, potentially making this region the largest sink for sediment in North America. Spatial patterns in sediment accumulation on the shelf are similar between centennial and Holocene time-scales, reflecting the dominance of the Copper River and Bering and Malaspina glaciers as sediment sources. Temporal variability in accumulation rates between centennial and Holocene time-scales exists for portions of the study area near fiords and demonstrates the considerable changes that occur in sediment supply during glacial advances and retreats.     

生态服务价值与方法研究

1Ecosystemservicesandtheirvalueoftheworld1.1EcosystemservicesHuman societies derive many essential goods from natural ecosystems, including seafood, game animals, fodder, fuelwood, timber, and pharmaceutical products (Constanza, 1997). These goods represent important and familiar parts of the economy. What has been less appreciated until recently is that natural ecosystems also perform fundamental life-support services without which human civilizations would cease to thrive. These include the…     

A high-resolution pigment and productivity record from the varved Ponte Tresa basin (Lake Lugano,Switzerland) since 1919: insight from an approach that combines hyperspectral imaging and high-performance liquid chromatography

Eutrophication, prompted by anthropogenic activities and climate change has led to multiple adverse effects in freshwater systems across the world. As instrumental measurements are typically short, lake sediment proxies of aquatic primary productivity (PP) are often used to extend the observational record of eutrophication back in time. Sedimentary pigments provide specific information on PP and major algal communities, but the records are often limited in the temporal resolution. Hyperspectral imaging (HSI) data, in contrast, provide very high seasonal (sub-varve-scale) resolution, but the pigment speciation is limited. Here, we explore a combined approach on varved sediments from the Ponte Tresa basin, southern Switzerland, taking the advantages of both methods (HSI and high performance liquid chromatography, HPLC) with the goal to reconstruct the recent eutrophication history at seasonal to interannual resolution. We propose a modified scheme for the calibration of HSI data (here: Relative Absorption Band Depth between 590 and 730 nm RABD_590–730) and HPLC-inferred pigment concentrations (here: ‘green pigments’ {chlorophyll a and pheophytin a}) and present a calibration model (R²?=?0.82; RMSEP?~?12%). The calibration range covers >?98% of the spectral index values of all individual pixels (68 µm?×?68 µm) in the sediment core. This allows us to identify and quantify extreme pigment concentrations related to individual major algal blooms, to identify multiple algal blooms within one season, and to assess interannual variability of PP. Prior to the 1930s, ‘green pigment’ concentrations and fluxes (~?50 µg g^?1;?~?2 µg cm^?2a^?1, chlorophyll a and pheophytin a) and interannual variability was very low. From the 1930s to 1964, chlorophyll a and pheophytin a increased by a factor of ~?4, and ββ-carotene appeared in substantial amounts (~?0.4 µg cm^?2a^?1). Interannual variability increased markedly and a first strong algal bloom with ‘green pigment’ concentrations as high as 700 µg g^?1 is observed in 1958. Peak eutrophication (~?12 µg cm^?2a^?1 chlorophyll a and pheophytin a) and very high interannual variability with extreme algal blooms (‘green pigment’ concentrations up to 1400 µg g^?1) is observed until ca. 1990, when eutrophication decreases slightly. Maximum PP values after 2009 are likely the result of internal nutrient cycling related to repeated deep mixing of the lake.     

Numerical modelling of the hydrocarbon generation of Tertiary source rocks intruded by doleritic sills in the Zhanhua depression,Bohai Bay Basin,China

An igneous hydrocarbon reservoir had been found in the Zhanhua depression, Bohai Bay Basin, eastern China. Two doleritic sills successively intruded into the immature source rock of the third member of the Shahejie Formation (Es3). The heat released from the magma changed the mineral composition of wall rocks and accelerated the maturity of organic matter. Thin hornfels and carbargilite zones were found next to the sills. The vitrinite reflectances (%R_o) of these heated wall rocks increased to at least 1.4% near the contacts (<50 m), and accumulation of oil was found in the hornfels zone and dolerite bodies. With the aim of understanding the influence of the sills on the hydrocarbon generation process, a complex heat conduction model was used to simulate the thermal history of the organic‐rich wall rocks, in which both the latent heat of crystallization of intrusions and vapourization heat of pore water in wall rocks were considered. The simulation results suggested that the cooling of each sill continued for about 0.1 Ma after its emplacement and the temperature of wall rocks was considerably raised. The peak temperature (T_peak) that wall rocks experienced can reach 460–650°C in the region of 10 m away from the contacts. The thermal model was qualitatively verified by comparing the experimental data of vitrinite reflectances and mineral geothermometers of the wall rocks with the simulation results. Furthermore, we modelled the hydrocarbon generation of the source rocks based on the simulated thermal history. In the region of about 100 m from the contacts, the organic matter was heated and partially transformed into hydrocarbon within only a few 1000 years, which was significantly faster than the normal burial generation process.     

近60年黄河水沙变化及其对三角洲沉积的影响

In order to find out the variation process of water-sediment and its effect on the Yellow River Delta, the water discharge and sediment load at Lijin from 1950 to 2007 and the decrease of water discharge and sediment load in the Yellow River Basin caused by human disturbances were analyzed by means of statistics. It was shown that the water discharge and sediment load into the sea were decreasing from 1950 to 2007 with serious fluctuation. The human activities were the main cause for decrease of water discharge and sediment load into the sea. From 1950 to 2005, the average annual reduction of water discharge and sediment load by means of water-soil conservation practices were 2.02×109 m3 and 3.41×108 t respectively, and the average annual volume by water abstraction for industry and agriculture were 2.52×1010 m3 and 2.42×108 t respectively. The average sediment trapped by Sanmenxia Reservoir was 1.45×108 t from 1960 to 2007, and the average sediment retention of Xiaolangdi Reservoir was 2.398×108 t from 1997 to 2007. Compared to the data records at Huanyuankou, the water discharge and sediment load into the sea decreased with siltation in the lower reaches and increased with scouring in the lower reaches. The coastline near river mouth extended and the delta area increased when the ratio of accumulative sediment load and accumulative water discharge into the sea (SSCT) is 25.4–26.0 kg/m3 in different time periods. However, the sharp decrease of water discharge and sediment load into the sea in recent years, especially the Yellow River into the sea at Qing 8, the entire Yellow River Delta has turned into erosion from siltation, and the time for a reversal of the state was about 1997.     

Denudation rates of a subequatorial orogenic belt based on estimates of sediment yields: evidence from the Paleozoic Appalachian Basin,USA

The Upper Mississippian (ca. 325 Ma) Pride Shale and Glady Fork Member in the Central Appalachian Basin comprise an upward‐coarsening, ca. 60‐m‐thick succession of prodeltaic‐delta front, interlaminated fine‐grained sandstones and mudstones gradational upwards into mouth‐bar and distributary‐channel sandstones. Analysis of laminae bundling in the Pride Shale reveals a hierarchy of tidal cycles (semi‐diurnal, fortnightly neap‐spring) and a distinct annual cyclicity resulting from seasonal fluvial discharge. These tidal rhythmites thus represent high‐resolution chronometers that can be used in basin analysis. Annual cycles average 10 cm in thickness, thus the bulk of the Pride Shale‐Glady Fork Member in any one vertical section is estimated to have accumulated in ca. 600 years. Progradational clinoforms are assumed to have had dips of 0.3–3° with a median dip of 1.7°; the latter infilled a NE‐SW oriented foreland trough up to 300 km long by 50 km wide in the relatively short time period of 90 kyr. The total volume of sediment in the Pride basin is ca. 900 km³ which, for an average sediment density of 2700 kg m^?3, equates to a total mass of ca. 2.4 × 10⁶ Mt. Thus, mass sediment load can be estimated as 27 Mt yr^?1. For a drainage basin area of 89 000 km², based on the scale of architectural channel elements and cross‐set thicknesses in the incised‐valley‐fill deposits of the underlying Princeton Formation, suspended sediment yields are estimated at ca. 310 t km^?2 yr^?1 equating to a mechanical denudation rate of ca. 0.116 mm yr^?1. Calculated sediment yields and inferred denudation rates are comparable to modern rivers such as the Po and Fly and are compatible with a provenance of significant relief and a climate characterized by seasonal, monsoonal discharge. Inferred denudation rates also are consistent with average denudation rates for the Inner Piedmont Terrane of the Appalachians based on flexural modelling. The integration of stratigraphic architectural analysis with a novel chronometric application highlights the utility of sedimentary archives as a record of Earth surface dynamics.