Abundance, diversity and succession of aquatic Coleoptera and Heteroptera in a cluster of artificial ponds in the North German Lowlands

Our study describes and evaluates environmental influences on assemblages of aquatic Coleoptera and Heteroptera in artificial ponds situated near Lake Steinhude in Lower Saxony (Germany). We determined temporal dynamics and colonization patterns for 14 ponds of different age. In total, we recorded 4941 individuals that represented 87 species of aquatic beetles and bugs. Between 30 and 40 species were found in most of the ponds. Heteropteran species of the families Corixidae and Notonectidae acted as pioneer species in new ponds, while aquatic coleopterans predominated in older ponds. The results of Canonical Correspondence Analyses (CCA) showed that among the key factors affecting community structure were land use, vegetation cover, water chemistry and the age of the ponds. We found that the distribution of adjacent ponds on areas with different land use has a positive influence on the diversity and abundance of the aquatic insect fauna.     

华北南缘古元古代末岩墙群侵位的磁组构证据

华北克拉通南缘的中条山及邻区广泛发育元古宙放射状基性岩墙群,与五台山-恒山和大同地区的北北西向基性岩墙群以及熊耳中条拗拉谷的火山岩在时空分布和地球化学方面均具有密切的相关性。中条山及邻区放射状基性岩墙群的宏观和微观流动构造(包括捕虏体、冲痕构造、矿物线理和定向斑晶)指示岩墙群以一定的仰角向北西侵位。通过该区岩墙群磁化率各向异性(AMS)测量得到磁组构的最大磁化率长轴优势方位分布图和磁组构各向异性特征分析进一步指示华北南缘古元古代末岩墙群从熊耳中条拗拉谷的底部向北西侵位。岩墙群的流动构造和磁组构的统计成果夯实了华北克拉通古元古代末基性岩墙群与熊耳中条拗拉谷的成生联系。     

The influence of marine and terrestrial source material on the composition of petroleum

This paper consists of two interrelated parts. In the first part, the influence of the composition of sediment organic matter on crude oil composition is discussed. The second part deals with the origin of normal paraffins in petroleum.Source beds with abundant terrestrial plant matter generate heavy hydrocarbons rich in five-ring naphthenes. Unless such source beds are exposed to a high temperature for a prolonged time, the oils released are also rich in five-ring naphthenes. Such oils are rare; thus far the only examples found are some Eocene Wilcox oils from the Texas Gulf Coast and some Eocene Green River oils from the Uinta Basin, Utah. Normally, oil source beds are not rich in terrestrial plant matter and the five-ring naphthene content of the source bed hydrocarbons, as well as that of the produced oils, is low.The n-paraffins generated by oil source beds rich in terrestrial plant matter are characterized by abnormally low (C₂₁ + C₂₂)/(C₂₈ + C₂₉) ratios of 0.6–1.2. In oils of dominantly marine origin, this ratio is in the range 1.5–5.0. The ratio of marine to terrestrial organic matter in source beds appears to influence both the naphthene composition and the n-paraffin composition of the generated oils.Evidence is presented that petroleum n-parainns originate from slow thermal cracking of fatty acids contained in fats and waxes. Reaction equations are discussed which explain the major geochemical observations, including the difference in carbon-number distribution of the assumed parental fatty acids and of their descendant n-paraffins. In normal oils, which originate mostly from fat rich marine organic matter, the n-paraffin concentration tapers off above C₂₀. The molecular weight range of the fatty acids of plant waxes is considerably higher than that of fats. If plant waxes contribute strongly to the oil source material, the molecular weight distribution of the petroleum n-paraffins formed is abnormal and high carbon numbers in the C₂₄-C₃₂ range dominate.     

Distribution of diatoms among intermittent ponds on the Atlantic Coastal Plain: development of a model to preduct drought periodicity from surface-sediment assemblages

Inferences of past climate from the fossil record in lakes rely on the accurate quantification of a relationship of fossilizing organisms to their environment. Whereas the relationship of diatoms to water chemistry parameters has been modeled in many systems, few studies adequately address the relationship of diatoms to physical properties, such as water depth or hydrology, that may be more directly tied to climate. We examined the composition of modern diatoms in surface sediments of 75 isolated ponds (mostly Carolina bays) of the Atlantic Coastal Plain to: (1) assess the influence of physical and chemical variables on the distribution of diatoms among ponds of the region, and (2) develop a model that predicts hydroperiod (a measure of pond permanence) from diatom assemblages. We constructed two hydroperiod calibration models: the first infers hydroperiod from the weighted-average optima and tolerances of taxa along the hydroperiod gradient, the second bases inferences on the hydroperiod estimates of compositionally similar samples. Both approaches incorporate a-priori and post-hoc tests of assumptions often inherent in the construction of transfer functions. Diatom assemblage composition had strong, approximately linear relationships to hydroperiod, water depth, and calcium concentration in non-metric multidimensional ordination space; effects of other variables, including pH, were non-linear or ambiguous. Overall, the assemblages reflected the dilute, acidic chemical characteristics of bays. The assemblages contained differing abundances of euterrestrial, benthic and planktonic taxa, depending on a pond's susceptibility to drying. A weighted-averaging regression model based on taxon-specific hydroperiod optima generated adequate, unbiased hydroperiod inferences from diatom species composition (r² = 0.81). This model may be used to infer past drought episodes from fossil diatom assemblages at appropriate sites on the Atlantic Coastal Plain.     

晋北地区中元古代岩墙群的地球化学特征和大地构造背景

晋北地区发育大规模的中元古代北北西向岩墙群，未变形和未变质，是华北克拉通前寒武纪构造演化研究的最显著标志，根据本区岩墙群的岩石学和地球化学研究，这些岩墙群的岩石属于板内大陆裂谷玄武岩系列，形成于大陆裂谷拉张的构造环境，与东侧的燕辽－中条拗拉槽内的火山岩岩石化学对比分析，本区岩墙群的基性岩浆可能来自拗拉槽深部，这些基性岩浆从拗拉槽的深部向北西方向侵位于晋北地区先存的构造裂隙中形成了基性岩墙群。     

准噶尔盆地新生代构造应力对石炭纪火山岩构造裂缝发育的控制

构造裂缝的发育对改善储层的储渗条件有着重要的作用,特别是火山岩这种非传统储层,构造裂缝的发育是其成为有效储层的必要条件。本文主要借助构造应力场有限元数值模拟这一成熟的方法对准噶尔盆地石炭纪火山岩构造裂缝的发育状况进行预测。其两个主要的步骤是首先对区域构造应力场进行模拟计算,然后结合岩石的强度指标判断构造裂缝的发育状况。通过对准噶尔盆地地质背景和构造演化的分析,明确了新生代构造应力场的的决定性作用和石炭纪火山岩的分布区域(划分出六个区域),建立了数值模拟的计算模型、确定了边界条件与载荷。通过二维有限元数值模拟(应用Ansys软件)得到了新生代盆地应力场的分布特征和应力值。结合岩石强度指标,对火山岩构造裂缝(张裂缝和剪裂缝)的发育进行了预测并圈出相应的区域,主要为盆地西北缘、中央坳陷中部、滴西1东部,彩参2周缘、大井-将军庙等地区,对石炭纪火山岩的油气勘探战略选区, 优化勘探部署具有重要指导意义。     

Proteins as a possible source material of low molecular weight petroleum hydrocarbons

Low temperature cracking experiments of a representative protein, at temperatures not far above the observed temperature range of 130–160°C of mature California oil source rocks, indicate the formation of all gaseous and of some gasoline range hydrocarbons of petroleum. Based on protein derivatives only it is estimated that a maximum of at least 3–8% by weight of the total organic matter of oil source sediments may be converted into such hydrocarbons. This is in addition to hydrocarbons originating from lipids.     

The deep subsurface temperature controlled origin of the gaseous and gasoline-range hydrocarbons of petroleum

In recent surface sediments there is no indication of any of the saturated C₃–C₇ gasolinerange hydrocarbons which are so common in petroleum. Appreciable gasoline-range hydrocarbon generation (85–180°C) of 80 ppm by weight of dry rock, or more, occurs only with increased temperature due to deeper burial, below about 8000 ft in the Los Angeles basin and below 12,500 ft in the Ventura basin. Because of the lower temperature gradient in the Ventura basin, the zone of substantial gasoline generation is considerably deeper there than in the Los Angeles basin. However, the subsurface temperature range over which substantial gasoline generation occurs is practically the same in the two basins. This demonstrates that the subsurface temperature, not depth, is the controlling factor in gasoline generation in source rocks. For appreciable gasoline generation somewhat higher subsurface temperatures are required than for equivalent generation of heavy hydrocarbons boiling above 325°C. Appreciable generation of the C₁–C₄ wet gas components of 75 ppm by weight of dry rock, or more, takes place quite deep also; in the Los Angeles basin it occurs below 10,000 ft.The composition of the gasoline-range hydrocarbons generated changes gradually with increasing depth, temperature and age of the shales. In deep strata the gasolines from shale cannot be distinguished from the gasolines of waxy crude oils in the same basin. The gasoline-range hydrocarbons mature with depth, temperature and age of the sediments, very much like the heavy hydrocarbons investigated earlier.Based on the similarity of analyses of heavy as well as of gasoline-range hydrocarbons from crude oils and from certain deep shales, a secure identification has been made of mature oil source beds in the Los Angeles and San Joaquin Valley oil basins of California. The combined results of these studies provide strong evidence for the origin of petroleum from the organic matter of sediments.     

On the depth,time and mechanism of origin of the heavy to medium-gravity naphthenic crude oils

Paraffinic crude oils are designated ‘primary’ because their composition is very close or identical to that of the hydrocarbons extracted from the corresponding oil source rocks. Heavy and medium-gravity naphthenic crude oils, on the other hand, typically are quite different compositionally from hydrocarbon mixtures in either mature or immature shales.The normal paraffin carbon number odd/even ratio 2C₂₉/(C₂₈ + C₃₀) of all the heavy to medium-gravity crude oils which could be analysed are in exactly the same range as is observed for the primary paraffinic crude oils, namely 0.95–1.42. The naphthene indices of the medium to heavy gravity naphthenic crude oils and of the primary paraffinic crude oils from the same area are identical or close. These facts are significant because both the n-paraffin carbon number odd/even ratio and the naphthene index of shale hydrocarbons are strongly depth and subsurface temperature dependent. The facts observed demonstrate beyond question that, in the same area, the paraffinic precursors of the heavy to medium-gravity naphthenic crude oils are generated and expelled in the identical depth range, and from the same mature relatively deep oil source beds as the primary paraffinic crude oils. Later, during and/or after a generally upward migration into oil reservoirs, the primary crude may be transformed compositionally into a naphthenic crude oil.In none of the five widely scattered oil basins studied are medium to heavy naphthenic crude oils found at temperatures greater than a limiting subsurface temperature. The abruptness of the temperature cutoff of the change in oil compositions in all five oil basins, as well as the average value of the cutoff temperature of 66°C (150°F), leaves no doubt that the mechanism of this crude oil transformation process is microbial.Optical activity, which was observed in narrow saturate hydrocarbon fractions of the 80–325°C range of all microbially transformed crude oils, but not in the primary untransformed oils, is strong additional evidence for the microbial nature of the crude oil transformation process. The observed optical activity is explained by the microbial digestion at different rates of optical antipodes present in the primary paraffinic crude oils.To gain perspective the vast scale of the microbial oil transformation process in nature is pointed out. Billions of tons of heavy to medium-gravity naphthenic crude oils, originating from the microbial transformation of primary paraffinic oils, are present in oil fields and tar sands all over the world.