基于可容纳空间变化的河流相演化新模式及其控藏作用——以莱州湾凹陷垦利A构造为例

为了厘清莱州湾凹陷馆陶组油气差异成藏机理，应用层序地层学原理，结合岩心、钻井、测井、地震等资料，对莱州湾凹陷垦利A构造馆陶组沉积期的沉积基准面及可容纳空间变化规律进行研究，建立了层序地层格架与河流相沉积演化模式，分析了河流相储层的控藏作用。结果表明：①馆陶组作为三级层序，内部可划分为3个体系域，由早期高可容纳空间体系域、低可容纳空间体系域和晚期高可容纳空间体系域构成。②馆陶组发育网状河、辫状河和曲流河3种河流相类型，受不同体系域的影响，三者在纵向上不断演化，导致储层垂向相变以及平面差异分布较为明显。③不同河流相的差异性决定了不同的油藏特征，早期发育的网状河储层侧向上相互切割拼接，垂向上存在稳定的泥岩夹层，导致横向连通性较好、垂向连通性较差，形成岩性-构造油藏；中期发育的辫状河储层在侧向和垂向上往复切割、相互叠置，侧向与垂向连通性均较好，形成构造-层状油藏；晚期发育的曲流河储层受大套泥岩隔层阻隔，侧向及垂向连通性均较差，形成孤立的岩性油藏。以上认识可为研究区的下一步勘探评价提供新的依据。     

埕岛地区中浅层河流相砂体输导性研究——以渤海海域埕岛地区新近系为例

河流相砂体是埕岛地区中浅层主要的油气输导层和储集层,研究其输导性对油气勘探具有重要意义。研究认为,断层相连是中浅层河流相砂体输导油气的前提,构造背景影响着油气输导方向;河道沉积砂体输导性最好,堤岸沉积砂体次之,泛滥平原沉积的砂体最差。不同岩性中细砂岩输导性最好,中砂岩次之,粉砂岩第三;输导砂体物性下限随着埋深增加而减少;砂体连通性越好,输导性越好。根据砂体宏观连通基本类型,建立了厚砂体直接连通型、微断层连通型和薄砂体或物性较差砂体连通型三种输导模式,并提出中浅层河流相砂体输导性的评价思路。     

阵发性洪水控制的河流型冲积扇沉积特征及沉积演化模式——以和什托洛盖盆地北缘现代白杨冲积扇为例

冲积扇由于其成因机制和控制因素极其复杂而难以用统一的沉积模式来表征其内部结构，因此需针对特定地质条件下的扇体分析沉积特征及建立演化模式。以和什托洛盖盆地北缘现代白杨冲积扇为例，通过对其各部位露头剖面的精细解剖及测量，并结合卫星图像及区域地质资料等，对干旱气候条件下受阵发性洪水控制的河流型冲积扇扇体的岩相特征、微相类型及其展布进行研究，并在此基础上建立了沉积模式，分析了沉积演化的控制因素。研究表明：白杨冲积扇建造过程可划分为洪水期、洪退期及间洪期3个期次，而扇体以洪水期厚层粗粒的席状化流体建造为主。洪水期自扇根到扇缘发育下切洪流微相、片流微相及非限制性洪流微相，同时在扇缘出现扇面水洼微相，且扇体周缘可发育饱水湿地。洪退期，扇体发育砾质/砂质带状河道微相，并可形成分流河道体系，但随着洪退过程的持续，分流河道数目及规模不断减小。间洪期，整个扇体以扇面改造再沉积作用为主，包括侵蚀滞留砾石层微相、风成砂微相、流沟微相及河流阶地微相，这一阶段扇体可完全废弃也可转变为河流沉积。各演化阶段洪水流体的性质及沉积微相的转变或扇体的建造/废弃均受控于阵发性洪水过程中洪水流量及沉积物负载量的变化。     

陆相含油气盆地沉积体系再思考:来自分支河流体系的启示

通过分析分支河流体系的基本特征，对分支河流体系在陆相含油气沉积盆地沉积体系研究和油气勘探中的意义进行分析和讨论。分支河流体系是指河流从某一顶点开始进入盆地并呈放射状展布的沉积体系，包括最大规模的巨型扇、中等规模的河流扇以及小规模的冲积扇。分支河流体系广泛发育在拉张、挤压、走滑和克拉通盆地中，占据了沉积盆地大部分地区；河道呈分支状分布，但不一定同时都在活动；河道规模向下游逐渐减小，泛滥平原和河道所占面积之比不断增加，沉积物粒度逐渐变细。分支河流体系的沉积模式与冲积扇模式外形相似，但内容相差很大。河流流域盆地梯度和流域面积与分支河流体系的表面坡降和面积具有正相关性。分支河流体系是随着现代地球信息技术发展而提出的，也是冲积扇沉积学、河流沉积学和陆相沉积体系研究不断深入的结果，是陆相盆地沉积学与现代计算机和地理信息技术融合发展的结果。分支河流体系的研究促进了扇状沉积体系分类描述的系统化，促进了沉积微相和沉积模式的多样化，促进了沉积过程响应解释的精细化，促进了源汇体系分析的定量化。分支河流体系启发了对陆相盆地沉积体系展布模式、陆相沉积体系中河流沉积作用、陆相盆地岩相古地理格局以及陆相盆地油气勘探潜力的再思考。研究分支河流体系对完善中国陆相沉积储层地质理论体系具有重要意义。     

Environmental factors controlling phytoplankton dynamics in a large floodplain river with emphasis on cyanobacteria

Harmful algal blooms are occurring in large river ecosystems and at the mouth of large rivers with increasing frequency. In lentic systems, the chemical and physical conditions that promote harmful algal blooms are somewhat predictable but tracking prevalence and conditions that promote harmful algal blooms in lotic systems is much more difficult. We captured two of the most extreme discharge years within the last 20 years occurring in the Upper Mississippi River, allowing a natural experiment that evaluated how major shifts in discharge drive environmental variation and associated shifts in phytoplankton. Statistical models describing significant environmental covariates for phytoplankton assemblages and specific taxa were developed and used to identify management‐relevant numeric breakpoints at which environmental variables may promote the growth of specific phytoplankton and/or cyanobacteria. Our analyses supported that potentially toxin‐producing cyanobacteria dominate under high phosphorus concentration, low nitrogen concentration, low nitrogen‐to‐phosphorus ratio, low turbulence, low flushing, adequate light and warm temperatures. Cyanobacteria dominated in 2009 when low discharge and low flushing likely led to optimal growth environments for Dolichospermum, Aphanizomenon and Microcystis. Rarely will a single factor lead to the dominance, but multiple positive factors working in concert can lead to cyanobacteria proliferation in large rivers. Certain isolated backwaters with high phosphorus, low nitrogen, warm water temperatures and low potential for flushing could benefit from increased connection to channel inputs to reduce cyanobacterial dominance. Numerous examples of this type of habitat currently exist in the Upper Mississippi River and could benefit from reconnection to channel habitats.     

The impact of geological uncertainty on primary production from a fluvial reservoir

Deposition of fluvial sandbodies is controlled mainly by characteristics of the system, such as the rate of avulsion and aggradation of the fluvial channels and their geometry. The impact and the interaction of these parameters have not received adequate attention. In this paper, the impact of geological uncertainty resulting from the interpretation of the fluvial geometry, maximum depth of channels, and their avulsion rates on primary production is studied for fluvial reservoirs. Several meandering reservoirs were generated using a process-mimicking package by varying several controlling factors. Simulation results indicate that geometrical parameters of the fluvial channels impact cumulative production during primary production more significantly than their avulsion rate. The most significant factor appears to be the maximum depth of fluvial channels. The overall net-to-gross ratio is closely correlated with the cumulative oil production of the field, but cumulative production values for individual wells do not appear to be correlated with the local net-to-gross ratio calculated in the vicinity of each well. Connectedness of the sandbodies to each well, defined based on the minimum time-of-flight from each block to the well, appears to be a more reliable indicator of well-scale production.     

A preliminary modeling analysis of water quality in Lake Okeechobee, Florida: Calibration results

To gain understanding of nutrient and phytoplankton dynamics in Lake Okeechobee, Florida, we developed and applied a deterministic, mass balance, water quality model at the whole-lake spatial scale. The model was calibrated to a comprehensive set of field data for 1985–1986, and then used to simulate the period 1973–1992. The model represented the mean behavior of in-lake total phosphorus, dissolved available phosphorus, total nitrogen and chlorophyll a concentrations reasonably well during the calibration period. The model did not represent dissolved available nitrogen concentrations very well, nor did it capture much of the observed temporal variability during the calibration period. The model results identified important information needs to improve our understanding of the nitrogen cycle including, sediment-water nitrogen fluxes, denitrification and nitrogen fixation. Results from the 1973–1992 simulation indicated that model assumptions and/or calibration parameters were not uniformly applicable over this period. Total phosphorus concentration results from this model were compared with results from two site-specific, empirical loading models for the lake. None of these models represented annual average concentrations uniformly well over the entire 20-year period, and none captured much of the observed inter-annual variability. External total phosphorus loadings and lake hydrology are not sufficient to fully describe total phosphorus dynamics in Lake Okeechobee. Other important factors are diffusive sediment-water fluxes, wind-induced sediment resuspension, and the spatial heterogeneity in the lake.     

Phytoplankton in a polluted subarctic lake before and after nutrient reduction

Phytoplankton and water chemistry were studied in a eutrophic subarctic Swedish lake before and after nutrient reduction. Pollution started in 1964 and the lake had received about 4.5 tons of phosphorus by the time the treatment plant was built in 1974. After that only 18–20 kg P yr^?1 entered the lake. Before nutrient reduction the phytoplankton consisted principally of three species, Dictyosphaerium pulchellum var. minutum, Chromulina cv. darlecarlica and Cryptomonas cv. ovata. Two years after the P-load was reduced Chlamydomonas spp and Mallomonas akrokomos predominated in the plankton and their dominance has been maintained during the period of study. Seasonal average phytoplankton biomass decreased from 11.2 g m^?3 in 1973 to 2.9 g m^?3 in 1980. Average seasonal total phosphorus concentrations decreased from 168 μgl^?1 in 1973 to 74 μgl^?1 in 1980. Average Secchi depth readings increased from 1.3 m in 1973 to 2.1 m in 1980. Blue-green algae never had any quantitative importance in the lake and no blooms were observed.     

长江陆溪口水道航道整治方案研究

陆溪口水道是长江中游的重点浅水道之一,由于汊道的兴衰交替,航槽也相应变迁,另外由于直港进口、中港汊道中部及出口处碍航浅滩的存在,导致航道维护困难。根据河床演变特点,确定稳定洲滩、增加直港进口分流、改善直港航行条件的工程措施。近十年河势相对稳定,但中港仍在持续弯曲发展,应抓住有利时机对该水道加以整治。     

Changes in phytoplankton composition in a Mediterranean coastal lagoon in the Cullera Estany (Comunitat Valenciana,Spain)

The Cullera Estany is a coastal lagoon located in a highly intensified agriculture and tourist area in Valencia. This coastal lagoon has connections with the sea that produce marine intrusion and generate a freshwater interface. Four sampling campaigns were carried out during 2010 in order to analyse the phytoplankton composition and its relation to nutrient content through a Redundancy Analysis. Temperature, dissolved oxygen, nitrite and salinity are the main factors controlling the dynamics of phytoplankton community. During July and October, there is water column stratification; meanwhile in March, there is a well‐mixed water column. In addition, in May and July campaigns, hypoxia/anoxia conditions are detected at the bottom. The most abundant phytoplankton groups are Diatoms and Cryptophyceae. Diatoms and Cyanophyceae respond positively to temperature while Cryptophyceae, Prasinophyceae and Dinophyceae respond to high salinity and dissolved oxygen values. Furthermore, picoplankton is correlated inversely with nutrient concentrations.