Dating basal peat: The geochronology of peat initiation revisited     

《Quaternary Geochronology》2022

Attributing the start of peat growth to an absolute timescale requires dating the bottom of peat deposits overlying mineral sediment, often called the basal peat. Peat initiation is reflected in the stratigraphy as a gradual transition from mineral sediment to increasingly organic material, up to where it is called peat. So far, varying criteria have been used to define basal peat, resulting in divergent approaches to date peat initiation. The lack of a universally applicable and quantitative definition, combined with multiple concerns that have been raised previously regarding the radiocarbon dating of peat, may result in apparent ages that are either too old or too young for the timing of peat initiation. Here, we aim to formulate updated recommendations for dating peat initiation. We provide a conceptual framework that supports the use of the organic matter (OM) gradient for a quantitative and reproducible definition of the mineral-to-peat transition (i.e., the stratigraphical range reflecting the timespan of the peat initiation process) and the layer defined as basal peat (i.e., the stratigraphical layer that is defined as the bottom of a peat deposit). Selection of dating samples is often challenging due to poor preservation of plant macrofossils in basal peat, and the representativity of humic and humin dates for the age of basal peat is uncertain. We therefore analyse the mineral-to-peat transition based on three highly detailed sequences of radiocarbon dates, including dates of plant macrofossils and the humic and humin fractions obtained from bulk samples. Our case study peatland in the Netherlands currently harbours a bog vegetation, but biostratigraphical analyses show that during peat initiation the vegetation was mesotrophic. Results show that plant macrofossils provide the most accurate age in the mineral-to-peat transition and are therefore recommendable to use for ¹⁴C dating basal peat. If these are unattainable, the humic fraction provides the best alternative and is interpreted as a terminus-ante-quem for peat initiation. The potential large age difference between dates of plant macrofossils and humic or humin dates (up to ∼1700 years between macrofossil and humic ages, and with even larger differences for humins) suggests that studies reusing existing bulk dates of basal peat should take great care in data interpretation. The potentially long timespan of the peat initiation process (with medians of ∼1000, ∼1300 and ∼1500 years within our case study peatland) demonstrates that choices regarding sampling size and resolution need to be well substantiated. We summarise our findings as a set of recommendations for dating basal peats, and advocate the widespread use of OM determination to obtain a low-cost, quantitative and reproducible definition of basal peat that eases intercomparison of studies.  相似文献   

Inversion of fault data with low diversity for stress: Principles and applications     

《Journal of Structural Geology》2015

Although a minimum of four independent, single-phase fault data are required to solve for a unique reduced stress tensor, we prove in this paper that a smaller number of fault data are sufficient in some instances to solve for part of the reduced stress tensor. One of the principal stress directions is determinable from either two faults with a common null shear direction on the fault planes or three faults with a common intersection in a principal stress plane of the fault planes. This direction is combined with the fault data to determine the possible ranges of other principal stress directions. Determining whether the direction is for the maximum, intermediate or minimum principal stress depends upon constraints provided by slip tendency or more fault data. This approach can also be applied to a set of four or more fault data with low orientation diversity. This new method is finally applied to two different sets of fault data from along the active Chelungpu fault, western Taiwan. The stress orientations determined from the method lie in acceptable ranges for the maximum/minimum principal stresses using other existing and comparable methods, such as the right dihedra/trihedra methods. They differ moderately in the maximum/minimum principal stress directions when compared to the moment tensor method for fault kinematic analysis. The new method has advantages over the right dihedra/trihedra methods in the accuracy of stress estimate and the independence of stress estimate upon the small number of faults that are not parallel to the dominant fault set(s).  相似文献   

贵州麻江下司寒武系杷榔组棘皮动物 始海百合新类型化石   总被引：1，自引：0，他引：1       下载免费PDF全文

赵元龙  彭进  伍孟银  罗绣春  文荣琴  刘玉娟 《地球科学》2015,40(2):249-260

和凯里生物群一样,贵州寒武系杷榔动物群也含有丰富的棘皮动物始海百合化石,包括两个属种即俞氏贵州始海百合 GuizhoueocrinusyuiZhao,ParsleyetPeng,2007及殷氏原始球状始海百合(新属新种)Protogloboeocrinusyini(gen.etsp. nov.).其中新属种是近期在杷榔组分布区南部贵州麻江下司淑里村杷榔组上部发现的,是凯里组中球形球状始海百合(GloboeocrinusglobolusZhao, ParsleyetPeng,2008)的原始属种,两者均具有发育的吸盘、长的茎、近于球形或椭球形的萼及较长 的腕.但新属种茎呈倒长锥柱形,缝孔长卵形,腕枝数少,两者区别明显.Protogloboeocrinusyini(gen.etsp.nov.)的发现及研 究,不仅追溯到凯里组球形球状始海百合的原始属种,了解两者演化规律是茎变短,萼变球形,缝孔变为圆形,腕枝数量增加, 捕食能力增强.而且还增添了杷榔组始海百合的多样性及其分区性:杷榔组分布区北部仅见Guizhouocrinusyui,南部仅见 Protogloboeocrinusyini(gen.etsp.nov.)   相似文献   

滇池北岸大清河湿地景观植物配置研究     

肖雪缘  陈坦  李煜  樊国盛 《湿地科学与管理》2015,(1):8-12

通过对大清河湿地植物分层次的筛选,根据生态学、湿地学、植物学、美学相关理论,依据植物的生态习性及湿地的区域划分,将大清河湿地划分为深水区、浅水区、沼泽区、水边及岸带区和陆地区五大区域,并分层次进行相应的植物配置,提出挺水植物+浮水植物+沉水植物、挺水植物+浮水植物、挺水植物片植、单层乔木片植、草本+挺水植物、乔木+灌木+草本6种配置模式。  相似文献   

Determinants of crop diversity in the regions of Bangladesh (1990–2008)          下载免费PDF全文

Sanzidur Rahman  Mohammad Mizanul Haque Kazal 《Singapore journal of tropical geography》2015,36(1):83-97

The paper measures the level of crop diversity and identifies factors influencing diversification using a panel data of 17 regions of Bangladesh covering a 19 year period (1990–2008). Results revealed the trends that agricultural areas allocated to high‐yielding variety rice, spices and vegetables has increased, while areas cultivating traditional rice, minor cereals, oilseeds, pulses, jute and sugarcane has declined at variable rates across regions with significant differences. The level of crop diversity is also significantly different across regions and has decreased in 2008 from its 1990 level in most regions except Faridpur, Khulna and Sylhet. Among the determinants, an increase in the relative prices of vegetables and urea fertilizer, extension expenditure, labour stock per farm, average farm size, irrigation and a reduction in livestock per farm significantly increase crop diversity. Price policies to improve vegetable prices and investment in irrigation infrastructure and extension services are suggested to promote crop diversity in Bangladesh.  相似文献   

基于COI序列比较中国和科威特养殖鲳鱼群体的遗传差异     

孙鹏 《海洋科学》2015,39(1):53-58

为探讨中国和科威特鲳鱼(Pampus)养殖群体的遗传差异和遗传多样性,本研究对两个鲳鱼群体线粒体细胞色素c氧化酶I亚基(COI)部分序列进行了比较和分析。通过PCR扩增和测序,共获得COI基因片段47条,定义了8个单倍型。两个群体的COI序列的A+T含量均高于G+C含量,在中国养殖群体中检测到4个变异位点,在科威特群体中检测到14个。两个群体的单倍型多样性水平较高(0.566~0.643),但核苷酸多样性水平均较低(0.0022~0.0030)。NJ系统发生树和遗传距离分析结果表明中国和科威特养殖群体的遗传差异较大,高于种内差异水平,因此两个养殖群体并非同一种鲳属鱼类。  相似文献   

2010-2011年深圳湾浮游植物季节变化及其与环境因子关系   总被引：3，自引：0，他引：3  

袁超  徐宗军  张学雷 《海洋湖沼通报》2015,(1):112-120

2010-2011年对深圳湾水采浮游植物进行了4个航次的现场调查,共鉴定出浮游植物5门45属83种,硅藻门占总种数的83.1%,甲藻门占10.8%。种类组成以广温广盐种和暖水种为主,中肋骨条藻(skeletonema costatum)为该海域常年优势种。此次调查发现深圳湾海域浮游植物丰度年波动范围为9.63~19904.0×103/L,平均值为964.5×103/L表现为秋季最高,夏、冬季次之,春季最低。浮游植物多样性指数及均匀度指数偏低,群落结构单一,稳定性较差。春季由于受到深圳河与降水的影响,水采浮游植物丰度最低;秋季各个环境条件适宜,浮游植物丰度达到最大;冬季温度成为限制浮游植物生长的重要因子。  相似文献   

葡萄糖和盐度对卤虫生长、养殖系统生物絮团形成及其微生物多样性的影响   总被引：3，自引：0，他引：3  

王娇  马灌楠  邓元告  隋丽英 《海洋与湖沼》2015,46(2):372-380

在零换水卤虫养殖系统中,研究葡萄糖和盐度对卤虫Artemia franciscana生长、卤水中生物絮团形成、水质及其微生物多样性的影响。实验设四组,每组三个平行,分别在盐度为50、100和150的养殖水体中添加葡萄糖(添加量随着卤虫的生长逐渐增加从每天12mg/L到37mg/L),对照组盐度为50且不添加葡萄糖。单位养殖水体为1L,卤虫起始密度约为1200ind/L,投喂浓缩杜氏藻Dunaliella viridis,养殖周期为20天。结果显示,添加葡萄糖可以显著提高生物絮团体积,降低水中的铵盐、亚硝酸盐、硝酸盐和总氮水平,提高卤虫总生物量(P0.05)。但随着盐度升高,卤虫生物量显著降低(P0.05),亚硝酸盐和总氮水平显著升高(P0.05),絮团体积有所升高。另外,葡萄糖添加和盐度对卤虫粗蛋白和脂肪酸含量无显著影响(P0.05)。PCR-DGGE分析表明,γ-变形菌纲(γ-proteobacterium)为生物絮团中优势菌群且以海洋细菌为主。与对照组相比,添加葡萄糖和升高盐度显著降低菌群丰富度指数(P0.05),环境承载力下降。本研究结果为高盐环境条件下生物絮团的形成机理及其在卤虫人工养殖中的应用提供了参考。  相似文献   

添加碳源和不同盐度对卤虫生长、养殖系统生物絮团形成及其微生物多样性的影响     

王娇  马灌楠  邓元告  隋丽英 《海洋与湖沼》2015,46(2)

在零换水卤虫养殖系统中,研究碳源添加和不同盐度对卤虫生长、卤水中生物絮团形成、水质及其微生物多样性的影响。实验设四组,每组三个平行,分别在盐度为50、100和150的养殖水体中添加葡萄糖,对照组盐度为50且不添加碳源。单位养殖水体为1L,卤虫起始密度约为1200个/L,投喂浓缩杜氏藻,养殖周期为2周。结果显示,添加葡萄糖显著提高生物絮团体积,降低水中的铵盐、亚硝酸盐、硝酸盐和总氮水平,提高卤虫总生物量(P<0.05)。盐度升高,卤虫生物量显著降低(P<0.05),亚硝酸盐和总氮水平显著升高(P<0.05),絮团体积有所升高。添加葡萄糖和不同盐度对卤虫粗蛋白和脂肪酸含量无显著影响(P>0.05)。PCR-DGGE分析表明,γ-变形菌纲为生物絮团中优势菌群且以海洋细菌为主。与对照组相比,添加葡萄糖和升高盐度显著降低菌群丰富度指数(Rr) (P<0.05),环境承载力下降。本研究结果为高盐环境条件下生物絮团的形成机理及其在卤虫人工养殖中的应用提供了参考。  相似文献   

基于线粒体COI 序列的洪泽湖河蚬(Corbicula fluminea)遗传多样性和种群结构分析     

李大命  张彤晴  唐晟凯  钟立强  刘小维 《海洋与湖沼》2015,46(6):1339-1346

为研究洪泽湖河蚬种群遗传多样性及其遗传结构, 采用线粒体细胞色素氧化酶Ⅰ基因(COI) 作为分子标记, 采用PCR 扩增洪泽湖4 个河蚬群体(顾勒河GLH、临淮LH、蒋坝JB 和高良涧GLJ) 的COI 基因片段并进行了序列测定和分析。结果表明, 614bp 长度的核苷酸片段中, 碱基A+T 的平 均含量为65.0%, 明显高于G+C 的含量(35.0%).共检测到73 个多态位点, 多态位点比例为11.9%, 77 个个体中共获22 个单倍型(GenBank 登录号: KM659000-KM659021), 其中包括3 个共享单倍型, 4 个群体的平均单倍型多样性指数h 为0.889, 平均核苷酸多样性指数π 为0.04499, 平均核苷酸差异 数K 为27.622, 其中蒋坝群体的遗传多样性最高, 顾勒河群体的遗传多样性最低。22 个单倍型间的 Kimura 2-paramter 遗传距离为0.002-0.100, 平均遗传距离为0.0514.NJ 法构建的分子系统树显示 22 个单倍型聚为2 个分支。4 个群体间的遗传距离达0.03729-0.04969, 基于群体间遗传距离构建的 NJ 系统树中, 高良涧群体和顾勒河群体聚为一支, 蒋坝群体和临淮群体聚集为一支。AMOVA 分析 表明, 洪泽湖河蚬四群体间总遗传分化系数F_st 为0.06325(P>0.05), 93.67%遗传变异存在于群体内部, 6.33%变异存在于群体间。中性检验结果和歧点分布图显示, 洪泽湖河蚬种群大小保持稳定, 未经历 明显的种群扩张。  相似文献