论四川盆地下、中三叠统蒸发岩的生成模式、成盐机理及找钾展望

四川盆地早中三叠统蒸发岩极为发育,时空分布甚广。蒸发岩的生成模式可分为两大类和四个亚类。即Ⅰ,潮间环境的为(1)泻湖盐湖;Ⅱ,潮上环境的为(2)滨海盐湖;(3)近岸盐湖和(4)远岸盐湖。不同生成模式中,其成盐机理虽对成钾皆不够理想,但仍有希望找到钾盐矿的地区和层段。     

四川盆地下中三叠统盐系地层古地磁研究与成盐条件有关问题探讨

四川盆地下中三叠统嘉陵江组—雷口坡组(T1j-T2L)盐系地层蒸发岩发育,是我国海相碳酸盐岩沉积区探盐找钾的重要地区层位。现通过四川盆地下中三叠统盐系地层古地磁样品的系统采集和测试工作,首次在我国建立了古地磁磁性地层剖面,并根据测定结果,结合地质资料,探索了四川盆地下中三叠统(T1j-T2L)成盐古气候条件及其时代归属等有关问题。     

四川盆地下中三叠统异常水点水化学特征及探盐找钾预测研究

四川盆地下中三叠统盐卤分布广泛,是四川探盐找钾的重要时代。通过区域地质背景条件分析,其盐类保存、水动力条件和水化学特征在不同水文地质区表现不一,反映在储层的水型也极不一致,按水中阴、阳离子优势组分异常水点分为SO4-Ca、SO4-Na和Cl-Na3种类型。利用异常水点离子的比例系数在海水浓缩曲线图上的落点位置,判别水点成因类型,从而发现盆地东北部宣汉、盆地西部平落和盆地东部万县向斜周边背斜水点具含钾溶滤水特征,值得重视和进一步开展找钾探索。     

川东地区嘉陵江组四段膏盐岩分布的沉积环境分析

四川盆地东部地区嘉陵江组嘉四段沉积环境是局限海台地蒸发岩相,水体封闭,有利成盐。以川东地区油气勘探的500余口实际钻井资料为基础,通过岩性微相的研究,探讨川东地区的古地貌特征,寻找成盐的微环境因素,有助于从区域上预测盐类的分布。T1j4盐湖主要分布在蒸发岩沉积中心——膏盆相,但位于膏盆相的周缘地带和膏盆内部堤坝周围,少部分分布在膏盆边缘相,区域上则主要分布在宣汉、达州、万县、云阳、垫江及渠县等地区,有一定的继承性。     

Chemical weathering and CO2 consumption in the Xijiang River basin, South China

Monthly samples of riverine water were collected and analyzed for the concentrations of major ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, HCO₃⁻, SO₄²⁻, Cl⁻, NO₃⁻), dissolved silicon, and total dissolved solids (TDS) at Wuzhou hydrological station located between the middle and lower reaches of the Xijiang River (XJR) from March 2005 to April 2006. More frequent sampling and analysis were carried out during the catastrophic flooding in June 2005. Stoichiometric analysis was applied for tracing sources of major ions and estimating CO₂ consumption from the chemical weathering of rocks. The results demonstrate that the chemical weathering of carbonate and silicate rocks within the drainage basin is the main source of the dissolved chemical substances in the XJR. Some 81.20% of the riverine cations originated from the chemical weathering processes induced by carbonic acid, 11.32% by sulfuric acid, and the other 7.48% from the dissolution of gypsum and precipitates of sea salts within the drainage basin. The CO₂ flux consumed by the rock chemical weathering within the XJR basin is 2.37 × 10¹¹ mol y^− 1, of which 0.64 × 10¹¹ mol y^− 1 results from silicate rock chemical weathering, and 1.73 × 10¹¹ mol y^− 1 results from carbonate rock chemical weathering. The CO₂ consumption comprises 0.38 × 10¹¹ mol during the 9-d catastrophic flooding. The CO₂ consumption from rock chemical weathering in humid subtropical zones regulates atmospheric CO₂ level and constitutes a significant part of the global carbon budget. The carbon sink potential of rock chemical weathering processes in the humid subtropical zones deserves extra attention.     

Influence of understory removal, thinning and P fertilization on N2fixation in a mature mesquite (Prosopis glandulosavar.glandulosa) stand

The natural abundance¹⁵N/¹⁴N method was used to estimate the influence of silvicultural and P fertilization treatments on N accretion, N₂fixation and N partitioning among tissues in a mature mesquiteProsopis glandulosavar.glandulosastand in Texas. The silvicultural treatments consisted of understory removal, herbicide treatment of brushy resprouts, thinning trees to single stems and 100 kg ha⁻¹P fertilization. The trees had a mean basal diameter of 17·8 cm with 8 to 35 cm range. The stand was slow growing with the increase in dry matter ranging from 0·465 Mg ha⁻¹year⁻¹to 0·701 Mg ha⁻¹year⁻¹for the 8 years after the treatments were applied. N accretion after 8 years ranged from 3·1 kg ha⁻¹year⁻¹to 4·4 kg ha⁻¹year⁻¹.Due to the range in δ¹⁵N of the leaves, twigs, branches and trunk, we used the weighted (by biomass) average δ¹⁵N per tree in calculations of the percent N derived from N₂fixation (%Ndfa). There was considerable variability in δ¹⁵N of the reference plants, i.e. from 3·3 to 5·9. In contrast there was low variability in the background δ¹⁵N of nearby soils (7·0±1·0). As the total above-ground biomass δ¹⁵N of a grass grown outside the influence of mesquite (7·8±0·58) had the same δ¹⁵N as the soil (7·5±1·0), we used the grass outside the influence of mesquite and the weighted tree mean δ¹⁵N to calculate % of N derived from N₂fixation.The decrease in intraspecific competition by thinning multistemed trees to single stemmed trees was the only treatment that significantly (p= 0·0001) increased growth. Interspecific competition, i.e. understory removal, did not increase growth. There were no significant differences in total N production or N fixation among treatment means. The most striking result was the highly positive correlation between tree δ¹⁵N and total N per tree and biomass per tree (R²= 0·90,F= 164·4, df. = 18, mean square error (MSE) = 0·155,p= 0·0001). This implies that the younger trees colonizing infertile soils relied more heavily on N₂fixation than larger trees which accumulated 1200 kg ha⁻¹more N under their canopies. The percentage N derived from N₂fixation ranged from 63 to 73% in the various treatments. Despite the high percentage of N derived from N₂fixation, the N₂fixation of the stand was very low, i.e. 1·98 to 2·80 kg N ha⁻¹year⁻¹, due to the low growth of the stand. We believe that comparisons of the whole tree weighted δ¹⁵N to background soil δ¹⁵N provides a more reasonable approach to estimate % N₂fixation than comparisons of leaves of fixers and reference plants.