阜康典型荒漠C3植物稳定碳同位素值的环境分析

通过对阜康典型荒漠C3植物稳定碳同位素值的分析。叶片炭同位素值在-23‰和-29‰之间变化,其中主要在-27‰附近波动。这与前人报道的世界上其他地区荒漠植物碳同位素值的变化非常一致。降水可以改变叶片碳同位素值的大小,降水越多,叶片碳同位素值越负,它们的变化幅度有物种的依赖性。叶片碳同位素值也受植物生长形式或期望寿命的影响,木本植物或寿命长的植物叶片碳同位素值要高。分析表明,利用该区土壤或陆相沉积中有机质碳同位素值可以判断气候的干湿变化：土壤或陆相沉积中有机质碳同位素值越高,气候则越干燥。     

论大陆岩石圈形成过程中的克拉通化阶段

流体控制着地球系统中质量和能量的传输。流体岩石反应过程在岩石圈中是十分普遍的现象。在流体流动体系中 ,流体在岩石裂隙中通过平流、扩散、水动力弥散和动力学弥散等方式进行输运并与岩石发生同位素交换反应。文章首先对封闭体系、“封闭”体系、开放体系以及缓冲体系中的同位素交换模型进行了简单讨论 ,然后在讨论氧同位素动力学交换机制的基础上 ,建立了平衡交换模型和动力学交换模型。结合流体流动的归一化速率、弥散系数和流体岩石的反应速率等变量 ,对流体岩石交换反应的流体运动方程中的Peclet数和Damk¨ohler数进行了讨论 ,并详细解释了它们在流体岩石交换反应过程中的物理意义和地质用途。     

中东亚干旱半干旱区C3植物δ13 C值的分布 及其对气候的响应*

植物化石和土壤中的有机质碳同位素指标常用来反映古气候的变化,然而碳同位素这个指标在特定地区反映气候的定量关系缺乏检验。研究剖面选择自中国的秦岭(34°14'24″N,106°55'30″E)到蒙古人民共和国北部,接近贝加尔湖地区(51°35'08″N, 100°45'49″E)的研究剖面线,选择了3种C₃植物(Artemisia scoparia, Ajania achilleides 和 Artemisia frigida),在剖面线上沿南北方向上每隔4'到5'采取一个样点,共选取161个C₃植物茎叶样品进行了δ¹³ C值测定。同时收集了剖面线附近气象站的降水、气温等资料,用插值方法得到每个采样点的气温、降水数据。分析表明:C₃植物的δ¹³ C值分布范围为-30 ‰ ~-22 ‰ ,其平均值为-26.81 ‰ ,该平均值较全球C₃植物δ¹³ C平均值偏正。通过对比C₃植物δ¹³ C与年均温、年均降水量、生长季节的干燥度等随纬度的变化规律,发现C₃植物δ¹³ C、年均降水量、生长季节的干燥度有非常一致的变化趋势,而C₃植物δ¹³ C和年均温不具有一致性。通过一元回归分析也同样发现C₃植物δ¹³ C与年均降水量呈线性负相关关系(y=-0.0077x-24.838,n=161,R²=0.4418,p=0.01),与生长季节的干燥度呈线性正相关关系(y=0.7328x-28.806,n=161,R²=0.3685,p=0.01),而与年均温度没有明显的相关关系(y=-0.0461x-26.756,n=161,R²=0.0232,p=0.01)。在本研究区C₃植物δ¹³ C对年均降水量和生长季节的干燥度响应十分显著,而对温度的响应不明显。研究区具有明显的降水和温度的梯度分布特征,是验证植物碳同位素与气候关系的理想场所,而土壤中的有机质碳同位素与其地面上的植物碳同位素息息相关。研究也说明,在本研究区或其他气候植物组合相似的地区可以利用古土壤中的有机质碳同位素来定量或半定量地反映古气候的变化。     

云南巍山—永平碰撞造山带走滑拉分盆地铜金多金属矿成矿流体系统：稳定同位素特征及热液来源

云南巍山—永平矿集区位于兰坪走滑拉分盆地南段,有铜金多金属中、小型矿床及矿化点140余处,盆地发育和成矿作用与印度—亚洲板块碰撞密切相关。为了探索该矿集区成矿热液的来源,研究了该区成矿流体的稳定同位素特征。区内成矿流体系统可分为紫金山子系统与公郎弧子系统。公郎弧子系统内铜钴矿床成矿流体的δD为-83.8‰~-69‰,δ18O为4.17‰~10.45‰,δ13C为-13.6‰~3.7‰,成矿流体主要来源于岩浆水及地层水。紫金山子系统内金、铅锌、铁矿床成矿流体的δD为-117.4‰~-76‰,δ18O为5.32‰~9.56‰,δ13C为-10.07‰~-1.5‰;锑矿成矿流体的δD为-95‰~-78‰,δ18O为4.5‰~32.3‰,δ13C为-26.4‰~-1.9‰,成矿流体来源于地层水以及岩浆水。受印度板块与亚洲板块碰撞造山作用的影响,在该盆地内,成矿流体自南西向北东大规模迁移过程中,先形成温度、盐度较高的公郎弧子系统,随着流体向北东推进,温度、盐度逐渐降低,流体成分发生变化,演变为紫金山子系统。     

Age model, physical properties and paleoceanographic implications of the middle Pleistocene core sediments in the Choshi area, central Japan

Abstract   A continuous, well-preserved core was obtained from the Choshi area, on the Pacific side of Japan, to investigate paleoceanographic and paleoclimatic changes around the northwestern Pacific region during the middle Pleistocene. Siliciclastic sequences in the core are divided into five formations – the Obama, Yokone, Kurahashi and Toyosato Formations in the Inubo Group and the Katori Formation, in ascending order. Examination of calcareous nannofossils and magnetic polarities detected four datums in the core sediments of the Inubo Group: the top of Reticulofenestra asanoi , the base of Helicosphaera inversa , the top of Pseudoemiliania lacunosa and the Brunhes–Matuyama boundary. Fourteen marine isotope stages (MIS24–MIS11) were identified in the δ¹⁸O and δ¹³C records based on detected datums and the graphic correlation with the standard stack oxygen isotope curve. Magnetic susceptibility and gamma-ray attenuation porosity evaluator density were also measured and low values characterize the glacial intervals. Biogenic sedimentation by primary production may be larger during the glacial periods because of invasions of nutrient-rich northern surface-waters related to the southward shift of the Kuroshio front in the Choshi area.     

Organic facies and geochemical aspects in Neogene neritic sediments of the Takafu syncline area of central Japan: Paleoenvironmental and sedimentological reconstructions

Abstract Organic petrological observations of kerogen macerals and organic geochemical analyses of carbon isotopes of kerogen macerals and biomarkers were conducted on Neogene neritic sediments of the Takafu syncline area of central Japan. The Senmi, Sakainomiya and Lower Shigarami Formations in that area were deposited at the neritic provinces on the southern edge of the paleo‐Japan Sea during the Late Miocene to Early Pliocene. Sedimentary organic matter in these formations was almost terrigenous in origin. Changes in kerogen maceral compositions reflect sedimentological and tectonic histories evaluated in previous studies from sedimentary facies and paleontology. It was found that carbon isotope ratios (δ¹³C) of kerogen macerals increased from ?28‰ to ?25‰ from the Sakainomiya to the lower part of the Lower Shigarami Formations. The cause of that increase was presumably the expansion of C₄ plants into southwest Japan. The timing was concordant with that of the expansion of C₄ plant grasslands in East Asia. The oxicity (oxic to anoxic) conditions of sea bottoms evaluated from pristane/phytane ratios varied. Particularly, in the lower part of the Senmi Formation, layers in which no steroid biomarkers could be detected were found, and had presumably formed under oxic conditions when strong biodegradation had occurred. Concentrations of regular (C₂₇–C₂₉) steranes and dinosteranes were higher in the Sakainomiya and Lower Shigarami Formations. This indicates that dinoflagellates‐dominant primary productions were higher at those stages. In addition, concentrations of diatomaceous biomarkers such as C₂₆ norsterane increased from the Lower Shigarami Formation, thus adding diatoms to the major producers. Furthermore, similar associations between the increases of δ¹³C values of kerogen macerals and concentrations of diatomaceous biomarkers were observed in the Takafu syncline area. Thus, the expansion of C₄ plants was possibly associated with the high production of diatom in the shallow‐marine areas of the paleo‐Japan Sea during the Neogene Period.     

Lithological and physical properties of core samples from the Sagara oil field: Oil occurrence in Sagara core samples

Abstract   A drilling and coring investigation of the Sagara oil field, central Honshu, Japan, was conducted to contribute to the understanding of hydrocarbon migration processes in a forearc basin. Core samples were analyzed to determine lithology, physical properties (specifically gas permeability) and the characteristics of oil occurrence. Gas permeability values greater than approximately 10⁻¹¹ m² constitute the basic precondition for any lithology to serve as a potential fluid conduit or reservoir in the Sagara oil field. Cores recovered from the 200.6-m-deep borehole were primarily composed of alternating siltstone, sandstone and conglomerate, all of which are correlated to the late Miocene Sagara Group. Both sandstone and conglomerate can be classified into two types, carbonate-cemented and poorly to non-cemented, based on matrix material characteristics. Oil stains are generally absent in the former lithology and more common in the latter. Variations in physical properties with respect to gas permeability values are directly related to the presence and character of carbonate cement, with higher permeabilities common in poorly to non-cemented rocks. The relationships between lithology, oil-staining, cementation and permeability indicate that cementation preceded oil infiltration and that cementation processes exerted significant control on the evolution of the reservoir.     

扎龙湿地包气带土壤水分垂直运移的稳定同位素研究

实测了扎龙湿地包气带土壤水以及芦苇的稳定同位素变化,通过建立模型和分析数据展开了湿地包气带土壤垂向水流运动情况的同位素示踪研究,分层计算了土壤水垂直运移量,建立起时段内通过土壤某一水平断面的土壤水垂直运移量与时段降雨量、时段土壤含水量变化的关系,分析结果对确定湿地垂向水流补给有重要意义。     

In situ cosmogenic ~(10)Be dating of the Quaternary glaciations in the southern Shaluli Mountain on the Southeastern Tibetan Plateau

It is generally considered that four-times ice age happened during the Quaternary epoch on the Tibetan Plateau. However, the research on the chronology of the four-times ice age is far from enough. The Shaluli Mountain on the Southeastern Tibetan Plateau is an ideal place for plaeo-glacier study, because there are abundant Quaternary glacial remains there. This paper discusses the ages of the Quaternary glaciations, based on the exposure dating of roche moutonnée, moraines and gla- cial erosion surfaces using in situ cosmogenic isotopes 10Be. It is found that the exposure age of the roche moutonnée at Tuershan is 15 ka, corresponding to Stage 2 of the deep-sea oxygen isotope, suggesting that the roche moutonnée at Tuershan is formed in the last glacial maximum. The expo- sure age of glacial erosion surface at Laolinkou is 130―160 ka, corresponding to Stage 6 of the deep-sea oxygen isotope. The oldest end moraine at Kuzhaori may form at 421―766 kaBP, corre- sponding to Stages 12―18 of the deep-sea oxygen isotope. In accordance with the climate charac- teristic of stages 12,14,16 and 18 reflected by the deep-sea oxygen isotope, polar ice cores and loess sequence, the oldest end moraine at Kuzhaori may form at stage 12 or stage 16, the latter is more possible.     

Lithium isotope fractionation in the southern Cascadia subduction zone

We present lithium (Li) abundances and isotope compositions for a suite of anhydrous olivine tholeiites (HAOTs) and hydrous basalt-andesitic (BA) lavas from the Mt. Shasta and Medicine Lake regions, California. The values of δ⁷Li vary from + 0.9‰ to + 6.4‰ and correlate inversely with distance from the trench. These data are consistent with continuous isotope fractionation of Li during dehydration of the subducted oceanic lithosphere, an interpretation corroborated by uniformly high pre-eruptive H₂O contents in basaltic andesites accompanied by high Li, Rb, Sr, Ba and Pb abundances. The subduction-derived component that was added to these hydrous magmas is shown to be very similar beneath both Mt. Shasta and Medicine Lake volcanoes despite characteristically distinct Li isotope compositions in the magmas themselves. More evolved andesites and dacites from Mt. Shasta have δ⁷Li from + 2.8 to + 6.9‰ which is identical with the range obtained for HAOTs and BA lavas from Mt. Shasta. Therefore, Li isotopes do not provide evidence for any other crustal component admixed to Mt. Shasta andesites or dacites during magmatic differentiation and magma mixing in the crust.