Provenance of LGM glacial till (sand fraction) across the Ross embayment,Antarctica

The provenance of Late Quaternary Ross Embayment till was investigated by comparing the coarse sand composition of East and West Antarctic source area tills with till samples from across the Ross Sea. The West Antarctic samples from beneath the Whillans (B) and Kamb (C) ice streams are petrologically distinct from samples of lateral moraines flanking several East Antarctic outlet glaciers. The characteristic assemblage of four West Antarctic samples includes felsic intrusive and detrital sedimentary lithic fragments, plagioclase and abundant quartz. In contrast, most of the ten East Antarctic till samples contains abundant mafic intrusive and detrital sedimentary lithic fragments as well as less abundant quartz. The distinctive composition of these source areas can be linked to 33 samples from 20 cores of Last Glacial Maximum (LGM) age till distributed across the Ross Sea. Western Ross Sea till samples exhibit mineralogic and lithological similarities to East Antarctic till samples, although these western Ross Sea tills contain higher percentages of felsic intrusive and extrusive lithic fragments. Eastern Ross Sea till samples are compositionally similar to West Antarctic till, particularly in their abundance of quartz and dearth of mafic and extrusive lithic components. Central Ross Sea till exhibits compositional similarities to both East and West Antarctic source terranes including a mafic lithic component, and marks the confluence of ice draining from East and West Antarctica during the LGM, thus West Antarctic-derived ice streams did not advance into the western Ross Sea. This indicates that even if pre-LGM equivalents of the present Siple Coast ice streams existed, they did not simply expand allowing West Antarctic-derived ice to dominate the LGM Ross Ice Sheet.     

Till studies and neotectonics in northwest Skiine, south Sweden

A mosaic distribution of Pre-Quatcrnary rocks in Skåne constitutes good conditions for using gravel analysis in till-stratigraphical work. Recently discovered neotcctonic movements and their effect on the composition, distribution, and correlation of tills are discussed. With examples from the Kullen arm, it is shown that compositional variability in a till bed, as cvidenl from gt-avel analysis, can be deciphered and is of great stratigraphical value.     

烃源岩生排烃组分法模型研究与应用

本文提出了一种新的烃源岩生排烃组分法模拟模型。组分法生烃模型根据热模拟实验得到的组分产率曲线模拟烃源的生烃史。排烃模型包括开放体系模型和间歇开放体系模型，分别用于模拟以压实作用为主要动力的孔隙排烃和以异常高压为主要动力的微裂缝排烃。这一模型根据孔隙温度、压力和烃类组成，采用热力学方法模拟孔隙体系流体体积和相态的变化、不同组分在各相中的分布，并由此求出各组分的排出量和总排烃量。对陕甘宁盆地古生界源岩生排烃史的模拟结果表明，该模型具有实用价值。     

Grain-size distribution and grain-size parameters of different till types on Hardangervidda, south Norway

Vorren, T. O. 1977 06 01: Grain-size distribution and grain-size parameters of differcnt till type on Hardangervidda, south Norway.
Grain-size characteristics for different till types on Hardangervidda havc been studied: Basal tills are finer grained than ablation tills: phyllitic basal tills are relatively rich in gravel and clay: basal tills derived from a semiporphyritic granite are poor in clay and have a deficiency of very coarse sand. Of the Folk a Ward's (1957) grain-size distribution parameters, sorting and kurtosis seem to he the most diagnostic parameters for distinguishing between different types of till. A linear corrclation betwen sorting and the other grain-size parameters is indicated for the basal tills.     

Lead isotope variability in olivine-hosted melt inclusions from Iceland

The lead isotope and trace element compositions of a suite of olivine-hosted melt inclusions in primitive lava flows from the Reykjanes Peninsula in Iceland show extreme variability. Much of this variability is present in the composition of inclusions from one hand specimen of Háleyjabunga, a depleted picrite lava shield that erupted 13 ka. ²⁰⁸Pb/²⁰⁶Pb compositions in this sample span 50-90% of the total range found in Atlantic MORB, indicating that high-amplitude compositional heterogeneity is present in the mantle source of melts that aggregated to form a single eruption. The trace element and isotopic trends in the melt inclusions are coincident with those in whole rock samples from young lava flows of the Reykjanes Peninsula, and extend the total range of variation towards more depleted compositions. The incompatible trace element and lead isotope compositions of the inclusions are strongly coupled and lie close to binary mixing trends between the extreme melt inclusion compositions. These relationships indicate that the trace element variation in the melt inclusions reflects heterogeneity in the composition of the mantle source entering the melting region under the Reykjanes Peninsula. Large positive Sr concentration anomalies are present in three of the inclusions, but do not correlate with indicators of mantle melting or source variations and are likely to arise by reaction with plagioclase during crustal storage. Fractional melting of heterogeneous mantle is predicted to generate melts with a wide range of compositions, filling a large volume in trace element-isotope space. However, the compositional variations observed in the melt inclusions lie close to binary mixing curves. These observations may be accounted for by a two-stage model of melt mixing. The first stage occurs in porous channels that transport melt in the mantle and takes place before inclusion entrapment. This mixing stage generates a bimodal distribution of melt compositions that is supplied from the channels to sub-Moho and lower crustal magma lenses. The second stage of mixing occurs in these chambers, producing the binary mixing trends recorded in the inclusion compositions. The distribution of isotopic compositions observed in the melt inclusions and whole rock samples from the Reykjanes Peninsula is therefore controlled by melt mixing. These results have important implications for the interpretation of basalt composition in terms of distinct compositional entities within the upwelling solid mantle under mid-ocean ridges and ocean islands.     

Enrichments of the mantle sources beneath the Southern Volcanic Zone (Andes) by fluids and melts derived from abraded upper continental crust

Mafic basaltic-andesitic volcanic rocks from the Andean Southern Volcanic Zone (SVZ) exhibit a northward increase in crustal components in primitive arc magmas from the Central through the Transitional and Northern SVZ segments. New elemental and Sr–Nd-high-precision Pb isotope data from the Quaternary arc volcanic centres of Maipo (NSVZ) and Infernillo and Laguna del Maule (TSVZ) are argued to reflect mainly their mantle source and its melting. For the C-T-NSVZ, we identify two types of source enrichment: one, represented by Antuco in CSVZ, but also present northward along the arc, was dominated by fluids which enriched a pre-metasomatic South Atlantic depleted MORB mantle type asthenosphere. The second enrichment was by melts having the characteristics of upper continental crust (UCC), distinctly different from Chile trench sediments. We suggest that granitic rocks entered the source mantle by means of subduction erosion in response to the northward increasingly strong coupling of the converging plates. Both types of enrichment had the same Pb isotope composition in the TSVZ with no significant component derived from the subducting oceanic crust. Pb–Sr–Nd isotopes indicate a major crustal compositional change at the southern end of the NSVZ. Modelling suggests addition of around 2 % UCC for Infernillo and 5 % for Maipo.     

The garnets in kimberlite and in the associated griquaite and ultramafic nodules

The mineralogy, chemistry and occurrence of the garnets in kimberlite and in the associated griquaite and ultramafic nodules have been investigated. It was found that the garnets in the ultramafic nodules have a composition similar to those in kimberlites. On the other hand, the garnets in the griquaite nodules have a completely different chemical composition from the former ones, and become extremely enriched in grossular in the grospydite and kyanite griquaite nodules.The O'Hara and Yoder hypothesis (1967) for the genesis of kimberlite seems to be in conflict with these findings. The distribution of diamonds in the different types of kimberlites and nodules, which have been investigated, also appears to contradict the above hypothesis.An alternative hypothesis, which considers the griquaite as the source material and the ultramafic nodules as the cumulus phases during the genesis of kimberlites, appears to be more feasible in the light of the present investigation. It is shown that the objections raised against eclogite as source material (Rickwood et al., 1968, p. 298) can be accommodated by considering the kyanite griquaite and grospydite nodules as residual fractions, derived from the partial melting of the griquaite parent. This model is used to explain the distribution of the diamonds, garnets and the different types of nodules in the different types of kimberlites.     

Distribution and type of sticky spots at the centre of a deglacial streamlined lobe in northeastern Manitoba,Canada

The distribution of basal drag zones (sticky spots) underneath palaeo‐ice streams or lobes is largely unknown. We investigated the centre of the large (300 km long and up to 400 km wide) deglacial Hayes Lobe in NE Manitoba, Canada, by focusing on surficial till and its composition to get insights into dispersal patterns and their potential relationships to areas of basal drag. Subglacial bed roughness is a good criterion to identify areas of basal drag, but till composition may provide important insights across smoother beds. The onset zone of the Hayes Lobe overlies Palaeozoic Carbonate Platform rocks, whereas the majority of the lobe overlies the low‐lying Canadian Shield. We show that, within a 3500‐km² central area of this lobe, calcareous detritus within the till has been transported over 100 km within subglacial environments of reduced ice‐bed coupling and fast ice flow. Six per cent of samples (n = 782), however, outline 0.2 to 4 km wide spots with a dominantly local composition. The glacial history and composition indicate that the till within these spots contains high inheritance from a pre‐Late Wisconsinan ice‐flow phase, which we suggest was protected beneath sticky spots (low erosion, high strength) during transport of substantial calcareous detritus to the area. Furthermore, our findings show that local till spots are present within streamlined landforms, as well as till blankets or veneers over bedrock. This diverse geomorphology indicates that the process of drumlinization within the deglacial Hayes Lobe does not appear to have been responsible for significant sediment transport or deposition across the study area. The overall record thus indicates potentially complex spatiotemporal shifts between calcareous till deposition, sticky conditions, erosion and drumlinization – which supports the subglacial bed mosaic model.     

简论中国层控铜铅锌矿床的稳定同位素地球化学特征

摘要：层控矿床是构造运动、岩浆活动和沉积作用的综合产物,按其大地构造环境和沉积建造可划分为４大类、１３个亚类。层控矿床的稳定同位素组成按这一分类呈明显的规律性。不同建造中硫化物的硫同位素组成与其来源有关,并随后期叠加改造作用的增强而趋于均一。铅同位素组成反映了时代由老变新,由正常铅－混合铅－异常铅的演化规律,μ值也有增大的趋势,由幔源铅逐渐向壳幔混合型过渡。其含矿流体氢、氧同位素组成为建造水,显示了岩浆水与大气降水的混合,在不同建造类型中存在着较大差异,并随后期叠加改造作用的增强向混合含矿流体方向演化。总之,层控矿床的稳定同位素组成,其背景值反映了原始沉积环境,并明显地受沉积建造类型控制,后期叠加改造作用也可造成同位素组成的不同程度的变化。     

Sedimentary characteristics of suspensions in London Stormwater

The paper reports the results of an investigation into the size and compositional variations of suspended solids during storm-runoff events in an urban catchment. Particle-size analysis indicates that the mass-size distribution for suspended sediments is typically bimodal, although the relative size, breadth and location of the peaks varies through the cycle and from one storm to another. The importance of particle aggregation on the size distributions is discussed and the role of organic particulates in this relation examined. The elemental composition is dominated by silicon and aluminium with the mineralogy being dominated by impure mixtures of quartzo-feldspathic material.The observed textural, compositional and mineralogical variations have been used as diagnostic properties in the identification of source materials and their transport history through the catchment.     

Sequence of till deposition and erosion in drumlins

Whittecar, G.R. & Mickelson, D. M. 1977 06 01: Sequence of till deposition and erosion in drumlins.
Extensive sand and gravel workings have exposed structural and compositional features of 17 gravel-cored drumlins of late Wisconsin age in eastern Wisconsin. The drumlins are blanketed by 3 m of sandy basal till which truncates lower tills of earlier advanccs, outwash gravels, and an overlying till which is conformable to the gravel bedding and indistinguishable in composition from the surface till. Sands and gravels in the interior of some drumlins are deformed into large overturned folds, and into elastic dikes of fine sand and silt which penetrate to the top of the drumlin and warp overlying gravels. Both the folds and horizontal bedding are truncated by either the drumlin edge or the till blanket.
We interpret the conformable, truncated, and in some cases folded, till as a basal till deposited during glacial advance. The capping, truncating till is viewed as a basal till left by retreating ice.
The following sequence of events is suggested: (1) advance of ice over outwash, and deposition of till in a zone mar the margin; (2) thickening of the ice and erosion of the drumlin shapes; (3) local folding of the gravels and continued erosion; (4) retreat of ice and deposition of basal till under thin ice; (5) deposition of localized ablation till and stratified deposits.     

Modern Bottom Sediments of Lake Onega: Structure,Mineralogical Composition,and Systematization of Rare-Earth Elements

The results of studying the structure and mineral composition of the Upper Holocene bottom sediments of Lake Onega are presented. It is established that there are two types of columns of bottom sediments, for which stratification of layers and formation of Fe–Mn crusts are determined by the diagenesis processes occurring under physicochemical conditions of sediment accumulation according to two scenarios. The distribution spectra of rare-earth elements (REEs) are different in the indicated types of columns, which is apparently attributed to the differences in the oxidation–reduction conditions at the water–sediment interface during the formation of REEs and possibly to the influence of hydrothermal processes.     

Patterns of rare earth and other trace elements in Paleogene and Miocene clayey sediments from the Mondego platform (Central Portugal)

In the present study the origin of clay deposits occurring in an inland platform, in central Portugal, was investigated by their mineralogical and chemical composition. The clay deposits, exploited for ceramic industry are composed of silt-clay facies, the Monteira Member and the Arroça Member, which are assigned to the Coja Formation (Paleogene) and the Campelo Formation (Miocene), respectively. These clayey facies show almost compositional homogeneity, especially concerning texture. The mineralogical composition of the Monteira Member displays slightly higher content in smectite and interstratified clay minerals, which is supported by the chemical composition of samples analyzed. Both members present similar REE patterns, displaying an intense weathering record and little variation in the source area composition. Minor element geochemistry suggests low content in heavy minerals and transition metals. REE patterns and ratios of geochemical parameters support the dominant metasedimentary provenance, with a granite source contribution and also mature recycled sediments of continental origin. The study results’ suggest that the clays of these two members have the same source in terms of lithology and recycled sediments from the Hesperian massif. During the deposition of the Arroça Member, a major remobilization of the Monteira Member is suggested, explaining the geochemical similarity of both facies.     

Origin of friable sediments of the Barents Sea shelf

The origin of friable sediments blanketing the Barents Sea shelf is considered. It is shown that their characteristic seismoacoustic record patterns reflect low degree of diagenetic transformations and indicates continuous sedimentation. According to traditional views, this single sedimentary complex also includes diamicton, and the section is interpreted as a three-unit structure: diamicton, which is considered a till; the overlying friable sediments accumulated under different conditions of deglaciation in glaciomarine settings; and the postglacial marine sediments. It is demonstrated that such views are inconsistent with geomorphologic features (datings by physical methods included) indicating a prolonged hiatus that separates epochs of the diamicton accumulation and formation of friable sediments. The analysis revealed that the composition, vertical succession, and lateral distribution of different lithological types of friable sediments are related to the regular spatiotemporal replacements of different facies settings in the transgressing Arctic sea rather than by the glacial process. This inference is confirmed by the composition of foraminiferal assemblages.     

内蒙古西部额济纳旗及邻区石炭系-二叠系烃源岩干酪根C同位素的特征和影响因素

许多研究者认为,烃源岩干酪根C同位素组成主要受干酪根类型的影响,可以作为评价烃源岩类型、沉积环境和进行油气源对比的重要指标,并得到广泛应用.对额济纳旗及邻区典型剖面石炭系-二叠系烃源岩有机碳(TOC)的丰度、地球化学特征、热演化特征和干酪根C同位素分布的研究表明.研究区石炭系-二叠系烃源岩为浅海陆棚相沉积环境形成的泥质岩,TOC含量中等,以Ⅱ类干酪根为主,烃源岩演化进入成熟-过成熟阶段,干酪根C同位素县有显著偏重的特点.并且干酪根C同位素组成明显与热演化程度和有机碳丰度有关,随着烃源岩演化程度的不断提高,重碳同位素不断富集,在成熟-过成熟阶段,对C同位素的影响可达4‰～6‰随着TOC含量的增加,干酪根C同位素显著偏轻,影响值可达4‰以上.由于研究区烃源岩已进入成熟-过成熟阶段,干酪根C同位素的分布在演化过程中已经发生较大变化,干酪根类型的影响相对降低或已不显著,不能再作为评价烃源岩干酪根类型的指标.     

我国主要含煤油气盆地煤系源岩PY－GC热解产物组成及意义

本文运用热解气相色谱（ＰＹ－ＧＣ）技术探讨了我国一些含煤油气盆地中煤系源岩热解产物的组成特征及意义。研究表明，不同盆地煤系源岩热解产物的差异主要表现在Ｃ+₅正构烷烃＋正构烯烃含量和芳环化合物的组成上，利用热解产物Ｃ₁-Ｃ₅、Ｃ₆-Ｃ₁₄正构烷烃＋正构烯烃和Ｃ+₁₅正构烷烃＋正构烯烃三个端元组分的相对含量可有效地判识煤系地层源岩有机质的产烃类型，研究表明ＰＹ－ＧＣ技术是一种值得推广的煤成烃评价方法。     

Relationships between sand input from rivers and the composition of sands from the beaches of Southern California*

During the period from 1967 through 1972, a sampling programme was completed to determine the economic potential of heavy metals in the beach and river sands of the southern California coastal zone. These samples were employed to test the hypothesis that sand composition in a given beach cell is dominantly controlled by the provenance draining into that cell and is not strongly influenced by longshore leakage from upcurrent cells. Sample sets obtained before and after the exceptional flood of 1969 made it possible to compare the sediment supplied by normal river flow with that supplied by a major flood. Multivariate statistical analysis of the heavy mineral distribution of southern California beaches and rivers indicate that the sand composition of the two northern cells is controlled by the dominantly sedimentary Transverse Range provenance, whereas the composition of the three southern cells is controlled by the dioritic Peninsular Ranges. Some leakage occurs between the two northern cells around the Point Dume-Hueneme-Mugu Canyon Zone, whereas no important southward mixing occurs between cells around the Palos Verdes-Redondo Canyon Zone. Even though the Santa Clara River flows mostly through sedimentary terrains, samples from this river strongly reflect the granodioritic source present in its headlands. Although the basic sand composition within each cell persists during major flooding, leakage between cells may increase following flooding and the compositional packages present may show evidence of greater mixing.     

Carbon isotopic composition and genetic types of natural gas in the Sichuan Basin,China

The origin and genetic types of natural gas in the Sichuan Basin are still disputed. To classify the origin and genetic types in different areas, the paper analyzes the carbon isotopic composition of gases and geologic features in the Sichuan Basin. The results showed that the gas sourced from terrestrial layers is typically characterized by terrestrial origin and was mainly accumulated nearby to form reservoir. The carbon isotopic composition of gas showed a normal combination sequence distribution, suggesting that natural gas in continental strata is not affected by secondary alteration or that this deformation is very weak. The gas source is singular, and only gas from the southern and northern Sichuan Basin shows the characteristic of mixed sources. However, marine gas presents the characteristics of an oil-formed gas. The carbon isotopic composition of natural gas in the western and central part of the basin mostly distributes in a normal combination sequence, and few of them showed an inversion, indicating that the gas perhaps had not experienced secondary alteration. The carbon isotopic composition of marine-origin gas in the southern, northern and eastern Sichuan Basin displays a completely different distribution pattern, which is probably caused by different mixing ratio of gas with multi-source and multi-period.     

Grain-size distribution of subglacial till and its realtion to glacial scrushing and abrasion

A subglacial till formed from a sandstone bedrock has a variable grain-size distribution which reflects its variable genesis. Glacial comminution processes were simulated by artificial mill experiments with fragments of the sandstone bedrock. Pure crushing caused disintegration along mineral boundaries into separate minerals, most mineral grains retaining their primary size during the crushing process. Abrasion produced cracks across the minerals and resulted in silt-sized rock flour. The experiments indicate that most of the sand-sized till material formed as a result of crushing, while the silt is mainly the result of abrasion. The sand and silt are both regarded as components resistant to further glacial comminution, but are formed by different comminution processes. By considering also the coarser till material, the general principles of glacial breakdown of resistant rocks from boulders to sand or silt can be illustrated. A matrix index and an abrasion index based on the mill experiments distinguish well between genetically different subglacial till types     

The use of correspondence analysis and principal component analysis as a tool for deducing metamorphic mineral crystallization in Mn-rich lithologies

Principal component analysis (PCA) and correspondence analysis (CA) have been used to identify several critical mineral crystallization factors during metamorphism of Mn-rich lithologies from the Iberian Massif, Spain. Three types of variables have been considered in the system: mineralogical variables, bulk composition variables and one physical variable (oxygen fugacity). PCA was applied to the compositional variables to obtain four components, which were used as new compositional variables. These, together with the mineralogical and physical variables, were treated in the CA. The plot of the variables on the factor 1-factor 2 plane reveals that tephroite crystallization is controlled by a compositional variable representing low values of ratio Si/(Mn+Fe) in the rocks. Moreover, it is possible to deduce from this plot the importance of high oxygen fugacity conditions for the crystallization of piemontite. The third factor shows that the crystallization of spessartine does not require very restrictive physical-chemical conditions.