A 180,000-year pollen record from Owens Lake, CA: terrestrial vegetation change on orbital scales

Pollen from the upper 90 m of core OL-92 from Owens Lake is a climatically sensitive record of vegetation change that indicates shifts in the plant associations representing warm and cold desertscrub, pinyon–juniper woodland, and pine–fir forest during the past 180,000 years. These changes are synchronized with glacial–interglacial cycles. During glacial and stadial climates, juniper woodland expanded downslope and replaced warm desert shrubs while upper montane and subalpine forests in the arid Inyo Mountains also expanded, and those in the Sierra Nevada were displaced by the ice cap and periglacial conditions. Conversely, during interglacial and interstadial climates, warm desert plants expanded their range in the lowlands, juniper and sagebrush retreated upslope, and montane and subalpine forests expanded in the Sierra Nevada. The reconstructed vegetation history demonstrates a regional climatic response, and the congruence of the pollen sequence with marine and ice cap oxygen isotope stratigraphies suggests a link between regional vegetation and global climate change at orbital scales.     

What is a Poor Quality Strong-Motion Record?

Some accelerograms are affected by non-standard recording and digitization problems that mean they are often not used in strong-motion studies. These non-standard problems cannot be corrected by the standard processing techniques that remove low and high-frequency noise from the time-history. Records from analogue instruments are more prone to these problems but even records from digital instruments, which are becoming increasingly common, can be affected by such errors. Since all strong-motion data is valuable it is important to know whether any useful information can be obtained from accelerograms that are affected by such problems. This article examines whether strong-motion records from analogue instruments that are missing their initial part due to late triggering of the instrument and also strong-motion records from digital instruments with low A/D converter resolution can be used for response spectral studies. It is found, by simulating such errors on high-quality strong-motion records, that good response spectral ordinates can be obtained from such `poor-quality' records within the period range of most engineering interest. This revised version was published online in July 2006 with corrections to the Cover Date.     

三门峡地区的红粘土磁性地层及环境记录

位于黄土高原东南缘的三门峡红粘土地层，以陕县指望剖面为其典型代表。厚度为74．3m的指望剖面由上部厚34m的黄土地层和下伏厚40.3m的红粘土沉积组成，黄土为L24－L33的连续风尘沉积，下部红粘土为RS1－RS5的沉积。磁性地层研究显示：M／Ga界线位于33.8m处，黄土与红粘土界线之上20cm，Ga/Gi界线位于56.25m处的RS3中下部。该区红粘土近5Ma至2.6Ma的风尘沉积夹河湖相沉积。指望剖面的红粘土地层磁化率较黄土高原内部偏高，总体特征一致，说明近5Ma来东亚季风在区域演化上的一致性。     

松辽盆地泉四段扶余油层地层层序新认识

松辽盆地泉四段扶余油层发育浅水湖泊三角洲相和浅水湖泊相，沉积构造环境属于闭塞浅水坳陷湖盆，其层序特征类似于稳定克拉通盆地层序，也类似于缓坡被动大陆边缘型盆地层序，气候是控制陆相坳陷盆地层序形成的主要因素，三级层序内总体应表现为水进体系域-高位体系域构成1个完整的层序，而低位体系域不发育。通过岩心、录井、地震等资料研究分析，认为泉四段扶余油层是1个三级层序，发育水进体系域和顶部薄层强制水退边缘体系域；泉四段与泉三段地层分界是其层序的底界；泉四段顶界地震反射层T2也是层序边界，是泉四段三级层序的顶界。精确识别和建立地层层序格架对石油勘探开发具有重要的指导意义。     

Lacustrine carbonate deposition in Middle Pennsylvanian cyclothems — the Upper Freeport Formation,Appalachian Basin,USA

The Upper Freeport Formation (Upper Allegheny Group, Middle Pennsylvanian) is one of the earliest non-marine cyclothems in the Appalachian Basin and contains carbonates, siliciclastics, and coal. A detailed facies analyses of 25 cores from the Upper Freeport Limestone in western Pennsylvania (Armstrong and Indiana Counties) identified four facies associations containing thirteen separate facies: rudstone-limestone (Association A), rudstone-laminated limestone (Association B), laminated limestone (Association C), and coal — siliciclastics (Association D). We interpreted them, respectively, as shallow, high energy lacustrine margin (A); littoral to sublittoral lacustrine (B); offshore lake (C); and vegetated swamp and marsh (D). The depositional environment is envisaged as an anastomosed channel system surrounded by extensive wetlands containing adjacent densely vegetated swamp and marsh areas and freshwater, carbonate-producing lakes.Lakes developed in the topographic lows of the alluvial plain, protected and filtered from siliciclastic deposition by vegetated swamps. These lakes were small in size (several square km), shallow, and stratified, as indicated by the abundance of laminated facies. They were hydrologically open, and interconnected by surface and ground waters. Carbonate production in this lacustrine system was not triggered by evaporative concentration but by biogenic algal production. Carbonates were continually being recycled, both physicochemically and biologically, within the depositional system. Various early diagenetic processes, including brecciation, pedogenesis and recrystallization, masked original evidence for transport mode. The Upper Freeport Limestone contains numerous features of palustrine carbonates, and provides a case study for one end-member of freshwater carbonate models, characterized by a very short period of subaerial exposure. Small-scale climatic changes or autocyclic processes such as small topographic differences, changes in local drainage patterns, and fluvial dynamics may have controlled Upper Freeport lake level changes.Facies analysis does not support a climate forcing as a control for cyclothem development of non-marine sequences during the Pennsylvanian. Tectonic and autocyclic processes better explain the evolution of these wetland (lacustrine/alluvial) systems with its associated coal formation.This is the seventh paper in a series of papers published in this issue on Climatic and Tectonic Rhythms in Lake Deposits.     

ENSO-coupled precipitation records (1959–2004) based on shells of freshwater bivalve mollusks (<Emphasis Type="Italic">Margaritifera falcata</Emphasis>) from British Columbia

We present the results of sclerochronologically calibrated growth and stable isotope analyses of the freshwater bivalve Margaritifera falcata collected from an agricultural, suburban setting near Vancouver, BC. The oxygen isotope range of shell aragonite can be explained by the temperature range during the growing season, assuming the water δ ¹⁸O composition remained constant. However, shell growth is strongly influenced by local summer precipitation and potentially runoff of nutrient-rich stormwater. About 44% of the variability of annual shell growth can be explained by amounts of local summer (June–September) rainfall. Local winter precipitation and El Niño–Southern Oscillation (ENSO) strength during the preceding year exert a weak, but significant control on shell growth. In combination, summer and winter precipitation can explain up to 50% of the variability in annual shell growth. Spectral analyses substantiate the effect of precipitation on shell growth and demonstrate that shell growth and ENSO are coupled by precipitation. Common spectral density was found at periods of 6.5–9 years, particularly between 1985 and 2004. Higher frequency oscillation corresponding to periods of 3–5 years occurred during the early 1970s, early to mid 1980s, and later 1990s. These results suggest that skeletal records of bivalve mollusks provide suitable archives of ENSO-coupled precipitation in areas where other climate proxies such as tree-rings and speleothems may not be available.     

原油物性演化规律新发现及其对页岩油勘探的启示

针对烃源岩生成的原油物性随热演化如何变化的问题,本文基于对准噶尔盆地玛湖凹陷下二叠统风城组和吉木萨尔凹陷中二叠统芦草沟组下段源储紧邻自生自储页岩油物性、地化特征、成藏特征及原油物性与烃源岩热演化关系的分析,综合烃源岩生烃热模拟实验结果与国内外相关文献资料,首次确认了咸化湖相烃源岩生成的原油物性与烃源岩热演化程度之间的变化规律。认为页岩油源岩生成的原油密度和黏度具有随热演化程度增强先增加而后降低的规律,其中生油高峰附近生成的原油非烃相对含量、密度和黏度最高。该认识不仅是对已有的石油地质学中原油物性随热演化规律认识的进一步厘定和修正,而且对页岩油甜点段、甜点区的选择以及页岩油原位转化等都有极为重要和现实的指导作用。     

The response of lake margin sedimentary systems to climatically driven lake level fluctuations: Middle Devonian,Orcadian Basin,Scotland

Lake margin sedimentary systems can provide highly sensitive records of sedimentary response to climate change. The Middle Old Red Sandstone of Northern Scotland comprises a thick succession of cyclic lacustrine sediments. Within this succession the deepest lake phase, the Achanarras fish bed, allows bed‐scale correlation over 160 km across the basin. This provides a unique opportunity to examine the character of synchronous lake margin deposits, and their response to climatically driven lake level fluctuations, across a large continental basin. Detailed characterization of two separate lake margin systems was carried out utilizing multiple sections in western Orkney, in the north, and Easter Ross, in the south. Seven facies have been recognized, which include upper and lower shoreface, deep lake, shallow lake, playa, turbidite and fluvial facies. Differences in vertical and lateral facies stacking patterns reflect the response of these systems to climatically driven fluctuations in lake level. Comparison of the northern and southern systems examined highlights the variable response of lake margin systems to the same climatic change and related lake level fluctuations. In the south, a greater fluvial influence is recognized on the development of the lake margin successions, whereas in the northern example, which lay on the downwind margin of the lake, shore zone facies are more commonly developed. The variability recognized can be accounted for by regional variations in sediment supply, coastal physiography, lake size, bathymetry and potential fetch. Lake level stability is also recognized as a major control on the development of lake margin sedimentary systems, as is the linked or unlinked relationship of the catchment and the lake basin climate for which a conceptual model is proposed.     

准噶尔盆地古近系生烃潜力与油气源特征研究

准噶尔盆地古近系是该盆地的一个潜在勘探层系,本文研究了研究区古近系烃源岩的生烃潜力及油气源特征。结果表明,准噶尔盆地古近系发育一定数量和规模的泥质烃源岩,有机质丰度达到了中等-好质量标准,类型以I型和Ⅱ型为主,目前主体处于低成熟-成熟演化阶段,因此具有一定的生烃、生油潜力。这得到了油气源对比研究的印证,典型油气地球化学特征均表现为油型,且为低成熟度,因此只能与古近系烃源岩对应,从而判断为古近系来源。这些油气主要分布在盆地南缘古近系烃源岩埋深较大区,表现出在"源控"基础上受成熟度影响的特征。准噶尔盆地古近系的油气勘探应以原油为主,并且重点目标区在南缘,特别是四棵树凹陷区。这些基础数据和认识还可供全球其它古近系含油气系统研究类比参考。