撞击事件对古环境的影响——来自ODP1144站A孔样品的证据

本文通过对ODP1144站A孔BM界线附近样品中微玻璃陨石的挑选和研究,确定在中更新世曾发生过地外物体撞击地球的灾变事件。样品中浮游有孔虫壳体碳氧同位素的对比研究表明,在微玻璃陨石事件发生的后期,曾发生了浮游有孔虫壳体碳氧同位素组成的变化,表现为δ13 C值的降低和δ18 O值的增加。文中还探讨了其形成的原因。     

准噶尔盆地地壳动力学与油气储集层沉积相模型

本文以地壳动力学观点对准噶尔盆地发生、发育序列进行了探讨。该盆地生长序次分为五个阶段：①前盆地发育阶段（Ｃ３前）：被动大陆边缘；②裂陷阶段（Ｃ３→Ｐ１）：火山弧后盆地－残余弧后盆地；③压陷阶段（Ｐ２→）：前陆盆地；④坳陷阶段：内陆湖泊盆地；⑤萎缩阶段（Ｒ→Ｑ）：内陆湖泊→盐湖盆地。其中，晚二叠世和中生代的压陷和坳陷阶段有利于油气储集层形成。并且建立了油气储层沉积模型：下二叠统为大陆火山喷发相→洪冲积扇相→河流相或三角洲相→海相或湖相；上二叠统和三叠系分缓坡型和陡岸型。缓坡型沉积模式为洪冲积扇相→河流相→三角洲相→滨浅湖亚相→半深湖亚相。陡岸型为洪冲积扇相→扇三角洲相→滨浅湖亚相→半深湖亚相及浊积扇相；侏罗系八道湾组和西山密组不仅为较好油气储层，同时亦为富煤单元，其沉积模式为过境河流相→冲积扇相→辫状河流相→辫状三角洲相→湖泊相，或者，洪冲积扇相→河流沼泽亚相→湖湾亚相→滨湖沼泽亚相→滨浅湖亚相。     

Palaeoenvironmental evolution of the Upper Permian Maomaolong Formation in Gannan area of the West Qinling: Based on ichnonetwork analysis

The continuous Permian-Triassic strata in West Qinling represent deep-marine deposits. In this paper,abundant trace fossils(seventeen ichnospecies,twelve ichnogenera)have been identified in the Upper Permian Maomaolong Formation in the Gannan area of the western Qinling orogen. As a new ichnologic method,ichnonetwork analysis focuses on the reconstruction of the community system composed of interconnected ichnotaxa,which provides useful means for studying the behavior and ecology of ichnocoenosis. In this study,an ichnonetwork analysis is conducted with trace fossils data obtained from the first hand filed trip. The results show that ichnocoenosisis structured in the Maomaolong Formaiton,and three ichnoassociations were controlled by palaeoenvironments: Palaeophycus-Lockeia-Arenicolites-Dictyodora-Planolites-Protovirgularia-Chondrites (C1,proximal turbidite zone),Palaeophycus-Lockeia-Arenicolites-Dictyodora-Protovirgularia-Phycodes-Chondrites-Helminthopsis (C2,turbidite transition zone-distal turbidite zone),and Palaeophycus-Nereites-Scolicia-Protovirgularia-Helminthopsis (C3,distal turbidite zone). The evolution from C1 to C3 in the Upper Permian Maomaolong Formation from the Gannan area of the West Qinling reveals the palaeoenvironmental changes from proximal turbidite zone to distal turbidite zone.     

Palaeoenvironmental control on sediment composition and provenance in the late Quaternary deltaic successions: a case study from the Po delta area (Northern Italy)

Accumulation of continental, deltaic and shallow‐marine sediments in the Po River coastal plain preserves a record of the Late Quaternary sea‐level changes and shoreline migrations. The palaeoenvironmental evolution of this area and the changes in composition and provenance of sediments have been investigated through integrated sedimentological, micropalaeontological (mainly foraminifers) and geochemical analyses of core S1, from the southern part of the Po River delta, within a chronological framework supported by radiocarbon dating and correlations with adjacent core sequences. Eleven lithofacies, grouped into five facies associations, and four palaeontological assemblages provide the basis to define the palaeoenvironmental reconstruction of this succession consisting, from the base to the top, of: (i) continental sediments accumulated during the Late Pleistocene; (ii) back‐barrier sediments marking the onset of Holocene sea‐level rise; (iii) transgressive sands deposited during the rapid landward migration of a barrier‐lagoon system; (iv) shallow‐marine and prodelta sediments with faunal associations indicating a gradual approach to the Po River mouth; and (v) sub‐recent delta front sands that form a considerable portion of the present coastal plain. Bulk chemical composition of sediments shows remarkable relationships with palaeoenvironments and locally improves facies characterizations. For example, they reveal carbonate leaching that emphasizes the occurrence of palaeosols in continental deposits or record enrichments in loss on ignition, S and Br, diagnostic of organic‐rich layers in back‐shore sediments. Selected geochemical elements (e.g. Mg and Ni) are particularly effective for the recognition of sediment provenances from the three main source areas observed in the subsurface deposits of the Po River coastal plain (e.g. Apenninic rivers, North Adriatic rivers and Po River). An Apenninic provenance is observed in continental and back‐barrier sediments. A North Adriatic provenance characterizes the transgressive sands and the shallow‐marine deposits; a significant Po River provenance is recorded in sediments related to the onset of the prodelta environment, confirmed by foraminiferal assemblages indicating remarkable increase in fluvial influxes. Copyright © 2006 John Wiley & Sons, Ltd.     

Variability in biomarkers of different saline basins in China

42 samples (sediments and crude oils) from 5 different saline/hypersaline basins of China were examined using variety of geochemical techniques. A pronounced even over odd distribution ofn-alkanes is observed for the Ejinur, Jianghan samples. Abundance of isoprenoid alkanes, dominated by phytane (C₂₀ up to 20 per cent in EOM), and C₂₅ and C₃₀ components is another outstanding feature of these studied lacustrine hypersaline settings, indicating important contributuions from archaebacteria. Gammacerane is a major component of some Eocene Jiangham samples and Cretaceous Taian sediments. Absolute concentration of phytane and gammacerane appears to be linearly related to chlorine and residual (reduced) sulfur contents of sediments from Jianghan basin, suggesting sulfur incoporation might have played an important role in the enhacement of these biomarkers in the anoxic hypersaline, alkaline settings. Wide range of organic sulfur compounds in immature samples of Jianghan Basin reflects a significant pathway for sulfur incorporation under hypersaline, extremely anoxic/reducing conditions, although for some structures a direct origin from some sulfur archaebacteria can not be excluded. Brackish salt marsh sediment and oil from Lenghu depression contain abundant lupane, strong OEP inn-alkane series, and predominance of C₂₉ steranes, suggesting a markedly input from vascular higher plants. The marginal marine evaporate sediments from the hypersaline Triassic Yangtze Platform is unique for its predominant, complete series of isoprenoid alkanes up to C₃₆ (abundant) and C₄₀ (trace). These long-chain isoprenoids are probably derived from phytoplanktons in addition to archaebacteria. The marked difference in biomarker distributions from the various suites of samples support that application of these biomarkers to help effectively characterize different saline basins. The molecular variation is, however, not only due to their discrepancy in biological sources, but also the extension of sulfate reduction and the availability of metal ions during early diagenesis.     

珠江三角洲PRD05孔的高分辨率介形类记录与晚第四纪古环境重建*

对珠江三角洲西江河口附近PRD05孔（113°11′ 02″E,22°31′24″N）的岩性和介形类的高分辨率分析表明,受海平面变化和河流作用的影响,研究区晚第四纪经历了多次环境变化。26600\{a BP\}以前为河流环境,底部为河道沙砾沉积,随后水动力条件减弱,发育河漫滩沉积。26600—13400\{a BP\} 前期发育泛滥平原相沉积,后期受末次冰期的影响,本区暴露地表遭受风化剥蚀,泛滥平原相沉积的上部风化成杂色黏土。珠江口地区冰后期海侵应开始于约13400\{a BP\}。13400—9000\{a BP\}为海侵初期,本区形成沼泽相沉积。9000—4850\{a BP\}为全新世大海侵时期,本区为持续的河口海湾环境,发育以海相—半咸水型为主的介形类动物群,发生了3次小规模的海平面波动,导致水体条件发生变化,从而影响了介形类动物群的组成和丰度。最大海侵发生于7500—7140\{a BP\}之间,PRD05孔主要介形类属种的丰度在这一阶段达到全新世最大值。4850\{a BP\}以来为持续海退期,河流作用增强,本区逐渐转变为上三角洲平原环境。     

陕北长城沿线先秦时期生业与环境的关系

探寻环境和文化的一些要素在时间序列上的耦合,已经成为人地关系研究的重要内容。在环境影响文化的方式上,一些解释模型也被构建起来,但从人类文化的角度来考察人地关系的研究还有待深入。生业模式作为人类从自然环境中获取食物来源的方式,与自然环境和生产技术都有密切的关系。通过对陕北长城沿线先秦时期考古资料的梳理,总结出生业模式4个阶段的发展过程,即农业活动的开始、农牧混合经济的出现、农牧混合经济的进一步发展以及游牧业的出现。通过对多个全新世剖面的总结和对比,区域气候变化大体可以分为3个阶段：11.0~8.5cal.kaB.P. 不稳定的升温期、8.5~3.8cal.kaB.P. 较为稳定的高温期以及3.8~2.2cal.kaB.P. 的干冷期。在此基础上,对不同阶段生业模式的文化和环境背景进行了分析,揭示了生业模式是多种因素共同作用的产物,并进而展现了研究区生业与环境之间复杂的对应关系,以此说明生业变化并非只受到环境变化的影响,也不是所有的环境变化都必然引起生业的变化。由于动植物考古和古环境变化研究在时空分辨率上还有待提高,以及对人类社会文化的认识还不够深入,目前还不能揭示生业与环境关联的细节及其复杂的环境-文化背景。     

重庆綦江地质公园地质遗迹特征及其地质意义

綦江地质公园发育木化石、恐龙足迹、恐龙骨骼化石、鱼化石、沉积构造、丹霞地貌等地质遗迹景观,木化石和恐龙足迹为园区的导向型景观。木化石分布在侏罗系中统沙溪庙组(J2s)上部砂岩层中,砂岩层含钙质结核,在约300×200m2的砂岩层内共埋藏有60多根木化石,其中一半木化石为钙化作用形成。恐龙足迹集中分布在白垩系上统夹关组(K2j)砂泥岩层中,岩层发育交错层理、波痕和泥裂。在夹关组的3个层位中共发现329个恐龙足迹,其分别属于甲龙类、鸟脚类和兽脚类。园区地质遗迹分布在一套河湖相沉积层中,其形成于内陆河湖网形成之时(如木化石),并随着四川盆地周围的湖泊系统解体而发展(如恐龙足迹),最终随着河流由堆积作用为主的阶段转变为以侵蚀作用为主的阶段而减弱(如丹霞地貌)。白垩纪上统夹关组的恐龙足迹群形成于干热的环境,多类型的恐龙足迹集中分布反映了白垩纪晚期(夹关期)恐龙种群的丰富,恐龙足迹的发现为区域内寻找白垩系地层的恐龙骨骼化石提供了依据。     

Morphometric analysis of sediment conduits on a bathymetric high: Implications for palaeoenvironment and hydrocarbon prospectivity

Canyons and other sediment conduits are important components of the deep‐water environment and are the main pathways for sediment transport from the shelf to the basin floor. Using 3‐D and 2‐D seismic reflection data, seismic facies and statistical morphometric analyses, this study showed the architectural evolution of five canyons, two slide scars and four gullies on the southern part of the Loppa High, Barents Sea. Morphometric parameters such as thalweg depth (lowest point on a conduit's base), wall depth (middle point), height, width and base width, sinuosity, thalweg gradient, aspect ratio (width/height) and cross‐sectional area of the conduits were measured at intervals of 250‐m perpendicular to the conduits’ pathways. Our results show that the canyons and slide scars in the study area widen down slope, whereas the gullies are narrow and short with uniform widths. The sediment conduits in the study area evolved in three stages. The first stage is correlated with a time when erosion and bypass were dominant in the conduits, and sediment transferred to the basin in the south. The second stage occurred when basin subsidence was prevalent, and a widespread fine‐grained sequence was deposited as a drape blanketing the canyons and other conduits. A final stage occurred when uplift and glacial erosion configured the entire southern Loppa High into an area of denudation. Our work demonstrates that the morphometric parameters of the canyons, slide scars and gullies generally have increasing linear trends with down‐slope distance, irrespective of their geometries. The morphometric analysis of the sediment conduits in the study area has wider applications for understanding depositional processes, reservoir distribution and petroleum prospectivity in frontier basins.     

关于沙漠环境演变几种研究指标的探讨

沙漠环境演变研究过程中,地层沉积序列和沙漠环境信息的重建是其研究重点。大量关于沙漠环境演变研究所取得的成果显示：在沙漠沉积地层时间序列测定中,光释光（OSL）测年比较适用,但其在高分辨率方面欠缺、精度稍差,实际研究中应该视实际情况把OSL测年与^14 C测年结合使用。在环境代用指标选择方4面,沉积粒度及地球化学元素比较适合沙漠环境演变研究;磁化率、碳酸钙、有机碳作为环境代用指标有一定的局限性,但研究中仍多使用;孢粉分析在较湿润区域的环境演变研究中作为环境代用指标效果较好,但在沙漠这个极度干旱、植被稀少的环境下适用性不强。