植物硅酸体的研究及在我国第四纪地质学中的初步应用

本文简述了国外植物硅酸体(植物蛋白石)这门新兴学科的进展情况,介绍了植物硅酸体研究在我国第四纪地质学中如古气候与古环境、地层时代、考古等方面的初步应用。     

Interaction between the controls on fluvial system development: tectonics,climate, base level and river capture – Rio Alias,Southeast Spain

Fluvial systems in uplifting terrain respond to tectonic, climatic, eustatic and local base‐level controls modified by specific local factors, such as river capture. The Rio Alias in southeast Spain is an ephemeral, transverse‐to‐structure fluvial system. The river drains two interconnected Neogene sedimentary basins, the Sorbas and Almeria basins, and crosses two major geological structures, the Sierras de Alhamilla/Cabrera and the Carboneras Fault Zone. Regional epeirogenic uplift resulted in sustained fluvial incision during the Quaternary, punctuated by major climatically driven periods of aggradation and dissection, which created a suite of five river terraces. The river terrace sequence was radically modified in the late Pleistocene by a major river capture (itself a response to regional tectonics), localized tectonic activity and eustatic base‐level change. The Rio Alias is defined by four reaches; within each the climatically‐generated, region‐wide, fluvial response was modified by tectonics, base‐level change or river capture to varying degrees. In the upper part of the basin (Lucainena reach), climate was the dominant control on river development, with limited modification of the sequence by uplift of the Sierra Alhamilla and local drainage reorganization by a local river capture. Downstream of the Sierra Alhamilla in the Polopus reach, the climatic signal is dominant, but its expression is radically modified by the response to a major river capture whereby the Alias system lost up to 70% of its pre‐capture drainage area. In the reach adjacent to the Carboneras Fault Zone (Argamason reach), modification of the terrace sequence by local tectonic activity and a resultant local base‐level fall led to a major local incisional event (propagating c. 3–4 km upstream from the area of tectonic disturbance). At the seaward end of the system (El Saltador reach) Quaternary sea‐level changes modified the patterns of erosion and incision and have resulted in steep incisional terrace profiles. The signals generated by regional tectonics and the Quaternary climate change can be identified throughout the basin but those generated by ongoing local tectonics, river capture and sea‐level change are spatially restricted and define the four reaches. The connectivity of the system from the headwaters to the coast decreased through time as incision progressed, resulting in changes in local coupling characteristics. Copyright © 2012 John Wiley & Sons, Ltd.     

Methane-derived authigenic carbonates from active hydrocarbon seeps of the St. Lawrence Estuary,Canada

Nearly 2000 pockmarks with diameters ranging from a few tens of meters up to 700 m are present on the seafloor of the St. Lawrence Estuary in eastern Canada. Coring of some pockmarks resulted in the recovery of various-sized and shaped carbonate concretions in a predominantly silty mud matrix. Petrographic and geochemical data on four authigenic carbonate concretions are reported as well as data from shell material in the unconsolidated sediment. Video observations and echo-sounder images indicate that the sampled pockmarks are actively gas venting. The video images show significant look-alike microbial mats in areas where gas is venting. The carbonate concretions are primarily made up of carbonate cements with varying percentage of shell fragments, micrite particles and fine-grained clastics. Orthorhombic crystal morphology and diagenetic fabrics including isopachous layers and botryoids characterize the aragonite cement. Oxygen isotopes ratios for the cement crusts do not record any thermal anomaly at the site of precipitation with δ¹⁸O_VPDB ratios (+3‰) in equilibrium with cold (5 °C) deep marine waters, whereas significant negative δ¹³C_VPDB ratios (−9.9 to −33.5‰) for cement and shell material within concretions indicate that the carbonates largely derive from the microbial oxidation of methane. The δ¹³C_VPDB ratios of aragonite shells (−2.7 to −5.6‰) taken from unconsolidated sediments at some distance from the concretions/vents show variable dilution of HCO₃⁻ with negative δ¹³C_VPDB ratios derived from microbial oxidation of methane with isotopically normal (0‰) marine bicarbonate. These results are in agreement with other lines of evidence suggesting that pockmarks formed through the recent and still active release of gas from a reservoir within the Paleozoic sedimentary succession.     

白令海DSDP188站氧同位素3期以来的古海洋与古气候记录

白令海南部DSDP188站沉积物生源组分分析显示,该地区表层生产力在MIS3早、晚期(3.3和3.1)以及MIS2期增加,而其他时期表层生产力相应降低,并且表层生产力的变化没有显示明显的冰期与间冰期旋回。沉积物的C/N比值反映了有机碳的混合来源,说明该地区表层生产力可能受陆源营养物质输入的影响。该站位沉积物的非生源组分分析显示,MIS3早、晚期陆源物质输入量增加,反映洋流加强和气候变化。MIS2出现两次陆源物质输入量的增加,显示了洋流和气候的波动。MIS3和末次冰消期碳屑丰度增加,但MIS2降低,指示MIS3和MIS1陆地天然火灾概率大,而MIS2天然火灾概率低,反映间冰期比冰期更容易发生天然火灾。     

晚第四纪冲绳海槽北段CaCO3含量的时空变化及其控制因素

对取自冲绳海槽北段的6个沉积岩心进行了CaCO3含量、粒度和铀系同位素分析，结合氧同位素数据和海槽其他钻孔的相应结果，探讨了冲绳海槽北部晚第四纪以来CaCO3含量的垂向与横向变化特征。结果表明，冲绳海槽北段沉积总体上表现为全新世CaCO3含量高、晚更新世CaCO3含量低的“大西洋型”碳酸盐演化特征，但冲绳海槽北段和中部的碳酸盐演化特征并不一致，海槽内西坡、槽底和东坡的不同部位其演化特征也存在较大差异。碳酸盐含量的变化与沉积物粒度特征密切相关，晚第四纪冲绳海槽碳酸盐演化的时空差异是多种因素相互作用的结果。     

河北平原三河市S9钻孔第四纪孢粉记录及其气候指示意义

为探讨更新世以来河北平原东部植被演化和气候变化特征,研究分析了大厂凹陷S9钻孔的孢粉植物群。根据S9钻孔中孢粉的分布,自下而上划分了6个孢粉组合,组合I和组合II为以针叶树为主的针阔叶混交林,组合IV—IV为疏林草原植被,整体为稀树草原型植被环境。根据孢粉组合的变化特征,还原了研究区更新世以来的气候变化规律: 研究区在早更新世气候温暖半干旱; 中更新世早期气候变冷,之后气候总体呈变暖变干旱的趋势; 晚更新世早期气候持续变暖,由湿润向干旱转变。研究区的孢粉演化模式与我国中北部许多地区的植被演化模式相似,同时与东亚、北太平洋以及南半球的气候变化特征表现出了较好的一致性。     

The Major Two-stage Shortening Deformation of the Northern Tibet and Tian Shan Area Since the Latest Oligocene

It seems to be progressively recognized that the stress of the India-Asia convergent front can be transferred rapidly through the southern and central Tibetan lithosphere to the northern Tibet, hence leading to the crustal thickening deformation there during or immediately after the onset of the India-Asia collision(ca.55 Ma).This study focuses on the late Cenozoic deformation and tectonic uplift of the northern Tibet and Tian Shan area.Detailed compilations of a variety of proxy data from sediments and bedrocks suggest that the northern Tibet and Tian Shan area underwent one stage of approximately synchronous widespread contractile deformation since 25–20 Ma, which seemed to decrease at circa 18 Ma as revealed by low-temperature thermochronological data.The latest Oligocene-early Miocene was also significant basin-forming episodes when many intermontane subbasins began to receive syntectonic sedimentation in the northeastern Tibet.Subsequently, the other phase of compressional deformation began to encroach more widely into the northern Tibet and Tian Shan area in episodic steps or continuously from 16–12 Ma to present.     

南海晚新生代地层结构特征、沉积厚度及沉积模式

本文综合地震、钻井及区域地质资料，通过分析地震相参数等，研究南海晚新生代（E3-Q）地层结构特征和沉积厚度变化，建立了晚新生代沉积模式，所取得的研究成果可为南海油气的进一步勘探开发提供有效的基础资料。     

Inconstancy in predator/prey ratios in Quaternary large mammal communities of Italy, with an appraisal of mechanisms

Constancy in predator/prey ratio (PPR) is a controversial issue in ecological research. Published reports support both constancy and inconstancy of the ratio in animal communities. Only a few studies, however, specifically address its course through time. Here we study the course of predator/prey ratio in communities of large Plio-Pleistocene mammals in Italy. After controlling for taphonomic biases, we find strong support for PPR inconstancy through time. Extinction, dispersal events, and differences in body size trends between predators and their prey were found to affect the ratio, which was distributed almost bimodally. We suggest that this stepwise dynamic in PPR indicates changes in ecosystem functioning. Prey richness was controlled by predation when PPR was high and by resources when PPR was low.