云南楚雄盆地上三叠统沉积及地球化学的海相特征

楚雄盆地为中生代形成的典型前陆盆地。三叠纪是其形成的主体阶段和盆山转换的重要时期,也是由海相向陆相沉积环境的转折期,同时上三叠统是楚雄盆地最重要的油气资源层系。通过对楚雄盆地上三叠统进行系统的沉积学、层序地层学和波动地质学分析,在上三叠统识别出3个三级层序,建立了层序地层格架和高频波动曲线。对层序地层格架内的碳、氧同位素和微量元素的特征进行分析,发现楚雄盆地晚三叠世诺利晚期—瑞替期沉积具有海相沉积环境的地球化学特征,同时综合多学科的研究成果,指出楚雄盆地该时期为一与海域相接的近海湖盆,并受到间歇性海侵的影响。而海相烃源岩与陆相烃源岩在生烃能力、分布规律等方面均具有较大的差异。因此,这一认识对于重新评价楚雄盆地晚三叠世烃源岩具有重要意义。     

东亚季风气候对Heinrich2事件的响应:来自石笋的高分辨率记录

据湖北省神农架天鹅洞一支石笋11个230Th年龄和254个δ18O数据,建立了28.5～22.0kaB.P.同位素分辨率平均约30a的东亚季风气候变化序列。该石笋δ18O曲线与南京葫芦洞石笋记录在重叠时段基本一致,说明本区石笋δ18O反映了区域性东亚季风经向环流特征。在24.3kaB.P.左右,石笋δ18O明显正偏,持续时间近1ka,指示一次显著的弱夏季风事件,与北大西洋倒数第二次冰漂碎屑事件(Heinrich2)同步发生,可视为东亚季风气候对H2事件的响应。高分辨率的δ18O序列揭示了H2事件的内部结构特征:(1)事件发生的突变性,石笋δ18O记录指示事件发生时在100a内δ18O从-8.59‰迅速正偏为-6.75‰,振幅达1.84‰;(2)事件结束的渐变性,δ18O正偏到-6.75‰后便以阶梯状缓慢负偏到-8.86‰至事件结束,持续时间近900a。这一过程与末次盛冰期东亚季风气候H1事件表现的季风强弱转换方式基本一致,说明末次盛冰期东亚季风气候H型事件具有共同的内部结构特征。研究表明,末次盛冰期东亚季风气候H事件的突变可能受北大西洋驱动并经青藏高原冰川变化放大。     

井资料高分辨率层序地层学

在准层序中进行层组一级地层单元的识别和对比是高分辨率层序地层学研究的主要难点.提出了一种综合应用井资料进行层组界面识别和对比的新方法.通过测井曲线形态特征、岩心观察、铸体薄片、X衍射、扫描电镜分析、FMI测井资料, 对工区内钙质夹层成因、泥岩电阻率差异、储层电阻率和海拔深度关系进行了研究.结果表明: 钙质夹层单层厚度在0.5~2m之间, 靠近风化壳和断层位置单层厚度大, 分布在水下分支河道底部和河口坝顶部; 低阻泥岩(4~5Ω·m)和高阻泥岩(> 10Ω·m) 分别来源于不同的沉积物源或者形成于不同的沉积相带; 储层电阻率随着海拔深度的增加而增加.因此, 钙质夹层可以作为层组界面识别和对比的标志, 利用泥岩电阻率差异可以确定层组的叠置关系, 判断储层连通性.据此, 建立了准噶尔盆地石南地区西山窑组含油层段等时地层格架, 确定了格架内储层的连通性及油水界面, 并且通过MDT测井资料进行了验证.在此等时地层格架内, 层组的发育顺序、叠置关系、空间展布形态、以及彼此之间的连通性都被定性、定量的表征出来.      

青藏高原新生代形成演化的整合模型——来自火成岩的约束

深部过程是青藏高原演化的主导因素,其他地质过程都可以看作是对深部过程的响应。因此,一个构造旋回(阶段)的地球动力学事件链可以概括为深部地质过程—幔源岩浆活动—壳源岩浆活动—陆壳增厚—地表隆升—表层剥蚀与沉积,其中幔源岩浆活动的研究成为追索青藏高原演化历史的关键环节。据此,青藏高原演化的关键性时间坐标为80、45、27、17、9和4Ma。青藏高原新生代火成岩具有三种展布形式:与雅鲁藏布缝合带平行的岩浆带、沿深大断裂展布的岩浆带和藏北离散性岩浆分布区,它们分别受控于大陆碰撞、大规模走滑和岩石圈拆沉构造体制,且都受控于印度—亚洲软流圈汇聚过程。据此,文中提出了一个描述青藏高原演化的整合模型:南北向地幔对流汇聚控制了岩石圈块体的相对运动,并最终导致印度—亚洲大陆的碰撞和沿碰撞带的大规模岩浆活动;碰撞之初(白垩纪末期),大陆岩石圈块体的刚性属性有利于应力的远程传递和块体旋转,沿块体边界分布的大型走滑断裂控制了岩浆活动的发生;随着挤压过程的持续进行,岩石圈块体的受热和变形,高原岩石圈的重力不稳定性增加,最终导致拆沉作用和软流圈物质的大规模上涌以及藏北高原的离散性岩浆活动。在高原演化中,岩石圈拆沉作用具有重要意义,许多地质事件的发生都与此有关。同时,软流圈的汇聚还导致软流圈物质的向东挤出,并因此造成青藏高原岩石圈的向东挤出和晚新生代的伸展构造。     

燕山地区新元古界青白口系沉积层序与地层格架研究

燕山地区是中国新元古界青白口系出露最好、层序较为完整的地区。从沉积特征研究入手,确定了各种沉积相、微相及沉积序列,在区内青白口系划分出4种沉积体系及5种沉积相、12种沉积亚相、16种微相。对副层序的主要类型及其特征进行了分析,结合层序界面和最大海泛面的研究,将区内青白口系划分出3个层序。在层序划分和对比基础上建立了燕山地区青白口纪的地层沉积格架并对其古地理演化进行了探讨。认为燕山青白口纪的沉积为华北陆块上真正的盖层沉积。     

陕西镇安西口石炭系-二叠系界线剖面综合地层学研究

对中国海相石炭—二叠系界线典型剖面陕西镇安西口剖面进行了生物地层、层序地层、磁性地层、事件地层多学科综合研究。在石炭—二叠系界线附近建立了4个牙形石生物带,自下而上依次为Streptogna-thoduselegantulus带,S·elongatus带,S·gracilis带和S·isolatus带。将研究区石炭—二叠系界线置于S·isolatus带的底界,较以带Pseudofusulinakrotowisphaeroidea-Dunbarinella(PD)带的底界为标志确定的石炭—二叠系界线层位低3·3m。在西口剖面上石炭统逍遥阶至下二叠统隆林阶,以初始海泛面作为层序界面,识别出12个四级层序(大体相当于副层序组),构成5个Ⅱ型三级层序。这5个三级层序及其对应的海平面变化与贵州独山、罗甸纳水、紫云扁平剖面同期地层中三级层序及海平面变化旋回之间显示出较好的对应关系。除下杨家河阶外,其余各阶的底界,包括逍遥阶、上杨家河阶、范家河阶、垭口阶及隆林阶的底界,基本上都位于沉积相转换点或其附近,即层序地层及海平面变化旋回的关键界面或其附近。表明这5个三级层序的关键界面与年代地层界线的关系相当密切。碳酸盐岩磁化率大小与碳酸盐岩微相存在一定的对应关系,显示相对海平面变化是控制碳酸盐岩磁化率大小的重要因素。另外,在重要地层界线附近常出现磁化率异常高值,说明碳酸盐岩磁化率可能作为地层划分对比的重要依据。西口地区晚石炭世逍遥期至早二叠世隆林期地层中可识别出两次明显的类辐射事件。第一次类辐射事件发生在Occidentoschwagerinaalpina-O·postgallowayi(OS)组合带底部,即下杨家河阶的底部。第二次辐射事件发生在Mccloudiaregularis-Par-aschwagerinafragosa-Robustoschwagerinaxiaodushanica(MPR)组合带底部,即范家河阶的底部。具有三级和三级以上隔壁的四射珊瑚动物群突然大量繁盛,代表四射珊瑚演化进程中一次重大变革。在陕西镇安石炭—二叠系界线附近,这个生物事件首现层位相当于类Pseudofusulinaurdalensi(PU)带下部,高于该带底界不到12m,以Xikouphyllum-Shaannanophyllum-Szechuanophyllum-Wentzellophyllum组合带为代表。在这个层位牙形石也发生了重要变化。各类地质事件记录出现的层位关系密切。在垭口阶底界各类地质事件记录吻合最好,隆林阶底界次之,然后是范家河阶底界。与上述3条界线相比,在镇安西口剖面上,以牙形石Streptognathodusisolatus的首现位置确定的石炭—二叠系界线事件地层特征不明显,既不是一个生物辐射演化面,碳酸盐岩磁化率变化也不太明显,在实际工作中不易使用。     

首都圈数字地震台网地震事件波形的管理与服务

介绍了首都圈数字地震台网地震事件波形数据的管理和服务系统的基本功能及使用方法,该系统利用GMT,SAC作为后台处理软件,通过perl,Unix Shell程序实现首都圈地震事件波形数据的网络发布。     

Adding the missing third and fourth dimensions to trajectory analysis in carbonate systems

We developed a seismic geomorphology-based procedure to enhance traditional trajectory analysis with the ability to visualize and quantify lateral variability along carbonate prograding-margin types (ramps and rimmed shelves) in 3D and 4D. This quantitative approach analysed the shelf break geometric evolution of the Oligo-Miocene carbonate clinoform system in the Browse Basin and delineated the feedback between antecedent topography and carbonate system response as controlling factor on shelf break rugosity. Our geometrical analysis identified a systematic shift in the large-scale average shelf break strike direction over a transect of 10 km from 62° to 55° in the Oligo-Miocene interval of the Browse Basin, which is likely controlled by far-field allogenic forcing from the Timor Trough collision zone. Plotting of 3D shelf break trajectories represents a convenient way to visualize the lateral variability in shelf break evolution. Shelf break trajectories that indicate contemporaneous along-strike progradation and retrogradation correlate with phases of autogenic slope system re-organization and may be a proxy for morphological stability of the shelf break. Shelf break rugosity and shelf break trajectory rugosity are not inherited parameters and antecedent topography does not dictate long-term differential movement of the shelf margin through successive depositional sequences. The autogenic carbonate system response to antecedent topography smooths high-rugosity areas by filling accommodation and maintains a relatively constant shelf break rugosity of ~150 m. Color-coding of the vertical component in the shelf break trajectory captures the creation and filling of accommodation, and highlights areas of the transect that are likely to yield inconsistent 2D sequence stratigraphic interpretations.     

Ephemeral rollover points and clinothem evolution in the modern Po Delta based on repeated bathymetric surveys

Reconstructions of ancient delta systems rely typically on a two-dimensional (2D) view of prograding clinothems but may miss their three-dimensional (3D) stratigraphic complexity which can, instead, be best documented on modern delta systems by integrating high-resolution geophysical data, historical cartography, core data and geomorphological reconstructions offshore. We quantitatively compare three precisely positioned, high-resolution multi-beam bathymetry maps in the delta front and pro delta sectors (0.3 to 10 m water depth) of Po di Pila, the most active of the modern Po Delta five branches. By investigating the detailed morphology of the prograding modern Po Delta, we shed new light on the mechanisms that control the topset to foreset transition in clinothems and show the temporal and spatial complexity of a delta and its pro delta slope, under the impact of oceanographic processes. This study documents the ephemeral nature of the rollover point at the transition between sandy topset (fluvial, delta plain to mouth-bar) and muddy seaward-dipping foreset deposits advancing, in this case, in >20 m of water depth. Three multibeam surveys, acquired between 2013 and 2016, document the complexity in space and time of the topset and foreset regions and their related morphology, a diagnostic feature that could not be appreciated using solely 2D, even very high-resolution, seismic profiles. In addition, the comparison of bathymetric surveys gathered with one-year lapses shows the migration of subaqueous sand dunes on the clinothem topset, the formation of ephemeral cut-and-fill features at the rollover point (few m below mean sea level), the presence of collapse depressions derived by sagging of sediments and fluid expulsion (possibly induced by storm waves) on the foreset, and splays of sand likely reflecting gravity flows on the lower foreset. Though the modern Po Delta is anthropogenic in many respects, its subaqueous clinothem can be studied as a scale model for ancient clinothems that are less resolved geometrically and far less constrained chronologically.     

Quantifying sand delivery to deep water during changing sea-level: Numerical models from the Quaternary Brazos Icehouse continental margin

Sequence stratigraphy for clastic continental margins predicts the development of sand-rich turbidite deposits during specific times in relation to base-level cycles. It is now widely understood that deltas can extend to the shelf-edge forced by high sediment flux and/or base level, providing a direct connection to transfer sediment and sand to the slope and basin floor even during high base level periods. Herein, we build a stratigraphic forward model for the last 120 kyr of the fluvio-deltaic to deep-water Brazos system (USA) where sediment partitioning along an Icehouse continental margin can be evaluated. The reduced-complexity stratigraphic forward model employs geologically constrained input parameters and mass balance. The modelled architecture is consistent with the location of depositional units previously mapped in the shelf. Sand bypasses the shelf and upper slope between 35 to 15 kyr before present and only about 20%–30% of all the sediment and sand supplied to the system is transferred to deep water. Several scenarios based on the initial Brazos model investigate the relationships between base level and deep-water sand ratio (DWSR). DWSR is defined as the relative amount of sand transferred to the deep-water portions of the system subdivided by the total sand input to the model. Linear correlations between DWSR and base level change rates or base level are very poor. Short-term variability due to local processes (for example avulsions) is superimposed to the long-term trends and mask the base level signal. DWSR for an entire base-level cycle is mainly controlled by the proportion of time the delta stays docked at the shelf-edge. Stratigraphic forward models are useful to complement field observations and quantify how different processes control stratigraphy, which is important for making predictions in areas with limited information.