Late Miocene–early Pliocene planktonic foraminifer event-stratigraphy of the Bajo Segura basin: A complete record of the western Mediterranean

The Bajo Segura basin (eastern Betic Cordillera) has one of the most complete late Miocene–early Pliocene marine records of the western Mediterranean. An updated planktonic foraminifer zonal scheme based on recent astronomically tuned biozones is presented for this interval, documenting a complete succession of biostratigraphic markers, from biozone MMi9 (earliest Tortonian) to MPl3 (latest early Pliocene), of likely significance for regional-scale correlation throughout the Mediterranean. The findings reveal a series of intrazonal events (some unreported until now in the Mediterranean Neogene basin), including the particularly interesting two influxes of the Globorotalia miotumida group during the Tortonian. These biostratigraphic findings are the basis for a framework of the major allostratigraphic units in the basin based on planktonic foraminifer event-stratigraphy: synthems Tortonian I, Tortonian II, Tortonian-Messinian I, Messinian II, and Pliocene. In addition, the timing of the main tectono-sedimentary and palaeogeographic events throughout the basin's evolution has been further constrained. Our results suggest that, at least in the Bajo Segura basin, the late-Messinian barren interval (non-distinctive zone) can be considered an ecobiostratigraphic zone (cenozone) characterized by dwarf fauna of planktonic foraminifera. Consequently, the Bajo Segura composite section can be regarded as a biostratigraphic reference section for Neogene basins in the Betic Cordillera and hence also in the Western Mediterranean.     

Geochemical characteristics of the Paleogene shales in the Dongying depression,eastern China

Fluctuations in lacustrine sedimentary environments significantly affect distributions of organic matter (OM), uranium, and other elements in shales. In this study a high-resolution geochemical record of fluctuations in the paleo-depositional environment of a terrestrial lake basin is provided on the basis of extensive samples collected from the Member 3 of the Paleogene Shahejie Formation (Es₃) of the Niu-38 well in the Dongying Depression, Eastern China. These samples were tested for total organic carbon (TOC), element concentrations, and biomarkers to study the evolution and fluctuation in the depositional environments of an ancient lake basin and associated geochemical response. The evolution and fluctuation of the sedimentary environment from a deep lake to a semi-deep lake and then to a shallow lake delta were indicated by geochemical response. During this evolution, the values of TOC, S₁, S₂, Sr, and Ts/(Ts + Tm) remarkably decreased, whereas those of Co, Ni, Rb, Na, Fe/Mn, Fe/(Ca + Mg), and C₂₉ mortane/C₂₉ hopane significantly increased. The deep lake basin shows depositional fluctuations, as indicated by rock lithofacies and their geochemical parameters. A close interrelationship was observed among U concentration, TOC content, and inorganic element content. Uranium concentrations are positively correlated with TOC contents, Ca and Sr concentrations, and Sr/Ba and Ca/Mg ratios but negatively with K, Na, Ba, and Rb contents and Fe/(Ca + Mg) and Fe/Mn ratios. The observed increase in U concentration in the lower Es₃ section is closely related to surface adsorption by clay minerals and OM, together with some replacements of Ca and Sr by U in the shales.     

Geological evolution and hydrocarbon potential of the salt-cored Hoodoo Dome,Sverdrup Basin,Arctic Canada

The evaporite-cored Hoodoo Dome on southern Ellef Ringnes Island, Sverdrup Basin, was examined to improve the understanding of its structural geological history in relation to hydrocarbon migration. Data from geological mapping, reflection seismic, thermal maturity and detrital apatite (U–Th)/He cooling ages are presented. Five stages of diapirism are interpreted from Jurassic to Recent times:1. 180 to 163 Ma (pre-Deer Bay Formation; development of a diapir with a circular map pattern).2. 163 to 133 Ma (Deer Bay to lower Isachsen formations; development of salt wings).3. 115 to 94 Ma (Christopher and Hassel formations; ongoing diapirism and development of an oval map pattern)4. 79 Ma (Kanguk Formation; reactivation of the central diapir).5. 42 Ma to 65 Ma (Eurekan Orogeny; tightening of the anticline).During phase1, the Hoodoo diapir was circular. During phase 2, salt wings formed along its margin. During phase 3, the Hoodoo Dome geometry evolved into a much larger, elongate, doubly plunging anticline. Phase 4 is inferred from thermochronology data as indicated by a cluster of cooling ages, but the extent of motion during that time is unknown. During Phase 5 the dome was tightened creating approximately 700 m of structural relief. Denudation since the end of the Eurekan Orogeny is estimated to be about 600 m.A one dimensional burial history model predicts hydrocarbon generation from Middle and Late Triassic source rocks between 140 and 66 Ma, with majority of hydrocarbon expulsion between 117 and 79 Ma. Hydrocarbon generation post-dates salt wing formation, so that this trap could host natural gas expelled from Triassic source rocks.     

Seismic geomorphology of cretaceous megaslides offshore Namibia (Orange Basin): Insights into segmentation and degradation of gravity-driven linked systems

This study applies modern seismic geomorphology techniques to deep-water collapse features in the Orange Basin (Namibian margin, Southwest Africa) in order to provide unprecedented insights into the segmentation and degradation processes of gravity-driven linked systems. The seismic analysis was carried out using a high-quality, depth-migrated 3D volume that images the Upper Cretaceous post-rift succession of the basin, where two buried collapse features with strongly contrasting seismic expression are observed. The lower Megaslide Complex is a typical margin-scale, extensional-contractional gravity-driven linked system that deformed at least 2 km of post-rift section. The complex is laterally segmented into scoop-shaped megaslides up to 20 km wide that extend downdip for distances in excess of 30 km. The megaslides comprise extensional headwall fault systems with associated 3D rollover structures and thrust imbricates at their toes. Lateral segmentation occurs along sidewall fault systems which, in the proximal part of the megaslides, exhibit oblique extensional motion and define horst structures up to 6 km wide between individual megaslides. In the toe areas, reverse slip along these same sidewall faults, creates lateral ramps with hanging wall thrust-related folds up to 2 km wide. Headwall rollover anticlines, sidewall horsts and ramp anticlines may represent novel traps for hydrocarbon exploration on the Namibian margin.The Megaslide Complex is unconformably overlain by few hundreds of metres of highly contorted strata which define an upper Slump Complex. Combined seismic attributes and detailed seismic facies analysis allowed mapping of headscarps, thrust imbrications and longitudinal shear zones within the Slump Complex that indicate a dominantly downslope movement of a number of coalesced collapse systems. Spatial and stratal relationships between these shallow failures and the underlying megaslides suggest that the Slump Complex was likely triggered by the development of topography created by the activation of the main structural elements of the lower Megaslide Complex.This study reveals that gravity-driven linked systems undergo lateral segmentation during their evolution, and that their upper section can become unstable, favouring the initiation of a number of shallow failures that produce widespread degradation of the underlying megaslide structures. Gravity-driven linked systems along other margins are likely to share similar processes of segmentation and degradation, implying that the megaslide-related, hydrocarbon trapping structures discovered in the Namibian margin may be common elsewhere, making megaslides an attractive element of deep-water exploration along other gravitationally unstable margins.     

中国盐湖沉积年代学研究进展

盐湖沉积记录了区域的气候和水文变化,是重要的古气候研究对象。年代学是盐湖古气候研究最重要的一项内容,是后续几乎所有工作的基础。盐湖沉积最常用的定年方法有₁₄C定年、铀系定年、光释光(OSL)定年、古地磁定年。受各种定年方法自身的局限性以及盐湖沉积特有的沉积特征,存在不同方法测出的年龄差异较大的现象。准确测定盐湖沉积的年代还较为困难,一定程度制约了盐湖古气候研究的发展。由于盐湖沉积有机质含量低,易受现代碳的污染,其₁₄C年代老于30 cal ka BP时,测出的年龄可能已饱和,需要谨慎对待。未来需要加强铀系定年和光释光定年等方法在盐湖沉积中的基础研究,并开发新的更好的测年方法,提高盐湖沉积测年的准确度,为深入开展盐湖古气候变化及成盐成矿规律研究提供坚实基础。     

粉末压片-X射线荧光光谱法测定盐湖样品中的主次元素

采用粉末样品压片制样,利用波长色散X射线荧光光谱仪对盐湖样品中K、Ca、Na、Mg、Cl、SO_4~(2-)等6个主次元素(组分)含量进行测定。使用化学定值得到的样品作为人工标样,其值作为标准样品参考值,建立了X射线荧光光谱法测定盐湖样品中主次元素的方法。经验证,该分析方法的准确度完全能够满足化学分析的要求,其相对标准偏差RSD7%,分析元素结果与化学法结果的相对误差均小于5%。     

Snow disaster characteristics in Palongzangbu River Basin and mitigation countermeasures for road engineering

The Palongzangbu River Basin contains the highest number of maritime province glaciers in China.There are 130 glacial lakes,64 snow avalanche sites and 28 glacial debris flow gullies distributed within the basin.Snow disasters play a controlling role in the Sichuan-Tibet Highway construction,due to the terrain's special characteristics of high altitude and large height differential.Segmentation mitigation countermeasures for the Sichuan-Tibet Highway are presented based on snow disaster severity level and damage mode of the road.In the Ranwu to Midui section,snow avalanches are regional disasters, so the line should be placed in sunny slopes.In the Midui Gully to Yupu section,the line should be placed in shady slopes and at higher elevations to reduce the risk of glacial lake outburst.In the Yupu to Guxiang section,all three snow disasters are minimal.In the Guxiang to Tongmai section,glacier debris flows are the major threat,thus the road should be placed in shady slopes.     

伊犁盆地伊昭井田煤层煤质特征研究

伊昭井田位于伊犁盆地中西部,煤层资源储量36亿t。赋煤层位为侏罗世水西沟群西山窑组,共含煤12层,其中可采煤层6层,3号煤层和5号煤层为井田主采煤层。对各煤层特征进行了研究,总结了各煤层特征及赋存规律及各煤层煤质特征及工业利用方向。对指导伊犁盆地的煤炭勘查、开发利用及生产布局具有积极意义。     

新疆乌恰萨热克铜矿北矿带库孜贡苏组沉积相、古流向、物源区及其找矿意义——来自砾石统计分析的证据

萨热克盆地库孜贡苏组是萨热克铜矿的赋矿层位,开展沉积相、物源区及古流向研究对隐伏铜矿的勘探具有重要意义。选取萨热克铜矿北矿带库孜贡苏组地表矿化最好的砾岩展开砾石统计分析,结果表明,偏斜度显示砾岩为冲积扇相沉积,砾石叠瓦状和砂岩斜层理产状统计显示古流向为北北东向;砾石成分主要为石英、石英砂岩、砂岩,石英岩等;粒度分布呈宽峰态或尖峰态;物源区为元古宇长城系阿克苏群变质岩剥蚀区;物源补给分为主河流补给和支河流补给2种方式。冲积扇相、古流向、物源区分析确定了矿体的范围、最优的勘探线布置方位和潜在的找矿靶区,具有很好的勘探意义。     

天水盆地新近纪伸展构造——来自沉积与构造变形方面的证据

天水盆地位于青藏高原东北缘高海拔挤压隆升区与鄂尔多斯低海拔伸展区的过渡部位,新构造活动强烈。然而,新构造活动对天水盆地的影响尚不清楚。通过对盆地的沉积环境、构造沉降、构造变形等方面的研究,结果显示:1盆地由风成堆积、洪积扇、河湖相与湖泊相沉积组成,代表沉积中心的河湖相与湖泊相沿控盆断裂(西秦岭北缘断裂、西和断裂与礼县-罗家堡断裂)分布;2盆地经历了16~14Ma、9.2~7.4Ma和3.6~2.6Ma三次加速沉降期;3控盆断裂在同沉积期为正断层。沉积中心沿断裂分布、快速沉降事件及生长正断层表明,天水盆地至少在中新世晚期受控于走滑伸展构造,记录了青藏高原向北东方向的构造挤出作用。