尼日尔三角洲盆地深水沉积的二元结构特征及层序划分

本文根据测井曲线及地震相特征,建立了深水层序界面划分的5种判别标准,将尼日尔三角洲盆地深水区中中新统一上中新统地层划分了6个三级层序,2个二级层序.根据深水沉积自身沉积旋回所具有的二元结构特征及三角洲与陆架区相对海平面变化之间的关系,将经典的三分体系域划分为二分体系域:异地沉积体系域和原地沉积体系域.其中,异地沉积体系域从基准面下降开始海侵早期,主要发育重力流沉积(块状搬运沉积、浊积扇);原地沉积体系域从海侵中、晚期—基准面上升最大位置结束,主要以原地沉降的泥质披覆沉积为主.本文分析了层序发育的影响因素,综合研究认为:气候条件、海平面变化、构造抬升、沉积物供给、大陆架宽窄等共同制约了研究区深水沉积层序的发育.     

水下分流河道砂体的叠置样式及其储层非均质性变化特征

在研究区目的层进行高分辨率层序地层研究的基础上,对分流河道微相的储层质量非均质性进行分析,应用不同级次基准面旋回成因的沉积学分析和表征储层质量非均质性的各项岩芯化验、统计学数据定量分析,指出基准面旋回因素对不同级次水下分流河道主体储层质量非均质性影响存在差异:单一水下分流河道和单期复合水下分流河道的储层质量非均质性呈正韵律变化,多期复合水下分流河道储层质量非均质性分布呈不规则趋势,多级次的基准面旋回及其伴随的可容纳空间变化所引起的沉积环境的变化影响水下分流河道储层非均质性.     

四川夏塞银铅锌多金属矿床1号矿体原生晕地球化学特征

四川夏塞银铅锌多金属矿床位于西南"三江"义敦岛弧构造带中段,是与绒伊措岩体密切相关的浅成中低温热液型银铅锌矿床。对夏塞矿区1号矿体9个中段采样分析,通过数理统计分析、分带序列研究、地球化学参数计算、建立剥蚀模型等方法,系统详细地研究了矿体原生晕地球化学特征。研究表明:(1)1号矿体原生晕找矿的主要指示元素:Ag、Pb、Zn、Cu、Sb、Hg、Cd、Sn,次要指示元素:Bi、W、B、As、Au、Mn;(2)原生晕轴向分带序列为:Hg-Pb-Bi-Sn-Cd-Zn-Cu-As-Ag-W-Au-Sb-Ba-V-Mo-Mn,出现"反分带"现象;(3)成矿过程存在多次叠加,轴向地球化学参数变化曲折,出现多次转折,反应成矿过程复杂。综合各项特征,推测1号矿体深部可能有盲矿存在。     

准噶尔盆地西北缘二叠系扇三角洲层序特征及砾岩油藏分布规律

岩性地层油气藏是我国陆上油气勘探的重点领域之一,本文针对我国西部前陆盆地勘探程度相对较低的中深层陆相砾岩油藏,选取准噶尔盆地西北缘八区中-下二叠统作为研究对象,综合岩心观察、测井和三维地震资料的精细解释,在开展层序地层学和沉积相研究的基础上重点解剖典型的扇三角洲砾岩油藏,分析层序地层格架内砾岩油藏的分布特征,揭示出研究区具有一扇多藏的油藏分布规律。勘探开发实践表明,研究区砾岩油藏主要发育于水进体系域扇三角洲前缘水下分流河道储集体中,其次为高水位体系域中,以物性遮挡岩性油藏、物性封闭岩性油藏以及断裂-岩性复合油藏为特征。     

Sequences and biofacies packages in the mid‐Cenozoic Gambier Limestone,South Australia: Reappraisal of foraminiferal evidence

The mid to outer neritic carbonates of the Gambier Limestone (Upper Eocene to lower Middle Miocene) can be divided into seven units by using criteria of sequence stratigraphy and foraminiferal biofacies. The boundaries fall mainly on erosional surfaces, even though the temporal duration of these surfaces appears to be largely beyond the resolution of foraminiferal biostratigraphy. The Eocene/Oligocene contact is distinctively unconformable in several sections, with at least part of the Upper Eocene sediments missing. Chert nodules, common to abundant in most sections, are associated with deep‐ or cool‐water benthic assemblages (> 100–200 m and <15°C), indicating cool, nutrient‐rich bottom conditions probably influenced by the Antarctic Circumpolar Current beginning during the Early Oligocene. The mid‐Oligocene fall in sea‐level was probably coupled with a major local uplift that removed at least part of the Lower Oligocene, an event widely recorded in the Australian‐New Zealand region. In areas weakly affected, this glacioeustatic lowstand is represented by chert‐free limestone and grey to pink dolomites in some sections, with a poorly preserved assemblage comprising few planktonic and deep‐water benthic species. Local unconformities separate regional unconformity‐bounded or allostratigraphic packages of strata to represent third‐order sequences. Although variations in local subsidence might have influenced accumulation space and sediment thickness, glacioeustatic influence on the packaging of the sequences and units of the Gambier Limestone was easily the more effective and concordant with the global patterns.     

Potassium‐argon dates from the Arltunga Nappe complex,northern territory

Twenty‐four mineral separates from the Arunta Complex, four from the metamorphosed Heavitree Quartzite (White Range Quartzite), and one whole rock sample of metamorphosed Bitter Springs Formation, all from the western part of the White Range Nappe of the Arltunga Nappe Complex, and two samples from the autochthonous basement west of the nappe have been dated by the K‐Ar method. The samples from the basement rocks form two groups. Those in the southern or frontal part of the nappe are of Middle Proterozoic (Carpentarian) age (1660–1368 m.y.), determined on hornblende, biotite, and muscovite. In the northern or rear part of the nappe, all but one of the muscovite samples and two biotites are of Middle Silurian to Early Carboniferous age (431–345 m.y.); the remainder of the biotite dates range from 1775 to 548 m.y. (including the two samples from the autochthon), and two hornblendes gave dates of 1639 and 2132 m.y. respectively. All the muscovite samples from the Heavitree Quartzite, and the whole rock sample from the Bitter Springs Formation gave Early to Middle Carboniferous dates (358–322 m.y.). The findings support the identification of the White Range Quartzite as the metamorphosed part of the Heavitree Quartzite, which in turn supports the interpretation of the structure of the area as a large, basement‐cored fold nappe. In addition, they date the time of the Alice Springs Orogeny as pre‐Late Carboniferous, which agrees with fossil evidence from elsewhere in the area. The Alice Springs Orogeny was accompanied by widespread greenschist facies meta‐morphism that progressively metamorphosed the Heavitree Quartzite and Bitter Springs Formation, and retrogressively metamorphosed the Arunta Complex. However, the basement rocks in the southern part of the nappe escaped this metamorphism and retain a Middle Proterozoic age, thus dating the time of the Arunta Orogeny in this region as Carpentarian or older.     

Biological and abiological processes in a simulated sedimentary system

A simulated sedimentary system, capable of being controlled and monitored for a considerable length of time without undue disturbance, has been assembled and applied to specific problems of the genesis of stratiform Pb‐Zn ore deposits. Results have been obtained relevant to: (i) the concentration of Pb and Zn from brines to underlying sediments; (ii) the behaviour of microorganisms in metal‐rich, highly saline environments; (iii) the precipitation diagenesis of calcium and magnesium carbonates; and (iv) the diagenesis of organic matter.

The experiment has demonstrated the feasibility of simulating a complex sedimentary environment in the laboratory and has indicated the potential of such systems for the investigation of geobiological problems.     

A reinterpretation of seismic data in the Laura Basin,Queensland

The results of the seismic surveys recorded during 1963 and 1968 for Marathon Petroleum and Crusader Oil in the Laura Basin, north Queensland, have been reinterpreted. Seismic reflections which dip almost continuously from 0.6 to 4.0 seconds reflection time may come from the base of and within an 8000 m sequence of Permo‐Carboniferous sediments, which may underlie the flat‐lying Mesozoic Laura Basin sediments and overlie the heavily folded Carboniferous‐Devonian sediments in the Hodgkinson Basin. Further seismic investigation of this area is recommended since a thick Permo‐Carboniferous sedimentary section here could be prospective for hydrocarbons.     

Crust restoration for the western Lachlan Orogen using the strain-reversal,area-balancing technique: implications for crustal components and original thicknesses

Strain reversal of structural/stratigraphic profiles at different scales in the western Lachlan Orogen provides a perspective on original crustal thickness estimates, the former depositional basin width of the proto-western Lachlan Orogen, the original sedimentary-fan thickness, and the possible length extent of lower crust lost by subduction. Retrodeformation using strain-reversal techniques allows basin reconstruction giving an original width of the western Lachlan Orogen basin receptor of between 800 km (minimum) and ～1150 km (maximum), depending on the amount of stratal duplication allowed in the turbidites. Crude area balancing of the regional cross-section, adding in sectional volume lost by erosion and assuming strain compatibility between the upper and lower crust, suggests that the predeformation crustal thickness ranges between 15 km and ～21 km, with a lower crustal thickness (oceanic lithosphere) of ～9 km and a turbidite fan thickness of ～6 km (minimum) and ～12 km (maximum allowable), respectively. Disparity between the calculated fan thickness and that derived from measured stratigraphic sections adjusted for strain (～6 km) indicates that some form of crustal stacking must be important in structural thickening of the turbidite crustal component. By varying shortening due to fault stacking, mass balance dictates the mismatch of the upper crustal (uc) and lower crustal (lc) retrodeformed lengths, and therefore provides an estimate of lower crustal loss by subduction. End members range from: (i) a 12 km-thick fan without fault duplication, a basin width of ～800 km where uc = lc giving no lower crustal loss by subduction; to (ii) a ～6 km fan, requiring duplication by faulting, a basin of ～1150 km where uc > lc, and ～360 km of lower crust length (～30%) lost by subduction. This suggests that the total thickness of underplated igneous material in the western Lachlan Orogen is low, probably < ～2 km.     

Heavitree Quartzite,a Neoproterozoic (ca 800–760 Ma), high‐energy,tidally influenced,ramp association,Amadeus Basin,central Australia

The Neoproterozoic Heavitree Quartzite is widespread in the Amadeus Basin and has correlatives in all of the major central Australian intracratonic basins. The origin of the formation is enigmatic, not only because of its widespread sheet‐like distribution and uniformity of composition, but also because intense silicification makes facies studies difficult. Recently discovered exposures at the eastern end of the basin are relatively free of diagenetic quartz allowing a detailed study of sedimentary structures and an understanding of the depositional architecture of the formation. The formation, which consists largely of pale‐tan or white quartzose sandstone interbedded with rare laminated mudstone and conglomerate intervals, was deposited in at least four depositional sequences. The sheet‐like nature of the sandstone results from an abundant supply of sediments deposited in a high‐energy, open, shelf‐like environment on a regionally subsiding, low‐gradient ramp. Environmental settings switched both laterally and temporally between sand waves deposited by reversing tidal flow and higher velocity unidirectional currents involving dunes and plane beds. In the early stages of deposition, mud‐dominated, tidal‐flat environments alternated with higher energy, sand‐dominated, tidally influenced settings. However, in the later stages of deposition a major eustatic sea‐level fall moved base‐level basinwards, earlier sediments were reworked by streams to form a ravinement surface, gravel was carried well into the basin and fines largely disappeared from the environment. Gravel deposition was followed by a return to high‐energy, tidally influenced deposits involving large sand waves or dunes. Towards the top of the formation sand waves deposited by reversing tidal currents gradually decline and are eventually replaced by dunes deposited by unidirectional current flow. The transition to the shallow‐marine, anoxic rocks of the Bitter Springs Formation is gradational in response to increased accommodation in a ramp setting which lacked a clearly defined shelf break. The Heavitree Quartzite was probably deposited as a direct response to the events surrounding the assembly and breakup of Rodinia, in particular peneplanation during regional uplift in response to a rising mantle plume followed by broad regional subsidence as the plume decayed prior to the breakup of the supercontinent. The large supply of quartz sand resulted from peneplanation associated with the rising plume and the lack of soil‐stabilising vascular plants, an environmental setting with no modern analogue. The ultimate disposition of fines is not known but, given the environment of deposition, it is likely that they were removed during peneplanation and bypassed the sag basin completely.