沉积地质学发展新航程——地震沉积学

地震沉积学是在地震地层学和层序地层学基础上发展起来的、沉积地质学与地球物理学相互交叉的新兴学科,在刻画薄层砂体、表征储集层和预测岩性圈闭等方面发挥了重要作用。在表述地震沉积学发展简史的基础上,介绍了地震沉积学的基本概念、基本原理和主要研究流程;在建立精细层序地层格架基础上,重点阐述了90°相移、分频处理与频谱分解、属性优选、地层切片、地球物理反演、地震岩性解释和RGB(红色、绿色、蓝色)地震属性融合等地震沉积学关键技术以及地震沉积相实例分析。认为中国地震沉积学应该围绕不同类型沉积盆地开展油气勘探阶段地震地貌学(地震沉积相模式)和复杂(多样)地震岩性学综合研究,在油气开发阶段,充分利用RGB地震属性融合等多种地球物理方法技术,开展多种成因类型砂体构型和储集层定量表征研究。综合研究表明,地震沉积学是沉积地质学发展的新航程。     

Porcellanite and the urban geology of Darwin,Northern Territory

Porcellanite is a siliceous duricrust which has developed within altered Cretaceous mudrocks in the Darwin city area and is well exposed in coastal cliffs to the north. Its distinctive geotechnical properties include low bulk density, variable strength that is highly dependent on moisture content, and relatively high (but inconsistent) durability. The porcellanite rock mass is inhomogeneous and anisotropic; it is unrippable at the surface, but becomes weaker with depth. It is also highly permeable in places, even karst‐like, due to solution cavities. These characteristics are common to all duricrusts and result from processes of solution, replacement and redeposition by silica‐laden groundwater. Such processes may have been intermittently active through most of the Cenozoic and there is evidence that they continue to the present. The upper 2–4 m of the porcellanite profile is made up of a brittle, high‐strength rock with a silica content approaching that of silcrete. The underlying altered and porous siltstone is much weaker and deforms plastically under loading, due to a cellular microfabric composed largely of opaline silica replacing clay minerals. Porcellanite has long been used as the main building stone in Darwin and is now quarried for shoreline filling. Although some of it is of select fill or road sub‐base quality, crushed porcellanite contains an excess of plastic fines making it unsuitable for basecourse. Porcellanite has been a failure as breakwater stone, despite producing blocks of adequate size.     

Gravity anomalies and subsurface geology in the Westerwald volcanic area, Germany

The area of the present study constitutes an alkaline volcanic province in the eastern sector of the Rhenish massif. A series of gravity measurements were carried out on the volcanic fields of the Westerwald. Three-dimensional modelling and wavelength filtering processing techniques were used to analyze the gravity data. The filtered Bouguer anomaly maps show two major regional gravity features: (a) Increasing Bouguer values towards the northeastern part of the study area could be caused by lateral lithological variations within the upper crust. (2) Local negative Bouguer values in the southwest correlate with magmatic materials of intermediate type. The modelling results indicate that the volcanics of the Westerwald are underlain by two different magmatic complexes at a depth in the range 3.3–10 km with density values of 2680 and 2750 kg/m³. The densities assigned to the local igneous intrusions are in the range of 2314–2948 kg/m³ and at depths between 0.4 and 1.3 km. In the NE a diabase bed was modelled to a maximum depth of approximately 1.6 km using the assigned density of 2800 kg/m³.     

Structural geology of Kusma-Sirkang section of the Kali Gandaki valley and its bearing on the tectonic framework of Nepal Himalaya

The rocks of the Kali Gandaki valley along the Kusma Sirkang section of Central West Nepal fall into two tectonic units having a marked difference in the grade of metamorphism. The units are demarcated by the NW-SE extending Phalebas Thrust which has been considered equivalent to the Chail Thrust of the Kumaon Himalaya by earlier workers. The Kusma Reverse Fault to the north parallels the Phalebas Thrust, both being related to Late Orogenic movements.The fold pattern shows at least four episodes, and it is believed that two of them existed prior to the main Himalayan orogeny of Tertiary time.     

Structural geology practice and learning,from the perspective of cognitive science

Spatial ability is required by practitioners and students of structural geology and so, considering spatial skills in the context of cognitive science has the potential to improve structural geology teaching and practice. Spatial thinking skills may be organized using three dichotomies, which can be linked to structural geology practice. First, a distinction is made between separating (attending to part of a whole) and combining (linking together aspects of the whole). While everyone has a basic ability to separate and combine, experts attend to differences guided by experiences of rock properties in context. Second, a distinction is made between seeing the relations among multiple objects as separate items or the relations within a single object with multiple parts. Experts can flexibly consider relations among or between objects to optimally reason about different types of spatial problems. Third, a distinction is made between reasoning about stationary and moving objects. Experts recognize static configurations that encode a movement history, and create mental models of the processes that led to the static state. The observations and inferences made by a geologist leading a field trip are compared with the corresponding observations and inferences made by a cognitive psychologist interested in spatial learning. The presented framework provides a vocabulary for discussing spatial skills both within and between the fields of structural geology and cognitive psychology.     

Facies architecture and sedimentology of a meandering fluvial system: a Palaeogene example from the Weisselster Basin, Germany

The Schleenhain open pit coal mine, located 30 km south of Leipzig, Germany, exposes Upper Eocene and Oligocene non-marine strata representing fluvial deposition in the centre of the Weisselster Basin. Active mining and successive cuts provided the rare opportunity to obtain a three-dimensional perspective of laterally extensive surface outcrops. These were used to construct a detailed fence diagram, which provided the basis for recognition of key architectural elements in the weakly consolidated meandering stream deposits. In addition to the eight basic architectural elements of Miall (1985 ), the element SL (shallow lake deposits) was newly defined and the element CH (channel) was subdivided into CHg (palaeo-river system) and CHk (small channel). The profiles contain parts of two fining-upward cycles, which are separated by an unconformity spanning the Early Oligocene. Deposits of the first cycle begin with transverse sand bars (downstream accretion deposits-DA) and point bars (lateral accretion deposits-LA). The upper part of the cycle is represented by overbank fines (OF) and the element SL, which consists of laterally discontinuous lenses of dark, plant-bearing, kaolinite-rich clays, that were deposited in shallow lakes adjacent to the active channel. Coal seams interlayered with palaeosols are the main constituents of element OF. Sheetlike bodies of medium to fine gravels (gravel bars and bedforms-GB) on an erosive coal surface mark the beginning of the second cycle. Dissolution of underlying Permian salts and sulphates prior to, during, and after the deposition of the Palaeogene strata caused the development of two synclines within the outcrop. Coal seams and clay horizons which thicken and dip towards the centre of the synclines, provide evidence for their chronological development.     

Structural geology of the Dugald River Zn---Pb---Ag deposit, Mount Isa Inlier, Australia

The sediment-hosted Zn---Pb---Ag deposit at Dugald River is situated 87 km northeast of Mount Isa, NW Queensland. It is a mid-scale base metal accumulation restricted to a black slate sequence of low metamorphic grade. The orebody is tabular and consists of fine- to medium-grained sulphides with a dominant mineralogy of sphalerite, pyrrhotite, pyrite, galena, quartz and muscovite. Three different ore types have been recognized based on mineralization textures; laminated, banded and brecciated. The present reserve stands at 38 million tons of ore averaging 13.0% Zn, 2.1% Pb and 42 g/t Ag. A structural investigation has revealed that six stages of deformation have affected the metasediments in the Dugald River area. The first four (D₁, D₂, D₃ and D₄) are characterized by the extensive development of folds and associated axial plane cleavage. They were all generated in a ductile regime and are of considerable significance for the structural evolution of this region as well as for the emplacement and localization of the sulphide mineralization. D₅ provides a transition towards brittle deformation developing strong kink folds with subhorizontal axial planes. D₆ was a brittle event, producing E-W-trending open folds and major NE and NW strike-slip faults crosscutting all the pre-existing structural elements plus segmenting the orebody. Correlation between the development of deformation and the formation of mineralization can be observed from macro- to microscales. Relationships of mineralization with folds and cleavage indicate a post-D₂ (dominant deformation event) and probably syn-D₄ deformation timing for the Zn---Pb---Ag mineralization at Dugald River, as suggested by the ubiquitous truncations of D₂ fabrics by ore mineral assemblages throughout the deposit.     

Macro‐ and micro‐sedimentology of a modern melt‐out till – Matanuska Glacier,Alaska, USA

The macro‐ and micro‐sedimentology of a supraglacial melt‐out till forming at the Matanuska Glacier was examined in relationship to the properties of the stratified basal zone ice and debris from which it is originating. In situ melting of the basal ice has produced a laminated to bedded diamicton consisting mainly of silt. Macroscopic properties include: discontinuous laminae and beds; lenses of sand, silt aggregates and open‐work gravel; deformed and elongate clasts of clay; widely dispersed pebbles and cobbles, those that are prolate usually with their long axes subparallel to parallel to the bedding. Evidence for deformation is absent except for localized bending of beds over or under rock clasts. Microscopic properties are a unique element of this work and include: discontinuous lineations; silt to granule size laminae; prolate coarse sand and rock fragments commonly with their long axis subparallel to bedding; subangular to subrounded irregular shaped clay clasts often appearing as bands; sorted and unsorted silt to granule size horizons, sometimes disrupted by pore‐water pathways. Limited deformation occurs around rock clasts and thicker parts of lamina. This study shows that in situ melting of debris‐rich basal ice can produce a laminated and bedded diamicton that inherits and thereby preserves stratified basal ice properties. Production and preservation of supraglacial melt‐out till require in situ melting of a stagnant, debris‐rich basal ice source with a low relief surface that becomes buried by a thick, stable, insulating cover of ice‐marginal sediment. Also required are a slow melt rate and adequate drainage to minimize pore‐water pressures in the till and overlying sediment cover to maintain stability and uninterrupted deposition. Many modern and ancient hummocky moraines down glacier of subglacial overdeepenings probably meet these process criteria and their common occurrence suggests that both modern and pre‐modern supraglacial melt‐out tills may be more common than previously thought.     

The Cretaceous/Tertiary boundary: sedimentology and micropalaeontology at El Mulato section, NE Mexico

ABSTRACT In the El Mulato section (NE Mexico), the Upper Cretaceous marly Méndez and the Lower Palaeogene marly Velasco Formations are separated by a clastic unit. Benthic foraminifera from both marly formations indicate lower bathyal depths. The clastic unit, in contrast, contains platform sands, muddy pebbles and neritic (shallow) faunas mixed with microspherules, indicating that it was allochthonously deposited into the deep basin. The diversity and the variability in origin of the components in the clastic unit, and its sedimentological features, support a model of deposition by turbidity currents related to mass-wasting processes triggered by the Cretaceous/Tertiary (K/T) boundary impact. Planktic foraminifera were affected by a catastrophic extinction at the K/T boundary, whereas benthic foraminifera show reorganization of the community structure rather than significant extinction. The benthic faunal turnover may have resulted from the drop in primary productivity after the asteroid impact at the end of the Cretaceous.     

Geological history and petroleum system of the Mittelplate oil field, Northern Germany

The geological history of Germany’s largest and most productive petroleum accumulation, the Mittelplate oil field in Schleswig-Holstein (Northern Germany), is reconstructed by simulating the structural and thermal evolution along a 2D cross-section. The Mittelplate field is located at the western flank of the Büsum salt dome at the transition from the Schleswig-Holstein mainland to the German North Sea Sector. Organic geochemical data confirm the Lower Jurassic Posidonia Shale to be the predominant oil source rock in the Schleswig-Holstein area. The studied section is characterized by salt walls and salt domes built up by Permian evaporites. Reconstruction of the structural and thermal evolution of the Mittelplate field by means of basin modelling reveals the dominating influence of salt dynamics on the entire petroleum system: The development of secondary rim-synclines during salt rise provided accommodation space for the deposition of the Posidonia Shale as well as the deltaic Middle Jurassic reservoir sandstones. The rise of the nearby Oldenswort salt wall controlled the timing of maturation and petroleum generation during Cenozoic times. Hydrocarbon migration from the Posidonia Shale into the reservoirs occurred up-dip from the deeper subsiding rim-syncline into the structural trap with the Middle Jurassic reservoir sandstones pinching out at the flank of the Büsum salt dome. Along the modelled 2D section the field’s recent temperature field and its complex reservoir architecture are reconstructed.     

Structural and engineering geology of the East Gate Landslide, Purcell Mountains, British Columbia, Canada

The East Gate Landslide is a prehistoric landslide that was reactivated in January 1997. The slope failure took place in the lower greenschist metasedimentary units of the Precambrian Horsethief Creek Group. The Grizzly Creek Thrust is a regional overturned fault that coincides with the location of the headscarp of the East Gate Landslide. Four discontinuity sets were recognised from detailed engineering geological mapping of the headscarp and surrounding area. The main scarp of the section reactivated in 1997 was sub-divided into three structural domains based on its position within the landslide, lithology, and orientation of the discontinuity sets. Limit-equilibrium techniques, finite-difference (FLAC) and distinct-element (UDEC) codes were used to investigate the failure mechanism of the 1997 event. The results of the field observations and numerical models suggest that the 1997 failure involved a complex mechanism incorporating components of rock-slumping, bi-planar, and pseudo-circular failure that was controlled by both the orientation of the discontinuity sets and reduced rock-mass quality due to tectonic deformation.     

Structural synthesis of the Northern Calcareous Alps, TRANSALP segment

The Northern Calcareous Alps (NCA) are the site of very large top-to-north convergent movements during Cretaceous–Tertiary Alpine mountain building. To determine the amount of shortening, the depth of detachment and the style of deformation, we retro-deformed an approximately 40 × 40 km area comprising the Lechtal and Allgäu Nappes. On the basis of all available geological data and processed sections of the TRANSALP reflection seismic experiment, coherent 3D models were constructed by splining lines from N–S cross-sections. Integration of 3D kinematic modeling and field data shows the following. The structure of the Lechtal Nappe is controlled by the Triassic Hauptdolomit. Four main thrusts link to a detachment at 2–6 km depth below sea level. Shortening estimates vary, from 25% (east) to 42% (west). Additional contraction is accommodated by folding. In the east the subjacent Allgäu Nappe can be traced about 10 km down-plunge, and is shortened by about one third. In the western part the downplunge width is at least 15–20 km, with restorable shortening of one third. The triple (Inntal, Lechtal, Allgäu Nappes) NCA nappe system was moved uniformly N–S to produce laterally heterogeneus shortening of 40–90 km or 50–67%. We suggest that the NCA are underlain by substantial amounts of buried Molasse sediments and/or overthrust units of Helvetic and Rheno-Danubian Flysch, indicating post-Eocene N–S shortening of at least 55 km. Restored to an initial configuration, the basin topography of the NCA reveals strong E–W thickness variations of the Triassic Wettersteinkalk and Hauptdolomit platform carbonates. Such variations may pertain to N–S trending growth faults, which were important precursors to later Jurassic extension of the Austroalpine passive margin. Such structures are unlikely to be seen in the conventional N–S cross-sections, but form an essential geometrical and mechanical element in later, convergent mountain building.     

藏北北羌塘盆地晚三叠世古风化壳地质地球化学特征及其意义

对最近在藏北羌塘盆地菊花山、肖茶卡、石水河等地区新发现的肖茶卡组顶部的粘土质角砾岩的地质、地球化学特征研究表明:其岩石矿物成分、结构构造、角砾层产状及剖面演化序列等与古风化壳的形成及其特征较为一致;相对于基岩,古风化壳的主量元素表现为CaO、CO2的淋失和SiO2、Al2O3、Fe2O3、K2O、Na2O、MnO、P2O5等不同程度的相对富集;古风化壳中的粘土质风化残积层的稀土元素具有明显的富集,表现为LREE含量远大于HREE的特征,存在明显的Ce的正异常以及Eu的负异常;微量元素除Mo、Sn和U外,粘土质风化残积层的其余元素含量均有明显的增加。这些特征从另一角度证实了北羌塘盆地晚三叠世存在明显的沉积间断。晚三叠世肖茶卡组顶部古风化壳的发现,为了解区域地壳发展史、古气候、古地理演化、层序地层的划分与对比、羌塘含油气盆地分析等提供了重要的依据。     

The Structural geology of the Troms Area (Barents-Sea)

This paper reviews the exploration history of the Barents Sea part of the Norwegian continental shelf. The main structural elements which so far have been identified in the Troms/Finnmark/Barents Sea region are outlined and discussed. Special attention is given to the selected Area I outside Troms, where according to latest government plans, drilling will start in 1978.At least two different fault systems are discribed in Area I. The salt diapirs in the Tromsø Basin and their location relative to the fault pattern are discussed. A schematic structural model for Area I is suggested.     

The Structural geology of the Troms Area (Barents-Sea)

This paper reviews the exploration history of the Barents Sea part of the Norwegian continental shelf. The main structural elements which so far have been identified in the Troms/Finnmark/Barents Sea region are outlined and discussed. Special attention is given to the selected Area I outside Troms, where according to latest government plans, drilling will start in 1978. At least two different fault systems are discribed in Area I. The salt diapirs in the Tromsø Basin and their location relative to the fault pattern are discussed. A schematic structural model for Area I is suggested.     

Multiproxy Analyses of Stratigraphy and Palaeoenvironment of the Late Palaeolithic Grabow Floodplain Site,Northern Germany

Changing river courses and fluctuations of the water table were some of the most fundamental environmental changes that humans faced during the Late Glacial, particularly as these changes affected areas intensively used for settlement and resource exploitation. Unfortunately, only a few stratigraphies have been documented in the North European plain that show the interaction between river development, vegetation history, and occupation by Late Palaeolithic humans. Here, we present the results of detailed stratigraphical studies (pedology, archaeology, chrono‐, tephra‐, and palynostratigraphy) at the Federmesser site Grabow 15 located in the broad Elbe River valley. The research aimed to produce a model of site formation based on a multiproxy approach, relating the local evidence to the palaeoenvironmental and settlement history of the wider region. After deposition of fluvial sands during the Late Pleniglacial in a braided setting, the river course developed locally toward a meandering system at the transition from the Older Dryas to the Allerød, while periodic flooding led to the deposition of floodplain sediments during the early Allerød. The floodplain was settled by people of the earliest “Federmessergruppen,” who are believed to have chosen this open floodplain area along the river for collecting and processing amber of local origin. Their artifacts became embedded in the aggrading floodplain sediments. In the late Allerød, floodplain sedimentation ceased and a Fluvisol‐type soil developed, indicating a trend toward geomorphic stability. The Fluvisol was then covered by silty floodplain sediments due to a rising water level during the late Younger Dryas resulting in the cessation of human occupation in the area. Subsequent organic‐rich Late Glacial/Holocene sediments preserved the settlement remains to the present.