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1.
Subsidence analyses from the Betic Cordillera, southeast Spain   总被引：1，自引：0，他引：1  
Fifty‐four Mesozoic–Cenozoic stratigraphic sections from the Betic Cordillera of southeast Spain have been analysed in order to estimate the timing and amount of lithospheric stretching that occurred at the western end of the Tethyan Ocean since the Hercynian Orogeny. The standard backstripping technique has been used in order to calculate the water‐loaded subsidence of basement for each section. Water‐loaded subsidence curves were then inverted in order to determine the variation of lithospheric strain rate as a function of time, which yields estimates of timing, magnitude and intensity of stretching. Rifting commenced during the Late Permian/Early Triassic times and continued intermittently throughout the Mesozoic in response to the opening of the Tethyan Ocean to the east and the opening of the Atlantic Ocean to the west. Two major events in the Permo‐Triassic/Early Jurassic and the Late Jurassic/Early Cretaceous can be clearly identified. Stretching factors are generally small (1.1–1.25) probably because the Betic Cordillera was located at the westernmost end of the Tethys. Peak strain rates of ～10?15 s?1 were obtained for Mesozoic rift events and these values are in broad agreement with those obtained throughout the Tethyan Realm. We have also analysed the Neogene extensional event, which played an important role in forming the existing Mediterranean Sea. A combination of well‐log information and calibrated seismic reflection data was modelled. Peak strain rates in these younger basins are almost one order of magnitude faster than those estimated for the Mesozoic basins. These higher values appear to be typical of back‐arc extensional basins elsewhere. To the west and north of the Betic Cordillera, the Guadalquivir foreland basin developed as extension took place further east. Backstripped sections from this basin clearly record the northward migration of foreland basin subsidence through time.  相似文献   

2.
The Triassic Moenkopi Formation in the Salt Anticline Region, SE Utah, represents the preserved record of a low‐relief ephemeral fluvial system that accumulated in a series of actively subsiding salt‐walled mini‐basins. Development and evolution of the fluvial system and its resultant preserved architecture was controlled by the following: (1) the inherited state of the basin geometry at the time of commencement of sedimentation; (2) the rate of sediment delivery to the developing basins; (3) the orientation of fluvial pathways relative to the salt walls that bounded the basins; (4) spatially and temporally variable rates and styles of mini‐basin subsidence and associated salt‐wall uplift; and (5) temporal changes in regional climate. Detailed outcrop‐based tectono‐stratigraphic analyses demonstrate how three coevally developing mini‐basins and their intervening salt walls evolved in response to progressive sediment loading of a succession of Pennsylvanian salt (the Paradox Formation) by the younger Moenkopi Formation, deposits of which record a dryland fluvial system in which flow was primarily directed parallel to a series of elongate salt walls. In some mini‐basins, fluvial channel elements are stacked vertically within and along the central basin axes, in response to preferential salt withdrawal and resulting subsidence. In other basins, rim synclines have developed adjacent to bounding salt walls and these served as loci for accumulation of stacked fluvial channel complexes. Neighbouring mini‐basins exhibit different styles of infill at equivalent stratigraphic levels: sand‐poor basins dominated by fine‐grained, sheet‐like sandstone fluvial elements, which are representative of nonchannelised flow processes, apparently developed synchronously with neighbouring sand‐prone basins dominated by major fluvial channel‐belts, demonstrating effective partitioning of sediment route‐ways by surface topography generated by uplifting salt walls. Reworked gypsum clasts present in parts of the stratigraphy demonstrate the subaerial exposure of some salt walls, and their partial erosion and reworking into the fill of adjoining mini‐basins during accumulation of the Moenkopi Formation. Complex spatial changes in preserved stratigraphic thickness of four members in the Moenkopi Formation, both within and between mini‐basins, demonstrates a complex relationship between the location and timing of subsidence and the infill of the generated accommodation by fluvial processes.  相似文献   

3.
A two‐dimensional kinematic model is presented for superimposed basins. It is based on a finite‐element algorithm in the Lagrangian system, which incorporates different stages of lithosphere stretching and shortening to simulate alternating extension and inversion. The Jiyang Basin, developed in the North China, is a superimposed basin comprising four proto‐type basins separated by several unconformities. Four‐phase extension and two‐phase inversion have developed in this basin since the Late Mesozoic era. The thermal history of the basin is modelled based on a seismic cross‐section across the basin. Tectonic subsidence (or uplift) histories from backstripping serve as the objective functions, and crustal thickness, as well as heat flow, provides additional constraints. Effects of different Mesozoic erosion on the thermal history are discussed. Modelling results show that the thermal history of the Jiyang Basin since the Late Mesozoic can be divided into six stages, including four phases of heating accompanied by following thermal attenuation, and two phases of cooling with following thermal recovery. The model also implies a variant pattern of thermal regime in the basin. In the deepest centres of the depressions, the maximum heat flow occurred during the Late Mesozoic, but in the slopes of the depressions, the maximum heat flow appeared in the Cenozoic era.  相似文献   

4.
Pro- vs. retro-foreland basins   总被引：1，自引：0，他引：1  
Alpine‐type mountain belts formed by continental collision are characterised by a strong cross‐sectional asymmetry driven by the dominant underthrusting of one plate beneath the other. Such mountain belts are flanked on either side by two peripheral foreland basins, one over the underthrust plate and one over the over‐riding plate; these have been termed pro‐ and retro‐foreland basins, respectively. Numerical modelling that incorporates suitable tectonic boundary conditions, and models orogenesis from growth to a steady‐state form (i.e. where accretionary influx equals erosional outflux), predicts contrasting basin development to these two end‐member basin types. Pro‐foreland basins are characterised by: (1) Accelerating tectonic subsidence driven primarily by the translation of the basin fill towards the mountain belt at the convergence rate. (2) Stratigraphic onlap onto the cratonic margin at a rate at least equal to the plate convergence rate. (3) A basin infill that records the most recent development of the mountain belt with a preserved interval determined by the width of the basin divided by the convergence rate. In contrast, retro‐foreland basins are relatively stable, are not translated into the mountain belt once steady‐state is achieved, and are consequently characterised by: (1) A constant tectonic subsidence rate during growth of the thrust wedge, with zero tectonic subsidence during the steady‐state phase (i.e. ongoing accretion‐erosion, but constant load). (2) Relatively little stratigraphic onlap driven only by the growth of the retro‐wedge. (3) A basin fill that records the entire growth phase of the mountain belt, but only a condensed representation of steady‐state conditions. Examples of pro‐foreland basins include the Appalachian foredeep, the west Taiwan foreland basin, the North Alpine Foreland Basin and the Ebro Basin (southern Pyrenees). Examples of retro‐foreland basins include the South Westland Basin (Southern Alps, New Zealand), the Aquitaine Basin (northern Pyrenees), and the Po Basin (southern European Alps). We discuss how this new insight into the variability of collisional foreland basins can be used to better interpret mountain belt evolution and the hydrocarbon potential of these basins types.  相似文献   

5.
The China–Mongolia border region contains many late Mesozoic extensional basins that together constitute a regionally extensive basin system. Individual basins within the system are internally composed of a family of sub‐basins filled with relatively thin sedimentary piles mostly less than 5 km in thickness. There are two types of sub‐basins within the basins, failed and combined, respectively. The failed sub‐basins are those that failed to continue developing with time. In contrast, the combined ones are those that succeeded in growing by coalescing adjacent previously isolated sub‐basins. Thus, a combined sub‐basin is bounded by a linked through‐going normal fault that usually displays a corrugated trace on map view and a shallower dip on cross‐section. Along‐strike existence of discrete depocenters and alternation of sedimentary wedges of different types validate the linkage origin of combined sub‐basins. Localized high‐strain extension resulted in large‐amount displacement on linked faults, but contemporaneously brought about the cessation of some isolated fault segments and the formation of corresponding failed sub‐basins in intervening areas between active linked faults. Some combined sub‐basins might have evolved into supradetachment basins through time, concurrent with rapid denudation of footwall rocks and formation of metamorphic core complexes in places. A tectonic scenario of the broad basin system can be envisioned as an evolution from early‐stage distributed isolated sub‐basins to late‐stage focused combined or/and supradetachment sub‐basins bounded by linked faults, accompanied by synchronous cessation of some early‐formed sub‐basins. Initiation of the late Mesozoic extension is believed to result from gravitational collapse of the crust that had been overthickened shortly prior to the extension. Compression, arising from collision of Siberia and the amalgamated North China–Mongolia block along the Mongol–Okhotsk suture in the time interval from the Middle to Late Jurassic, led to significant shortening and thickening over a broad area and subsequent extensional collapse. Pre‐ and syn‐extensional voluminous magmatism must have considerably reduced the viscosity of the overthickened crust, thereby not only facilitating the gravitational collapse but enabling the lower‐middle crust to flow as well. Flow of a thicker crustal layer is assumed to have occurred coevally with upper‐crustal stretching so as to diminish the potential contrast of crustal thickness by repositioning materials from less extended to highly extending regions. Lateral middle‐ and lower‐crustal flow and its resultant upward push upon the upper crust provide a satisfying explanation for a number of unusual phenomena, such as supracrustal activity of the extension, absence or negligibleness of postrift subsidence of the basin system, less reduction of crustal thickness after extension, and non‐compression‐induced basin inversion, all of which have been paradoxical in the previous study of the late Mesozoic basin tectonics in the China–Mongolia border region.  相似文献   

6.
The subsidence and exhumation histories of the Qiangtang Basin and their contributions to the early evolution of the Tibetan plateau are vigorously debated. This paper reconstructs the subsidence history of the Mesozoic Qiangtang Basin with 11 selected composite stratigraphic sections and constrains the first stage of cooling using apatite fission track data. Facies analysis, biostratigraphy, palaeo‐environment interpretation and palaeo‐water depth estimation are integrated to create 11 composite sections through the basin. Backstripped subsidence calculations combined with previous work on sediment provenance and timing of deformation show that the evolution of the Mesozoic Qiangtang Basin can be divided into two stages. From Late Triassic to Early Jurassic times, the North Qiangtang was a retro‐foreland basin. In contrast, the South Qiangtang was a collisional pro‐foreland basin. During Middle Jurassic‐Early Cretaceous times, the North Qiangtang is interpreted as a hinterland basin between the Jinsha orogen and the Central Uplift; the South Qiangtang was controlled by subduction of Meso‐Tethyan Ocean lithosphere and associated dynamic topography combined with loading from the Central Uplift. Detrital apatite fission track ages from Mesozoic sandstones concentrate in late Early to Late Cretaceous (120.9–84.1 Ma) and Paleocene–Eocene (65.4–40.1 Ma). Thermal history modelling results record Early Cretaceous rapid cooling; the termination of subsidence and onset of exhumation of the Mesozoic Qiangtang Basin suggest that the accumulation of crustal thickening in central Tibet probably initiated during Late Jurassic–Early Cretaceous times (150–130 Ma), involving underthrusting of both the Lhasa and Songpan–Ganze terranes beneath the Qiangtang terrane or the collision of Amdo terrane.  相似文献   

7.
New seismic reflection profiles from the Tugrug basin in the Gobi‐Altai region of western Mongolia demonstrate the existence of preserved Mesozoic extensional basins by imaging listric normal faults, extensional growth strata, and partially inverted grabens. A core hole from this region recovered ca. 1600 continuous meters of Upper Jurassic – Lower Cretaceous (Kimmeridgian–Berriasian) strata overlying Late Triassic volcanic basement. The cored succession is dominated by lacustrine and marginal lacustrine deposits ranging from stratified lacustrine, to subaqueous fan and delta, to subaerial alluvial‐fluvial environments. Multiple unconformities are encountered, and these represent distinct phases in basin evolution including syn‐extensional deposition and basin inversion. Prospective petroleum source and reservoir intervals occur, and both fluid inclusions and oil staining in the core provide evidence of hydrocarbon migration. Ties to correlative outcrop sections underscore that, in general, this basin appears to share a similar tectono‐stratigraphic evolution with petroliferous rift basins in eastern Mongolia and China. Nevertheless, some interesting contrasts to these other basins are noted, including distinct sandstone provenance, less overburden, and younger (Neogene) inversion structures. The Tugrug basin occupies an important but perplexing paleogeographic position between late Mesozoic contractile and extensional provinces. Its formation may record a rapid temporal shift from orogenic crustal thickening to extensional collapse in the Late Jurassic, and/or an accommodation zone with a Mesozoic strike‐slip component.  相似文献   

8.
Regional seismic reflection profiles tied to lithological and biostratigraphic data from deep exploration wells have been used to determine the structure and evolution of the poorly known basins of northern Somalia. We recognize six major tectonostratigraphic sequences in the seismic profiles: Middle‐Late Jurassic syn‐rift sequences (Adigrat and Bihen Group), ?Cenomanian‐Campanian syn‐rift sequences (Gumburo Group), Campanian‐Maastrichtian syn‐rift sequences (Jesomma Sandstones), Palaeocene post‐rift sequences (Auradu Limestones), Early‐Middle Eocene post‐rift sequences (Taleh Formation) and Oligocene‐Miocene (Daban Group) syn‐rift sequences. Backstripping of well data provides new constraints on the age of rifting, the amount of crustal and mantle extension, and the development of the northern Somalia rifted basins. The tectonic subsidence and uplift history at the wells can be explained by a uniform extension model with three episodes of rifting punctuated by periods of relative tectonic quiescence and thermal subsidence. The first event initiated in the Late Jurassic (~156 Ma) and lasted for ~10 Myr and had a NW‐SE trend. We interpret the rift as a late stage event associated with the break‐up of Gondwana and the separation of Africa and Madagascar. The second event initiated in the Late Cretaceous (~80 Ma) and lasted for ~20–40 Myr. This event probably correlates with a rapid increase in spreading rate on the ridges separating the African and Indian and African and Antarctica plates and a contemporaneous slowing down of Africa's plate motion. The backstripped tectonic subsidence data can be explained by a multi‐rift extensional model with stretching factor, β, of 1.09–1.14 and 1.05–1.28 for the first and second rifting events, respectively. The model, fails, however, to completely explain the slow subsidence and uplift history of the margin during Early Cretaceous to Late Cretaceous. We attribute this slow subsidence to the combined effect of a sea‐level fall and regional uplift, which caused a major unconformity in northern Somalia. The third and most recent event occurred in the Oligocene (~32 Ma) and lasted for ~10 Myr. This rift developed along the Gulf of Aden and reactivated the Guban, Nogal and Daroor basins, and is related to the opening of the Gulf of Aden. As a result of these events the crust and upper mantle were thinned by up to a factor of two in some basins. In addition, several distinct petroleum systems developed. The principal exploration play is for Mesozoic petroleum systems with the syn‐rift Oligocene‐Miocene as a subordinate objective owing to low maturity and seal problems. The main seals for the different plays are various shales, some of which are also source rocks, but the Early Eocene evaporites of the Taleh formations can also perform a sealing role for Palaeogene or older generated hydrocarbons migrating vertically.  相似文献   

9.
Tectonic subsidence and uplift may be recorded by concomitant sedimentation, not only from decompacted accumulation curves but also from the evolving depositional environment relative to sea level at the time. In thrust belts there are two types of processes capable of generating vertical movements, each with different wavelengths and amplitudes. Regional subsidence is driven by flexural loading by the orogenic hinterland, the thrust belt and accumulated sediments of the underlying foreland lithosphere. Within this flexure, the foreland thrust belt will generate areas of local uplift, notably at the crests of thrust anticlines. In this contribution we examine how these processes have interacted to influence relative sea level as recorded by late Neogene sediments in an array of basins developed above and adjacent to the Maghrebian thrust belt of central Sicily. Two particular periods are addressed, the late Tortonian to early Messinian (Terravecchia Formation) and early to early late Pliocene. The earlier of these is characterized by a deltaic complex that formed prograding depositional geometries, migrating into perched basins. Collectively, however, these units are transgressive and migrate back towards the orogen. A depositional model is presented that links the migration of facies belts to subsidence caused by accentuated tectonic loading in the hinterland and break-back thrust sequences across the basins. We infer that a palaeobathymetric profile of underfilled sub-basins resulted and that this influenced the pattern of evaporite accumulation during Mediterranean desiccation in Messinian times. The Pliocene sediments, accumulated under renewed global sea levels, prograded towards the foreland. A waning tectonic load in the hinterland driving isostatic rebound, uplift and coastal offlap is the proposed explanation. This contribution is a case history for the depositional evolution of dominantly submarine thrust systems and their record of relative sea-level changes.  相似文献   

10.
Tectonic inversion models predict that stratigraphic thickening and local facies patterns adjacent to reactivated fault systems should record at least two phases of basin development: (1) initial extension‐related subsidence and (2) subsequent shortening‐induced uplift. In the central Peloncillo Mountains of southwestern New Mexico, thickness trends, distribution, and provenance of two major stratigraphic intervals on opposite sides of a northwest‐striking reverse fault preserve a record of Early Cretaceous normal displacement and latest Cretaceous–Paleogene reverse displacement along the fault. The Aptian–Albian Bisbee Group thickens by a factor of three from the footwall to the hanging‐wall block, and the Late Cretaceous?–Eocene Bobcat Hill Formation is preserved only in the footwall block. An initial episode of normal faulting resulted in thickening of upper Aptian–middle Albian, mixed siliciclastic and carbonate deposits and an up section change from coarse‐grained deltas to shallow‐marine depositional conditions. A second episode of normal faulting caused abrupt thickening of upper Albian, quartzose coastal‐plain deposits across the fault. These faulting episodes record two events of extension that affected the northern rift shoulder of the Bisbee basin. The third faulting episode was oblique‐slip, reverse reactivation of the fault and other related, former normal faults. Alluvial and pyroclastic deposits of the Bobcat Hill Formation record inversion of the Bisbee basin and development of an intermontane basin directly adjacent to the former rift basin. Inversion was coeval with latest Cretaceous–Paleogene shortening and magmatism. This offset history offers significant insight into extensional basin tectonics in the Early Cretaceous and permits rejection of models of long‐term Mesozoic shortening and orogen migration during the Cretaceous. This paper also illustrates how episodes of fault reactivation modify, in very short distances (<10 km), regional patterns of subsidence, the distribution of sediment‐source areas, and sedimentary depositional systems.  相似文献   

11.
Abstract Low‐angle detachment faults and thrust‐sheet top basins are common features in foreland basins. However, in stratigraphic analysis their influence on sequence architecture is commonly neglected. Usually, only eustatic sea level and changing flexural subsidence are accounted for, and when deformation is considered, the emphasis is on the generation of local thrust‐flank unconformities. This study analyses the effects of detachment angle and repetitive detachment activation on stratigraphic stacking patterns in a large thrust‐sheet top basin by applying a three‐dimensional numerical model. Model experiments show that displacement over low‐angle faults (2–6°) at moderate rates (～5.0 m kyr?1) results in a vertical uplift component sufficient to counteract the background flexural subsidence rate. Consequently, the basin‐wide accommodation space is reduced, fluvio‐deltaic systems carried by the thrust‐sheet prograde and part of the sediment supply is spilled over towards adjacent basins. The intensity of the forced regression and the interconnectedness of fluvial sheet sandstones increases with the dip angle of the detachment fault or rate of displacement. In addition, the delta plain is susceptible to the formation of incised valleys during eustatic falls because these events are less compensated by regional flexural subsidence, than they would be in the absence of fault displacement.  相似文献   

12.
Interpretation of long‐offset 2D depth‐imaged seismic data suggests that outer continental margins collapse and tilt basinward rapidly as rifting yields to seafloor spreading and thermal subsidence of the margin. This collapse post‐dates rifting and stretching of the crust, but occurs roughly ten times faster than thermal subsidence of young oceanic crust, and thus is tectonic and pre‐dates the ‘drift stage’. We term this middle stage of margin development ‘outer margin collapse’, and it accords with the exhumation stage of other authors. Outer continental margins, already thinned by rifting processes, become hanging walls of crustal‐scale half grabens associated with landward‐dipping shear zones and zones of low‐shear strength magma at the base of the thinned crust. The footwalls of the shear zones comprise serpentinized sub‐continental mantle that commonly becomes exhumed from beneath the embrittled continental margin. At magma‐poor margins, outer continental margins collapse and tilt basinward to depths of about 3 km subsea at the continent–ocean transition, often deeper than the adjacent oceanic crust (accreted later between 2 and 3 km). We use the term ‘collapse’ because of the apparent rapidity of deepening (<3 Myr). Rapid salt deposition, clastic sedimentation (deltaic), or magmatism (magmatic margins) may accompany collapse, with salt thicknesses reaching 5 km and volcanic piles 1525 km. This mechanism of rapid salt deposition allows mega‐salt basins to be deposited on end‐rift unconformities at global sea level, as opposed to deep, air‐filled sub‐sea depressions. Outer marginal collapse is ‘post‐rift’ from the perspective of faulting in the continental crust, but of tectonic, not of thermal, origin. Although this appears to be a global process, the Gulf of Mexico is an excellent example because regional stratigraphic and structural relations indicate that the pre‐salt rift basin was filled to sea level by syn‐rift strata, which helps to calibrate the rate and magnitude of collapse. We examine the role of outer marginal detachments in the formation of East India, southern Brazil and the Gulf of Mexico, and how outer marginal collapse can migrate diachronously along strike, much like the onset of seafloor spreading. We suggest that backstripping estimates of lithospheric thinning (beta factor) at outer continental margins may be excessive because they probably attribute marginal collapse to thermal subsidence.  相似文献   

13.
Stratigraphic data from petroleum wells and seismic reflection analysis reveal two distinct episodes of subsidence in the southern New Caledonia Trough and deep‐water Taranaki Basin. Tectonic subsidence of ~2.5 km was related to Cretaceous rift faulting and post‐rift thermal subsidence, and ~1.5 km of anomalous passive tectonic subsidence occurred during Cenozoic time. Pure‐shear stretching by factors of up to 2 is estimated for the first phase of subsidence from the exponential decay of post‐rift subsidence. The second subsidence event occured ~40 Ma after rifting ceased, and was not associated with faulting in the upper crust. Eocene subsidence patterns indicate northward tilting of the basin, followed by rapid regional subsidence during the Oligocene and Early Miocene. The resulting basin is 300–500 km wide and over 2000 km long, includes part of Taranaki Basin, and is not easily explained by any classic model of lithosphere deformation or cooling. The spatial scale of the basin, paucity of Cenozoic crustal faulting, and magnitudes of subsidence suggest a regional process that acted from below, probably originating within the upper mantle. This process was likely associated with inception of nearby Australia‐Pacific plate convergence, which ultimately formed the Tonga‐Kermadec subduction zone. Our study demonstrates that shallow‐water environments persisted for longer and their associated sedimentary sequences are hence thicker than would be predicted by any rift basin model that produces such large values of subsidence and an equivalent water depth. We suggest that convective processes within the upper mantle can influence the sedimentary facies distribution and thermal architecture of deep‐water basins, and that not all deep‐water basins are simply the evolved products of the same processes that produce shallow‐water sedimentary basins. This may be particularly true during the inception of subduction zones, and we suggest the term ‘prearc’ basin to describe this tectonic setting.  相似文献   

14.
Minibasins are fundamental components of many salt-bearing sedimentary basins, where they may host large volumes of hydrocarbons. Although we understand the basic mechanics governing their subsidence, we know surprisingly little of how minibasins subside in three-dimensions over geological timescales, or what controls such variability. Such knowledge would improve our ability to constrain initial salt volumes in sedimentary basins, the timing of salt welding and the distribution and likely charging histories of suprasalt hydrocarbon reservoirs. We use 3D seismic reflection data from the Precaspian Basin, onshore Kazakhstan to reveal the subsidence histories of 16, Upper Permian-to-Triassic, suprasalt minibasins. These minibasins subsided into a Lower-to-Middle Permian salt layer that contained numerous relatively strong, clastic-dominated minibasins encased during an earlier, latest Permian phase of diapirism; because of this, the salt varied in thickness. Suprasalt minibasins contain a stratigraphic record of symmetric (bowl-shaped units) and then asymmetric (wedge-shaped units) subsidence, with this change in style seemingly occurring at different times in different minibasins, and most likely prior to welding. We complement our observations from natural minibasins in the Precaspian Basin with results arising from new physical sandbox models; this allows us to explore the potential controls on minibasin subsidence patterns, before assessing which of these might be applicable to our natural example. We conclude that due to uncertainties in the original spatial relationships between encased and suprasalt minibasins, and the timing of changes in style of subsidence between individual minibasins, it is unclear why such complex temporal and spatial variations in subsidence occur in the Precaspian Basin. Regardless of what controls the observed variability, we argue that vertical changes in minibasin stratigraphic architecture may not record the initial (depositional) thickness of underlying salt or the timing of salt welding; this latter point is critical when attempting to constrain the timing of potential hydraulic communication between sub-salt source rocks and suprasalt reservoirs. Furthermore, temporal changes in minibasin subsidence style will likely control suprasalt reservoir distribution and trapping style.  相似文献   

15.
徐州煤矿区土地利用格局演变分析   总被引：43，自引：1，他引：42  
卞正富  张燕平 《地理学报》2006,61(4):349-358
利用徐州东矿区1979年、1987年、2001年三个年份的遥感影像分析了矿区景观要素及其景观格局的变化规律。从1979年到1987年,沉陷积水面积增加299.35%,农用地减少7.83%,建设用地增加48.4%。从1987年到2001年,东矿区农用地减少了13.04%,建设用地增加了37.62%,而沉陷积水区增加了137.26%;农用地的9.55%转变为建设用地,5.15%转变为沉陷积水区;建设用地的5.25%转变为农用地,主要集中于报废矿井工业广场附近,是由于部分地方小煤矿关闭后,一些废弃物堆场得到了复垦,3.21%转变为沉陷积水区,主要也是分布在各矿工业广场附近;有14.86%的沉陷积水区转变为农用地,主要位于原沉陷积水区的边缘部分,有10.88%转变为建设用地,主要集中在韩桥矿和权台矿的工业广场范围内。因此,应该加强对沉陷积水区的复垦和综合治理,因地制宜发展生态农业、养殖业、林业、牧业及其加工业,最大限度地利用土地资源。  相似文献   

16.
Multiple episodes of extensional tectonism dominated the formation of Mesozoic fault-bounded basins on the Grand Banks of Newfoundland, the Irish Continental Shelf and the central North Sea. A range of structural and stratigraphic responses in the Jeanne d'Arc, Porcupine and Moray Firth basins support widespread synchronous tectonic controls on sedimentation during one of these episodes, the Late Cimmerian. Rifting was preceded by a phase of related tectonism during which subsidence rates began to vary across broad areas but without significant fault block rotation. This Late Cimmerian ‘onset warp’ pattern of subsidence is considered to have been essential in the establishment of restricted anoxic basins from latest Oxfordian through Kimmeridgian (sensu gallico) time and the development of one prolific layer of organic-rich source rocks. The most prominent and widely recognized structural/lithostratigraphic response to Late Cimmerian rifting was the deposition of sediment wedges. Tithonian to early Valanginian strata generally thicken- into northerly trending faults in the Jeanne d'Arc and Porcupine basins, indicating that extensional stress was orientated WNW-ESE across a very broad area. The misalignment of this regional Late Cimmerian extensional stress with local inherited structural fabric may be responsible for transpressional uplift of individual fault blocks in the Outer Moray Firth basin. Sedimentological responses to Late Cimmerian rifting were varied, though a common lithofacies stacking pattern is recognized. Variably thick conglomerates and/or sandstones were widely deposited at the start of rift deformation, while palaeoenvironments ranged from alluvial and braid plain to submarine fan even within individual basins. The relatively coarse basal sediments fine upwards into a second layer of commonly organic-rich shales and mark The widest variations in palaeoenvironments and sediment thicknesses occurred during the last phase of Late Cimmerian rift tectonism, though all three basins show evidence of decreasing water depths, increasing oxygen levels and increasing grain size. This lithofacies stacking pattern of relatively coarse to fine to coarse (reservoir/source/reservoir) and the development of bounding unconformities are largely attributable to progressive changes in rift-controlled subsidence. Rift basin subsidence rates are interpreted to increase from a low at initiation of faulting to a mid-rift peak, followed by slowing subsidence to the end of extension. A number of counteracting crustal mechanisms that may account for progressive variations in rift-induced subsidence are considered.  相似文献   

17.
Provision of accommodation space for aggradation in Holocene deltaic basins is usually ascribed to eustatic sea‐level rise and/or land subsidence due to isostasy, tectonics or sediment compaction. Whereas many Holocene deltas contain peat, the relative contribution of peat compaction to total subsidence has not yet been quantified from field data covering an entire delta. Subsidence due to peat compaction potentially influences temporal and spatial sedimentation patterns, and therefore alluvial architecture. Quantification of the amount and rate of peat compaction was done based on (1) estimates of the initial dry bulk density of peat, derived from a relation between dry bulk density and organic‐matter content of uncompacted peat samples and (2) radiocarbon‐dated basal peat used to reconstruct initial levels of peat formation of currently subsided peat samples. In the Rhine‐Meuse delta, peat compaction has contributed considerably to total basin subsidence. Depending on the thickness of the compressible sequence, weight of the overburden and organic‐matter content of peat, subsidence of up to approximately 3 m in a 10‐m thick Holocene sequence has been calculated. Calculated local subsidence rates of peat levels are up to 0.6 mm year?1, averaged over millennia, which are twice the estimated Holocene‐averaged basin subsidence rates of 0.1–0.3 mm year?1 in the study area. Higher rates of subsidence due to compaction, on the order of a few mm year?1, occur over decades to centuries, following a substantial increase in effective stress caused by sediment loading. Without such an increase in effective stress, peat layers may accumulate for thousands of years with little compaction. Thus, the contribution of peat compaction to total delta subsidence is variable in time. Locally, up to 40% of total Holocene accommodation space has been provided by peat compaction. Implications of the large amount of accommodation space created by peat compaction in deltaic basins are: (1) increased sediment trap efficiency in deltas, which decelerates delta progradation and enhances the formation of relatively thick clastic sequences and (2) enhanced local formation of thick natural levees by renewing existing accommodation space.  相似文献   

18.
Oldlands are complex surfaces of low relief preserved on Precambrian shields and cratons and Paleozoic massifs. Interpretation of their character and age is difficult, but as a consequence of its particular location and of conceptual developments, much of the Australian Craton is now susceptible to analysis in terms of exhumation, etching, and multistage development. Exhumed surfaces of many ages are recorded. Long periods of weathering and erosion generated low relief, although recurrent block tectonics produced a differentiated topography and also resulted in regolithic veneers, some of them with mineral concentrations that later became duricrusts. The associated landforms are of various ages, but are mostly of Early and Middle Tertiary ages. Cretaceous and Early to Middle Tertiary etch forms are widely developed and preserved. Earlier Mesozoic (Jurassic, Triassic) surfaces are also represented or implied. Many cratonic landforms are related to the subsurface weathering and subsequent erosion to which oldlands have been subjected, to the exploitation of fractures in the basement rocks, to underprinting from fracture zones in the basement, and to deep erosion, causing rivers to breach alien structures. Multistage as well as two-stage forms are common, and pre-weathered detritus derived from regoliths was contributed to adjacent basins. [Key words: oldland, etch surface, underprinting, duricrust, paleosurface.]  相似文献   

19.
Henri Vogt  Thea Vogt 《Geomorphology》2007,86(3-4):480-495
Detailed study of two dry depressions in the Baikal rift system: the E–W Khoito Ghol-Tunka-Bistraya depression and the SW–NE Gusinoje–Ivolga depression, aims to provide a better understanding of tectonic control on the intershoulder relief evolution after the rift opened. Both depressions are grabens and both feature a suite of 10–20 km-wide basins alternating with more or less massive highs. Field and laboratory analysis shows that this pattern is of recent tectonic origin and that local breaking-up and subsidence followed the general sinking which originally formed the grabens. The subsidence belts seem to have gradually shifted north and northeastwards. Geomorphological analysis reveals that in both depressions the highs are remnants of a former pediment which was broken up. The young basins display numerous relevant hydrographic anomalies of the secondary channels and a general water-logging. They also suggest that the subsidence belts have gradually shifted north-and northeastwards. In the Gusinoje–Ivolga depression evidence was found of a Plio-Pleistocene river course, parallel to the Selenga river, which was later dismantled by the breaking-up. This depression, parallel to the Baikal rift and belonging to the Mesozoic system of grabens in the Caledonian fold belt, seems to have been included into the general system of rifts during the Pliocene tectonic phase. As for the main hydrographic axes, the Selenga river was set on a Palaeogene-age planation surface before the first tectonic phase and kept its original course. The Irkut river flowed in the Khoito Gol–Tunka–Bistraya depression after the first tectonic phase and was not affected by the later breaking-up. In contrast, the secondary drainage network is largely discordant. Despite their different geotectonic contexts, the two depressions show a similar development of relief pattern,which poses the question of the style of rift dynamics after the main Pliocene tectonic phase.  相似文献   

20.
The Celtic Sea basins lie on the continental shelf between Ireland and northwest France and consist of a series of ENE–WSW trending elongate basins that extend from St George’s Channel Basin in the east to the Fastnet Basin in the west. The basins, which contain Triassic to Neogene stratigraphic sequences, evolved through a complex geological history that includes multiple Mesozoic rift stages and later Cenozoic inversion. The Mizen Basin represents the NW termination of the Celtic Sea basins and consists of two NE–SW-trending half-grabens developed as a result of the reactivation of Palaeozoic (Caledonian, Lower Carboniferous and Variscan) faults. The faults bounding the Mizen Basin were active as normal faults from Early Triassic to Late Cretaceous times. Most of the fault displacement took place during Berriasian to Hauterivian (Early Cretaceous) times, with a NW–SE direction of extension. A later phase of Aptian to Cenomanian (Early to Late Cretaceous) N–S-oriented extension gave rise to E–W-striking minor normal faults and reactivation of the pre-existing basin bounding faults that propagated upwards as left-stepping arrays of segmented normal faults. In common with most of the Celtic Sea basins, the Mizen Basin experienced a period of major erosion, attributed to tectonic uplift, during the Paleocene. Approximately N–S Alpine regional compression-causing basin inversion is dated as Middle Eocene to Miocene by a well-preserved syn-inversion stratigraphy. Reverse reactivation of the basin bounding faults was broadly synchronous with the formation of a set of near-orthogonal NW–SE dextral strike-slip faults so that compression was partitioned onto two fault sets, the geometrical configuration of which is partly inherited from Palaeozoic basement structure. The segmented character of the fault forming the southern boundary of the Mizen Basin was preserved during Alpine inversion so that Cenozoic reverse displacement distribution on syn-inversion horizons mirrors the earlier extensional displacements. Segmentation of normal faults therefore controls the geometry and location of inversion structures, including inversion anticlines and the back rotation of earlier relay ramps.  相似文献   

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