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1.
Detailed seismic reflection data combined with regional magnetic, gravity and geological data indicate that the Drummond Basin originated as a backare extensional basin associated with Late Devonian and Early Carboniferous active margin tectonism in the northern New England Fold Belt. Seismic reflection data have been used to generate a two-way time map of seismic basement, providing a clear view of the basinal geometry and structural development. Broadscale structural asymmetry of the basin implies that simple shear along a deep, upper-crustal detachment provided the extensional mechanism and generated an inter-related set of listric normal faults and associated transfer faults, as well as steeply-dipping planat normal faults. The orientation of normal faults near the basin margins appears to have been controlled by regional basement structural trends. Transfer-fault trends were approximarely orthogonal to the line of plate convergence as assessed from the orientation of coeval are, forcare and subduction complex stratorectonic elements. Three distinct phases of infill are represented in the basinal stratigraphic succession. The first consists largely of volcanics and volcaniclastics, indicating that effusive magmatism and extension were closely associated in space and time. The second is quartzose and of basement derivation, but was not derived from footwall blocks at the faulted basinal margins to the east and north. Uplifted hanging-wall crust beyond the western basinal margin, a product of west-directed simple shear detachment, was the likely source terrain. The final infill phase consisted of volcaniclastics considered to have been derived from a coeval volcanic are to the east. Major faults at the basin margins provided conduits for magmatism during extensional basin development, and long after the basinal history was complete. During the Late Carboniferous and mid-Triassic, the basin was affected by two discrete episodes of compressional deformation. This led to inversion with the development of folds, and reverse and wrench faults now seen at the surface.  相似文献   

2.
We report on new stratigraphic, palaeomagnetic and anisotropy of magnetic susceptibility (AMS) results from the Amantea basin, located on‐shore along the Tyrrhenian coast of the Calabrian Arc (Italy). The Miocene Amantea Basin formed on the top of a brittlely extended upper plate, separated from a blueschist lower plate by a low‐angle top‐to‐the‐west extensional detachment fault. The stratigraphic architecture of the basin is mainly controlled by the geometry of the detachment fault and is organized in several depositional sequences, separated by major unconformities. The first sequence (DS1) directly overlaps the basement units, and is constituted by Serravallian coarse‐grained conglomerates and sandstones. The upper boundary of this sequence is a major angular unconformity locally marked by a thick palaeosol (type 1 sequence boundary). The second depositional sequence DS2 (middle Tortonian‐early Messinian) is mainly formed by conglomerates, passing upwards to calcarenites, sandstones, claystones and diatomites. Finally, Messinian limestones and evaporites form the third depositional sequence (DS3). Our new biostratigraphic data on the Neogene deposits of the Amantea basin indicate a hiatus of 3 Ma separating sequences DS1 and DS2. The structural architecture of the basin is characterized by faulted homoclines, generally westward dipping, dissected by eastward dipping normal faults. Strike‐slip faults are also present along the margins of the intrabasinal structural highs. Several episodes of syn‐depositional tectonic activity are marked by well‐exposed progressive unconformities, folds and capped normal faults. Three main stages of extensional tectonics affected the area during Neogene‐Quaternary times: (1) Serravallian low‐angle normal faulting; (2) middle Tortonian high‐angle syn‐sedimentary normal faulting; (3) Messinian‐Quaternary high‐angle normal faulting. Extensional tectonics controlled the exhumation of high‐P/low‐T metamorphic rocks and later the foundering of the Amantea basin, with a constant WNW‐ESE stretching direction (present‐day coordinates), defined by means of structural analyses and by AMS data. Palaeomagnetic analyses performed mainly on the claystone deposits of DS1 show a post‐Serravallian clockwise rotation of the Amantea basin. The data presented in this paper constrain better the overall timing, structure and kinematics of the early stages of extensional tectonics of the southern Tyrrhenian Sea. In particular, extensional basins in the southern Tyrrhenian Sea opened during Serravallian and evolved during late Miocene. These data confirm that, at that time, the Amantea basin represented the conjugate extensional margin of the Sardinian border, and that it later drifted south‐eastward and rotated clockwise as a part of the Calabria‐Peloritani terrane.  相似文献   

3.
A new subtype of Gilbert-type fan deltas, ‘the trapezoidal fan delta’, characterized by the absence of bottomset deposits, is recognized in the south-western active margins of the Corinth rift in central Greece. They are formed adjacent to master extensional listric faults and developed by progradation either onto a subaqueous basin escarpment or across a subaerial platform where alluvial fans have accumulated. Simultaneously with master fault activity, displacements on counter faults along intrabasinal basement highs produced fan delta foreset deposits. Furthermore, footwall imbrication and uplift along the listric faults, as well as transfer fault displacement, have strongly influenced the pattern of fan delta sedimentation.  相似文献   

4.
The Alhama de Murcia and Crevillente faults in the Betic Cordillera of southeast Spain form part of a network of prominent faults, bounding several of the late Tertiary and Quaternary intermontane basins. Current tectonic interpretations of these basins vary from late‐orogenic extensional structures to a pull‐apart origin associated with strike–slip movements along these prominent faults. A strike–slip origin of the basins, however, seems at variance both with recent structural studies of the underlying Betic basement and with the overall basin and fault geometry. We studied the structure and kinematics of the Alhama de Murcia and Crevillente faults as well as the internal structure of the late Miocene basin sediments, to elucidate possible relationships between the prominent faults and the adjacent basins. The structural data lead to the inevitable conclusion that the late Miocene basins developed as genuinely extensional basins, presumably associated with the thinning and exhumation of the underlying basement at that time. During the late Miocene, neither the Crevillente fault nor the Alhama de Murcia fault acted as strike–slip faults controlling basin development. Instead, parts of the Alhama de Murcia fault initiated as extensional normal faults, and reactivated as contraction faults during the latest Miocene–early Pliocene in response to continued African–European plate convergence. Both prominent faults presently act as reverse faults with a movement sense towards the southeast, which is clearly at variance with the commonly inferred dextral or sinistral strike–slip motions on these faults. We argue that the prominent faults form part of a larger scale zone of post‐Messinian shortening made up of SSE‐ and NNW‐directed reverse faults and NE to ENE‐trending folds including thrust‐related fault‐bend folds and fault‐propagation folds, transected and displaced by, respectively, WNW‐ and NNE‐trending, dextral and sinistral strike–slip (tear or transfer) faults.  相似文献   

5.
Lower Cretaceous early syn‐rift facies along the eastern flank of the Eastern Cordillera of Colombia, their provenance, and structural context, reveal the complex interactions between Cretaceous extension, spatio‐temporal trends in associated sedimentation, and subsequent inversion of the Cretaceous Guatiquía paleo‐rift. South of 4°30′N lat, early syn‐rift alluvial sequences in former extensional footwall areas were contemporaneous with fan‐delta deposits in shallow marine environments in adjacent hanging‐wall areas. In general, footwall erosion was more pronounced in the southern part of the paleorift. In contrast, early syn‐rift sequences in former footwall areas in the northern rift sectors mainly comprise shallow marine supratidal sabkha to intertidal strata, whereas hanging‐wall units display rapid transitions to open‐sea shales. In comparison with the southern paleo‐rift sector, fan‐delta deposits in the north are scarce, and provenance suggests negligible footwall erosion. The southern graben segment had longer, and less numerous normal faults, whereas the northern graben segment was characterized by shorter, rectilinear faults. To the east, the graben system was bounded by major basin‐margin faults with protracted activity and greater throw as compared with intrabasinal faults to the west. Intrabasinal structures grew through segment linkage and probably interacted kinematically with basin‐margin faults. Basin‐margin faults constitute a coherent fault system that was conditioned by pre‐existing basement fabrics. Structural mapping, analysis of present‐day topography, and balanced cross sections indicate that positive inversion of extensional structures was focused along basin‐bounding faults, whereas intrabasinal faults remained unaffected and were passively transported by motion along the basin‐bounding faults. Thus, zones of maximum subsidence in extension accommodated maximum elevation in contraction, and former topographic highs remained as elevated areas. This documents the role of basin‐bounding faults as multiphased, long‐lived features conditioned by basement discontinuities. Inversion of basin‐bounding faults was more efficient in the southern than in the northern graben segment, possibly documenting the inheritance and pivotal role of fault‐displacement gradients. Our observations highlight similarities between inversion features in orogenic belts and intra‐plate basins, emphasizing the importance of the observed phenomena as predictive tools in the spatiotemporal analysis of inversion histories in orogens, as well as in hydrocarbon and mineral deposits exploration.  相似文献   

6.
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   

7.
Our current understanding on sedimentary deep-water environments is mainly built of information obtained from tectonic settings such as passive margins and foreland basins. More observations from extensional settings are particularly needed in order to better constrain the role of active tectonics in controlling sediment pathways, depositional style and stratigraphic stacking patterns. This study focuses on the evolution of a Plio-Pleistocene deep-water sedimentary system (Rethi-Dendro Formation) and its relation to structural activity in the Amphithea fault block in the Corinth Rift, Greece. The Corinth Rift is an active extensional basin in the early stages of rift evolution, providing perfect opportunities for the study of early deep-water syn-rift deposits that are usually eroded from the rift shoulders due to erosion in mature basins like the Red Sea, North Sea and the Atlantic rifted margin. The depocentre is located at the exit of a structurally controlled sediment fairway, approximately 15 km from its main sediment source and 12 km basinwards from the basin margin coastline. Fieldwork, augmented by digital outcrop techniques (LiDAR and photogrammetry) and clast-count compositional analysis allowed identification of 16 stratigraphic units that are grouped into six types of depositional elements: A—mudstone-dominated sheets, B—conglomerate-dominated lobes, C—conglomerate channel belts and sandstone sheets, D—sandstone channel belts, E—sandstone-dominated broad shallow lobes, F—sandstone-dominated sheets with broad shallow channels. The formation represents an axial system sourced by a hinterland-fed Mavro delta, with minor contributions from a transverse system of conglomerate-dominated lobes sourced from intrabasinal highs. The results of clast compositional analysis enable precise attribution for the different sediment sources to the deep-water system and their link to other stratigraphic units in the area. Structures in the Amphithea fault block played a major role in controlling the location and orientation of sedimentary systems by modifying basin-floor gradients due to a combination of hangingwall tilt, displacement of faults internal to the depocentre and folding on top of blind growing faults. Fault activity also promoted large-scale subaqueous landslides and eventual uplift of the whole fault block.  相似文献   

8.
Field exposures of Lower Cretaceous strata in the Oliete sub-basin (eastern Spain) allow identification of syn-rift features such as listric and planar normal faults, rotated fault blocks, fault-related folds, sharp thickness variations and wedge-shaped sedimentary geometries, as well as intra-rift angular unconformities defined by the erosive truncation of rotated fault blocks and the onlap of upper units. The combined use of both stratigraphic and extensional tectonic features at the outcrop scale has allowed us to characterise different syn-sedimentary tectonic events and their correlation between the footwall and the hangingwall block of the major extensional Gargallo fault. Such events have been interpreted as induced by the major Gargallo fault activity, and they are the basis for proposing a polyphase evolutionary model for this master fault. Data indicate that the deformation tends not to be concentrated on the major fault; instead, it is distributed over a wide area. We interpret that both the interlayered detachment levels in the pre-rift (especially the Late Triassic Keuper Facies) and syn-rift series, together with the rheology of the sedimentary pile, play an important role in transmitting deformation from master faults to hangingwall and footwall blocks.  相似文献   

9.
The base of the Late Devonian–Early Carboniferous Drummond Basin, a major backarc extensional feature in eastern Australia which formed in response to detachment faulting, is extensively exposed in central Queensland. Here a crystalline basin floor is overlain by the Silver Hills Volcanics, a synrift sequence of predominantly silicic ash flow tuffs and lavas ranging to over 2 km in thickness. Detailed mapping of faults and stratigraphic logging of thickness changes within the Silver Hills Volcanics have allowed the rift-phase structural architecture that accompanied initial subsidence near the basin margin to be resolved. A complex mosaic of block faults with throws of up to 1 km is indicated. Locally developed mosaics may conform to, or depart from, the configuration predicted by the detachment faulting model. Structural fabric of the basement was a critical determinant of the extensional geometry. Distributed shear along pre-existing penetrative planar fabrics is considered to have accommodated hangingwall extension at lower strain rates whereas the propagation of tension fractures and the development of block faults by failure on pre-existing, brittle, basement dislocations facilitated extension at higher strain rates. The detachment fault inferred to lie beneath the extended hangingwall carapace has not been mapped at the surface and is thought to dissipate into a broad zone of distributed shear within basement to the east of the basin. Volcanism coincided with the initiation of extensional movements at which time deep crustal repositories for evolved magma were tapped by extensional fractures. The main extensional faults cutting the basinal succession were not used as conduits for magmatic products which were sourced from the basin margin and from extended hinterland to the east.  相似文献   

10.
Although fault growth is an important control on drainage development in modern rifts, such links are difficult to establish in ancient basins. To understand how the growth and interaction of normal fault segments controls stratigraphic patterns, we investigate the response of a coarse-grained delta system to evolution of a fault array in a Miocene half-graben basin, Suez rift. The early Miocene Alaqa delta complex comprises a vertically stacked set of footwall-sourced Gilbert deltas located in the immediate hangingwall of the rift border fault, adjacent to a major intrabasinal relay zone. Sedimentological and stratigraphic studies, in combination with structural analysis of the basin-bounding fault system, permit reconstruction of the architecture, dispersal patterns and evolution of proximal Gilbert delta systems in relation to the growth and interaction of normal fault segments. Structural geometries demonstrate that fault-related folds developed along the basin margin above upward and laterally propagating normal faults during the early stages of extension. Palaeocurrent data indicate that the delta complex formed a point-sourced depositional system developed at the intersection of two normal fault segments. Gilbert deltas prograded transverse into the basin and laterally parallel to faults. Development of the transverse delta complex is proposed to be a function of its location adjacent to an evolving zone of fault overlap, together with focusing of dispersal between adjacent fault segments growing towards each other. Growth strata onlap and converge onto the monoclinal fold limbs indicating that these structures formed evolving structural topography. During fold growth, Gilbert deltas prograded across the deforming fold surface, became progressively rotated and incorporated into fold limbs. Spatial variability of facies architecture is linked to along-strike variation in the style of fault/fold growth, and in particular variation in rates of crestal uplift and fold limb rotation. Our results clearly show that the growth and linkage of fault segments during fault array evolution has a fundamental control on patterns of sediment dispersal in rift basins.  相似文献   

11.
《Basin Research》2018,30(Z1):311-335
The analysis of volcano‐sedimentary infill in sedimentary basins constitutes a challenge for basin analysis and hydrocarbon exploration worldwide. In order to understand the contribution of volcanism to the sedimentary record in rift basins, we study the Jurassic effusive‐explosive volcanic infill of an inverted extensional depocentre at the Neuquén Basin, Argentina. A cause and effect model that evaluates the relationship between volcanism and sedimentation was devised to develop a conceptual model for the tectono‐stratigraphic evolution of this volcanic rift basin. We show how the variations in the volcanism, coupled with the activity of extensional faults, determined the types of volcanic edifices (i.e., composite volcanoes, graben‐calderas, and lava fields). Volcanic edifices controlled the stacking patterns of the volcanic units as well as sedimentary systems. The landform of the volcanic edifices, as well as the styles and scales of the eruptions governed the sedimentary input to the basin, setting the main variables of the sedimentary systems, such as provenance, grain size, transport and deposition and geometry. As a result, the contrasting volcaniclastic input, from higher volcaniclastic input to lower volcaniclastic input, associated with different subsidence patterns, determined the high‐resolution syn‐rift infill patterns of the extensional depocentre. The cause and effect model presented in this study isolates the variables of the volcanic environments that control the sedimentary scenarios. We suggest that, by adjusting the first order input parameters of the model, these cause and effect scenarios could be adapted to similar rift basins, in order to establish predictive facies models with stratigraphic controls, and the impact of volcanism on their stratigraphic records.  相似文献   

12.
Deposition of a 2700-m-thick clastic platform succession in a N-S striking basin in northern Chile began in the Early Devonian during a global sea-level rise. A transition to terrestrial facies took place at the Early-Late Carboniferous boundary when the Gondwana glaciation began and global sea-level dropped. On the platform, interbedded cross-bedded or bioturbated sandstones, offshore tidal dunes and sand waves, and mudstones and tempestites suggest switching intertidal and shallow or deep subtidal environments. However, evidence for subaerial erosion indicates a significant regression during the Early Devonian. In an adjacent and deeper N-S striking sub-basin to the W, up to 3600 m of turbidites were deposited from the Late Devonian to the Late Carboniferous by mainly southerly palaeocurrents. Turbidites accumulated in coarse-grained proximal sand lobes in the N, and in fine-grained lobe fringe and basin plain environments in the S, with alternating upward-thinning and upward-thickening cycles typical of tectonically controlled aggradational turbidite systems. The sedimentological data indicate that the deeper basin depositional system evolved to a large extent independently from the platform system. Sediment in the deeper basin is less mature and more poorly sorted than that on the platform, suggesting that detritus bypassed the platform and was shed directly from the source areas into the western basin. The only depositional link between the platform and deeper basin systems seems to be longshore platform currents which may have funnelled minor quantities of mature sand into the deeper basin via bypass canyons. Although platform and deeper basin evolved in a common extensional tectonic setting, the platform reflects eustatic changes of sea-level whereas deposition in the deeper basin records syndepositional tectonics.  相似文献   

13.
In the mid‐Cretaceous Lasarte sub‐basin (LSB) [northeastern Basque‐Cantabrian Basin (BCB)] contemporaneous and syn‐depositional thin‐ and thick‐skinned extensional tectonics occur due to the presence of a ductile detachment layer that decoupled the extension. Despite the interest in extension modes of rift basins bearing intra‐stratal detachment layers, complex cases remain poorly understood. In the LSB, field results based on mapping, stratigraphic, sedimentological and structural data show the relationship between growth strata and tectonic structures. Syn‐depositional extensional listric faults and associated folds and faults have been identified in the supra‐detachment thin‐skinned system. But stratigraphic data also indicate the activation of sub‐detachment thick‐skinned extensional faults coeval with the development of the thin‐skinned system. The tectono‐sedimentary evolution of the LSB, since the Late Aptian until the earliest Late Albian, has been interpreted based on thin‐ and thick‐skinned extensional growth structures, which are fossilized by post‐extensional strata. The development of the thin‐skinned system is attributed to the presence of a ductile detachment layer (Upper Triassic Keuper facies) which decoupled the extension from deeper sub‐detachment basement‐involved faulting under a regional extensional/transtensional regime.  相似文献   

14.
Understanding the relationships between sedimentation, tectonics and magmatism is crucial to defining the evolution of orogens and convergent plate boundaries. Here, we consider the lithostratigraphy, clastic provenance, syndepositional deformation and volcanism of the Almagro‐El Toro basin of NW Argentina (24°30′ S, 65°50′ W), which experienced eruptive and depositional episodes between 14.3 and 6.4 Ma. Our aims were to elucidate the spatial and temporal record of the onset and style of the shortening and exhumation of the Eastern Cordillera in the frame of the Miocene evolution of the Central Andes foreland basin. The volcano‐sedimentary sequence of the Almagro‐El Toro basin consists of lower red floodplain sandstones and siltstones, medial non‐volcanogenic conglomerates with localised volcanic centres and upper volcanogenic coarse conglomerates and breccia. Coarse, gravity flow‐dominated (debris‐flow and sheet‐flow) alluvial fan systems developed proximal to the source area in the upper and medial sequence. Growing frontal and intrabasinal structures suggest that the Almagro‐El Toro portion of the foreland basin accumulated on top of the eastward‐propagating active thrust front of the Eastern Cordillera. Synorogenic deposits indicate that the shortening of the foreland deposits was occurring by 11.1 Ma, but conglomerates derived from the erosion of western sources suggest that the uplift and erosion of this portion of the Eastern Cordillera has occurred since ca.12.5 Ma. An unroofing reconstruction suggests that 6.5 km of rocks were exhumed. A tectono‐sedimentary model of an episodically evolving thick‐skinned foreland basin is proposed. In this frame, the NW‐trending, transtensive Calama–Olacapato–El Toro (COT) structures interacted with the orogen, influencing the deposition and deformation of synorogenic conglomerates, the location of volcanic centres and the differential tilt and exhumation of the foreland.  相似文献   

15.
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   

16.
This paper describes the evolution of an extensional basin in regard to the nature and sequence stratigraphic arrangement of its carbonate deposits. The purpose of this study is to evaluate the respective effects of tectonism, eustasy, climate and oceanography on a carbonate sedimentary record. The case study is the early to mid‐Jurassic age carbonate succession of the Southern Provence Sub‐basin (SE France), located within the southern part of the extensional Western European Tethyan Margin. This work is based on sedimentologic, biostratigraphic (using ammonites and brachiopods) and sequence stratigraphic analysis of the carbonate facies of the Cherty Reddish Limestone Formation (late Sinemurian to earliest Bajocian). These strata were deposited in shoreface to lower offshore depositional environments. The succession of the various environments together with the recognition of key stratigraphic surfaces allow us to define four second‐order depositional sequences; of late Sinemurian to earliest Pliensbachian, early Pliensbachian to late Pliensbachian, earliest Toarcian to middle Aalenian and late Aalenian to early Bathonian ages. The architecture of the depositional sequences (thickness and facies variations within the systems tracts, wedge‐shaped geometries) reflects a strong tectonic control. The sub‐basin was structured by extensional faults (oriented approximately 070–090/250–270). Sea‐level variations, fluctuations in carbonate production and preservation, and environmental changes were also significant controlling factors of the carbonate deposition. The interplay of the tectonic control with the other factors resulted in five main phases in the sedimentary evolution of the sub‐basin: (1) dominant tectonic control during the initial rifting stage (late Sinemurian to early Pliensbachian); (2) increasing extensional tectonics (mid‐Pliensbachian); (3) global climato‐eustatic sea‐level fall (latest Pliensbachian) and global climato‐eustatic sea‐level rise plus hypoxia/anoxia (early Toarcian); (4) relative sea‐level fall linked to tectonic uplift related to the ‘Mid‐Cimmerian phase’ (mid‐Aalenian) and (5) oceanographic events (upwelling) and reduction in carbonate production (hypoxia/anoxia) plus tectonic downwarping (late Aalenian/earliest Bajocian).  相似文献   

17.
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   

18.
The Dzereg Basin is an actively evolving intracontinental basin in the Altai region of western Mongolia. The basin is sandwiched between two transpressional ranges, which occur at the termination zones of two regional‐scale dextral strike‐slip fault systems. The basin contains distinct Upper Mesozoic and Cenozoic stratigraphic sequences that are separated by an angular unconformity, which represents a regionally correlative peneplanation surface. Mesozoic strata are characterized by northwest and south–southeast‐derived thick clast‐supported conglomerates (Jurassic) overlain by fine‐grained lacustrine and alluvial deposits containing few fluvial channels (Cretaceous). Cenozoic deposits consist of dominantly alluvial fan and fluvial sediments shed from adjacent mountain ranges during the Oligocene–Holocene. The basin is still receiving sediment today, but is actively deforming and closing. Outwardly propagating thrust faults bound the ranges, whereas within the basin, active folding and thrusting occurs within two marginal deforming belts. Consequently, active fan deposition has shifted towards the basin centre with time, and previously deposited sediment has been uplifted, eroded and redeposited, leading to complex facies architecture. The geometry of folds and faults within the basin and the distribution of Mesozoic sediments suggest that the basin formed as a series of extensional half‐grabens in the Jurassic–Cretaceous which have been transpressionally reactivated by normal fault inversion in the Tertiary. Other clastic basins in the region may therefore also be inherited Mesozoic depocentres. The Dzereg Basin is a world class laboratory for studying competing processes of uplift, deformation, erosion, sedimentation and depocentre migration in an actively forming intracontinental transpressional basin.  相似文献   

19.
The thickness and distribution of early syn‐rift deposits record the evolution of structures accommodating the earliest phases of continental extension. However, our understanding of the detailed tectono‐sedimentary evolution of these deposits is poor, because in the subsurface, they are often deeply buried and below seismic resolution and sparsely sampled by borehole data. Furthermore, early syn‐rift deposits are typically poorly exposed in the field, being buried beneath thick, late syn‐rift and post‐rift deposits. To improve our understanding of the tectono‐sedimentary development of early syn‐rift strata during the initial stages of rifting, we examined quasi‐3D exposures in the Abura Graben, Suez Rift, Egypt. During the earliest stage of extension, forced folding above blind normal fault segments, rather than half‐graben formation adjacent to surface‐breaking faults, controlled rift physiography, accommodation development and the stratigraphic architecture of non‐marine, early syn‐rift deposits. Fluvial systems incised into underlying pre‐rift deposits and were structurally focused in the axis of the embryonic depocentre, which, at this time, was characterized by a fold‐bound syncline rather than a fault‐bound half graben. During this earliest phase of extension, sediment was sourced from the rift shoulder some 3 km to the NE of the depocentre, rather than from the crests of the flanking, intra‐basin extensional forced folds. Fault‐driven subsidence, perhaps augmented by a eustatic sea‐level rise, resulted in basin deepening and the deposition of a series of fluvial‐dominated mouth bars, which, like the preceding fluvial systems, were structurally pinned within the axis of the growing depocentre, which was still bound by extensional forced folds rather than faults. The extensional forced folds were eventually locally breached by surface‐breaking faults, resulting in the establishment of a half graben, basin deepening and the deposition of shallow marine sandstone and fan‐delta conglomerates. Because growth folding and faulting were coeval along‐strike, syn‐rift stratal units deposited at this time show a highly variable along‐strike stratigraphic architecture, locally thinning towards the growth fold but, only a few kilometres along‐strike, thickening towards the surface‐breaking fault. Despite displaying the classic early syn‐rift stratigraphic motif recording net upward‐deepening, extensional forced folding rather than surface faulting played a key role in controlling basin physiography, accommodation development, and syn‐rift stratal architecture and facies development during the early stages of extension. This structural and stratigraphic observations required to make this interpretation are relatively subtle and may go unrecognized in low‐resolution subsurface data sets.  相似文献   

20.
The Upper Cretaceous Wahweap Formation accumulated in the active Cordilleran foreland basin of Utah. Soft‐sediment deformation structures are abundant in the capping sandstone member of the Wahweap Formation. By comparing with well‐established criteria, a seismogenic origin was determined for the majority of structures, which places these soft‐sediment deformation features in a class of sedimentary features referred to as seismites. A systematic study of the seismite trends included their vertical and horizontal distribution and a semi‐quantitative intensity analysis using a scale from 1 to 5 that is based on magnitude, sedimentary structure type, and the predominance of inferred process of hydroplastic deformation, liquefaction or fluidization. In addition, orientations of soft‐sediment fold axes were recorded. Construction of a northwest‐to‐southeast stratigraphic and seismite intensity cross‐section demonstrates: (1) reduction in stratigraphic thickness and percentage of conglomerates to the southeast, (2) the presence of lower seismite, middle nonseismite, and upper seismite zones within the capping sandstone (permitting subdivision of the capping sandstone member), and (3) elimination of the nonseismite zone and amalgamation of the lower and upper seismite zones to the southeast. Regional isoseismal contour maps generated from the semi‐quantitative analysis indicate a decrease in overall intensity from northwest to southeast in the upper and lower seismic zones and in sandstone within 5 m stratigraphically of the contact between the upper and capping sandstone members. In addition, cumulative seismite fold orientations support a west–northwest direction towards regional epicentres. Isoseismal maps are used to distinguish the effects of intrabasinal normal faulting from those of regional orogenic thrusting. Thus, this study demonstrates the utility of mapping seismites to separate the importance of regional vs. local tectonic activity influencing foreland basin sedimentation by identifying patterns that delineate palaeoepicentres associated with specific local intrabasinal normal faults vs. regional trends in soft‐sediment deformation related to Sevier belt earthquakes.  相似文献   

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