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1.
Numerical models were used to investigate the effects of differential compaction on strain development and early fracturing in an early cemented high‐relief Triassic carbonate platform prograding onto basinal sediments, whose thickness increases basinward. Results show that basinal sediment compaction induces stretching of internal platform and slope strata in prograding platforms. When sediments are early cemented, such extensional strain is accommodated by the generation of syndepositional fractures. The amount of stretching is predicted to increase from the oldest to the youngest layers, due to the thickening of the compactable basinal sequences towards the external parts of the platform. Stretching is also controlled by the characteristics of the basin: the thicker and the more compactable the basinal sediments, the larger will be the stretching. Numerical modelling has been applied to the Ladinian–Early Carnian carbonate platform of the Esino Limestone (Central Southern Alps of Italy). This case study is favourable for numerical modelling, as it is well exposed and both its internal geometry (inner platform, reef and prograding clinostratified slope deposits) and the relationship with the adjacent basin can be fully reconstructed, as the Alpine tectonic overprint is weak in the study area. Evidence for early fracturing (fractures filled by fibrous cements coeval with the platform development) is described and the location, orientation and width of the fractures measured. The fractures are mainly steeply dipping and oriented perpendicularly to the direction of progradation of the platform, mimicking local platform‐margin trends. The integration of numerical models with field data gives the opportunity to quantify the extension triggered by differential compaction and predict the possible distribution of early fractures in carbonate platforms of known geometry and thickness, whereas the interpretation of early fractures as the effects of differential compaction can be supported or rejected by the comparison with the results of ad hoc numerical modelling.  相似文献   

2.
In the Sella platform of the Dolomite Alps, the horizontal beds of the Raibl Formation directly overlie the Upper Schlern Dolomite (Cassian Dolomite of some authors). The Schlern Dolomite comprises steep clinoforms, together with a few tens of metres of horizontal topset beds in the platform interior. Two-dimensional seismic modelling techniques were used to determine the seismic-response of this interesting situation. To perform this, two different lithological models were constructed based on outcrops of the Sella south face. The first model is that of a rapidly prograding platform with slow aggradation in the platform interior. The second model shows clinoforms toplapping against the topset beds of the platform interior. P-wave velocities and bulk densities were assigned to the lithostratigraphical units in accordance with values from a similar study, involving the same formations. The vertical-incidence method was used to construct perfectly migrated time sections and depth sections of reflectivity. These were convolved with zero-phase Ricker wavelets of different peak frequencies to produce the final synthetic seismic sections. Using conventional, low frequencies (e.g. 25 Hz), the seismic response of the two models is almost identical. The topset beds and the Schlern-Raibl contact appear as one event. In a real seismic survey, both sections would be interpreted as toplap of Schlern clinoforms against the Raibl Formation. At higher frequencies (75 Hz), however, differences are revealed. The angle of progradation in the progradation & aggradation model becomes visible, as opposed to the horizontal surface in the progradation & toplap model. Topset beds are resolved separate from the Raibl Formation, but still appear to form a single dipping pseudo-toplap surface. Another modelling technique, simulating unmigrated sections, shows few differences between the two models even at high frequencies. In addition, the clinoforms are disturbed by the refraction of rays. This study demonstrates that, even under ideal acquisition and processing conditions, the seismic tool can introduce a pseudo-toplap. This implies that toplap in a seismic section is not necessarily toplap in outcrop.  相似文献   

3.
Deposition and subsidence analysis, coupled with previous structural studies of the Sevier thrust belt, provide a means of reconstructing the detailed kinematic history of depositional response to episodic thrusting in the Cordilleran foreland basin of southern Wyoming, western interior USA. The Upper Cretaceous basin fill is divided into five megasequences bounded by unconformities. The Sevier thrust belt in northern Utah and southwestern Wyoming deformed in an eastward progression of episodic thrusting. Three major episodes of displacement on the Willard‐Meade, Crawford and ‘early’ Absaroka thrusts occurred from Aptian to early Campanian, and the thrust wedge gradually became supercritically tapered. The Frontier Formation conglomerate, Echo Canyon and Weber Canyon Conglomerates and Little Muddy Creek Conglomerate were deposited in response to these major thrusting events. Corresponding to these proximal conglomerates within the thrust belt, Megasequences 1, 2 and 3 were developed in the distal foreland of southern Wyoming. Two‐dimensional (2‐D) subsidence analyses show that the basin was divided into foredeep, forebulge and backbulge depozones. Foredeep subsidence in Megasequences 1, 2 and 3, resulting from Willard‐Meade, Crawford and ‘early’ Absaroka thrust loading, were confined to a narrow zone in the western part of the basin. Subsidence in the broad region east of the forebulge was dominantly controlled by sediment loading and inferred dynamic subsidence. Individual subsidence curves are characterized by three stages from rapid to slow. Controlled by relationships between accommodation and sediment supply, the basin was filled with retrogradational shales during periods of rapid subsidence, followed by progradational coarse clastic wedges during periods of slow subsidence. During middle Campanian time (ca. 78.5–73.4 Ma), the thrust wedge was stalled because of wedge‐top erosion and became subcritical, and the foredeep zone eroded and rebounded because of isostasy. The eroded sediments were transported far from the thrust belt, and constitute Megasequence 4 that was mostly composed of fluvial and coastal plain depositional systems. Subsidence rates were very slow, because of post‐thrusting rebound, and the resulting 2‐D subsidence was lenticular in an east–west direction. During late Campanian to early Maastrichtian time, widespread deposits of coarse sediment (the Hams Fork Conglomerate) aggraded the top of the thrust wedge after it stalled, prior to initiation of ‘late’ Absaroka thrusting. Meanwhile Megasequence 5 was deposited in the Wyoming foreland under the influence of both the intraforeland Wind River basement uplift and the Sevier thrust belt.  相似文献   

4.
This paper describes the development of a regressive-to-transgressive shoreline wedge within the Middle Jurassic Tarbert Formation in the Oseberg South area (northern North Sea), as interpreted from core and log data from more than hundred wells. The wedge is described in terms of four facies associations (FA1–FA4). The lower, regressive portion of the wedge (FA1–FA2) contains both coarsening upward wave/storm-dominated shoreline deposits as well as coal-bearing paralic deposits, and was deposited during ascending regression. The upper, transgressive portion of the wedge (FA3–FA4) is characterised by wave-dominated estuarine deposits, exhibiting an upward change from inner to central to outer estuarine deposits. In contrast to some earlier studies, it is argued that this part was deposited during accretionary transgression. The present study documents an estuarine system that developed without any preceding fall of relative sea level and valley incision. It is argued that differential fault-induced subsidence created a broad gentle sag wherein one or several estuarine systems developed as the depositional system became transgressive. The subtle fault-induced subsidence is related to the tectonic evolution in the North Sea Basin.  相似文献   

5.
Evolution of the late Cenozoic Chaco foreland basin, Southern Bolivia   总被引：3，自引：1，他引：3  
Eastward Andean orogenic growth since the late Oligocene led to variable crustal loading, flexural subsidence and foreland basin sedimentation in the Chaco basin. To understand the interaction between Andean tectonics and contemporaneous foreland development, we analyse stratigraphic, sedimentologic and seismic data from the Subandean Belt and the Chaco Basin. The structural features provide a mechanism for transferring zones of deposition, subsidence and uplift. These can be reconstructed based on regional distribution of clastic sequences. Isopach maps, combined with sedimentary architecture analysis, establish systematic thickness variations, facies changes and depositional styles. The foreland basin consists of five stratigraphic successions controlled by Andean orogenic episodes and climate: (1) the foreland basin sequence commences between ～27 and 14 Ma with the regionally unconformable, thin, easterly sourced fluvial Petaca strata. It represents a significant time interval of low sediment accumulation in a forebulge‐backbulge depocentre. (2) The overlying ～14–7 Ma‐old Yecua Formation, deposited in marine, fluvial and lacustrine settings, represents increased subsidence rates from thrust‐belt loading outpacing sedimentation rates. It marks the onset of active deformation and the underfilled stage of the foreland basin in a distal foredeep. (3) The overlying ～7–6 Ma‐old, westerly sourced Tariquia Formation indicates a relatively high accommodation and sediment supply concomitant with the onset of deposition of Andean‐derived sediment in the medial‐foredeep depocentre on a distal fluvial megafan. Progradation of syntectonic, wedge‐shaped, westerly sourced, thickening‐ and coarsening‐upward clastics of the (4) ～6–2.1 Ma‐old Guandacay and (5) ～2.1 Ma‐to‐Recent Emborozú Formations represent the propagation of the deformation front in the present Subandean Zone, thereby indicating selective trapping of coarse sediments in the proximal foredeep and wedge‐top depocentres, respectively. Overall, the late Cenozoic stratigraphic intervals record the easterly propagation of the deformation front and foreland depocentre in response to loading and flexure by the growing Intra‐ and Subandean fold‐and‐thrust belt.  相似文献   

6.
The Ericson Formation was deposited in the distal foredeep of the Cordilleran foreland basin during Campanian time. Isopach data show that it records early dynamic subsidence and the onset of basin partitioning by Laramide uplifts. The Ericson Formation is well exposed around the Rock Springs uplift, a Laramide structural dome in southwestern Wyoming; the formation is thin, regionally extensive, and does not display the wedge‐shaped geometry typical of foredeep deposits. Sedimentation in this area was controlled both by activity in the thrust belt and by intraforeland tectonics. The Ericson Formation is ideally situated both spatially and temporally to study the transition from Sevier to Laramide (thin‐ to thick‐skinned) deformation which corresponded to the shift from flexural to dynamic subsidence and the demise of the Cretaceous foreland basin system. We establish the depositional age of the Ericson Formation as ca. 74 Ma through detrital zircon U–Pb analysis. Palaeocurrent data show a generally southeastward transport direction, but northward indicators near Flaming Gorge Reservoir suggest that the intraforeland Uinta uplift was rising and shedding sediment northward by late Campanian time. Petrographic data and detrital zircon U–Pb ages indicate that Ericson sediment was derived from erosion of Proterozoic quartzites and Palaeozoic and Mesozoic quartzose sandstones in the Sevier thrust belt to the west. The new data place temporal and geographic constraints on attempts to produce geodynamic models linking flat‐slab subduction of the oceanic Farallon plate to the onset of the Laramide orogenic event.  相似文献   

7.
Abstract Simple elastic plate models have been used to determine the stratigraphic patterns that result from prograding sediment loads. The predicted patterns, which include coastal offlap/onlap and downlap in a basinward direction, are generally similar to observations of stratal geometry from Cenozoic sequences of the U.S. Atlantic and Gulf Coast margins. Coastal offlap is a feature of all models in which the water depth and elastic thickness of the lithosphere, T e (which is a measure of the long-term strength of the lithosphere), are held constant, and is caused by a seaward shift in the sediment load and its compensation as progradation proceeds. The coastal offlap pattern is reduced if sediments prograde into a subsiding basin, since subsidence causes an increase in the accommodation space and loading landward of a prograding wedge. The stratal geometry that results is complex, however, and depends on the sediment supply, the amount of subsidence, and T e. If the sediment supply to a subsiding basin proceeds in distinct 'pulses' (due, say, to different tectonic events in a source region) then it is possible to determine the relationship between stratal geometry and T e. Coastal offlap and downlap are features of most models where the lithosphere either has a constant T e slowly increases Te with time, or changes T e laterally; however, in the case where sediments prograde onto lithosphere that rapidly increases T e with rime, the offlap can be replaced by onlap. Lithospheric flexure due to prograding sediment loads is capable of producing a wide variety of stratal geometries and may therefore be an important factor to take into account when evaluating the relative role of tectonics and eustatic sea-level changes in controlling the stratigraphic record.  相似文献   

8.
The formation processes of the late Neogene sedimentary basins in Northern Hokkaido have been investigated on the basis of rock magnetism, structural geology and numerical modelling. Untilted site‐mean directions of remanent magnetization of the Wakkanai Formation, obtained from oriented core samples in Horonobe, suggest remarkable counterclockwise block rotation (ca. 70°) since the late Neogene. Uniform microscopic fabric of the siliceous sediments was inferred from the alignment of the principal axes of the anisotropy of magnetic susceptibility (AMS). After correction for tectonic rotation, the maximum axis of AMS, which reflects the sedimentary fabric of the dominant paramagnetic minerals, is in an E‐W direction, which is concordant with the influx direction of diatomaceous particles into the N‐S elongate sedimentary basins. The difference in the bulk initial magnetic susceptibility of the siliceous sediments of the Wakkanai Formation between the depocenter of the basin and its peripheral part implies that terrigenous non‐magnetic fraction has been sorted out during transportation of the detrital grains as gravity flows. As for the development mechanism of the N‐S elongate late Neogene basins in Northern Hokkaido, their depocenter arrangement and subsidence pattern indicates dextral motions upon a longitudinal fault zone along the Eurasian convergent margin. Dislocation modelling was adopted to explain vertical displacement and rotational motion around the study area and successfully restored the deformation pattern based on the assumption of dextral slip at a left‐stepping part of a strand of the transcurrent fault.  相似文献   

9.
The change from continental to marine conditions in the Middle Carboniferous on Brøggerhalvøya started at the end of the Bashkirian with short-term transgressive events at the top of the Brøggertinden Formation. Local basin subsidence was responsible for the pulsatory nature of the transgression. The establishment of a shallow marine carbonate-dominated environment is represented by the Moscovian Scheteligfjellet Member which overlies the post-Caledonian red beds of the Brøggertinden Formation. The Scheteligfjellet Member is the lowermost member of the Nordenskioldbreen Formation and shows distinct lateral facies variations. Three facies associations can be distinguished: lagoonal facies, shoal facies and open marine facies. The succeeding two members were deposited in subtidal areas of the carbonate platform. A basin subsidence event at the Carboniferous/Permian boundary was responsible for a short shift into deeper depositional environments during a time of worldwide regression. After this a continuous regression led to supratidal conditions at the top of the Nordenskioldbreen Formation.  相似文献   

10.
This article presents combined stratigraphic, sedimentological, subsidence and provenance data for the Cretaceous–Palaeogene succession from the Zhepure Mountain of southern Tibet. This region records the northernmost sedimentation of the Tethyan passive margin of India, and this time interval represents the transition into continental collision with Asia. The uppermost Cretaceous Zhepure Shanpo and Jidula formations record the transition from pelagic into upper slope to delta‐plain environments. The Palaeocene–lower Eocene Zongpu Formation records a carbonate ramp that is overlain by the deep‐water Enba Formation (lower Eocene). The upper part of the Enba Formation records shallowing into a storm‐influenced, outer shelf environment. Detrital zircon U–Pb and Hf isotopic data indicate that the terrigenous strata of the Enba Formation were sourced from the Lhasa terrane. Unconformably overlying the Enba Formation is the Zhaguo Formation comprising fluvial deposits with evidence of recycling from the underlying successions. Backstripped subsidence analysis indicates shallowing during latest Cretaceous‐earliest Palaeocene time (Zhepure Shanpo and Jidula formations) driven by basement uplift, followed by stability (Zongpu Formation) until early Eocene time (Enba Formation) when accelerated subsidence occurred. The provenance, subsidence and stratigraphy suggest that the Enba and Zhaguo formations record foredeep and wedge‐top sedimentation respectively within the early Himalayan foreland basin. The underlying Zongpu Formation is interpreted to record the accumulation of a carbonate ramp at the margin of a submarine forebulge. The precursor tectonic uplift during latest Cretaceous time could either record surface uplift over a mantle plume related to the Réunion hotspot, or an early signal of lithospheric flexure related to oceanic subduction, continental collision or ophiolite obduction. The results indicate that the collision of India with Asia occurred before late Danian (ca. 62 Ma) time.  相似文献   

11.
Platform carbonates diagenesis in salt basins could be complex due to potential alterations of fluids related and non-related to diapirism. This paper presents the diagenetic history of the Hettangian to Pliensbachian platform carbonates from the Tazoult salt wall area (central High Atlas, Morocco). Low structural relief and outcrop conditions allowed to define the entire diagenetic evolution occurred in the High Atlas diapiric basins since early stages of the diapiric activity up to their tectonic inversion. Precipitation of dolomite and calcite from both warmed marine-derived and meteoric fluids characterised diagenetic stages during Pliensbachian, when the carbonate platforms were exposed and karstified. Burial diagenesis occurred from Toarcian to Middle Jurassic, due to changes of salt-induced dynamic related to increase in siliciclastic input, fast diapir rise and rapid burial of Pliensbachian platforms. During this stage, the diapir acted as a physical barrier for fluid circulation between the core and the flanking sediments. In the carbonates and breccias flanking the structures, dolomite and calcite precipitated from basinal brines, whereas carbonate slivers located in the core of the structure, were affected by the circulation of Mn-rich fluids. The final diagenetic event is characterised by the income of meteoric fluids into the system during uplift caused by Alpine orogeny. These results highlight the relevant influence of diapirism on the diagenetic modifications in salt-related basins in terms of diagenetic events and involved fluids.  相似文献   

12.
Vertical trends in architecture and facies of delta systems are preserved in a clastic wedge of an expanding marine half-graben in which tectonics, eustatic sea-level change and climatic change are roughly known from independent evidence. The studied half-graben is situated on Crete (Greece) and part of a larger, E-W-trending extensional domain situated north of the Hellenic subduction zone. The extension seems to be related to the southward migration of the trench (roll-back) in early Late Miocene times. The infill pattern is discussed in the light of theoretical fault-growth models for expanding half-grabens. The geometry of the half-graben fill is typically wedge shaped, with a thickness of nearly 1000 m near the fault scarp thinning to c. 50 m about 20 km away from the scarp. The lower part of the wedge (Stratified Prina Series) contains coarsening-upward units representing progradational, shallow-marine deltas. At the base of the wedge these units are thin and retrogradationally stacked. Upwards in the succession, the units become composite (coarsening-upward subunits), thicker and finer grained. The composite structure, the thickening and the fining trend is related to progressive increase in accommodation space inherent in fault growth. Rapid deepening of the basin from the photic zone (evidenced by intercalated coral and stromatolite beds) up to a depth of 900 m started at the top of the Stratified Prina Series. The deepening continued over some tens of metres of marly sediments of the base of the Kalamavka Formation and may be related to structural collapse of the fault block. After the structural collapse, basin depth remained more or less constant and basin infilling occurred by progradation of deep-water delta systems. These systems are characterized by a muddy delta slope with channelized conglomerates, and by mainly aggradation of prodelta turbidites deposited in small lobes at the base of slope.  相似文献   

13.
Important aspects of the Andean foreland basin in Argentina remain poorly constrained, such as the effect of deformation on deposition, in which foreland basin depozones Cenozoic sedimentary units were deposited, how sediment sources and drainages evolved in response to tectonics, and the thickness of sediment accumulation. Zircon U‐Pb geochronological data from Eocene–Pliocene sedimentary strata in the Eastern Cordillera of northwestern Argentina (Pucará–Angastaco and La Viña areas) provide an Eocene (ca. 38 Ma) maximum depositional age for the Quebrada de los Colorados Formation. Sedimentological and provenance data reveal a basin history that is best explained within the context of an evolving foreland basin system affected by inherited palaeotopography. The Quebrada de los Colorados Formation represents deposition in the distal to proximal foredeep depozone. Development of an angular unconformity at ca. 14 Ma and the coarse‐grained, proximal character of the overlying Angastaco Formation (lower to upper Miocene) suggest deposition in a wedge‐top depozone. Axial drainage during deposition of the Palo Pintado Formation (upper Miocene) suggests a fluvial‐lacustrine intramontane setting. By ca. 4 Ma, during deposition of the San Felipe Formation, the Angastaco area had become structurally isolated by the uplift of the Sierra de los Colorados Range to the east. Overall, the Eastern Cordillera sedimentary record is consistent with a continuous foreland basin system that migrated through the region from late Eocene through middle Miocene time. By middle Miocene time, the region lay within the topographically complex wedge‐top depozone, influenced by thick‐skinned deformation and re‐activation of Cretaceous rift structures. The association of the Eocene Quebrada del los Colorados Formation with a foredeep depozone implies that more distal foreland deposits should be represented by pre‐Eocene strata (Santa Barbara Subgroup) within the region.  相似文献   

14.
Eleven shallow cores display 315 m of the >700 m thick Lower and Middle Triasic successional of the Svalis Dome, a Salt diapir in the central south-western Barents Sea. The Svalis Dome was uplifted in the late Mesozoic. and Trisassic rocks suherop below Quaternary till around the Upper Palaeozoic core of the dome. Deposition of the Triassic succession took place in deep shelf to basinal environments below storm wave base. The succession is dated by macrofossils and palynomorphs and can be assigned to four formations. The basal beds of the shaly greenish grey Havert Formation (Griesbachian) occur above Permian bioclastic carbonate. The Klappmyss Formation (Smithian) in the lower part contains gravity flow sands deposited as submarine fans pussible triggered by tectonic movements along the adjacent ault zones overlian by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe overlain by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe Formation, and was deposited in a large bight by restricted water circulation. The Snadd Formation. on top, representes a marine shelf unit deposited in front of an emerging land area in the north-east. A minimum of six higher order transgressive-regressive sequences are recognized at the Svalis Dome and these are correlated with other Arctic areas.  相似文献   

15.
The wedge‐top depozone in the southern Taiwan foreland basin system is confined by the topographic front of the Chaochou Fault to the east and by a submarine deformation front to the west. The Pingtung Plain, Kaoping Shelf and Kaoping Slope constitute the main body of the wedge‐top depozone. In a subaerial setting, the alluvial and fluvial sediments accumulate on top of the frontal parts of the Taiwan orogenic wedge to form the Pingtung Plain proximal to high topographic relief. In a submarine setting, fine‐grained sediments accumulate on the Kaoping Shelf and dominant mass‐wasting sediment forms the Kaoping Slope. Wedge‐top sediments are deformed into a series of west‐vergent imbricated thrusts and folds and associated piggyback basins. A major piggyback basin occurs in the Pingtung Plain. Four smaller piggyback basins appear in the shelf–slope region. Many small‐sized piggyback basins developed over ramp folds in the lower slope region. Pliocene–Quaternary deep marine to fluvial sediments about 5000 m thick have been deposited on top of the frontal orogenic wedge in southern Taiwan. Sedimentary facies shows lateral variations from extremely coarse fluvial conglomerates proximal to the topographic front (Chaochou Fault) to fine‐grained deep marine mud close to the deformation front near the base of the slope. The stratigraphic column indicates that offshore deep‐water mud is gradationally overlain by shallow marine sands and then fluvial deposits. The transverse cross‐section of the wedge‐top depozone in the southern Taiwan is a doubly tapered prism. The northern boundary of the wedge‐top depozone in southern Taiwan is placed along the southern limit of the Western Foothills where the frontal orogenic wedge progressively changes southward to a wedge‐top depozone (Pingtung Plain), reflecting ongoing southward oblique collision between the Luzon Arc and the Chinese margin. The wedge‐top depozone is bounded to the south by the continent–ocean crust boundary. The deep slope west of the Hengchun Ridge can be viewed as an infant wedge‐top depozone, showing initial mountain building and the beginning of wedge‐top depozone.  相似文献   

16.
This paper develops a tectono‐stratigraphic model for the evolution and drowning of Early Jurassic carbonate platforms. The model arises from outcrop analysis and Sr isotope dating of successions exposed in the Betic Cordillera in southeastern Spain. Here, an extensive Early Jurassic (Sinemurian) carbonate platform developed on the rifted Tethyan margin of the Iberian Plate. The platform was dissected by extensional faults in early jamesoni times (ca. 191 Ma) and again in late ibex times (ca.188 Ma) during the Pliensbachian stage. Extensional faults and fault block rotation are shown to control the formation of three sequence boundaries that divide the platform stratigraphy (the Gavilan Formation) into three depositional sequences. The last sequence boundary marks localised drowning of the platform and deposition of the deeper water Zegri Formation, whereas adjacent platforms remain exposed or continue as the site of shallow‐marine sediment accumulation. This study is based on mapping, facies analysis and dating of platform carbonates exposed in three tectonic units within the zone: Gabar, Ponce and Canteras. Facies analysis leads to the recognition of facies associations deposited in carbonate ramp environments and adjacent to synsedimentary, marine, fault scarps. Sr isotope dating enables us to correlate platform‐top carbonates from the different tectonic units at a precision equivalent to ammonite zones. A sequence stratigraphic analysis of sections from the three tectonic units is carried out using the facies models together with the Sr isotope dates. This analysis indicates a clear tectonic control on the development of the stratigraphy: depositional sequences vary in thickness, have wedge‐shaped geometries and vary in facies, internal geometries and systems tracts from one tectonic unit to another. Criteria characterising depositional sequences and sequence boundaries from the Gabar and Ponce units are used to establish a tectono‐stratigraphic model for carbonate platform depositional sequences and sequence boundaries in maritime rifts, which can be applied to other less well‐exposed or subsurface successions from other sedimentary basins. Onlapping transgressive and progradational highstand systems tracts are recognised on dip slope ramps. Falling stage and lowstand systems tracts are developed as thick breccia units in hangingwall areas adjacent to extensional faults. Sequence boundaries vary in character, amplitude and/or duration of sea‐level fall and persistence across the area. Some boundaries coalesce onto the Canteras unit, which remained as a relatively positive area throughout the early Pliensbachian (Carixian). The carbonate platform on the Ponce tectonic unit drowned in the latest Carixian (davoei biozone). However, the adjacent tectonic units remained emergent and developed a long‐lived sequence boundary, indicating tectonic subsidence as the major cause for platform drowning. The stratigraphic evolution of this area on the rifted southern Iberian margin indicates that a widespread restricted shallow‐water carbonate platform environment accumulating peritidal carbonates evolved with faulting to a more open‐marine setting. Sr dating indicates that this transition took place around the Sinemurian–Pliesbachian boundary and it was driven by local fault‐related subsidence together with likely post‐faulting regional subsidence.  相似文献   

17.
This paper investigates several wedge structures formed in continental deposits covering marine sediments deposited during MIS 5 along the central Patagonian coast of Argentina. The size and surface microtexture characteristics of the infilling sediments are consistent with a depositional environment dominated by aeolian transport. Fragments of Andean volcanic rocks (glass shards) in the wedge‐fill suggest long‐distance transport via a westerly component of wind direction. The wedges are interpreted as products of deep seasonal frost action in frozen ground, which produced open cracks that filled rapidly with partially non‐local aeolian sediments. Many wedges cross cut carbonate crusts that formed under permafrost conditions in coastal Patagonia. The radiocarbon dating of carbonate crusts yielded an age of 25–27 kyr bp , while wedge‐fill sediments are OSL dated to 14 670 ± 750 yr bp . This indicates that ground wedge formation occurred during a cold event (the Antarctic Cold Reversal period) that interrupted the permafrost degradation following the Last Glacial Maximum.  相似文献   

18.
In recent years, contrasting seismic tomographic images have given rise to an extensive debate about the occurrence and implications of migrating slab detachment beneath southern Italy. One of the most pertinent aspects of this process is the concentration of the slab pull force, and particularly its surface expression in terms of vertical motions and related basin subsidence/uplift. In this study we focused on shallow‐water to continental, Pliocene‐Quaternary basins that formed on top of the Apennine allochthonous wedge after its emplacement onto a large foreland carbonate platform domain (Apulian Platform). Due to the thick‐skinned style of deformation controlling the Pliocene‐Pleistocene stages of continental shortening, a high degree of coupling with the downgoing plate appears to characterize the late tectonic evolution of the southern Apennines. Therefore, the wedge‐top basins analysed in this study, although occurring on the deformed edge of the overriding plate, are capable of recording deep geodynamic processes affecting the slab. Detailed stratigraphic work on these wedge‐top basins points to a progressive SE‐ward migration of basin subsidence from c. 4 to c. 2.8 Ma over a distance of about 140 km along the strike of the Apennine belt. Such a migration is consistent with a redistribution of slab‐pull forces associated with the progressive lateral migration at a mean rate in the range of 12–14 cm y–1 of a slab tear within the down‐going Adriatic lithosphere. These results yield fundamental information on the rates of first‐order geodynamic processes affecting the slab, and on related surface response.  相似文献   

19.
《Basin Research》2018,30(Z1):513-531
Barremian‐Aptian sedimentary successions along the northern Arabian margin have been described as a transition from a siliciclastic to a carbonate‐dominated marine environment, deposited upon a low‐relief shelf or platform formed as a consequence of continuous regional subsidence. A long (360 m) core from northern Israel offers a unique look at this transition, providing valuable insights for the palaeoceanography, geometry and ventilation conditions that lead to Oceanic Anoxic Event 1 (OAE1) in this region. Results from high‐resolution elemental, mineralogical, sedimentological and petrophysical analyses carried out revealed the emplacement of abundant mass‐transport deposits (MTDs) during the Late Barremian and the Aptian. The transplanted units are characterized by fine grained calcareous shales with elevated organic matter, sulphur and iron contents. The scarcity or absence of bioturbation in the disturbed sequences provides a hint to the sediment/water interface conditions. However, a decrease in sulphur and iron occurring at the contact between the shales and the MTDs is explained as increased oxic conditions at the sediment‐water interface as a result of turbulence and mixing associated with the descending sediment masses. Such recurrent events ventilation of the low‐energy basinal environment during the Late Barremian and Aptian, predate the wide‐scale establishment of OAE1 in the northern Arabian margin. Moreover, the identification of coarse‐grained MTDs within deep‐water calcareous sediments indicates a much steeper gradient of the northern Arabian margin, challenging previous studies.  相似文献   

20.
The propagation of the deformation front in foreland systems is typically accompanied by the incorporation of parts of the basin into wedge‐top piggy‐back basins, this process is likely producing considerable changes to sedimentation rates (SR). Here we investigate the spatial‐temporal evolution of SR for the Tremp–Jaca Basin in the Southern Pyrenees during its evolution from a wedge‐top, foreredeep, forebulge configuration to a wedge‐top stage. SR were controlled by a series of tectonic structures that influenced subsidence distribution and modified the sediment dispersal patterns. We compare the decompacted SR calculated from 12 magnetostratigraphic sections located throughout the Tremp–Jaca Basin represent the full range of depositional environment and times. While the derived long‐term SR range between 9.0 and 84.5 cm/kyr, compiled data at the scale of magnetozones (0.1–2.5 Myr) yield SR that range from 3.0 to 170 cm/kyr. From this analysis, three main types of depocenter are recognized: a regional depocenter in the foredeep depozone; depocenters related to both regional subsidence and salt tectonics in the wedge‐top depozone; and a depocenter related to clastic shelf building showing transgressive and regressive trends with graded and non‐graded episodes. From the evolution of SR we distinguish two stages. The Lutetian Stage (from 49.1–41.2 Ma) portrays a compartmentalized basin characterized by variable SR in dominantly underfilled accommodation areas. The markedly different advance of the deformation front between the Central and Western Pyrenees resulted in a complex distribution of the foreland depozones during this stage. The Bartonian–Priabonian Stage (41.2–36.9 Ma) represents the integration of the whole basin into the wedge‐top, showing a generalized reduction of SR in a mostly overfilled relatively uniform basin. The stacking of basement units in the hinterland during the whole period produced unusually high SR in the wedge‐top depozone.  相似文献   

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