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1.
Understanding the relationship between sedimentation and tectonics is critical to the analysis of stratigraphic evolution in foreland basins. Previous models of foreland basins have explained stratal development, but were done generally under the assumption that steady allogenic forcing produces a steady stratigraphic response. They did not consider autogenic shoreline behaviour during the development of the subsidence pattern characteristic of foreland basins. We present a mathematical model and flume experiments that explore how subsidence and sediment‐supply rates control the shoreline trajectory and the stratal patterns that fill foreland basins. Through these models, we found differing autogenic responses in the rate and direction of shoreline migration, and these generated three distinct styles of stratal architecture, despite the constant external forcing (i.e. constant sediment discharge and basin substrate tilting). The first response was ‘autoretreat’, where shoreline migration switched from initial progradation to retrogradation. The second response was progradation followed by constant aggradation of the shoreline. The third response was maintained progradation with a markedly accelerating rate. We termed this latter newly observed autogenic behaviour ‘shoreline autoacceleration’. These three modes of shoreline behaviour and their accompanying stratal architecture provide a basic framework for the relationship between sedimentation and tectonic activity in foreland basins under the simplified conditions presented here.  相似文献   

2.
Grain size trends in basin stratigraphy are thought to preserve a rich record of the climatic and tectonic controls on landscape evolution. Stratigraphic models assume that over geological timescales, the downstream profile of sediment deposition is in dynamic equilibrium with the spatial distribution of tectonic subsidence in the basin, sea level and the flux and calibre of sediment supplied from mountain catchments. Here, we demonstrate that this approach in modelling stratigraphic responses to environmental change is missing a key ingredient: the dynamic geomorphology of the sediment routing system. For three large alluvial fans in the Iglesia basin, Argentine Andes we measured the grain size of modern river sediment from fan apex to toe and characterise the spatial distribution of differential subsidence for each fan by constructing a 3D model of basin stratigraphy from seismic data. We find, using a self‐similar grain size fining model, that the profile of grain size fining on all three fans cannot be reproduced given the subsidence profile measured and for any sediment supply scenario. However, by adapting the self‐similar model, we demonstrate that the grain size trends on each fan can be effectively reproduced when sediment is not only sourced from a single catchment at the apex of the system, but also laterally, from tributary catchments and through fan surface recycling. Without constraint on the dynamic geomorphology of these large alluvial systems, signals of tectonic and climate forcing in grain size data are masked and would be indecipherable in the geological record. This has significant implications for our ability to make sensitive, quantitative reconstructions of external boundary conditions from the sedimentary record.  相似文献   

3.
Formation of alluvial stratigraphy is controlled by autogenic processes that mix their imprints with allogenic forcing. In some alluvial successions, sedimentary cycles have been linked to astronomically‐driven, cyclic climate changes. However, it remains challenging to define how such cyclic allogenic forcing leads to sedimentary cycles when it continuously occurs in concert with autogenic forcing. Accordingly, we evaluate the impact of cyclic and non‐cyclic upstream forcing on alluvial stratigraphy through a process‐based alluvial architecture model, the Karssenberg and Bridge (2008) model (KB08). The KB08 model depicts diffusion‐based sediment transport, erosion and deposition within a network of channel belts and associated floodplains, with river avulsion dependent on lateral floodplain gradient, flood magnitude and frequency, and stochastic components. We find cyclic alluvial stratigraphic patterns to occur when there is cyclicity in the ratio of sediment supply over water discharge (Qs/Qw ratio), in the precondition that the allogenic forcing has sufficiently large amplitudes and long, but not very long, wavelengths, depending on inherent properties of the modelled basin (e.g. basin subsidence, size, and slope). Each alluvial stratigraphic cycle consists of two phases: an aggradation phase characterized by rapid sedimentation due to frequent channel shifting and a non‐deposition phase characterized by channel belt stability and, depending on Qs/Qw amplitudes, incision. Larger Qs/Qw ratio amplitudes contribute to weaker downstream signal shredding by stochastic components in the model. Floodplain topographic differences are found to be compensated by autogenic dynamics at certain compensational timescales in fully autogenic runs, while the presence of allogenic forcing clearly impacts the compensational stacking patterns.  相似文献   

4.
Fluvio‐deltaic stratigraphy develops under continuous morphodynamic interactions of allogenic and autogenic processes, but the role and relative contribution of these processes to the stratigraphic record are poorly understood. We analysed synthetic fluvio‐deltaic deposits of several accommodation‐to‐supply cycles (sequences) with the aim to relate stratigraphic variability to autogenic and allogenic controls. The synthetic stratigraphy was produced in a series of long time‐scale (105 years) numerical experiments with an aggregated process‐based model using a typical passive‐margin topography with constant rates of liquid and solid river discharge subjected to sinusoidal sea‐level fluctuation. Post‐processing of synthetic stratigraphy allowed us to quantify stratigraphic variability by means of local and regional net sediment accumulation over equally spaced time intervals (1–10 kyr). The regional signal was subjected to different methods of time‐series analysis. In addition, major avulsion sites (>5 km from the coastline) were extracted from the synthetic stratigraphy to confirm the interpretations of our analyses. Regional stratigraphic variability as defined in this study is modulated by a long‐term allogenic signal, which reflects the rate of sea‐level fluctuation, and it preserves two autogenic frequency bands: the intermediate and high‐frequency components. The intermediate autogenic component corresponds to major avulsions with a median inter‐avulsion period of ca. 3 kyr. This component peaks during time intervals in which aggradation occurs on the delta plain, because super‐elevation of channel belts is a prerequisite for large‐scale avulsions. Major avulsions occur occasionally during early stages of relative sea‐level fall, but they are fully absent once the coast line reaches the shelf edge and incision takes place. These results are consistent with a number of field studies of falling‐stage deposition in fluvial systems. The high‐frequency autogenic component (decadal to centennial time scales) represents mouthbar‐induced bifurcations occurring at the terminal parts of the system, and to a lesser extent, partial or small‐scale avulsions (<5 km from the coastline). Bifurcation intensity correlates strongly with the rate of progradation, and thus reaches its maximum during forced regression. However, its contribution to overall stratigraphic variability is much less than that of the large‐scale avulsions, which affect the entire area downstream of avulsion nodes. The results of this study provide guidelines for predicting fluvio‐deltaic stratigraphy in the context of co‐existing autogenic and allogenic processes and underscore the fact that the relative importance and the type of autogenic processes occurring in fluvio‐deltaic systems are governed by allogenic forcing.  相似文献   

5.
Sediment flux from an uplifting fault block   总被引：5，自引：1，他引：4  
The stratigraphy of rift basins is a direct result of sediment liberation and transport through catchment–fan systems whose dynamics are controlled by both external and internal factors. We investigate the response of catchment–fan systems established across an active normal fault to variations in both tectonic and climatic boundary conditions. Numerical experiments show that the ratio of fan area to catchment area provides a sensitive indicator of tectonic activity. A step decrease in fault slip rate results in a delayed response by the catchment–fan systems; the response time is ∼50 kyr for a variety of parameter values. Decreased slip rate also gives rise to an abrupt but transient pulse in sediment discharge from the fans due to a drop in the hangingwall subsidence rate. In contrast, variations in climatic activity, using precipitation rate as a proxy, produce extremely rapid responses throughout the catchment–fan system. Thus, high-frequency climatic changes will overprint lower frequency tectonic variations in the stratigraphic record of fan deposits. Finally, we map out possible combinations of fault geometry, fault slip rate and precipitation rate that allow fan progradation and high rates of sediment discharge from the system.  相似文献   

6.
A three‐dimensional quantitative stratigraphic forward model is employed to investigate the controls leading to the Messinian events in the lacustrine Pannonian Basin of Central Paratethys, and the link between the Messinian salinity crisis in the Mediterranean and the late Miocene‐Pliocene stratigraphy of the Pannonian Basin. Subsurface geological data show that a prominent unconformity surface formed during Messinian time in the Pannonian Basin associated with a sudden forced regression, abrupt basinward shift of facies and a subsequent, prolonged lowstand normal regression. The lowstand prograding series filled up the shallow basin fast, while, at the same time, the marginal areas of the basin were subject to tectonic inversion. The Dionisos program used in this research is built on a nonlinear water‐driven sediment diffusion process, and it employs multiple sediment classes, basin flexure and compaction. Four different scenarios were built in the experiments to test possible basin histories with different rates and timing of tectonic inversion. Each scenario was modelled in two versions: including and not including a lake‐level fall in the Messinian. The results confirm that the Pannonian Basin in the study area has undergone a tectonic inversion since the Messinian, although the exact rates of uplift at different locations remain uncertain. The unconformity and the observed stratigraphic architecture and facies pattern could be modelled adequately only in the versions that applied a Messinian lake‐level fall. Our research concludes that the Messinian unconformity in the Pannonian Basin was caused by an absolute lake‐level drop, likely linked to the desiccation of the Mediterranean, followed by subsidence and normal regression in the basin centre and concomitant tectonic inversion and uplift along the basin margins.  相似文献   

7.
A major issue in tectonics and sedimentation is the role of cross‐stream tectonic tilting in steering channels. The general idea is that channels will be attracted to lateral maxima in subsidence rate. A physical experiment performed in 1999 at the St. Anthony Falls Laboratory, however, was in conflict with the idea and showed that fluvial channels and resulting stratigraphy can be insensitive to even relatively strong lateral variation in subsidence. Here, we present results from an experiment which uses a simplified relay‐ramp geometry with laterally variable uplift and subsidence to test a hypothesis developed from the earlier experiment: Tectonic tilting steers channels only when the ratio of the time scales describing lateral channel mobility to tectonic deformation is sufficiently large. Occupation time by experimental channels and sand fraction in the deposit (a proxy for channel deposition) both increase with subsidence rate indicating strong steering of channels by tectonic forcing. We also found that, due to local incision, uplift lengthened the time scale for lateral channel migration relative to subsidence. Comparing channel mobility at the beginning of the experiment, with no tectonic forcing, to later tectonic stages of the experiment indicates that active tectonics increased the channel time scale. The interplay of channel steering with uplift and subsidence led to cyclic appearance and disappearance of an autogenic lake in the hanging‐wall basin. This lake was associated with alternation between channels going around vs. across the adjoining upstream uplifted footwall region. This creation and filling of the lake under constant tectonic forcing (constant fault slip rate) in the hanging wall created subaerial fan‐delta parasequences separated by fluvial deposits.  相似文献   

8.
Rates of accommodation and sediment supply are the principal controls on stacking patterns in siliciclastic basin fills. Stratigraphic inversion is aimed at reconstruction of these controls from the detrital record. Efforts to ‘explain’ siliciclastic basin fills have been focused on analysis and numerical modelling of sequence geometry in response to changes in accommodation, whereas comparatively few studies have attempted to address the role of sediment supply. The compositional and textural properties of siliciclastic basin fills are linked with the evolution of drainage basins through the principle of climatic–physiographic control of sediment production and supply. Application of this principle leads to a method of compositional analysis for distinguishing sequences controlled by high-frequency changes in the rate of accommodation from sequences controlled by high-frequency variations in the rate of sediment supply (order of 10 kyr). This method does not require detailed time control. Changes in rate and type of sediment supplied to depositional systems in response to environmental perturbations in drainage basins are explored in greater detail by means of a numerical model of sediment production under various scenarios of climatic and tectonic forcing. Simulation experiments suggest that drainage basins respond differently to high-frequency tectonic and climatic perturbations. Synthetic time series of cyclically forced sediment production display different types of asymmetric variations in grain size, accumulation rate and residence time of sediments in response to tectonic and climatic forcing. The results also highlight the role of vegetation as the principal modulator of climate forcing, and show that the nonlinear response to climate change may frustrate any attempts at providing broad generalizations of the system's responses. The modelling results confirm the usefulness of a combined analysis of sediment composition and sequence geometry, and the mathematically rich behaviour of the system suggests that further development of this approach is likely to increase our ability to reconstruct forcing mechanisms and initial boundary conditions from the detrital record.  相似文献   

9.
The Sivas Basin, located in the Central Anatolian Plateau of Turkey, is a foreland basin that records a complex interaction between sedimentation, salt tectonics and regional shortening during the Oligo‐Miocene leading to the formation of numerous mini‐basins. The Oligocene sedimentary infill of the mini‐basins consists of a thick continental succession, the Karayün Formation, comprising a vertical succession of three main sub‐environments: (i) playa‐lake, (ii) fluvial braided, and (iii) saline lacustrine. These sub‐environments are seen as forming a large Distributive Fluvial System (DFS) modified through time as a function of sediment supply and accommodation related to regional changes in climate and tectonic regime. Within neighbouring mini‐basins and despite a similar vertical stratigraphic succession, subtle variations in facies assemblages and thickness are observed in stratigraphic units of equivalent age, thus demonstrating the local control exerted by halokinesis. Stratigraphic and stratal patterns reveal in great detail the complex interaction between salt tectonics and sedimentation including different types of halokinetic structures such as hooks, wedges and halokinetic folds. The regional variations of accommodation/sediment supply led to coeval changes in the architectural patterns recorded in the mini‐basins. The type of accommodation regime produces several changes in the sedimentary record: (i) a regime dominated by regional accommodation limits the impact of halokinesis, which is recorded as very small variations in stratigraphic thickness and facies distribution within and between mini‐basins; (ii) a regime dominated by localized salt‐induced accommodation linked to the subsidence of each individual mini‐basin enhances the facies heterogeneity within the DFS, causing sharp changes in stratigraphic thickness and facies assemblages within and between mini‐basins.  相似文献   

10.
The stratigraphic development of an Upper Jurassic syn‐rift succession exposed at outcrop in the Inner Moray Firth Basin has been investigated using high‐resolution biostratigraphy and sedimentology. A continuous 970 m thick section, exposed in the hangingwall of the Helmsdale Fault was logged in detail. The succession spans 8 Ma and contains eight lithofacies types, which indicate deposition in a deep marine setting. Boulder beds contain large, angular clasts, with bed thicknesses typically >2 m and poor sorting suggesting deposition by debris flows. An inverse clast stratigraphy is observed; the oldest boulder beds contain sandstone clasts of Upper Old Red Sandstone (ORS) with younger debris flows containing clasts of Middle ORS calcareous siltstone. A marked change from siliciclastic to carbonate dominated sedimentation occurred during the Early Tithonian, interpreted primarily as a result of change in lithologies in the footwall catchment from sandstone to calcareous siltstone, which reduced supply of siliciclastic sediment. Secondary factors are identified as increased aridity in the Early Tithonian, which reduced sand supply from the hinterland and a third‐order Early Tithonian eustatic sea‐level rise, which trapped coarser clastic sediment within the hinterland. Biostratigraphy allows calculation of variations in sedimentation rates with recognition of: (1) an early rift phase characterised by sandy turbidite deposition, when sedimentation rates averaged 0.08 m/ky, (2) a rift climax phase from the Early Kimmeridgian where sedimentation rates increased steadily to a maximum of 0.64 m/ky in the Early Tithonian, with strata dominated by boulder scale clast‐supported debris flows and (3) a late stage of rifting from the mid Tithonian, where sedimentation rates decreased to 0.07 m/ky. Overall sedimentation rates are comparable to those of other deep marine rift basins. Unroofing a resistant lithology on the footwall of a rift has important implications for siliciclastic sediment supply in rift basins.  相似文献   

11.
Although many once‐deforested areas of the eastern United States are now revegetated, impacts of this disturbance on watershed processes may persist. In this study, lake sediment stratigraphy and magnetism were used to assess the recovery of a small watershed in the southern Blue Ridge Mountains following abrupt reduction of human impacts. Average sediment yields were found to be higher than those of less disturbed basins nearby, and lower than those reported from the early twentieth‐century Piedmont Province. Temporal trends in sediment yield appear to reflect both meteorological and land‐use histories. Although most of the lake sediment is magnetically similar to bottomland sources, two instances of local upland sediment input, possibly related to human activities, are evident in the record. Interpreting relationships between sediment yield and changing environmental influences is impeded by poor temporal control in the methodology as well as by the intrinsic dynamics of the fluvial system.  相似文献   

12.
A Bayesian approach to inverse modelling of stratigraphy, part 1: method   总被引：2，自引：0，他引：2  
The inference of ancient environmental conditions from their preserved response in the sedimentary record still remains an outstanding issue in stratigraphy. Since the 1970s, conceptual stratigraphic models (e.g. sequence stratigraphy) based on the underlying assumption that accommodation space is the critical control on stratigraphic architecture have been widely used. Although these methods considered more recently other possible parameters such as sediment supply and transport efficiency, they still lack in taking into account the full range of possible parameters, processes, and their complex interactions that control stratigraphic architecture. In this contribution, we present a new quantitative method for the inference of key environmental parameters (specifically sediment supply and relative sea level) that control stratigraphy. The approach combines a fully non‐linear inversion scheme with a ‘process–response’ forward model of stratigraphy. We formulate the inverse problem using a Bayesian framework in order to sample the full range of possible solutions and explicitly build in prior geological knowledge. Our methodology combines Reversible Jump Markov chain Monte Carlo and Simulated Tempering algorithms which are able to deal with variable‐dimensional inverse problems and multi‐modal posterior probability distributions, respectively. The inverse scheme has been linked to a forward stratigraphic model, BARSIM (developed by Joep Storms, University of Delft), which simulates shallow‐marine wave/storm‐dominated systems over geological timescales. This link requires the construction of a likelihood function to quantify the agreement between simulated and observed data of different types (e.g. sediment age and thickness, grain size distributions). The technique has been tested and validated with synthetic data, in which all the parameters are specified to produce a ‘perfect’ simulation, although we add noise to these synthetic data for subsequent testing of the inverse modelling approach. These tests addressed convergence and computational‐overhead issues, and highlight the robustness of the inverse scheme, which is able to assess the full range of uncertainties on the inferred environmental parameters and facies distributions.  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.
We describe the tectono‐sedimentary evolution of a Middle Jurassic, rift‐related supra‐detachment basin of the ancient Alpine Tethys margin exposed in the Central Alps (SE Switzerland). Based on pre‐Alpine restoration, we demonstrate that the rift basin developed over a detachment system that is traced over more than 40 km from thinned continental crust to exhumed mantle. The detachment faults are overlain by extensional allochthons consisting of upper crustal rocks and pre‐rift sediments up to several kilometres long and several hundreds of metres thick, compartmentalizing the distal margin into sub‐basins. We mapped and restored one of these sub‐basins, the Samedan Basin. It consists of a V‐shape geometry in map view, which is confined by extensional allochthons and floored by a detachment fault. It can be restored over a minimum distance of 11 km along and about 4 km perpendicular to the basin axis. Its sedimentary infill can be subdivided into basal (initial), intermediate (widening) and top (post‐tectonic) facies tracts. These tracts document (1) formation of the basin initially bounded by high‐angle faults and developing into low‐angle detachment faults, (2) widening of the basin and (3) migration of deformation further outboard. The basal facies tract is made of locally derived, poorly sorted gravity flow deposits that show a progressive change from hangingwall to footwall‐derived lithologies. Upsection the sediments develop into turbidity current deposits that show retrogradation (intermediate facies tract) and starvation of the sedimentary system (post‐tectonic facies tract). On the scale of the distal margin, the syn‐tectonic record documents a thinning‐ and fining‐upward sequence related to the back stepping of the tectonically derived sediment source, progressive starvation of the sedimentary system and migration of deformation resulting in exhumation and progressive delamination of the thinned crust during final rifting. This study provides valuable insights into the tectono‐sedimentary evolution and stratigraphic architecture of a supra‐detachment basin formed over hyper‐extended crust.  相似文献   

15.
The volume and grain-size of sediment supplied from catchments fundamentally control basin stratigraphy. Despite their importance, few studies have constrained sediment budgets and grain-size exported into an active rift at the basin scale. Here, we used the Corinth Rift as a natural laboratory to quantify the controls on sediment export within an active rift. In the field, we measured the hydraulic geometries, surface grain-sizes of channel bars and full-weighted grain-size distributions of river sediment at the mouths of 47 catchments draining the rift (constituting 83% of the areal extent). Results show that the sediment grain-size increases westward along the southern coast of the Gulf of Corinth, with the coarse-fraction grain-sizes (84th percentile of weighted grain-size distribution) ranging from approximately 19 to 91 mm. We find that the median and coarse-fraction of the sieved grain-size distribution are primarily controlled by bedrock lithology, with late Quaternary uplift rates exerting a secondary control. Our results indicate that grain-size export is primarily controlled by the input grain-size within the catchment and subsequent abrasion during fluvial transport, both quantities that are sensitive to catchment lithology. We also demonstrate that the median and coarse-fraction of the grain-size distribution are predominantly transported in bedload; however, typical sand-grade particles are transported as suspended load at bankfull conditions, suggesting disparate source-to-sink transit timescales for sand and gravel. Finally, we derive both a full Holocene sediment budget and a grain-size-specific bedload discharged into the Gulf of Corinth using the grain-size measurements and previously published estimates of sediment fluxes and volumes. Results show that the bedload sediment budget is primarily comprised (~79%) of pebble to cobble grade (0.475–16 cm). Our results suggest that the grain-size of sediment export at the rift scale is particularly sensitive to catchment lithology and fluvial mophodynamics, which complicates our ability to make direct inferences of tectonic and palaeoenvironmental forcing from local stratigraphic characteristics.  相似文献   

16.
This article deals with the stratigraphic record of a climatic or tectonic perturbation of an experimental coupled catchment‐fan system. Following Bonnet & Crave's results (2003), which suggest that it is possible to differentiate between climatic or tectonic causes of surface uplift of an erosional topography from the record of sediment flux output, we design a new experimental device to test this proposition in the sedimentary signal. This device allows the study of a coupled erosion–sedimentation system at the laboratory scale for given and changing uplift and rainfall rates. On the basis of experimental results, we propose a methodology to study alluvial fan architecture from large‐scale geometries to stacking pattern and sequence analysis. In these experiments, the erosional perturbation resulting from climate or tectonic forcing induces a typical dynamic in terms of both sediment supply and the ratio between the sediment and water supply, which controls the transport capacity. The four possible forcings (rainfall rate and uplift rate increase or decrease, respectively) then result in unique dynamics of the combined parameters such as the fan slope, apex aggradation, mean sedimentation rate, grain size distribution, bed thickness and frequency and facies stacking. We first analyse large‐scale geometries (onlap, toplap, downlap or truncation) and then fine‐scale sedimentological features (fining, thinning, coarsening, thickening) in order to discriminate the nature of the forcing. This conceptual model could be adapted to real world alluvial fans in order to recognize and separate the driving mechanisms from each other.  相似文献   

17.
The <1.5‐km thick Fiq Member of the Ghadir Manqil Formation, Huqf Supergroup, Oman, contains a succession of Marinoan‐age glacially and non‐glacially influenced deposits overlain by a transgressive, 13C‐depleted, deep‐water dolostone (Hadash Formation) that deepens up into the marine shales and siltstones of the Masirah Bay Formation. The Fiq Member and Hadash–Masirah Bay Formations are well exposed in the core of the Jebel Akhdar of northern Oman and provide a valuable insight into the processes operating during a Neoproterozoic glacial epoch and its aftermath. The Fiq Member comprises seven stratigraphic units (F1–F7) of proximal and distal glacimarine, non‐glacial sediment gravity flow, and non‐glacial shallow marine facies associations. These units can be correlated over almost the entire Neoproterozoic outcrop belt (ca. 80 km) of the Jebel Akhdar. Four units contain glacimarine rainout diamictites, commonly at the top of cycles beneath strong lithofacies dislocations suggesting flooding. The units are thought to have been generated by combined glacio‐isostatic and glacio‐eustatic forcing caused by changing volumes of terrestrial glacier ice. The lateral persistence and thickness of massive diamictite units increase upwards in the stratigraphy, the youngest (F7) diamictite being abruptly overlain by the Hadash Formation. Correlation of lithofacies associations across the rift basin and palaeocurrents indicate that siliciclastic sediment and glacially entrained debris were derived from both basin margins. Open‐water conditions existed during interglacials, attested to by the presence of wave‐rippled sandstones in the western part of the basin. The Hadash carbonate also exhibits variations between east and west, showing that despite an overall deep‐water depositional setting, rift margin and intrabasinal structure continued to exert a control on facies development during the post‐glacial aftermath. Onlap of basin margins continued through the deposition of the Masirah Bay Formation. The sedimentology and stratigraphy of the Fiq Member and Hadash–Masirah Bay Formations have a number of implications for the Snowball Earth hypothesis. The overall stratigraphic evolution of the Fiq Member suggests a dynamic, temperate/polythermal style of glaciation, perhaps nucleated on uplifted continental or rift margin topography, with marine‐terminating glaciers. Some transgressions coupled to deglaciations within the Fiq glacial epoch were accompanied by minor deposition of carbonate. However, final deglaciation triggered the deposition of a <8‐m thick, deep‐water dolomite contaminated with siliciclastics, with a lithofacies assemblage still reflecting the underlying bathymetric template, followed by relatively deep marine shales and siltstones. The preservation of relatively deep marine Masirah Bay sediments above the Fiq basin margin suggests either tectonic collapse of the rift shoulder or, more likely, rapid eustatic rise accompanying deglaciation.  相似文献   

18.
Sedimentary basins are affected by a large number of forcing factors during their evolution and as a result, it is often difficult to isolate the contribution of each individual factor. Many forcing factors are temporally and spatially heterogeneous; they do not affect all parts of the basin in the same way and at the same time. We show that this heterogeneity can be used to identify the contributions of forcing factors by comparing various parts of a basin. This approach is applied to the Pannonian Basin, a back‐arc basin located in Central Europe. In the basin, the amounts of crustal extension, tectonic inversion and sediment influx varied in space and time, while the connection with the marine realm fluctuated. In this study we focus on two currently unresolved issues: firstly, we establish by what processes and from what directions the basin was filled in, and secondly, we investigate whether the basin was affected by the Messinian Salinity Crisis. The analysis of seismic and well data in the previously less studied SE part of the basin demonstrate that progradation occurred from the southern and eastern basin margins, complementing the previously described progradation from the northwestern and northern basin margins. Elsewhere in the basin, an unconformity observed in the progradational basin infill is intensely debated to be the result of either the Messinian Salinity Crisis (MSC) or basin inversion. Having the advantage of minor Pliocene–Quaternary amounts of inversion in the studied part of the basin we show that no regional unconformity is present in the studied stratigraphic interval, which implies that the effects of the MSC on the basin were minor. We infer that being aware of the fact that the effects of relative sea/lake‐level fluctuations may vary significantly across a basin is critical for understanding the evolution of semi‐enclosed basins.  相似文献   

19.
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   

20.
Common basin models assume that the post‐rift tectonic evolution of most basins is usually associated with tectonic quiescence. However, tectonic inversion during the post‐rift phase has been proposed for several sedimentary basins worldwide, but how and why it happens is still a matter of debate, especially in intracontinental settings where the lithosphere is old and thick. Here, we use geological and geophysical data from the Rio do Peixe Basin in NE Brazil to show evidence that intracontinental sedimentary basins can be tectonically inverted by far‐field compressive stresses acting on pre‐existing weakness zones of lithospheric‐scale where stresses can concentrate and inversion can occur. Geomorphological and field data combined with seismic reflection, gravimetric and borehole data show that: (a) inversion occurred along two main Precambrian lithospheric‐scale shear zones, the Patos (E‐W trending) and Portalegre (NE‐SW trending), which had already been reactivated as basin‐bounding faults during the earlier rift stage; (b) post‐rift reactivation affected (mostly) the original master normal faults with the largest rift displacements, and locally produced new reverse faults; (c) during contraction, deformation was partitioned between fault reactivation and buckling of the incompetent sediment pushed against the hard basement; (d) all these signs of inversion have been observed in the field and can be demonstrated on seismic reflection profiles; and (e) combined gravimetric and seismic data show that the main structures of the basin were followed by an inversion. These data are consistent with the operation of WSW‐ENE horizontal maximum compressive stress as a result of combined pushes of the Mid‐Atlantic Ridge (towards the W) and the Andes (towards the E), responsible for the post‐rift oblique inversion of normal faults inherited from the rift phase and formed with vertical maximum compressive stress.  相似文献   

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