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1.
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   

2.
Interactions between fold and thrust belt deformation, foreland flexure and surface mass transport are investigated using a newly developed mathematical model incorporating fully dynamic coupling between mechanics and surface processes. The mechanical model is two dimensional (plane strain) and includes an elasto‐visco‐plastic rheology. The evolving model is flexurally compensated using an elastic beam formulation. Erosion and deposition at the surface are treated in a simple manner using a linear diffusion equation. The model is solved with the finite element method using a Lagrangian scheme with marker particles. Because the model is particle based, it enables straightforward tracking of stratigraphy and exhumation paths and it can sustain very large strain. It is thus ideally suited to study deformation, erosion and sedimentation in fold–thrust belts and foreland basins. The model is used to investigate how fold–thrust deformation and foreland basin development is influenced by the non‐dimensional parameter , which can be interpreted as the ratio of the deformation time scale to the time scale for surface processes. Large values of imply that the rate of surface mass transport is significantly greater than the rate of deformation. When , the rates of surface processes are so slow that one observes a classic propagating fold–thrust belt with well‐developed wedge top basins and a largely underfilled foreland flexural depression. Increasing causes (1) deposition to shift progressively from the wedge top into the foredeep, which deepens and may eventually become filled, (2) widespread exhumation of the fold–thrust belt, (3) reduced rates of frontal thrust propagation and possible attainment of a steady‐state orogen width and (4) change in the style and dynamics of deformation. Together, these effects indicate that erosion and sedimentation, rather than passively responding to tectonics, play an active and dynamic role in the development of fold–thrust belts and foreland basins. Results demonstrate that regional differences in the relative rates of surface processes (e.g. because of different climatic settings) may lead to fold–thrust belts and foreland basins with markedly different characteristics. Results also imply that variations in the efficiency of surface processes through time (e.g., because of climate change or the emergence of orogens above sea level) may cause major temporal changes in orogen and basin dynamics.  相似文献   

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

4.
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   

5.
The Coastal Range in eastern Taiwan contains the remnants of the Pliocene–Pleistocene retro‐foredeep basin of the ongoing Penglai orogeny. These sedimentary successions record the earliest exhumation of the Central Range, Taiwan. We dated detrital Plio‐Pleistocene sediments in the Coastal Range using multiple thermochronometers [fission‐track, zircon (U–Th)/He and U/Pb dating] to document changes in exhumation rate through time. Fission‐track grain ages in 2–4‐Myr‐old sediments were not reset by the Penglai orogeny and reflect the early stage removal of the sedimentary cover. This early stage, when exhumation rates were low, could encompass both the accretionary wedge phase of the orogen and the early arc–continent collision. Sediments younger than 2‐Myr‐old yield Pliocene zircon fission‐track grain ages and suggest that exhumation, transport and deposition occurred within 0.4–1.5 Myr. The recorded onset of rapid exhumation in the Pliocene is contemporaneous with other major tectonic changes in the region, including an increase in subsidence rate in both the pro‐ and retro‐foredeep basins and a change in the wedge kinematics from internal shortening to underplating.  相似文献   

6.
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   

7.
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   

8.
The Molasse Basin of Switzerland evolved through a distinct late Neogene history with initial development as a classic foredeep or foreland basin in response to loading of the lithosphere by the Alpine orogen. In the central and western foreland, the foredeep behaviour was terminated by deformation and uplift of the Jura Mountains in the distal regions of the foredeep. Following the Jura deformation the Plateau Molasse remained largely undeformed as it rode ‘piggy‐back’ style above the decollement feeding displacement into the Jura. Sediment accumulation data for the Molasse suggests that sedimentation in the Plateau Molasse region continued until the basin was inverted at about 5 Ma. We present a mechanical model for this sequence of events in which deformation jumps across much of the basin to the distal Jura because of the dip on the weak evaporitic decollement and the wedge‐shape of the foredeep basin. Subsequently, the Plateau Molasse remained largely undeformed as a result of continued sedimentation in a wedgetop basin, where the physical properties and geometry of the orogenic wedge combine to produce a critical wedge whose critical surface slope would be less than zero and thus should dip towards the Alpine interior. Accommodation space is created over this negative surface–slope segment of the wedge and sedimentation maintains this slope near zero, stabilizing the wedge. We present a simple analytical theory for the necessary conditions for such a ‘negative‐alpha basin’ to develop and be maintained. We compare this theory to the late Neogene evolution of the Alps, Molasse Basin and Jura Mountains and infer physical properties for the decollement.  相似文献   

9.
Foreland basin systems   总被引：32，自引：1，他引：32  
A foreland basin system is defined as: (a) an elongate region of potential sediment accommodation that forms on continental crust between a contractional orogenic belt and the adjacent craton, mainly in response to geodynamic processes related to subduction and the resulting peripheral or retroarc fold-thrust belt; (b) it consists of four discrete depozones, referred to as the wedge-top, foredeep, forebulge and back-bulge depozones – which of these depozones a sediment particle occupies depends on its location at the time of deposition, rather than its ultimate geometric relationship with the thrust belt; (c) the longitudinal dimension of the foreland basin system is roughly equal to the length of the fold-thrust belt, and does not include sediment that spills into remnant ocean basins or continental rifts (impactogens). The wedge-top depozone is the mass of sediment that accumulates on top of the frontal part of the orogenic wedge, including ‘piggyback’ and ‘thrust top’ basins. Wedge-top sediment tapers toward the hinterland and is characterized by extreme coarseness, numerous tectonic unconformities and progressive deformation. The foredeep depozone consists of the sediment deposited between the structural front of the thrust belt and the proximal flank of the forebulge. This sediment typically thickens rapidly toward the front of the thrust belt, where it joins the distal end of the wedge-top depozone. The forebulge depozone is the broad region of potential flexural uplift between the foredeep and the back-bulge depozones. The back-bulge depozone is the mass of sediment that accumulates in the shallow but broad zone of potential flexural subsidence cratonward of the forebulge. This more inclusive definition of a foreland basin system is more realistic than the popular conception of a foreland basin, which generally ignores large masses of sediment derived from the thrust belt that accumulate on top of the orogenic wedge and cratonward of the forebulge. The generally accepted definition of a foreland basin attributes sediment accommodation solely to flexural subsidence driven by the topographic load of the thrust belt and sediment loads in the foreland basin. Equally or more important in some foreland basin systems are the effects of subduction loads (in peripheral systems) and far-field subsidence in response to viscous coupling between subducted slabs and mantle–wedge material beneath the outboard part of the overlying continent (in retroarc systems). Wedge-top depozones accumulate under the competing influences of uplift due to forward propagation of the orogenic wedge and regional flexural subsidence under the load of the orogenic wedge and/or subsurface loads. Whereas most of the sediment accommodation in the foredeep depozone is a result of flexural subsidence due to topographic, sediment and subduction loads, many back-bulge depozones contain an order of magnitude thicker sediment fill than is predicted from flexure of reasonably rigid continental lithosphere. Sediment accommodation in back-bulge depozones may result mainly from aggradation up to an equilibrium drainage profile (in subaerial systems) or base level (in flooded systems). Forebulge depozones are commonly sites of unconformity development, condensation and stratal thinning, local fault-controlled depocentres, and, in marine systems, carbonate platform growth. Inclusion of the wedge-top depozone in the definition of a foreland basin system requires that stratigraphic models be geometrically parameterized as doubly tapered prisms in transverse cross-sections, rather than the typical ‘doorstop’ wedge shape that is used in most models. For the same reason, sequence stratigraphic models of foreland basin systems need to admit the possible development of type I unconformities on the proximal side of the system. The oft-ignored forebulge and back-bulge depozones contain abundant information about tectonic processes that occur on the scales of orogenic belt and subduction system.  相似文献   

10.
Abstract Low‐angle detachment faults and thrust‐sheet top basins are common features in foreland basins. However, in stratigraphic analysis their influence on sequence architecture is commonly neglected. Usually, only eustatic sea level and changing flexural subsidence are accounted for, and when deformation is considered, the emphasis is on the generation of local thrust‐flank unconformities. This study analyses the effects of detachment angle and repetitive detachment activation on stratigraphic stacking patterns in a large thrust‐sheet top basin by applying a three‐dimensional numerical model. Model experiments show that displacement over low‐angle faults (2–6°) at moderate rates (～5.0 m kyr?1) results in a vertical uplift component sufficient to counteract the background flexural subsidence rate. Consequently, the basin‐wide accommodation space is reduced, fluvio‐deltaic systems carried by the thrust‐sheet prograde and part of the sediment supply is spilled over towards adjacent basins. The intensity of the forced regression and the interconnectedness of fluvial sheet sandstones increases with the dip angle of the detachment fault or rate of displacement. In addition, the delta plain is susceptible to the formation of incised valleys during eustatic falls because these events are less compensated by regional flexural subsidence, than they would be in the absence of fault displacement.  相似文献   

11.
The Patagonian Magallanes retroarc foreland basin affords an excellent case study of sediment burial recycling within a thrust belt setting. We report combined detrital zircon U–Pb geochronology and (U–Th)/He thermochronology data and thermal modelling results that confirm delivery of both rapidly cooled, first‐cycle volcanogenic sediments from the Patagonian magmatic arc and recycled sediment from deeply buried and exhumed Cretaceous foredeep strata to the Cenozoic depocentre of the Patagonian Magallanes basin. We have quantified the magnitude of Eocene heating with thermal models that simultaneously forward model detrital zircon (U–Th)/He dates for best‐fit thermal histories. Our results indicate that 54–45 Ma burial of the Maastrichtian Dorotea Formation produced 164–180 °C conditions and heating to within the zircon He partial retention zone. Such deep burial is unusual for Andean foreland basins and may have resulted from combined effects of high basal heat flow and high sediment accumulation within a rapidly subsiding foredeep that was floored by basement weakened by previous Late Jurassic rifting. In this interpretation, Cenozoic thrust‐related deformation deeply eroded the Dorotea Formation from ca. 5 km burial depths and may be responsible for the development of a basin‐wide Palaeogene unconformity. Results from the Cenozoic Río Turbio and Santa Cruz formations confirm that they contain both Cenozoic first‐cycle zircon from the Patagonian magmatic arc and highly outgassed zircon recycled from older basin strata that experienced burial histories similar to those of the Dorotea Formation.  相似文献   

12.
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13.
An integrated provenance analysis of the Upper Cretaceous Magallanes retroarc foreland basin of southern Chile (50°30′–52°S) provides new constraints on source area evolution, regional patterns of sediment dispersal and depositional age. Over 450 new single‐grain detrital‐zircon U‐Pb ages, which are integrated with sandstone petrographic and mudstone geochemical data, provide a comprehensive detrital record of the northern Magallanes foreland basin‐filling succession (>4000‐m‐thick). Prominent peaks in detrital‐zircon age distribution among the Punta Barrosa, Cerro Toro, Tres Pasos and Dorotea Formations indicate that the incorporation and exhumation of Upper Jurassic igneous rocks (ca. 147–155 Ma) into the Andean fold‐thrust belt was established in the Santonian (ca. 85 Ma) and was a significant source of detritus to the basin by the Maastrichtian (ca. 70 Ma). Sandstone compositional trends indicate an increase in volcanic and volcaniclastic grains upward through the basin fill corroborating the interpretation of an unroofing sequence. Detrital‐zircon ages indicate that the Magallanes foredeep received young arc‐derived detritus throughout its ca. 20 m.y. filling history, constraining the timing of basin‐filling phases previously based only on biostratigraphy. Additionally, spatial patterns of detrital‐zircon ages in the Tres Pasos and Dorotea Formations support interpretations that they are genetically linked depositional systems, thus demonstrating the utility of provenance indicators for evaluating stratigraphic relationships of diachronous lithostratigraphic units. This integrated provenance dataset highlights how the sedimentary fill of the Magallanes basin is unique among other retroarc foreland basins and from the well‐studied Andean foreland basins farther north, which is attributed to nature of the predecessor rift and backarc basin.  相似文献   

14.
In order to evaluate the relationship between thrust loading and sedimentary facies evolution, we analyse the progradation of fluvial coarse‐grained deposits in the retroarc foreland basin system of the northern Andes of Colombia. We compare the observed sedimentary facies distribution with the calculated one‐dimensional (1D) Eocene to Quaternary sediment‐accumulation rates in the Medina wedge‐top basin and with a three‐dimensional (3D) sedimentary budget based on the interpretation of ～1800 km of industry‐style seismic reflection profiles and borehole data. Age constraints are derived from a new chronostratigraphic framework based on extensive fossil palynological assemblages. The sedimentological data from the Medina Basin reveal rapid accumulation of fluvial and lacustrine sediments at rates of up to ～500 m my?1 during the Miocene. Provenance data based on gravel petrography and paleocurrents reveal that these Miocene fluvial systems were sourced from Upper Cretaceous and Paleocene sedimentary units exposed to the west in the Eastern Cordillera. Peak sediment‐accumulation rates in the upper Carbonera Formation and the Guayabo Group occur during episodes of coarse‐grained facies progradation in the early and late Miocene proximal foredeep. We interpret this positive correlation between sediment accumulation and gravel deposition as the direct consequence of thrust activity along the Servitá–Lengupá faults. This contrasts with one class of models relating gravel progradation in more distal portions of foreland basin systems to episodes of tectonic quiescence.  相似文献   

15.
We present field and seismic evidence for the existence of Coniacian–Campanian syntectonic angular unconformities within basal foreland basin sequences of the Austral or Magallanes Basin, with implications for the understanding of deformation and sedimentation in the southern Patagonian Andes. The studied sequences belong to the mainly turbiditic Upper Cretaceous Cerro Toro Formation that includes a world‐class example of conglomerate‐filled deep‐water channel bodies deposited in an axial foredeep depocentre. We present multiple evidence of syntectonic deposition showing that the present internal domain of the fold‐thrust belt was an active Coniacian–Campanian wedge‐top depozone where deposition of turbidites and conglomerate channels of Cerro Toro took place. Cretaceous synsedimentary deformation was dominated by positive inversion of Jurassic extensional structures that produced elongated axial submarine trenches separated by structural highs controlling the development and distribution of axial channels. The position of Coniacian‐Campanian unconformities indicates a ca. 50–80 km advance of the orogenic front throughout the internal domain, implying that Late Cretaceous deformation was more significant in terms of widening the orogenic wedge than all subsequent Andean deformation stages. This south Patagonian orogenic event can be related to compressional stresses generated by the combination of both the collision of the western margin of Rocas Verdes Basin during its closure, and Atlantic ridge push forces due to its accelerated opening, during a global‐scale plate reorganization event.  相似文献   

16.
The Andean Orogen is the type‐example of an active Cordilleran style margin with a long‐lived retroarc fold‐and‐thrust belt and foreland basin. Timing of initial shortening and foreland basin development in Argentina is diachronous along‐strike, with ages varying by 20–30 Myr. The Neuquén Basin (32°S to 40°S) contains a thick sedimentary sequence ranging in age from late Triassic to Cenozoic, which preserves a record of rift, back arc and foreland basin environments. As much of the primary evidence for initial uplift has been overprinted or covered by younger shortening and volcanic activity, basin strata provide the most complete record of early mountain building. Detailed sedimentology and new maximum depositional ages obtained from detrital zircon U–Pb analyses from the Malargüe fold‐and‐thrust belt (35°S) record a facies change between the marine evaporites of the Huitrín Formation (ca. 122 Ma) and the fluvial sandstones and conglomerates of the Diamante Formation (ca. 95 Ma). A 25–30 Myr unconformity between the Huitrín and Diamante formations represents the transition from post‐rift thermal subsidence to forebulge erosion during initial flexural loading related to crustal shortening and uplift along the magmatic arc to the west by at least 97 ± 2 Ma. This change in basin style is not marked by any significant difference in provenance and detrital zircon signature. A distinct change in detrital zircons, sandstone composition and palaeocurrent direction from west‐directed to east‐directed occurs instead in the middle Diamante Formation and may reflect the Late Cretaceous transition from forebulge derived sediment in the distal foredeep to proximal foredeep material derived from the thrust belt to the west. This change in palaeoflow represents the migration of the forebulge, and therefore, of the foreland basin system between 80 and 90 Ma in the Malargüe area.  相似文献   

17.
Sedimentary bodies emplaced by mass‐wasting processes and exceeding tens of metres of thickness and a hundred of square kilometres in area are widespread in the Cretaceous–Pleistocene marine successions of the Northern Apennines of Italy. At least 10 such bodies are present in the stratigraphic record of the Oligo‐Miocene foredeep during the northeastern, time‐transgressive migration of the accretionary wedge‐foredeep system. The term mass‐wasting complex (MWC) is here adopted for these bodies to emphasize their multistory emplacement mechanism and polymictic composition with variously deformed slabs of different lithology, age and provenance. As one of the more intriguing features, their occurrence was associated with changes in turbidite deposition from basin plain to slope. Wide sectors of the internal margin of the basin (lobe‐fan) and even of the basin plain become a slope at the front of the accretionary wedge for a limited period of time (temporary slope). The temporary slope supplied the intrabasinal components of the MWCs, whereas the diffused extrabasinal components came from the front of the accretionary wedge. Therefore, an enhanced instability of the entire foredeep‐wedge system occurred systematically and cyclically. As a consequence, many variously consolidated sediments were transferred into the foredeep basin invading the depocentre and forcing the turbidite deposition towards the foreland, in a more northeasterly position. The presence of such MWCs therefore conditioned basin size and geometry in an analogous way as that reported for some modern convergent margins, as in the case of Costa Rica. Normal sedimentation was restored on top of the MWC only after the levelling of topographic irregularities.  相似文献   

18.
The Northern Apennines provide an example of long‐term deep‐water sedimentation in an underfilled pro‐foreland basin first linked to an advancing orogenic wedge and then to a retreating subduction zone during slab rollback. New palaeobathymetric and geohistory analyses of turbidite systems that accumulated in the foredeep during the Oligocene‐Miocene are used to unravel the basin subsidence history during this geodynamic change, and to investigate how it interplayed with sediment supply and basin tectonics in controlling foredeep filling. The results show an estimated ca. 2 km decrease in palaeowater depth at ca. 17 Ma. Moreover, a change in basin subsidence is documented during Langhian time, with an average decompacted subsidence rate, during individual depocentre life, that increased from <0.3 to 0.4–0.6 mm y?1, together with the appearance of a syndepositional backstripped subsidence bracketed between 0.1 and 0.2 mm y?1. This change prevented the basin from complete filling during late Miocene and is interpreted as the foredeep response to initial rollback of the downgoing Adriatic slab. Thus, the Northern Apennine system provides an example of a pro‐foreland basin that experienced both a slow‐ and high‐subsidence regime as a consequence of the advancing then retreating evolution of the collisional system.  相似文献   

19.
《Basin Research》2018,30(3):426-447
Integration of detrital zircon geochronology and three‐dimensional (3D) seismic‐reflection data from the Molasse basin of Austria yields new insight into Oligocene‐early Miocene palaeogeography and patterns of sediment routing within the Alpine foreland of central Europe. Three‐dimensional seismic‐reflection data show a network of deep‐water tributaries and a long‐lived (>8 Ma) foredeep‐axial channel belt that transported Alpine detritus greater than 100 km from west to east. We present 793 new detrital zircon ages from 10 sandstone samples collected from subsurface cores located within the seismically mapped network of deep‐water tributaries and the axial channel belt. Grain age populations correspond with major pre‐Alpine orogenic cycles: the Cadomian (750–530 Ma), the Caledonian (490–380 Ma) and the Variscan (350–250 Ma). Additional age populations correspond with Eocene‐Oligocene Periadriatic magmatism (40–30 Ma) and pre‐Alpine, Precambrian sources (>750 Ma). Although many samples share the same age populations, the abundances of these populations vary significantly. Sediment that entered the deep‐water axial channel belt from the west (Freshwater Molasse) and southwest (Inntal fault zone) is characterized by statistically indistinguishable age distributions that include populations of Variscan, Caledonian and Cadomian zircon at modest abundances (15–32% each). Sandstone from a shallow marine unit proximal to the northern basin margin consists of >75% Variscan (350–300 Ma) zircon, which originated from the adjacent Bohemian Massif. Mixing calculations based on the Kolmogorov–Smirnoff statistic suggest that the Alpine fold‐thrust belt south of the foreland was also an important source of detritus to the deep‐water Molasse basin. We interpret evolving detrital zircon age distributions within the axial foredeep to reflect a progressive increase in longitudinal sediment input from the west (Freshwater Molasse) and/or southwest (Inntal fault zone) relative to transverse sediment input from the fold‐thrust belt to the south. We infer that these changes reflect a major reorganization of catchment boundaries and denudation rates in the Alpine Orogen that resulted in the Alpine foreland evolving to dominantly longitudinal sediment dispersal. This change was most notably marked by the development of a submarine canyon during deposition of the Upper Puchkirchen Formation that promoted sediment bypass eastward from Freshwater Molasse depozones to the Molasse basin deep‐water axial channel belt. The integration of 3D seismic‐reflection data with detrital zircon geochronology illustrates sediment dispersal patterns within a continental‐scale orogen, with implications for the relative role of longitudinal vs. transverse sediment delivery in peripheral foreland basins.  相似文献   

20.
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   

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