Foreland Basin Research Papers - Academia.edu (original) (raw)

s u m m a r y Arsenic (As) is a trace element in the Earth's crust. However, its presence in elevated concentrations in groundwaters of major aquifers around the world raises concern about its primary source(s). A close look at the global... more

s u m m a r y Arsenic (As) is a trace element in the Earth's crust. However, its presence in elevated concentrations in groundwaters of major aquifers around the world raises concern about its primary source(s). A close look at the global distribution of known As enriched areas reveals an intriguing systematic pattern, where most of the As enriched aquifers are parts of large sedimentary basins adjoining major orogenic belts, suggesting the existence of a large-scale geological process. Many of these sedimentary basins may be tectonically regarded as foreland basins that developed by lithospheric flexure at the time of mountain building processes (orogenesis) along convergent plate boundaries. Arsenic enrichment in the groundwater of these foreland basin aquifers may be ultimately sourced to crustal evolution processes related to plate tectonics, along with transportation of As-enriched magmatic rocks from the depth to surficial deposits, which subsequently release or mobilize the As to groundwater under conducive surficial biogeochemical processes. Circulating As-laden hydrothermal fluids may also be derived from magmas and form part of the discharge in the surficial hot springs in arc environments. These hydrothermal-genic deposits in orogenic belts may also act as the primary provenance for the As-laden sediments that are transported into foreland basins by wind, glacial erosion, and/or streams. Ultimately, the As-laden foreland sediments serve as modern-day aquifers, where the sediments release As into groundwater by water-rock interaction during various biogeochemical processes under conducive hydrogeochemical conditions. The significance of this hypothesis is that it proposes the existence of a common primary source for globally dispersed geogenic As-enriched aquifers, that have been so far mostly studied as individual occurrences. The proposed hypothesis can explain the widespread presence of As in areas as diverse as the Indus-Ganges-Brahmaputra basin (Himalayan orogen), the Chaco-Pampean basin (Andean orogen), Rocky mountain basin (Western Cordilleran orogen), New England and northeastern USA (the Applachian orogen).

The lithofacies constitution of unconsolidated sediments exposed in Ramnagar cliff indicates sedimentation in sinuous channels, associated flood plain areas and ponds that were developed within the Ganga River valley. The Khadar surface... more

The lithofacies constitution of unconsolidated sediments exposed in Ramnagar cliff indicates sedimentation in sinuous channels, associated flood plain areas and ponds that were developed within the Ganga River valley. The Khadar surface represents a raised river valley terrace into which the main river channel along with its narrow floodplain is incised. Ramnagar cliff section has revealed a variety of deformation structures that indicate repeated tectonic activity in the area. Important tectonic features exposed by the cliff section are reverse faults, folds, cracks filled with sparry calcite and soft sediment structures indicating liquefaction of sediments affected by faulting and folding. Optically stimulated luminescence (OSL) dating of sediments and field relationships of tectonic elements indicate that the Ganga River migrated near to Varanasi 40 ka following a tectonic event in the area. Since then, it meandered freely within its valley until 7 ka when another tectonic event took place and Ramnagar cliff was raised to its present heights. The cliff surface was degraded by gulling activity for about 4000 years before it was occupied by man at around 3000 years BP.

Passive margins have existed somewhere on Earth almost continually since 2740 Ma. They were abundant at 1900–1890, 610–520, and 150–0 Ma, scarce at ca. 2445–2300, 1600–1000, and 300–275 Ma, and absent before ca. 3000 Ma and at 1740–1600.... more

Passive margins have existed somewhere on Earth almost continually since 2740 Ma. They were abundant at 1900–1890, 610–520, and 150–0 Ma, scarce at ca. 2445–2300, 1600–1000, and 300–275 Ma, and absent before ca. 3000 Ma and at 1740–1600. The fluctuations in abundance of passive margins track the first-order fluctuations of the independently derived seawater 87Sr/86Sr secular curve, and the compilation thus appears to be robust. The 76 ancient passive margins for which lifespans could be measured have a mean lifespan of 181 m.y. The world-record holder, with a lifespan of 590 m.y., is the Mesoproterozoic eastern margin of the Siberian craton. Subdivided into natural age groups, mean lifespans are 186 m.y. for the Archean to Paleoproterozoic, 394 m.y. for the Mesoproterozoic, 180 m.y. for the Neoproterozoic, 137 m.y. for the Cambrian to Carboniferous, and 130 m.y. for the Permian to Neogene. The present-day passive margins, which are not yet finished with their lifespans, have a mean age of 104 m.y. and a maximum age of 180 m.y. On average, Precambrian margins thus had longer, not shorter, lifespans than Phanerozoic ones—and this remains the case even discounting all post-300 Ma margins, most of which have time left. Longer lifespans deeper in the past is at odds with the widely held notion that the tempo of plate tectonics was faster in the Precambrian than at present. It is entirely consistent, however, with recent modeling by Korenaga [Korenaga, J., 2004. Archean geodynamics and thermal evolution of Earth. Archean Geodynamics and Environments, AGU Geophysical Monograph Series 164, 7–32], which showed that plate tectonics was more sluggish in the Precambrian. The abundance of passive margins clearly tracks the assembly, tenure, and breakup of Pangea. Earlier parts of the hypothesized supercontinent cycle, however, are only partly consistent with the documented abundance of passive margins. The passive-margin record is not obviously consistent with the proposed breakup of Nuna (Columbia), the assembly of Rodinia, or the assembly or breakup of the putative Pannotia. An alternative model is put forth involving (a) formation of two or more supercratons during the late Paleoproterozoic, (b) a Mesoproterozoic interval dominated by lateral accretion of arcs rather than by continental breakup and dispersal, (c) wholesale collision to form Rodinia by the end of the Mesoproterozoic, and (d) staged breakup of Rodinia through much of the Neoproterozoic.

The Tibetan Plateau and the Himalayan region formed after 55–50 Ma, as a result of the intracontinental collision of the Indian and Eurasian plates, occupying the east–west trending, high-altitude Himalaya and Karakorum ranges in the... more

The Tibetan Plateau and the Himalayan region formed after 55–50 Ma, as a result of the intracontinental collision of the Indian and Eurasian plates, occupying the east–west trending, high-altitude Himalaya and Karakorum ranges in the south and the vast Tibetan Plateau to the north of central Asia. The tectonic evolution of Tibet began between the late Palaeozoic and the Cenozoic, and the Himalayan mountain system evolved in a series of stages beginning 50–35 Ma and is still active. Active tectonics significantly affect upheaval and the rate of erosion in the Himalaya. Therefore, different foreland basins of the Tibetan Plateau (e.g. the Lhasa terrane, the Hoh Xil Basin, the Qaidam Basin, and the Jiuquan Basin) and the Himalayan foreland basins (e.g. Gondwanaland Basin and the Siwalik and Quaternary basin) experience direct effects in terms of tectonic and sedimentary evolution. For the tectonic evolution and provenance analysis of foreland basins in the Tibetan Plateau and the Nepal Himalaya, researchers have adopted various techniques in past studies: This paper discusses petrography, U–Pb geochronology, and seismic reflection. Provenance analyses have illustrated that the sediments of the Southern Tibetan foreland basin (i.e. the Lhasa terrane) derive from the Qiangtang, Tethys Himalaya, and southwest Australia. Similarly, the sediments of the Central Tibetan basin derive from the Qilian, Kunlun-Qimantagh, and the Altyn Mountains; the sediments of northern side of the Tibetan foreland basin, from Qilian Shan Mountain; and the sediments of the Nepal Himalayan foreland basin, from the Tethys, Higher, and Lesser Himalaya.

The oblique Segre ramp zone between the eastern and central Pyrenees constitutes one of the major unsolved problems in the southern Pyrenees. Its geometry and evolution not only solve the eastern boundary of the South Central Unit but is... more

The oblique Segre ramp zone between the eastern and central Pyrenees constitutes one of the major unsolved problems in the southern Pyrenees. Its geometry and evolution not only solve the eastern boundary of the South Central Unit but is also an advanced step for the recognition of the whole evolution of the southern Pyrenees.
A network of 15 perpendicular seismically supported cross-sections is presented in this work. Some of these are balanced and restored, allowing shortening calculations. Cross-cutting relationships between structures and syntectonic sediments in addition to internal geometries of these sediments were extensively studied to constrain the timing of thrusting.
The final versions of these 15 cross-sections are the result of a double loop of testing based on: a) the comparison of thrust geometries, rotation, amount of shortening and ages of thrusting between different cross-sections, and b) the fit between restored cross-sections and maps (palinspastic maps). The resultant structure is geometrically homogeneous and geologically consistent. The agreement between restored cross- sections and maps results in a 3D restoration.
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The network of cross-sections shows the varying structure of the southern Pyrenean cover thrust sheets along the strike for ~150 km from the easternmost cross-section J-1 to the westernmost cross-section J-13. The evolution, shortening and rates of shortening for the southern Pyrenean thrust sheets can be briefly summarised as follows:
The positive inversion of the Mesozoic extensional basins and further southward motion restrained the irregular geometry of the upper and older Pyrenean thrust sheets (Pedraforca and South Pyrenean Unit) and also their limits (Segre thrust). The Vallfogona thrust branched eastwards with the Segre thrust (South Central unit) carrying the previously emplaced and blocked Pedraforca thrust sheets on its hanging wall, after 47 Ma. The eastern margin of the South Central Unit (Segre thrust zone) was emergent to the synorogenic surface and exposed to erosion throughout its evolution. The western margin was blind and accretionary during Middle-Upper Eocene. These two contrasting geometries were controlled by the original disposition of the Keuper décollement level.
Cross-section J-3 shows the most complete geological record for calculating shortening and timing. The total amount of shortening is ~70 km for the cover thrust sheets. Shortening including all south-directed structures south of the North Pyrenean Fault is 88.5 km.
During the uppermost Cretaceous-Paleocene time (83-55 Ma), the rates of shortening were extremely low (<0.5 mm/a). From Early Ilerdian (55 Ma) to Middle Lutetian (47 Ma) the rates of shortening increased until 4.4 mm/a, mainly during the second half of this period. The lower rates of shortening (1.3-2.6 mm/a) characterised the period ranging from Middle Lutetian (47 Ma) to Early Miocene. The end of thrusting migrated from 34.4 Ma (J-1 section) in the east to 23 Ma (Riglos section) and younger to the west. The end of thrusting propagated at a rate of 11 mm/a in the eastern Pyrenees (34.4-29 Ma) and 21 mm/a in the central Pyrenees (29-23 Ma and younger).

The Kaskapau Formation spans Late Cenomanian to Middle Turonian time and was deposited on a low-gradient, shallow, storm-dominated muddy ramp. Dense well log control, coupled with exposure on both proximal and distal margins of the basin... more

The Kaskapau Formation spans Late Cenomanian to Middle Turonian time and was deposited on a low-gradient, shallow, storm-dominated muddy ramp. Dense well log control, coupled with exposure on both proximal and distal margins of the basin allows mapping of sedimentary facies over about 35 000 km 2 . The studied portion of the Kaskapau Formation is a mudstonedominated wedge that thins from 700 m in the proximal foredeep to 50 m near the forebulge about 300 km distant. Regional flooding surfaces permit mapping of 28 allomembers, each of which represent an average of ca 125 kyr. More than 200 km from shore, calcareous silty claystone predominates, whereas 100 to 200 km offshore, mudstone and siltstone predominate. From about 30 to 100 km offshore, centimetre-bedded very fine sandstone and mudstone record along-shelf (SSE)-directed storm-generated geostrophic flows. Five to thirty kilometres from shore, decimetre-bedded hummocky cross-stratified fine sandstone and mudstone record strongly oscillatory, wave-dominated flows whereas some gutter casts indicate shore-oblique, apparently mostly unidirectional geostrophic flows. Nearshore facies are dominated by swaley cross-stratified or intensely bioturbated clean fine sandstone, interpreted as recording, respectively, areas strongly and weakly affected by discharge from distributary mouths. Shoreface sandstones grade locally into river-mouth conglomerates and sandstones, including conglomerate channel-fills up to 15 m thick. Locally, brackish lagoonal shelly mudstones are present on the extreme western margin of the basin. There is no evidence for clinoform stratification, which indicates that the Kaskapau sea floor had extremely low relief, lacked a shelf-slope break, and was probably nowhere more than a few tens of metres deep. The absence of clinoforms probably indicates a long-term balance between rates of accommodation and sediment supply. Mud is interpreted to have been transported >250 km offshore in a sea-bed nepheloid layer, repeatedly re-suspended by storms. Fine-grained sediment accumulated up to a 'mud accommodation envelope', perhaps only 20 to 40 m deep. Continuous re-working of the sea floor by storms ensured that excess sediment was redistributed away from areas that had filled to the 'accommodation envelope', being deposited in areas of higher accommodation further down the transport path. The facies distributions and stratal geometry of the Kaskapau shelf strongly suggest that sedimentary facies, especially grain-size, were related to distance from shore, not to water depth. As a result, the '100 to 1 Present address: Imperial Oil Resources, 201 >300 m' depth interpreted from calcareous claystone facies for the more central parts of the Interior Seaway, might be a significant overestimate.

The geomorphic, tectonic and seismic aspects of the Ganga plain have been studied by several workers in the recent decades. However, the northern part of this tectonically active plain has been the prime focus in most of the studies. The... more

The geomorphic, tectonic and seismic aspects of the Ganga plain have been studied by several workers in the recent decades. However, the northern part of this tectonically active plain has been the prime focus in most of the studies. The region to the south of the Ganga River requires necessary attention, especially, regarding the seismic activities. The region lying immediately south of the Outer Himalayas (i.e. the Ganga plain) responds to the stress regime of the Himalayan Frontal Thrust Zone by movement along the existing basement faults (extending from the Indian Peninsula) and creating new surface faults within the sediment cover as well. As a result, several earthquakes have been recorded along these basement faults, such as the great earthquakes of 1934 and 1988 associated with the East Patna Fault. Large zones of ground failure and liquefaction in north Bihar (close to the Himalayan front), have been recorded associated with these earthquakes. The present study reports the soft sediment deformation structures from the south Bihar associated with the prehistoric earthquakes near the East Patna Fault for the first time. The seismites have been observed in the riverine sand bed of the Dardha River close to the East Patna Fault. Several types of liquefaction-induced deformation structures such as pillar and pocket structure, thixotropic wedge, liquefaction cusps and other water escape structures have been identified. The location of the observed seismites within the deformed zone of the East Patna Fault clearly indicates their formation due to activities along this fault. However, the distance of the liquefaction site from the recorded epicenters suggests its dissociation with the recorded earthquakes so far and hence possibly relates to any prehistoric seismic event. The occurrence of the earthquakes of a magnitude capable of forming liquefaction structure in the southern Ganga plain indicates the transfer of stress regime far from the Himalayan front into the peninsular region through these basement faults. Northward extension of the East Patna Fault coincides with the region of the Himalayan front, which corresponds to a less slip potential. Therefore, an association of frequent earthquakes in this region indicates strain release along the East Patna Fault.

The architecture of foreland basins and the resulting distribution of clastic sediments are related to the constant interplay between tectonics and sedimentation. Specifically, basin floor modifications strongly influence dimensions,... more

The architecture of foreland basins and the resulting distribution of clastic sediments are related to the constant interplay between tectonics and sedimentation. Specifically, basin floor modifications strongly influence dimensions, continuity and connections of sand-size and fine-grained deposits. Given the increasing need to identify deep potential reservoir deposits, the large-scale definition of clastic porous targets and their seals is a matter of interest for oil and gas industry. Here, we present the reconstruction of the Po Plain and Northern Adriatic Foreland Basin (with an extent of ca. 40,000 km2) and its Pliocene- Pleistocene evolution, as an example of a sedimentary clastic system controlled by strongly non-cylindrical foreland geometry. The study is based on the basin-scale mapping of six unconformity-bounded sequences, performed by interpreting a dense network of seismic lines and correlating well-log data. This provides a three-dimensional model of the step-by-step evolution of the basin and description of the sediment dispersal pattern. We found that the basin records the change from a continuous (cylindrical) to highly fragmented (non- cylindrical) foredeep geometry during Late Pliocene. In the Northern Apennines case the main factors driving the development of a non-cylindrical geometry are mainly related to inherited inhomogeneity in the downgoing block linked to its Mesozoic extensional faulting, and the relative orientation of these lineaments with respect to the direction of orogen migration. During the late Pliocene-Pleistocene the two directions progressively became close to parallel, and the Northern Apennines system reacted changing from a cylindrical to a non-cylindrical state.

The Kaskapau and Cardium Formations span Late Cenomanian to Early Coniacian time and were deposited on a low-gradient foredeep ramp. The studied portion of the Kaskapau Formation spans ca 3AE5 Myr and forms a mudstone-dominated wedge... more

The Kaskapau and Cardium Formations span Late Cenomanian to Early Coniacian time and were deposited on a low-gradient foredeep ramp. The studied portion of the Kaskapau Formation spans ca 3AE5 Myr and forms a mudstone-dominated wedge thinning from 700 to <50 m from SW to NE over ca 300 km. In contrast, the Cardium Formation spans about 2AE1 Myr, is about 100 m thick, sandstone-rich and broadly tabular. The Kaskapau and Cardium Formations are divided, respectively, into 28 and nine allomembers, each bounded by marine flooding surfaces. Kaskapau allomembers 1 to 7 show about 200 km of offlap from the forebulge, accompanied by progradation of thin sandstones from the eroded forebulge crest. In contrast, Kaskapau allomembers 8 to 28 and Cardium allomembers C1 to C9 show overall onlap onto the forebulge of about 350 km, and contain no forebulge-derived sandstones. This broad pattern is interpreted as recording a latest Cenomanian pulse of tectonic loading which led to shoreline back-step in the proximal foredeep and coeval uplift of the forebulge, leading to erosion. The advance of the sediment wedge after Kaskapau allomember 7 is attributed primarily to the isostatic effect of a distributed sediment load; the advance of the orogenic wedge had a subordinate effect on subsidence of the forebulge. For Kaskapau allomembers 1 to 6, isopachs trend north to south, suggesting a load directly to the west; allomembers 7 to 28 show an abrupt rotation of isopachs to NW-SE, suggesting that the load shifted several hundred kilometres to the south. This re-orientation might be related to a change from an approximately orthogonal to a dextral transpressive stress regime.

C. R. Acad. Sci. Paris, Sciences de la Terre et des planètes / Earth and Planetary Sciences 332 (2001) 37-44  2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS. Tous droits réservés S1251-8050(00)01487-7/FLA... more

C. R. Acad. Sci. Paris, Sciences de la Terre et des planètes / Earth and Planetary Sciences 332 (2001) 37-44  2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS. Tous droits réservés S1251-8050(00)01487-7/FLA Abstract -North-Pyrenean foreland basin evolution during Palaeogene times (Adour basin) : stratigraphic constraints. The study of 50 wells correlated according to the principles of High Resolution Sequence Stratigraphy, shows that the Adour basin is filled during two main steps. (1) The Palaeocene is characterised by aggradational carbonate platforms, passing southward to turbiditic sedimentation. During this initiation stage, the carbonate production balances accommodation space creation. The Ypresian-Priabonian is characterised by large progradational deltaic systems, migrating westward. During this stage, siliciclastic supply was higher than accommodation space creation. This basin is interpreted during Palaeocene to Middle Eocene as a compressional basin due to lithospheric buckling. The foreland history starts during the Upper Eocene to Oligocene.  2001 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS

The 14 km wide Valdorria outcrop (Pennsylvanian, Northern Spain) is one of the few examples of entirely exposed flat-topped and high relief carbonate platforms reported in the fossil rock record. Laterally and vertically traceable stratal... more

The 14 km wide Valdorria outcrop (Pennsylvanian, Northern Spain) is one of the few examples of entirely exposed flat-topped and high relief carbonate platforms reported in the fossil rock record. Laterally and vertically traceable stratal patterns expose three phases of growth. Phase I is a 430 m thick platform to slope succession that prograded over 6 km, and is dated as Early Bashkirian (Akavasian–Askynbashian). Phase II aggraded and prograded, exhibiting 180 m thickness of cyclical platform top deposits, dated as Late Bashkirian (Asatauian). Phase III is a mound-shape structure that developed over the platform top of Phase II as a new phase of platform nucleation. It is 535 m thick and 2 km wide, and dated as Late Bashkirian (Asatauian–Transition interval). The observed changes of growth styles during platform evolution, from a prograding to an aggrading–prograding system, and a rapid aggradational phase, are inferred to be controlled by flexural subsidence in the active Cantabrian foreland basin, at the Variscan orogenic front. The metre-scale shallowing-upward cycles of the platform top are most probably due to glacioeustasy, as evidenced by well-recorded subaerial exposure surfaces superimposed on subtidal deposits, and by a stratal pattern recurrent in a short interval of about 160 Kyr. Observations of outcropping Bashkirian cyclothems in an isolated carbonate system, devoid of siliciclastic input, are relevant for a better understanding of the impact of high-frequency sea-level fluctuations on the carbonate factory. Moreover, progradation of the platform margin during Phase I reaches a rate of 2500 m/Myr, and 1810 m/Myr during Phase II; rates that are high when compared to other Pennsylvanian examples. The aggradation rate of 447 m/Myr calculated for Late Bashkirian–Transition interval (Phases I and II; uncorrected for compaction, missing beats and erosion) is uncommonly high in comparison to coeval Pennsylvanian examples. The platform exhibits a self-nourishing prograding microbial boundstone-dominated slope. Thus, the slope shedding model applies well to Valdorria. However, Phase II recorded eustatic variations able to inhibit the slope microbial boundstone factory during low sea-level stands; this is marked by common slope red-stained breccias synchronous to platform top subaerial exposure phases. Contrarily, periods of relative high sea-level and rapid subsidence in Phase III registered a greater development of cemented microbial boundstone. These observed, partly opposing relationships of sea-level stands, shedding modes and slope architecture provide an improvement of the currently used slope shedding model. The overall architecture of the Valdorria outcrop compares well with that of other contemporaneous platforms, such as Sierra del Cuera and Bolshoi Karatau. Valdorria shares the high-relief and flat-topped, steep slopes, cyclothemic patterns and occurrence of karst features with the Pricaspian Basin platforms (Tengiz, Karachaganak and Kashagan), with minor variations in facies distribution of the internal platform. Furthermore, the continuous seismic-scale outcrop of Valdorria, together with its isolated setting and asymmetrical growth, makes it an additional good candidate for potential subsurface analogues of hydrocarbon-bearing systems.

This paper shows the evolution of time-constrained two-dimensional scaled analogue models of doubly vergent thrust systems in the presence of syntectonic sedimentation. Two sets of experiments were considered: (1) the addition of a... more

This paper shows the evolution of time-constrained two-dimensional scaled analogue models of doubly vergent thrust systems in the presence of syntectonic sedimentation. Two sets of experiments were considered: (1) the addition of a syntectonic layer composed of a polymer and overlying sand in the prowedge; and (2) the addition to the previous condition of a progradational sedimentary load. Results from the first set of experiments indicate that the foreland fold-and-thrust belt has a strong relationship with the competence of the syntectonic layers. When the competence is low, the deformation produces tight asymmetric detachment-folds. As the competence increases, the fold-and-thrust belt shows breaktrough folds with longer and better defined foreland-vergence. Results from the second set of experiments indicate that structural vergence is determined by the sense of progradation of the syntectonic layers, and in the case of strong aggradation at the prowedge, extension and reactive diapirism form contemporaneously with the contraction. Three end-members are proposed for mountain front thrust systems formed in the presence of syntectonic polymer and sand sedimentation: (1) outcropping foldand-thrust belt sequence, in the case of no syntectonic sedimentation; (2) long displacement blindthrust sheets, in the case of under-filled basins and (3) short displacement blind-thrust sheets, in the case of over-filled basins. All results indicate that ductile units at the base of syntectonic layers increase the displacement of the underlying frontal thrusts at the prowedge, and reduce the critical taper. Results also indicate that at very high sedimentary rates and hyper-critical taper conditions the prowedge collapses. Conclusions drawn from this research may be applied as an analogue to foreland evolution and to evaluate hydrocarbon generation, migration, and entrapment in thrust belts in areas where seismic imaging is generally poor.

A B S T R A C T Fold-and-thrust belts (FTBs) can be segmented both across and along strike because of various factors including tectonic and stratigraphic inheritance. In this study, we investigated along/across-strike structural... more

A B S T R A C T Fold-and-thrust belts (FTBs) can be segmented both across and along strike because of various factors including tectonic and stratigraphic inheritance. In this study, we investigated along/across-strike structural interactions in a FTB propagating toward a foreland which displays contrasted lithological sequences. A set of analogue models was performed in a compressional box where a single viscous level of varying width was interbedded within a frictional series. The tectonic interaction between the viscous and the frictional provinces was tested both along and across strike. Results indicate that a frictional province influences the along-strike tectonic evolution of an adjacent viscous province. This influence decreases when the width of the viscous province increases. The frictional provinces control the taper, structural style, obliquity of the structures' trend and ki-nematics of the shallow deformation front of the viscous province. Results evidence how far a frictional province can impact the deformation of an adjacent viscous province. For frictional-viscous wedges, it appears that the critical taper theory, which is generally applied in 2-D, should be likely considered in terms of 3-D. Moreover, the kinematics of the deep deformation front shows mutual influences between the adjacent viscous and fric-tional provinces. Experimental results are compared to natural examples in the Kuqa Basin (Southern Tian Shan, China) and the Salt Range (Pakistan), and give an insight to a better understanding of the dynamics of fold-and-thrust belts bearing a viscous décollement, such as salt.

Ganga Megafan is one of several megafans, developed in the northern and central part of the Ganga Plain, that formed during the middle Late Pleistocene under conditions of higher sediment-water discharge and higher regional slopes than... more

Ganga Megafan is one of several megafans, developed in the northern and central part of the Ganga Plain, that formed during the middle Late Pleistocene under conditions of higher sediment-water discharge and higher regional slopes than today. Incision by the Ganga River exposes 15±30 m thick megafan deposits in the valley walls and cliffs. Ganga Megafan deposits can be separated into four zones: Zone I Ð Gravelly braided streams; Zone II Ð Sandy braid plain; Zone III Ð Anastomosing channel plain; and Zone IV Ð Meandering channels with broad inter¯uve areas. Deposits of each zone show distinct facies associations. Palaeocurrents fan from SW to SE and E, while the grain size decreases from proximal to distal fan. At present, fan-building activity is highly subdued and is restricted only to the northernmost 5±10 km wide belt of Piedmont plain. q

Upper Cretaceous units on the Menderes-Tauride Block show a transition from a passive continental margin to a pelagic basin. This transition is related to the emplacement of ophiolitic nappes. The pelagic sediments were studied in the... more

Upper Cretaceous units on the Menderes-Tauride Block show a transition from a passive continental margin to a pelagic basin. This transition is related to the emplacement of ophiolitic nappes. The pelagic sediments were studied in the Aydıncık and Arslanköy (Mersin) areas in the central Tauride region, and in the Munzur Mountains in eastern Tauride region. In the Aydıncık area Upper Cretaceous units consist of Upper Campanian carbonate breccias with rudist fragments; Upper Campanian-Lower Maastrichtian slope-to-basinal sediments overlie these carbonate breccias disconformably. In the Arslanköy area the Upper Campanian-Maastrichtian Yavca Formation consists of Globotruncana-bearing biomicrites, siliciclastic turbidites, calciturbidites and debris flows and overlies Jurassic-Cretaceous platform carbonates disconformably. The uppermost levels of the Liassic-Cenomanian platform carbonates in the Munzur Mountains are composed of Cenomanian Hippurites/Orbitolina-bearing reefal limestones and then Turonian-Campanian Globotruncanidae-bearing biomicrites. The stratigraphic sequence in the Menderes-Tauride Block shows that rifting to form a northern Neotethyan basin took place in the Triassic and gave rise to the Inner Tauride Ocean. From Jurassic to Cenomanian times, the northern part of the Menderes-Tauride Platform formed a passive continental margin. In the Late Cretaceous the Inner Tauride Ocean is believed to have commenced intra-oceanic, northward subduction. Inner Tauride oceanic crust-derived nappes were emplaced southward onto the Menderes-Tauride Block. Flexural foreland basins in which pelagic sediments were deposited were formed in the Taurus Mountains related to southward thrusting and the emplacement of the ophiolite nappes.

A 2400 m-thick sedimentary column belonging to the Toro Negro Formation was recorded along the Quebrada del Yeso, Sierra de Los Colorados (Vinchina Basin), La Rioja province, NW Argentina. The Vinchina basin is a good example of a closed... more

A 2400 m-thick sedimentary column belonging to the Toro Negro Formation was recorded along the Quebrada del Yeso, Sierra de Los Colorados (Vinchina Basin), La Rioja province, NW Argentina. The Vinchina basin is a good example of a closed basin surrounded by the Precordillera fold and thrust belt to the west and basementcored
blocks to the north, south (Western Sierras Pampeanas) and east (Sierra de Famatina). Seven facies associations (FA) are described and interpreted to represent fluvial, lacustrine and alluvial environments developed in the southern part of the Vinchina basin from the Late Miocene until the earliest Pleistocene. The depositional evolution of the formation was divided in four phases. Phase I (∼7–6.6 Ma) represents sedimentation in medial (FA I) to distal (FA II) parts of a southward directed distributive fluvial system with a retrogradational pattern. During phase II (6.6–6.1Ma), the distributive fluvial system was replaced by a mixed clastic-evaporitic shallow lake (FA III) in a high aggradational basin. In phase III (∼6.1–5 Ma) the eastward progradation of a
fluvial system (FA IV) was recorded as a distal clastic wedge. Finally, phase IV (∼5-2.4Ma) records two depositional cycles of proximal clastic wedge progradation of fluvial-dominated piedmonts (FAV, FAVII) from the
southwest (Sierra de Umango) and/or the west (Precordillera) with an intervening playa lake (FA VI).
Two new U-Pb ages obtained from zircons in volcanic ash layers confirm the Late Miocene age of the lower member of the Toro Negro Formation and permit a tight correlation with the central part of the basin (Quebrada de La Troya section). The sedimentation rate calculated for the dated lacustrine-fluvial interval is higher than the corresponding one in La Troya area suggesting a higher subsidence in the southern part of the basin. During the Late Miocene (∼7-6.6Ma) the ephemeral drainage was controlled by an arid to semiarid climate and initially dissipated mostly internally as terminal fan/distributive fluvial systems descending from the north. A thick lacustrine interval developed in the southern part of the basin between ∼6.6 and 6.1 Ma during a period of high subsidence and closed drainage. Besides, this interval coincides with increased aridity recorded in other basins in the Northwest of Argentina. By ∼6.1 Ma the area started to receive the first coarse-grained sediments heralding the progradation of a clastic wedge from the southwest-west (Sierra de Umango and Precordillera) which fully developed during the rest of the Pliocene to the earliest Pleistocene (∼5–2.4 Ma). The 6.1–2.4 Ma interval records ameliorating climate conditions.

The Toro Negro Formation is a foreland sequence in western La Rioja province, Argentina, which records the late-stage tectonic evolution of the Vinchina Basin. Together with the underlying Vinchina Formation, these two units represent one... more

The Toro Negro Formation is a foreland sequence in western La Rioja province, Argentina, which records the late-stage tectonic evolution of the Vinchina Basin. Together with the underlying Vinchina Formation, these two units represent one of the thickest and longest continually exposed foreland sections in northwest Argentina. The Vinchina basin is uniquely situated between the Toro Negro and Umango blocks of the Western Sierra Pampeanas to the north and south, the Precordillera to the west, and the Sierra de Famatina to the east. New U-Pb dating of volcanic tephra provides improved age constraints on the pace of sedimentation, and U-Pb ages of detrital zircons serve to strengthen existing provenance interpretations. We show that deposition of the Toro Negro Formation spans roughly 6.9 to 2.3 Ma: Late Miocene to Early Pleistocene. A high-relief, erosional unconformity with the underlying Vinchina Formation developed sometime between 9.3 and 6.9 Ma, although stratigraphic considerations suggest it spanned only the later part of this time interval (perhaps 7.5e6.9 Ma). Above this unconformity, undecompacted sedimentation rates are remarkably high at ~1.2 mm/yr, slowing to ~0.3 mm/yr after ~6 Ma. An unconformity in the upper part of the section is constrained to occur sometime between 5.0 and 3.0 Ma, probably beginning not long after 5.0 Ma. The timing of both unconformities broadly Matches the timing of inferred tectonic events in the Sierra Famatina ~50 km to the east, the Fiambal a basin to the north, and the Bermejo basin to the south, suggesting they May record regional tectonism at these times. Provenance interpretations of detrital zircon spectra are consistent with previous interpretations based on sediment petrography. They show that provenance did not change significantly during the course of Toro Negro deposition, precluding major tectonically-induced drainage reorganization events. Sediments were derived primarily from the north (Toro Negro Block) and west (Precordillera). The data are consistent with a subtle increase in sediment supply from the Precordillera beginning around 6.5 Ma.

The Segre and Pamplona oblique faults are the most prominent features of the southern Pyrenees. During the Tertiary compression, the Segre Fault constituted a system of oblique ramps, which formed by the reactivation of the previous... more

The Segre and Pamplona oblique faults are the most prominent features of the southern Pyrenees. During the Tertiary compression, the Segre Fault constituted a system of oblique ramps, which formed by the reactivation of the previous margin of the Mesozoic extensional basin. The Segre oblique ramps were emergent at the synorogenic surface and erosive during its complete evolution in Eocene and Oligocene times. In contrast, the western margin of the South Central Unit constituted by the Mediano and Boltaña anticlines, was mostly Bccretional and blind. The Pamplona Fault evolved alike the Segre Fault but with much less Tertiary southward tectonic transport over the basal thrust of the system. The tectonic inversion of the thick Mesozoic basins located to the W of the Pamplona and Segre faults also pro-duced a topographic inversion. As a product of this topographic inversion, the synchronous Tertiary deposition took place in the former Mesozoic structural highs: the Ripoll and Ebro basins to the E of the Segre Fault and the Pamplona basin to the E of the Pamplona Fault.

In NW Europe, the late Carboniferous Variscan collision between the Laurussia and the Armorica-Gondwana continental blocks led to the development of a crustal-scale north-verging thrust system along the southern Laurussian margin. In... more

In NW Europe, the late Carboniferous Variscan collision between the Laurussia and the Armorica-Gondwana continental blocks led to the development of a crustal-scale north-verging thrust system along the southern Laurussian margin. In northern France, the 3-D geometry and kinematics
of the Variscan deformation front have been investigated on the basis of reprocessing and interpreting 532 km of industry-level seismic reflection profiles. This extensive seismic imaging provides new constraints on the structural and kinematic features of the orogenic front. It particularly emphasizes the localization of displacement along the main frontal thrust zone that accommodated more than 50 km
of total displacement of the allochthonous units above the foreland. It also highlights the induced large underthrusting of the foreland basin below the frontal thrust zone, and its truncation in a general out- of-sequence mode of thrust propagation. We built structural maps that led to better delineating a major NW-SE lateral ramp along the main frontal thrust. The Mid-Upper Devonian series within the flexured foreland were deformed at depth by N060–080° trending and N110–130° trending syn-sedimentary normal faults that led to their south-to southwestward thickening. These pre-existing structures along the margin have exerted a primary control on the ensuing dynamics and geometry of the Northern Variscan Front by localizing both the frontal and lateral ramps during thrust wedge growth.

RESUMEN Se efectúa una revisión y actualización de la estratigrafía de las secuencias paleógenas y neógenas expuestas en las Sierras Pampeanas Noroccidentales y Precordillera septentrional de La Rioja. Aquí se reconocen tres princi-pales... more

RESUMEN Se efectúa una revisión y actualización de la estratigrafía de las secuencias paleógenas y neógenas expuestas en las Sierras Pampeanas Noroccidentales y Precordillera septentrional de La Rioja. Aquí se reconocen tres princi-pales áreas de afl oramientos: 1. Sierra de Los Colorados (depocentro Vinchina), 2. Sierras de Yanso y La Flecha (depocentro La Troya) y 3. Quebrada de Santo Domingo-sierra del Peñón. Las rocas cenozoicas más antiguas corresponden a los estratos rojos de la Formación Puesto La Flecha, compuesta mayormente por areniscas y fangolitas depositadas en ambientes fl uviales de baja energía y lacustres efímeros durante el intervalo Eoceno tardío-Oligoceno temprano. La unidad es sucedida por un espeso conjunto de areniscas correspondientes a la Formación Vallecito (Oligoceno tardío-Mioceno temprano), formada principalmente por el apilamiento de secuencias de dunas eólicas. La Formación Cerro Morado (Mioceno temprano a medio) incluye dos miembros, el inferior compuesto por areniscas y fangolitas, junto a escasos conglomerados, y el superior de naturaleza volcánica y volcaniclástica. El inicio de la sedimentación de la Formación Vinchina, ocurrido entre los 16-15 Ma, marcó el comienzo de la sedimentación en la antefosa de la cuenca de antepaís. La mayor parte de la Formación Vinchina está compuesta por areniscas y fangolitas, con proporción subordinada de conglomerados y escasas evaporitas, mayormente depositadas por sistemas fl uviales de baja energía, asociados a depósitos lacustres efí-meros y eólicos. En el depocentro La Troya estas rocas son sucedidas por conglomerados, areniscas y pelitas de la Formación Zapallar; mientras que en el depocentro de Vinchina, mediando una superfi cie de fuerte incisión, se depositaron areniscas, fangolitas y conglomerados de la Formación Toro Negro (Mioceno más tardío-Pleis-toceno temprano) que representa el progresivo avance hacia el este de los cabalgamientos precordilleranos. Finalmente, conglomerados gruesos, brechas y areniscas, registran la canibalización de las cuencas de antepaís. Este intervalo corresponde a la Formación El Corral (Plioceno tardío-Pleistoceno) y registra la sedimentación, en gran medida sintectónica, en abanicos aluviales y sistemas fl uviales multicanalizados de alta energía. ABSTRACT Cenozoic stratigraphy of the foreland basins of the Sierras Pampeanas Noroccidentales and Precordillera of La Rioja. A review and update of the Paleogene and Neogene sequences cropping out in the Sierras Pampeanas Norocciden-tales and Precordillera of La Rioja is presented. Three main depositional areas are recognized: 1. Sierra de Los Colorados (Vinchina depocenter), 2. Sierras de Yanso and La Flecha (La Troya depocenter) and, 3. Quebrada de Santo Domingo-sierra del Peñón. The oldest Cenozoic rocks are red-beds of the Puesto La Flecha Formation composed of sandstones and mudstones deposited in low-energy fl uvial and ephemeral lacustrine environments. Radiometric, magnetostratigraphic and paleontological information locates this unit in the Upper Eo-cene-Lower Oligocene interval. The former unit is succeeded by a thick set of eolian sandstones corresponding to the Vallecito Formation (Upper Oligocene-Lower Miocene), formed mainly by the stacking of dune deposits. The Cerro Morado Formation (Lower to Middle Miocene) includes two members, the lower one composed of sandstones and mudstones, along with few conglomerates, and the upper one of volcanic and volcaniclastic nature. The beginning of the sedimentation of the Vinchina Formation, which occurred between 16 and 15 Ma, marked the onset of sedimentation in a retroarc foreland basin. Most of the Vinchina Formation is composed of sandstones and mudstones, with a subordinate proportion of conglomerates and few evaporites, all of them deposited by low-energy river systems, associated with ephemeral lakes and eolian deposits. In the La Troya depocenter these rocks are succeeded by conglomerates, sandstones and mudstones belonging to the Zapallar

The sub-Andean Huallaga basin is part of the modern retroforeland basin system of Peru. It corresponds to a thrust-and-fold belt superimposed on inverted and halokinetic structures and is characterized by Eocene-Pliocene, thick... more

The sub-Andean Huallaga basin is part of the modern retroforeland basin system of Peru. It corresponds to a thrust-and-fold belt superimposed on inverted and halokinetic structures and is characterized by Eocene-Pliocene, thick synorogenic series that have controlled the burial history of petroleum systems. Sedimentological analysis and a sequentially restored cross-section based on seismic data and new field studies show three sequences of synorogenic deposits. The Eocene (Lower Pozo member) developed in shoreface environments, when the basin morphology corresponded to a foresag depozone linked to an orogenic unloading period. The Middle Eocene sequence (Upper Pozo member) developed in shallow marine environments and recorded a change in Andean geodynamics and the retroforeland basin system. The basin morphology corresponded to a foredeep depozone linked to an orogenic loading period. This configuration remained until the Middle Miocene (Chambira Formation). The Middle Miocene-Pliocene sequence recorded the onset of the modern sub-Andean Huallaga basin that became a wedge-top depozone. Thrust propagation occurred in a deltaic environment, which evolved progressively to an alluvial system linked to the modern Amazon River. q

The Western foreland basin in Taiwan originated through the oblique collision between the Luzon volcanic arc and the Asian passive margin. Crustal flexure adjacent to the growing orogenic load created a subsiding foreland basin. The... more

The Western foreland basin in Taiwan originated through the oblique collision between the Luzon volcanic arc and the Asian passive margin. Crustal flexure adjacent to the growing orogenic load created a subsiding foreland basin. The sedimentary record reveals progressively changing sedimentary environments influenced by the orogen approaching from the East. Based on sedimentary facies distribution at five key stratigraphic horizons, paleogeographic maps were constructed. The maps highlight the complicated basin-wide dynamics of sediment dispersal within an evolving foreland basin.

1] The Patagonian Andes record the Cretaceous demise of the quasi-oceanic Rocas Verdes back-arc basin and formation of the Magallanes foreland basin. For >500 km along the strike of the mountains, this tectonic transition is marked by a... more

1] The Patagonian Andes record the Cretaceous demise of the quasi-oceanic Rocas Verdes back-arc basin and formation of the Magallanes foreland basin. For >500 km along the strike of the mountains, this tectonic transition is marked by a sandstone-mudstone package that records the beginning of turbiditic sand deposition and fan growth. Sandstone modal analyses and U-Pb detrital zircon spectra show changes in rock composition and provenance across the transition on a basin-wide scale, indicating it has tectonic significance and is related to orogenic uplift and the progressive evolution of the Andean fold-thrust belt. Spatial variations in transition zone characteristics indicate the foreland basin's central and southern sectors were fed by different sources and probably record separate fans. At Bahía Brookes, on Tierra del Fuego, foreland basin sedimentation began at least after 88-89 Ma, and possibly after ∼85 Ma, several million years after it did ∼700 km away at the northern end of the basin. This event coincided with increased arc volcanism and the partial obduction of the basaltic Rocas Verdes basin floor onto continental crust. By 81-80 Ma, conglomerate deposition and increased compositional and provenance complexity, including the abundance of metamorphic lithic fragments, indicate that the obducted basaltic floor first became emergent and was eroding. The results suggest that the beginning of turbidite sedimentation in the Magallanes foreland basin and the progressive incorporation and exhumation of deeply buried rocks in the Andean fold-thrust belt, occurred later in southern Patagonia than in the north by a few million years.

New paleocurrent data indicate that the widespread Late Silurian and Devonian flysch and molasse succession in Maine was deposited in an ancestral, migrating foreland basin adjacent to an advancing Acadian orogenic belt. The... more

New paleocurrent data indicate that the widespread Late Silurian and Devonian flysch and molasse succession in Maine was deposited in an ancestral, migrating foreland basin adjacent to an advancing Acadian orogenic belt. The foreland-basin sequence spread across a varied Silurian paleogeography of deep basins and small islands—the vestiges of an intraoceanic arc complex that not long before had collided with the Laurentian passive margin during the Ordovician Taconic Orogeny. We report paleocurrents from 43 sites representing 12 stratigraphic units, the most robust and consistent results coming from three units: Madrid Formation (southwesterly paleoflow), Carrabassett Formation (northerly paleoflow), and Seboomook Group (westerly paleoflow). Deformation and regional metamorphism are sufficiently intense to test the limits of paleocurrent analysis requiring particular care in retrodeformation.

Economic concentrations of detrital gold are rare in young foreland basins due to paucity of significant gold sources, and a paucity of sediment recycling processes during filling of the foreland basin. Gold shed into the foreland basins... more

Economic concentrations of detrital gold are rare in young foreland basins due to paucity of significant gold sources, and a paucity of sediment recycling processes during filling of the foreland basin. Gold shed into the foreland basins is typically widely dispersed in an overwhelming volume of immature basin-fill detritus of no economic significance. In the actively forming Canterbury Basin of New Zealand, minor gold concentration occurs at the mountain front in the bed of the Rakaia River, and 60 km downstream on beaches and the crest of foredunes at the river mouth. The Cretaceous–Tertiary Denver and Western Canada Basins in North America also have minor gold concentrations at the mountain front, and minor gold dispersal into the basin. Tectonic quiescence in the middle Tertiary in the Denver Basin kept gold within 20 km of the mountain front, where renewed uplift in late Tertiary caused minor economic concentrations to form in modern streams. Gold has been transported ca. 200 km across the Western Canada basin by progressive recycling of gravel during slow (ca. 10 to 50 m/Ma) middle Tertiary–Recent regional uplift and tilting, but little concentration has occurred. Development of significant placers in a foreland basin, the generally accepted setting for the Witwatersrand Au-U palaeoplacers, appears to require specific tectonic conditions during and/or after basin evolution to drive the sedimentary recycling necessary for significant placer development. Such tectonic conditions have not occurred in an any of the three young foreland basins examined in this study.

Ganga Megafan is one of several megafans, developed in the northern and central part of the Ganga Plain, that formed during the middle Late Pleistocene under conditions of higher sediment-water discharge and higher regional slopes than... more

Ganga Megafan is one of several megafans, developed in the northern and central part of the Ganga Plain, that formed during the middle Late Pleistocene under conditions of higher sediment-water discharge and higher regional slopes than today. Incision by the Ganga River exposes 15±30 m thick megafan deposits in the valley walls and cliffs. Ganga Megafan deposits can be separated into four zones: Zone I Ð Gravelly braided streams; Zone II Ð Sandy braid plain; Zone III Ð Anastomosing channel plain; and Zone IV Ð Meandering channels with broad inter¯uve areas. Deposits of each zone show distinct facies associations. Palaeocurrents fan from SW to SE and E, while the grain size decreases from proximal to distal fan. At present, fan-building activity is highly subdued and is restricted only to the northernmost 5±10 km wide belt of Piedmont plain. q

This paper presents new litho, chrono and magnetostratigraphic data from cores of 23 exploratory boreholes drilled in the Abalario and marshlands areas of the lower Guadalquivir basin (the western sector of the Guadalquivir foreland... more

This paper presents new litho, chrono and magnetostratigraphic data from cores of 23 exploratory boreholes drilled in the Abalario and marshlands areas of the lower Guadalquivir basin (the western sector of the Guadalquivir foreland basin, SW of Spain). The lithologic logs of these boreholes identify four main sedimentary formations, namely: Almonte Sand and Gravel, Lebrija Clay and Gravel, Marismas Clay and Abalario Sand, respectively interpreted as proximal-alluvial, distal-alluvial, alluvial-estuarine and aeolian. From radiocarbon and magnetostratigraphic data, these formations were dated as Upper Pliocene to Holocene. In the marshlands area, three main sedimentary sequences are present: an Upper Pliocene to Lower Pleistocene sequence of the Almonte and Lebrija (lower unit) formations, a Pleistocene sequence of the Lebrija (upper unit) and the lower Marismas formations, and a latest Pleistocene to present-day sequence of the upper Marismas Formation. The three sequences began as a rapid alluvial progradation on a previously eroded surface, and a subsequent alluvial retrogradation. In the third sequence, estuarine and marsh sediments accumulated on top of the alluvial sediments. The aeolian sands of the Abalario topographic high developed coeval to alluvial and estuarine sedimentation after the first alluvial progradation, and continuously until the present. Correlation with the surrounding areas show that the sequences are the result of the forebulge uplift of the northern margin of the basin (Sierra Morena) and the adjacent Neogene oldest sediments of their northern fringe, both form the main source area of the study formations. This uplift occurred simultaneous to the flexural subsidence (SSE tilting) of the southern part of the basin, where sedimentary aggradation dominated.

The basement of the Moesian Platform is extremely heterogeneous, including rocks ascribed to the Archean, Palaeoproterozoic and Neoproterozoic. Largely concealed by the Palaeozoic to Cenozoic platform cover, the basement exposed in the... more

The basement of the Moesian Platform is extremely heterogeneous, including rocks ascribed to the Archean, Palaeoproterozoic and Neoproterozoic. Largely concealed by the Palaeozoic to Cenozoic platform cover, the basement exposed in the tectonic block of Central Dobrogea contains mainly Neoproterozoic-Eocambrian turbidites (the Histria Formation), deformed under very low grade metamorphic conditions at the end of the Neoproterozoic, in the "Cadomian" or "Baikalian" events. The Histria Formation includes channelized, midfan turbidites and distal, outer fan turbidites, forming two sandstone dominated, upward coarsening and thickening sequences, separated by a much thinner, upward fi ning and thinning sequence. Sedimentological, mineralogical and petrological studies are consistent with the model that the turbiditic basin was sourced by a continental margin dominated by an active volcanic arc. From various lines of evidence, a foreland basin as the tectonic setting f...

A basin axial-channel belt was largely responsible for the observed distribution of coarse-grained gravity-flow deposits in the Tertiary Puchkirchen and basal Hall formations of the Molasse foreland basin in Upper Austria. Elements of... more

A basin axial-channel belt was largely responsible for the observed distribution of coarse-grained gravity-flow deposits in the Tertiary Puchkirchen and basal Hall formations of the Molasse foreland basin in Upper Austria. Elements of this depositional system, mapped in three-dimensional (3D) seismic-reflection data, include channel-belt thalweg, mass-transport complexes, overbank wedge, overbank lobe, and tributary channel. The primary objective of this paper is to develop a comprehensive understanding of the sedimentary processes that were prevalent in the channel-belt complex through the analysis of well data, including drill cores and wireline logs, in conjunction with 3D seismic interpretations. Sedimentation in the 3-6 km wide channel belt was commonly focused within smaller channel elements, 1-2 km in width. These elements consist of upward fining and thinning gravity-flow deposit successions, which record the waning of flows in the channel setting. Chaotically bedded fine-grained units, including debris-flow deposits, slumped material, and rafted sediment blocks are common in the channel belt locally. Overbank sedimentation, from flows that spilled over the margins of the smaller channel elements, was common within the confines of the axial channel belt (inner levees). A significant amount of fine-grained material overtopped the margin of the axial channel belt, lapping onto the confining basin slopes and ultimately accumulating in upward fining sediment wedges up to 200-300 m high. As a result of the piling up of overbank wedges onto basin slopes, they too are characterized by a morphologic expression comparable to that of inner levees. Overbank wedges are incised by tributary channels oriented perpendicular to the axial channel belt, formed through slumping and the focusing of low-density currents that originated from flow-stripping upstream. They were backfilled by thin-bedded turbidities sourced directly from the axial channel belt. Tabular silt beds were deposited from flow-stripping at outer channel meander bends locally, resulting in the deposition of overbank lobes; breaching of the channel belt levee also resulted in the deposition of upward fining and thinning turbidites in overbank settings periodically. Confinement of the depositional system within the narrow foredeep had a profound effect on sediment distribution. Lateral migration of the axial channel belt was limited, and as a result, coarse-grained material stacked nearly vertically for approximately 8 myr. Channelbelt avulsion was not possible because of a lack of available space within the foredeep trough. The architecture of overbank units was influenced by marginal basin slopes; accommodation space for sand accumulation in overbank areas was limited and thus, overbank lobes only formed in limited locations. Sedimentation in the basin was also influenced by active Alpine fold-thrust belt structuring.

Progressive unconformities result from a simultaneous interference of sedimentation, erosion, and tectonic processes. For the purpose of simulating the geometry of these structures occurring on the front of active folds in foreland basin... more

Progressive unconformities result from a simultaneous interference of sedimentation, erosion, and tectonic processes. For the purpose of simulating the geometry of these structures occurring on the front of active folds in foreland basin margins, we propose a 2D forward kinematic model. By analogy to several natural examples of syntectonic basins, the syncline frontal hinge typically displays a curved rather than a kinked shape. This model is incremental, and assumes that deformation in the limb of growth strata consists of simple shear parallel to pregrowth strata. It is possible to introduce erosional events at any time of kinematics history. Syntectonic basins associated to emergent structures were modelled, focusing on the syncline frontal hinge and the forelimb of the anticline, without regarding the type of fold. We show that growth stratal final geometry is closely dependent on (1) the behaviour of the synclinal hinge (hinge migration model versus limb rotation model); (2) the erosion of pre-and syntectonic beds, and the attitude of the erosional surface; (3) the evolution of the (R) ratio (amount of deformation/sediment thickness). Simulating several theoretical tectono-sedimentary scenarios, we show how growth strata geometry provides a very fine recording of every variation of the (R) ratio during amplification of folding. As an example, we propose a kinematic evolution for the classical Sant Llorenc de Morunys structures, resulting from its forward reconstruction. D

A Mesozoic foreland-basin complex formed along the northern Yangtze plate during subduction of this plate under the Qinling -Dabieshan orogenic belt along the Mianlue suture. As the Yangtze plate moved northwestwards and was obliquely... more

A Mesozoic foreland-basin complex formed along the northern Yangtze plate during subduction of this plate under the Qinling -Dabieshan orogenic belt along the Mianlue suture. As the Yangtze plate moved northwestwards and was obliquely subducted under the Qinling -Dabieshan (Middle -Late Triassic), a flysch foredeep developed in the Diebu -Songpan in the western part of the northern Yangtze plate. During the Late Triassic, a nonmarine molasse basin first formed in the eastern part of the northern Yangtze plate in response to initial collision there. This molasse clastic wedge prograded over the former marine basin and was accompanied by a change from high-sinuosity river systems flowing into basinal lakes, to higher gradient braidplains. Complete oceanic closure along the Mianlue suture during the Middle Jurassic produced a more extensive east -west molasse basin with rivers, deltas and lakes. During Late Jurassic through Early Cretaceous, the depocenter of the nonmarine molasse basin migrated continually from east to west because of intracontinental deformation associated with clockwise rotation of the Yangtze plate relative to the North China plate. In this time interval, the basin was again dominated by fluvial and lake-delta deposition and rivers continued to disperse sediments southwards into the basin. q

The relationships between oblique or lateral ramps in fold-and-thrust belts and their impact on syntectonic fluvial drainage are analysed in this review. Both ancient and recent cases from Cenozoic belts are examined. The southern flank... more

The relationships between oblique or lateral ramps in fold-and-thrust belts and their impact on syntectonic fluvial drainage are analysed in this review. Both ancient and recent cases from Cenozoic belts are examined. The southern flank of the Pyrenees provides good examples to decipher the long-term effects of oblique ramps on fluvial arrangement. Recent examples from the Indus River across the front of the Himalayas in northwest Pakistan, the frontal domains of the Andes in Bolivia and the northwest Zagros Mountain Belt provide examples of the short-term interaction between oblique or lateral thrust ramps and foreland drainage systems. The interpretation of these case studies, some of them developed on top of blind thrust ramps, can facilitate the analysis of drainage distortions in active complex tectonic regions.

The relationships between oblique or lateral ramps in fold-and-thrust belts and their impact on syntectonic fluvial drainage are analysed in this review. Both ancient and recent cases from Cenozoic belts are examined. The southern flank... more

The relationships between oblique or lateral ramps in fold-and-thrust belts and their impact on syntectonic fluvial drainage are analysed in this review. Both ancient and recent cases from Cenozoic belts are examined. The southern flank of the Pyrenees provides good examples to decipher the long-term effects of oblique ramps on fluvial arrangement. Recent examples from the Indus River across the front of the Himalayas in northwest Pakistan, the frontal domains of the Andes in Bolivia and the northwest Zagros Mountain Belt provide examples of the short-term interaction between oblique or lateral thrust ramps and foreland drainage systems. The interpretation of these case studies, some of them developed on top of blind thrust ramps, can facilitate the analysis of drainage distortions in active complex tectonic regions. Oblique ramps are present either permanently or episodically at different scales in all fold-and- thrust belts. The simplest scenario is related to piggyback basins, which display an oblique ramp linked to each frontal thrust termination. This oblique ramp forms the natural outlet for confined longitudinal systems along the piggyback basin. The change in topography across the ramp con- strains the position of deltaic deposits between a subaerial fluvial system deposited in its hanging- wall and an open marine system deposited in its footwall. Fluvial systems can also develop either in the hangingwall or in the footwall of larger oblique ramps that grow by the tectonic inversion of earlier structures. The growth of a large oblique ramp beneath a fluvial system operates in the same way as oblique ramps related to piggyback basins. However, its larger scale causes a larger differential topographic elevation across it, accommodating fluvial deposits in its hangingwall and deep marine turbidites in its footwall. In opposition, large oblique ramps growing in front of river systems create a topographic barrier that deflects the drainage. A complication of the interaction of oblique ramps and drainage occurs where two opposed oblique ramps form a tectonic reentrant. These tectonic reentrants form at different scales and are characterized by lower topography. The confined domains concentrate rivers flowing out from surrounding higher topographic deformed regions. Further development of deeper thrusts can uplift these reentrants, modifying the previous concentrated drainage and diverting the river courses towards regions with lower topography. As an example, the late Miocene longitudinal fluvial system flowing along the foreland basin of the Zagros during the deposition of the lower Agha Jari Formation was shifted to the southwest in the earliest Pliocene by the uplift of the Pusht-e Kuh Arc. The present river configuration is incising through the Pusht-e Kuh Arc anticlines and flows towards the lowlands of the Dezful Embayment (tectonic reentrant), limited by two major oblique ramps along the Mountain Front Flexure. The large-scale Mountain Front Flexure confines the Tigris River towards the southwest of the front of the Pusht-e Kuh Arc.

A 2400 meter-thick sedimentary column belonging to the Toro Negro Formation was recorded along the Quebrada del Yeso, Sierra de Los Colorados (Vinchina Basin), La Rioja province, NW Argentina. The Vinchina basin is a good example of a... more

A 2400 meter-thick sedimentary column belonging to the Toro Negro Formation was recorded along the Quebrada del Yeso, Sierra de Los Colorados (Vinchina Basin), La Rioja province, NW Argentina. The Vinchina basin is a good example of a closed basin surrounded by the Precordillera fold and thrust belt to the west and basement-cored blocks to the north, south (Western Sierras Pampeanas) and east (Sierra de Famatina). Seven facies associations (FA) are described and interpreted to represent fluvial, lacustrine and alluvial environments developed in the southern part of the Vinchina basin from the Late Miocene until the earliest Pleistocene. The depositional evolution of the formation was divided in four phases. Phase I (~7-6.6 Ma) represents sedimentation in medial (FA I) to distal (FA II) parts of a southward directed distributive fluvial system with a retrogradational pattern. During phase II (6.6-6.1Ma), the distributive fluvial system was replaced by a mixed clastic-evaporitic shallow lake (FA III) in a high aggradational basin. In phase III (~6.1-5 Ma) the eastward progradation of a fluvial system (FA IV) was recorded as a distal clastic wedge. Finally, phase IV (~5-2.4Ma) records two depositional cycles of proximal clastic wedge progradation of fluvial-dominated piedmonts (FAV, FAVII) from the southwest (Sierra de Umango) and/or the west (Precordillera) with an intervening playa lake (FA VI). Two new U-Pb ages obtained from zircons in volcanic ash layers confirm the Late Miocene age of the lower member of the Toro Negro Formation and permit a tight correlation with the central part of the basin (Quebrada de La Troya section). The sedimentation rate calculated for the dated lacustrine-fluvial interval is higher than the corresponding one in La Troya area suggesting a higher subsidence in the southern part of the basin. During the Late Miocene (~7-6.6Ma) the ephemeral drainage was controlled by an arid to semiarid climate and initially dissipated mostly internally as terminal fan/distributive fluvial systems descending from the north. A thick lacustrine interval developed in the southern part of the basin between ~6.6 and 6.1 Ma during a period of high subsidence and closed drainage. Besides, this interval coincides with increased aridity recorded in other basins in the Northwest of Argentina. By ~6.1 Ma the area started to receive the first coarse-grained sediments heralding

A sedimentological investigation of the Neogene deposits of the Zagros foreland basin in SW Iran reveals a continuous and largely gradational passage from supratidal and sabkha sediments at the base (represented by the Gachsaran... more

A sedimentological investigation of the Neogene deposits of the Zagros foreland basin in SW Iran reveals a continuous and largely gradational passage from supratidal and sabkha sediments at the base (represented by the Gachsaran Formation) to carbonates and marine marls (Mishan Formation with basal Guri carbonate member) followed by coastal plain and meandering river deposits (Agha Jari Formation) and finally to braided river gravel sheets (Bakhtyari Formation). This vertical succession is interpreted to represent the southward migration of foreland basin depozones (from distal foredeep and foredeep to distal wedge-top and proximal wedge-top, respectively) as the Zagros fold–thrust belt migrated progressively southward towards the Arabian foreland. This vertical succession bears a striking similarity to modern depositional environments and sedimentary deposits observed in the Zagros region today, where one passes from mainly braided rivers in the Zagros Mountains to meandering river...