Foreland Basins System Research Papers (original) (raw)

Three-dimensional seismic mapping of interpretative sub-surface time slice sections, incorporating age data and detailed structural observations places constraints on the structural architecture and stratigraphic evolution of the Icotea pull-apart basin in the central Maracaibo basin, Venezuela. All four fault-bounded sides of the Icotea basin, its ,3-km-thick Eocene basin fill of clastic sediments and faults pre-dating the opening of the basin can be mapped in three dimensions. The development of the Icotea basin provides an excellent observational basis for understanding the structural history of three sets of regionally extensive faults and testing two models for the formation of pull-apart basins in general. Three main fault trends produced at different periods in the formation of the Cretaceous-Recent Maracaibo basin are mapped using 3D seismic data in the central part of the basin: (1) N-NE-striking normal faults, including the Icotea fault; these faults formed originally during Late Jurassic-Early Cretaceous rifting and reactivated as left-lateral strike-slip faults during late Paleocene-Eocene convergent deformation between the Caribbean and South American plates; (2) NW striking faults formed by late Paleocene-Eocene overthrusting of the Caribbean plate and downward flexure of the South American plate to create a major foreland basin depocenter; and (3) NE-striking normal faults, of pre-Cretaceous age, were reactivated during late Paleocene-Eocene plate convergence. Three-dimensional architecture of the Icotea basin interpreted from five time slices through the basin and its flank areas supports the simple pull-apart model for the Eocene opening of the Icotea basin. The amount of extension across the suite of normal faults ranges between 0.8 and 2.25 km. This range of offset is consistent with some previous estimates of minor left-lateral displacement along the Icotea fault but is inconsistent with either low-angle or high-angle thrusting during Eocene time, as inferred from previous interpretations of widely spaced two-dimensional seismic lines. The normal faults that formed the pull-apart basin reactivated pre-existing faults due to plate flexure.

- by
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- Geology, Geophysics, Interpretation, Early Cretaceous

Although only recognized as a discrete stratigraphic unit since 1949, the Cedar Mountain Formation represents tens of millions of years of geological and biological history on the central Colorado Plateau. This guidebook represents an attempt to pull together the results of recent research on the lithostratigraphy, chronostratigraphy, sequence stratigraphy, chemostratigraphy, and biostratigraphy of these medial Mesozoic strata that document the dynamic and complex geological history of this region. Additionally, these data provide a framework by which to examine the history of terrestrial faunas during the final breakup of Pangaea. In fact, the medial Mesozoic faunal record of eastern Utah should be considered a keystone in understanding the history of life across the northern hemisphere.
Following a period of erosion and sediment bypass spanning the Jurassic–Cretaceous boundary, sedimentation across the quiescent Colorado Plateau began during the Early Cretaceous. Thickening of these basal Cretaceous strata across the northern Paradox Basin indicate that salt tectonics may have been the predominant control on deposition in this region leading to the local preservation of fossiliferous strata, while sediment bypass continued elsewhere. Thickening of overlying Aptian strata west across the San Rafael Swell provides direct evidence of the earliest development of a foreland basin with Sevier thrusting that postdates geochemical evidence for the initial development of a rain shadow.

- by James Kirkland and +1
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- Paleoclimatology, Salt Tectonics, Paleolimnology, Vertebrate Paleontology

The Quaternary geodynamic evolution and the tectonic
processes active along the Central and Northern Apennines
thrust fronts and in the adjacent Padane-Adriatic foredeep
domains are analysed and discussed.
A reinterpretation of the available geophysical and geological
data reveals that the south-eastward prolongation of
the Apennines thrust front in the Adriatic Sea is most likely located
along the north-eastern side of the Adriatic ridge, i.e., in
a more external position with respect to traditional interpretations.
Further south, the Apennine thrust front is segmented
in correspondence with the Tremiti lithospheric right-lateral
transfer zone.
This new interpretation of the Apennine thrust front bears
some relevant implications since it rejuvenates to Late Quaternary
the most recent contractional deformations in its
Adriatic portion. This is consistent with the Late Quaternary
activity of the buried thrust-related folds associated with the
Apennine front along the Marche coastal belt and in the Po
Plain documented by geomorphological analysis and by seismic
refl ection profi les. Moreover, active shortening associated
with the Apennines accretionary prism in the Po Plain and
in the central and northern Adriatic Sea is documented by GPS
data and by historical and instrumental seismicity.
The Quaternary evolution of one of the active thrust-related
folds recognised in the Po Plain subsurface (the Mirandola
anticline) has been investigated in detail by backstripping
high-resolution stratigraphic data. Our results show decreasing
relative uplift rates during the Quaternary. However, tectonic
relative uplift rate of about 0.16 mm/a can still be recognised
during the last 125 ka. Horizontal shortening faster than
1 mm/a should be expected in agreement with available GPS
data.
Furthermore, the SW-ward (or W-ward) increasing dip of
the foreland monocline in the Po Plain and in the centralnorthern
Adriatic and the asymmetric distribution of the Quaternary
to Recent subsidence indicate a still active fl exural retreat
of the subducting lithosphere in these domains.
The Quaternary to Recent fl exural retreat of the subducting
Adriatic lithosphere and the related frontal accretion of
the Apennines prism are framed in a coherent geodynamic
scenario characterized by a retreating west-directed subduction
zone, which is the natural evolution of the Neogene geodynamic
history.

The Messinian foredeep deposits of the Apennines have been
studied for many years and their stratigraphy has been recently revised in various papers. However, these studies have not taken into consideration the Southern Laga Basin of Northern Abruzzo, which
is believed to have been the largest and most rapidly subsiding turbiditic depocenter of the Apennine foredeep during the Messinian, together with the basin buried under the Po Plain.
Taking a physical stratigraphic approach, a new stratigraphic
scheme is proposed for the deepest portion of the Laga basin. This makes it possible to document the striking similarities of Messinian depositional events recorded in the Southern Laga Basin with those recognised in other sectors of the Apenninic foreland. The correlative
depositional events together with the palaeoenvironmental interpretation of well-framed depositional units makes it possible to mark the vertical transition from deep marine to lacustrine and fluvio-deltaic environments, encouraging reconsideration of the real
bathymetry of the Southern Laga Basin in Northern Abruzzo. The four Messinian units which were recognised correspond to discrete evolutionary steps of the Southern Laga Basin marking the transition from a foredeep to a wedge-top basin. Regional geologic considerations suggest that these depositional events were strongly controlled by the large-scale tectonic evolution of the Apennine foreland, which thus preserves a similar tectonic and sedimentary history over a wide area.

- by Andrea Artoni
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- Stratigraphy, Tectonics, Foredeep Basins, Foreland Basins System

The Argentine broken foreland has been the subject of continuous research to determine the uplift and exhumation history of the region. High-elevation mountains are the result of NeS reverse faults that disrupted a WeE Miocene Andean foreland basin. In the Sierra de Ambato (northern Argentine broken foreland) the reverse faults offset Neogene sedimentary rocks (Aconquija Fm., ~9 Ma) and affect the basement comprising Paleozoic metamorphic rocks that have been dated at ~477À470 Ma. In order to establish a chronology of these faults affecting the previous continuous basin we date the formation age of clay minerals associated with fault gouge using the KeAr dating technique. Clay mineral formation is a fundamental process in the evolution of faults under the brittle regime (<<300 C). KeAr ages (9 fractions from 3 samples collected along a transect in the Sierra de Ambato) vary from Late Devonian to Late Triassic (~360e220 Ma). This age distribution can be explained by a long lasting brittle deformation history with a minimum age of ~360 Ma and a last clay minerals forming event at ~220 Ma. Moreover, given the progression of apparent ages decreasing from coarse to fine size fractions (~360À311 Ma for 2À1 mm grain size fraction, ~326À286 Ma for 1e0.2 mm and ~291À219 Ma of <0.2 mm), we modeled discrete deformation events at ~417 Ma (ending of the Famatinian cycle), ~317e326 Ma (end of Gond-wanic orogeny), and ~194e279 Ma (Early Permian-Jurassic deformation). According to our data, the Neogene reactivation would not have affected the KeAr system neither generated a significant clay minerals crystallization in the fault gouge, although an exhumation of more than 2 Km is recorded in this period from stratigraphic data.

- by Julieta Nóbile
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- Faulting (Structural Geology), Clay Minerals, Foreland Basins System, Dating

In the outermost region of the southeastern Pyrenees, a suite of thrusted folds detach above an upper Eocene salt that was about 300 m thick before deformation. The foremost anticlines formed during the Oligocene and represent a small amount of shortening. In map view; they display a relay pattern slightly oblique to the margin of the salt layer, where deformation stops. The three-dimensional edge effects caused by the pinch-out of the Cardona salt play an important role in the development of the frontal structures in the southeastern Pyrenees. Fold evolution has been reconstructed by interpreting variations along the strike of the folds as an indicator of deformation sequence. Where the sedimentary pile contains an upper detachment, thrusts developed fishtail geometries in which thrusts of alternating vergence were stacked up. Where an upper detachment is lacking, a thrusted anticline formed, into whose core salt migrated during the early phases of folding. Whether or not an upper ...

- by Jaume Vergés Masip
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- Salt Tectonics, Foreland Basins System, Pyrenees
- by Peter D Clift
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- Geology, Geophysics, Tectonics, Climate

In the outermost region of the southeastern Pyrenees, a suite of thrusted folds detach above an upper Eocene
salt that was about 300 m thick before deformation. The foremost anticlines formed during the Oligocene and represent a small amount of shortening. In map view, they display a relay pattern slightly oblique to the margin of the salt layer, where deformation stops. The three-dimensional edge effects caused by the pinch-out of the Cardona salt play an important role in the development of the frontal structures in the southeastern Pyrenees. Fold evolution has been reconstructed by interpreting variations along the strike of the folds as an indicator of deformation sequence. Where the sedimentary pile contains an upper detachment, thrusts developed fishtail geometries in which thrusts of alternating vergence were stacked up. Where an upper detachment is lacking, a thrusted anticline formed, into whose core salt migrated during the early phases of folding. Whether or not an upper detachment is present, anticlines continued to amplify during and after thrusting. Folding blocked further slip on some thrusts and promoted the development of pop-up structures.

- by M. Sans and +1
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- Salt Tectonics, Foreland Basins System, Pyrenees

- by Sorin-Corneliu Radan
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- Geology, Geodynamics, Foreland Basins System, Models

Three Upper Miocene hardgrounds have been analysed in this study, outcropping in the Latium-Abruzzi Apennines (Italy). The central Apennine hardgrounds all lie on top of the Latium-Abruzzi carbonate ramp succession and in each case are overlain by hemipelagic Orbulinamarls; these marls are linked to plate flexure-related to drowning and coeval input of terrigenous sediments. The hardground age ranges from Tortonian to Early Messinian. Phosphate precipitation in the investigated hardgrounds was confined to a thin layer (up to 15 cm) close to the sediment water interface. Here oxic to suboxic conditions prevailed, resulting in early-diagenetic iron cycling and subsequent phosphogenesis in oxygenated bottom-waters. Glaucony only occurs in the planktonic-rich marls that overlie and infill the phosphatized hardground level in the Latium-Abruzzi succession. An upwelling flux triggered phosphogenesis, promoting the early lithification of the sea floor on the platforms. After upwelling event neritic carbonate production could not be re-established on the Latium-Abruzzi platform because of the persisting eutrophic conditions and the high rates of tectonic subsidence and terrigenous input linked to Appennine orogenesis. The Latium-Abruzzi phosphorites are coeval with the Tortonian phosphogenic phase reported in the Mediterranean. Despite being a global event, regional and local factors played a major role in the hardground deposition at each site.

- by Antonello Simonetti and +2
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- Carbonate Diagenesis and Stratigraphy, Foreland Basins System, Carbonate Sedimentology

In the northern part of the Calchaquí Valley (NW Argentina), Palaeogene Andean foreland sediments are represented by a 1400-metre-thick continental succession (QLC: Quebrada de Los Colorados Formation) consisting of claystones, siltstones, sandstones, and conglomerates representing sedimentation in fluvialalluvial plains and alluvial fan settings. To understand the main syn-and postsedimentary variables controlling the clay mineral assemblages of this succession, we have studied the fine-grained clastic sediments by X-ray diffraction and electron microscopy, along with a detailed sedimentary facies analysis, for two representative sections. In the northern section, the whole succession was sampled and analysed by XRD, whereas in the second section, a control point 15 km to the south, only the basal levels were analysed. The XRD study revealed a strong contrast in clay mineral assemblages between these two sections as well as with sections in the central Calchaquí Valley studied previously. In the northernmost part of the study area, a complete evolution from smectite at the top to R3 illite/smectite mixed-layers plus authigenic kaolinite at the bottom, through R1-type mixed-layers in between, has been recognized, indicating the attainment of late diagenesis. In contrast, the clay mineral assemblages of equivalent foreland sediments cropping out only 15 km to the south contain abundant smectite and micas, subordinate kaolinite and chlorite, and no I/S mixed-layers to the bottom of the sequence. Early diagenetic conditions were also inferred in a previous study for equivalent sediments of the QLC Formation cropping out to the south, in the central Calchaquí Valley, as smectite occurs in basal strata. Burial depths of approximately 3000 m were estimated for the QLC Formation in the central and northern Calchaquí Valley; in addition, an intermediate to slightly low geothermal gradient can be considered likely for both areas as foreland basins are regarded as hypothermal basins. Consequently, the attainment of late diagenesis in the northernmost study area cannot be explained by significant differences in burial depth nor in geothermal gradient in relation to the section 15 km to the south nor with the central Calchaquí Valley. The formation of R3 mixed-layer I/S and authigenic kaolinite in the northern study area was most likely controlled by the circulation of hot, deep fluids along the reverse faults that bounded the Calchaquí valley. These faults were active during the Cenozoic, as evidenced by the syndepositional deformation features preserved in the studied sediments. Stress could also have been a driving force in burial diagenesis at the R3 mixed-layer I/S stage in these young continental sediments.

- by Fernando Nieto
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- Geology, Geophysics, Diagenesis, Foreland Basins System

Geological, geochronological and geochemical evidence suggest that several distinct parts of the Neoproterozoic orogen developed at the active margin of Gondwana are preserved in Moesia and South Carpathians. Parts of a Neoproterozoic volcanic arc and foreland basin are preserved in East Moesia while the Alpine Danubian Nappes preserve remnants of a Pan- African (Cadomian) volcanic arc and its marginal backarc basin. The East Moesian basement exposed in Central Dobrogea includes Pre-Cambrian tholeiitic metabasites from Altin Tepe showing arc/back arc affi nities, subjected to a "Cadomian" deformation together with the Neoproterozoic-Early Cambrian turbidites of Histria Formation. In subsurface of South Dobrogea, a Neoproterozoic volcano-sedimentary suite with alkali basalts, related to rifting of the Precambrian Moesian crust, was deformed during latest Neoproterozoic thusting. The Precambrian basement of the Danubian Nappes includes Pan-African island arc metavolcanics (D...

- by Viorica Iancu
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- Geology, Foreland Basins System, Proterozoic, Precambrian

- by Antonello Simonetti and +1
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- Carbonate Diagenesis and Stratigraphy, Foreland Basins System, Carbonate Sedimentology

The main rivers which drain the east and southeast side of the Eastern Carpathians and those that drain the Southern
Carpathians have been analysed regarding the sediment transit, the change of the riverbeds and the type of channel deposits. In
this paper, attention is focused on the concavity of the stream profile. On this basis, we tried to determine the evolution of some
Carpathian rivers and thus estimate their long-term evolutionary tendencies.
The concavity index of the east-Carpathian rivers shows a trend to increase from north to south from the Eastern Carpathians
to the Carpathian Bend and the Bucegi Mountains. The explanation of this situation required a review of the evolutionary stages
of the Eastern Carpathians, in order to establish the age and the evolutionary tendencies of the river network in our study area:
the Rivers Suceava, Moldova and Bistrit¸a have followed the same courses since the Sarmathian (approximately 13.5 million
years ago); the Trotus¸ River, between 10 million and 5.4 million years ago); the Rivers Putna, Buza˘u, Prahova, and Ialomit¸a
suffered the most important changes, so the age of their present course is about 2.5 million years.
The rivers could be grouped according to the mathematical model which fits best: the exponential, exponential–logarithmic,
and logarithmic model. Finally, we tried to correlate the age of the river with the form of its longitudinal profile. The customary
theoretical models require that: the older a river is, the more its concavity should increase in the headwater area and should
asymptotically approach a longitudinal equilibrium profile or ‘‘grade’’ as Davis calls it. However, the Carpathian rivers do not
follow this general tendency. What we have demonstrated is that age had no influence on the form of the longitudinal profiles
for the rivers on the exterior side of the Carpathians. This is because tectonic uplift was important, and this phenomenon is still
present today with values of over 6 mm/year.

- by dumitriu dan
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- Physical Geography, Geology, Geomorphology, Quaternary

The geologic characteristics of foredeeps and accretionary wedges suggest that these features are distinguishable on the basis of the direction of the associated subduction. East-north-east-dipping subduction-related accretionary wedges show high relief and broad outcrops of metamorphic rocks. They are associated with shallow foredeeps with low subsidence rates. In contrast, west- dipping subduction-related accretionary wedges show low relief and involve mainly sedimentary cover. The related foredeeps are deep and have high subsidence rates. This differentiation is useful both for oceanic and continental subductions, e.g., eastern vs. western Pacific subductions, or east- dipping Alpine vs. west-dipping Apenninec subductions. In a cross section of the Alps the ratio of the area of the orogen to the area of the foredeeps is at least 2:1, whereas this ratio is 0.22:1 for the Apennines. These ratios explain why foredeeps related to east- or northeast-dipping subduction are quickly filled and are bypassed by clastic rocks, whereas foredeeps related to west-dipping subduction maintain a deep-water environment longer. These differences support the presence of an "eastward" asthenospheric counterflow relative to the "westward" drift of the lithosphere detected in the hot-spot reference frame, even in the Mediterranean where no hot spots are present. In this interpretation, the Apennines foredeep was caused by the "eastward" push of the mantle acting on the subducted slab, whereas the foredeeps in the Alps were caused by the load of the thrust sheets and the downward component of movement of the upper Adriatic plate; these forces contrast with the upward component of the "eastward" mantle flow.

- by Carlo Doglioni
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- Foredeep Basins, Subsidence, Foreland Basins System, Plate Tectonics

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 for the turbiditic sedimentation is favoured, although a forearc origin was also proposed. The paper presents an overview of the main sedimentological, mineralogical and petrographical data on the turbidites, and discusses the palaeogeographic and geodynamic signifi cance of the succession in a wider context of the southern margin of the East European Craton. KEYWORDS. Central Dobrogea, foreland basin, Moesian Platform, Neoproterozoic, turbidites 2. Geological and tectonic framework of Moesia The Moesian Platform represents a lowland area, surrounded to the north and west by the Alpine belt of the South Carpathians and to the south by the Balkans (Fig. 1B). The Eastern platform margin is represented by the Peceneaga-Camena Fault (Mrazec, 1912), which runs NW from Lake Razelm on the Black Sea shore to the Vrancea zone of the East Carpathians bend zone and juxtaposes the exposed Neoproterozoic platform basement against the Triassic and Jurassic sediments of the Cimmerian North Dobrogea orogen (Figs 2A & 2B). Seismic data indicate that a 10 km step of the Moho occurs along this fault (Rădulescu et al., 1976). The Moesian Platform consists of two segments separated by the Intramoesian Fault: East Moesia, with a Neoproterozoic ("Baikalian-Cadomian") and Caledonian ("Ardennian)" cratonization, and West Moesia with a Variscan cratonization of the basement (

- by Sorin-Corneliu Radan
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- Geodynamics, Foreland Basins System, Models, Proterozoic

- by M. Sans and +1
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- Salt Tectonics, Foreland Basins System, Pyrenees

Variations in clay-mineral assemblages in ancient continental deposits are frequently used to reconstruct past climate changes. In active settings, volcanic events can supply highly labile volcaniclastic material, which can easily be transformed into smectite via diagenesis, which can produce a noticeable footprint in clay-mineral assemblages. Southern Central Andean foreland deposits are appropriate case studies to ascertain whether the climatic signal was preserved in the clay assemblages of their fine-grained sediments as tectonic uplift, volcanism, and sedimentation have been interacting since the Cretaceous. We have studied a 1400-m-thick coarsening-upward Palaeogene succession of the Tin Tin basin (northern Calchaquí Valley, Argentina), applying X-ray diffraction (XRD), electron microscopy, and detailed sedimentary facies analysis with the aim of comparing tendencies in the vertical fluctuations of clay minerals with evidence from sedimentological facies. Illite-muscovite plus smectite account for 78% to 100% of the clay minerals in the fine fraction, with kaolinite and chlorite in subordinate amounts. The vertical variation of sedimentary settings from an overbank/ lacustrine domain to fluvial braided plains and an aeolian dune field suggests a gradual increase in aridity upsection. However, smectite abundances do not show a gradual decreasing trend compatible with progressively lower hydrolyzing conditions; their relative abundances vary widely throughout the section, depicting pulse-like, abrupt fluctuations. Despite the absence of field evidence for volcanic influence, several indications of volcanic and volcaniclastic material have been found under scanning electron microscopy (SEM) in levels with high smectite abundances from the middle to the top of the succession. They include quartz crystals showing embayments and skeletal forms, with smectite filling the voids, microcrystalline silica, as well as heulandite crystals in close association with authigenic smectite. The XRD analyses of these levels evidence well-crystallized smectite, which is characteristic of a volcaniclastic origin. Therefore, the increase in smectite abundance in these beds reflects a significant volcaniclastic contribution, which is also evidenced by a centimetre-thick ash layer topward in the sequence. The only smectite-rich level near the base of the Tin Tin section also contains well-crystallized smectite associated with heulandite, thus probably evidencing volcaniclastic input. We infer that most of the smectite in these sediments formed during early diagenesis, probably through the dissolution of labile tuffaceous material. Textural and morphological analysis by SEM is essential to determine whether clay-mineral assemblages could be interpreted in terms of palaeoclimate.

- by Fernando Nieto
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- Geology, Climate Change, Electron Microscopy, Scanning Electron Microscopy

River systems of part of the Himalayan foreland, northern Bihar plains, India, are described in terms of their channel morphology, hydrology and suspended sediment characteristics. A simple classification of the river systems based mainly on the source area characteristics is proposed: (i) mountain-fed, (ii) foothills-fed, (iii) plains-fed and (iv) mixed-fed rivers. Distinct differences are noted between these classes of river systems. Most rivers show evidence of channel movement, mainly by avulsion, but cutoffs also occur locally. The mountain-fed rivers are characterized by very high discharge and low suspended sediment concentration and the plains-fed rivers have relatively low discharge and high suspended sediment concentration. The foothill-fed rivers have moderate values of discharge and suspended sediment concentration. The mountain-fed rivers have built megafans of large extent, whereas the foothills-fed and plains-fed rivers have formed muddy interfan areas. Semi-quantitative estimates of water and sediment flux suggest that about 99.9% of the mass transfer into the plains is water, with the remaining 0.1'%, being sediment, and that 10' s of the latter (0.01% of the total) is retained in the basin, the remainder being transferred to the Bengal Fan

- by Rajiv Sinha
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- Geology, Sedimentology, Mass Transfer, Hydrology

Based on calcareous nannofossils and planktonic foraminifera1 biostratigraphic data from flysch sequences, we give evidence for the paleoenvironmental evolution of Gavrovo and Ionian foreland basins (External Hellenides, Etoloakarnania region). Our data suggest that the onset of clastic sedimentation in both foreland basins in the study area is chronostratigraphically placed at Late Eocene (from 36.2-34.4 Ma; nannofossil biozones NP19-20, planktonic foraminifera biozones P16-17). During the earliest Oligocene (NP21-22 nannofossil biozones/34.4-32.45 Ma), both basins represent restricted accumulation of sediments, mainly composed of clays and silts. The presence of thick flysch deposits, accumulated during Early Oligocene (33.4-30 Ma, nannofossil zone NP23), indicates an increasing rate of sediment supply. The flysch sequences in the Ionian basin are associated with a distal depositional environment, while in the same time the sedimentation in the external part of Gavrovo basin is related to a more proximal environment that is gradually deepening. On the contrary, the internal part of Gavrovo basin is characterised by deep-water facies, deposited in the Early Oligocene. At the end of Early Oligocene and the onset of Late Oligocene (nannofossil zone NP24/30-27.2 Ma, planktonic foraminifera zone P21), the deposition of coarse grained sediments in both basins indicates a shift to shallower depositional environment. The accumulation of fine-grained sediments during Late Oligocene (27.2-23.2 Ma, NP25 nannofossil biozone) in the Ionian basin marks the youngest flysch sediments in the Etoloakarnania region and specifies the time of the Gavrovo nappe emplacement on the Ionian zone. Moreover the emplacement of Pindos nappe on the Gavrovo zone is estimated between 30-27.2 Ma (NP24 biozone) as supported by the nannofossil analysis of samples in front of Pindos thrust.

- by spilios sotiropoulos
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- Evolutionary Biology, Geology, Ecology, Biostratigraphy

376 M. SANS, JA MUNOZandJ. VERGES of the foreland-verging thrusts to intersect the surface (Gordy et al, 1977; Charles worth et al, 1987) disregarding internal structure. The term triangle zone has also been defined as the structure... more

- by Jaume Vergés
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- Geology, Stress, Foreland Basins System, Geometry

Cenozoic strata in the central Andes of northwestern Argentina record the development and migration of a regional foreland basin system analogous to the modern Chaco-Paraná alluvial plain. Paleocene-lower Eocene fluvial and lacustrine deposits are overlain by middle-upper Eocene hypermature paleosols or an erosional disconformity representing 10-15 Myr. This 'supersol/disconformity' zone is traceable over a 200,000 km 2 area in the Andean thrust belt, and is overlain by 2-6 km of upward coarsening, eastward thinning, upper Eocene through lower Miocene fluvial and eolian deposits. Middle Miocene-Pliocene fluvial, lacustrine, and alluvial fan deposits occupy local depocenters with contractional growth structures. Paleocurrent and petrographic data demonstrate westerly provenance of quartzolithic and feldspatholithic sediments. Detrital zircon ages from Cenozoic sandstones cluster at 470-491, 522-544, 555-994, and 1024-1096 Ma. Proterozoic-Mesozoic clastic and igneous rocks in the Puna and Cordillera Oriental yield similar age clusters, and served as sources of the zircons in the Cenozoic deposits. Arc-derived zircons become prominent in Oligo-Miocene deposits and provide new chronostratigraphic constraints. Sediment accumulation rate increased from ∼20 m/Myr during Paleocene-Eocene time to 200-600 m/Myr during the middle to late Miocene. The new data suggest that a flexural foreland basin formed during Paleocene time and migrated at least 600 km eastward at an unsteady pace dictated by periods of abrupt eastward propagation of the orogenic strain front. Despite differences in deformation style between Bolivia and northwestern Argentina, lithosphere in these two regions flexed similarly in response to eastward encroachment of a comparable orogenic load beginning during late Paleocene time.

- by Barbara Carrapa
- •
- Geology, Geophysics, Tectonics, Foreland Basins System

An extensive carbonate system in the Gulf of Papua (GoP), developed in the late Oligocene-middle Miocene, was buried by huge influx of siliciclastics originated from Papua New Guinea. Major episodes of siliciclastic influx in the carbonate system are related to tectonic activity in the fold and thrust belt during the Oligocene Peninsular Orogeny, late Miocene Central Range Orogeny, and late Pliocene renewed uplift and exhumation of peninsular region. Siliciclastics did not influence the carbonate deposition during the late Oligocene-middle Miocene, since they were accumulated in the Aure Trough, proximal foreland basin protecting the carbonate system. The most significant burial of the carbonate system started during the late Miocene-early Pliocene in the result of the Central Range Orogeny. However, the largest influx was related to the renewed uplift of the Papuan Peninsula during the early late Pliocene. The shelf edge prograded w150 km and formed more than 80% of the modern shelf. This high siliciclastic influx was also enhanced by the ''mid'' Pliocene global warmth period and intensified East Asian monsoons at 3.6-2.9 Ma. Although many publications exist on carbonate-siliciclastic mixing in different depositional environments, this study helps understand the carbonate-siliciclastic interactions in space and time, especially at basinal scale, and during different intervals of the carbonate system burial by siliciclastic sediments.

- by Andre Droxler
- •
- Geology, Geophysics, Tectonics, Sea Level

The foreland monocline dips underneath thrust belts and accretionary wedges, both in oceanic and continental
subduction zones. We present new data on the dip of the monocline in the frontal part of two orogens, the Alps and the
Apennines. There is an overall difference between the dip of the relative monoclines, and there is also a strong lateral
variation along both arcs. In the Alps, the regional dip varies between 0³ in the remote foreland, to an average of 2^3³ at
the front of the thrust belt below the foredeep, to about 5³ beneath the external thrust-sheets within 40 km from the
leading edge of the accretionary wedge. The regional dip of the monocline in the Apennines has an average of 4^5³ at
the front of the thrust belt below the foredeep, to about 10³ beneath the external thrust-sheets within 40 km from the
leading edge of the accretionary wedge. There are areas where the dip exceeds 20³. The Apennines though
topographically lower than the Alps present higher monocline dips and a deeper foredeep. Moreover, there are
variations in the dip of the monocline moving along the strike of the two belts: the low values coincide with Permian^
Mesozoic inherited horsts, whereas the steeper values correspond to basinal areas, and they usually match the salients of
the thrust belt front. Within the salients the distance between thrust ramps increases. Therefore, there are two orders of
mean values of the dip of the foreland monocline, the first at the orogen scale (more than 1000 km wavelength), the
second at the regional scale (100^200 km wavelength) within the single orogen. Lateral variations in the lithospheric
buoyancy due to the inherited Mesozoic stretching may explain the second order variations in foreland dip, but not the
first order mean values which seem to be more sensitive to the geographic polarity of the subduction rather than to the
lithospheric composition which is rather similar in the Alpine and in the central-northern Apennines slabs.

- by Carlo Doglioni
- •
- Geodynamics, Subsidence, Foreland Basins System, Plate Tectonics

- by Cecilia del Papa
- •
- Geology, Geophysics, Diagenesis, Foreland Basins System

The main rivers which drain the east and southeast side of the Eastern Carpathians and those that drain the Southern Carpathians have been analysed regarding the sediment transit, the change of the riverbeds and the type of channel deposits. In this paper, attention is focused on the concavity of the stream profile. On this basis, we tried to determine the evolution of some Carpathian rivers and thus estimate their long-term evolutionary tendencies. The concavity index of the east-Carpathian rivers shows a trend to increase from north to south from the Eastern Carpathians to the Carpathian Bend and the Bucegi Mountains. The explanation of this situation required a review of the evolutionary stages of the Eastern Carpathians, in order to establish the age and the evolutionary tendencies of the river network in our study area: the Rivers Suceava, Moldova and Bistriţa have followed the same courses since the Sarmathian (approximately 13.5 million years ago); the Trotuş River, between 10 million and 5.4 million years ago); the Rivers Putna, Buzȃu, Prahova, and Ialomiţa suffered the most important changes, so the age of their present course is about 2.5 million years. The rivers could be grouped according to the mathematical model which fits best: the exponential, exponential-logarithmic, and logarithmic model. Finally, we tried to correlate the age of the river with the form of its longitudinal profile. The customary theoretical models require that: the older a river is, the more its concavity should increase in the headwater area and should asymptotically approach a longitudinal equilibrium profile or ''grade'' as Davis calls it. However, the Carpathian rivers do not follow this general tendency. What we have demonstrated is that age had no influence on the form of the longitudinal profiles for the rivers on the exterior side of the Carpathians. This is because tectonic uplift was important, and this phenomenon is still present today with values of over 6 mm/year.

- by Maria RADOANE
- •
- Physical Geography, Geology, Geomorphology, Quaternary

A review of the overall features of the late Palaeozoic-early Mesozoic orogen of Southwest Japan and its Korean hinterland allows a new geodynamic model for the building of the east Asian margin to be proposed. During middle Carboniferous to early Permian times, an oceanic basin formed in a passive margin environment at a moderate spreading rate as the Honshu continental block drifted away from the Sino-Korean continent. During that period, paralic platform conditions and extensional synsedimentary tectonics prevailed in Korea. In middle Permian times, the closure of the oceanic area was responsible for Yakuno ophiolite obduction and high pressure metamorphism while highly subsiding coal basins developed in the emerged Korean hinterland. Thereafter, in late Permian times, when the Honshu block collided with the Asian margin (Akiyoshi orogeny), locally derived terrestrial clastic sedimentation in Korea has succeeded coal measure deposition with local unconformity. In early Triassic times, the collision was completed and regional uplift of the thickened crust resulted in the deposition of thick distal siliciclastic rocks in rapidly subsiding hinterland troughs (Korea) and flyschoid deposition in the Tamba foreland basin (outer zone of Southwest Japan). Middle to late Triassic medium-to low-pressure metamorphism, large-scale transcurrent tectonics and associated calc-alkaline synkinematic plutonism in the Hida and Ogcheon belts represent a post-collisional feature of the Akiyoshi orogenic event. Post-tectonic intrusives and terrestrial deposits post-date intracratonic tectonics at ca. 200 Ma. Thus, the Akiyoshi orogeny of Southwest Japan is a result of continental drift and ensuing collisional rewelding of a fragment of Sino-Korea: the Honshu microcontinent.

- by Dominique Cluzel
- •
- Earth Sciences, High Pressure, South Korea, Geodynamics

- by Goffredo Mariotti
- •
- Earth Sciences, Geodynamics, Subsidence, Foreland Basins System