Foreland Basin System Research Articles

Evolution and sedimentation in a forebulge environment: example of the late Eocene Uitoé Limestone, New Caledonia, Southwest Pacific

New litho- and biostratigraphic data for the Uitoé Limestone on the southwest coast of New Caledonia constrain its age to the E13–E15 zone (late middle–late Eocene or late Bortonian–Runangan in the New Zealand nomenclature). From the base up, the limestone sequence records a shallowing trend with evidence of emergence followed abruptly by deep basinal turbidite, indicating rapid submersion. Comparison with the adjacent area to the northwest shows that the Uitoé Limestone is part of a diachronous carbonate ramp extending in age from middle to late Eocene. Moreover, a forebulge environment is confirmed for this unit which, at a larger scale, was deposited on the distal part of a foreland basin system that had been propagating southeastwards through New Caledonia since the Paleocene. The Uitoé Limestone and its thin turbidite cover represent the youngest sedimentary deposits in a forebulge environment prior to the collisional stage and obduction of the allochthonous units over New Caledonia.

Detrital zircons from Cretaceous midcontinent strata reveal an Appalachian Mountains–Cordilleran foreland basin connection

U-Pb ages ( n = 403) of detrital zircons from the Dakota Formation in western Iowa and eastern Nebraska provide evidence for westward-flowing fluvial systems that stretched from the Appalachian highlands to the western U.S. Cordilleran foreland basin during Albian–Cenomanian time. Approximately 78% of detrital zircon grains match the ages of Grenvillian (1.3–1.0 Ga), Pan-African (750–500 Ma), and Paleozoic (500–310 Ma) bedrock sources located within the present-day Appalachian Mountains. The presence of minor detrital zircon grains of Paleoproterozoic (2.5–1.5 Ga) or Archean age (>2.5 Ga) indicates that northern source regions in Minnesota, Wisconsin, and Canada did not contribute a significant volume of sediment, as had been previously interpreted. Based on similarities between detrital zircon signatures in the midcontinent strata and time-equivalent Cordilleran foreland basin strata, Appalachian sources may have contributed a previously unrecognized volume of sediment to the Albian–Cenomanian foreland basin system. Sediment flux from the Appalachian region to the Cordilleran foreland basin during middle Cretaceous time may have been related to increased uplift and exhumation due to passage over a mantle plume track.

Neogene tectonostratigraphic evolution of allochthonous terranes in the eastern Calabrian foreland (southern Italy)

Along the Ionian side of the Calabrian Arc, Neogene-Quaternary successions overlie the Hercynian basement made up of crystalline-metamorphic tectonic units and their Mesozoic-Tertiary cover. The Neogene successions rest unconformably along the eastern border of the Sila Massif and form the Neogene basin fills. In the external portion of basins, Oligocene-Lower to Middle Miocene clastic successions, overling the variegated clay of the Sicilide Complex, outcrop. The Miocene-Quaternary evolution of the northern Calabria was mainly associated with the accrectionary processes creating Miocene wedge-top depozones onto the growing orogenic belt and flexed Adria passive margin. Middle Miocene deposits accumulated in longitudinal wedge-top depozones of the Calabrian foreland-basin system, partitioned into three depocentres: the Rossano, Ciro, and Crotone basins. The surface, subsurface and aerial-photo analyses has provided new geological data, which better define the architecture and development of the allochthonous terranes outcropping in the northeastern wedge-top basins of the Calabrian Arc. The main onland outcrop of allochthonous units is represented by the so-called Cariati Nappe. Structural investigations allowed to characterize the surface and subsurface tectonic structures detailing the style and timing of the Cariati Nappe emplacement. This structure consists of a complex NW-SE oriented back-thrust (top to the west) propagated starting from the late Tortonian time. During Messinian-Pleistocene the allochthonous terranes were involved and reworked by left-lateral NW-SE oriented transpressive fault zones. Progressive propagation of these transpressive structures compartmentalised pre-Messinian formerly continuous basin, creating distinct asymmetric depocentres during the Messinian and Pliocene. The entire Ionian Calabrian margin experienced accretion during the Neogene in consequence of which portion of Varicoulered Clays, overlain by Oligocene-Miocene successions, were extruded and emplaced into the wedge-top basins.

Cenozoic sedimentation and exhumation of the foreland basin system preserved in the Precordillera thrust belt (31-32°S), southern central Andes, Argentina

Andean retroarc compression associated with subduction and shallowing of the oceanic Nazca plate resulted in thin-skinned thrusting that partitioned and uplifted Cenozoic foreland basin fill in the Precordillera of west-central Argentina. Evolution of the central segment of the Precordillera fold-thrust belt is informed by new analyses of clastic nonmarine deposits now preserved in three intermontane regions between major east directed thrust faults. We focus on uppermost Oligocene-Miocene basin fill in the axial to frontal Precordillera at 31–32°S along the Rio San Juan (Albarracin and Pachaco sections) and the flank of one of the leading thrust structures (Talacasto section). The three successions record hinterland construction of the Frontal Cordillera, regional arc volcanism, and initial exhumation of Precordillera thrust sheets. Provenance changes recorded by detrital zircon U-Pb age populations suggest that initial shortening in the Frontal Cordillera coincided with an early Miocene shift from eolian to fluvial accumulation in the adjacent foreland basin. Upward coarsening of fluvial deposits and increased proportions of Paleozoic clasts reflect cratonward (eastward) advance of deformation into the Precordillera and resultant structural fragmentation of the foreland basin into isolated intermontane segments. Apatite (U-Th)/He thermochronometry of basin fill constrains to 12–9 Ma the most probable age of uplift-induced exhumation and cooling of Precordillera thrust sheets. This apparent pulse of exhumation is evident in each succession, suggestive of rapid, large-scale exhumation by synchronous thrusting above a single decollement linking major structures of the Precordillera.

Fluvial deposition during transition from flexural to dynamic subsidence in the Cordilleran foreland basin: Ericson Formation, Western Wyoming, USA

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

Stratigraphic and provenance evolution of the Southern Apennines foreland basin system during the Middle Miocene to Pliocene (Irpinia-Sannio successions, Italy)

The paper deals with original stratigraphic, petrographic and structural data concerning the evolution of the southern Apennines chain (Italy). The main Langhian to Pliocene deposits cropping out in the northern sector of the southern Apennines foreland basin system (Sannio-Irpinia area) have been studied and correlated in order to document the effects of tectonic changes on the evolution of sandstone detrital modes and stratigraphic architecture. The studied sandstone units can be grouped in five key intervals: a) Numidian Flysch, mostly formed by Langhian mature quartzarenitic deposits and conformable Serravallian post-Numidian successions, formed by arkosic and calciclastic arenaceous-pelitic beds (foreland depozones); b) Langhian to Tortonian San Giorgio Fm., mostly composed of quartzofeldspatic sandstones (foredeep depozone); c) Tortonian to Early Messinian, quartz-feldspatic and partly sedimentary-carbonatoclastic petrofacies, thrust-top successions (Vallone Ponticello, Villanova del Battista and San Bartolomeo fms.); d) Late Messinian quartzolithic to quartzofeldspatic sandstones (Torrente Fiumarella, Anzano Molasse and Tufo-Altavilla unit), which can be referred to infilled thrust-top basins; e) unconformity-bounded Pliocene quartzofeldspatic sandstone strata (wedge-top depozones), characterized by synsedimentary tectonic activity.Detrital modes of the Serravallian through Middle Pliocene sandstones of the southern Apennines foreland basin system testify clear provenance relations from the accreted terranes forming the southern Apennine thrust-belt. The studied clastics show almost the same blended (quartz-feldspatic) composition; this condition could be related to the tectonic transport over thrust ramp of source rocks, as suggested by the tectonic evolutionary model. This study, dealing with sedimentary provenance analysis and tectonostratigraphic evolution, provides an example of the close relations between clastic compositions and foreland basin system development in southern Apennines.

Stratigraphy, composition and provenance of argillaceous marls from the Calcare di Base Formation, Rossano Basin (northeastern Calabria)

AbstractThe Calcare di Base Formation is a part of the Rossano Basin characterizing the Foreland Basin System of northeastern Calabria. Messinian argillaceous marls from the Calcare di Base Formation have been studied to characterize the sedimentary evolution of this formation during the post-orogenic phases of the Calabria–Peloritani Arc. The mineralogical assemblage of the argillaceous marls is dominated by phyllosilicates (illite, chlorite, illite/smectite mixed layers and traces of kaolinite), carbonate minerals (calcite, aragonite and dolomite), quartz and traces of feldspars (both K-feldspars and plagioclase), gypsum and celestine. The palaeoweathering index records changes at the source, reflecting variations in the tectonic regime as shown in the A–CN–K plot, where the studied samples describe a trend typical of a source area in which active tectonism allows erosion of all zones within weathering profiles developed on source rocks. The studied samples are derived from an environment in which non-steady-state weathering conditions prevailed. This trend could record deformational events that affected the Mediterranean area during the Miocene. The Th/Sc versus Zr/Sc ratios and Al–Zr–Ti plot suggest that the samples likely record a recycling effect from their basement rocks. The geochemical proxies of these samples suggest a provenance from a mainly felsic source. The Messinian argillaceous marls record that deposition probably occurred in a semi-closed marine environment mainly subject to hypersalinity with local episodes of meteoric water influx, during a period characterized by persistent dry and warm/arid conditions alternating with relatively wet conditions.

Pre-obduction records of Eocene foreland basins in central New Caledonia: an appraisal from surface geology and Cadart-1 borehole data

The Bourail Anticline in central New Caledonia has been a target for petroleum exploration since the 1950s. It is a broad structure in which a 4-km-thick pile of Eocene turbidite (Eocene Bourail Flysch) is exposed. The Cadart-1 exploration borehole (1930 m deep) was drilled on the anticlinal axis in 1999, intersecting the Paleogene and underlying Late Cretaceous sedimentary rocks. A sedimentological, stratigraphic and provenance analysis is presented. Volcanic debris appears progressively in the upper part of the flysch, becoming predominant upwards along with the intercalation of upward-thickening and -coarsening debris flow breccia. Clinopyroxene and basalt clasts in the upper part of the flysch were derived from enriched tholeiite (E-MORB) of the Poya Terrane. The Eocene paleogeography can be interpreted as a foreland basin system with a depocentre close to the area of Bourail Anticline, an accretionary complex to the northwest and a forebulge to the southeast. This system migrated southeastward through New Caledonia from the Paleocene to the Late Eocene.

Sedimentation model of piggyback basins: Cenozoic examples of San Juan Precordillera, Argentina

Abstract Piggyback basins are one of the most important sediment storage systems for foredeep basins within foreland basin systems, so understanding the dynamics of sediment accumulation and allocyclic changes is essential. Three alluvial systems are proposed here to depict sediment movement along the piggyback basin: piedmont, axial and transference systems. We propose differentiation between open continental piggyback basins that include a transference system that is able to deliver sediment to the foredeep and closed piggyback basins that are isolated. Two idealized models of sedimentation in piggyback basins are proposed. For open piggyback basins we identify four stages: (a) the incision stage; (b) the confined low accommodation system tract; (c) the high accommodation system tract; and (d) the unconfined low accommodation system tract. Meanwhile two stages are proposed for closed ones: (a) the high accommodation system tract; and (b) the low accommodation system tract. To test these models, Quaternary deposits and a Miocene unit are analysed. The first one is controlled by climatic changes, and the second is related to tectonic activity in the Precordillera.

Mass-transport deposits in a Variscan wedge-top foreland basin (Pisuerga area, Cantabrian Zone, NW Spain)

Large-scale mass-transport deposits (MTDs) from two wedge-top depocentres in a Variscan foreland-basin system (Cantabrian Zone, Iberian Massif, northern Spain) have been studied to gain a better understanding of the processes involved in comparable deposits found in modern submarine environments. The well-exposed outcrops allow documenting the composition, internal organization and lateral changes of the MTD units, and, additionally, to know their frequency and significance in a tectonically active depositional setting. The synorogenic 5000 m-thick succession that contains these resedimented units comprises seven major tectonically controlled sequences, whose bounding unconformities were recognised by seismic-scale stratal patterns, such as fault-propagation and growth-fold geometries (wedging, truncation and onlap). These major sequences range between 4 and 0.4 Myr in duration and between 1300 and 200 m in thickness and display an overall shallowing-upward trend, from a basal MTD and deep-water sediments (prodeltaic mudstone wedges, turbidites) to shallow-marine carbonates and deltaic deposits. Each major sequence consists of one or more transgressive–regressive high-frequency sequences, up to several hundred metres in thickness, showing rapid lateral changes of facies associations across the wedge-top depocentres. The MTD units are composed of megaclasts (up to 2 km long and 360 m thick) embedded in mudstones, matrix- and clast-supported breccias and conglomerates with variable internal organization, and subordinate turbidite sandstones, deposited from slides, and gravity flows from cohesive debris flows to high-density turbidites. These en masse deposits originated from the failure of shelf to slope reaches and some of them constitute multiepisodic units resulting from several large-scale collapse events. These collapses could have been triggered by several factors, mainly related to the growth of fault-propagation anticlines during thrust emplacement. The ensuing tectonic overload would lead to strong flexural subsidence and to the modification of the basin profile. Both the major sequences and the MTD units are a useful tool for correlating the highly deformed and faulted successions across the three fault-bounded synclines and establishing a coherent stratigraphic framework.

Detrital zircon geochronology of Cordilleran retroarc foreland basin strata, western North America

AbstractWe present a compilation of 8717 U‐Pb analyses from 95 detrital zircon samples of Jurassic‐Eocene North American Cordillera foreland basin strata. Of these samples, 30 are new and previously unpublished. Variation in detrital zircon age spectra between samples records erosion or recycling of basement and cover rocks within the Cordilleran orogenic wedge. Each sample can be classified into one of six major provenance groups, whose age spectra suggest derivation from (1) Mesozoic eolianites of the western United States, (2) Paleozoic passive margin strata of the western United States, (3) Paleozoic passive margin strata of western Canada, (4) the Mogollon Highlands, (5) the Cordilleran magmatic arc, or (6) Yavapai‐Mazatzal Province crystalline basement rocks. Referencing these provenance interpretations to their location and stratigraphic deposition age produces a detailed spatial and temporal record of sediment dispersal within the foreland basin system. Late Jurassic provenance is dominated by recycling of Mesozoic eolianites from sources in the Sevier thrust belt. Cretaceous‐Eocene provenance is dominated by recycling of the passive margin, with increasing complexity upsection. We interpret that this provenance transition records a basin‐wide unroofing sequence. A composite age‐probability plot of 1539 young (<250 Ma) detrital zircons reveals at least four age‐abundance peaks that we interpret to represent periodic high‐flux magmatism in the Cordilleran arc.

Flexural versus dynamic processes of subsidence in the North American Cordillera foreland basin

Dynamic subsidence related to subduction is an important process in retroarc foreland basin systems. Dynamic subsidence in the North American retroarc foreland has been proposed as dominant in the Late Cretaceous; however, questions remain about the nature of the subcrustal load and the basin response to such processes. We present new isopach data using 130 data points covering a large portion of the U.S. and a revised flexural analysis of the Sevier foreland. Higher rigidity associated with the Wyoming craton can best model flexural subsidence directly prior to ~81 Ma. We constrain the transition from flexural to nonflexural subsidence to ~81 Ma and correlate this with large Late Cretaceous progradation. The locus of subsidence and the location of the subducted Shatsky oceanic plateau suggest that dynamic loading from viscous flow above the subducting plate is the mechanism driving dynamic subsidence in the retroarc foreland basin of the North American Cordillera.

Link between thrust tectonics and sedimentation processes of stratigraphic sequences from the southern Apennines foreland basin system, Italy

We discuss here tectonics and sedimentation processes occurring during continent-continent collision and relationships between accretionary processes on overplate, flexural lithosphere on underplate and related controls on clastic sedimentation in developing foreland basin systems. This paper focuses on and clastic sedimentation developed during the sequential history of the southern Italy orogenic system. These clastic trends, covering a large time span from pre-collisional Early Mesozoic to the present, may contribute: (1) to the paleogeographic and paleotectonic reconstructions of the southern Italy portions of the western Mediterranean orogen, and (2) to the general models of complex relationships between clastic sedimentation and paleotectonic history of other major orogens. The evolutionary record of Earth’s processes preserved in the form of sedimentary rocks has been pivotal in paleogeographical and paleotectonic reconstructions of source/basin systems. Compositional trends of clastic strata through space and time are used to infer the structural history of adjacent mountain belts and to monitor the key geodynamic changes during orogenic processes (e.g. Dickinson, 1985, 1988; Critelli & Ingersoll, 1994; Critelli, 1999). The controls on the composition and dispersal pathways of clastic strata along the convergent plate margins have long been debated (e.g. Dickinson, 1988; Ingersoll et alii, 1995). Clastic infilling of sedimentary basins in orogenic systems have been used as important indicators of tectonic activity and climatic changes. In the orogenic systems, clastic sedimentation may record the accretionary processes, the accomodation of the thrust units, and the flexural features of the foreland plate. The development of an orogenic wedge during continental collision results in thickening of the crust. The excess mass of this thickened crust acts as a load on the underthrust plate, causing it to be flexed downwards close to the load, so developing a foreland basin (e.g. Beaumont, 1981; Sinclair and Allen, 1992). During plate convergence, the vertically acting load of the mountain belt migrates over the foreland plate, thus resulting in the migration of the associated foreland basin. The foreland is the region between the front of a thrust belt and the adjacent craton (e.g. Dickinson, 1974; Bally and Snelson, 1980; Allen et alii, 1986; Miall, 1995). Large volumes of clastic sediment are derived from erosion of the thrust belt and deposited in the foreland basin. The foreland basin generally is defined as an elongate trough that forms between a linear contractional orogenic belt and the stable craton, mainly in response to flexural subsidence caused by thrust-sheet loading in the orogen.Foreland basin stratigraphy records tectonic, eustatic, and climatic changes at convergent plate margins (e.g. Miall, 1995). The formation of unconformities is the results of the interplay of temporal variations in the erosion and lateral progradation rates of the orogenic wedge, as well as tectonic and eustatic sea-level changes (e.g. Beaumont, 1981; Jordan, 1981; Schedl & Wiltsc hko, 1984; Peper et alii, 1995).

High-pressure metamorphism in the Early Variscan subduction complex of the SW Iberian Massif

Several units exposed in the boundary area of the Ossa Morena Zone (OMZ) and the South Portuguese Zone (SPZ) preserve petrographic and thermobarometric evidence for an early metamorphic episode (M1), developed under a high-P, low to intermediate-T gradient, related to Early Variscan subduction in the SW Iberian Massif. In the OMZ, these are the Cubito–Moura Unit (Pmin~9.2kbar and T=395±45°C), blueschists from its basal mélange (Pmin~12.4kbar and T=310±11°C), and the underlying Fuenteheridos Group (P=10.9±0.4kbar and T=449±31°C). The equivalent units in the SPZ are the La Minilla Formation (P=8.7±0.4kbar and T=388±16°C) and the lawsonite pseudomorphs-bearing Pulo do Lobo Formation. All these units formed part of an approximately NE verging orogenic wedge (present coordinates) developed by the accretion of subducted slabs of the outermost margin of Gondwana and other elements of the Rheic Ocean realm, from at least the Middle Devonian to the lowermost Tournaisian. High-pressure rocks were subsequently emplaced on more internal zones of the OMZ that only experienced a younger high-T, low to intermediate-P metamorphism (M2). This high-T event was coeval with magmatic activity from the uppermost Devonian to the Middle Mississippian, probably as a consequence of transtensional lithospheric thinning and/or delamination of the lower crust and mantle lithosphere of the Gondwana margin. Pre-Late Devonian synorogenic sedimentation in forearc and back-arc basins of the subduction complex evolved to a Late Devonian–Middle Mississippian foreland basin system in early collisional stages. Finally, a new Middle–Late Mississippian fold-and-thrust belt with opposite (SW) vergence and new foreland basins developed during late collisional stages.

Thick-skinned tectonics in the Oriente foreland basin of Ecuador

Abstract The Oriente Basin is part of the retro-arc foreland basin system that developed in the zone of transition between the Central Andes and the Northern Andes since Late Cretaceous times. It is deformed by thick-skinned tectonics related to the inversion of pre-Cretaceous extensional fault systems, which have broken the basin into three tectonic domains during three mean periods of inversion (Late Cretaceous–Palaeocene, Early Eocene and Miocene). The northern part of the present-day Sub-Andean wedge-top corresponded, during the Late Cretaceous, to the forebulge depozone. The NNE–SSW Sacha–Shushufindi Corridor (SSC) extends from the northern region of the Oriente foredeep to the Sub-Andean Cutucú Cordillera. It results from inversion of the Late Triassic–Early Jurassic rifting. The eastern Capiron–Tiputini Inverted System (CTIS) results from the inversion of the normal faults of the Late Jurassic back-arc basin. The Ishpingo–Tambococha–Tiputini (ITT) trend is located in the present-day forebulge depozone of the basin. This position presents favourable conditions for oil biodegradation. Source rocks throughout the Oriente Basin are immature or poorly mature. A large part of oil accumulations must be explained by long-distance migration from the west, before the Eocene uplift of the Cordillera Real, or from the south.

The Qs problem: Sediment volumetric balance of proximal foreland basin systems

AbstractAlthough the stratigraphy of sedimentary basins depends on the balance between the magnitude and grain‐size characteristics of the sediment supply (Qs) and the spatial distribution of tectonic subsidence generating accommodation σ(x), Qs is problematical to measure in present‐day sediment routing systems and formidably difficult to predict in their ancient counterparts. This challenge was tackled by treating the sediment discharge from the outlet of mountain catchments as the result of incision by a drainage network with a bulk diffusivity based on the length over which the mean annual rainfall is concentrated. The size, relief and slope of palaeo‐catchments acting as feeders for sediment routing systems are used to run simulations of sediment discharge and bulk diffusivity for a range of annual precipitation values. A wide range of observable geological phenomena can be used to converge on the most likely solutions for Qs, including depositional volumes in the basin, and bedrock thermochronology and detrital cosmogenic nuclide dating to constrain catchment erosion rates. Modelled sediment discharges can be checked with estimates derived from global regressions. The sediment efflux of mountain catchments serves as a boundary condition for down‐system sediment transport and deposition. Variations in the volumetric ratio of sediment supply to available accommodation, Qs/σ(x), determines patterns of transverse versus longitudinal (axial) sediment dispersal. The volumetric ratio may change as a result of variations in climatic parameters, tectonic uplift rate and catchment expansion. An abrupt climate change to higher precipitation values promotes higher Qs/σ(x), but transient landscape response causes a return to values close to the baseline, generating a distinctive down‐system extension of a gravel ‘spike’. Catchment expansion has a similar, but more prolonged, effect on gravel progradation. In contrast, a change in tectonic forcing, such as an increase in slip rate on a border fault, causes little change in Qs/σ(x), because increased subsidence compensates for the increased sediment supply. Studies of mid Eocene–Oligocene sediment routing systems in the south‐central Pyrenees allow the discrimination of different types of proximal wedge‐top sedimentary systems on the basis of the volumetric ratio of Qs to accommodation σ(x): (i) small, steep, local fan systems in tectonically ponded, underfilled basins, supplied by low sediment discharges; (ii) tectonically guided, long‐range, axial systems fed by large sediment discharges from widely spaced palaeovalleys; and (iii) large, shallow‐sloping transverse megafans burying underlying defunct or active tectonic structures, supplied by high to very high sediment discharges. Understanding the role of variations in Qs helps to explain the syntectonic evolution of proximal foreland basin systems. The Oligocene–Miocene North Alpine Foreland Basin, Switzerland, is qualitatively identified as a high‐Qs example, the Miocene–Recent northern Apennines of Italy as a low‐Qs example and the Eocene‐Oligocene southern Pyrenees of Spain as intermediate in character.

Thick-skin orogen–foreland interactions and their controlling factors, Northern Andes of Colombia

Abstract The study draws from reflection seismic, in-situ stress and low-temperature geochronology data on the Eastern Cordillera–Llanos foreland basin system of Colombia, which is an example of the retro-wedge of the orogen with an advancing subduction zone. The system was obliquely converging during deposition of the Lower Oligocene–Lower Miocene Carbonera to recent Guayabo formations, recording it by the northeastward depocentre shift in the proximal Llanos Basin. While the southern portion of the foreland did not flex and undergo flexural normal faulting after Carbonera deposition, the northern portion did. The earthquake data indicate that the northern Eastern Cordillera undergoes strengthening by internal deformation, while the southern segment is already strong enough to undergo significant displacements dominantly along its bounding fault systems. Furthermore, the southern segment initiated detachment of the first thick-skin blocks from the proximal Llanos Basin. Such co-existence of different convergence maturity stages along the orogen strike allows unravelling of its development starting with internal deformation and foreland flexure, followed by mountain building and large-scale boundary fault displacements, to the large-scale foreland deformation. The onset of new foreland accretion seems to be controlled by the resistance of the foreland plate to flexing, given that the orogenic engine continues to drive convergence. Supplementary material: Discussion of evidences for dextral transpression in the Eastern Cordillera, data on exhumation history of the Eastern Cordillera and colour versions of Figures 4–6 are available at http://www.geolsoc.org.uk/SUP18629

Tectonostratigraphy of the Cenozoic Tumaco forearc basin (Colombian Pacific) and its relationship with the northern Andes orogenic build up

The new tectono-stratigraphic setting of the Tumaco forearc basin based on outcrop logging, cutting description from deep oil wells, new biostratigraphy on calcareous nanofossils and sandstone petrography allows a margin scale comparison of the basin response to the Caribbean and Farallón/Nazca subduction under the South American margin. The results are compared to the laterally continuous Ecuadorian Borbón forearc basin and other southern Colombian basins: Patía sub-basin, Upper Magdalena Valley and southern Putumayo-Caguán basins. The proposed basement of the Tumaco basin is a Colombian Caribbean Oceanic Plateau (CCOP) sliver docked with Santonian-Campanian island arcs that was incorporated into the Colombian Pacific forearc during the Paleocene to Eocene. The filling of the Tumaco basin started with the Oligocene Unidad 1 Sur and the Early-Middle Miocene Cayapas/Viche/Angostura/Formations in a bathyal depositional setting. At Late Miocene to Holocene, a succession of volcaniclastic units was deposited in shallower environments: the Chagüí, San Agustín and Cascajal formations, and the recent volcaniclastic fans. The Late Cretaceous evolution of Northern Andes in Colombia was influenced by the collision and fragmentation of the Colombian Caribbean Oceanic Plateau, producing in the west the Tumaco block basement and an oceanic remnant basin in Patía Valley. The convergence between the Farallón/Nazca and South American plates since Paleocene allowed the development of the Pacific forearc as well as shortening leading to the uplift of the Central Cordillera and formation of the foreland basin system, which later was divided into the Upper Magdalena Valley broken foreland basin and the southern part of the Putumayo-Caguán foreland basin. Since Miocene, events in addition to plate convergence as the collision of the Baudó-Panamá Arc and the subduction of Carnegie Ridge perturbed the subduction zone in southern Colombia. The integration of all of these tectonic events offers a new improved dynamic framework for the evolution of this region. Un Nuevo marco tectono-estratigráfico para la cuenca de antearco de Tumaco basado en la descripción de afloramientos y de ripios de pozos profundos, nueva bioestratigrafía de nanofósiles calcáreos y petrografía de areniscas permite inferir cómo es la respuesta de la cuenca a la subducción de las placas Caribe y Farallón/Nazca bajo el margen de Suramérica. Los resultados son comparados con la colindante cuenca de Borbón en Ecuador y otras cuencas del sur de Colombia: sub-cuenca de Patía y las cuencas del Valle Superior del Magdalena y del Putumayo-Caguán en su parte sur. El basamento propuesto para la Cuenca de Tumaco es una astilla del Plateau Oceánico Colombo-Caribeño (CCOP) acoplada con arcos de isla de edad Santoniano-Campaniano que fue incorporada dentro del antearco Pacífico Colombiano entre el Paleoceno y el Eoceno. El relleno de la cuenca de Tumaco comenzó con la Formación Unidad 1 Sur en el Oligoceno y las Formaciones Cayapas/Viche/Angostura en el Mioceno medio-tardío en un ambiente de depósito batial. Entre el Mioceno tardío y el Holoceno, una secuencia de unidades volcaniclásticas definidas por las Formaciones Chagüí, San Agustín y Cascajal y los abanicos volcaniclásticos recientes fue depositada en ambientes más someros. La evolución de los Andes Norandinos en Colombia durante el Cretácico tardío estuvo influenciada por la colisión y fragmentación del Plateau Oceánico Colombo-Caribeño que produjo en el oeste el bloque de basamento de la cuenca de Tumaco y una cuenca oceánica remanente en el valle del Patía. La convergencia de las placas Farallón/Nazca permitieron el desarrollo del antearco Pacífico, así como también del acortamiento cortical que permitió el levantamiento de la Cordillera Central y el desarrollo del sistema de cuencas antepaís, el cual fue dividido en la cuenca rota de antepaís del valle superior del Magdalena y la parte sur de la cuenca de antepaís del Putumayo-Caguán. Desde el Mioceno, eventos adicionales a la convergencia de placas, tales como la colisión del arco de Baudó-Panamá y la subducción del ridge de Carnegie modificaron la zona de subducción en el sur de Colombia. La integración de todos estos eventos tectónicos permite establecer un marco dinámico mejorado para entender la evolución en esta región.

Provenance and accommodation pathways of late Quaternary sediments in the deep-water northern Ionian Basin, southern Italy

The northern Calabria along the southeastern coast of Italy provides a favorable setting in which to study complete transects from continental to deep-marine environments. The present northern Ionian Calabrian Basin is a wedge-top basin within the modern foreland-basin system of southern Italy. The Ionian margin of northern Calabria consists of a moderately developed fluvial systems, the Crati and Neto rivers, and diverse smaller coastal drainages draining both the Calabria continental block (i.e., Sila Massif) and the southern Apennines thrust belt (i.e., Pollino Massif). The main-channel sand of the Crati and Neto rivers is quartzofeldspathic with abundant metamorphic and plutonic lithic fragments (granodiorite, granite, gneiss, phyllite and sedimentary lithic fragments). Sedimentary lithic fragments were derived from Jurassic sedimentary successions of the Longobucco Group. The mud samples contain mostly phyllosilicates, quartz, calcite, feldspars and dolomite. Traces of gypsum are present in some samples. The I–S mixed layers, 10Å-minerals (illite and micas), chlorite and kaolinite are the most abundant phyllosilicates, whereas smectite and chlorite/smectite mixed layers are in small amounts. The geochemical signatures of the muds reflect a provenance characterized by both felsic and mafic rocks with a significant input from carbonate rocks. Furthermore, the degree of source-area weathering was most probably of low intensity rather than moderately intense because CIA values for the studied mud samples are low. Extrapolation of the mean erosion budget from 1 to 25Ma suggests that at least 5 to 8km of crust have been removed from the Calabrian orogenic belt and deposited in the marine basins. The Calabrian microplate played an important role in the dynamic evolution of southern Italian fossil and modern basins, representing the key tectonic element of the entire orogenic belt.

Regional structure and kinematic history of the Cordilleran fold-thrust belt in northwestern Montana, USA

The Cordilleran thrust belt of northwestern Montana (United States) has received much less attention than its counterparts in the western interior of USA and Canada. The structure of the thrust belt in this region is well preserved and has not been strongly overprinted by Cenozoic extension, providing an opportunity to reconstruct its geometry and to relate it to the foreland basin system. The thrust belt in this region consists of a frontal part of highly deformed Paleozoic, Mesozoic, and Paleocene sedimentary rocks, and a western region dominated by a >15-km-thick succession of Proterozoic Belt Supergroup strata underlain by faults of the Lewis thrust system. The frontal part can be subdivided into the foothills and the Sawtooth Range. At the surface, the foothills show deformed Mesozoic and Paleocene rocks; at depth, refl ection seismic data indicate numerous thrust faults carrying Paleozoic strata. The Sawtooth Range, south from the Lewis thrust salient, is defi ned by steeply dipping imbricate thrusts that detach at the basal Cambrian stratigraphic level. The Sawtooth Range plunges northward beneath the Lewis thrust salient and diverges into a pair of independent thrust systems that form the Flathead and Waterton duplexes in Canada. The relatively minor internal deformation in the western part of the thrust belt resulted from the great rheological strength of the Belt Supergroup rocks and initial high taper of the preorogenic stratigraphic wedge. A new ~145-km-long balanced cross section indicates ~135 km of shortening, a value similar to that in the southern part of the Canadian thrust belt. Previous work and new conventional and isotopic provenance data from the foreland basin and U-Pb ages from crosscutting intrusive rocks establish a preliminary kinematic model for this segment of the Cordilleran thrust belt. The emerging pattern is a relatively simple forelandward progression of thrusting events. Most shortening in the Lewis thrust system, Sawtooth Range, and foothills occurred roughly between mid-Campanian and Early Eocene time (ca. 75‐52 Ma), yielding a shortening rate of ~5.9 mm/yr. This pattern differs from the pattern of shortening in the better known Sevier thrust belt to the south, where regional far-traveled Proterozoic quartzitebearing thrust sheets were mainly active during Early Cretaceous time. From Middle Eocene to Early Miocene time, this sector of the Cordillera collapsed, generating a number of extensional depocenters.