Foreland Area Research Articles

Benefits of migration in relation to nutritional condition and predation risk in a partially migratory moose population

The costs and benefits of alternative migratory strategies are often framed in the context of top-down and bottom-up effects on individual fitness. This occurs because migration is considered a costly behavioral strategy that presumably confers explicit benefits to migrants in the form of either decreased predation risk (predation risk avoidance hypothesis) or increased nutrition (forage maturation hypothesis). To test these hypotheses, we studied a partially migratory moose (Alces alces) population and contrasted explicit measures of predation risk (i.e., offspring survival) and nutrition (i.e., accumulation of endogenous energy reserves) between resident and migratory subpopulations. We relied on data collected from migratory and nonmigratory radio-marked moose (n = 67) that inhabited a novel study system located in coastal Alaska between 2004 and 2010. In this area, 30% of the population resides year-round on a coastal foreland area, while 48% migrate to either a small island archipelago or a subalpine ridge system (the remainder exhibited one of six different low-occurrence strategies). Overall, we determined that accumulation of body fat during the growing season did not differ between migratory or resident modalities. However, calf survival was 2.6-2.9 times higher for individuals that migrated (survival, islands = 0.49 +/- 0.16 [mean +/- SE], n = 35; ridge = 0.52 +/- 0.16, n = 33) than those that did not (survival, resident = 0.19 +/- 0.08, n = 57). Our results support the predation risk avoidance hypotheses, and suggest that migration is a behavioral strategy that principally operates to reduce the risk of calf predation and does not confer explicit nutritional benefits. We did not directly detect trade-offs between predation risk and nutrition for migratory individuals. Yet we identify an indirect life history mechanism that may mildly dampen the apparent fitness benefits of migration. The proximate factors accounting for differences in migration-specific neonate survival are likely linked to accessibility of refugial habitats for moose at local and landscape scales, landscape factors that affect hunting efficacy of large carnivores, and interactions with rural human communities. Conservation of ungulate populations can be aided by integrating knowledge about migratory behavior, life history strategies, and factors that alter ungulate vulnerability, particularly those induced by human activity.

The analysis of technology of drilling with roller bits on the Carpathian foreland area in the years 1995-2011

The analysis of technology of drilling with roller bits on the Carpathian foreland area in the years 1995-2011

Paleo and Neo-Tectonics of the Mosul Fault and its Impact on the Tectonics of the Foreland Area of Iraq

Paleo and Neo-Tectonics of the Mosul Fault and its Impact on the Tectonics of the Foreland Area of Iraq

Neogene syn-tectonic sedimentation in the eastern margin of Arakan–Bengal basins, and its implications on for the Indian–Asian collision in western Myanmar

The Arakan Basin is one of the major sedimentary basins formed in the frontal part of the Himalayan orogenic belt since the Late Cenozoic. Defining one of the four major sedimentary basins of Myanmar, it is geomorphologically and tectonically differentiated from the others. The study area along the westernmost edge of Myanmar is separated from the Arakan Yoma (Indo–Burman Ranges) by a narrow coastal strip and is bordered by the Bay of Bengal to the west.Regional stratigraphic correlation and the geological age of the siliciclastic sequences were established based on planktonic foraminiferal zonation. Deep marine slope and shelf environments during Early- to Middle Miocene (ca. 21.5–11Ma), and a southward prograded shelf–delta environment during Late Miocene to Pliocene time were determined.The Early Miocene underthrusting along the Himalayan front is well documented by the forced-regressive sedimentation patterns in the slope and shelf systems, sediments of which derived from the paleo-Ganges–Brahmaputra river systems in the Bengal–Arakan basins. Sequential evolution of the Miocene successions manifests in forced regressive wedged systems tracts. These evolved through slope by-passing and slumping and, following deep-marine channel in-filling, began to accumulate an increasing sediment load due to the rapid fall of sea level by the uplift in the hinterlands during the Early- to early-Middle-Miocene.The formation of a shelf–delta systems marks a dramatic shift in the evolution of the southward prograding delta systems following a eustatic sea-level low. In the foreland areas, erosional off-loading with foreland uplifting caused a wide active fluvial systems and formed transverse rivers distally in the late-Middle- to Late-Miocene.

Structural setting of the Adriatic basin and the main related petroleum exploration plays

Most of the oil and gas resources located within the Adriatic domain are genetically linked to the flexure of the Adria continental margin and to the evolution of the Apennines fold and thrust belt. The source rocks contained in the pre-flexure epi-continental successions reached the maturity window during the flexural subsidence or, alternatively, the flexural accommodating siliciclastic flysch themselves generated and stored hydrocarbons. The petroleum exploration plays of the Adriatic domain are tentatively classified in this paper, according to their geological evolution with respect to the Apennines fold and thrust belt.The description of the geological evolution of these structures and related petroleum plays are described, including plays set in undeformed or poorly deformed foreland areas. A new isochrones map showing the structural setting of the substratum at the level of the Fucoidi Fm. is presented. Several different groups of structures can be recognized in the Adriatic domain, that can be connected to the final phases of deformation of the Apennines, or to the interaction with the Dinarides fold and thrust belt front to the east.

Tectonic development of the North Patagonian Andes and their related Miocene foreland basin (41°30′‐43°S)

The Northern Patagonian Andes have been constructed through multiple mechanisms that range from tectonic inversion of extensional structures of Early to Middle Jurassic age in the Main Andes to Oligocene in the Precordilleran region. These have acted during two distinctive orogenic stages, first in late Early Cretaceous and later in Miocene times Late Oligocene extension separates these two contractional periods and is recorded by half‐grabens developed in the retroarc region. The last contractional stage coexists with an eastward foreland expansion of the late Miocene arc whose roots are presently exposed as minor granitic stocks and volcanic piles subordinately in the Main Andes, east of the present arc. As a consequence of this orogenic stage a foreland basin has developed, having progressed from 18 Ma in the main North Patagonian Andes, where the mountain front was flooded by a marine transgression corresponding to the base of the Ñirihuau Formation, to 11 Ma in the foreland area. Cannibalization of this foreland basin occurred initially in the hinterland and then progressed to the foreland zone. Blind structures formed a broken foreland at the frontal zone inferred from growth strata geometries. During Pliocene to Quaternary times most of the contractional deformation was dissipated in the orogenic wedge at the time when the arc front retracted to its present position.

Structure and U–Pb zircon geochronology in the Variscan foreland of SW Sardinia, Italy

New field mapping, U–Pb zircon geochronology and structural analysis of the southernmost Sardinia metamorphic basement, considered a branch of the Variscan foreland, indicate that it is, in part, allochthonous and was structurally emplaced within the foreland area, rather than being older depositional basement beneath the foreland succession. The Bithia Formation, classically considered part of the ‘Southern Sulcis metamorphic Complex’ (and here termed the Bithia tectonic unit, or BTU), is a greenschist facies metamorphic unit commonly interpreted as Precambrian in age. New geochronology of felsic volcanic rocks in the BTU, however, yield a U–Pb zircon age of 457.01 ± 0.17 Ma (Upper Ordovician). Thus, the depositional age of the unit is younger than the weakly metamorphosed Lower Cambrian rocks of the adjacent foreland succession. New detailed mapping and analysis of the field relationships between the BTU and foreland succession indicates that their contact is a mylonitic shear zone. The metamorphic character, general lithology, and deformational history of the BTU are similar to those of units in the Variscan Nappe Zone located northeast of the foreland area. We reinterpret the BTU as a synformal klippe of material related tectonically to the Variscan Nappe Zone. We infer that it was thrust over and became infolded into the foreland during late stages of the Variscan contractional deformation. Copyright © 2012 John Wiley & Sons, Ltd.

Repeated eastward shifts of arc magmatism in the Southern Andes: A revision to the long-term pattern of Andean uplift and magmatism

Abstract The Southern Andes have been built through the stacking of crustal sheets in discrete periods during the last 100 My. The first important shortening took place in Late Cretaceous at the time of eastward arc expansions potentially linked to two areas of subducted slab shallowings of 200 and 800 km wide respectively. These shallowings have progressed to two smaller flat slabs in Eocene times, where rather anhydrous subducted slabs generated a discontinuous arc emplaced in the foreland area at the time of mountain building. Discrete segments of the former Late Cretaceous slab shallowings would have fallen down at this time producing early slab steepening settings where within-plate products and extensional basins developed such as in the southern Chubut Province. Then Late Oligocene times coincide with the final steepening of the broad Late Cretaceous to Eocene shallow subduction zone with the emplacement of voluminous volcanic plateaux in central Patagonia and extensional basins in the hinterland zone. Lately a long quiescence period was interrupted by the development of three Miocene shallow subduction settings more than 400 km long each, evidenced by arc expansions and associated with Andean construction. Most of these areas were extensionally reactivated in the last 5 My at the time of retraction and steepening of formerly shallow subduction zones, being associated with voluminous mantle derived materials and shallow asthenospheric injection. While some of these shallow subduction configurations could be explained by subduction of highly buoyant oceanic lithosphere related to seismic ridges, in particular those of the Aluk/Farallones and Chilean ridges, other mechanisms remain more speculative. The alternation of shallow subduction zones and their steepening in the last 100 My in the Southern Andes explain location and timing of main magmatic fluxes in the arc and retroarc areas, as well as the presence of coeval foreland mountain systems east of the Main Andes.

U/Pb ages on detrital zircons in the southern central Andes Neogene foreland (36°–37°S): Constraints on Andean exhumation

Abstract U/Pb dating on detrital zircons was performed in the Pampa de Carrizalito depocenter of the Late Miocene foreland basin associated with the Southern Central Andes orogenic front. This reveals Andean and pre-Andean components in magmatic derived zircons inhomogeneously distributed through the sequence. Andean, Grenville, Pampean, Famatinian and Gondwanic components reveal a complex source distribution from either the Main Andes, Coastal Cordillera and basement foreland areas. These are discussed showing different patterns in the context of the Andean orogenic cycle. Cretaceous and Jurassic components that are partly related to Mesozoic batholiths, developed at the western slope of the Andes at these latitudes, have a very contrasting behavior through the sequence: While Jurassic grains are represented from base to top, Cretaceous ones dilute upwardly. This is explained through the progressive uplift of the Southern Central Andes that could have created a barrier to Cretaceous and Jurassic detritus, while the older ones could have had either an alternative source area represented by the inverted rift system of the Huincul Ridge in the foreland area and the Cordillera del Viento in the hinterland area or the reworking of Jurassic sedimentary sequences of the Neuquen basin. Finally, a progressive enrichment in pre-Andean components to the top of the sequence is interpreted as related to the development of a broken foreland and the consequent rapid expansion of the orogenic front at the time of development of a slab shallowing setting in the region as shown by previous works.

Tectonic evidence for the ongoing Africa‐Eurasia convergence in central Mediterranean foreland areas: A journey among long‐lived shear zones, large earthquakes, and elusive fault motions

We investigate the role of the Africa‐Eurasia convergence in the recent tectonic evolution of the central Mediterranean. To this end we focused on two sectors of the Adriatic‐Hyblean foreland of the Apennine‐Maghrebian chain as they allow tectonic evidence for relative plate motions to be analyzed aside from the masking effect of other more local tectonic phenomena (e.g., subduction, chain building, etc.). We present a thorough review of data and interpretations on two major shear zones cutting these foreland sectors: the E‐W Molise‐Gondola in central Adriatic and the N‐S Vizzini‐Scicli in southern Sicily. The selected foreland areas exhibit remarkable similarities, including an unexpectedly high level of seismicity and the presence of the investigated shear zones since the Mesozoic. We analyze the tectonic framework, active tectonics, and seismicity of each of the foreland areas, highlighting the evolution of the tectonic understanding. In both areas, we find that current strains at midcrustal levels seem to respond to the same far‐field force oriented NNW‐SSE to NW‐SE, similar to the orientation of the Africa‐Eurasia convergence. We conclude that this convergence plays a primary role in the seismotectonics of the central Mediterranean and is partly accommodated by the reactivation of large Mesozoic shear zones.

Sedimentary and tectonic evolution in the eastern Po-Plain and northern Adriatic Sea area from Messinian to Middle Pleistocene (Italy)

In the last 15 years, several Eni-Agip multidisciplinary studies were focused on the buried Messinian–Pleistocene succession of the eastern Po Plain and northern Adriatic Sea. A detailed revision of the biostratigraphy, chronostratigraphy, sedimentology, seismic interpretation and sequence stratigraphy was performed using the very large Eni subsurface dataset including regional 2D and 3D seismic surveys and over 500 deep wells. The new basin-scale geological model of the area is presented in this paper. During the Messinian and the Plio-Pleistocene the eastern sector of the Po Plain and the northern Adriatic Sea were part of the northern Apennine foreland basin. In this time span, the tectono-sedimentary evolution of the area largely coincides with the development of the Po Plain-Adriatic Foredeep (PPAF), of its ramp and foreland areas and of the related northern Apennine thrust-top basins. During latest Tortonian–Pliocene interval, as a consequence of the severe Apennine compressional tectonics, the PPAF underwent four major phases of deformation and depocenter migration towards the foreland (NE). These phases also generated four basin-scale tectonic unconformities referred here as Late Tortonian Unc., Intra-Messinian Unc., Intra-Zanclean Unc. and Gelasian Unc. The Messinian to Pleistocene PPAF sedimentary succession can be subdivided in four allogroups bounded by the basin-scale tectonic-generated unconformities: EM (pre- and syn-evaporitic Messinian), LM (post-evaporitic Messinian–early Pliocene), EP (early-middle Pliocene) and LP (late Pliocene–Pleistocene). The allogroup boundaries are produced by major compressional events generating phases of migration of the foredeep depocenters towards the foreland and abrupt changes in type and distribution of depositional systems. The foredeep succession is mainly composed of turbidites with prevailing highly-efficient Type I turbidite systems. Turbidite sand/sandstone lobes and turbidite basin plain deposits are the most common facies associations. Allogroup EM: the foredeep is subdivided in two different depocenters by the Emilia-Romagna arc. The foredeep succession is represented by the turbidite sandstones and shales of the Bagnolo Fm. Shelfal, marginal marine and evaporitic sediments are deposited in the Veneto and northern Adriatic foreland basin. Allogroup LM: during the post-evaporitic Messinian, the turbidites of the Fusignano Fm. are deposited within the foredeep basin, while most of the foreland area is subaerially exposed and eroded by deep incised-valleys. The base of the Pliocene corresponds to an abrupt eustatic rise. Poorly-efficient turbidites of the Canopo Fm. deposited within the foredeep basin. The foreland is interested by a rapid southward progradation following the transgressive phase. Allogroup EP: activation of the inner thrust of the Ferrara fold-belt and foredeep fragmentation. Deposition of highly-efficient turbidites belonging to the Porto Corsini and “inner” Porto Garibaldi Fms. Deposition of condensed shales in the foreland area. Allogroup LP: complete deformation of the Ferrara folds and of the northern Adriatic thrust-and-fold belt. Onset of a new foredeep basin in the eastern Veneto and northern Adriatic Sea and sedimentation of the highly-efficient turbidites of “outer” Porto Garibaldi and Carola Fms. During the middle Pleistocene the Po Plain progradation leads to the complete filling of the foreland basin.

Late Miocene–early Pliocene onset of N–S extension along the southern margin of the Central Andean Puna Plateau: Evidence from magmatic, geochronological and structural observations

Extensional faulting typifies many of the Earth's Cenozoic orogenic plateaus. The Altiplano–Puna Plateau in the southern central Andes is the world's second largest orogenic plateau; it contains a rich array of extensional fractures and normal faults with closely associated mafic volcanic flows, dykes, and cones. This is in stark contrast to the foreland areas, which record protracted shortening and continuous eastward growth of the mountain belt. Within the Puna area a kinematic change-over from shortening to extension has previously been inferred to have occurred during the Quaternary. However, our research in the southern Puna, together with earlier petrologic investigations in the south-central part of the plateau, indicates an earlier onset for the extensional tectonism. Our analysis has focused on the eastern portion of the Cordillera de San Buenaventura in the southernmost part of the plateau, where we mapped two Upper Miocene–Pliocene volcanic units associated with extensional faulting — the Aguada Alumbrera Ignimbrite and the La Hoyada Volcanic Complex. The structural inventory of these units records N–S extensional deformation in the Puna associated with the development of E–W oriented fractures, dykes, normal and strike–slip faults, and folds. New 40Ar/ 39Ar dating of magmatic rocks together with their relationships with the mapped structures reveal that widespread extension in the southern Puna had already commenced by ~ 5 Ma, and possibly as early as 7 Ma. Although the extensional structures on the Puna are typically associated with mafic volcanism, the Upper Miocene–Pliocene La Hoyada Volcanic Complex hosts dykes of intermediate compositions. Mafic to intermediate magmatism and extensional tectonism in this region is thus contemporaneous with, and structurally akin to, that in the central and northern parts of the plateau. The ubiquitous cogenetic relationship between mafic volcanism and extensional tectonism, both within the Puna Plateau and along its eastern flanks, clearly indicates that the normal faulting is a regional phenomenon that is broadly coeval with an inferred rapid and large-scale uplift of the Altiplano–Puna Plateau and a decrease in plate convergence rates. These observations are compatible with a mantle-delamination scenario, in which the delamination of lithospheric mantle may have produced an ensuing weakening of the crust and regional uplift, which may in turn have generated the conditions necessary to trigger gravitational extensional collapse, beginning in the late Miocene to early Pliocene.

Past and present interaction between the catchment and the valley floor: Upper Osoblaha basin, NE Sudetes slope and foreland

The Osoblaha basin includes the north-eastern slope of the Zlatohorska Vrchovina ridge and the north-eastern foreland area of the undulating Głubczyce Plateau. Rainfall ranges from 1000 mm/year in the highlands to 650–700 mm/year on the Głubczyce Plateau. The mountain part of the Osoblaha basin was already penetrated by humans in prehistoric times. Miners extracted gold from the alluvia and later from the slope covers. Their activities have left traces such as extant pits in sediments. Iron and other ores were mined and processed there from the early Middle Ages onwards. In the 12th or 13th century at the latest, settlements and towns were founded for mining (e.g. Janov, Zlate Hory) and by farmers who tilled the land at the foot of the valley slopes. This exploitation of the mountainous part of the basin caused significant clearance of beech forests as the wood was used to manufacture charcoal. The deforestation of the valley slopes or the introduction of spruce forests in lieu of the beech forests changed the circulation of rain and thaw water. Exposed slope covers were prone to erosion or liquefaction and transfer towards the mountain valleys. Flood episodes caused the sedimentation of clayey overbank deposits, which cover the valley floor. The considerable cohesion of these sediments was conducive to the formation of meandering or anastomosing channels which were a typical feature of the Osoblaha valley floor in the area around the confluence of the Zlaty Potok–Prudnik in the second half of the 18th century and in the 19th century. The Głubczyce Plateau is a 30–40 km wide area consisting of undulating plateaux ranging from 320 to 240 m a.s.l. These are dissected by dry valleys and descend gently towards the north. Fertile soils, the abundance of local streams and a climate conducive to farming led to this area being settled by farming and herding communities as early as the Neolithic period, around 7000 BP. This initiated the deforestation process and increased soil erosion, shown by the colluvia accumulated in the valley heads of dry valleys and by alluvial fan sediments close to their mouths where they entered the main valleys. The last stage of farming colonisation of this part of the Osoblaha basin, initiated by Slavs, had already led to the development of a dense network of settlements and considerable deforestation in the Mediaeval Period.

Moho deepening and shallow upper crustal delamination beneath the central Apennines

Geologic interpretation of seismic data along the eastern half of the CROP 11 deep seismic reflection profile, running across the central Apennines, indicates that the Adriatic Moho deepens gradually from 34 km in the foreland areas to 47 km beneath the core of the belt. This deepening is in agreement with local Moho depths estimated from teleseismic receiver functions at several stations installed along the CROP 11 profile. On the contrary, DSS (Deep Seismic Soundings) data image the Moho at shallower depths. The deepening of the Adriatic Moho illustrated in this paper supports the westward downgoing of a portion of Adriatic continental crust and is consistent with the regional gravity anomalies, provided that very high-density rocks are present above the Moho at the core of the central Apennine belt. We discuss geophysical and geologic data in the framework of alternative models of delamination of the Adriatic crust at different depth.

S-Wave Attenuation Characteristics beneath the Vrancea Region in Romania: New Insights from the Inversion of Ground-Motion Spectra

The S -wave attenuation characteristics beneath the Vrancea region in Romania are analyzed from the spectra (frequency range 0.5–20 Hz) of more than 850 recordings at 43 accelerometric stations of 55 intermediate-depth earthquakes ( M 4.0–7.1) that occurred in the Vrancea seismogenic zone. The method commonly chosen for this type of investigation in the case of crustal earthquakes is the generalized inversion technique (GIT) (e.g., Andrews, 1986; Castro et al. , 1990). Yet the Vrancea dataset is entirely different from common crustal datasets. Because of the strong clustering of the hypocenters within a very small focal volume, there are only few crossing ray paths from sources to receivers. As a consequence, inhomogeneities in the attenuation properties are not averaged out, which leads to unphysical results if the standard GIT approach is adopted. The problem is discussed qualitatively by performing tests with synthetic data and solved quantitatively by adapting the GIT technique in view of these peculiarities. With the optimally adapted inversion scheme, it is possible to unravel differences in the attenuation characteristics between two (or more) sets of stations. The results show that the attenuation of seismic waves is roughly comparable in the low frequency range (<4–5 Hz) but stronger by up to an order of magnitude at higher frequencies within the Carpathian mountain arc as compared with the foreland area. Modeling this strongly frequency-dependent lateral variation of seismic attenuation by a significantly lower Q beneath Vrancea (1) provides a very good fit of observed strong-motion characteristics, (2) sheds new light on the distribution of intensities of the previous strong earthquakes, (3) will have strong implications for future hazard assessment, and (4) is fully compatible with structural models from deep seismic sounding, tomography, and teleseismic attenuation.

Seismic crustal structure between the Transylvanian Basin and the Black Sea, Romania

In order to study the lithospheric structure in Romania a 450 km long WNW–ESE trending seismic refraction project was carried out in August/September 2001. It runs from the Transylvanian Basin across the East Carpathian Orogen and the Vrancea seismic region to the foreland areas with the very deep Neogene Focsani Basin and the North Dobrogea Orogen on the Black Sea. A total of ten shots with charge sizes 300–1500 kg were recorded by over 700 geophones. The data quality of the experiment was variable, depending primarily on charge size but also on local geological conditions. The data interpretation indicates a multi-layered structure with variable thicknesses and velocities. The sedimentary stack comprises up to 7 layers with seismic velocities of 2.0–5.9 km/s. It reaches a maximum thickness of about 22 km within the Focsani Basin area. The sedimentary succession is composed of (1) the Carpathian nappe pile, (2) the post-collisional Neogene Transylvanian Basin, which covers the local Late Cretaceous to Paleogene Tarnava Basin, (3) the Neogene Focsani Basin in the foredeep area, which covers autochthonous Mesozoic and Palaeozoic sedimentary rocks as well as a probably Permo-Triassic graben structure of the Moesian Platform, and (4) the Palaeozoic and Mesozoic rocks of the North Dobrogea Orogen. The underlying crystalline crust shows considerable thickness variations in total as well as in its individual subdivisions, which correlate well with the Tisza-Dacia, Moesian and North Dobrogea crustal blocks. The lateral velocity structure of these blocks along the seismic line remains constant with about 6.0 km/s along the basement top and 7.0 km/s above the Moho. The Tisza-Dacia block is about 33 to 37 km thick and shows low velocity zones in its uppermost 15 km, which are presumably due to basement thrusts imbricated with sedimentary successions related to the Carpathian Orogen. The crystalline crust of Moesia does not exceed 25 km and is covered by up to 22 km of sedimentary rocks. The North Dobrogea crust reaches a thickness of about 44 km and is probably composed of thick Eastern European crust overthrusted by a thin 1–2 km thick wedge of the North Dobrogea Orogen.

Review and New Insights on Foreland Tectonics in Western Taiwan

Taiwan is located on the boundary between the Eurasian and Philippine Sea plates. As a result, foreland tectonics in western Taiwan can be divided into two domains: pre-orogenic extensional structures and those of the outer part of the fold-and-thrust belt that mingled with syn-orogenic normal fault reactivation. This paper proposes a synthetic model for foreland tectonics in western Taiwan, and advances possible mechanisms by which pre-existing normal faults might have affected the evolving thrust tectonics in foreland areas of western Taiwan. The sedimentary basins of pre-orogenic extensional tectonics are of two types—Paleogene and Neogene—which reflect two stages of continental rifting. Results from several studies have been synthesized to provide a tectonic map displaying the regional distribution of tectonic settings at different stages and the trends of normal faults in the basins. The similarity of the en echelon patterns of arrangement for both the Neogene and Paleogene tectonic and structural settings, as shown by the tectonic map, strongly suggests that the entire foreland area was influenced by regional dextral shear. We also provide a detailed description of structures in each tectonic setting, and propose a tectonic evolution model for Cenozoic basin architecture in western Taiwan. Among the pre-orogenic sedimentary basins, the Neogene ones, in which normal faults extend to the frontal areas of the fold-and-thrust belt in western Taiwan, open northeastward. Structural analysis of the thrust fault geometry indicates that, during development of the fold-and-thrust belt on the rifted continental margin in western Taiwan, the pre-existing normal faults in northwestern Taiwan were reactivated to form inversion structures of various types on different scales, depending on the angle between the strike of the normal faults and the direction of maximum compressive stress field. In southwestern Taiwan, where normal fault reactivation is absent from the eastern part of the foreland areas, pre-existing normal faults interacted with developing low-angle thrusts in the inner part of the fold-and-thrust belt. Normal fault reactivation, regardless of how it occurs, thus plays an important role in forming the deformation front of the fold-and-thrust belt. Based on this view, we propose that the orocline or tectonic arc of the island has been influenced more by normal fault reactivation than by the morphology of basement highs.

Crustal Velocity Structure and Seismic Activity in the Tianshan‐Pamir Conjunctive Zone

AbstractUsing recording data from a temporary seismic network, we obtained P wave velocity structure of the Tianshan‐Pamir conjunctive zone by tomographic inversion, revealing the heterogeneity of crustal structure and its relations to seismic activity. The results show that the collision between the Tianshan and Pamir caused strong crustal deformation on the western edge of the Tarim basin and resulted in basement uplift zones in the foreland areas. The crust is separated into several blocks by deep faults and some of them are wrapped within mountain belts. The deep crust of the Kashi depression has a relatively stable structure with less deformation, however, the crust of the Tianshan and western Kunlun shows a velocity feature of shortening and thickening, moreover, heating or thermal perturbation can be observed near the crust‐mantle boundary in the areas adjacent to the Tarim basin. Most earthquakes in this area are concentrated around high velocity blocks in the western end of the Tarim basin. We infer that the frequent earthquakes in the Tianshan‐Pamir conjunctive zone can be attributed to the interaction and stress adjustment between these blocks, while the earthquakes in the Jiashi area are related to the penetration of tectonic activity from Tianshan into the Tarim basin and the heterogeneous structure of the crust.

Oil reservoirs in foreland basins charged by thrustbelt source rocks: insights from numerical stress modelling and geometric balancing in the West Carpathians

Abstract The West Carpathian thrustbelt advanced northeastwards over the European Platform. Its thrust sheets comprise sediments of the Early Cretaceous rifts that evolved on a passive margin of the European Platform, the Late Cretaceous-Paleocene basins formed by rift inversion, and the Eocene-Oligocene flexural basin. Geochemical analyses established a clear link between pooled oils in the foreland and the Oligocene Menilite Formation inside the thrustbelt. In order to understand the driving forces for this oil migration scenario, finite-element models of fault-propagation and fold-bend folds are used to study the mean stress distribution in the thrust sheets and the foreland. Mean stress has a profound control on the pore fluid pressure through the relationship affected by sediment porosity, and sediment skeleton and fluid compressibilities. Modelling results suggest that only fault-propagation folds are capable of generating foreland-directed mean stress gradients as they are characterized by a large foreland area of decreased mean stress, by coupled increased/decreased mean stress areas on advancing/receding sides of the ramp tip, and an overall mean stress decrease inside the thrust sheet in the direction towards the foreland. This interpretation is in accordance with the dominant fold-and-thrust style in the Western Carpathians inferred from balanced cross-section restoration. It shows that frontal fault-propagation folding was active during the late Oligocene-Early Miocene, providing an effective tectonic driving force for hydrocarbon migration from source rocks inside the thrustbelt towards reservoirs in the foreland.

Investigation of iodine concentration in salt, water and soil along the coast of Zhejiang, China

We aim to describe the environment iodine concentration in salt, water and soil along Zhejiang Province coast in the China foreland. It will be helpful for us to judge whether this area is insufficient in iodine and universal iodized salt is necessary or not. We collected iodized salt samples, drinking water samples (tap water in the towns, and well water or spring water in the villages), water samples from different sources (ditches, lakes, rivers) and soil samples through random sampling in June, 2005. Salt, water and soil iodine was detected by arsenic-cerium redox method. Statistical analysis was expressed as mean+/-SEM by Windows SPSS 13.0. (1) The iodine concentration in salt was 27.9+/-4.33 mg/kg (n=108). (2) Seventy-five water samples were collected. The water iodine value was 0.6-84.8 microg/L (mean of 11.66 mug/L). The watershed along the Qiantang River has significantly higher iodine content than the water in Lin'an in mountain area (P<0.01). The iodine content and mean iodine content of tap water, well or spring water and natural water sources were 4.30+/-2.43 microg/L (n=34), 23.59+/-27.74 microg/L (n=19) and 12.72+/-10.72 microg/L (n=22) respectively. This indicated that among environmental water sources, the ditch iodine content was the highest with river water iodine being the lowest (P<0.01). (3) Soil iodine value was 0.11-2.93 mg/kg (mean of 1.32 mg/kg). Though there was no statistical difference of soil iodine in different districts (P=0.131), soil iodine content correlated positively with water iodine content. Iodine concentration in salt accords with national policy of adding iodine in salt. Foreland has more iodine in water than mountain area. The data reflected that water and soil iodine in foreland area was not high, which suggests universal iodized salt should be necessary. Environment iodine has relatively close association with pollution.