Insights into syndepositional fault movement in a foreland basin; trends in seismites of the Upper Cretaceous,Wahweap Formation,Kaiparowits Basin,Utah, USA

The Upper Cretaceous Wahweap Formation accumulated in the active Cordilleran foreland basin of Utah. Soft‐sediment deformation structures are abundant in the capping sandstone member of the Wahweap Formation. By comparing with well‐established criteria, a seismogenic origin was determined for the majority of structures, which places these soft‐sediment deformation features in a class of sedimentary features referred to as seismites. A systematic study of the seismite trends included their vertical and horizontal distribution and a semi‐quantitative intensity analysis using a scale from 1 to 5 that is based on magnitude, sedimentary structure type, and the predominance of inferred process of hydroplastic deformation, liquefaction or fluidization. In addition, orientations of soft‐sediment fold axes were recorded. Construction of a northwest‐to‐southeast stratigraphic and seismite intensity cross‐section demonstrates: (1) reduction in stratigraphic thickness and percentage of conglomerates to the southeast, (2) the presence of lower seismite, middle nonseismite, and upper seismite zones within the capping sandstone (permitting subdivision of the capping sandstone member), and (3) elimination of the nonseismite zone and amalgamation of the lower and upper seismite zones to the southeast. Regional isoseismal contour maps generated from the semi‐quantitative analysis indicate a decrease in overall intensity from northwest to southeast in the upper and lower seismic zones and in sandstone within 5 m stratigraphically of the contact between the upper and capping sandstone members. In addition, cumulative seismite fold orientations support a west–northwest direction towards regional epicentres. Isoseismal maps are used to distinguish the effects of intrabasinal normal faulting from those of regional orogenic thrusting. Thus, this study demonstrates the utility of mapping seismites to separate the importance of regional vs. local tectonic activity influencing foreland basin sedimentation by identifying patterns that delineate palaeoepicentres associated with specific local intrabasinal normal faults vs. regional trends in soft‐sediment deformation related to Sevier belt earthquakes.     

Predicting sediment flux from fold and thrust belts

The rate of sediment influx to a basin exerts a first-order control on stratal architecture. Despite its importance, however, little is known about how sediment flux varies as a function of morphotectonic processes in the source terrain, such as fold and thrust growth, variations in bedrock lithology, drainage pattern changes and temporary sediment storage in intermontane basins. In this study, these factors are explored with a mathematical model of topographic evolution which couples fluvial erosion with fold and thrust kinematics. The model is calibrated by comparing predicted topographic relief with relief measured from a DEM of the Central Zagros Mountains fold belt. The sediment-flux curve produced by the Zagros fold belt simulation shows a delay between the onset of uplift and the ensuing sediment flux response. This delay is a combination of the natural response time of the geomorphic system and a time lag associated with filling, and then subsequently uplifting and re-eroding, the proximal part of the basin. Because deformation typically propagates toward the foreland, the latter time lag may be common to many ancient foreland basins. Model results further suggest that the response time of the bedrock fluvial system is a function of rock resistance, of the width of the region subject to uplift and erosion, and, assuming a nonlinear dependence of fluvial erosion upon channel gradient, of uplift rate. The geomorphic response time for the calibrated Zagros model is on the order of a few million years, which is commensurate with, or somewhat larger than, typical recurrence intervals for episodes of thrusting. However, model experiments also highlight the potential for significant variations in both geomorphic response time and in sediment flux as a function of varying rock resistance. Given a reasonable erodibility contrast between resistant and erodible lithologies, model sediment flux curves show significant sediment flux variations that are related solely to changes in rock resistance as the outcrop pattern changes. An additional control on sediment flux to a basin is drainage diversion in response to folding or thrusting, which can produce major shifts in the location and magnitude of sediment source points. Finally, these models illustrate the potential for a significant mismatch between tectonic events and sediment influx to a basin in cases where sediment is temporarily ponded in an intermontane basin and later remobilized.     

Superposed deformation in turbidites and syn-sedimentary slides of the tectonically active Miocene Waitemata Basin, northern New Zealand

The Miocene Waitemata Basin was deposited on a moving base provided by the Northland Allochthon, which was emplaced in the Late Oligocene, as a new convergent plate boundary was established in northern New Zealand. The basin experienced complex interaction between tectonic and gravity‐driven shallow deformation. Spectacular examples of the resulting structures exposed on eastern Whangaparaoa Peninsula 50 km north of Auckland provide a world‐class example of weak rock deformation, the neglected domain between soft‐sediment and hard rock deformation. Quartz‐poor turbidite sequences display a protracted sequence of deformations: D1, synsedimentary slumping; D2, large scale deeper‐seated sliding and extensional low‐angle shearing, associated with generation of boudinage and broken formation; D3, thrusting and folding, indicating transport mostly to the SE; D4, thrusting and folding in the opposite direction; D5, further folding, including sinistral shear; D6, steep faults. The deformation sequence suggests continuous or intermittent southeastward transport of units with increasing sedimentary and structural burial. By phase D3, the rocks had passed from the soft‐sediment state to low levels of consolidation. However, with a compressive strength of ～5 MPa they are weak rocks even today. Such weak‐rock deformation must be important in other sedimentary basins, especially those associated with active convergent plate boundaries and with immature source areas for their sediments.     

Unravelling the widening of the earliest Andean northern orogen: Maastrichtian to early Eocene intra‐basinal deformation in the northern Eastern Cordillera of Colombia

The onset of deformation in the northern Andes is overprinted by subsequent stages of basin deformation, complicating the examination of competing models illustrating potential location of earliest synorogenic basins and uplifts. To establish the width of the earliest northern Andean orogen, we carried out field mapping, palynological dating, sedimentary, stratigraphic and provenance analyses in Campanian to lower Eocene units exposed in the northern Eastern Cordillera of Colombia (Cocuy region) and compare the results with coeval succession in adjacent basins. The onset of deformation is recorded in earliest Maastrichtian time, as terrigenous detritus arrived into the basin marking the end of chemical precipitation and the onset of clastic deposition produced by the uplift of a western source area dominated by shaly Cretaceous rocks. Disconformable contacts within the upper Maastrichtian to middle Palaeocene succession document increasing supply of quartzose sandy detritus from Cretaceous quartzose rocks exposed in eastern source areas. The continued unroofing of both source areas produced a rapid shift in depositional environments from shallow marine in Maastrichtian to fluvial‐lacustrine systems during the Palaeocene‐early Eocene. Supply of immature Jurassic sandstones from nearby western uplifts, together with localized plutonic and volcanic Cretaceous rocks, caused a shift in Palaeocene sandstones composition from quartzarenites to litharenites. Supply of detrital sandy fragments, unstable heavy minerals and Cretaceous to Ordovician detrital zircons, were derived from nearby uplifted blocks and from SW fluvial systems within the synorogenic basin, instead of distal basement rocks. The presence of volcanic rock fragments and 51–59 Ma volcanic zircons constrain magmatism within the basin. The Maastrichtian–Palaeocene sequence studied here documents crustal deformation that correlates with coeval deformation farther south in Ecuador and Peru. Slab flattening of the subducting Caribbean plate produced a wider orogen (>400 km) with a continental magmatic arc and intra‐basinal deformation and magmatism.     

The Late Ordovician deglaciation sequence of the SW Murzuq Basin (Libya)

Rocks of Late Ordovician to Silurian age are well exposed on the western rim of the Murzuq Basin (Ghat‐Tikiumit area, Libya) where seismic‐scale exposures allow spectacular insights into the growth and decay of the Late Ordovician (Hirnantian) ice sheet. The final deglaciation left a complex topography with a combination of subglacial morphologies and proglacial depositional systems. This paper documents the glacial and proglacial palaeo‐topography that controls the accumulation of a postglacial transgressive depositional system and the Rhuddanian (Early Silurian) shales. The glacial relief directly contributed to an important hiatus, with the Rhuddanian deposits at the base of the remnant glacial troughs being 3 Ma older than at the top of the topographic highs. The source‐rock in the Murzuq Basin is of Early Rhuddanian age, so it is present only in the deepest part whereas geomorphic traps are formed within the highs of the relict postglacial topography. The transgressive system, recognised for its good reservoir potential, is considered to play a key‐role in the petroleum system, linking the source rock deposited in the ancient topographic lows with the reservoir rocks in the topographic highs. This study aims to demonstrate the importance of palaeo‐glaciological reconstructions for petroleum exploration of the Ordovician–Silurian in North Africa.     

东昆仑迪木那里克铁矿地质特征与找矿标志

迪木那里克铁矿位于阿尔金大断裂南侧,矿体主要赋存于中-上奥陶统祁曼塔格群浅变质的碎屑岩-火山碎屑岩中.矿体多呈似层状、条带状产出,部分矿体塑性变形较强,矿体与地层产状基本一致,层控作用比较明显;矿石主要为条带状石英-磁铁矿和块状磁铁矿矿石;矿石品位较低(TFe=20%～40%);围岩蚀变特征明显.该铁矿属沉积变质型铁矿.综合研究发现,可利用矿区地层、构造、岩石蚀变情况、航磁异常等作为矿区和区域找矿标志.     

Syn‐orogenic fluid flow in the Jaca basin (south Pyrenean fold and thrust belt) from fracture and vein analyses

This study aims at understanding the origin and nature of syn‐orogenic fluid flow in the Jaca basin from the South Pyrenean fold and thrust‐belt, as recorded in calcite and quartz veins of the Sierras Interiores (Spain) and the turbiditic basin, which cover upper Cretaceous to Late Eocene syntectonic deposits. The fracture network consists of a classical pattern of transverse and longitudinal fractures related to Layer Parallel Shortening (LPS) and folding respectively. Veins filled equally about the third of fractures in the carbonate shelf and turbidites. Carbon and oxygen isotopes of calcite veins mostly indicate precipitation from isotopically buffered water, consistent with high water‐rock interaction. In the Sierras Interiores, petrographical observations and fluid inclusion microthermometry are consistent with two distinct stages of precipitation. The first stage is characterized by relatively low Th and low salinities (155–205 °C and 0.5–3.2 wt% eq. NaCl). The second stage, which was characterized both by the formation of mode‐I joints and by mode‐I reactivation of pre‐existing veins, shows higher Th and salinities (215–270 °C and 2.2–5.7 wt% eq. NaCl). Waters recorded in the second stage are interpreted to have interacted with underlying Triassic evaporites and flowed along major thrusts before vein precipitation, which are locally in thermal disequilibrium with host‐rocks. We suggest the transition from a rather closed hydrological system during the first stage of vein formation, interpreted to have occurred during Eaux‐chaudes thrusting (upper Lutetian‐Bartonian), to a more open hydrological system during the second stage, which likely occurred during Gavarnie thrusting (Priabonian‐early Rupelian). Finally, we also document the migration in space and time of hydrothermal pulses along the South Pyrenean Foreland Basin, related to the westward propagation of major thrusts during the Pyrenean orogeny.     

Palaeomagnetism of the Ordovician dolerites of the Crozon Peninsula (France)

Summary. In order to obtain a Lower Palaeozoic pole for the Armorican Massif and to test the origin of the Ibero-Armorican arc, the Ordovician dolerites of the Crozon peninsula have been palaeomagnetically studied. The samples show a multicomponent magnetization which has been revealed by AF and thermal demagnetization and thoroughly investigated with rock magnetic experiments, polished section examinations and K/Ar dating. Four groups of directions have been recognized, often superimposed on each other in an individual sample. One component (D) has always the lowest blocking temperatures and coercivities and is considered to be of viscous origin, acquired recently in situ or in the laboratory during storage. Two components (A and B) are interpreted to be of secondary origin and to correspond to the observed K/Ar age distribution between 300 and 190 Myr. These ages represent the time interval between two regional thermo-tectonic events, associated with the Hercynian orogeny and the intrusion of dykes related to the early opening of the Central Atlantic Ocean and the Bay of Biscay. A fourth component (C) could be of Ordovician or younger Palaeozoic age; it is not clear whether the age of the magnetization is pre- or post-folding, but a pre-folding age would yield a direction of magnetization similar to Ordovician results from the Iberian peninsula. The latter interpretation suggests a fairly high palaeolatitude, which is in agreement with a glacio-marine postulated for sediments overlying the dolerite sills.     

Ordovician tectonic shift in the western North China Craton constrained by stratigraphic and geochronological analyses

The western North China Craton (W-NCC) comprises the Alxa Terrane in the west and the Ordos Block in the east; they are separated by the Helanshan Tectonic Belt (HTB). There is an extensive debate regarding the significant Ordovician tectonic setting of the W-NCC. Most paleogeographic reconstructions emphasized the formation and rapid subsidence of an aulacogen along the HTB during the Middle–Late Ordovician, whereas paleomagnetic and geochronologic results suggested that the Alxa Terrane and the Ordos Block were independent blocks separated by the HTB. In this study, stratigraphic and geochronologic methods were used to constrain the Ordovician tectonic processes of the W-NCC. Stratigraphic correlations show that the Early Ordovician strata comprise ~500-m-thick tidal flat and lagoon carbonate successions with a progressive eastward onlap, featuring a west-deepening shallow-water carbonate shelf. In contrast, the Late Ordovician strata are composed of ~3,000-m-thick abyssal turbidites in the west and ~400-m-thick shallow-water carbonates in the east, defining an eastward-tapering basin architecture. Early Ordovician detrital zircons with ages of ~2,800–1,700 Ma were derived from the Ordos Block; the Late Ordovician turbidites were sourced from the western Alxa Terrane, based on zircon ages clustered at ~1,000–900 Ma. The petrographic modal composition and zircon age distribution imply a provenance shift from a stable craton to a recycled orogen in the Middle Ordovician. These shifts define a tectonic conversion from a passive continental margin to a foreland basin at ~467 Ma, resulting in the eastward progradation of the turbidite wedge around the HTB, the eastward backstepping of the carbonate platform in the east and the eastward expansion of orogenic thrusting in the western Alxa Terrane. This tectono-sedimentary shift coincided with the advancing subduction of the southern Paleo-Asian Ocean beneath the Alxa Terrane, generating the western Alxa continental arc and the paired retro-arc foredeep in the east under a compressional tectonic regime.     

Palaeomagnetism and K—Ar age of the Upper Ordovician Alcaparrosa Formation, Argentina

Summary. Palaeomagnetic data from 71 hand samples of igneous rocks of Late Ordovician age exposed in western Argentina (31.3°S, 69.4°W, Alcaparrosa Formation) are given. Stable remanent magnetization was isolated in the majority of samples; they yield a palaeomagnetic pole at 56°S 33°E ( N = 8, α₉₅= 16°). Whole rock K-Ar age determinations yield an age of 416 ± 10 Myr for a pillow lava of the Alcaparrosa Formation.
Palaeomagnetic data for South America, Africa, Australia, Antarctica and India suggest that Gondwana was a unit at least as far back as 1000 Myr. The palaeomagnetic data define a rapid polar migration for Gondwana in Ordovician time which is consistent with the widespread occurrences of Late Ordovician glacial deposits across this supercontinent.     

四川省溪口滑坡运动特征的离散元模拟

通过离散元分析拟合了溪口滑坡碎屑流的运动过程和主要特征,认为滑坡解体后是以碎屑流方式完成运移和停积过程。     

Lower crustal involvement in upper crustal thrusting

Summary. Basement structures mapped in the Devonian Adavale Basin, eastern Australia, indicate two styles of lower-crustal involvement in the formation of upper-crustal structures. The first style is typified by thrust features in the upper-crustal sedimentary section and basement, a response to lower-crustal shortening over a wide area. The second style includes lower-crustal thrusting and thickening in a limited region, with associated uplift of the upper crust. These two styles suggest that the upper and lower crust were mechanically decoupled during Palaeozoic compressive episodes.     

Gravitational deformation and inherited structural control on slope morphology in the subduction zone of north‐central Chile (ca. 29–33°S)

Subduction zones provide direct insight into plate boundary deformation and by studying these areas we better understand tectonic processes and variability over time. We studied the structure of the offshore subduction zone system of the Pampean flat‐slab segment (ca. 29–33°S) of the Chilean margin using seismic and bathymetric constraints. Here, we related and analysed the structural styles of the offshore and onshore western fore‐arc. Overlying the acoustic top of the continental basement, two syn‐extensional seismic sequences were recognised and correlated with onshore geological units and the Valparaíso Forearc Basin seismic sequences: (SII) Pliocene‐Pleistocene and (SI) Miocene‐Pliocene (Late Cretaceous (?) to Miocene‐Pliocene) syn‐extensional sequences. These sequences are separated by an unconformity (i.e. Valparaíso Unconformity). Seismic reflection data reveal that the eastward dipping extensional system (EI) recognised at the upper slope can be extended to the middle slope and controlled the accumulation of the older seismic package (SI). The westward dipping extensional system (EII) is essentially restricted to the middle slope. Here, EII cuts the eastward dipping extensional system (EI), preferentially parallel to the inclination of the older sequences (SI), and controlled a series of middle slope basins which are filled by the Pliocene‐Pleistocene seismic sequence (SII). At the upper slope and in the western Coastal Cordillera, the SII sequence is controlled by eastward dipping faults (EII) which are the local reactivation of older extensional faults (EI). The tectonic boundary between the middle (eastern outermost forearc block) and upper continental slope (western coastal block) is a prominent system of trenchward dipping normal fault scarps (ca. 1 km offset) that resemble a major trenchward dipping extensional fault system. This prominent structural feature can be readily detected along the Chilean erosive margin as well as the two extensional sets (EI and EII). Evidence of slumping, thrusting, reactivated faults and mass transport deposits, were recognised in the slope domain and locally restricted to some eastern dipping faults. These features could be related to gravitational effects or slope deformation due to coseismic deformation. The regional inclination of the pre‐Pliocene sequences favoured the gravitational collapse of the outermost forearc block. We propose that the structural configuration of the study area is dominantly controlled by tectonic erosion as well as the uplift of the Coastal Cordillera, which is partially controlled by pre‐Pliocene architecture.     

Large-scale velocity field and strain tensor in Iran inferred from GPS measurements: new insight for the present-day deformation pattern within NE Iran

A network of 26 GPS sites was implemented in Iran and Northern Oman to measure displacements in this part of the Arabia–Eurasia collision zone. We present the GPS velocity field obtained from three surveys performed in 1999 September, 2001 October and 2005 September and the deduced strain tensor. This study refines previous studies inferred from only the two first surveys. Improvements are significant in NE Iran. The present-day shortening rate across the mountain belts of NE Iran is estimated to 5 ± 1 mm yr⁻¹ at about N11°, 2 ± 1 mm yr⁻¹ of NS shortening across the eastern Kopet Dag and 3 ± 1 mm yr⁻¹ of NS shortening across Binalud and Kuh-e-Sorkh. Our GPS measurements emphasize the varying character of the Kopet Dag deformation between its southeastern part with prevailing thrusting at low rates and its northwestern part with dominant strike-slip activity at increasing rates. The principal axes of the horizontal strain tensor appears very homogeneous from the Zagros to the Alborz and the Kopet-Dag (N20°) and in eastern Iran (Makran and Lut block: N30°). Only NW Iran suffers a variable strain pattern which seems to wrap the Caspian basin. The strain tensor map underlines the existence of large homogeneous tectonic provinces in terms of style and amplitude of the deformation.     

Mass‐transport complexes as markers of deep‐water fold‐and‐thrust belt evolution: insights from the southern Magdalena fan,offshore Colombia

Mass wasting is an important process in the degradation of deep‐water fold‐and‐thrust belts. However, the relationship between mass‐transport complex (MTC) emplacement and the timing and spatial progression of contractional deformation of the seabed have not been extensively studied. This study uses high‐quality, 3D seismic reflection data from the southern Magdalena Fan, offshore Colombia to investigate how the growth of a deep‐water fold‐and‐thrust belt (the southern Sinú fold belt) is recorded in the source, distribution and size of MTCs. More than nine distinct, but coalesced MTCs overlie a major composite basal erosion surface. This surface formed by multiple syn‐ and post‐tectonic mass‐wasting events and is thus highly diachronous, thereby recording a protracted period of tectonism, seascape degradation and associated sedimentation. The size and source location of these MTCs changed through time: the oldest ‘detached’ MTCs are relatively small (over 9–100 km² in area) and sourced from the flanks of growing anticlines, whereas the younger ‘shelf‐attached’ MTCs are considerably larger (more than 200–300 km²), are sourced from the shelf, and post‐date the main phase of active folding and thrusting. Changes in the source, distribution and size of MTCs are tied to the sequential nucleation, amplification and along‐strike propagation of individual structures, showing that MTCs can be used to constrain the timing and style of contractional deformation, and seascape evolution in time and space.     

Structural development of the Tertiary fold-and-thrust belt in east Oscar II Land, Spitsbergen

The Tertiary deformation in east Oscar II Land, Spitsbergen, is compressional and thin-skinned, and includes thrusts with ramp-flat geometry and associated fault-bend and fault-propagation folds. The thrust front in the Mediumfjellct-Lappdalen area consists of intensely deformed Paleozoic and Mesozoic rocks thrust on top of subhorizontal Mesozoic rocks to the east. The thrust front represents a complex frontal ramp duplex in which most of the eastward displacement is transferred from sole thrusts in the Permian and probably Carboniferous strata to roof thrusts in the Triassic sequence. The internal geometries in the thrust front suggest a complex kinematic development involving not only simple 'piggy-back', in-sequencc thrusting, but also overstep as well as out-of-sequence thrusting. The position of the thrust front and across-strike variation in structural character in east Oscar II Land is interpreted to be controlled by lithological (facies) variations and/or pre-existing structures, at depth, possibly cxtensional faults associated with the Carboniferous graben system.     

Rb-Sr whole rock and U-Pb zircon datings of the granitic-gabbroic rocks from the Skålfjellet Subgroup, southwest Spitsbergen

Recent remapping and new age determinations has shed light on the understanding of Precambrian rocks northwest of Hornsund, southwest Spitsbergen. The Skålfjellet Subgroup has been regarded as the eastern equivalent of the Vimsodden Subgroup, and both of these occur within the Precambrian Eimfjellet Group of southwest Spitsbergen. Although the Eimfjellet Group is considered to be older than the oldest unconformity in the area, the age of the rocks has not been known. The granitic-gabbroic rocks in the Skålfjellet Subgroup have been considered to be the products of granitisation for many years, but recent observations show that they are exotic blocks incorporated into the basic eruptive rocks which are the main constituents of the subgroup. These plutonic rocks have a wide range of compositions, from syenite via granite to gabbroic cumulates, which suggests the existence of a well-differentiated plutonic body at depth.
U-Pb zircon and Pb evaporation datings yielded magmatic ages of ca. 1,100 to 1,200 Ma, and a conformable age has been obtained by Rb-Sr whole rock dating. Detrital zircons from the micaceous schists of the Isbjørnhamna Group, which underlies the Skålfjellet Subgroup, show a poorly defined discordia with an upper intercept age of ca. 2,200 Ma and a lower intercept age of ca. 360 Ma. These dating results define the magmatic age of the granitic-gabbroic rocks as late Mesoproterozoic, early Grenvillian. This age is in broad agreement with that of the metavolcanic rock clasts of the Pyttholmen meta-pyroclastic-conglomeratic unit at Vimsodden, which is considered to be the westernmost occurrence of the Skålfjellet Subgroup.
A Rb-Sr whole rock age determination of the shaly phyllites from the Deilegga Group was performed in order to place constraints on the age of younger Precambrian event; however, no good isochron was obtained.     

SOIL PROCESSES AND DEVELOPMENT RATES IN THE QUARTERMAIN MOUNTAINS, UPPER TAYLOR GLACIER REGION, ANTARCTICA

Soil‐forming processes and soil development rates are compared and contrasted on glacial deposits in two adjacent and coeval valleys of the Quartermain Mountains, which are important because they display Miocene glacial Stratigraphy and some of the oldest landforms in the McMurdo Dry Valleys. More than 100 soil profiles were examined on seven drift sheets ranging from 115 000 to greater than 11.3 million years in age in Beacon Valley and Arena Valley. Although the two valleys contain drifts of similar age, they differ markedly in ice content of the substrate. Whereas Arena Valley generally has ‘dry‐frozen’ permafrost in the upper 1 m and minimal patterned ground, Beacon Valley contains massive ice buried by glacial drift and ice cored rock glaciers and has ice‐cemented perma‐frost in the upper 1 m and considerable associated patterned ground. Arena Valley soils have twice the rate of profile salt accumulation than Beacon Valley soils, because of lower available soil water and minimal cryoturbation. The following soil properties increase with age in both valleys: weathering stage, morphogenetic salt stage, thickness of the salt pan, the quantity of profile salts, electrical conductivity of the horizon of maximum salt enrichment, and depth of staining. Whereas soils less than 200 000 years and older soils derived from sandstone‐rich ground moraine are Typic Anhyorthels and Anhyturbels, soils of early Quaternary and older age, particularly on dolerite‐rich drifts, are Petronitric Anhyorthels. Arena Valley has the highest pedodiversity recorded in the McMurdo Dry Valleys. The soils of the Quartermain Mountains are the only soils in the McMurdo Dry Valleys known to contain abundant nitrates.     

Flexural uplift of the Stara Planina range, central Bulgaria

The Stara Planina is an E–W-trending range within the Balkan belt in central Bulgaria. This topographically high mountain range was the site of Mesozoic through early Cenozoic thrusting and convergence, and its high topography is generally thought to have resulted from crustal shortening associated with those events. However, uplift of this belt appears to be much younger than the age of thrusting and correlates instead with the age of Pliocene–Quaternary normal faulting along the southern side of the range. Flexural modelling indicates the morphology of the range is consistent with flexural uplift of footwall rocks during Pliocene–Quaternary displacement on S-dipping normal faults bounding the south side of the mountains, provided that the effective elastic plate thickness of 12  km under the Moesian platform is reduced to about 3  km under the Stara Planina. This small value of elastic plate thickness under the Stara Planina is similar to values observed in the Basin and Range Province of the western United States, and suggests that weakening of the lithosphere is due to heating of the lithosphere during extension, perhaps to the point that large-scale flow of material is possible within the lower crust. Because weakening is observed to affect the Moesian lithosphere for ≈10  km beyond (north of) the surface expression of extension, this study suggests that processes within the uppermost mantle, such as convection, play an active role in the extension process. The results of this study also suggest that much of the topographic relief in thrust belts where convergence is accompanied by coeval extension in the upper plate (or 'back arc'), such as in the Apennines, may be a flexural response to unloading during normal faulting, rather than a direct response to crustal shortening in the thrust belt.     

Cosmogenic Be dating of a sackung and its faulted rock glaciers, in the Alps of Savoy (France)

Sackungs are the largest gravitational deformation observed in mountains. They are characterized by the long-term slowness of the movements, but their mechanism is still not well understood. Nowadays cosmic ray exposure (CRE) dating methods allow dating the morphologic structures involved in sackung and can contribute at the understanding of their origin. In the Alps, the 5.3 km long Arcs sackung initiated during the activity of rock glaciers. Three samples from these faulted rock glaciers provide their first CRE ages and show that at 2000 m elevation these block accumulations moved during the Younger Dryas and stopped in early Holocene. Six ¹⁰Be ages of fault scarps show that the Arcs sackung lasted only a few thousand years and stopped at about 8462 ± 432 ¹⁰Be yr. They also reveal that deformation migrated upslope in agreement with a mechanism of flexural toppling of vertical layers. This unique and long gravitational event, characterized by migration of the deformation, does not support earthquake shaking as triggering mechanism for individual faults. It shows that, in the upper Isère valley, slope deformation was delayed of several thousand years after glacial debuttressing, and is not anymore active despite its fresh morphology.