Mountain Group Research Articles

Sequence stratigraphy and formalization of the Middle Uinta Mountain Group (Neoproterozoic), central Uinta Mountains, Utah: A closer look at the western Laurentian Seaway at ca. 750 Ma

The mid-Neoproterozoic (ca. 750Ma) Uinta Mountain Group (UMG), northeast Utah, USA, records transgressions of an epicontinental sea at least 150 million years before inception of the Laurentian western passive margin. This work refines middle UMG stratigraphy by formalizing three lithostratigraphic formations and interpreting a sequence stratigraphic framework in the central part of the Uinta Mountains. Middle UMG marine and fluvial-deltaic facies associations comprise eight depositional sequences within a kilometer-thick upward-fining composite sequence. These depositional sequences form one progradational–aggradational (“lowstand”) sequence set (PASS) and one aggradational–progradational (“highstand”) sequence set (APSS). Depositional sequences were deposited within a tide- and wave-affected epicontinental seaway that received sediment from a south-flowing fluvial system proximally sourced in the Neoarchean southern Wyoming Province to the north and from a separate system of major, west-flowing trans-Laurentian rivers distally sourced in the Grenville orogen, the mid-continent granite province, and the Yavapai and Mazatzal provinces to the south and east.Middle UMG fluvial-marine paleogeography strengthens the genetic link with the coeval Big Cottonwood and Little Willow formations (Utah), the Chuar Group (Arizona), and upper Pahrump Supergroup (California), which collectively indicate a ca. 770–740Ma epicontinental seaway existed across much of western Laurentia before 700Ma rifting and 600Ma formation of the Cordilleran passive margin. Long-term marine transgression onto continental Laurentia was likely caused by supercontinent breakup, particularly rifting of the Tarim and South China blocks from the remainder of Rodinia. Poorly constrained autocyclic drivers (delta lobe switching, channel avulsion) and allocyclic drivers (climatic fluctuations, local tectonism) controlled higher frequency depositional cycles superimposed on this long-term transgression. Western Laurentia thus records prolonged (750–600Ma) episodic basin formation, mafic volcanism, and faulting before establishment of a continental terrace after 600Ma. The Neoproterozoic western Laurentian epicontinental seaway can be used as a tie-point with other continents to help constrain the original continental configuration of Rodinia.

Characteristics of flora and plant cover of Nuratau relic mountains (South Kyzylkum)

The article is devoted to the specific features of the floristic composition and plant cover of the Nuratau relic mountains of the South Kyzylkum compared to another group of the low mountains located in the central and southwestern parts of the Kyzylkum Desert. It has been suggested that the flora of the studied territory undergoes mountain genesis, which is proved by actual examples.

Application of the rainfall infiltration breakthrough (RIB) model for groundwater recharge estimation in west coastal South Africa

Recharge estimation in arid and semi-arid areas is very challenging. The chloride mass balance method applied in western South Africa fails to provide reliable recharge estimates near coastal areas. A relationship between rainfall events and water level fluctuations (WLF) on a monthly basis was proposed in the rainfall infiltration breakthrough (RIB) model for the purpose of groundwater recharge estimation. In this paper, the physical meaning of parameters in the CRD and previous RIB models is clarified, and the RIB model is reviewed with the algorithm improved to accommodate various time scales, namely, daily, monthly and annual scales. Recharge estimates on a daily and monthly basis using the revised RIB approach in 2 study areas, one in a sandy alluvial aquifer (Riverlands) and the other in the Table Mountain Group (TMG) shallow unconfined aquifer (Oudebosch), are presented, followed by sensitivity analysis. Correlation analysis between rainfall and observed WLF data at daily scale and monthly scale, together with recharge estimates obtained from other methods, demonstrates that the RIB results using monthly data are more realistic than those for daily data, when using long time series. Scenarios using the data from Oudebosch with different rainfall and groundwater abstraction inputs are simulated to explore individual effects on water levels as well as recharge rate estimated on a daily basis. The sensitivity analysis showed that the recharge rate by the RIB model is specifically sensitive to the parameter of specific yield; therefore, the accurate representative specific yield of the aquifer needs to be selected with caution. The RIB model demonstrated in these two cases can be used to estimate groundwater recharge with sufficiently long time series of groundwater level and rainfall available in similar regions. In summary, the RIB model is best suited for shallow unconfined aquifers with relatively lower transmissiv ity; the utility of the RIB model for application in different climatic areas under different hydrogeological conditions needs to be further explored.

Topographies of Anticolonialism: The Ecopoetical Sublime in the Caucasus from Tolstoy to Mamakaev

Topographies of Anticolonialism: The Ecopoetical Sublime in the Caucasus from Tolstoy to Mamakaev

Crustal growth and tectonic evolution of the Mojave crustal province: Insights from hafnium isotope systematics in zircons

Coupled U-Pb ages and Hf isotopic ratios in zircons from Proterozoic basement and three siliciclastic cover sequences in southern California provide important insights into the formation of the southern Mojave crustal province and its incorporation into southwestern Laurentia. Hafnium isotopic ratios measured in >800 zircons, coupled with new and previously reported U-Pb ages, suggest that the crystalline basement of the Mojave crustal province formed from four main components: 1) mantle components ranging from depleted to moderately enriched; 2) metasedimentary framework rocks derived from 2.6 to 2.4 Ga and 2.0 to 1.8 Ga crust; 3) 1.79 to 1.64 Ga intrusive rocks that reflect mixing of mantle-derived melts and crust; and 4) Mesoproterozoic (1.4 to 1.2 Ga) anorthosite and granitic to syenitic intrusive rocks. Initial Hf isotopic ratios of detrital zircons in siliciclastic cover sequences suggest varying degrees of insularity of the Mojave province during assembly of southwestern Laurentia. The Mesoproterozoic Pinto Mountain Group appears entirely derived from Mojave province basement. In contrast, Neoproterozoic quartzites of the Big Bear Group had a distal provenance, either an unexposed, older, western subprovince of the Mojave crustal province lacking ca. 1.7 Ga magmatic rocks or from a distinctive Paleo- and Mesoproterozoic basement province far to the east within Laurentia. Zircons in latest Neoproterozoic to Cambrian quartzites reflect provenance from an integrated transcontinental drainage network delivering sediment to the craton edge and westward into the Cordilleran miogeocline.

Tree-ring–based summer mean temperature variations in the Adamello–Presanella Group (Italian Central Alps), 1610–2008 AD

Abstract. Climate records from remote mountain sites and for century-long periods are usually lacking for most continents and also for the European Alps. However, detailed reconstructions of climate parameters for pre-instrumental periods in mountain areas, suffering of glacial retreat caused by recent global warming, are needed in the view of a better comprehension of the environmental dynamics. We present here the first annually-resolved reconstruction of summer (JJA) mean temperature for the Adamello–Presanella Group (Central European Alps), one of the most glaciated mountain groups of the Italian Central Alps. The reconstruction has been based on four larch tree-ring width chronologies derived from living trees sampled in four valleys surrounding the Group. The reconstruction spans from 1610 to 2008 and the statistical verification of the reconstruction demonstrates the positive skill of the tree-ring dataset in tracking summer temperature variability also in the recent period.

An Early Jurassic brachiopod-dominated seep deposit enclosed by serpentinite, eastern Oregon, USA

Many Paleozoic and Mesozoic hydrocarbon-seep deposits are typified by superabundant dimerelloid brachiopods. By contrast, Cenozoic and modern seeps have been and still are dominated by mollusks and tube worms. To date, five genera of the rhynchonellide superfamily Dimerelloidea have been confirmed to have lived at hydrocarbon seeps. Here, we look into the paleoecology of another dimerelloid genus, studying an unusual limestone body in the Blue Mountains Province of eastern Oregon, USA. This limestone block, found in the vicinity of the town of Seneca, is characterized by a mass occurrence of a dimerelloid brachiopod assigned to the species Sulcirostra paronai. The above block, along with two other sizeable exotic blocks of sedimentary rock scattered in its immediate periphery, and small pods of Sulcirostra limestone scattered in its wider periphery are enclosed in serpentinite. The brachiopod limestone predominantly consists of early diagenetic phases including clotted micrite and fibrous, banded and botryoidal cement. Negative δ13C values of these carbonate phases as low as −23.5‰ agree with precipitation resulting from the oxidation of hydrocarbons. Petrographic and isotopic evidence reveals that the dimerelloids lived at a seep on the Early Jurassic seafloor. The age assignment is based on Sinemurian ammonoids associated with Sulcirostra in one of the exotic blocks from the direct periphery of the main deposit. The exotic blocks are attributed to the Lower Jurassic Keller Creek Formation. The occurrence of the Sulcirostra limestone within serpentinite calls for an evaluation of the possibility that the Jurassic chemosynthesis-based ecosystem was driven by serpentinization, given the presence of chemosymbiotic communities on the modern seafloor where hydrogen and methane anomalies are generated by serpentinization. The nature of the contacts between the blocks of sedimentary rock including the Sulcirostra limestone and the surrounding serpentinite reveals that these lithologies were juxtaposed by tectonic processes, probably thrusting of the Keller Creek Formation strata, as well as other Aldrich Mountains Group rocks, over the serpentinites. No unambiguous evidence has been found that supports a derivation of seepage fluids from serpentinization, yet it is obvious that Sulcirostra lived at a hydrocarbon seep, confirming the association of the superfamily Dimerelloidea with seep environments for one more genus.

Ecological and biodiversity gradients across alpine dry grassland habitats: implications for an endangered species

Dry grasslands are of great interest for nature conservation in Europe, because they have a central role in the conservation of numerous rare and endangered species. In this study carried out in the Brenta mountain group (Italian alps), we investigated the effect of environmental factors mainly controlled by topography, on the biodiversity trends across different dry grassland habitats where the threatened alpine stenoendemic Erysimum aurantiacum grows. Plant community data and ecological factors were analysed by means of a multi‐habitat CCA approach and by analysis of biodiversity gradients in 7 natural and semi‐natural habitats. We found that species turnover and biodiversity patterns vary as a function of multi‐factorial ecological gradients. For the single habitats, elevation gradient was the main factor explaining compositional variation, followed by inclination and proportion of exposed rock surface. Despite its endangered status, E. aurantiacum showed a relatively high degree of ecological plasticity across these semiarid grassland habitats that probably allows it to survive in different environments, including in some cases those impacted by human activities. This prompts for habitat‐ more than species‐level conservation actions. According to their characteristics and threats, habitat‐specific management practices are recommended for long term conservation of plant species communities in the different ecological niches.

Quaternary climate and environmental changes have shaped genetic differentiation in a Chinese pheasant endemic to the eastern margin of the Qinghai-Tibetan Plateau

The geological complexity generated by the uplift of the Qinghai-Tibetan Plateau and the resulting habitat heterogeneity have functioned together with climatic oscillations in the Quaternary to have a profound impact on the patterns of genetic diversity and demography of the fauna in this region. To understand the effect of the climatic and environmental shifts of the Quaternary on intraspecific genetic patterns and evolutionary history, we investigated the population genetic structure of the blue eared pheasant (Crossoptilon auritum), an endemic bird inhabiting the easternmost region of the plateau. Our phylogeographic analysis of mitochondrial DNA sequences and eight autosomal microsatellites reveals that the blue eared pheasant is subdivided into four distinct subpopulations: a central group (Huzhu and Taizi Mountains), a southern Zoige group, a southernmost Wanglang group and the northernmost Helan Mountain group. These groups are likely to have diverged in the Pleistocene, corresponding to geological changes and the interglacial–glacial climate oscillations that occurred at the eastern margin of the Qinghai-Tibetan Plateau. These subpopulations thus represent major conservation units, especially for the isolated Helan subpopulation. Our findings provide evidence of population divergence driven by complex Quaternary climate and environmental changes and, once more, highlight the importance of phylogeographic studies for conservation endeavours.

Torrentiality – Morphohydrographical conditions in the Sebeş Basin (The Parâng Mountains Group, Southern Carpathians)

This paper presents the morpho-hydrographical characteristics that define the torrential system inside the Sebes basin (the Parâng Mountains). The manifestation of torrential erosion takes place on river basins of different sizes. In order to bring out the quantitative and qualitative differences in the stream discharge structure, we resorted to the determination of some geomorphometrical indices such as: the number of river segments, the frequency of elementary thalwegs, incipient or total torrentiality. The great density of the temporary valleys network, along with the emphasized slope of the ditches and flanks generate a high instability. The local differentiations of the geological sublayers and the complementarity of the use of the Cindrel, Lotru and Sureanu mountain areas generate its own answer forms on the aggressive action of the torrential rainfalls on elementary segments with temporary functionality, as well as on permanent hydrographic thoroughfares. The tributary streams received by the Sebes River in the Carpathian sector have small hydrographic basins and they do not exceed rank 4 in the Horton-Strahler classification system. Torrentiality is stimulated by the combined effect of snowmelt and spring rains, but mostly by the aggressiveness of the torrential summer rains, which take over a modified geomorphological background through excessive depasturage, deforestation and hydropower harnessing. The streams and the floods, through the accumulation of high volumes and energies, produce slope damages, riverbed shifts, blockages and the destruction of communications infrastructure, and material loss.

Study regarding ecotourism development on Parang mountains group.

Along with the development of ecotourism worldwide came the recognition of the benefitsof this tourism as optimal mechanismoptimal exploitation of tourism resources and landscape.National governments should involve managers of protected areas and tourism industry in developingand implementing plans for sustainable tourism. They should be part of national strategies forsustainable development and should be included in individual management plans of protected areas.Through ecotourism can be provided the widening spectrum of traditional economic activities, notmarginalize or replace them because the local economy and not be subject to external influences andinternal changes. Presented work aims to present ecotourism as a model of sustainable tourismdevelopment in Parang, especially in protected areas, but in others a fragile environment. This analysishas a dual purpose: on the one hand the integral and sustainable development of natural and culturalresources, to improve the quality of life in local communities and on the other hand satisfy tourists'motivations and requirements in accordance with environmental conservation and resources for futuregenerations future.

GEOCHEMICAL PERSPECTIVE ON ORIGINS AND CONSEQUENCES OF HEUWELTJIE FORMATION IN THE SOUTHWESTERN CAPE, SOUTH AFRICA

Heuweltjies are large (20 m diameter) raised mounds, spread throughout much of the South-West Cape region of South Africa. Many heuweltjies have a thick basal calcrete layer. Our analyses of this calcrete layer indicate at the landscape level it contains several tonnes per hectare of Ca, Mg, Na and K. These amounts are surprisingly large considering that the underlying Table Mountain Group sedimentary rocks contain low concentrations of these elements. The low present-day input rates of these elements from rainfall suggest that the calcrete must have formed under a different climate and depositional regime. We propose that some of these elements are derived from marine aerosol deposits. This is supported by the mean 87 Sr/ 86 Sr ratios obtained from the calcrete layer of 0.71303, which is much lower than that of the immediate underlying rocks (mean 0.74936). The δ 13 C values for calcretes (−4.5 to −8‰ PDB ) suggest that Cape heuweltjies are sinks of atmospheric CO 2 as the calcrete 13 C is different from local limestones and dolomites, which have δ 13 C values close to zero.

Multiple Reinjections and Crystal-mush Compaction in the Beacon Sill, McMurdo Dry Valleys, Antarctica

The Beacon Sill, a member of the Jurassic Ferrar group of the Transantarctic Mountains, South Victoria Land, is a 150 m thick tholeiitic diabase intrusion. Uniform on a field and macroscopic scale, it displays chemical and textural variability indicative of a sustained and complex history of emplacement and differentiation. Emplacement of the sill consisted of at least two, and probably four, discrete massive injections of magma, each averaging � 35 m thick, over a time span of � 100 years. The final injection event is marked by a 30 m thick interval of significantly finer-grained rock at the sill center.These fine-grained textures can be successfully reproduced by combining the results of thermal and crystal growth models, but only if the sill was a multiple intrusion. With the exception of a minor reinjection event captured in the chilled margin of the sill, earlier reinjection events are not evident texturally, most probably because of textural overprinting during prolonged cooling after initial crystallization. The dominant process involved in the postemplacement differentiation of the Beacon Sill was compactiondriven redistribution of interstitial liquid. Transfer of residual liquid from the compacting lower solidification front to the dilating upper solidification front resulted in characteristic chemical and mineralogical effects, such as the depletion of the lower half of the sill and the enrichment of the upper half of the sill in incompatible elements (e.g. TiO2, Zr) and modal granophyre. Based on thermodynamic models, most of the compaction occurred at a crystallinity of roughly 33%. Geochemical profiles are distinctly segmented, suggesting that the sill was repeatedly split and reinjected with fresh magma near the center after compaction had redistributed the interstitial liquid within the partially solidified magma. The recognition of evidence for reinjection and compaction in a macroscopically uniform, relatively quickly cooled sill suggests that these processes may be common in the construction of sills and other mesoscale igneous intrusions in general.

Microgeographic Differentiation in Historical Yemen Inferred by Morphometric Distances

This study analyzed the variations in space of 8 body dimensions and 11 measures of the head of 1,244 adult Yemenite males, collected in 1933/34 by Coon in Yemen and in Hadhramawt. The aim was to evaluate the presence of geographic microdifferentiation of the populations settled in the different regions of Yemen at the time. Coon sub-divided the sample into six geographical areas according to birthplace and ethnicity of the individuals: Tihamah, the Western Mountains, the Central Plateau, the South Coast, the Eastern Mountains, and Hadhramawt. The results of ANCOVA (age as covariate) show that the observed differences of all variables among the six groups were highly statistically significant. Tukey's post-hoc test reveals higher statistically significant differences among four main groups: (1) Tihamah; (2) the Western Mountains and Central Plateau; (3) the Eastern Mountains; and (4) the Southern Coast and Hadhramawt. Multiple discriminant analysis carried out using only the data of the 11 measures of the head, the more "genetically" determined variables, confirmed these differences. Indeed, the first canonical variate well separates the groups with the Tihamah, Southern Coast and Hadhramawt on the one side and the Eastern Mountains, Western Mountains and Central Plateau on the other. The second canonical variate separates the Tihamah, Western Mountains and Central Plateau from the Eastern Mountains, Southern Coast and Hadhramawt. In conclusion, the Yemenite population seems to be composed of three morphologically distinct groups and an Eastern Mountains group which is positioned between the group formed by the Southern Coast and Hadhramawt and the Western Mountains and Central Plateau group. The Tihamah is the most distant from all the other groups. These differences are probably due to the presence/absence of geographical and cultural barriers that have favored/blocked the gene flow over the years. Indeed, the entire coastal bell, through the centuries, has constituted one of the principal commercial routes between the East, Africa, and the eastern Mediterranean, while the high inland mountains have isolated the remaining communities. This data is also confirmed by genetic studies. Finally, the average height (162.6 cm) of the global Yemenite population, compared to data from the other six middle-eastern Arab countries and Egypt, was found to be 3-6 cm less. This characteristic will be further studied, analyzing variations in average height according to the different age classes in order to evaluate any possible secular changes.

Microgeographic Differentiation in Historical Yemen Inferred by Morphometric Distances

This study analyzed the variations in space of 8 body dimensions and 11 measures of the head of 1,244 adult Yemenite males, collected in 1933/34 by Coon in Yemen and in Hadhramawt. The aim was to evaluate the presence of geographic microdifferentiation of the populations settled in the different regions of Yemen at the time. Coon sub-divided the sample into six geographical areas according to birthplace and ethnicity of the individuals: Tihamah, the Western Mountains, the Central Plateau, the South Coast, the Eastern Mountains, and Hadhramawt. The results of ANCOVA (age as covariate) show that the observed differences of all variables among the six groups were highly statistically significant. Tukey’s post-hoc test reveals higher statistically significant differences among four main groups: (1) Tihamah; (2) the Western Mountains and Central Plateau; (3) the Eastern Mountains; and (4) the Southern Coast and Hadhramawt. Multiple discriminant analysis carried out using only the data of the 11 measures of the head, the more “genetically” determined variables, confirmed these differences. Indeed, the first canonical variate well separates the groups with the Tihamah, Southern Coast and Hadhramawt on the one side and the Eastern Mountains, Western Mountains and Central Plateau on the other. The second canonical variate separates the Tihamah, Western Mountains and Central Plateau from the Eastern Mountains, Southern Coast and Hadhramawt. In conclusion, the Yemenite population seems to be composed of three morphologically distinct groups and an Eastern Mountains group which is positioned between the group formed by the Southern Coast and Hadhramawt and the Western Mountains and Central Plateau group. The Tihamah is the most distant from all the other groups. These differences are probably due to the presence/absence of geographical and cultural barriers that have favored/blocked the gene flow over the years. Indeed, the entire coastal belt, through the centuries, has constituted one of the principal commercial routes between the East, Africa, and the eastern Mediterranean, while the high inland mountains have isolated the remaining communities. This data is also confirmed by genetic studies. Finally, the average height (162.6 cm) of the global Yemenite population, compared to data from the other six middle-eastern Arab countries and Egypt, was found to be 3–6 cm less. This characteristic will be further studied, analyzing variations in average height according to the different age classes in order to evaluate any possible secular changes.

Forced regressive tidal flats: response to falling sea level in tide-dominated settings

Abstract During forced regression, the coastline advances seaward irrespective of sediment supply and relocates to a topographically lower position. Forced-regressive deposits are a component of the falling-stage systems tract. They are recognized by a basal unconformity which records erosion during the seaward facies shift, and are in turn capped by another unconformity due to subaerial exposure or wave ravinement during subsequent transgression. In wave-dominated settings, the basal “regressive surface of marine erosion” is a scoured surface cut by wave action, because erosion is needed to maintain the seaward-sloping bathymetric profile in equilibrium with the wave energy. The response to falling sea level in tide-dominated settings has not been as thoroughly discussed. The stratal architecture of the Lower Cambrian Gog Group of the southern Canadian Rocky Mountains reveals a new mechanism for the formation of this surface landward of the lever point of balance between sedimentation and erosion in the subtidal environment. Subtidal parasequences of the Lake O’Hara Member are typically composed of thin-bedded mudstone and ripple cross-laminated sandstone, followed by Skolithos pipe rock and thin- to medium-bedded cross-stratified sandstone overlain by thick-bedded cross-stratified sandstone. However, at the top of the Lake O’Hara Member, an erosional surface truncates a pipe-rock interval and the expected capping cross-stratified sandstones are absent. Overlying this surface, the Lake Oesa Member comprises tidal-flat deposits composed mainly of thinly interbedded mudstone and sandstone. This jump in facies at the erosional surface can be explained as a response to a fall in sea level. As the shoreline is forced to regress, the laterally continuous tidal flats advance and the pre-existing shallow-subtidal compound dunes are scoured by strong tidal currents, along with waves, that gradually carve a new equilibrium profile. We argue that the accretion of intertidal flats on top of subtidal sands is an overlooked yet predictable component of falling-stage systems tracts in tide-dominated settings.

Constraining the timing and provenance of the Neoproterozoic Little Willow and Big Cottonwood Formations, Utah: Expanding the sedimentary record for early rifting of Rodinia

U–Pb ages of detrital zircon spectra indicate that the Little Willow Formation in the Wasatch Range, Utah, is not a part of a Paleoproterozoic basement complex (∼1700–1800Ma) as previously thought, but is a metamorphosed part of the Big Cottonwood Formation (∼750Ma). The youngest detrital zircon grains in the metamorphic Little Willow and unmetamorphic Big Cottonwood Formations are 750–850Ma. These young zircons form a small, but persistent population possibly from Rodinia rift-related magmatism. The majority of the zircons are Grenville-age with other smaller populations derived from the Laurentian anorogenic granites, Mazatzal/Yavapai terranes, and Wyoming Craton. The distribution of new U–Pb detrital zircon ages from the Little Willow Formation has a high statistical probability of similarity to the detrital zircon spectra previously reported from both the Big Cottonwood Formation and the Uinta Mountain Group. Based on these similarities, we propose that the Little Willow Formation represents some of the earliest sediment shed into the Uinta rift basin during the earliest-known phases of Rodina break-up in western Laurentia. The Little Willow is not, therefore of Paleoproterozoic or Archean age as is shown on existing geologic maps.Lu–Hf isotopes in detrital zircons from the Little Willow and Big Cottonwood Formations compared with potential source regions provide evidence that the sediment could have been derived from eastern Laurentia and thus requiring a transcontinental river to transport the sediment ∼2000km. The U–Pb and Lu–Hf values from the Little Willow and Big Cottonwood Formations correspond well with the ∼1.0Ga Grenvillian basement, 1.4Ga A-type Granites intruding the Central and Western Yavapai, evolved portion of the 1.7–1.8Ga Santaquin Complex, and the 1.6–3.0Ga Farmington Canyon Complex (Wyoming Craton).

Evidence of climate change impact upon glaciers’ recession within the Italian Alps

We present evidence of climate change impact upon recent changes of glaciers within Lombardy region, in Northern Italy. We illustrate the recent area evolution of a set of 249 glaciers in the area using three surface area records for 1991, 1999 and 2003. The 1999 and 2003 surface area data are processed by combining glacier limits manually digitized upon registered color orthophotos and differential GPS (DGPS) glaciers’ surveys. Glaciers’ area was 117.4 km2 in 1991, 104.7 km2 in 1999, and to 92.4 km2 2003, with a 21% reduction. Glaciers smaller than 1 km2 accounted for 53% of the total loss in area (13.1 km2 during 1991–2003). The area change rate was higher lately, with ca. 11.7 % reduction during 1999–2003. We split Alps and fore Alps of Lombardy into six mountain groups, and we separately investigate relative area variations. We use climate series from local stations within each group to assess climate change during a 30-year window (1976–2005). We focus upon temperature and snow cover depth at thaw, known to impact glaciers’ changes. We compare local year-round temperature anomalies against global ones to evidence enhanced warming within this area, and we investigate the correlation of our target climate variables against NAO. Eventually, we highlight the link between the rate of change of our climate variables to the observed scaling of area loss against glaciers’ size, showing that in rapidly warming areas glaciers’ size affects less relative melting.

Sedimentological–ichnological model for tide‐dominated shelf sandbodies: Lower Cambrian Gog Group of western Canada

AbstractDunes and bars are common elements in tide‐dominated shelf settings. However, there is no consensus on a unifying terminology or a systematic classification for thick sets of cross‐stratified sandstones. In addition, their ichnological attributes have hardly been explored. To address these issues, the properties, architecture and ichnology of compound cross‐stratified sandstone bodies contained in the Lower Cambrian Gog Group of the southern Canadian Rocky Mountains are described here. In these transgressive sandstones, five types of compound cross‐stratified sandstone are distinguished based on foreset geometry, sedimentary structures and internal heterogeneity. These represent four broad categories of subtidal sandbodies: (i) compound‐dune fields; (ii) sand sheets; (iii) sand ridges; and (iv) isolated dune patches; tidal bars comprise a fifth category but are not present in the Gog Group. Compound‐dune fields are characterized by sigmoidal and planar cross‐stratified sandstone in coarsening‐upward and thickening‐upward packages (Type 1); these are mostly unburrowed, or locally contain representatives of the Skolithos ichnofacies, but are intercalated with intensely bioturbated sandstone containing the archetypal Cruziana ichnofacies. Sand‐sheet complexes, also composed of compound dunes, cover more extensive subtidal areas, and comprise three adjacent subenvironments: core, front and margin. The core is characterized by thick‐bedded sets of cross‐stratified sandstone (Type 2). A decrease of bedform size at the front is recorded by wedges of thinner‐bedded, low‐angle and planar cross‐stratified sandstone (Type 3) exhibiting dense Skolithos pipe‐rock ichnofabric. The margin is characterized by interbedded sandstone and mudstone, and hummocky cross‐stratified sandstone. Sand‐sheet deposits exhibit clear trends in trace‐fossil distribution along the sediment transport path, from non‐bioturbated beds in the core to Skolithos ichnofacies at the front, and a depauperate Cruziana ichnofacies at the margin. Tidal sand ridges are large elongate sandbodies characterized by large sigmoid‐shaped reactivation surfaces (Type 4). Sand ridges display clear ichnological trends perpendicular to the axis of the ridge, with no bioturbation or a poorly developed Skolithos ichnofacies in the core, a depauperate Cruziana ichnofacies in lee‐side deposits, and Cruziana ichnofacies at the margin. While both tidal ridges and tidal bars migrate by means of lateral accretion, the latter occur in association with channels while the former do not. Because tidal bars tend to occur in brackish‐water marginal‐marine settings, their ichnofauna are typically of low diversity, representing a depauperate Cruziana ichnofacies. Isolated dune patches developed on sand‐starved areas of the shelf, and are represented by lenticular sandbodies with sigmoidal reactivation surfaces (Type 5); they typically lack trace fossils, but the interfingering muddy deposits are intensely bioturbated by a high‐diversity fauna recording the Cruziana ichnofacies. The variety of sandbody types in the Gog Group reflects varying sediment supply and location on the inner continental shelf. These, in turn, governed substrate mobility, grain size, turbidity, water‐column productivity and sediment organic matter which controlled trace fossil distribution.

A spatial assessment of riverine ecosystems and water supply in a semi‐arid environment

AbstractA spatial assessment was conducted in the semi‐arid area of South Africa, to: (1) identify priority areas for the conservation of river and groundwater ecosystems; (2) examine surface and groundwater quality for human consumption and (3) investigate the rehabilitation of degraded areas to highlight ‘win‐win’ situations for both environmental and human use. A systematic conservation plan was produced, highlighting river conservation areas (river types, fish species and connectivity areas), moderate‐impact management areas (groundwater‐surface water interaction and recharge areas) and river rehabilitation areas. The proposed river selections would achieve the biodiversity targets of 33 (66%) of the 50 river types; feasible rehabilitation would increase this to 92%. The greatest groundwater‐surface water interaction and recharge (30 to > 50 mm−1) values are concentrated around the mountainous regions of the Little Karoo. This is because the main aquifers in the mountains, table mountain group (TMG) quartzites, yield naturally good quality water for human consumption. River reaches of unacceptable surface water quality were classified as degraded water resource delivery areas where the poor water quality was primarily due to saline return flows from irrigation and the impacts of other anthropogenic activities including abstraction of freshwater which otherwise would have diluted the return flows. Only the middle reaches of the Gouritz and Groot Rivers represent a possible win–win situation for both the environment and human use. Copyright © 2010 John Wiley & Sons, Ltd.