Mountain Group Research Articles

The influence of mountain boots on gait

Mountain boots are heavier than everyday shoes and imprison the ankle joint; these characteristics may affect normal walking. The purpose of this study was to analyze temporal gait in a group of mountaineers who use these boots. Gait parameters were compared to those assessed for the same group wearing everyday shoes. A conductive walkway system was used for gait analysis; each mountaineer performed 3 runs at normal speed and 3 runs at fast speed, first wearing everyday shoes and then wearing mountain boots. The parameters determined were gait cycle duration (s), the durations of single support (SLS), double support (DLS) and single step (expressed as percentages of cycle duration), and the gait speed (m/s). Results with everyday shoes were compared to those with mountain shoes using the t test. Statistically significant differences between the two types of shoes were found in the SLS and DLS values in both normal and fast gait. These differences are attributed to the fact that mountain boots affect the gait in a variety of ways, such as the longer lever arm of the foot. In the long term, the increased single support and decreased double support may predispose to joint overload and arthritis development.

Lithofacies control in detrital zircon provenance studies: Insights from the Cretaceous Methow basin, southern Canadian Cordillera

High-frequency sampling for detrital zircon analysis can provide a detailed record of fine-scale basin evolution by revealing the temporal and spatial variability of detrital zircon ages within clastic sedimentary successions. This investigation employed detailed sampling of two sedimentary successions in the Methow/Methow-Tyaughton basin of the southern Canadian Cordillera to characterize the heterogeneity of detrital zircon signatures within single lithofacies and assess the applicability of detrital zircon analysis in distinguishing fine-scale provenance changes not apparent in lithologic analysis of the strata. The Methow/ Methow-Tyaughton basin contains two distinct stratigraphic sequences of middle Albian to Santonian clastic sedimentary rocks: submarine-fan deposits of the Harts Pass Formation/Jackass Mountain Group and fluvial deposits of the Winthrop Formation. Although both stratigraphic sequences displayed consistent ranges in detrital zircon ages on a broad scale, detailed sampling within each succession revealed heterogeneity in the detrital zircon age distributions that was systematic and predictable in the turbidite succession but unpredictable in the fluvial succession. These results suggest that a high-density sampling approach permits interpretation of finescale changes within a lithologically uniform turbiditic sedimentary succession, but heterogeneity within fluvial systems may be too large and unpredictable to permit accurate fine-scale characterization of the evolution of source regions. The robust composite detrital zircon age signature developed for these two successions permits comparison of the Methow/MethowTyaughton basin age signature with known plutonic source-rock ages from major plutonic belts throughout the Cretaceous North American margin. The Methow/ Methow-Tyaughton basin detrital zircon age signature matches best with source regions in the southern Canadian Cordillera, requiring that the basin developed in close proximity to the southern Canadian Cordillera and providing evidence against large-scale dextral translation of the Methow terrane.

Reservoir characterization of a Permian deep-water sandstone, East Ford field, Delaware basin, Texas

Deep-water sandstones of the Delaware Mountain Group in west Texas and southeast New Mexico contained an estimated 1.8 billion bbl of original oil in place, but primary recovery from these fields is commonly less than 20%. East Ford field in Reeves County, Texas, which produces from the Ramsey sandstone in the upper Bell Canyon Formation, went directly from primary production to tertiary recovery by CO2 flooding. Field production has increased from 30 to more than 185 BOPD. Oil recovery has been improved by the CO2 flood, but not as much as expected. Geologic heterogeneities such as interbedded siltstones are apparently influencing reservoir displacement operations in the East Ford unit.A depositional model of the East Ford unit was developed using data from Bell Canyon outcrops and subsurface data. The Ramsey sandstones were deposited by turbidity currents in a basin-floor setting. The sandstones are interpreted as having been deposited in a channel-levee system that terminated in broad lobes; overbank splays filled topographically low interchannel areas. Injection wells located in splay sandstones apparently have poor communication with wells in channel sandstones, perhaps because communication is restricted through levee and channel-margin deposits. The south part of the unit is responding well to the flood because the injection and production wells are in the same interconnected lobe depositional environment.

A marginal marine ichnofauna from the Blaiklock Glacier Group (?Lower Ordovician) of the Shackleton Range, Antarctica

ABSTRACTA diverse arthropod-dominated ichnofauna, associated with a poorly preserved crustacean fauna and soft-bodied ?medusoid impressions, is described from the Blaiklock Glacier Group of the north-western Shackleton Range (Coats Land), Antarctica. The ichnofauna consists of Asaphoidichnus, Beaconites, Didymaulichnus, Diplichnites, Gordia, ?Laevicyclus, Merostomichnites, Monomorphichnus, Palaeophycus, Planolites, Rusophycus, Selenichnites, and Taphrhelminthoides (ichnogen nov.). Three new ichnotaxa are recognised: Taphrhelminthoides antarcticus n. ichnogen. et ichnosp. is a bilobate trail, composed of two parallel flat lobes, separated by a median ridge with a characteristic figure-of-eight pattern. Merostomichnites gracilis n. ichnosp. is characterised by its proportions (external:internal width ratio >3) and series of 10 to 12, thin, linear tracks. Selenichnites antarcticus n. ichnosp. is characterised by small elongate horseshoe-shaped marks, the medial portion showing three to five transverse scratch-marks.The palaeoenvironment is interpreted as extremely shallow marine water, possibly a tide-dominated estuary, based on sedimentological evidence and the composition of the ichnofauna. Radiometric and palaeomagnetic data indicate that this assemblage is Lower Ordovician in age, representing the first autochthonous Ordovician fossiliferous succession to be described from Antarctica. The succession shows several sedimentological and palaeontological similarities with the basal units of the Ordovician Table Mountain Group in South Africa, supporting palaeogeographic models placing the Palaeozoic Blaiklock basin close to the Ordovician Table Mountain basin.

Is the rock partridge Alectoris graeca saxatilis threatened in the Dolomitic Alps?

AbstractChanges in abundance and the risk of extinction of the rock partridge Alectoris graeca saxatilis in the Dolomitic Alps were investigated using a density‐dependent model that incorporated dispersal and environmental stochasticity. The study was based on spring and summer counts collected from sample areas in geographically distinct mountain groups. Extinction probability was investigated by simulating a discrete population and a metapopulation consisting of local populations connected by dispersal. Persistence was not guaranteed when the species was examined as a discrete population. When we used a metapopulation approach, the persistence was assured but local extinctions with subsequent recolonizations of a number of empty areas were observed. The analysis was repeated using hunting statistics, when there were no restrictions on hunting policies, and a similar high extinction pattern was found. Our simulations suggested that long‐term persistence of rock partridge could be guaranteed only when immigration was included into the demographic model. However, if the increased population's fragmentation recorded since the 1950s persists the extinction of some of the subpopulations appears inevitable.

Structure of the Carrizo Mountain Group, southeastern Carrizo Mountains, west Texas: A transpressional zone of the Grenville orogen

The west Texas segment of the Grenville orogen includes an oblique, dextral, transpressive zone. The orogen exposed near Van Horn, Texas, displays a transition from the mid‐amphibolite‐facies metamorphic core to a foreland fold and thrust belt. In this paper, detailed structural mapping and analyses, presented for key exposures of the metamorphic rocks, the Mesoproterozoic Carrizo Mountain Group, show a southeastward increase in number of deformational phases and intensity of deformation. The central portion is dominated by oblique northwest convergence, which produced two phases of northwest verging folds and synchronous, oblique reverse and dextral shearing. The thick parts of pre‐tectonic mafic plutons, which had been emplaced as locally discordant sills, control the spatial distribution of structures. Two dominant phases of folds form Type 0 interference patterns (essentially coaxial and coplanar; i.e., fold tightening was dominant). This central belt also contains en echelon reverse to oblique shear zones and comprises a transfer zone within the orogen between structurally higher and lower major shear zones. Overall, the mapped part of the central Carrizo Mountains represents localized dextral transpression within a larger region dominated by reverse motion, possibly indicating a change through time from orthogonal to oblique contraction. Further south in the Bass Canyon region, the earlier fold generations are refolded into Type 2 (“mushroom”) interference patterns. These structures show a westward vergence and are kinematically linked to those further north across a zone of disharmonic folding and heterogeneous shear. The structure and kinematics of the polyphase deformation and ductile shearing in the metamorphic portion of the orogen is compatible with that seen in the foreland fold‐thrust belt, suggesting that in both foreland and hinterland, transpression was a characteristic feature of the west Texas Grenville orogeny. The timing and kinematics of deformation in the Van Horn exposures contrasts with that seen in the Llano uplift, but compares favorably with those of the Natal belt, South Africa, a relationship with implications for recently proposed reconstructions of Rodinia.

The main Plant community types of the alpine belt of the Apennine chain

ABSTRACT This paper deals with the occurrence of the main plant community types occurring within the alpine bioclimatic belt in the Central Apennines. The study area was represented by three mountain groups, the Gran Sasso, Maiella and Laga mountains. These three mountain chains are those in which, out of the entire Apennine area, alpine vegetation is best expressed. The vegetation has been investigated following the Braun-Blanquet phytosociological approach. During the field work 135 relevés were collected. The raw data were further treated with multivariate analysis procedures to find objective clusters on a statistical basis. Several plant community types, belonging to different phytosociological classes, such as Elyno-Seslerietea, Salicetea herbaceae, Thlaspietea rotundifolii, Asplenietea trichomanis, were identified. In particular two new phytosociological associations, Galio-Silenetum acaulis and Potentillo-Festucetum alfredianae, and several new subassociations are described in this paper. In order to express the occurrence and autonomy of the Apennine alpine bioclimatic belt also in coenological terms, a new Seslerion apenninae sub-alliance, named Leontopodio-Elynenion, is here proposed.

Relay Mountain Group, Tyaughton–Methow basin, southwest British Columbia: a major Middle Jurassic to Early Cretaceous terrane overlap assemblage

The upper Middle Jurassic to Lower Cretaceous Relay Mountain Group is the lower part of the northern Tyaughton–Methow basin, southwestern British Columbia. The Relay Mountain Group consists of ~2700–3400 m of clastic rocks that we subdivide into three formal formations. The Callovian and lower Oxfordian Tyoax Pass Formation is marine shale and sandstone turbidites. The Teepee Mountain Formation consists of upper Oxfordian to Valanginian shallow marine clastic rocks with common Buchia and fluvial and marginal marine facies in the upper part of the unit in the northwest. These rocks overlie the lower formation across an abrupt conformable to disconformable contact. The Hauterivian (and Barremian?) Potato Range Formation consists of clastic rocks that are marine in the southeast, mainly nonmarine to the northwest, and derived from the west. This unit displays an abrupt conformable to disconformable contact with the middle formation and locally rests above the lower formation across an angular unconformity. The Relay Mountain Group and correlative strata of the southeastern Coast Belt form an overlap assemblage above the Bridge River and Cadwallader (including Methow) terranes and link them by late Middle Jurassic time. The early Relay Mountain Group appears to have been a fore-arc basin, possibly along an oblique–convergent margin in the middle unit. The upper unit indicates major changes to a back-arc basin linked to the Ottarasko, and possibly Gambier, arc to the west. This is the oldest probable link (~130 Ma) between the southeastern and southwestern Coast belts.

Tectonic setting and provenance of the Neoproterozoic Uinta Mountain and Big Cottonwood groups, northern Utah: constraints from geochemistry, Nd isotopes, and detrital modes

The Neoproterozoic Uinta Mountain Group was deposited in an east-trending intracratonic rift bounded on the north by an active fault system and opening into a shallow sea on the west where the Big Cottonwood Group was deposited in an estuary. Although this rift may have been associated with the early stages in the breakup of Rodinia, it was not an aulacogen. Geochemical, Nd isotope, and detrital mode studies indicate that Uinta Mountain Group sediments were derived from mixed Archean and Paleoproterozoic sources with the former dominating. Big Cottonwood Group sediments appear to have been derived predominantly from Paleoproterozoic sources. The Archean sediment source is the Wyoming craton, and source rocks comprised dominantly granites enriched in Th, U, Y, Zr, Hf, and REE. The relative abundance of enriched granite implied by sedimentary rocks of the Uinta Mountain Group indicates that the Wyoming craton is anomalous compared to other Archean cratons. CIA values and A–CN–K relationships in shales of the Uinta Mountain and Big Cottonwood groups indicate high degrees of weathering of sources, probably in subtropical to tropical climates supporting a near-equatorial location for southwestern Laurentia at about 800 Ma. Differences in the Nd isotopic composition between the Big Cottonwood Group and Neoproterozoic sedimentary rocks in western Utah and northeast Nevada suggest a northwest-striking uplift in northwest Utah, possibly ancestral to the Paleozoic Toole–Uinta arch.

Depositional landforms and environmental change in the headward vicinity of Dias Beach, Cape Point

The southern portion of the Cape Peninsula is characterised by a number of geomorphic features that reveal evidence of fluctuating sea levels and past environments. These include pronounced wave-cut platforms and the remnants of fossilised dunes. This paper reports on a unique Late Quaternary sedimentary sequence preserved within a steep-sided ravine between Cape Point and Cape Maclear at the southern tip of the Cape Peninsula. The site is situated headward of Dias Beach, where erosion has exploited a Cretaceous dolerite dyke that has intruded the Ordovician Table Mountain Group sandstone. The sediments have been incised during the Holocene, and the resultant gullies present exposed faces whose lithostratigraphy attests to a variety of geomorphic processes, which were active during the Late Pleistocene. The two main deposits reveal contrasting sedimentary structures, representing very different depositional environments. Immediately above the active dune cordon, which flanks the modern beach, a sequence of aeolianite (calcarenite) displays a variety of low-angle planar and high-angle cross bedding. This calcarenite is moderately cemented, but not completely lithified. Overlying this sequence, above an abrupt unconformity, is a massive colluvial deposit comprising unconsolidated, quartzose sand, as well as angular sandstone clasts in a number of lags. This deposit does not display any sedimentary structures. The uppermost section of the aeolianite was dated by thermoluminescence to 185 ka. The aeolian lithofacies is interpreted to be the product of aeolian deposition by onshore winds during the transition period following the 220 ka Penultimate Interglacial, the period when sea-level initiated its retreat towards the 150 ka Penultimate Glacial Lowstand. The colluvial deposit is interpreted as the midfan remains of an alluvial/colluvial fan formed by debris flow and sheetwash. Optically stimulated luminescence (OSL) dates from the base (83 ka) and the top (32 ka) of the main fan exposure suggest emplacement during the Last Glacial. Whereas the aeolianite is regarded as the product of an onshore depositional phase, the emplacement process of the colluvial fan suggests the increased presence of moisture. This, in turn, may imply a wetter environment for the southwestern Cape during the Last Glacial. It is known that the Last Glacial was generally drier over the summer-rainfall region of South Africa, but the situation for the present winter-rainfall region remains unclear. The findings from this study support the notion that conditions for the winter-rainfall region of the southwestern Cape may have been wetter prior to the termination of the Last Glacial.

The hydrogeology of the Uitenhage Artesian Basin with reference to the Table Mountain Group Aquifer

The Uitenhage Artesian Basin (UAB) lies in the Eastern Cape and is South Africa’s most important artesian groundwater basin, supplying approximately 1 400 Ml/yr (44 l/s) of water from springs for domestic use to Uitenhage, as well as supporting large citrus irrigation schemes. Groundwater from this basin has been extensively utilised from the early part of the 20 th century, including periods of over-exploitation resulting in the declaration of a groundwater control area to limit abstraction to sustainable rat es. The aquifer comprises fractured Table Mountain Group (TMG) sandstones confined in the eastern part of the basin by overlying Cretaceous siltstones and mudstones, resulting in artesian conditions. The Coega Fault is a major structural feature dividing the basin into separate systems, viz. the southern Swartkops Aquifer and the northern Coega Ridge Aquifer, that are hydrogeological ly independent of each other. The Elands River syncline divides the Swartkops Aquifer further into the Kruisrivier and Bethelsdor p Units. Borehole yields commonly range from 5 to 10 l/s and the groundwater quality is excellent with low salinities. Water hardening, however, is required due to the acidic and corrosive nature of the groundwater, typical of other Table Mountain Group aquifers in South Africa. Using 14 C data, the age of the groundwater in the basin ranges from 1 500 to 28 000 years with a calculated flow rate of 0.8 m/a. From the chloride mass balance method, recharge rates are determined to be 25 to 55% of annual rainfall. Groundwa ter temperatures generally show that depths of groundwater strikes do not necessarily correspond with depth of origin, indicating a complex groundwater circulation pattern within the basin. Whilst the UAB has been well studied locally, a basin-scale hydrogeological characterisation is considered to be necessary, followed by recommendations and formulation of a management plan to ensure the continued sustainability of groundwater supply from this national asset.

ABSTRACT: Sequence Stratigraphy of the Permian Delaware Mountain Group, Basin Floor Setting, Delaware Basin, West Texas and Southeastern New Mexico: Application of Stacking Pattern Analysis

ABSTRACT: Sequence Stratigraphy of the Permian Delaware Mountain Group, Basin Floor Setting, Delaware Basin, West Texas and Southeastern New Mexico: Application of Stacking Pattern Analysis

The maximum Ice Age (LGM) glaciation of the Central- and South Karakorum: an investigation of the heights of its glacier levels and ice thicknesses as well as lowest prehistoric ice margin positions in the Hindukush, Himalaya and in East-Tibet on the Minya Konka-massif

A continuing prehistoric ice stream network between the Karakorum main crest and the Nanga Parbat massive has been evidenced, which, flowing down from the current Baltoro- and Chogolungma glaciers and filling the Shigar valley as well as the Skardu Basin, has flowed together with the Gilgit valley glacier to a joint Indus parent glacier through the Indus gorge. The ice stream network received an influx by a plateau glacier covering the Deosai plateau, which was connected through outlet glaciers to the ice filling of the Skardu Basin and the Astor glacier at the Nanga Parbat, as well as to the lower Indus glacier. The field observations introduced here in part confirm the results as to the Ice Age glacier surface area of Lydekker, Oestreich and Dainelli, but go beyond it. In additon, a reconstruction of the surface level of this ice stream network and its glacier thicknesses up to the highest regions of the present-day Karakorum valley glaciers has been carried out for the first time. In the area under investigation the Karakorum ice stream network showed three ice cupolas, culminating at an altitude of 6200–6400 m. Between the mountain groups towering 1000–2000 m higher up, they communicated with each other over the transfluence passes in a continuous glacier surface without breaks in slope. In the Braldu- and Basna valley ice thicknesses of 2400–2900 m have been reached. In the Skardu Basin, where the glacier thickness had decreased to c. 1500–1000 m, the ELA at an ice level of 3500-3200 m asl had fallen short to the extent that from here on down the Indus glacier a surface moraine cover has to be suggested. However, 80% of the surface of the ice stream network was devoid of debris and had an albedo of 75-90%. The lowest joint glacier terminus of the ice stream network was situated - as has already been published in 1988 – in the lower Indus valley at 850–800 m asl. The reconstructed maximum extension of the ice stream network has been classified as belonging to the LGM in the wider sense (60–18 Ka BP). Four Late Glacial glacier positions (I–IV), with a decreasing ice filling of the valleys, have been differentiated, which can be locally recognized through polish lines and lateral moraine ledges.

Are grouse populations unstable at the southern end of their range?

The long‐term temporal dynamics of four grouse species in the Italian Alps have been investigated in the attempt to reveal if the populations exhibit the tendency to cycle at the southern edge of their European range. Hunting statistics or count data were collected as total number of individuals shot or counted each year from five provinces. For the province of Trento data were available at the level of mountain groups and a more detailed investigation was carried out. The results from Trento were compared with the more general findings from the other four Italian provinces. Time series analysis was performed to investigate the pattern of cycle and autoregressive models were used to describe the density dependence structure. In general, the populations showed a weak or no tendency to regular fluctuations: rock ptarmigan Lagopus mutus and black grouse Tetrao tetrix populations exhibited the highest tendency to cycle with periods of 5–9 years while capercaillie Tetrao urogallus never showed regular fluctuations. Hazel grouse Bonasa bonasia cyclic dynamics were restricted to a few populations of Trento. When time series from Trento were corrected for hunting effort the detection of cycle among populations sharply increased but no differences in the strength of second order density dependence or in the period length was observed. A linear first order autoregressive model explained better the intrinsic structure of the majority of populations. We compare the findings with studies conducted on populations of northern Europe and suggest possible reasons for the reduced tendency to cycle in the grouse populations of the Italian Alps.

Oxygen and hydrogen isotope geochemistry of thermal springs of the Western Cape, South Africa: Recharge at high altitude?

A number of thermal springs with temperature up to 64°C are found in the Western Cape Province of South Africa. The average δ 13C value of gas (CO 2+CH 4) released at three springs is −22ℵ, which is consistent with an entirely biogenic origin for the C and supports previous investigations which showed that the springs are not associated with recent or nascent volcanic activity. Most springs issue from rocks of the Table Mountain Group, where faulted and highly jointed quartzites and sandstones of the Cape Fold Belt act as the main deep aquifer. The δD and δ 18O values of the springs range from −46 to −18ℵ and from −7.3 to −3.9ℵ, respectively. Although the thermal springs have isotope compositions that plot close to the local meteoric water line, their δD and δ 18O values are significantly lower than ambient meteoric water or groundwater. It is, therefore, suggested that the recharge of most of the thermal springs is at a significantly higher altitude than the spring itself. The isotope ratios decrease wuth increasing distance from the west coast of South Africa, which is in part related to the continental effect. However, a negative correlation between the spring water temperature and the δ 18O value in the thermal springs closest to the west coast indicates a progressive in increase in the average altitude of recharge away from the coast.

Molecular Systematics of Pikas (Genus Ochotona) Inferred from Mitochondrial DNA Sequences

The phylogenetic relationships among worldwide species of genus Ochotona were investigated by sequencing mitochondrial cytochrome b and ND4 genes. Parsimony and neighbor-joining analyses of the sequence data yielded congruent results that strongly indicated three major clusters: the shrub–steppe group, the northern group, and the mountain group. The subgeneric classification of Ochotona species needs to be revised because each of the two subgenera in the present classification contains species from the mountain group. To solve this taxonomic problem so that each taxon is monophyletic, i.e., represents a natural clade, Ochotona could be divided into three subgenera, one for the shrub–steppe species, a second for the northern species, and a third for the mountain species. The inferred tree suggests that the differentiation of this genus in the Palearctic Region was closely related to the gradual uplifting of the Tibet (Qinghai-Xizang) Plateau, as hypothesized previously, and that vicariance might have played a major role in the differentiation of this genus on the Plateau. On the other hand, the North American species, O. princeps, is most likely a dispersal event, which might have happened during the Pliocene through the opening of the Bering Strait. The phylogenetic relationships within the shrub–steppe group are worth noting in that instead of a monophyletic shrub-dwelling group, shrub dwellers and steppe dwellers are intermingled with each other. Moreover, the sequence divergence within the sister taxa of one steppe dweller and one shrub dweller is very low. These findings support the hypothesis that pikas have entered the steppe environment several times and that morphological similarities within steppe dwellers were due to convergent evolution.

Geology and geochronology of Grenville-age rocks in the Van Horn and Franklin Mountains area, west Texas: Implications for the tectonic evolution of Laurentia during the Grenville

New U-Pb zircon and 40 Ar/ 39 Ar geochronological data for the Mesoproterozoic rocks at Van Horn, far west Texas, indicate that metarhyolite, quartzite, phyllite, and metabasalt of the Carrizo Mountain Group were formed ca. 1380–1330 Ma and are probably a southern part of the Southern Granite–Rhyolite province of W.R. Van Schmus and coworkers. These rocks were thrust over the ca. 1250 Ma carbonate-basalt-rhyolite sequence of the Allamoore and Tumbledown Formations and the younger Hazel Conglomerate (ca. 1035 Ma). The Castner Marble and Mundy Breccia of the Franklin Mountains near El Paso are coeval, and probably correlative, with the Allamoore-Tumbledown sequence. The ca. 1120 Ma granite and rhyolite boulders in the Hazel Formation are coeval with the Red Bluff Granite Suite and rhyolite of the Thunderbird Formation, both occurring in the Franklin Mountains, indicating that formation of granite and rhyolite was widespread in far west Texas at this time. Although these rocks are temporally related to the classic Grenvillian events of eastern North America and the Llano uplift of central Texas, they contrast starkly in their much lower (lowest greenschist) metamorphic grade and degree of deformation. It is likely that the Allamoore-Tumbledown-Castner-Mundy sequences, with their shallow-water sedimentary rocks and bimodal volcanic assemblages, accumulated ca. 1250 Ma in rift basins that formed on the southern margin of Laurentia during Grenville orogenesis. Renewed or continued extensional tectonism is implied by the presence of ca. 1120 Ma alkaline granitic and/or basaltic rocks in the Franklin Mountains, at Pajarito Mountain in New Mexico, in the Apache Group of southern Arizona, and in the Pahrump Group of the Death Valley region of southeastern California; all of these occurrences have been attributed to accumulation in rift basins. The striking alignment of these occurrences suggests that they were formed along a zone of transcurrent faulting that extended along the southern margin of Laurentia during Grenvillian (Mesoproterozoic) time.

Ultrastructure and morphology of Chuariacircularis ( ) from the Neoproterozoic Visingsö Group, Sweden

The organic-walled microfossil Chuaria circularis [Walcott, C.D., 1899. Precambrian fossiliferous formations. Geol. Soc. Am. Bull. 10, 199–244] Vidal and Ford [Vidal, G., Ford, T.D., 1985. Microbiotas from the Late Proterozoic Chuar Group (Northern Arizona) and Uinta Mountain Group (Utah) and their chronostratigraphic implications. Precambrian Res. 28, 349–389] from the Visingsö Group in Sweden have been re-examined using reflected and transmitted light, scanning electron and (SEM) transmission electron (TEM) microscopy. Specimens extracted from the rock matrix and those in situ, compressed on the bedding planes, were both studied. Besides previously described external wall surface, a psilate internal surface of Chuaria vesicle was observed. Transmission electron microscopy revealed a single-layered, electron-dense and homogeneous wall ultrastructure of the microfossil. Similar wall ultrastructure has been observed in other acid resistant microfossils from Lower Cambrian rocks. Various stages of the microfossils’ wall degradation were observed and are discussed in the paper. An overview of morphological interpretations and the history of research of C. circularis is presented.

ABSTRACT: Sequence Stratigraphy of the Permian Delaware Mountain Group, Delaware Basin, West Texas

ABSTRACT: Sequence Stratigraphy of the Permian Delaware Mountain Group, Delaware Basin, West Texas

Finding spatial regularity in mosaic landscapes: two methods integrated

Two methods were employed to find spatial regularity in a complicated mountain landscape of Beijing, China on the basis of functional and structural affinities. The first approach applied Affinity Analysis based on species composition to landscape. The mosaic diversity of the landscape was 3.5298 >3, which means the study landscape is complex and controlled by multiple environmental gradients. These landscape types were divided into 3 parts according to the mean affinity values of 0.2143 and 0.7857 (0.5 +/-1 SD). Modal sites are the central types of the landscape, which include a zonal broad-leaved forest of the region and a conifer plantation replacing the former. Outliers are found in the highest altitude and the lowest, both have few species in common with the above two modal types. The remaining landscape types are intermediate sites, which are transitional between modals and outliers, broadly distributed throughout mountain environments. Neighbor types have more species in common than those more widely separated, which probably distributed adjacently in space or in similar quality habitat. The other method employed is the new TWINSPAN analysis by substituting spatial neighboring data of landscape types for species composition data. It clearly divided the landscape types into three groups, i.e., subalpine, middle and low mountain groups, which were correlated with altitude, as well as influenced by human disturbance. The new TWINSPAN classification method is more reliable in finding spatial gradient of patchy landscapes than affinity analysis; however, affinity analysis is useful in finding species diversity pattern and the importance of landscape types in a region. Integrating advantages of the two methods could supply complete and reliable information on how landscape types are distributed in space, which environmental gradient dominates the spatial distribution of the landscape types, as well as where important and unusual types are located.