Quaternary records of pika, Ochotona, in North America

Mead, Jim I. 1987 06 01: Quaternary records of pika, Ochotona , in North America. Boreas , Vol. 16, pp. 165–171. Oslo. ISSN 0300–9483.
Pika (Lagomorpha: Ochotona ) have lived in North America since the Hemphillian land mammal age (late Pliocene). At least three species, O. whartoni (extinct giant pika), O. princeps (the living species), and unidentified large and small forms, lived in North America during the Quaternary. Forty-six localities of Quaternary-age pika are recorded. Many localities are actually site clusters, where packrat (Rodentia: Neotoma ) middens or stratified sediments record pika fossils of many ages. Packrat middens in the arid west have provided pika dung pellets directly associated with plant macrofossils. Individual dung pellets provide direct radiocarbon dates and microhistological remains permit dietary reconstructions. Pika lived in northeastern portions of the continent during the Illinoian glacial age and possibly earlier. During the Wisconsinan glacial period, pika stayed in the mountainous west, but an exception exists. It is proposed that pika were not restricted to rocky/talus slopes during the Pleistocene, as is the living species in North America, and therefore should not be used as an indicator of ecological niche. Equable climates (cooler summers) may have been all that was needed for pika to migrate to new territories, areas without talus.     

Molecular identification of the extinct mountain goat, Oreamnos harringtoni (Bovidae)

Campos, P. F., Willerslev, E., Mead, J. I., Hofreiter, M. & Gilbert, M. T. P. 2009: Molecular identification of the extinct mountain goat, Oreamnos harringtoni (Bovidae). Boreas , 10.1111/j.1502-3885.2009.00111.x. ISSN 0300-9483.
Harrington's mountain goat ( Oreamnos harringtoni ), an extinct North American herbivore, is one of the least known mammals of the Pleistocene. Fossil specimens are predominantly known from dry cave localities throughout the arid American west – the Grand Canyon, Colorado Plateau, Nevada and Mexico. Morphological analysis of the recovered fossils suggests a close phylogenetic relationship between Harrington's mountain goat and the extant mountain goats from the American northwest ( Oreamnos americanus ). However, the degree of genetic similarity between the two species, and their overall placement within the Caprinae, is not clear. In this study, we recovered and sequenced the first DNA fragments from O. harringtoni in order to investigate these relationships. Genetic analysis further supports the morphological hypothesis that O. harringtoni and O. americanus are two distinct species.     

Mapping groundwater quality variables using PCA and geostatistics: a case study of Bajo Andarax,southeastern Spain

Abstract

A case study is presented for the application of statistical and geostatistical methods to the problem of estimating groundwater quality variables. This methodology has been applied to the investigation of the detrital aquifer of the Bajo Andarax (Almería, Spain). The use of principal components analysis is proposed, as a first step, for identifying relevant types of groundwater and the processes that bring about a change in their quality. As a result of this application, three factors were obtained, which were used as three new variables (VI: sulphate influence; V2: thermal influence; and V3: marine influence). Analysis of their spatial distribution was performed through the calculation of experimental and theoretical variograms, which served as input for geostatistical modelling using ordinary block kriging. This analysis has allowed a probabilistic representation of the data to be obtained by mapping the three variables throughout the aquifer for each sampling point. In this way, one can evaluate the spatial and temporal variation of the principal physico-chemical processes associated with the three variables VI, V2 and V3 implicated in the groundwater quality of the detrital aquifer.     

Origin and migration of palaeofluids in the Upper Visean of the Campine Basin, northern Belgium

Upper Visean limestones in the Campine Basin of northern Belgium are intensively fractured. The largest and most common fractures are cemented by non-ferroan, dull brown-orange luminescent blocky calcite. First melting temperatures of fluid inclusions in these calcites are around -57°C, suggesting that precipitation of the cements occurred from NaCl-CaCl₂-MgCl₂ fluids. The final melting temperatures (T_m^ice) are between -5 and -33°C. The broad range in the T_m^ice data can be explained by the mixing of high salinity fluids with meteoric waters, but other hypotheses may also be valid. Homogenization temperatures from blocky calcite cements in the shelf limestones are interpreted to have formed between 45 and 75°C. In carbonates which were deposited close to and at the shelf margin, precipitation temperatures were possibly in the range 70-85°C and 72-93°C, respectively. On the shelf, the calcites have a δ¹⁸O around -9.3‰ PDB and they are interpreted to have grown in a fluid with a δ¹⁸O between −3.5 and +1.0‰ SMOW. At the shelf margin, blocky calcites (δ¹⁸O∼ - 13.5‰ PDB) could have precipitated from a fluid with a δ¹⁸O betweenn -4.0 and -1.1‰ SMOW. The highest oxygen isotopic compositions are comparable to those of Late Carboniferous marine fluids (δ¹⁸O= - 1‰ SMOW). The lowest values are more positive than a previously reported composition for Carboniferous meteoric waters (δ¹⁸O= -7‰ SMOW). Precipitation is likely to have occurred in marine-derived fluids, which mixed with meteoric waters sourced from near the Brabant Massif. Fluids with a similar negative oxygen isotopic composition and high salinity are actually present in Palaeozoic formations. The higher temperature range in the limestones near the shelf margin is explained by the upward migration of fluids from the ‘basinal’ area along fractures and faults into the shelf.     

Toward an Understanding of Biogenic-silica Dissolution in Seawater – An Initial Rate Approach Applied between 40 and 90 °C

Summary The kinetics of phytoplankton frustule dissolution has generally been studied as the appearance of silicic acid in a batch reactor. Unfortunately, this approach, though often illuminating, has not so far been successful because of the difficulty of parameterising the full reaction curve. This current study shows how the initial rate approach to chemical kinetics offers a way around this bottleneck, thereby allowing much chemical kinetics information about frustule dissolution to be collected. The technique is shown to be flexible and suited to short reaction times which facilitate detailed quantitative kinetics investigation, indeed, as would be expected in a solution phase, kinetics study. The technique is exemplified by a dissolution study of uncleaned frustules of Cyclotella crypticaat 40 °C and above. The frustules were found to yield the same dissolution rate after 5 weeks dark storage, at 4 °C. Meanwhile, log dissolution rate was found to vary linearly with pH, with gradient 0.38 ± 0.01 (r ²=0.990). Linearity was upheld even at pHs as high as 14. Finally, a robust Arrhenius plot was established between 40 and 90 °C yielding an activation energy for dissolution of 84 ± 3 kJ mol ⁻¹. Follow through with the Eyring equation yielded an activation enthalpy, ΔH ^‡, and an activation entropy, ΔS ^‡, of 81 and 85 J mol ⁻¹ K ⁻¹, respectively. The discussion brings salient aspects of existing knowledge about diatom frustule dissolution kinetics into the wider context of silicate mineral dissolution.     

On the entrainment of sediment and initiation of bed defects: insights from recent developments within turbulent boundary layer research

Sediment entrainment and the initiation of bed defects has commonly been ascribed to the impact of high velocity sweeps upon mobile sand beds. Results of visualization experiments suggest that these sweep impacts are grouped and may define ‘patches’of entrainment upon a mobile bed that may be wider than an individual sweep impact. Additionally, the presence of longitudinal ribs of sediment generated by sweep impacts may stabilize the position of sweeps and low speed streaks. These observations are interpreted in the light of recent boundary layer research which suggests the formation of multiple hairpin shaped vortices within turbulent flows: these are postulated to generate multiple sweeps that manifest themselves as entrainment patches on a mobile bed. These features of the turbulent boundary layer and its modification by sweep generated sediment ridges can be used to propose a model for bed defect formation and the subsequent development of current ripples.     

Geochemical Evidence for Mantle Origin and Crustal Processes in Volcanic Rocks from Popocatepetl and Surrounding Monogenetic Volcanoes, Central Mexico

Elemental, isotopic, and mineral compositions as well as rocktextures were examined in samples from Popocatépetl volcanoand immediately surrounding monogenetic scoria cones of theSierra Chichinautzin Volcanic Field, central Mexico. Magma generationis strongly linked to the active subduction regime to the south.Rocks range in composition from basalt to dacite, but Popocatépetlsamples are generally more evolved and have mineral compositionsand textures consistent with more complicated, multi-stage evolutionaryprocesses. High-Mg calc-alkaline and more alkaline primitivemagmas are present in the monogenetic cones. Systematic variationsin major and trace element compositions within the monogeneticsuite can mostly be explained by polybaric fractional crystallizationprocesses in small and short-lived magmatic systems. In contrast,Popocatépetl stratovolcano has produced homogeneous magmacompositions from a shallow, long-lived magma chamber that isperiodically replenished by primitive basaltic magmas. The currenteruption (1994–present) has produced silicic dome lavasand pumice clasts that display mingling of an evolved daciticcomponent with an olivine-bearing mafic component. The longevityof the magma chamber hosted in Cretaceous limestones has fosteredinteraction with these rocks as evidenced by the chemical andisotopic compositions of the different eruptive products, contact-metamorphosedxenoliths, and fumarolic gases. Popocatépetl volcanicproducts display a considerable range of ⁸⁷Sr/⁸⁶Sr (0·70397–0·70463)and _Nd (+6·2 to +3·0) whereas Pb isotope ratiosare relatively homogeneous (²⁰⁶Pb/²⁰⁴Pb 18·61–18·70;²⁰⁷Pb/²⁰⁴Pb 15·56–15·60). KEY WORDS: Popocatépetl; Sierra Chichinautzin Volcanic Field; arc petrogenesis; radiogenic isotopes     

PHYSICAL IMPACTS OF CLIMATIC CHANGE ON DELTAIC COASTAL SYSTEMS (I): AN APPROACH

The evaluation of the impact of climate change on deltaic systems implies studying a multi-component system in which the complexity of links is high enough to present doing it as a whole. Because of this, it is a reasonable approach to study separately the behaviour of each element, to be afterwards linked into a general conceptual model for deltaic behaviour. Moreover, in the case of largely regulated deltas, the main impacts of climatic change will be marine-related since those related to the catchment areas will be severely damped by river regulation and management policies. This fact implies that coastal fringes may become the main frontier between the delta and climatic change effects. In this context, a methodology to study climatic change impacts on deltaic coastal fringes is here presented. It will be further developed on two companion papers dealing with the study of driving terms and coastal response. As coastal processes act at different time and space scales, determining the reference – initial – situation must be done taking into account the inherent system dynamics. It is thus unrealistic to characterize the initial stage as a static one. In order to avoid this simplistic approach, a comprehensive approach to the coastal system must be employed, with three different scales (long-term/large scale, medium term/scale and episodic).