Ecometrics and the paleoecological implications of Pleistocene faunas from the western coastal plains of the Cape Floristic Region,South Africa

The Pleistocene ungulate communities from the western coastal plains of South Africa's Cape Floristic Region (CFR) are diverse and dominated by grazers, in contrast to the region's Holocene and historical faunas, which are relatively species-poor and dominated by small-bodied browsers and mixed feeders. An expansion of grassy habitats is clearly implied by the Pleistocene faunas, but the presence of ruminant grazers that cannot survive the summer dry season typical of the region today suggests other important paleoecological changes. Here we use dental ecometrics to explore the paleoecological implications of the region's Pleistocene faunas. We show that the dental traits (hypsodonty and occlusal topography) of the ungulates that occurred historically in the CFR track annual and summer aridity, and we use these relationships to reconstruct past aridity. Our results indicate that the Pleistocene faunas signal paleoenvironments that were on average less arid than today, including during the summer, consistent with other lines of evidence that suggest a higher water table and expansion of well-watered habitats. Greater water availability can be explained by lower temperature and reduced evapotranspiration during cooler phases of the Pleistocene, probably coupled with enhanced groundwater recharge due to increased winter precipitation.     

THE TUNGUSKA EVENT AND THE METEORS WITH TERMINAL FLARES

The comparison of the Tunguska body explosion with the effect of terminal flares of meteors and fireballs leads us to the conclusion that these events are of a similar nature but differ only by their scale. We consider that the dynamics of progressive breaking and evaporation of meteoric bodies during their entry into the terrestrial atmosphere could explain the terminal burst. An extremely porous body model for the Tunguska meteorite was analysed and rejected as unsatisfactory. The realistic values of the initial velocity (～30 km/sec) and of the inclination angle for the Tunguska's trajectory (5–15°) give orbital elements not in contradiction with the cometary origin of the Tunguska body.     

The U-Pb systematics of angrite Sahara 99555

Angrite Sahara 99555 (hereafter SAH), precisely dated by Baker et al. (Baker J., Bizzarro M., Wittig N., Connelly J. and Haack H. (2005) Early planetesimal melting from an age of 4.5662 Gyr for differentiated meteorites. Nature436, 1127-1131), has been proposed as a new reference point for the early Solar System timescale and for calculation of the revised minimum age of our Solar System. The Pb-Pb age of SAH of 4566.18 ± 0.14 Ma, reported by Baker et al., differs from the Pb-Pb age of D’Orbigny, another basaltic angrite, of 4564.42 ± 0.12 Ma (Amelin Y. (2008) U-Pb ages of angrites. Geochim. Cosmochim. Acta72, 221-232), despite the fact that the relative ⁵³Mn-⁵³Cr and ¹⁸²Hf-¹⁸²W ages of these meteorites are identical. Here I report U-Pb data for 21 whole rock and pyroxene fractions from SAH, analyzed using the same approach as D’Orbigny (Amelin, 2008). These fractions contain between 1.3 and 8.9 pg of total common Pb, slightly more than analytical blank. Measured ²⁰⁶Pb/²⁰⁴Pb ratios are between 625 and 2817 for D’Orbigny, blank-corrected ²⁰⁶Pb/²⁰⁴Pb ratios are between 1173 and 6675. Eight acid-washed whole rock fractions yielded an isochron age of 4564.86 ± 0.38 Ma, MSWD = 1.5. Data for pyroxene fractions plot mostly above the whole rock isochron, and do not form a linear array in ²⁰⁷Pb/²⁰⁶Pb vs. ²⁰⁴Pb/²⁰⁶Pb isochron coordinates. The ²⁰⁷Pb^∗/²⁰⁶Pb^∗ model dates of the pyroxene fractions vary from 4563.8 ± 0.3 to 4567.1 ± 0.5 Ma. The difference between whole rock and pyroxene U-Pb systematics may be a result of re-distribution of radiogenic Pb at a mineral grain scale several million years after crystallization. Complexities of Sm-Nd, Lu-Hf, and possibly ²⁶Al-²⁶Mg mineral systematics of SAH, described previously, may be related to the same process that caused the re-distribution of radiogenic Pb. Disturbance of isotopic chronometers renders SAH an imperfect anchor for the early Solar System timescale. The problems with age determination revealed by the studies of SAH call for greater attention in Pb-isotopic dating of angrites and other achondrites.     

Fumarolic activity of Avachinsky and Koryaksky volcanoes, Kamchatka, from 1993 to 1994

 Volcanic gas and condensate samples were collected in 1993–1994 from fumaroles of Koryaksky and Avachinsky, basaltic andesite volcanoes on the Kamchatka Peninsula near Petropavlovsk–Kamchatsky. The highest-temperature fumarolic discharges, 220  °C at Koryaksky and 473  °C at Avachinsky, are water-rich (940–985 mmol/mol of H₂O) and have chemical and isotopic characteristics typical of Kamchatka–Kurile, high- and medium-temperature volcanic gases. The temperature and chemical and water isotopic compositions of the Koryaksky gases have not changed during the past 11 years. They represent an approximate 2 : 1 mixture of magmatic and meteoric end members. Low-temperature, near-boiling-point discharges of Avachinsky Volcano are water poor (≈880 mmol/mol); Their compositions have not changed since the 1991 eruption, and are suggested to be derived from partially condensed magmatic gases at shallow depth. Based on a simple model involving mixing and single-step steam separation, low water and high CO₂ contents, as well as the observed Cl concentration and water isotopic composition in low-temperature discharges, are the result of near-surface boiling of a brine composed of the almost pure condensed magmatic gas. High methane content in low-temperature Avachinsky gases and the 220  °C Koryaksky fumarole, low C isotopic ratio in CO₂ at Koryaksky (–11.8‰), and water isotope data suggest that the "meteoric" end member contains considerable amounts of the regional methane-rich thermal water discovered in the vicinity of both volcanoes. Received: 2 May 1996 / Accepted: 5 November 1996     

The shear strength of clay-filled bedding planes in limestones - back-analysis of a slope failure in a phosphate mine, Israel

The failure of a slope in a phosphate mine by shear-sliding along a clay-filled bedding plane in limestone, and by separation across a tension crack at the back, is back-analysed. The failure cannot be explained using laboratory measured values of the shear strength parameters. In order to simulate field conditions better two physical models of the bedding plane were prepared for testing under triaxial compression. Cylindrical cores with an inclined saw-cut discontinuity were filled with remoulded montmorillonite. It is shown that failure in the models initiates along the contacts between the clay infilling and the limestone boundaries, and not through the clay itself, as would be intuitively expected. Furthermore, it is argued that in the analysis of rock slope stability in general, and particularly in the case of clay-filled discontinuities, the influence of paleo-overburden stress on frictional resistance must be resolved before the appropriate constitutive law can be established for analysis.     

Phosphorus metabolism in anthropogenically transformed lagoon ecosystems: The Comacchio lagoons (Ferrara, Italy)

Inorganic phosphorus dynamics were investigated with the use of ³²P in the hypertrophic Comacchio lagoons (NE Adriatic) during an extremely dense, quasi-permanent bloom of picocyanobacteria. Concentrations of dissolved inorganic phosphate (DIP) in waters of the blooming lagoons were usually near the detection limit (0.01 μmoles·dm⁻³). DIP uptake rates by microplankton at near-ambient concentrations (0.01 to 0.1 μmoles·dm⁻³) were in the range of 9.6 to 16.1 nmoles P·dm⁻³·min⁻¹, and turnover times were 1.5 to 3 min. The turnover time was >40 h in the eutrophic coastal waters of the adjacent Adriatic Sea. The uptake rate of DIP depended on its initial concentration. In water samples artificially enriched with DIP, the uptake rate rose to its maximum of 0.10 to 0.13 μmoles P·dm⁻³·min⁻¹ (or 6 to 7 μmoles·dm⁻³·h⁻¹) when the initial concentration of DIP was elevated to 10 to 20 μmoles·dm⁻³. The potential capacity of microplankton in the water samples to consume and retain DIP was estimated at 25 μmoles·dm⁻³. Specific features are discussed of phosphorus metabolism in the anthropogenically transformed lagoon ecosystem with an anomalous food web with few animals.     

Spatial and vertical distributions of elements in sediments of the Colorado River delta and Upper Gulf of California

The abundance of major components (Fe, Ca, K, and organic carbon) and trace elements was analyzed in surface sediments and core samples from the Colorado River delta (CRD) and the Upper Gulf of California (UGC) using instrumental neutron activation analysis.The spatial distribution patterns of the elements studied are consistent with the model of sedimentary dynamics proposed for this area [Mar. Geol. 158 (1999) 125]: intense tidal resuspension of sediments in the delta with subsequent transport of suspended particulate matter in a southerly direction, followed by sedimentation of fine-grained material in a depocenter near the southwestern margin of the UGC. Concentrations of most of the elements are higher in the surface sediments of this depocenter. The gradual mixing of terrigenous and marine biogenic materials, normally expected for the estuarine sediments, was not detected in the CRD–UGC system because of homogenization of the sediments by tides and wind.Vertical profiles of element contents in samples of the sediment core collected in the depocenter area revealed (i) almost no anthropogenic contamination of the area by environmentally important trace elements such as Cr, Co, Sb, and As; (ii) a twofold decrease of Fe, Sc, Cr, and Co in upper core sediments; and (iii) the enrichment of the sediments at 60–62 cm depth in the core, in calcium carbonate, Ca, Sr, and the Eu_n/Sm_n shale-normalized ratio along with a depletion in this layer of Fe, Sc, Cr, Co, light rare-earth elements (REEs), and some other elements of terrigenous origin, presumably caused by the dilution of fluvial terrigenous material by biogenic carbonates, which were probably introduced at this level in the sediments by the action of a strong episodic winter storm, followed by the advective transport of shell fragments from the coastal clam banks or as a result of strong planktonic bloom.     

The remineralization of organic carbon on the North Carolina continental slope

The sources and fates of metabolizable organic carbon were examined at three sites on the North Carolina slope positioned offshore of Cape Fear, Cape Lookout and Cape Hatteras. The¹³C/¹²C compositions (δ¹³C) of the solid phase organic matter, and the dissolved inorganic carbon (ΣCO₂) produced during its oxidation, suggested that the labile fraction was predominantly marine in origin. The ΣCO₂ concentration gradient across the sediment-water interface, and by inference the ΣCO₂ flux and production rate, increased northward from Cape Fear to Cape Hatteras. Methane distributions and ΣCO₂ δ¹³C values suggest that the rate of anaerobic diagenesis increased northward as well. The differences in sedimentary biogeochemistry are most likely driven by an along-slope gradient of reactive organic carbon flux to the seabed. This trend in reactive organic carbon flux correlates well with macrofaunal densities previously observed at the three sites. Proximity to the shelf and the transport of particulate material by surface boundary currents may control the deposition of metabolizable material on the Carolina slope.Evidence for methanogenesis was found only on the Cape Hatteras slope. The methane, which was produced at a depth of approximately 1 m in the seabed, was consumed nearly quantitatively in the biologically mixed layer as it diffused upward. Irrigation of the sediments by infauna may have provided the necessary oxidant for the consumption of the methane.     

On the possibility of the determination of water's optic characteristics versus relative transparency

Translated by V. Puchkin.