Contrasting geochemical signatures on land from the Middle and Late Permian extinction events

The end of the Palaeozoic is marked by two mass‐extinction events during the Middle Permian (Capitanian) and the Late Permian (Changhsingian). Given similarities between the two events in geochemical signatures, such as large magnitude negative δ¹³C anomalies, sedimentological signatures such as claystone breccias, and the approximate contemporaneous emplacement of large igneous provinces, many authors have sought a common causal mechanism. Here, a new high‐resolution continental record of the Capitanian event from Portal Mountain, Antarctica, is compared with previously published Changhsingian records of geochemical signatures of weathering intensity and palaeoclimatic change. Geochemical means of discriminating sedimentary provenance (Ti/Al, U/Th and La/Ce ratios) all indicate a common provenance for the Portal Mountain sediments and associated palaeosols, so changes spanning the Capitanian extinction represent changes in weathering intensity rather than sediment source. Proxies for weathering intensity chemical index of alteration, ?W and rare earth element accumulation all decline across the Capitanian extinction event at Portal Mountain, which is in contrast to the increased weathering recorded globally at the Late Permian extinction. Furthermore, palaeoclimatic proxies are consistent with unchanging or cooler climatic conditions throughout the Capitanian event, which contrasts with Changhsingian records that all indicate a significant syn‐extinction and post‐extinction series of greenhouse warming events. Although both the Capitanian and Changhsingian event records indicate significant redox shifts, palaeosol geochemistry of the Changhsingian event indicates more reducing conditions, whereas the new Capitanian record of reduced trace metal abundances (Cr, Cu, Ni and Ce) indicates more oxidizing conditions. Taken together, the differences in weathering intensity, redox and the lack of evidence for significant climatic change in the new record suggest that the Capitanian mass extinction was not triggered by dyke injection of coal‐beds, as in the Changhsingian extinction, and may instead have been triggered directly by the Emeishan large igneous province or by the interaction of Emeishan basalts with platform carbonates.     

Seismic observations at an overstep of the western North Anatolian Fault (Abant–Sapanca region, Turkey)

The course of the active North Anatolian Fault system from Lake Abant to Lake Sapanca was traced by its high micro-earthquake activity. If approaching from the east this section includes a broad south to north overstep (fault offset) of the main fault. Local seismicity has been recorded in this area by a semi-permanent network of 8 stations since 1985 within the frame of the Turkish–German Joint Project for Earthquake Research. The effect of the overstep and its complex fracture kinematics are reflected by the seismicity distribution, the variations of composite fault-plane solutions, and by the spatial coda-Q distribution. Areas of different stress orientation can be distinguished and assigned to different groups of faults. The stresses and the tectonic pattern only in part correspond to a simple model of an extensional overstep and its correlative pull-apart basin. Other types of deformation involved are characterized by normal faulting on faults parallel to the general course of the main strike-slip fault and by synthetic strike-slip faults oriented similar to Riedel shears. Shear deformation by this fault group widely distributed in an area north and east of the main fault line may play an important role in the evolution of the overstep. The development of a pull-apart basin is inhibited along the eastern half of the overstep and compatibility of both strands of the main fault (Bolu–Lake Abant and Lake Sapanca– Izmit–Marmara Sea) seems to be achieved with the aid of the fault systems mentioned. The extension of the missing part of the pull-apart basin seems to be displaced to positions remote from the Lake Abant–Lake Sapanca main fault line, i.e. to the Akyaz?–Düzce basin tract. Highest Q-values (lowest attenuation of seismic waves) were found in the zone of highest seismicity north and west of the overstep which is the zone of strongest horizontal tension. If high coda-Q is an indicator for strong scattering of seismic waves it might be related to extensional opening of fractures.     

Heat island and oasis effects of vegetative canopies: Micro-meteorological field-measurements

Dry-bulb temperature, dew-point, wind speed, and wind direction were measured in and around an isolated vegetative canopy in Davis CA from 12 to 25 October 1986. These meteorological variables were measured 1.5 m above ground along a transect of 7 weather stations set up across the canopy and the upwind/downwind open fields. These variables were averaged every 15 minutes for a period of two weeks so we could analyze their diurnal cycles as well as their spatial variability. The results indicate significant nocturnal heat islands and daytime oases within the vegetation stand, especially in clear weather. Inside the canopy within 5 m of its upwind edge, daytime temperature fell by as much as 4.5 °C, whereas the nighttime temperature rose by 1 °C. Deeper into the canopy and downwind, the daytime drop in temperature reached 6 °C, and the nighttime increase reached 2 °C. Wind speed was reduced by ~ 2 ms^–1 in mild conditions and by as much as 6.7 ms^–1 during cyclonic weather when open-field wind speed was in the neighborhood of 8 ms^–1. Data from this project were used to construct correlations between temperature and wind speed within the canopy and their corresponding ambient, open-field values.With 10 Figures     

A review of: “Physical fluid dynamics”

Abstract

by D. J. Tritton, Second Edition, Oxford University Press XVII + 519 pp. Hardback (ISBN 0–19–854489–8) $35.00; paperback (ISBN 0–19–854493–6) $16.95; 1988.     

An exceptional eruption: Mt. Niragongo,Jan. 10th, 1977

The two westernmost volcanoes of the Virunga range (Zaïre Rep.) have just offered simultaneous eruptions. The volcano Niragongo delivered an exeeptionally short, yet important, eruption on 10 Jan. 1977. More than 20 × 10 m³ of molten melilite nephelinite were drained from the 3,270 m suspended lava-lake and spread over 20 km² in less than one hour. This put an end to the half-a-century old sub-permanent lava-lake activity which had rendered Niragongo known world-wide. This event happened during a flank eruption (the new Murara vent) of the close-by sister-volcano, Nyamlagira. This Murara event is quite similar to the many previous ones observed during the last 40 years. Neither of the two outbursts did have, even slightly, any detectable effect on each other. Yet, this simultaneity is probably not due to mere coïncidence.     

Geochemistry and lithofacies of Permo-Carboniferous carbonaceous rocks from the southwestern edge of the Bohemian Massif (Germany). A contribution to facies analysis of continental anoxic environments

The Permo-Carboniferous Schmidgaden, Weiden, Erbendorf and Stockheim basins from southern Germany host discontinuous seams of high ash coal and carbargillites which were mined for hard coal, explored for uranium and only recently have proved their source rock potential for gaseous and fluid hydrocarbons. Alteration and facies of these carbonaceous beds were geologically and chemically investigated. During silicification which is exclusively confined to the carbonaceous interbeds of pyroclastic depositions, element depletion prograded except for Zn, Pb, U. The anoxic environments under consideration may be subdivided into fluvial/swamp (Upper Westphalian beds from Schmidgaden, Weiden, Erbendorf and Stockheim) and lacustrine depositions (Upper Stephanian and Upper Autunian carbargillites from Erbendorf, Weiden-Bechtsrieth). SiO₂, MgO, CaO, Mo and Zr have proved to be most suitable for recognition of these environments, whereas, U, K₂O and notably Cu/Zn are less appropriate. In the ternary plots displaying the organic chemistry of extracts of these carbonaceous beds fluvial swamps have low and lacustrine beds high contents of saturated hydrocarbons. All samples show a pronounced OEP (=odd even predominance) of n-alkanes which partly are environment-controlled (terrestrial origin), partly maturity-controlled. The high iso- and cyclo-alkanes of Schmidgaden and bimodal n-alkyl distribution point to a contribution of algal material. Finally four basin types bearing carbonaceous rocks are discussed with respect to their economic potential and compared with basins elsewhere (Cerilly, Lodève, St. Hippolyte, Uinta): type I: intramontane fault-bounded basin (swamp), type II: volcanic-depression with steep relief (swamps), type III: halfgraben (lake), type IV: volcanic-depression with smooth relief (lake). Types I and II are of interest for hard coal, organic-hosted U-deposits and mainly gasprone; types III and IV, however, show good source-rock potential for crude oil.