Geochemical correlations between effusive and explosive silicic volcanics in the Saraykent region (Yozgat), central Anatolia,Turkey

Two main volcanic events are distinguished between Saraykent and Akçakışla in the Yozgat province of central Anatolia: (1) early Late Cretaceous–Palaeocene effusive activity, that produced a sequence of intermediate to felsic ‘basal lavas’; and (2) marginally later Palaeocene explosive activity that formed a series of covering ignimbrite flows. Due to their close temporal and spatial relation, geochemical comparisons were made between the silicic members of the lavas and ignimbrites, to identify chemical groups and their relative petrogenesis. The basal lavas range from calc‐alkaline basaltic andesites to dominant rhyolites. Based on trace element correlations three main geochemical groups were identified: the Akçakışla rhyolites (present as domes); Akçakışla rhyodacites‐dacites (lava flows); and Ozan‐Saraykent rhyolites (lava flows). Large‐ion lithophile elements have been mobile in all the groups, but mainly in the Akçakışla rhyolites. Rare earth element (REE) patterns show marked similarity between the Ozan and Saraykent basal lavas. The Akçakışla dome rhyolites are more fractionated with lower La_N/Yb_N ratios (c.10), whereas the Akçakışla basal lavas have much higher La_N/Yb_N ratios (c.30). The chemical coherence and petrographic similarities between the Saraykent and Ozan lavas suggest a single suite related via fractionation. Three geochemical groups were also established for the ignimbrites: Saraykent ignimbrite; Bağlıca ignimbrite‐Toklu‐Kızıldağ crystal tuffs; and Keklikpınar ignimbrite. The ignimbrites, like the basal lavas, display a pronounced depletion in Ba on ORG‐normalized plots. Relative to the basal lavas, chondrite‐normalized patterns for the ignimbrites are different in displaying negative Eu anomalies that indicate feldspar fractionation. The lack of geochemical overlap or coherence between any of the lava and ignimbrite groups suggests that they represent distinct eruptive events and are not related in any simple volcanic development and cogenetic sense. Two geochemical features are common to all the volcanic rock groups: (1) the presence of a Nb‐Ta anomaly, which is generally accepted as a crustal signature; and (2) the relatively low Y abundances which appear characteristic for the region as a whole. These fundamental features of the local silicic volcanism largely reflect source composition and effects. Copyright © 2002 John Wiley & Sons, Ltd.     

Cryptotephra from the 74 ka BP Toba super-eruption in the Billa Surgam caves,southern India

The ～74 ka BP Youngest Toba Tuff (YTT), from the largest known Quaternary volcanic eruption, has been found for the first time as a non-visible (crypto-) tephra layer within the Billa Surgam caves, southern India. The occurrence of the YTT layer in Charnel House Cave provides the first calendrical age estimate for this much debated Pleistocene faunal sequence and demonstrates the first successful application of cryptotephrochronology within a cave sequence. The YTT layer lies ～50 cm below a major sedimentological change, which is related to global cooling around the MIS 5 to MIS 4 transition. Using this isochronous event layer the Billa Surgam Cave record can be directly correlated with other archaeological sites in peninsular India and palaeoenvironmental archives across southern Asia.     

Analysis of mutations in the p53 tumor suppressor gene and Ki- and Ha-ras proto-oncogenes in hepatic tumors of European flounder (Platichthys flesus).

DNA from five tumors, three other-injured livers and two normal liver tissue samples from the European flounder were analyzed for mutations in exons 5-8 of the tumor suppressor gene p53 and at codons 12, 13 and 61 of Ha- and Ki-ras proto-oncogenes. No tumor-specific mutations were identified by direct sequencing and single-strand conformation polymorphism of these genes. A number of silent polymorphisms were noted in p53. In addition to a need for more extensive analyses of flounder liver tumor samples for ras or p53 mutations, other cancer-related genes should be investigated.     

Temporal variability in the maternal environment and its effect on seed size and seed quality in Flourensia cernua DC. (Asteraceae).

The biological phenomenon commonly referred to as maternal effect occurs whenever the environment exerts an influence upon the mother that is later expressed in characteristics of her offsprings. For example, the environmental conditions experienced by a mother plant during flowering and fruiting can modify the quality of her descendants (seeds), and even interrupt their development. Between-year variation in minimum temperature and the classic, between-year variation in precipitation represent an unpredictable environment for winter blooming plants in arid zones. In this study, we investigated the effect of maternal environment (temperature and precipitation) on seed size and seed quality in F. cernua, over a 5-year period. Results indicated that the proportion of filled seeds, as well as their size, increased with higher absolute minimum temperatures during seed formation, and that, to a lesser extent, both the precipitation occurred during the same period and the annual precipitation also have a positive influence on seed size. In this way, environmental conditions prevailing during seed formation exerted a strong maternal effect on the size and quality of seeds produced and, probably also, in the developmental possibilities of F. cernua seedlings. This effect was subject to important, between-year variation.     

Vertical migration ofcentropages typicus (copepoda) in Chesapeake Bay,with some thoughts on migration studies

Centropages typicus was collected at two hour intervals over a diel cycle at a station near the Chesapeake Bay mouth. The species migrated upward at dusk and downward at dawn. Neither light, temperature, salinity, nor density appeared to cue the migration. Attention is drawn to the need for information on the extent and regularity of migration by individual organisms, and how the lack of such information may lead to poor interpretations of migration data.     

First data on U-Pb SHRIMP-II isotopic dating based on zircons of ash sediments from Cenozoic depressions in Southwest of Primorie

U-Pb (SHRIMP-II) isotopic dating has been conducted for zircons of the ash sediments of the Ust’-Suifun Suite, which was the final stage of Late Cenozoic explosive volcanism in Southwest Primorskii krai. These pyroclastic units are widespread within sediments that fill in Cenozoic depressions including large coalfields. The concordant dates (23.7–24.6 Ma) are in line with the results of the K-Ar determinations for volcanic tephra (23.6–27.1 Ma) and correspond to the beginning of the active phase of spreading and taphrogenesis in the neighboring Trench of the Sea of Japan. These processes started as early as the Eocene and are reflected in the continental vicinity with the formation of riftogenic depressions and the occurrence of a peculiar gas volcanism.     

A theoretical model of Fanaroff-Riley I jets

A fluid model of the jets in Fanaroff-Riley I class, for extended extragalactic radio sources, based on the idea that they are turbulent low Mach number supersonic flows consisting of relativistic and nonrelativistic plasma, has been developed. Mean flow approach and modified mixing length theory by Prandtl are used to obtain a corresponding mathematical tool. It is assumed that magnetic field is weak. Boundary conditions concerned the problem of the jet propagation through a non-uniform atmospheres of an elliptical galaxies are considered. Short discussion of the observational data determining the choice of the input parameters of the jets is given.     

Principal Components Analysis of Rainfall and Associated Synoptic Models of the Southwest Monsoon over India

Summary  The summer monsoon circulation shows various spatial and temporal oscillations and often a combination of systems produces an integrated effect. In this study phases of the southwest (SW) monsoon have been identified in an objective manner with the help of T-mode principal component analysis (PCA) of weekly rainfall anomalies. Mean composite charts have been prepared utilising all available upper air data (1977–1986) for each category of the SW monsoon epochs identified by the PCA. These sets of charts have been constructed for both the strong and weak phases associated with the first four significant principal components (PCs). A well defined east-west oriented trough system, extending from about 28° N Latitude/65° E Longitude to 20° N Latitude/90° E Longitude, in the lower levels, has been the main feature associated with the strong phase of the monsoon corresponding to PC I. The trough in the lower levels is more marked in the eastern half compared to the western half in both the sets of charts associated with strong phases of the monsoon related to the PC II and PC III. With PC II, the position of the troughs in the lower levels is further north of its location in PC III. The east-west trough system associated with the strong phase of PC IV has a large southward tilt with height. The charts corresponding to the weak phases of these PCs have synoptic features, such as the position of the trough close to the foothills of the Himalayas, and the shifting of middle and upper tropospheric anticyclones to the south. The study suggests an objective method of interpretation of principal components by utilising synoptic data. In addition, synoptic models and data sets corresponding to different phases of the monsoon can also be prepared in an objective manner by such PCA. Received July 18, 1997 Revised April 30, 1999     

A numerical Round Robin on tunnels under seismic actions

Although the seismic behaviour of shallow circular tunnels in soft ground is generally safer than aboveground structures, some tunnels were recently damaged during earthquakes. In some cases, damage was associated with strong ground shaking and site amplification, which increased the stress level in the tunnel lining. Pseudo-static and simplified dynamic analyses enable to assess transient changes in internal forces during shaking. Nevertheless, experimental evidences of permanent changes in internal loads in the tunnel lining would suggest that a full dynamic analysis including plastic soil behaviour should be performed when modelling the dynamic interaction between the tunnel and the ground. While sophisticated numerical methods can be used to predict seismic internal forces on tunnel structures during earthquakes, the accuracy of their predictions should be validated against field measurements, but the latter are seldom available. A series of centrifuge tests were therefore carried out at the University of Cambridge (UK) on tunnel models in sand, in the framework of a research project funded by the Italian Civil Protection Department. A numerical Round Robin on Tunnel Tests was later promoted among some research groups to predict the observed behaviour by means of numerical modelling. In this paper, the main results of five selected numerical predictions are summarized and compared with the experimental results.