A meter-scale cyclicity in the Middle Devonian of northwestern Meseta (Morocco): Is it a Milankovitch signature?

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Experimental observations on fungal diagenesis of carbonate substrates

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Evolution of paleofluids at the Variscan thrust front in eastern Belgium

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Evolution of helicobacter pylori positivity in infants born from positive mothers

To evaluate the mother-child transmission of anti-Helicobacter pylori antibodies, we investigated 562 pregnant women by means of a commercially available second-generation enzyme-linked immunosorbent assay for the detection of mti-H. pylori IgG (Malakit Helicobacter pylori). One hundred twenty-eight of the 562 women had a positive serology for H. pylori.13C-Urea breath tests were performed in 85 seropositive and in 65 randomly selected seronegative subjects. These breath tests were positive in 82 of the 85 (96.5%) seropositive and in none of the seronegative subjects, reflecting the actual presence of H. pylori in the gastric mucosa of the seropositive women. Cord blood levels for the Malakit Helicobacter pylori were positive in all infants born to seropositive mothers and negative in those born to seronegative mothers. In all infants the previously positive titers had turned negative by the age of 3 months. At the age of 12 to 15 months13C-urea breath tests were performed in 67 infants born to seropositive mothers. These breath tests were positive in only one infant. By the time the13C-urea breath tests were performed, the serology had turned negative in all infants with the exception of the one with the positive breath test. We conclude that the IgG antibodies against H. pylori cross the placental barrier and that, despite the present H. pylori infection in the mothers, infants born to these H. pylori-positive women do not appear to have an increased risk of developing a H. pylori’-associated gastritis during the first year of life. © 1994 Raven Press, Ltd. New York.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Analyse radiométrique de glauconies par les méthodes au strontium et à l'argon: l'oligo-miocène de Belgique

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Dinosaur tracksite in an early liassic tidal flat in Northern Italy: Paleoenvironmental reconstruction from sedimentology and geochemistry

Lateral and vertical sedimentological, ichnological, and geochemical characteristics of a tracksite at Lavini di Marco (Southern Alps, Northern Italy) allowed for the reconstruction of a semi-arid, coastal, life-sustaining environment for sauropods and theropods that lived in the western margin of tropical Pangaea at the Triassic-Jurassic transition. Isotopic analyses reveal that there was little influence of meteoric water in the diagenetic transformation of trampled sediments. Consequently, freshwater lenses were probably ephemeral, but could still sustain some vegetation and support animal life. The environment was dominated by the presence of marine waters in sediment pores. Intense evaporation caused partial dolomitization in the morphologically "low lying" parts of the site by modified marine waters. Dolomite precipitation favored the preservation, via early cementation, of dinosaur footprints by carbonates and, possibly, other soluble minerals. Early cementation in semiarid and arid settings could play a major role in the fossilization of dinosaur footprints on carbonate tidal flats. Dinosaur footprints provide unequivocal proof of subaerial exposure of the platform, which has important consequences for both cyclo- and sequence stratigraphic studies. Commonly, bed surfaces in Alpine outcrops are scarce and paleontologic studies have had to rely upon vertical outcrop faces. In this case, the recognition of dinoturbation structures becomes very important. At Lavini we had the opportunity to study the same footprints both on the bedding surface and in bed cross-section. Here we provide detailed descriptions of dinoturbation structures that should aid in the recognition of subaerial exposure surfaces in Mesozoic tidal flats. The preserved footprints at Lavini indicate that fossilization of ichnofaunas is possible in a variety of subenvironments within a tidal flat, in a general inter-supratidal setting characterized by alternating periods of seawater influx and dryness.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

An emplacement mechanism for the mega-block zone within the Chicxulub crater, (Yucatan, Mexico) based on chemostratigraphy

To better constrain the emplacement mechanism of the so-called mega-block zone, a structurally complex unit of target rocks within the Chicxulub impact structure, the stratigraphic coherence of this zone is tested using its strontium isotopic composition. Forty-eight samples across the 616 m sequence of deformed Cretaceous rocks in the lower part of the Yaxcopoil-1 core, drilled by ICDP in 2002, were analyzed for their 87Sr/86Sr isotope ratio. The oceanic anoxic event 2 (OAE2 event), located near the base of the core forms the only stratigraphic anchor point. From this point upward to approximately 1050 m depth, the 87Sr/86Sr trend shows small oscillations, between approximately 0.7074 and 0.7073, characteristic of Cenomanian to Santonian values. This is followed by an increase to approximately 0.7075, similar to the one reported in the seawater strontium curve during the Campanian. Scattered Sr isotope ratios are attributed to local diagenetic effects, such as those expected from the possible presence of hot, impact-induced dikes and hydrothermal fluid flow, originating from the thick central melt sheet. The absence of Upper Maastrichtian Sr isotope values may result from the removal of upper target lithologies during the impact cratering process. Based on these results, the displaced Cretaceous sequence in Yax-1 appears to have preserved its stratigraphic coherence. During the modification stage, it probably moved as a whole into the annular basin during collapse of the crater wall, thereby breaking up into discrete units along previously weakened detachment zones. This model is consistent with the emplacement mechanism postulated by Kenkmann et al. (2004)

Mg, Sr and Sr isotope geochemistry of a Belgian Holocene speleothem: Implications for paleoclimate reconstructions

In this study, variations in Mg/Ca, Sr/Ca and 87Sr/86Sr ratios in a Holocene Belgian speleothem (cave secondary carbonate deposit) are interpreted in terms of changes in water residence time and changes in weathering processes, possibly induced by changes in West European climate. A stalagmite from the Pere Noel cave (Belgium) was dated with the TIMS U/Th method and was deposited between ~ 13 and ~ 2 ka BP. The 1000 Mg/Ca ratio varies between 4.9 and 26, and displays short-term changes but no significant long-term trend. The 1000 Sr/Ca ratio varies between 0.09 and 0.31 and displays both short-term changes and a long-term decreasing trend from 12.9 to 3.5 ka. In parallel, the Sr isotopic composition of the speleothem decreases from 0.7090 at 12.9 ka to 0.7088 at 3.5 ka. The Sr isotope ratio is higher than expected from the overlying limestone (87Sr/86Sr = 0.7081) which implies an external source of radiogenic Sr, most probably from a silicate phase. Short-term and long-term changes in Mg/Ca, Sr/Ca as well as long-term changes of 87Sr/86Sr ratios can be explained by changes in the dissolution and precipitation processes of the host limestone. These processes are controlled by changes in water residence times linked to changes in the water excess (precipitation minus evapo-transpiration). (C) 2000 Elsevier Science B.V. All rights reserved.SCOPUS: cp.jinfo:eu-repo/semantics/publishe