Organic geochemical studies of a Messinian evaporitic basin, northern Apennines (Italy)—II Isoprenoid and n-alkyl thiophenes and thiolanes

Series of n-alkyl and isoprenoid thiophenes and thiolanes, most of which have not been previously reported, have been identified in an extract from a Messinian (Upper Miocene) marl layer deposited under hypersaline, euxinic conditions. The identifications were based on mass spectra and Chromatographic data of synthesized reference compounds and on comparison of mass spectra, relative retention times and response on the FPD. Their specific structures and their distribution patterns show similarities with those of the alkanes. Inorganic sulphur is therefore considered to be incorporated into specific lipid moieties from (archae)bacterial and/or algal input during diagenesis. A biosynthetic origin of these compounds is also possible, however. The organic sulphur compounds encountered are thought to be indicators of a hypersaline depositional environment.     

Trace-element patterns at the Cretaceous-Tertiary boundary—Consequences of a large impact

The earlier discovery of high concentrations of iridium and osmium at the very base of the Tertiary in marine pelagic sequences, has led to the hypothesis that the impact of a large projectile on Earth terminated the Mesozoic era.This paper describes the distribution of other trace elements in samples closely spaced around the Cretaceous-Tertiary boundary. We found an enrichment of Co, Cr, Ni, As, Sb and Se, and a depletion of the rare earth elements (REE), coupled with the anomalously high concentration of Ir and Os. Also, in the enrichment layer, problematic sanidine spherules occur which may be spheres, ablated from the impacting projectile or microtektites.The REE depletion could not only be demonstrated in the basal millimetres of the relatively thick (～ 10 cm) boundary marl bed of the Barranco del Gredero section, Caravaca, Spain, but also in the boundary clay of the Stevns Klint section—the “Fiskeler”—Denmark. In these boundary clay beds are also the highest concentrations of Ir recorded [44 and 86.7 ppb (1 ppb = 10^?9 g/g), respectively].This REE depletion is tentatively connected with the low REE concentration in common meteorites. In that case the basal millimetres are dominated by a meteoritic component and represent a “fall-out” layer of the impact event. This in turn would imply low terrestrial dilution at impact on Earth, suggesting that the projectile might have fallen into the ocean.Identification of the projectile remains speculative; especially the high As, Sb and Se anomalies are problematic. These latter may point to a projectile of uncommon composition, possibly a comet.An integrated scenario of a possible sequence of events is presented, chiefly based on the interpretation of micropaleontological, lithological, geochemical and stable isotope data of the studied sections.The direct and indirect effects of an impact leading to mass extinction constitute a complicated problem and may comprise a sudden temperature rise, a poisoning by cyanide or arsenic, and a few years suppression of sunlight, or preferably, a combination of these effects.     

Apparent-dip protactor

This simple apparent-dip protractor for geological sections permits the immediate plotting of all inclined beds, even when their strike is not perpendicular to the section. The implement (Fig. 1) is actually an L-shaped protractor marked, in addition to its true angular center — for use when the angle of section is 90° — with a scale of offset pivot points corresponding to various angles of section (Fig. 6). As a single straight scale of dips would extend to infinity, a separate set of scales (black) for slight dips completes the range (Fig. 9).

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Zusammenfassung Dieses einfache Winkelmaß für scheinbares Einfallen ermöglicht bei geologischen Profilen das unmittelbare Einzeichnen, mit der richtigen Neigung, auch von Schichten, die nicht senkrecht zum Profil streichen. Das Gerät (Fig. 1) ist eigentlich ein L-förmiger Gradbogen; jedoch außer dem wirklichen Mittelpunkt der Gradteilung — zu verwenden wenn der Profilwinkel 90° ist — zeigt er zusätzlich eine Reihe von versetzten Drehpunkten, die für andere Profilwinkel gelten (Fig. 6). Da aber eine einzige gerade Fallwinkel-Skala sich ins Unendliche erstrecken müßte, wird der Bereich ergänzt durch ein zweites System (schwarz) für flaches Einfallen (Fig. 9).

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Résumé Ce simple rapporteur à pendages apparents permet de dessiner immédiatement, sur les coupes géologiques, l'inclinaison correcte des couches même quand leur direction n'est pas perpendiculaire à la coupe. L'instrument (Fig.1) n'est qu'un rapporteur en forme d'un L; or, outre le centre véritable de l'échelle graduée — à utiliser quand l'angle de coupe est 90° — il y a une échelle de pivots excentriques, correspondant à d'autres angles de coupe (Fig. 6). Parce qu'une seule échelle rectiligne de pendages devrait s'étendre à l'infini, elle est complétée par un deuxième système (en noir) pour pendages faibles (Fig. 9).

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The use of low frequencies in a full‐waveform inversion and impedance inversion land seismic case study

Velocity model building and impedance inversion generally suffer from a lack of intermediate wavenumber content in seismic data. Intermediate wavenumbers may be retrieved directly from seismic data sets if enough low frequencies are recorded. Over the past years, improvements in acquisition have allowed us to obtain seismic data with a broader frequency spectrum. To illustrate the benefits of broadband acquisition, notably the recording of low frequencies, we discuss the inversion of land seismic data acquired in Inner Mongolia, China. This data set contains frequencies from 1.5–80 Hz. We show that the velocity estimate based on an acoustic full‐waveform inversion approach is superior to one obtained from reflection traveltime inversion because after full‐waveform inversion the background velocity conforms to geology. We also illustrate the added value of low frequencies in an impedance estimate.