Seasonal Pattern In the High-Elevation Fluvial Travertine From the Jiuzhaigou National Nature Reserve, Sichuan, Southwestern China

The Jiuzhaigou National Nature Reserve on the Tibetan Plateau (Sichuan, southwestern China) is characterized by the deposition of fluvial travertine in a spectacular array of shoals, waterfalls, pool dams, and multicolored lakes. This is possibly the highest vegetated travertine setting of the world, from 2200 to 2900 m above sea level, an environment sensitive to minimal changes in temperature and precipitation regime. The evolution of the system is driven by two seasonal monsoon climate patterns with a wet spring-summer travertine deposition and then a dry fall-winter characterized by no precipitation or erosion. Spring and phreatic-vadose deposits transition from laminated columnar calcite to clotted micrite encrustation, possibly correlated with a mid-Holocene peak in precipitation and high lake levels in the Northeastern Tibetan area connected to glacial advance. The most peculiar features are the fluvial shoals, a rather uncommon travertine surface consisting of two main superimposed facies of alternating weak- and strong-turbulence water flow. The low-turbulence facies consists of clotted micrite encrustation of mosses and cyanobacteria filaments, and platy calcite crystals covering algal filaments. The high-water-turbulence facies show seasonal alternation of diatom-rich bundles of Phormidium sp. (late spring) with algal Oocardium stratum levels (summerfall). Upslope and downslope of the shoals, the precipitation of calcium carbonate results in the formation of prograding waterfalls and dam-pool systems that encrust macrophytes with microspar and clotted micrite. Encrusted chironomids larvae tubes are present in the waterfall walls up to an elevation of 2860 m, possibly the highest ever recorded. Early diagenetic processes such as dissolution of diatom frustules take place over the span of several years, a slower phenomenon compared to other travertine occurrences. In this high-elevation extreme setting, travertine sand and gravel bar deposits are produced by the exposure to severe weathering of a section of the valley that is bypassed through an underground karst system during the winter dry season. High-elevation travertine probably has a low preservation potential, but it appears to be more sensitive to climate changes than other depositional settings, especially in the Himalayan-Tibetan area, where the extent of the Quaternary glacial advances and retreats is still a matter of debate

The Messinian salinity crisis: open problems and possible implications for Mediterranean petroleum systems

Abstract: A general agreement on what actually happened during the Messinian salinity crisis (MSC) has been reached in the minds of most geologists but, in the deepest settings of the Mediterranean Basin, the picture is still far from being finalized and several different scenarios for the crisis have been proposed, with different significant implications for hydrocarbon exploration. The currently accepted MSC paradigm of the ‘shallow-water deep-basin’ model, which implies high-amplitude sea-level oscillations (> 1500 m) of the Mediterranean up to its desiccation, is usually considered as fact. As a consequence, it is on this model that the implications of the MSC events on the Mediterranean petroleum systems are commonly based. In fact, an alternative, deep-water, non-desiccated scenario of the MSC is possible: it (i) implies the permanence of a large water body in the Mediterranean throughout the entire Messinian salinity crisis, but with strongly reduced Atlantic connections; and (ii) envisages a genetic link between Messinian erosion of the Mediterranean margins and deep brine development. In this work, we focus on the strong implications of an assessment of the petroleum systems of the Mediterranean and adjoining areas (e.g. the Black Sea Basin) that can be based on such a non-desiccated MSC scenario. In particular, the near-full basin model delivers a more realistic definition of Messinian source-rock generation and distribution, as well as of the magnitude of water-unloading processes and their effects on hydrocarbon accumulation

The onset of the Messinian salinity crisis in the deep Eastern Mediterranean basin

Astronomical tuning of the Messinian pre-salt succession in the Levant Basin allows for the first time the reconstruction of a detailed chronology of the Messinian salinity crisis (MSC) events in deep setting and their correlation with marginal records that supports the CIESM (2008) 3-stage model. Our main conclusions are (1) MSC events were synchronous across marginal and deep basins, (2) MSC onset in deep basins occurred at 5.97 Ma, (3) only foraminifera-barren, evaporite-free shales accumulated in deep settings between 5.97 and 5.60 Ma, (4) deep evaporites (anhydrite and halite) deposition started later, at 5.60 Ma and (5) new and published 87Sr/86Sr data indicate that during all stages, evaporites precipitated from the same water body in all the Mediterranean sub-basins. The wide synchrony of events and 87Sr/86Sr homogeneity implies inter-sub-basin connection during the whole MSC and is not compatible with large sea-level fall and desiccation of the Mediterranean

Применение метода контрольных возмущений для определения характерных узлов присоединения комплексной нагрузки при расчетах динамической устойчивости

Рассматривается влияние способа замещения комплексной нагрузки на характер электромеханических переходных процессов в электрических системах (ЭС) от действия больших возмущений. Показано, что установить общие рекомендации относительно способа замещения нагрузки в сложных ЭС затруднительно. Предлагается для опреде­ления характерных узлов нагрузки, оказывающих существенное влияние на характер динамического перехода, применять известный метод контрольных возмущений. Приводятся результаты сравнительных расчетов с использованием предлагаемой методики

Associative language descriptions �;�� www.elsevier.com/locate/tcs

AbstractThe new Associative Language Description (ALD) model, a combination of locally testable and constituent structure ideas, is proposed, arguing that in practice it equals context-free (CF) grammars in explanatory adequacy, yet it provides a simple description and it excludes mathematical sets based on counting properties, which are rarely (if ever) used in compiler construction or in computational linguistics. The ALD model has been recently proposed as an approach consistent with current views on brain organization. ALD is a “pure”, i.e., nonterminal-free definition. The strict inclusion of ALD languages in CF languages is proved, based on a lemma which strengthens the Pumping Lemma for CF languages. Basic nonclosure and undecidability properties are considered and compared with those of CF languages. It is shown that the hardest context-free language is in ALD, that there exists a hierarchy of ALD languages and that each ALD tree language enjoys the noncounting property of parenthesized CF languages. Typical technical languages (Pascal, HTML) can be rather conveniently described by ALD rules

Comment on “Carbonate deposition and diagenesis in evaporitic environments: The evaporative and sulphur-bearing limestones during the settlement of the Messinian Salinity Crisis in Sicily and Calabria” by Caruso et al., 2015. Palaeo3, 429, 136–162

A recent paper by Caruso et al. (2015) dealing with the Calcare di Base of Sicily and Calabria reintroduced an earlier idea that onset on the Messinian salinity crisis is diachronous. The paper provided a stratigraphic correlation of five sections together with the reference section of Falconara and Gibliscemi (Sicily) in order to establish the diachronous nature of restricted saline conditions. In our opinion their conclusions are not supported by the data, and the paper contains some stratigraphic errors that depend on a flawed presentation of the main stratigraphic concepts provided over the past few years covering the deposits of the Messinian salinity crisis in Sicily. In this discussion we challenge the stratigraphic conclusion of Caruso et al. (2015) holding that: a) they did not fully consider the different types of deposits included in the Calcare di Base unit and consequently did not recognize the large scale unconformity at the base of the brecciated limestone (Calcare di Base type 3); b) they did not provide univocal criteria for the definition of the onset of the Messinian salinity crisis; c) they hold the idea that the onset of the salinity crisis must be coincident with the onset of the evaporites, concept which is not necessarily true; d) they arbitrarily correlated different evaporitic deposits formed during different stages of the MSC; e) they provided a stratigraphic correlation of the study sections and their tuning with the insolation curve that lacks of reliable stratigraphic constraints. Consequently, they have presented an unreliable schematic evolution of the Caltanissetta basin

Overview of the literature on the catalytic processes used for sorbitol double dehydration to isosorbide

International audienc

Overview of the literature on the catalytic processes used for sorbitol double dehydration to isorsobide

International audienc