塔里木盆地中新生代海侵和海相地层研究的新进展

中新生代海侵是塔里木盆地地质发展史上的重要事件之一。通过对新近发现的古生物化石和海相地层资料研究，本文提出了早白垩世、晚白垩世、古近纪的海侵范围的新认识。同时，依据露头和钻井资料提出了中新世海水分布的新范围。这些新成果对厘定塔里木盆地中新生代地层时代，建立整个盆地中新生代地层格架和油气远景分析具有重要意义。     

A weight-of-evidence approach to assessing the ecological impact of organotin pollution in Dutch marine and brackish waters; combining risk prognosis and field monitoring using common periwinkles (Littorina littorea)

In the present study an integrated ecological risk assessment based on multiple lines of evidence (LOEs) was evaluated in order to better assess the risk from TBT in Dutch harbours and open coastal waters. On the basis of spatial distributions of measured tributyltin (TBT) concentrations in sediments and suspended matter, predictions of the intersex index (ISI) in Littorina littorea and the ecological risk expressed as the Potentially Affected Fraction (PAF) of species were made. The results were compared to actual ISI measurements and presence of L. littorea in the field. The PAF calculated on the basis of TBT levels for open coastal waters ranged from 4.2% to 15.3%; for harbours it ranged from 3.5% to 26.9%. Significant intersex levels were observed only in waters where the risk was calculated above 10% PAF. This study suggests that the absence of L. littorea from some harbours with high ecological risk values can be explained by high TBT concentrations. A call is made for the use of integrated approaches like weight-of-evidence (WOE) to help practitioners improve ecological risk assessment.     

Mio-Pliocene magnetostratigraphy in the southern Carpathian foredeep and Mediterranean–Paratethys correlations

A full understanding of the Mio-Pliocene palaeogeographical and palaeoenvironmental changes in the circum-Mediterranean region during the Messinian Salinity Crisis (MSC) is at present hampered by the lack of reliable chronostratigraphic correlations between the Mediterranean and Paratethys regions. Here, we present magnetostratigraphic ages for the Upper Miocene to Pliocene deposits of the southern Carpathian foredeep in Romania. These ages are in good agreement with those recently obtained from the eastern Carpathian foredeep and define a new chronology for the eastern Paratethys. The Meotian/Pontian boundary is not biostratigraphically constrained in our sections, but according to the geological map of the region arrives at ∼5.8 Ma. The Pontian/Dacian boundary is dated at c. 4.8 Ma and the Dacian/Romanian boundary at c. 4.1 Ma. The main part of the MSC (5.96–5.33 Ma) is thus represented by the Pontian Stage, but the observed palaeoenvironmental and biostratigraphic changes in our sections of the eastern Paratethys do not indicate any relation with the dramatic desiccation and reflooding events of the Mediterranean.     

Provenance analysis as a key to orogenic exhumation: a case study from the East Carpathians (Romania)

Provenance analysis of the sediments from foredeep basins is crucial in understanding the contemporaneous orogenic exhumation processes. We report in this paper complex sediment provenance analysis using sandstone petrography and mudstone geochemistry, combined with magnetic susceptibility of the Upper Miocene to Pliocene deposits from Focşani foredeep basin (Romania). Data show a change of source area between 5 and 6 Ma, from an active volcanic arc towards a recycled orogenic belt, concurrent with an important increase of accumulation rate. This change was triggered by exhumation and erosion of the outer nappes from East Carpathians.     

Crystal morphology and surface structures of orthorhombic MgSiO3 in the presence of divalent impurity ions

Many rheological and transport properties of rocks are determined by the grain boundary structures of their constituent minerals. These grain boundaries often also hold a high concentration of dopant ions. Here, as a first step towards modelling the transport and rheological behaviour of the lower mantle, we report the results of lattice static simulations on the surface structures of Fe²⁺ and Ca²⁺-doped orthorhombic MgSiO₃-perovskite. For all the surfaces we studied, the energies of the doped structures are lowered, sometimes by more than 1 J/m², with respect to the pure surfaces. From our calculated crystal morphologies, we predict that the grains become more tabular as the concentration of Fe²⁺ ions increases, while under equilibrium conditions the grains are cubic. By calculating the replacement energies of Mg²⁺ by Fe²⁺ and Ca²⁺ ions in the six outermost surface layers, we conclude that these divalent ions would tend to segregate onto the crystal surfaces. We suggest, therefore, that the grain boundary structure and rheology of MgSiO₃-perovskite dominated rocks will be strongly affected by the presence of minor elements in the lower mantle.