The Lake Manzala of Egypt: an ambiguous future

The Lake Manzala of Egypt has a relatively short history and its future, however, is uncertain. The lake which was the biggest coastal wetland along the Mediterranean Coast is moving toward its disappearance by two opposite forces, one of them is the shrinking of the water body by siltation of sediments coming from agricultural lands and the abundance of weeds and swamp vegetation as well as the drying practices for agriculture, whereas the other force incorporates the removal of the coastal sand bar separating the lake from the Mediterranean Sea by erosion, which should eventually lead to the conversion of the lake into a coastal embayment instead of being a closed coastal lagoon. The study provided a spatiotemporal change analysis of the lake using remotely sensed data.     

Ultrastructure of a microbial mat-generated phosphorite

Optical and SEM observations of phosphorites reveal that mineralization is concentrated on ooids and micro-oncoids. The coated grains occur within microbial mats. Microbial mats represent the formational environment of the ooids and oncoids. Both coated grains and mats exhibit similar filamentous micro-organisms. The mat filaments show no fixed orientation and they merge with the concentrically oriented filaments of the coated grains. The branching nature and chlamydospore-like structures of filaments suggest that both mat and coated grains have been formed by fungi. Some coated grains appear to have been slightly disturbed and sometimes mobilized from their sites of formation due to separation from the parent mat resulting perhaps from contraction/fragmentation. The voids so created within the mat had been later filled with either micrite or sparite.     

Transition from shoshonitic to adakitic magmatism in the eastern Pontides,NE Turkey: Implications for slab window melting

The formation of the eastern Pontides orogenic belt has been widely assigned to a northward subduction of the Neotethyan oceanic slab during the late Mesozoic–Cenozoic. Here we provide an alternate model based on new geological, geochemical and isotopic data. The magmatic activity in the far south of the belt started in the early Campanian with shoshonitic trachyandesites and associated pyroclastics. This sequence is covered by the late Campanian–early Maastrichtian reefal limestones and another stage of high-K volcanism represented by analcimized leucite-rich ultrapotassic rocks of the Maastrichtian–early Paleocene (?) ages. The shoshonitic and ultrapotassic rocks, with K₂O contents ranging from 0.26 to 6.95 wt.%, display broadly similar rare earth and multi-element distribution patterns. Both rock types are enriched in LILE and LREE and depleted in HFSE (Nb, Ta and Ti), suggesting a subduction-enriched mantle source for the magma generation. Subsequently, during the late Paleocene, a stage of acidic magmatism (SiO₂ of 53.25–73.61 wt.%) that shows adakitic geochemical characteristics including high Sr/Y (46–416) and La/Yb (11–51) and low Y (2.6–12.2 ppm), is documented characterized by melting of a mafic source such as the MORB crust with garnet in the residue. The adakitic magmatism began at ~ 56 Ma and migrated toward the north through time, culminating with porphyritic andesites (~ 47 Ma) that were emplaced in the Gumushane–Bayburt line and its vicinity. North of this line, coeval magmas show typical calc-alkaline nature and continued to develop toward further north until the middle to late Eocene. Based on the spatial and temporal variations in the magmas generated in the eastern Pontides orogenic belt, we propose a new geodynamic model to explain the tectonomagmatic evolution of these rocks and correlate the adakitic magmatism to ridge subduction and slab window process within a south-dipping subduction zone. Our model is in contrast to the previous proposals which envisage partial melting or delamination of thickened lower continental crust due to the collision in the south during the Paleocene–Eocene.     

Physical Libration of the Moon: An Extended Problem

Astronomy Reports - The work is devoted to the study of the physical libration of the Moon. Interest in the traditional topic related to the rotation of the Moon is stirred up by the activity of...     

Geochemical Indicators of “Camouflaged” Pyroclastic Material in the Upper Jurassic–Lower Cretaceous Deposits of the Eastern Russian Platform

Doklady Earth Sciences - Based on the results of studying the lithological–geochemical features of the Upper Jurassic–Lower Cretaceous mudrocks and black shales in the Eastern Russian...     

The influence of geodynamic factors on the lithification of sedimentary deposits in the stratisphere

The peculiarities of the processes of postsedimentary lithification and their dynamics in various geostructural areas (cratons, young platforms, and orogens) are considered. The direct and indirect impacts of geodynamic factors on these processes are substantiated.     

Convection Regime of the Development of an Impulse–Buoyant Transient Jet Submerged in a Homogeneous Fluid

An intergral model of a transient vertical impulse–buoyant jet is suggested. The model contains a universal equation describing the propagation of the upper boundary of the convection front depending on the strength of the point source of buoyancy and momentum. The convective regime of jet propagation is considered, which includes a class of self-similar solutions corresponding to the buoyancy sources, whose strength varies with time following power and exponential laws. The obtained numerical solutions are compared with available experimental data on the profiles of vertical velocity and buoyancy on the jet axis.     

Nonmarine Cretaceous palynology of northern Kordofan,Sudan, with notes on fossil Salviniales (water ferns)

A palynological investigation of 164 samples from 18 water wells in northern Kordofan, Sudan, enabled the recognition of five informal zones based on pollen and spore assemblages ranging in age from Albian to Maastrichtian. The youngest (late Campanian-Maastrichtian) assemblages are restricted to the Bagbag Basin, whereas Albian-Cenomanian (to Turonian) sediments are widespread to the east and west of the Bagbag area. Impressions of Salvinia floating leaves from outcrops of the upper Hamrat el Wuz Formation, western part of the study area, are among the oldest occurrences of this water fern and indicate a Campanian-Maastrichtian age for these sediments.The vertical distribution of hygrophilous (pteridophytic spores) versus xerophilous (ephedroids and possibly small, weakly sculptured tricolporates) elements in the palynofloras suggests widespread moist or even aquatic habitats in the Albian-Cenomanian and Campanian-Maastrichtian. A shift towards drier conditions occurred in the late Cenomanian-Turonian. Throughout the Cretaceous, however, there may have been extensive arid/semiarid areas of non-deposition and seasonally dry periods. Some characteristics of the local palynofloras are attributed to its inner continental position. Rare Albian-Cenomanian and Campanian-Maastrichtian dinoflagellates could be interpreted as lacustrine phytoplankton rather than as evidence for marine influence.