Constraints on sedimentary ages of the Chuanlinggou Formation in the Ming Tombs,Beijing, North China Craton: LA-ICP-MS and SHRIMP U–Pb dating of detrital zircons

Detrital zircons in five sedimentary samples, MC1 to MC5, from the bottom of the Chuanlinggou Formation in the Ming Tombs District, Beijing, were dated with the LA-ICP-MS and SHRIMP U–Pb methods. Age spectra of the five samples show a major peak at 2500 Ma and a secondary peak at 2000 Ma, suggesting their provenances were mainly from the crystalline basement of the North China Craton and the Trans-North China Orogen. The youngest zircon has an age of 1673 ± 44 Ma, indicating that the Chuanlinggou Formation was deposited after this age. From sample MC4 to MC5, lithology changed from a clastic rock (fine-grained sandstone) to a carbonate rock (fine-grained dolomite), suggesting that the depositional basin became progressively deeper. The age spectrum of sample MC5 shows a major peak at 2500 Ma and a secondary peak at 2000 Ma. Sample MC4, which is stratigraphically lower than sample MC5, only had one peak at 2500 Ma. We conclude that there was a transgressive event when sediments represented by MC5 was deposited, and seawater carried ca. 2000 Ma clastic materials to the basin where the Chuanlinggou Formation was deposited, leading to the addition of ca. 2000 Ma detritus. Our research indicates that the source area for the sediments became more extensive with time. We conclude that the Chuanlinggou Formation in the Ming Tombs District was deposited in a low-energy mud flat sedimentary environment in the inter-supra tidal zone because it is mainly composed of silty mudstone and fine-grained sandstone with relatively simple sedimentary structures.     

Basic formation mechanisms of Lake Doroninskoye soda water,East Siberia,Russia

The primary scientific goal of studying salt lakes is to better understand the formation of small continental-type hydrogeochemical systems. Many scientists have attributed the metamorphism of the chemical composition of salt lakes to the evaporative concentration of water. However, the formation of soda water is inconsistent with this hypothesis. Thus, analyzing intrabasinal biochemical processes and water—rocks interactions during the evaporative concentration of water allows us to understand the major mechanisms of the formation and evolution of water compositions. Therefore, the aim of this paper is to identify the key processes involved in the formation of the chemical composition of the water in Lake Doroninskoye. An analysis of the distribution of major components shows that Na⁺, HCO₃ ^?, CO₃ ^2?, and Cl^? are dominant in this water. High concentrations of these elements are the result of evaporative water concentration. Calcium, magnesium, and potassium are not accumulated because the water is saturated in minerals containing these elements. The main barrier to the growth of the sulfate content of water is sulfate reduction. This process also contributes to the additional reproduction of carbon dioxide, which reacts with the products of the hydrolysis of aluminosilicates OH^? to form HCO₃ ^? and CO₃ ^2?, thus further contributing to the natural processes of soda formation.     

Flooding a landscape: impact of Holocene transgression on coastal sedimentology and underwater archaeology in Kiladha Bay (Greece)

Franchthi Cave, bordering Kiladha Bay, in Greece, is a key archaeological site, due to its long occupation time, from?~?40,000 to?~?5000 year BP. To date, no clear evidence of Neolithic human dwellings in the cave was found, supporting the assumption that Neolithic people may have built a village where there is now Kiladha Bay. During the Neolithic period/Early Holocene, wide areas of the bay were indeed emerged above sea level. Bathymetric and seismic data identified a terrace incised by a valley in?~?1 to 2 m sediment depth. Eight sediment cores, up to 6.3-m-long, were retrieved and analysed using petrophysical, sedimentological, geochemical, and chronostratigraphic methods. The longest core extends into the exposure surface, consisting of a layer of carbonate rubble in a finer matrix, representing weathering processes. Dated organic remains place this unit at?~?8500 cal year BP. It is overlain by stiff silty mud representing an estuarine environment. This mud is capped by reduced sediments with roots marking an exposure surface. A shell-layer, dated to?~?6300 cal year BP, overlies this terrestrial sequence, reflecting the marine transgression. This layer occurs at 10.8 mbsl, 7.7 m deeper than the global sea level at that time, suggesting tectonic subsidence in the area. It is overlain by finer-grained marine carbonate-rich sediments. The top of the core shows traces of eutrophication, pebbles and marine shells, all likely a result of modern anthropogenic processes. These results are interpreted in the context of human occupation: the exposed surface contains pottery sherds, one dating to the Early to Middle Neolithic period, indicating that Neolithic people were present in this dynamic landscape interacting with a migrating coastline. Even if the artefacts are isolated, future investigations of the submerged landscape off Franchthi Cave might lead to the discovery of a Neolithic village, which eventually became buried under marine sediments.     

Spatial Relations of Gold-Ore Deposits and Cretaceous Granitoid Magmatism in the Chukotka Peninsula

Analysis of the spatial relations of gold ore occurrences and the enclosing geological environment in the Chukotka Autonomous Okrug (ChAO) has shown that Au–quartz ore occurrences in turbidites are located predominantly in areas of the Early Cretaceous granitoid magmatism with the thick collision-type continental crust. The Cu–Au porphyry deposits are located in areas with complete development of Early Cretaceous magmatism within the outer zone of the Okhotsk–Chukchi volcanoplutonic belt (OChVB). The Au–Ag epithermal deposits are located in the areas of the Late Cretaceous granitoid magmatism within the inner and outer zones of the OChVB. The prospects of island-arc complexes for searching for Kuroku-type Au-bearing ore objects are available.     

Redkinian Biota of Macroscopic Fossils from the Northwestern East European Platform (South Ladoga Region)

The stratigraphic distribution of microfossils and macroscopic fossil biota in Vendian deposits of the South Ladoga region (northwestern East European Platform) is analyzed. In the sequence of the Shotkusa- 1 well, three taxonomically heterogeneous microfossil assemblages are distinguished: two of them refer to the Redkinian age (Starorusskaya Fm.) and one to the Kotlinian age (Vasileostrovskaya Fm.). Deposits of the Starorusskaya Fm. contain Redkinian biota of macroscopic fossils, of which the most characteristic representatives are Chuaria circularis, Doushantuophyton lineare, Morania zinkovi, Orbisiana simplex, and Redkinia spinosa. These new findings expand the paleontological characteristics of Upper Vendian deposits, also providing additional criteria for distinguishing the Redkinian horizon in the northwestern East European Platform.     

The First Results of U–Pb Isotope Dating of Detrital Zircons from the Upper Mesoproterozoic Gulliksenfellet Quartzite (Southern Part of Wedel Jarlsberg Land,Southwest Spitsbergen)

The first results of U–Pb isotopic dating (LA–ICP–MS) of detrital zircons from metasedimentary rocks of the pre-Devonian basement of the SW part of western Spitsbergen (from Upper Mezoproterozoic Gulliksenfellet quartzite) showed ages ranging from 1700 ± 25 to 2948 ± 27 Ma.     

Geodynamic Evolution Model of the Major Structures of Amerasian Basin

We have analyzed the geodynamic evolution of the lithosphere and upper mantle of the Amerasian basin based on the stress-strain state simulation. It is shown that the asthenospheric spreading in the return upflow region of the mantle convection, results in formation of two local uplifts, which can be interpreted as Lomonosov Ridge and Mendeleev/Alfa Ridge. The further long-term action of the mantle convection leads to formation of Makarov and Podvodnikov Basins.     

Shear Tectonic Fabric in the Atlantic Ocean and Its Relation to the Geodynamic Condition of the Upper Mantle and Intraplate Deformations

The tectogenesis of the Atlantic Ocean segments is complicated by the axial difference in spreading half-velocities, which causes additional shear displacements between the lithospheric blocks along the transform faults. The intensity of these processes and density of the fault zones iis related to the presence of “cold” sublithospheric lenses along the MAR at a depth of 500 km.     

Comparison of Supercontinent Cycles in the Metallogeny of Rare Earth Elements

The distribution of integrated resources of large and superlarge deposits (LSLDs) of rare earth elements (REEs) is compared to the current model of supercontinent cyclicity during Earth’s evolution. It is found that REE LSLDs are related predominantly to igneous complexes (carbonatite, nepheline syenites, syenite-alkaline granites, subalkaline granites), which are often additionally enriched in the hypergenic zone. A certain part of the resources is concentrated in independent hypergenic formations represented by placers and ion-adsorbed clays. Each supercontinent cycle—Kenoran, Columbian, Rodinian, Pangean, and Amasian—is expressed in the REE metallogeny in particular way: we revealed significant intercycle variations in the amount of REE LSLDs, the variety of their types, total accumulated resources, and some other characteristics.