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The article presents a quiz on various chemistry topics, including questions on amines, organic compounds, hybridization, and oxidation numbers.

This paper investigates transport mechanisms involving carbonate cementation in Eocene, tight-oil sandstones in Bohai Bay Basin, China, to determine potential mass transfer between adjacent mudstones and sandstones. Evidence from petrology, geochemistry, and numerical modeling suggests two generations of carbonate cementation: (1) early nonferroan calcite (formed at 28°C-41°C) and dolomite (formed at 45°C-63°C); and (2) later ferroan calcite (formed at 105°C-124°C) and ankerite (formed at 101°C-137°C). Based on a one-dimensional model for a coupled sandstone-mudstone system under low and high temperatures, different distribution patterns of carbonate cements reflect episodic concentration gradients that led to diffusive transport of bicarbonate species during progressive burial. Firstly, extensive precipitation of early nonferroan calcite followed by dolomite at or near mudstone-sandstone contacts resulted from initial concentration gradients related to different compositions in primary mineral assemblages. Secondly, introduction of aqueous CO2 from adjacent mudstones into sandstones resulted in dissolution of early nonferroan carbonates and led to diffusive transport of bicarbonate species. These bicarbonate species were incorporated with Fe2+ and subsequently reprecipitated as ferroan carbonate minerals at distances greater than 2 m (>6.6 ft) from sandstone-mudstone contacts. Therefore, short-distance diffusive transport is inferred to have been the predominant transport mechanism associated with carbonate cementation. Large-scale mass transfer between sandstones and adjacent mudstones occurred in a relatively open geochemical system on a very local scale. Numerical model results show that low porosity zones (2.6%-5.1%) exhibit coherence with high abundances of carbonate cements (13.9%-21.2%). Tightly cemented intervals were created by different generations of carbonate cementation and resulted in destruction of sandstone reservoir porosity. [ABSTRACT FROM AUTHOR]

The evolution of dolomite sand is depicted using the example of eight surface outcrops in the "Franconian Dolomite" of Jurassic sequences of southeastern Bavaria/SE Germany. Cathodoluminescence and scanning electron microscope images in combination with extensive sediment petrographic and geochemical research prove that at least two dolomite phases occur (1. Upper Jurassic, 2. Upper Cretaceous), each with subsequent leaching phases and formation of dolomite sands. The first leaching phase is the result of dissolution capacities in conjunction with the first karstification of the Franconian Upper Jurassic Dolomite during the Early Cretaceous. The second intensive dissolution occurred after the second dolomitisation during the Early Tertiary in the zone of epikarst as well. Recently another (third) kind of dolomite sand forms on the rock surfaces of the dolomite outcrops in the Franconian Alb. Petrographical and chemical research of this study was focused on those dolomite sands that resulted from the second leaching phase, i.e. from the most intensive chemical weathering under humid climate during the Early Tertiary. The genesis of microapatites found on the surface and in the intracrystalline porosity of the etched rhombohedra is attributed only to dolomite sands of this weathering period. This second phase of dolomite sand formation is of special characteristic because of the stoichiometric composition of these dolomites. [ABSTRACT FROM AUTHOR]

The article discusses how large rocks at Racetrack Playa in Death Valley National Park of California are moving on a flat landscape without any gravitational force and human or animal intervention. Also cited are the types of the moving rocks, namely, dolomite and syenite, and the use of time-lapse photography to observe the rock movements.