Sedimentological characteristics and new detrital zircon SHRIMP U–Pb ages of the Babulu Formation in the Fohorem area, Timor-Leste

<div><p>Sedimentological characteristics and zircon provenance dating of the Babulu Formation in the Fohorem area, Timor-Leste, provide new insights into depositional process, detailed sedimentary environment and the distribution of source rocks in the provenance. Detrital zircon sensitive high-resolution ion microprobe (SHRIMP) U–Pb ages range from Neoarchean to Triassic, with the main age pulses being Paleozoic to Triassic. In addition, the maximum deposition ages based on the youngest major age peak (<i>ca</i> 256–238 Ma) of zircon grains indicate that the basal sedimentation of the Babulu Formation occurred after the early Upper Triassic. The formation consists predominantly of mudstone with minor sandstone, limestone and conglomerate that were deposited in a deep marine environment. These deposits are composed of six lithofacies that can be grouped into three facies associations (FAs) based on the constituent lithofacies and bedding features: basin plain deposits (FA I), distal fringe lobe deposits (FA II) and medial to distal lobe deposits (FA III). The predominance of mudstone (FA I) together with intervening thin-bedded sandstones (FA II) suggest that the paleodepositional environment was a low energy setting with slightly basin-ward input of the distal part of the depositional lobes. Discrete and abrupt occurrences of thick-bedded sandstone (FA III) within the FA I mudstone suggests that sandstone originated from a collapse of upslope sediments rather than a progressive progradation of deltaic turbidites. This combined petrological and geochronological study demonstrates that the Babulu Formation in the Fohorem area of the Timor-Leste was initiated as a submarine lobe system in a relatively deep marine environment during the Upper Triassic and represents the extension of the Gondwana Sequence at the Australian margin.</p></div

Phase Transformation of Alternately Layered Bi/Se Structures to Well-Ordered Single Crystalline Bi₂Se₃ Structures by a Self-Organized Ordering Process

Multilayer films composed of alternating layers of Bi and Se[Bi­(4.55 Å)/Se­(6.82 Å)]_<i>n</i> (Bi4Se6), [Bi­(6.13 Å)/Se(12.26) Å]_<i>n</i> (Bi6Se12), and [Bi­(4.86 Å)/Se­(18.46 Å)]_<i>n</i> (Bi4Se18)were fabricated by controlling the layer thickness at the atomic scale using thermal evaporation techniques. After annealing treatment, the Bi4Se18 alternately layered film shows a single phase of Bi₂Se₃ rhombohedral crystalline structure with the characteristic density of single crystal Bi₂Se₃, whereas the Bi6Se12 and Bi4Se6 films show locally disordered Bi₂Se₃ crystalline structure. The effectively controlled layered structure in the as-grown Bi4Se18 film enhances the Bi–Se chemical bonding state. The formation of a layered crystalline structure during the annealing process increased as the thickness of Se increased. After interdiffusion and the crystallization process, alternately layered Bi4Se18 films become stable Bi₂Se₃ single crystals with a continuous and uniform layered structure. Finally, in the Bi–Se system, atomically controlled multilayers with an optimized ratio of each unit layer can be transformed to a perfect single-crystalline structure on oxidized Si with an amorphous phase through a self-organized ordering process