Guanghai Shi

Bio: Guanghai Shi is an academic researcher from China University of Geosciences (Beijing). The author has contributed to research in topics: Metamorphism & Clastic rock. The author has an hindex of 4, co-authored 4 publications receiving 965 citations. Previous affiliations of Guanghai Shi include Chinese Academy of Sciences.

Ion Microprobe U-Pb Age and Zr-in-Rutile Thermometry of Rutiles from the Daixian Rutile Deposit in the Hengshan Mountains, Shanxi Province, China

Abstract: The Daixian rutile deposit is located in the Hengshan Mountains in the Trans-North China Orogen; it is con sidered to be one of the largest rutile deposits in China, with 6 million metric tons (Mt) of contained titanium. Most of the rutile ores are hosted in garnet-free anthophyllite gneiss with minor Mg hornblende, feldspar, quartz, phlogopite, rutile, zircon, and titanite. Rutile grains are euhedral, 0.02 to 0.50 mm in size, contain 98.649 to 99.784 wt % TiO 2, and form chains, thin layers along the foliation, and dense aggregates. Rutiles are compositionally homogeneous and contain no detectable mineral inclusions except local ilmenite lamellae and zircon. Crystallization temperatures of the rutile are estimated at ~640°C at 0.7 GPa, and ~647°C without pres sure calibration according to the Zr-in-rutile thermometer, recording amphibolite facies metamorphism of an intermediate P/T ratio series. Variations in Nb versus Cr in rutiles indicate a connection of the ores to mafic protolith; not a pelitic rock derived from aluminous sedimentary rocks. SIMS U-Pb analyses of rutiles from the deposit yield a mean 207 Pb/ 207 Pb age of 1780.2 ± 9.6 Ma. Considering the closure temperature (up to ~650°C), grain sizes and recrystallization of the rutile, this age is more likely to represent closure and/or recrystallization time rather than peak metamorphism period, so the rutile deposit formed not younger than ~1780 Ma. This unique garnet-free rutile deposit was metamorphosed from mafic rocks in amphibolite facies during the Paleoproterozoic or Archean, being distinct from any other metamorphic rutile deposits, such as the known eclogite-related types.

Phylogenomics resolves the timing and pattern of insect evolution

Abstract: Insects are the most speciose group of animals, but the phylogenetic relationships of many major lineages remain unresolved. We inferred the phylogeny of insects from 1478 protein-coding genes. Phylogenomic analyses of nucleotide and amino acid sequences, with site-specific nucleotide or domain-specific amino acid substitution models, produced statistically robust and congruent results resolving previously controversial phylogenetic relations hips. We dated the origin of insects to the Early Ordovician [~479 million years ago (Ma)], of insect flight to the Early Devonian (~406 Ma), of major extant lineages to the Mississippian (~345 Ma), and the major diversification of holometabolous insects to the Early Cretaceous. Our phylogenomic study provides a comprehensive reliable scaffold for future comparative analyses of evolutionary innovations among insects.

An ammonite trapped in Burmese amber.

Abstract: Amber is fossilized tree resin, and inclusions usually comprise terrestrial and, rarely, aquatic organisms. Marine fossils are extremely rare in Cretaceous and Cenozoic ambers. Here, we report a record of an ammonite with marine gastropods, intertidal isopods, and diverse terrestrial arthropods as syninclusions in mid-Cretaceous Burmese amber. We used X-ray-microcomputed tomography (CT) to obtain high-resolution 3D images of the ammonite, including its sutures, which are diagnostically important for ammonites. The ammonite is a juvenile Puzosia (Bhimaites) and provides supporting evidence for a Late Albian-Early Cenomanian age of the amber. There is a diverse assemblage (at least 40 individuals) of arthropods in this amber sample from both terrestrial and marine habitats, including Isopoda, Acari (mites), Araneae (spiders), Diplopoda (millipedes), and representatives of the insect orders Blattodea (cockroaches), Coleoptera (beetles), Diptera (true flies), and Hymenoptera (wasps). The incomplete preservation and lack of soft body of the ammonite and marine gastropods suggest that they were dead and underwent abrasion on the seashore before entombment. It is most likely that the resin fell to the beach from coastal trees, picking up terrestrial arthropods and beach shells and, exceptionally, surviving the high-energy beach environment to be preserved as amber. Our findings not only represent a record of an ammonite in amber but also provide insights into the taphonomy of amber and the paleoecology of Cretaceous amber forests.