Baoyu Jiang

A synoptical classification of the Bivalvia (Mollusca)

Preface This classification summarizes the suprageneric taxonomy of the Bivalvia for the upcoming revision of the Bivalvia volumes of the Treatise on Invertebrate Paleontology, Part N.

Studies on the Early Cretaceous Longzhaogou and Jixi Groups of eastern Heilongjiang, northeast China, and their bearing on the age of supposedly Jurassic strata in eastern Asia

Abstract The coal-bearing Longzhaogou and Jixi Groups in eastern Heilongjiang, northeast China, consist of alternating marine and non-marine deposits containing abundant marine animal and plant fossils. The Jixi Group also yields members of the Johel Fauna that is widely distributed in northern and eastern China. The two groups have been considered as Jurassic or mainly Jurassic in age for a long time. However, recent studies documented that the ammonites, bivalves, dinoflagellates, angiosperms and sporopollens are all of Early Cretaceous rather than Jurassic age. It has been demonstrated that: (1) the Longzhaogou and Jixi Groups and their equivalents, the Johel Group of China and the Transbaikalian Group of Russia, are of Early Cretaceous age, (2) the Barremian-Albian was also a very important period of coal accumulation in northeastern China and perhaps in all of eastern Asia, (3) there existed a large shallow embayment connecting with the Palaeo-Pacific in eastern Heilongjiang, and it was the climate of the embayment that controlled the origin and development of the animal and plant communities of northeastern China during the Early Cretaceous. Correlation between formations in the Jixi and Longzhaogou Groups has also been revised in this paper.

New evidence suggests pyroclastic flows are responsible for the remarkable preservation of the Jehol biota

The lower Cretaceous Yixian and Jiufotang formations contain numerous exceptionally well-preserved invertebrate, vertebrate and plant fossils that comprise the Jehol Biota. Freshwater and terrestrial fossils of the biota usually occur together within some horizons and have been interpreted as deposits of mass mortality events. The nature of the events and the mechanisms behind the exceptional preservation of the fossils, however, are poorly understood. Here, after examining and analysing sediments and residual fossils from several key horizons, we postulate that the causal events were mainly phreatomagmatic eruptions. Pyroclastic density currents were probably responsible for the major causalities and for transporting the bulk of the terrestrial vertebrates from different habitats, such as lizards, birds, non-avian dinosaurs and mammals, into lacustrine environments for burial. Terrestrial vertebrate carcasses transported by and sealed within the pyroclastic flows were clearly preserved as exceptional fossils through this process.

Oxygen deficiency in Lake Sihetun; formation of the Lower Cretaceous Liaoning Fossillagerstätte (China)

The redox state of Lake Sihetun, represented by the Lower Cretaceous Yixian Formation (western Liaoning, China), is evaluated to understand the formation of this Konservat-Lagerstätte. Lake evolution is subdivided into four phases, of which Phases 2 and 3 exhibit excellent fossil preservation. Exceptional preservation and mass mortality events within Phase 2 were previously attributed to synsedimentary volcanism and oxygen deficiency. However, the volcanic trigger for mass mortality events remains enigmatic and distinction between anoxia and dysoxia has not been put forward so far. To resolve the redox state of the lake during Phase 2, 5394 diameters of pyrite framboid pseudomorphs in 29 thin sections from three localities have been measured. Framboid size distributions reveal that Lake Sihetun was governed by dysoxic bottom waters with spells of anoxia, recording pronounced environmental stress. Hence, holomictic, eutrophic conditions were episodically replaced by meromictic interludes. Spatial variations in redox state were common and oxic conditions were detected in two of the three studied localities. Concentrated iron sulphide layers resulted from biofilms at the lake floor or the development of microenvironments around organic remains, which preserved highly reactive organic compounds. In contrast, sediments of Phase 3 record oxic conditions and an entirely holomictic lake.