Palaeoworld最新文献

The Longmenshan region is the geographical boundary between the Sichuan Basin and the eastern Tibetan Plateau, but whether it is the tectonic boundary between the Yangtze Block and Songpan-Garze terrane is still controversial. Meanwhile, the Early Devonian floral differentiation between the Longmenshan region and the southern part of the Yangtze Block, such as Yunnan and Guizhou provinces, also leads to controversy. Here we report U-Pb ages of detrital zircons from Lower Devonian sandstones of the Longmenshan region, providing evidence to discuss the tectonic affinity of the Longmenshan region and possible reasons for the Early Devonian floral differentiation. Detrital zircon U-Pb age patterns show that the Pingyipu Group defines three principal age populations of 2.6–2.4 Ga, 1.2–0.7 Ga, and 0.7–0.5 Ga, with two minor distributions of 1.8–1.5 Ga and 480–420 Ma. This U-Pb age spectrum is consistent with that of the Lower Devonian Danlin Formation of Guizhou, indicating that the Pingyipu Group and the Danlin Formation might share the same or similar sources. Together with fossil evidence, it is suggested that the Devonian sedimentary successions in the Longmenshan region are deposited in the western margin of the Yangtze Block, indicating the western boundary of this block is likely in somewhere to the west of Longmenshan fault, such as the Longriba fault. The Neoproterozoic strata located between the Longmenshan region and Yunnan–Guizhou provinces contain dominant Paleoproterozoic detrital zircons (2.1–1.9 Ga), however, this population is almost absent in the Pingyipu Group and the Danlin Formation, suggesting that there might not exist a denudation area (about 3000 masl) to supply sediments for Lower Devonian strata and separate the Longmenshan region and Guizhou. Therefore, the Early Devonian floral differentiation between the Longmenshan region and Yunnan–Guizhou provinces might not be caused by tectonic or mountainous barriers as previously suggested, but instead, might be caused by different depositional ages of the strata at a finer temporal resolution and environmental factors, such as different climatic conditions and/or habitat heterogeneity.

Many new specimens (36 in total) of gastropods were collected from the Ordovician Alai Formation of the Chiatsun Group at Jiacun village, Nyalam County, southern Xizang (Tibet). These gastropods comprise five species assigned to two genera, including Maclurites parviumbilicatus Yu, M. cf. nyalamensis Yu, M. cf. xizangensis Yu, M. cf. subconicus Yu, and “Hormotoma” ordosensis Yu, forming a Maclurites-“Hormotoma” association. All the species are described in detail herein, and some of which are redefined. This fauna is of middle to late Darriwilian age, and palaeoecologically characterised by species of shallow-water within the photic zone. A comparison of the Maclurites community with the contemporary gastropod fauna from the Zhuozishan Formation exposed along the west margin of the North China Block shows a close palaeogeographical affinity. The occurrences of Ordovician gastropods from China are analyzed biogeographically and the results reveal that the peri-Gondwana gastropod faunal turnover event was initiated during the Middle to Late Ordovician transition. The coincident faunal turnover and the lithofacies changes in the Himalaya and western margin of North China suggest that tectonic activities and relative sea-level changes may account for the biogeographical affinities of some specific fossil groups in peri-Gondwanan regions.

The Pennsylvanian rugose corals are not well understood in Northwest China due to their low diversity and restricted distribution under the impact from coeval Gondwana glaciation. In this study, nine rugose coral species of eight genera are described from the Shiqiantan and Jingou formations (Moscovian to Kasimovian stages) in the new Shuangjingzi Section, northern Xinjiang, Northwest China. These species include dissepimented solitary rugose corals (Arctophyllum shuangjingziense n. sp., Arctophyllum intermedium, Caninophyllum ürümqiense, Gshelia qitaiensis, Pseudotimania aff. junggarensis, Pseudozaphrentoides paramapingensis), and non-dissepimented solitary corals (Amplexizaphrentis sp., Bradyphyllum bellicostatum and Hapsiphyllum sp.). This coral assemblage includes local taxa of the Junggar Basin, with a few common elements from Urals Mountains, Novaya Zemlya, and Spitsbergen in northwestern Palaeotethys Ocean. The composition of the Shuangjingzi corals is characterized by the medium-large dissepimentarium Caninophyllum ürümqiense-Gshelia qitaiensis assemblage, indicating open shallow carbonate environments. Compared with the Shiqiantan Formation, the obvious increase in the abundance of narrow-dissepimentarium corals of Gshelia in the upper Jingou Formation, implies that low-energy environments could have developed, with an increase of shales in this interval.

We report isolated postcranial materials newly excavated from the Middle Jurassic Dongdaqiao Formation in Chaya County, Qamdo City, eastern Tibet. The specimens are assignable to Eusauropoda based on the following combination of characters: huge size of caudal vertebrae and humeral shaft, weakly developed amphicoelous caudal centrum, femoral distal ends with two condyles and a shallow intercondylar groove, and rod-like transverse process of the anterior caudal vertebra with its base not extending to the neural arch. Due to the fragmentary nature of the specimens, we refrain from assigning them to lower taxonomic levels or new species of sauropod until more complete materials are excavated from Qamdo. Nevertheless, the new materials from Qamdo demonstrate that some gigantic sauropods migrated to eastern Tibet during the Middle Jurassic and were more widely distributed than previously known.

Cretaceous ammonites are still poorly known in Tibet, western China. Here we describe a new heteromorph ammonite fauna from the Lower Member of the Lakang Formation in the Lhozhag County, southern Tibet. Material of at least five genera are recognized, including Aspinoceras, ? Hemihoplites, Heteroceratidae gen. et sp. indet, ? Mortoniceras and Parancyloceras, among which three genera are reported from this area for the first time. This ammonite fauna indicates that the age of the Lakang Formation is approximately late Hauterivian to Albian (Early Cretaceous). This study proves that the Lakang Formation was not contemporaneous with the adjacent Gamba Group, which is slightly younger, different from a previous interpretation.

A foraminiferal fauna, consisting of 8 species of fusulines and 24 species of smaller foraminifers, is reported from the middle part of the Xiala Formation in the Tangra Yumco section in central Lhasa Block. The dominance of fusuline Nankinella-Chusenella assemblage and smaller foraminifera Hemigordiopsis indicates a Capitanian (late Guadalupian) age. Quantitative methods including Cluster analysis (CA) and Non-metric Multidimensional Scaling (NMDS) are employed to explore the palaeobiogeographic relationship among the Lhasa, South Qiangtang, Baoshan and Tengchong blocks as well as the localities within these blocks, based on a compilation of Guadalupian fusulines from the four blocks. Results of CA and NMDS for the Guadalupian fusulines from twelve localities show that different localities in the Lhasa Block have a close palaeobiogeographic relationship, indicating a unified environment for the whole Lhasa Block during the Guadalupian. Results of CA and NMDS from four blocks show that the Lhasa and Tengchong blocks have a closer relationship in palaeobiogeographic characteristics, whereas the South Qiangtang and Baoshan blocks are relatively closer. All these results indicate that the Mesotethys Ocean might have opened to a considerable width, forming a palaeogeographic barrier to allow for the discrepancy of palaeobiogeographic characteristics between the Lhasa-Tengchong and the South Qiangtang-Baoshan blocks.

Body sizes of organisms underpin their ecological functions and evolutionary trajectories. Previous studies have shown that significant reduction in body size — the Lilliput effect — occurred in the aftermath of the Permian–Triassic mass extinction (PTME) and that body size did not rebound until to the late Middle Triassic (Ladinian). Here we describe three new gastropod specimens, identified as Toxoconcha sp., with unprecedented large shell sizes among Triassic gastropods, from the Qingyan biota of Guizhou, China. Meanwhile, a new dataset on the gastropod size of Lopingian (Late Permian) to Middle Triassic is presented. The largest specimen we found is ∼350 mm in height while its shell volume is estimated to be 1358661 (= 6.13 log₁₀) mm³. As the largest record of the Triassic gastropod shells, these new fossils from Qingyan suggest that gastropod body size rebounded from the post-PTME Lilliput effect as early as the Anisian. Rapid gigantism has been reported in Middle Triassic marine reptiles, and the occurrence of giant gastropods in Qingyan suggests a convergent morphological response to the unique ecological and environmental conditions of the Middle Triassic.