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| Bach Long Vi Formation | |
|---|---|
| Name | Bach Long Vi Formation |
| Type | Geological formation |
| Period | Cretaceous |
| Region | Gulf of Tonkin |
| Country | Vietnam |
Bach Long Vi Formation The Bach Long Vi Formation is a Cretaceous stratigraphic unit exposed in the Gulf of Tonkin and on islands off the northern Vietnamese coast, notable for its complex sedimentary sequences and tectonic implications. Studies of the unit have been conducted by Vietnamese institutions and international teams linking regional Red River Fault histories, South China Sea evolution, and broader Indochina Block tectonics. The formation provides data relevant to understanding Paleozoic–Mesozoic transitions, regional orogeny episodes, and basin development associated with the Sunda Plate interactions.
The stratigraphy of the Bach Long Vi Formation has been described in regional mapping campaigns that correlate exposures with the Krong Pa Formation, Phu Phan Formation, and units of the Red River Delta; fieldwork integrates data from the Vietnam National University, the Institute of Geology (Vietnam), and international groups from University of Oxford and University of Tokyo. Stratigraphic columns show alternating beds that are lithologically comparable to sequences reported in the Tonkin Gulf Basin and correlated with scatterings of Cretaceous strata on the Hainan Island margin and along the Gulf of Tonkin Fault Zone. Biostratigraphic ties use faunal assemblages comparable to those in the Yangtze Platform and isotopic markers paralleling work from the Sichuan Basin.
Lithologies reported include sandstone, siltstone, shale, and intermittent limestone horizons, with mineral assemblages containing quartz, feldspar, clay minerals, and calcite; petrographic studies reference methods developed at Smithsonian Institution and analytical protocols from the U.S. Geological Survey. Heavy-mineral suites reported in detrital studies exhibit garnet, zircon, and tourmaline consistent with provenance signals tied to the Himalaya and South China Block uplift events recorded by zircon U–Pb studies conducted using instrumentation at Stanford University and Geological Survey of Japan. Clay-mineralogy analyses reference standards used by the International Clay Minerals Society.
Absolute and relative dating efforts employ biostratigraphy, zircon U–Pb geochronology, and radiometric tie-points, paralleling protocols used in studies at ETH Zurich and Lamont–Doherty Earth Observatory. Age assignments for the formation broadly place it within the Cretaceous, with debated subdivisions correlating to stages recognized in the International Commission on Stratigraphy timescale. Detrital zircon populations compared to age spectra from the Tarim Basin, Cathaysia Block, and Yangtze Craton help refine depositional timing and linkages to regional magmatic pulses recorded by researchers at Academia Sinica and Chinese Academy of Sciences.
Fossil content reported in the Bach Long Vi exposures includes marine microfossils, benthic invertebrates, and occasional macrofaunal remains; paleontological surveys have referenced techniques from the Natural History Museum, London and collections curated at the Vietnam Museum of Nature. Foraminifera, nannofossils, and brachiopod occurrences have been used to correlate assemblages with those documented from the Gondwana-derived margins and the South China Sea basin; comparative taxonomic work cites faunal lists similar to records from Borneo, Laos, and Hainan. Paleoecological interpretations draw on models developed at University of Cambridge and University of California, Berkeley to infer depositional environments and biodiversity patterns.
Tectonic interpretations place the Bach Long Vi Formation within a complex setting influenced by the Red River Fault system, the opening of the South China Sea, and plate interactions involving the Eurasian Plate and the Philippine Sea Plate. Structural analyses reference seismic profiles acquired in joint surveys with institutions such as the Norwegian Geotechnical Institute and the Asian Development Bank-funded programs, linking folding, thrusting, and strike-slip features to regional orogenic events like the India–Asia collision and subsequent extrusion of the Indochina Block. Models of basin evolution incorporate work by researchers at PERG (Petroleum Exploration Research Group) and comparative analogues from the East China Sea margins.
The unit has been evaluated for hydrocarbon potential, with petroleum system analyses referencing basin models used by the Petrovietnam and exploratory work by companies associated with the Petroleum Institute of Vietnam. Reports discuss reservoir-quality sandstones, potential source-rock intervals, and mineral occurrences analogous to deposits worked in the Gulf of Thailand and the South China Sea basins; resource assessments cite methodologies from the International Energy Agency and the World Petroleum Council. Non-hydrocarbon resources, including aggregate and potential trace-metal concentrations, have been sampled following protocols used by the United Nations Development Programme in regional resource appraisals.
Initial descriptions and mapping of the Bach Long Vi lithologies appeared in Vietnamese geological bulletins coordinated by the Institute of Geology (Vietnam) and later expanded by collaborative projects with the Vietnamese Academy of Science and Technology and foreign partners from France and Japan. Key field campaigns involved teams from the British Geological Survey and academic institutions such as Harvard University and Kyoto University, producing stratigraphic syntheses, petrological reports, and geochronological datasets. Ongoing research programs integrate sedimentology, paleontology, and geophysics supported by grants from bodies including the National Science Foundation and regional initiatives under the ASEAN framework.
Category:Geologic formations of Vietnam