Lower Triassic mixed carbonate and siliciclastic setting with Smithian–Spathian anoxic to dysoxic facies, An Chau basin, northeastern Vietnam

In the An Chau basin in northeastern Vietnam, the Olenekian (Lower Triassic) stage comprises mixed carbonate and siliciclastic shallow marine to marginal basin deposits that extend into the southern Nanpanjiang basin in South China. The upper Lang Son Formation, which is dominated by siliciclastic f...

Full description

Saved in:
Bibliographic Details
Published in:Sedimentary geology 2014-03, Vol.300, p.28-48
Main Authors: Komatsu, Toshifumi, Naruse, Hajime, Shigeta, Yasunari, Takashima, Reishi, Maekawa, Takumi, Dang, Huyen T., Dinh, Tien C., Nguyen, Phong D., Nguyen, Hung H., Tanaka, Gengo, Sone, Masatoshi
Format: Article
Language:English
Subjects:
Anoxic to dysoxic facies
Basins
Carbonates
Deposition
Depositional environment
Limestone
Lower Triassic
Marine
Mudstone
Nanpanjiang basin
Ripples
Slopes
Smithian–Spathian boundary
Tethys
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:In the An Chau basin in northeastern Vietnam, the Olenekian (Lower Triassic) stage comprises mixed carbonate and siliciclastic shallow marine to marginal basin deposits that extend into the southern Nanpanjiang basin in South China. The upper Lang Son Formation, which is dominated by siliciclastic facies, is composed of storm- and wave-influenced shallow marine and slope deposits. The overlying and interfingering Bac Thuy Formation consists of tidal flat, wave-influenced carbonate platform, slope, and marginal basin plain deposits. The tidal flat deposits are composed mainly of lenticular, wavy-bedded, or thin flat-bedded carbonates containing desiccation cracks and ripples that are indicative of bidirectional paleocurrents. The platform carbonates are characterized by wave ripples, ooids, and abundant marine mollusks and microfossils; the molluscan fossil assemblage primarily contains Smithian ammonoids such as Owenites koeneni. The slope deposits are characterized by limestone breccia and slump beds. The marginal basin plain deposits consist of classical turbidite beds, minor limestone breccia, and hemipelagic mudstone and marl containing the Spathian ammonoids Tirolites and Columbites. The turbidite sets may represent frontal splay environments in the marginal basin plain. These Olenekian carbonate and siliciclastic facies are typical of a transgressive succession. The Smithian–Spathian boundary and the anoxic to dysoxic facies of the latest Smithian are characterized by organic-rich dark gray limestone and mudstone deposits intercalated in the succession of slope to marginal basin plain facies, which are composed mainly of gravity flow and hemipelagic deposits. The organic-rich deposits show no evidence of bioturbation and are characterized by low-diversity fauna. Clastics in the marginal basin plain deposits were apparently supplied from the west; hence, the paleocurrent direction of the siliciclastic gravity flows was approximately eastward.
ISSN:0037-0738
DOI:10.1016/j.sedgeo.2013.10.009