scholarly journals Rare Earth Element Characteristics of Marine Carbonates from Xisha Islands, South China Sea: Implications for the Effect of Dolomitization on REEs

2020 ◽  
Author(s):  
Xikai Wang ◽  
Xiao-Ming Liu ◽  
Xiaofeng Liu
Keyword(s):  
Rare Earth ◽  
South China Sea ◽  
Rare Earth Element ◽  
South China ◽  
Earth Element ◽  
Xisha Islands ◽  
China Sea ◽  
Marine Carbonates

scholarly journals Formation of Tubular Carbonates within the Seabed of the Northern South China Sea

Minerals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 768
Author(s):  
Yuedong Sun ◽  
Jörn Peckmann ◽  
Yu Hu ◽  
Xudong Wang ◽  
Shanggui Gong ◽  
...  
Keyword(s):  
Rare Earth ◽  
South China Sea ◽  
Rare Earth Element ◽  
South China ◽  
Earth Element ◽  
Anaerobic Oxidation Of Methane ◽  
Fluid Migration ◽  
Bottom Currents ◽  
China Sea ◽  
Carbonate Formation

A remarkable exposure of tubular authigenic carbonates was found on the seafloor in the Dongsha area of the South China Sea (SCS). The tubular carbonates, around 2–3 cm in diameter and usually less than 10 cm in length, represent broken fragments of once-larger pipes that now protrude from muddy sediments. The morphology, carbon and oxygen stable isotope compositions, and trace and rare earth element contents of the carbonates were analyzed to decipher the mode of carbonate formation. The tubular carbonates exhibit a dark brown coating of iron and manganese hydrous oxides, indicating prolonged exposure to oxic bottom waters. The carbonate content of the micritic pipes falls between 12.5 and 67.3 wt.% with an average of 42.0 wt.%, suggesting formation within the sediment. This inference is supported by trace and rare earth element patterns including a moderate enrichment of middle rare earth elements. Low δ13C values (as low as −50.3‰, Vienna Pee Dee Belemnite (VPDB)) suggest that carbonate precipitation was induced by the anaerobic oxidation of methane. The unusually positive δ18O values of the carbonates (as high as +5.3‰, VPDB) are believed to reflect the destabilization of locally abundant gas hydrate. Taken together, it is suggested that pipe formation was initiated by sediment-dwelling organisms, such as crustaceans or bivalves. The burrows subsequently acted as conduits for upward fluid migration. The lithification of the sediment directly surrounding the conduits and the partial filling of the conduits with carbonate cement resulted in the formation of tubular carbonates. Turbidity currents, sediment slumps, or the vigorous emission of fluids probably induced the fragmentation of tubular carbonates within the sediment. The carbonate fragments had been further subjected to winnowing by bottom currents. This study provides insight into the interaction of megafauna burrowing with fluid migration and carbonate formation at hydrocarbon seeps, highlighting the role of bottom currents and mass wasting on the formation of fragmented tubular carbonates.

Facies character and geochemical signature in the late Quaternary meteoric diagenetic carbonate succession at the Xisha Islands, South China Sea

2021 ◽  
Vol 40 (3) ◽  
pp. 94-111
Author(s):  
Wanli Chen ◽  
Xiaoxia Huang ◽  
Shiguo Wu ◽  
Gang Liu ◽  
Haotian Wei ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Late Quaternary ◽  
Xisha Islands ◽  
China Sea ◽  
Geochemical Signature
Sign in / Sign up

Export Citation Format

Share Document