The effects of diagenetic processes and fluid migration on rare earth element and organic matter distribution in seep-related sediments: A case study from the South China Sea

2020 ◽  
Vol 191 ◽  
pp. 104233
Author(s):  
Linying Chen ◽  
Meng Jin ◽  
Xudong Wang ◽  
Hongbin Wang ◽  
Niu Li
Keyword(s):  
Organic Matter ◽  
Rare Earth ◽  
South China Sea ◽  
South China ◽  
Earth Element ◽  
Fluid Migration ◽  
Matter Distribution ◽  
Diagenetic Processes ◽  
Organic Matter Distribution

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.

scholarly journals 3D Numerical Modelling and Sensitivity Analysis of the Processes Controlling Organic Matter Distribution and Heterogeneity. A Case Study from the Toarcian of the Paris Basin

2018 ◽  
Author(s):  
Benjamin Bruneau ◽  
Marc Villié ◽  
Mathieu Ducros ◽  
Benoit Chauveau ◽  
François Baudin ◽  
...  
Keyword(s):  
Sensitivity Analysis ◽  
Organic Matter ◽  
Primary Productivity ◽  
Critical Parameters ◽  
Strong Impact ◽  
Paris Basin ◽  
Matter Distribution ◽  
Organic Matter Accumulation ◽  
Organic Matter Distribution

The active debate about the processes governing the organic-rich sediment deposition generally involves the relative roles of elevated primary productivity and enhanced preservation related to anoxia. However, other less spotlighted factors could have a strong impact on such deposits: e.g. residence time into the water column (bathymetry), sedimentation rate, transport behavior of organo-mineral floccules on the sea floor. They are all strongly interrelated and may be obscured in the current conceptual models inspired from most representative modern analogues (i.e. upwelling zones and stratified basins). To improve our comprehension of organic matter distribution and heterogeneities, we conducted a sensitivity analysis on the processes involved in organic matter production and preservation which have been simulated within a 3D stratigraphic forward model. The Lower-Middle Toarcian of the Paris Basin was chosen as a case study as it represents one of the best documented example of marine organic matter accumulation. The relative influence of the critical parameters (bathymetry, diffusive transport, oxygen mixing rate and primary production) on the output parameters (Total Organic Carbon, and oxygen level), determined performing a Global Sensitivity Analysis, shows that, in the context of a shallow epicontinental basin, a moderate primary productivity (> 175 gC.m-².yr-1) can led to local anoxia and organic matter accumulation. We argue that, regarding all the processes involved, the presence and distribution of organic-rich intervals is linked as a first-order parameter to the morphology of the basin (e.g. ramp slope, bottom topography). These interpretations are supported by very specific ranges of critical parameters which allowed to obtain output parameter values in accordance with the data. This quantitative approach and its conclusions open new perspectives about the understanding of global distribution and preservation of organic-rich sediments.

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