scholarly journals Organic matter characterization and distribution in sediments of the terminal lobes of the Congo deep-sea fan: Evidence for the direct influence of the Congo River

2015 ◽  
Vol 369 ◽  
pp. 182-195 ◽  
Author(s):  
Elsa Stetten ◽  
François Baudin ◽  
Jean-Louis Reyss ◽  
Philippe Martinez ◽  
Karine Charlier ◽  
...  
Keyword(s):  
Organic Matter ◽  
Deep Sea ◽  
Direct Influence ◽  
Congo River ◽  
Sea Fan

Two new species of Cossura (Cossuridae, Annelida) from the terminal lobes of the Congo River deep-sea fan

2017 ◽  
Vol 97 (5) ◽  
pp. 881-888
Author(s):  
Anna Zhadan
Keyword(s):  
New Species ◽  
Deep Sea ◽  
Anterior Margin ◽  
Posterior Part ◽  
Entire Body ◽  
Congo River ◽  
Two New Species ◽  
Dark Pigmentation ◽  
Sea Fan ◽  
Scanning Electron

Two new species of Cossura Webster & Benedict, 1887 were found in material collected during sampling from the terminal lobes of the Congo deep-sea fan. They were described using light and scanning electron microscopy. Cossura platypus sp. nov. has 15–17 thoracic chaetigers, a prostomium longer than it is wide, with a widely rounded anterior margin, an abruptly expanded posterior prostomial ring the same length as the peristomium, without a mid-ventral notch, a branchial filament attached to the midlength of chaetiger 3, and a pygidium with three anal cirri. Cossura platypus sp. nov. is similar to C. brunnea Fauchald, 1972 but differs in the shape of the prostomium, which is widely rounded anteriorly in C. platypus sp. nov. and is broadly triangular in C. brunnea; furthermore, C. platypus sp. nov.is uniformly pale, whereas C. brunnea has dark pigmentation. Cossura candida Hartman, 1955 differs from C. platypus sp. nov. in the conical shape of the prostomium and 24–35 thoracic chaetigers. Cossura flabelligera sp. nov. has 16–19 thoracic chaetigers, a conical prostomium, and a branchial filament arising from the posterior part of chaetiger 2; the entire body, including the chaetae, is covered by a thick mucous sheath similar to the tunic of flabelligerids. Cossura flabelligera sp. nov. resembles C. longocirrata Webster & Benedict, 1887 in the position of the branchial filament, the shape of the prostomium, and the number of thoracic chaetigers; it differs in having a thick mucous sheath. This character seems to be unique for the Cossuridae.

scholarly journals The Congo deep-sea fan: Mineralogical, REE, and Nd-isotope variability in quartzose passive-margin sand

2021 ◽  
Vol 91 (5) ◽  
pp. 433-450
Author(s):  
Eduardo Garzanti ◽  
Germain Bayon ◽  
Bernard Dennielou ◽  
Marta Barbarano ◽  
Mara Limonta ◽  
...  
Keyword(s):  
Grain Size ◽  
Deep Sea ◽  
Chemical Weathering ◽  
Passive Margin ◽  
Mineral Concentration ◽  
River Sand ◽  
Size Dependent ◽  
Congo River ◽  
Sea Fan ◽  
Quartz Grains

ABSTRACT The Congo deep-sea fan, the largest on Earth fed entirely with anorogenic detritus, is characterized by quartzose to pure quartzose sand, reflecting multiple recycling coupled with extreme chemical weathering in cratonic equatorial Africa. The very youthful lower course of the Congo River connects directly to a steep canyon, where detritus including quartz grains up to a few millimeters in diameter is funneled towards Atlantic Ocean floors and deposited at abyssal depths more than a thousand kilometers away from shore. This article illustrates for the first time in detail the mineralogical and geochemical signatures of Congo Fan sands and discusses the factors controlling their intersample and intrasample variability as a key to understand how sediment is generated, recycled, and finally transferred to the deep sea. Compositional variability is largely grain-size-dependent. Combined petrographic and Raman spectroscopy analyses demonstrate that quartz increases in coarser samples and size classes, whereas feldspars are concentrated in finer sizes, plagioclase relative to K-feldspar and orthoclase relative to microcline, defining an order of mechanical and chemical durability among detrital tectosilicates. Because of overwhelming quartz abundance and very low heavy-mineral concentration, quartz contributes significantly to the REE budget and up to 40–50% of Nd in coarser samples, characterized by εNd values as low as –21. The strong grain-size-dependent variability of εNd suggests that quartz carries a markedly more negative εNd signature than monazite and other detrital components. This is chiefly ascribed to the durability of quartz grains, able to survive repeated cycles of weathering and diagenesis through Proterozoic and Phanerozoic time better than all other minerals. Neodymium model ages are influenced less by grain size and quartz abundance but more by the Sm/Nd ratio of different detrital components, and samples hydrodynamically enriched in LREE-rich minerals display TNd,CHUR and TNd,DM ages 1.2–1.4 Ga younger than samples enriched in HREE minerals. Not all detritus in the Congo Fan is supplied transversally by the Congo River. Forward-mixing calculations based on mineralogical data indicate that sand entrained northward by longshore currents mixes progressively with Congo River sand along the northernmost Angola coast, penetrates in the Soyo estuary, and is eventually captured in the canyon and transferred to the deep-sea fan, where it is estimated to represents 7 ± 2% of turbidite deposits.

scholarly journals Energy transfer in the Congo deep-sea fan: From terrestrially-derived organic matter to chemosynthetic food webs

2017 ◽  
Vol 142 ◽  
pp. 197-218 ◽  
Author(s):  
A.M. Pruski ◽  
C. Decker ◽  
E. Stetten ◽  
G. Vétion ◽  
P. Martinez ◽  
...  
Keyword(s):  
Organic Matter ◽  
Energy Transfer ◽  
Food Webs ◽  
Deep Sea ◽  
Sea Fan

scholarly journals Origin and distribution of the organic matter in the distal lobe of the Congo deep-sea fan – A Rock-Eval survey

2017 ◽  
Vol 142 ◽  
pp. 75-90 ◽  
Author(s):  
François Baudin ◽  
Elsa Stetten ◽  
Johann Schnyder ◽  
Karine Charlier ◽  
Philippe Martinez ◽  
...  
Keyword(s):  
Organic Matter ◽  
Deep Sea ◽  
Sea Fan ◽  
Rock Eval ◽  
Distal Lobe

scholarly journals Deoxygenation dynamics on the western Nile deep-sea fan during sapropel S1 from seasonal to millennial timescales

2021 ◽  
Vol 17 (3) ◽  
pp. 1025-1050
Author(s):  
Cécile L. Blanchet ◽  
Rik Tjallingii ◽  
Anja M. Schleicher ◽  
Stefan Schouten ◽  
Martin Frank ◽  
...  
Keyword(s):  
Organic Matter ◽  
Primary Productivity ◽  
Deep Sea ◽  
Nile Delta ◽  
Sediment Cores ◽  
Benthic Fauna ◽  
Early Summer ◽  
Authigenic Carbonates ◽  
Terrigenous Input ◽  
Sea Fan

Abstract. Ocean deoxygenation is a rising threat to marine ecosystems and food resources under present climate warming conditions. Organic-rich sapropel layers deposited in the Mediterranean Sea provide a natural laboratory to study the processes that have controlled changes in seawater oxygen levels in the recent geological past. Our study is based on three sediment cores spanning the last 10 000 years and located on a bathymetric transect offshore from the western distributaries of the Nile delta. These cores are partly to continuously laminated in the sections recording sapropel S1, which is indicative of bottom-water anoxia above the western Nile deep-sea fan. We used a combination of microfacies analyses and inorganic and organic geochemical measurements to reconstruct changes in oxygenation conditions at seasonal to millennial timescales. Millimetre-thick laminations are composed of detrital, biogenic and chemogenic sublayers reflecting seasonal successions of sedimentation. Dark layers reflect the deposition of summer floods and two types of light layers correspond to autumn plankton blooms and authigenic carbonates formed in the water column during spring–early summer, respectively. The isotopic signature of the authigenic carbonates suggests permanent anoxic to euxinic bottom waters resulting in high levels of anaerobic remineralization of organic matter and highlights their potential to reconstruct seawater chemistry at times when benthic fauna was absent. Ratios of major elements combined with biomarkers of terrestrial and marine organic matter and redox-sensitive compounds allow changes in terrigenous input, primary productivity and past deoxygenation dynamics on millennial timescales to be tracked. Rapid fluctuations of oxygenation conditions in the upper 700 m water depth occurred above the Nile deep-sea fan between 10 and 6.5 ka BP, while deeper cores recorded more stable anoxic conditions. Synchronous changes in terrigenous input, primary productivity and past oxygenation dynamics after 6.5 ka BP show that runoff-driven eutrophication played a central role in rapid oxygenation changes in the south-eastern Levantine Basin. These findings are further supported by other regional records and reveal time-transgressive changes in oxygenation state driven by rapid changes in primary productivity during a period of long-term deep-water stagnation.

Palynofacies reveal fresh terrestrial organic matter inputs in the terminal lobes of the Congo deep-sea fan

2017 ◽  
Vol 142 ◽  
pp. 91-108 ◽  
Author(s):  
Johann Schnyder ◽  
Elsa Stetten ◽  
François Baudin ◽  
Audrey M. Pruski ◽  
Philippe Martinez
Keyword(s):  
Organic Matter ◽  
Deep Sea ◽  
Terrestrial Organic Matter ◽  
Sea Fan
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