Giant seafloor depressions caused by slope failures and bottom currents on the Namibia continental margin

In this contribution seismic facies of the Paleocene sequence are characterized in offshore basins of Uruguay through the study of a 2D seismic database. Seven seismic horizons were identified, limiting six sedimentary intervals with different characteristics. Hence, the complexity of the Paleocene sequence is greater than suggested by other studies. Seismic facies located in the basis of the sequence can be interpreted as sandy deposits related to the action of both turbidity and bottom currents. The identification of these deposits agrees with the expected Cretaceous source rocks, in addition to the importance of the overlying Paleocene shales as a regional seal. The results of this work open interesting exploratory perspectives in the continental margin of Uruguay. FACIES SÍSMICAS DO PALEOCENE NA MARGEM CONTINENTAL DO URUGUAI (AMÉRICA DO SUL) ResumoNesta contribuição, as fácies sísmicas da sequência do Paleoceno são caracterizadas em bacias offshore do Uruguai através do estudo de uma base de dados sísmica 2D. Foram identificados sete horizontes sísmicos, limitando seis intervalos sedimentares com diferentes características. Neste estudo verifica-se que a complexidade da seqüência do Paleoceno é maior do que a sugerida por outros estudos. A fácies sísmicas localizadas na base da sequência podem ser interpretadas como sendo depósitos arenosos resultantes da ação de correntes de turbidez e de fundo. Estes depósitos correspondem a rochas-fonte cretáceas, estando cobertas regionalmente por importantes rochas selantes correspondentes a folhelhos do Paleoceno. Os resultados deste trabalho abrem interessantes perspectivas exploratórias na margem continental do Uruguai.Palavras-chave: Paleoceno. Facies Sísmicas. Margem Continental do Uruguai.

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Magma emplacement: an important trigger leading to slope failures in deep-water areas of northern continental margin of South China Sea

Geological Journal ◽

10.1002/gj.2838 ◽

2016 ◽

Vol 51 ◽

pp. 96-107 ◽

Cited By ~ 2

Author(s):

Y. Ma ◽

S. Z. Li ◽

J. Q. Lin ◽

Q. Y. Liang ◽

Y. H. Shi ◽

...

Keyword(s):

South China Sea ◽

Continental Margin ◽

South China ◽

Deep Water ◽

Slope Failures ◽

China Sea ◽

Magma Emplacement

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Ferruginous bioforms accumulations in deep marine environments: an approach to their origin and formation mechanisms in the Transitional Zone province of the Galician Continental Margin (NW Iberian Peninsula)

10.5194/egusphere-egu2020-4165 ◽

2020 ◽

Author(s):

Ángel Enrique López-Pérez ◽

Belén Rubio ◽

Daniel Rey ◽

Luís Pinheiro

Keyword(s):

Steady State ◽

Continental Margin ◽

Deep Ocean ◽

Direct Consequence ◽

Transitional Zone ◽

Ocean Floor ◽

Bottom Current ◽

Formation Mechanisms ◽

Bottom Currents ◽

Sea Bottom

Ferruginous tubular structures concretions are widely distributed over the seafloor surrounding the Gran Burato depression in the Transitional Zone (TZ) province of the Galician Continental Margin (NW Iberian Margin). These bioforms-like structures are created by iron oxides precipitations into the tube-dwelling macrozoobenthos as a result of Fe2+ upward diffusion and O2 ventilation and diffusion acting in the water-sediment interphase in a non-steady state early diagenesis. X-ray diffraction analyses display that goethite is the main mineralogical component of these bioforms-like structures. Furthermore, non-steady state diagenesis has been identified by several oxidations fronts recognised in three piston cores, reflecting that the redoxcline has not achieved the deeper equilibrium in the study area. Afterwards, these ferruginous tubes were eroded, remobilised and redistributed over the seabed by bottom currents. Ocean-floor observations show erosion and sea-bottom current structures as ripples, grooves, erratic blocks, accumulations of pteropods and carbonate crusts associated with hardgrounds. Sedimentation rates calculated in a piston core display very low values for the last 30 cal ka BP (mean of 1.57 cm ky&#8722;1) with a marked hiatus between 17.80 to 10.45 cal ka BP, meanwhile abraded surfaces have been identified by high-resolution seismic data confirming erosional processes in this area of the TZ province. We conclude that the ferruginous bioforms accumulation over the deep-ocean floor is indicative of a present-day vigorous seafloor current acting and eroding the sediments of the TZ province. This bottom current is a direct consequence of the general seafloor elevation of the TZ province that causes constriction of the water masses (MOW and LSW) that induces a general intensification of the bottom currents and greater erosional capacity. This erosional process causes the continuous oxygenation of the upper sediments, and it prevents to reach the steady-state diagenesis, playing this fact an essential role in the ferruginous formations and accumulations in the study area.

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