Pockmarks on the South Aquitaine Margin continental slope: The seabed expression of past fluid circulation and former bottom currents

Michel, G.; Dupré, Stéphanie; Baltzer, Agnès; Ehrhold, Axel; Imbert, Patrice; Pitel, Mathilde; Loubrieu, B.; Scalabrin, Carla; Lazure, Pascal; Marié, Louis; Geldof, Jean-Baptiste; Deville, É.

doi:10.1016/j.crte.2017.10.003

Cited by 26 publications

(12 citation statements)

References 54 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…4) without any clear relation with the southwards stream bottom direction of the Deep Western Boundary Current (Meinen et al, 2013). This means that based on our data, abyssal currents did not modify the studied pockmarks geometric shapes (Andersen et al, 2008;Michel et al, 2017…”

Section: Contourites Oceanic Currents and Buried Sedimentary Bodies supporting

confidence: 62%

The abyssal giant pockmarks of the Black Bahama Escarpment: Relations between structures, fluids and carbonate physiography

Cavailhès

Gillet

Guiastrennec-Faugas

et al. 2020

Preprint

View full text Add to dashboard Cite

Abstract. This study reports the discovery of spectacular abyssal giant pockmarks located at the toe of the Bahamian carbonate platform, along the Black Bahama structurally-controlled Escarpment (BBE) that exhibits up to 4 km of submarine elevation above the San Salvador Abyssal Plain (SSAP). Analysis of seismic reflection and bathymetric data collected during the CARAMBAR 2 cruise revealed the presence of 29 pockmarks; their water depths range from −4584 m to −4967 m whereas their bathymetric depressions are elliptical in shape, range in diameter from 255 m to 1819 m, and in depth from 30 m to 185 m. The pockmarks alignment trends parallel to the BBE as well as the structural lineaments of the area, exclusively between 2200 and 5000 m from its toe, and overlies a buried carbonate bench in which a high-amplitude seismic anomaly has been detected. The pockmark density interestingly increases where the recognized structural lineaments intersect the BBE. The aforementioned observations suggest an atypical relationship between the spatial occurrence of the abyssal fluid releases, the carbonate platform tectonic structures, the buried carbonate bench that underlies the hemipelagites in the San Salvador abyssal plain and the physiography of the area. Indeed, the ground water entrance during low-level stands, the dissolution of evaporites by meteoric water, the platform-scale thermal convection and the seawater entrance at the platform edge most probably act in concert to favor the circulation of brines and therefore the corrosion within the Bahamian carbonate platform. These mechanisms are particularly efficient along the structural heterogeneities (i.e. faults and fractures) which act as fluid conduits and control the physiography of the area by maintaining the location of the sedimentary pathways. The dense fluids migrate along the faults towards the BBE free edge and are subsequently trapped into the buried carbonate bench that laterally disappears below the low-permeability deep-sea hemipelagics of the SSAP. In consequence, the trapped corrosive fluids dissolve the carbonates preferentially along the tectonic structures such as the Samana Fracture Zone, at the origin of the BBE curvature and triggers collapse-structures in the overlying fine-grained deposits generating giant pockmarks. This structurally-directed process of dissolution is believed to have played a major role in the BBE 5–6 km erosional retreat and also probably explains the occurrence of plunge pools in the area.

show abstract

Section: Contourites Oceanic Currents and Buried Sedimentary Bodies supporting

confidence: 62%

The abyssal giant pockmarks of the Black Bahama Escarpment: Relations between structures, fluids and carbonate physiography

Cavailhès

Gillet

Guiastrennec-Faugas

et al. 2020

Preprint

View full text Add to dashboard Cite

show abstract

“…We compile 33 unique data sources that quantitatively identify at least one of the anomalies of interest in the current iteration of the SEAFLEA database (Riedel et al, 2002;Mazurenko & Soloviev, 2003;MIMES, 2004;Levin & Mendoza, 2007;Paull et al, 2007;Sahling et al, 2008;Sellanes et al, 2008;Greinert et al, 2010;Olu et al, 2010;Riedel et al, 2010;Jessen et al, 2011;Batang et al, 2012;Jin et al, 2012;Pierre et al, 2012;Römer et al, 2012;Bowden et al, 2013;Han et al, 2013;Römer et al, 2014;Sahling et al, 2014;Seismic Water Bottom Anomalies Map Gallery, 2014;Skarke et al, 2014;Johnson et al, 2015;Paull et al, 2015;Ruff et al, 2015;Szpak et al, 2015;Åström et al, 2016;Merle & Embley, 2016;Hoshino et al, 2017;Michel et al, 2017;Zhang et al, 2017;Åström et al, 2018;Gafeira et al, 2018;Riedel et al, 2018). The SEAFLEA database is a community effort with multiple individuals and research groups contributing data (Phrampus et al, 2019).…”

Section: Seaflea Distributionmentioning

confidence: 99%

A Global Probabilistic Prediction of Cold Seeps and Associated SEAfloor FLuid Expulsion Anomalies (SEAFLEAs)

Phrampus

Lee

Wood

2020

Geochem Geophys Geosyst

View full text Add to dashboard Cite

A newly compiled, open-source database of focused fluid flow sites (e.g., cold seeps) and associated SEAfloor FLuid Expulsion Anomalies (SEAFLEAs) reveals a variable distribution of anomalies across global continental margins. The SEAFLEA distribution is heavily biased toward North American continental margins, with most observations between 100-and 200-m water depth globally, and with an equal distribution between active and passive margins. Using a machine learning classification methodology based on outlier detection algorithms, we predict the probability of encountering a SEAFLEA globally. Results show the highest probability in regions with multiple SEAFLEA observations and parametrically similar regions concentrated on continental margins. In general, geologic, biologic, and chemical predictors are the best predictors of SEAFLEAs. We validate our results using a random and geospatial validation technique that reveals our methods are robust to random variations in observations, but that certain margins, such as the Svalbard Margin, represent parametrically distinct locals. These distinct regions have control over the global distribution of predicted anomalies due to their unique features. Our final prediction on a global 5 × 5 arc minute grid reveals that the average probability of encountering a SEAFLEA is 33.1 ± 17.7% on active margins and 31.2 ± 18.9% on passive margins, showing equal likelihood of encountering fluid expulsion between passive and active margins. Therefore, the lateral compaction on active margins does not increase the likelihood of fluid expulsion relative to the predominantly vertical compaction on passive margins. These results however say nothing of the fluid flux rates or density of expulsion features.

show abstract

“…The first group comprises 826 depressions of 100 to 200 m in diameter and 15 m in depth on average. These large pockmarks are exclusively located along the continental slope mainly below 350 m water depth (Michel et al, 2017). A second group of 696 depressions, mapped by means of high‐resolution bathymetry, is present on the shelf, with small dimensions of less than 5 m in diameter on average with a depth of less than 30–40 cm.…”

Section: Fluid Systems Offshore the Aquitaine Marginmentioning

confidence: 99%

The Aquitaine Shelf Edge (Bay of Biscay): A Primary Outlet for Microbial Methane Release

Dupré

Loubrieu

Cartigny

et al. 2020

Geophysical Research Letters

View full text Add to dashboard Cite

A few thousand (2,612) seeps are releasing microbial methane bubbles from the seafloor at the Aquitaine Shelf edge (Bay of Biscay) at shallow water depths (140-220 m). This methane contributes to the formation of meter-scale subcircular carbonate structures, which are (sub)outcropping over 375 km 2 . Based on in situ flow rate measurements and acoustic data, and assuming steady and continuous fluxes over time, the methane entering the water column is estimated at 144 Mg/yr. Microbial methane circulation has been ongoing for at least a few thousand years. This discovery highlights the importance of microbial methane generation, disconnected from deep thermogenic sources and gas hydrates, at continental shelves. The shelf edge may be viewed as a focus area for methane circulation and release and related diagenesis, all having an impact on the shaping of continental shelves and potentially on the oceanic and atmospheric carbon budget. Plain Language Summary At the Aquitaine Shelf of the Bay of Biscay (Northeast AtlanticOcean), the recent acoustic, chemical, and visual investigations of microbial methane release at the seafloor have led to the discovery of a vast fluid system. This methane escapes as bubbles from the seafloor into the seawater at 2,612 sites, all located at shallow water depths (140-220 m) along the edge of the continental shelf. Methane-derived authigenic carbonates that are by-products of gas seepage cover the (sub) seafloor over a large area of 375 km 2 . These carbonates form subcircular meter-scale pavements and mounds, less than 2 m in height above the surrounding seafloor. Based on the growth rate of authigenic carbonates, it can be inferred that methane circulation has occurred for at least a few thousand years. The amount of methane released from the Aquitaine Shelf seafloor into the water column, estimated at 144 t/yr, questions the fate of the methane in the ocean and its possible passage to the atmosphere with therefore consequent potential contribution to the oceanic and atmospheric carbon budget over time.

show abstract

Pockmarks on the South Aquitaine Margin continental slope: The seabed expression of past fluid circulation and former bottom currents

Cited by 26 publications

References 54 publications

The abyssal giant pockmarks of the Black Bahama Escarpment: Relations between structures, fluids and carbonate physiography

The abyssal giant pockmarks of the Black Bahama Escarpment: Relations between structures, fluids and carbonate physiography

A Global Probabilistic Prediction of Cold Seeps and Associated SEAfloor FLuid Expulsion Anomalies (SEAFLEAs)

The Aquitaine Shelf Edge (Bay of Biscay): A Primary Outlet for Microbial Methane Release

Contact Info

Product

Resources

About