Repeated fluid expulsions during events of rapid sea-level rise in the Gulf of Lion, western Mediterranean Sea

Abstract

Based on a High-Resolution 3D seismic block acquired in the Gulf of Lion in 2004–2005 we investigated fluid pipes and pockmarks on the top of the interfluve between the Hérault canyon and the Bourcart canyon both created by turbidity currents and gravity flows from the shelf to the deep basin in the north-western Mediterranean Sea. Combining the geometry of the potential fluid pipes with the induced deformation of surrounding sediments leads then to the ability to differentiate between potential fluid sources (root vs source) and to better estimate the triggering mechanisms (allochtonous vs. autochtonous cause). We linked together a set of derived attributes, such as Chaos and RMS amplitude, to a 3D description of pipes along which fluids may migrate. As previously shown in other basins, the induced deformation, creating cone in cone or V-shaped structures, may develop in response to the fluid pipe propagation in unconsolidated sediments in the near surface. The level at the top of a cone structure is diachronous. It means that stratigraphic levels over this surface are deformed at the end of the migration. They collapse forming a depression called a pockmark. These pipes are the result of repeated cycles of fluid expulsion that might be correlated with rapid sea-level rise instead of sediment loading. The most recent event (MIS 2.2 stage) has led to the formation of a pockmark on the modern seafloor. It has been used as a reference for calculating the effect of a rapid sea-level rise on fluid expulsion. As all physical and geometrical parameters are constrained, we were able to define that a + 34 m of sea level rise may account for triggering fluid expulsion from a very shallow silty-sandy layer at 9 m below seafloor since the last glacial stage. This value is consistent with a sea level rise of about 102 m during this period. This study shows that the episodic nature of fluid release resulted from hydromechanical processes during sea-level rise due to the interactivity between high pressure regimes and principal in situ stresses.

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

“…These estimations seem consistent with a depth of ~ 1 km inferred from the 60° dipping normal faults (Anderson, 1951; Fig. 6c) commonly bounding collapsing structures such as sketched in usual pockmark models (Gay et al, 2017).…”

Types of fluid-related features controlled by sedimentary cycles and fault network in deepwater Nigeria

“…The crater-like nature of these pockmarks suggests an erosional action of fluid release, commonly related to an overpressured buried reservoir of gas, oil or interstitial water, or a combination of the three (Hovland and Judd, 1988). According to Gay et al (2012Gay et al ( , 2017, the fluid pipe induces a deformation of surrounding unconsolidated…”

Pipe Formation by Fluid Focalization in Bilayered Sediments

“…The fluid penetrates the granular layer, forming a finger, which propagates upwards until reaching the granular free surface. At long times (Figure 4a, t = 98.52 s), the central fluidized zone has a specific shape well known in the geophysical context as the "stem and corolla" shape, with a vertical chimney topped by a flared area, also referred to as a "funnel and pipe" structure [5,32]. Note that the granular layer fluidization is coupled with percolation around the central zone since the initial invasion (Figure 4a, t = 3.24 s), and the lateral invasion due to this process increases in time (Figure 4a, t = 98.52 s).…”