Diversity and Dynamics of the Processes of Mud Volcanism and of Shale Mobilization in the Southeastern Caribbean

Deville, Eric¹, Anne Battani¹, Sophie-Helene Guerlais¹, Siegfried Lallemant², Alain Mascle¹, Alain Prinzhofer¹ (1) Institut Francais du Petrole, Rueil-Malmaison, France (2) Université de Cergy-Pontoise, Cergy-Pontoise, France

Subsurface sediment mobilization is a widely developed process in the southeastern Caribbean, notably from the Barbados prism to the onshore Trinidad. The sediments expelled by the mud volcanoes are liquefied clay-rich and sandy material issued from deep horizons and various shallower formations pierced by the mud conduits. Both, offshore and onshore, the mud expelled is rich in thin angular and mechanically damaged quartz grains related to shearing processes. This suggests that the initial sedimentary mobilization could have occurred partly in sandy horizons. Exotic clasts result mostly from hydrofracturing and are expelled during catastrophic events. The offshore area also exhibits trends of structures corresponding to sub-circular massive uplift of well-preserved sediments (turbidites and hemipelagics). Mud volcanism corresponds to fluid displacement, whereas massive sedi­mentary extrusion corresponds to uplift of stratified solid levels for which the deep cause could be the intrusion of mud plugs. Both are dynamic phenomena controlled by the devel­opment of overpressure at depth. The regime of expulsion of the fluids varies according to cyclic phases. Low-frequency cycles are punctuated by catastrophic events. They could be related to the opening of pre-existing hydraulic fracture network during the rise of pressure conditions at depth favoring successive fluid release and cyclic pressure decrease. Such processes could be enhanced by a threshold effect when fluids are over-saturated with gas. In that case, sudden massive degassing of large volume of initially dissolved gas is possi­ble, resulting in a sudden rise in the fluid pressure in gas-charged mud chambers.