Submarine slide blocks and associated soft-sediment deformation in deep-water basins: A review

Abstract

a b s t r a c tThree-dimensional (3D) seismic and outcrop data are used to review the significance of submarine slide blocks and associated soft-sediment deformation structures in deep-water basins. Submarine slide blocks are generated during major instability events in a variety of geological settings and their size exceeds that of boulders, which are <4.1 m. Slide blocks can be~500 m high by >4.5 km long on a number of continental margins, presenting internal folding, thrusting and rolling over basal brecciaconglomerate carpets. In addition, soft-sediment deformation structures such as foliated strata, intrafolial folds, tiling, bookshelf sliding and dilational jogs reflect important shearing within blocks and their basal glide planes. This work proposes that buried blocks and associated coarse-grained debrites are capable of forming prolific reservoir intervals for hydrocarbons and mineralization. Three-dimensional leakage factor models show the bulk of fluid flow to be focused in vertical and horizontal surfaces within, and immediately below displaced blocks. The generation of large slide blocks can also mark the sudden release of overburden pressure, and result in the loss of seal competence above existing hydrocarbon fields. Ultimately, this review clarifies the present-day understanding on the modes of formation of submarine slide blocks, confirming their economic importance in deep-water basins throughout the world.

Basement–cover structural relationships in the Kaladgi Basin, southwestern India: Indications towards a Mesoproterozoic gravity gliding of the cover along a detached unconformity

“…In the present work, the continuous outcrops near Jamkhandi and isolated outcrops near Bilgi and to the northwest of Bilgi (Fig. 16), in the zone of extension, have comparable dimensions of megaslide blocks as described by Alves (2015). The zone of contraction (Fig.…”

“…16) in the Kaladgi Basin. A third similarity exists when compared with the extensional structures formed by tensile stresses in the proximal part of the sliding block during block movement (Alves, 2015). These extensional structures include square to rectangular blocks or to more laterally continuous ridges separated by listric normal faults (e.g.…”

“…Peel et al 1995). A second similarity of diagnostic features of slide blocks at seismic scales (Alves, 2015) with that of the structures of the Mesoproterzoic cover in the Kaladgi Basin is the internal deformation in the blocks in the contractional domain. For example in the contractional domain, large scale thrusting, shearing and folding characterize the internal deformations of the megaslide blocks of SE Brazil (Gamboa and Alves 2015).…”

“…Due to poor or no exposures of the physical contact between the Mesoproterozoic cover and the underlying basement in the Kaladgi Basin, the features like ramp & flats in the basal shear surfaces and the soft sediment deformation structures in the ductile detachments as described in Alves (2015), could not be observed. Furthermore, structures such as slide foliation, intrafolial folds, tiling structures, stretched clasts, imbricated strata, bookshelf sliding as parts of soft sediment deformation related to megaslides (Alves, 2015) do not occur at the base of the Mesoproterzoic cover rocks in the Kaladgi Basin. Draganits et al 2008, documented and described soft sediment structures like large grooved lineations and tool marks from the base of giant submarine landslides in the Neoproterozoic Phe formation of the northwest Himalayas.…”

Exhumed lateral margins and increasing flow confinement of a submarine landslide complex

“…Lateral margins are part of the basal shear surface and typically form steep planar surfaces (for example, Fig. ) perpendicular or sub‐parallel to the direction of net displacement (Frey‐Martínez et al ., ; Bull et al ., ; Gamberi et al ., ; Alves, ; Ortiz‐Karpf et al ., ). Basal shear surfaces can have a thickness forming a basal shear zone ( sensu Alves & Lourenço, ) and can be modified by further failure events, creating complex and composite features, which can be later modified by differential compaction (Alves, ).…”