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The buildup of a continental rise and its morphological patterns depend on sediment transport and deposition via downslope slumps, turbidity currents, along‐slope contourites and other deepwater currents. These delivery mechanisms are central to source‐to‐sink reconstructions, yet untangling their individual roles is not straightforward. The current study focuses on the sink section of the Nile system at the northern Levant continental rise (eastern Mediterranean). During the Pliocene, fluvial systems from northern Africa and the Levant margin supplied sediments to the study area. This supply decreased significantly during the Quaternary because of two processes: (a) The aridification of North Africa made the Nile River the predominant contributor to the basin; (b) the topographic rise of the Levant landmass severely limited fluvial supply. Meanwhile, on‐going counter‐clockwise marine currents became the prevalent supply system to the Levant margin, and downslope sediment‐transport became the only source to the northern Levant continental rise, which became a significant sink of the larger Nile system. These conditions provide an excellent natural laboratory for understanding the individual role of downslope sediment‐transport processes in building a continental rise. This research is based on single‐channel sparker seismic data, multibeam bathymetry and four 7–8 m long piston‐cores collected over the northern Levant continental rise at water depths of 1200–1800 m, together with available multibeam bathymetry and industrial multi‐channel seismic reflection data. The results show a major depositional changeover during the Pliocene‐Quaternary transition from concordant aggradation to repeated deposition of >12 sediment wave subunits, interpreted as upslope migrating cyclic steps. Quantitative analysis of the sediment wave morphology at the seafloor and subsurface, along with core data, indicates that the immediate sediment source was the nearby shelf. The supply was regulated by basinward‐landward shifts of the shore‐parallel marine currents during lowstand‐highstand conditions (respectively). Hence, this case study highlights the connection between sea‐level change and sedimentation patterns on a continental rise. [ABSTRACT FROM AUTHOR]

[1] The Levant continental margin, eastern Mediterranean, is usually defined as a passive margin that developed between the late Paleozoic-early mid-Mesozoic. Previous studies suggest that the margin is composed of two segments with different structural characteristics. The southern segment (south of the Carmel Structure) was formed by tifting, whereas the origin of the northern segment is not known. The present study focuses on the northern segment, which is a key for understanding the tectonic history of the eastern Mediterranean. Investigation is carried out offshore on two scales: (1) deep crustal observations, analysis of seismic refraction and magnetic data and their comparison with other continental margins worldwide; and (2) shallow crustal-scale observations of recent tectonic deformations, based on multichannel and single-channel seismic reflection profiles. Integration of the deep and shallow observations with reevaluation of geological data onland show strong structural resemblance between the northern Levant segment and other transform margins. A modified scenario is suggested for the formation and development of the Levant basin and its margins, combining all previous studies into one simple picture, where a signature of older structures on more recent features is evident. Located in the midst of the progressive Afro-Eurasian collision, the northern Levant presents a unique lifecycle for transform margins worldwide, from formation to reactivation. Citation: Schattner, U., and Z. Ben-Avraham (2007), Transform margin of the northern Levant, eastern Mediterranean: From formation to reactivation, Tectonics, 26, TC5020, doi:10.1029/ 2007TC002112.

[1] The Levant continental margin is divided into two major segments by the Carmel structure, which extends from the Dead Sea fault into the eastern Mediterranean. New seismic reflection data over the unexplored northern segment are used for completing the structural framework of the Levant area, together with existing data south of it. Inclusive depth structural maps of the area were produced for the base Pliocene and base Messinian evaporites. Previous studies indicate that differences between the two segments are well expressed in the deep crustal structure. The present study, which focuses mainly on the shallow section, shows that these differences are maintained throughout the accumulation of young sedimentary units, and even in the bathymetry. This preservation of segmentation, both in the shallow and in the deep structure, insinuates that the two segments were formed through different continental breakup processes, which continue to dictate the style of sediment accumulation. Citation: Ben-Avraham, Z., U. Schattner, M. Lazar, J. K. Hall, Y. Ben-Gai, D. Neev, and M. Reshef (2006), Segmentation of the Levant continental margin, eastern Mediterranean, Tectonics, 25, TC5002, doi: 10.1029/2005TC001824.

Recently acquired bathymetric and high-resolution seismic data from the upper slope of Santos Basin, southern Brazilian margin, reveal a major geomorphological feature in the SW Atlantic that is interpreted as a carbonate ridge - the Alpha Crucis Carbonate Ridge (ACCR). The ACCR is the first megastructure of this type described on the SW Atlantic margin. The ~17 × 11-km-wide ring-shaped ACCR features tens of >100-m-high steep-sided carbonate mounds protruding from the surrounding seabed and flanked by elongated depressions. Comet-like marks downstream of the mound structures indicate that the area is presently influenced by the northward flow of the Intermediate Western Boundary Current (IWBC), a branch of the Subtropical Gyre that transports Antarctic Intermediate Water. Abundant carbonate sands and gravels cover the mounds and are overlain by a biologically significant community of living and dead ramified corals and associated invertebrates. The IWBC acts as a hydrodynamic factor that is responsible for both shaping the bottom and transporting coral larvae. We contend that the ACCR was formed by upward fluid flow along active sub-surface faults and fractures that formed by lateral extension generated by the ascending movement of salt diapirs at depth. The ACCR provides an important modern and accessible analogue for a seabed carbonate build-up related to sub-surface hydrocarbon systems.

We present new evidence for the existence of a large pockmark field on the continental slope of the Santos Basin, offshore southeast Brazil. A recent high-resolution multibeam bathymetric survey revealed 984 pockmarks across a smooth seabed at water depths of 300-700 m. Four patterns of pockmark arrays were identified in the data: linear, network, concentric, and radial. Interpretation of Two-dimensional multi-channel seismic reflection profiles that crosscut the surveyed area shows numerous salt diapirs in various stages of development (e.g. salt domes, walls, and anticlines). Some diapirs were exposed on the seafloor, whereas the tops of others (diapir heads) were situated several hundreds of meters below the surface. Extensional faults typically cap these diapirs and reach shallow depths beneath the seafloor. Our analysis suggests that these pockmark patterns are linked to stages in the development of underlying diapirs and their related faults. The latter may extend above salt walls, take the form of polygonal extensional faults along higher-level salt anticlines, or concentric faults above diapir heads that reach close to the seafloor. Seismic data also revealed buried pockmark fields that had repeatedly developed since the Middle Miocene. The close spatio-temporal connection between pockmark and diapir distribution identified here suggests that the pockmark field extends further across the Campos and Espírito Santo Basins, offshore Brazil. Spatial overlap between the pockmark field topping a large diapir field and a proliferous hydrocarbon basin is believed to have facilitated the escape of fluid/gas from the subsurface to the water column, which was enhanced by halokinesis. This provides a possible control on fossil gas contribution to the marine system over geological time.