Analysis of offshore seismic lines suggests that a strong relationship exists between tectonic structures and fluid migration in accretionary prisms. However, only few field analogues of plumbing systems and their tectonic frameworks have been investigated in detail until now. The uplifted accretionary prism of the Hikurangi Margin (North Island, New Zealand) exposes early to late Miocene mudrocks in coastal cliffs of Cape Turnagain and in the Akitio syncline, south-east of the Pongaroa city. These outcrops display tubular carbonate concretions corresponding to complex subsurface plumbing networks of paleo-seeps within Miocene trench slope basins. We present here, new results on the spatial distribution of these tubular carbonate concretions, with particular attention to their relation to tectonic structures. In the Pongaroa area, tubular carbonate concretions in lower Miocene mudrocks occur along a N-S trend, while in middle Miocene strata they occur along a NNE-SSW direction. The N-S trend parallels a major fault zone (i.e. the Breakdown fault zone), which separates two wide synclines, the Waihoki and the Akitio synclines. During the Early-Middle Miocene, the Breakdown fault zone controlled the evolution of the Akitio trench slope basin constituting its western edge. The NNE-SSW strike parallels the axis of the Akitio syncline and is also parallel to the present-day subduction front. Our results therefore show that tubular concretions are parallel to post-Middle Miocene second order folding and thrusting in the northeastern limb of the Akitio syncline. In the Cape Turnagain area, tubular concretions occur in the western limb of the Cape Turnagain syncline, in the footwall of the major seaward-verging Cape Turnagain fault. This suggests that fluid migrations may occur not only in the crests of anticlines, as observed offshore for present-day plumbing system of cold seeps, but also in the footwalls of thrust faults. All these observations show that the spatial distribution of tubular concretions is controlled by regional tectonic structures with paleo-fluid migrations related to major deformation episodes of the accretionary prism. Thus, we distinguish three episodes events that likely triggered fluid migration leading to the formation of the tubular concretions: (1) In the Early Miocene, shortly after the onset of development of the Akitio trench slope basin, on its inner (western) edge; (2) During the late Middle Miocene, during an extensional deformation episode on the western limb of the Akitio trench slope basin; (3) At the end of the Late Miocene, during a second major shortening period at the footwall of major thrust fault, such as in the Cape Turnagain area.
Abstract. -The seaward extension of onshore formations and structures were previously almost unknown in Provence. The interpretation of 2D high-resolution marine seismic profiles together with the integration of sea-bottom rock samples provides new insights into the stratigraphic, structural and paleogeographic framework of pre-Messinian Salinity Crisis (MSC) deposits of the Provence continental shelf. Seven post-Jurassic seismic units have been identified on seismic profiles, mapped throughout the offshore Provence area and correlated with the onshore series. The studied marine surface and sub-surface database provided new insights into the mid and late Cretaceous paleogeography and structural framework as well as into the syn-and post-rift deformation in Provence. Thick (up to 2000 m) Aptian-Albian series whose deposition is controlled by E-W-trending faults are evidenced offshore. The occurrence and location of the Upper Cretaceous South-Provence basin is confirmed by the thick (up to 1500 m) basinal series downlaping the Aptian-Albian unit. This basin was fed in terrigenous sediments by a southern massif ("Massif Méridional") whose present-day relict is the Paleozoic basement and its sedimentary cover from the Sicié imbricate. In the bay of Marseille, thick syn-rift (Rupelian to Aquitanian) deposition occurred (>1000 m). During the rifting phase, syn-sedimentary deformations consist of dominant N040 to N060 sub-vertical faults with a normal component and N050 drag-synclines and anticlines. The syn-rift and early post-rift units (Rupelian to early Burdigalian) are deformed and form a set of E-W-trending en echelon folds that may result from sinistral strike-slip reactivation of N040 to N060 normal faults during a N-S compressive phase of early-to-mid Burdigalian age (18-20 Ma). Finally, minor fault reactivation and local folding affect post-rift deposits within a N160-trending corridor localized south of La Couronne, and could result from a later, post-Burdigalian and pre-Pliocene compressive phase.
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