The Pleistocene Cape Kidnappers Section in New Zealand: Orbitally-forced controls on active margin sedimentation?

International audienc

Study of two carbonate seepages from Lower to Upper Miocene Hikurangi active margin (New Zealand, North Island)

International audienceThe study focuses on the analysis of tubular carbonate concretions outcropping in two areas in the New Zealand Hikurangi active margin: the Akitio syncline and Cape Turnagain. This work intends to enlighten the role of pipes involved in fluids circulation and to compare them from two former basins having evolved from lower/ middle Miocene (Akitio) and upper Miocene (Cape Turnagain). In both cases, the host rock is composed of very fine-grained muddy sediments (calcareous mudstones) containing a lot of framboidal pyrites, quartz, feldspar and very few and poorly diversified fauna indicating paleoenvironmental stressed depositional settings. Con- cerning the tubes themselves, they differ drastically on a morphological point of view: They are cylindrical and very large in Cape Turnagain, whereas they are rugose and far smaller in Akitio. In the Akitio syncline, the biggest tubes are characterized by a lot of late cross-cutting fracturation and brecciation stages, filled by softly deformed monomict fluidized muds. More-over, association of framboidal pyrite, authigenic quartz and bitumen lining was observed in pre-fracturation/pre-injection sequence. In the case of Cape Turnagain, diagenesis sequence is highlighted by complex dissolution/cementation stages (early calcite/dolomite cemen- tation, framboidal pyrite, aragonitic crust). Neither late fluidized infills were observed nor late fracturing. 80 stable isotope (δ18O/δ13C) analysis were carried on micro-samples. All these data are completed by cathodolu- minescence analysis associated to major and minor chemical analysis (SEM/EDS elemental measurements) In Akitio basin, two main origins of carbonate cements and mud infilling were revealed: anaerobic oxidation of microbial CH4 and temperature increasing in the later stages. The building of tube framework took place in early reducing environment followed by later infilling of the tubes, using the pre-existing “plumbing system”. In Cape Turnagain, early dissociation of gas hydrates below the sea floor and reduction of CO2 as a by-product of methanogenesis are involved (Nyman, 2009). Finally, tube formation differs strongly between these two areas: they were both differently early built and they moreover experienced hotter late fluid circulation in Akitio than those of Cape Turnagain

Study of two carbonate seepages from lower to upper miocene Hikurangi active margin (New Zealand, North Island)

International audienceThe study focuses on the analysis of tubular carbonate concretions outcropping in two areas in the New-Zealand Hikurangi active margin: the Akitio syncline and Cape Turnagain. This work intends to enlighten the role of pipes involved in fluids circulation and to compare them from two former basins having evolved from lower/middle Miocene (Akitio) and upper Miocene (Cape Turnagain)

Evolution tectono sédimentaire Mio-pléistocène à Ibiza : conséquences de la crise de salinité

International audienc

Tectonic evolution of the active Hikurangi subduction margin, New Zealand, since the Oligocene.

International audienc

Study of two carbonate seepages from Lower to Upper Miocene Hikurangi active margin (New Zealand, North Island)

International audienceThe study focuses on the analysis of tubular carbonate concretions outcropping in two areas in the New Zealand Hikurangi active margin: the Akitio syncline and Cape Turnagain. This work intends to enlighten the role of pipes involved in fluids circulation and to compare them from two former basins having evolved from lower/ middle Miocene (Akitio) and upper Miocene (Cape Turnagain). In both cases, the host rock is composed of very fine-grained muddy sediments (calcareous mudstones) containing a lot of framboidal pyrites, quartz, feldspar and very few and poorly diversified fauna indicating paleoenvironmental stressed depositional settings. Con- cerning the tubes themselves, they differ drastically on a morphological point of view: They are cylindrical and very large in Cape Turnagain, whereas they are rugose and far smaller in Akitio. In the Akitio syncline, the biggest tubes are characterized by a lot of late cross-cutting fracturation and brecciation stages, filled by softly deformed monomict fluidized muds. More-over, association of framboidal pyrite, authigenic quartz and bitumen lining was observed in pre-fracturation/pre-injection sequence. In the case of Cape Turnagain, diagenesis sequence is highlighted by complex dissolution/cementation stages (early calcite/dolomite cemen- tation, framboidal pyrite, aragonitic crust). Neither late fluidized infills were observed nor late fracturing. 80 stable isotope (δ18O/δ13C) analysis were carried on micro-samples. All these data are completed by cathodolu- minescence analysis associated to major and minor chemical analysis (SEM/EDS elemental measurements) In Akitio basin, two main origins of carbonate cements and mud infilling were revealed: anaerobic oxidation of microbial CH4 and temperature increasing in the later stages. The building of tube framework took place in early reducing environment followed by later infilling of the tubes, using the pre-existing “plumbing system”. In Cape Turnagain, early dissociation of gas hydrates below the sea floor and reduction of CO2 as a by-product of methanogenesis are involved (Nyman, 2009). Finally, tube formation differs strongly between these two areas: they were both differently early built and they moreover experienced hotter late fluid circulation in Akitio than those of Cape Turnagain

Study of two carbonate seepages from lower to upper miocene Hikurangi active margin (New Zealand, North Island)

International audienceThe study focuses on the analysis of tubular carbonate concretions outcropping in two areas in the New-Zealand Hikurangi active margin: the Akitio syncline and Cape Turnagain. This work intends to enlighten the role of pipes involved in fluids circulation and to compare them from two former basins having evolved from lower/middle Miocene (Akitio) and upper Miocene (Cape Turnagain)

Study of two carbonate seepages from lower to upper miocene Hikurangi active margin (New Zealand, North Island)

International audienceThe study focuses on the analysis of tubular carbonate concretions outcropping in two areas in the New-Zealand Hikurangi active margin: the Akitio syncline and Cape Turnagain. This work intends to enlighten the role of pipes involved in fluids circulation and to compare them from two former basins having evolved from lower/middle Miocene (Akitio) and upper Miocene (Cape Turnagain)

Turbidite systems in the inner forearc domain of the Hikurangi convergent margin (New zealand): new constraints on the development of trench-slope basins

International audienceThe development of trench-slope basins on subduction wedges is strongly related to subduction processes. Theseconfined basins form on the lower trench slope, and their edges consist of structurally controlled linear bathymetric highs. In this particular setting, sedimentary processes may be controlled both by tectonism and by sea-level changes. Thus, the study of the sedimentary record may permit evaluation of the spatial and temporal contribution of tectonic activity on the development and stratigraphic evolution of trench-slope basins. The recent evolution of the Hikurangi subduction wedge (North Island of New Zealand) is characterized by the uplift and subaerial emergence of the trench­slope break, which has provided good exposure of the Miocene Akitio trench-slope basin. Identification of the main sedimentary discontinuities, reconstruction of the geometry of the sedimentary units, and paleocurrent studies were undertaken in the Akitio basin in order to propose a stratigraphic and structural scheme for the evolution of this emerged trench­slope break. Deep-sea facies associations are representative of three main fine-grained gravity-driven systems that may develop during various stages of development of mature trench-slope basins. These are, from base to top, large submarine slides (olistostrome deposits), fine-grained sand-rich submarine fans, and low-gradient submarine ramps (sheet-like turbidites). This basin-fill megasequence constitutes a lowstand systems tract, which can be subdivided into basin-floor fan, slope fan, and progradingwedge complex. Slope facies associations are common and highlight the important contribution of slope processes to the basin sediment budget. Rapid shifts of facies and important paleoenvironmental changes, reflecting slope creation or modification, characterize five major discontinuities that are related to regional tectonic events (i.e., onset of subduction at 25 Ma, beginning of regional subsidence at 15 Ma) or local tectonic events (i.e., local uplift of structural edges of the Akitio trench-slope basin at 17.5 Ma and 16.5 Ma, acceleration of subsidence at 13.2 Ma). Moreover, we show that the timing of development of some lowstand system tracts (i.e., of slope fans and of prograding-wedge complexes) may also be controlled largely by changes in style and/or amplitude of tectonic activity