The IGUANES cruise took place in May 2013 on the R/V L’Atalante along the Demerara passive transform margin off French Guiana and Surinam. Seismic, multibeam and chirp acquisitions were made. Piston cores were collected for pore geochemistry and sedimentology. A mooring was deployed on the sea-bottom for 10 months (temperature, salinity, turbidity and current measurements). This new dataset highlights the lateral variability of the 350 km-long Guiana–Surinam transform margin due to the presence of a releasing bend between two transform segments. The adjacent Demerara Plateau is affected by a 350 km-long giant slide complex. This complex initiated in Cretaceous times and was regularly reactivated until recent times. Since the Miocene, contourite processes seem to be active due to the onset of the North Atlantic Deep Water (NADW) bottom current. A main NADW water vein flows towards SE, eroding slide headscarps and allowing the deposition of contourite drifts. Numerous depressions looking like comet tails or comet scours record this flow. Some of those were interpreted before the cruise as active pockmarks. Pore geochemistry and core analysis do not show any evidence of present-day gas seepage. AbstractThe IGUANES cruise took place in May 2013 on the R/V L’Atalante along the Demerara passive transform margin off French Guiana and Surinam. Seismic, multibeam and chirp acquisitions were made. Piston cores were collected for pore geochemistry and sedimentology. A mooring was deployed on the sea-bottom for 10 months (temperature, salinity, turbidity and current measurements). This new dataset highlights the lateral variability of the 350 km-long Guiana–Surinam transform margin due to the presence of a releasing bend between two transform segments. The adjacent Demerara Plateau is affected by a 350 km-long giant slide complex. This complex initiated in Cretaceous times and was regularly reactivated until recent times. Since the Miocene, contourite processes seem to be active due to the onset of the North Atlantic Deep Water (NADW) bottom current. A main NADW water vein flows towards SE, eroding slide headscarps and allowing the deposition of contourite drifts. Numerous depressions looking like comet tails or comet scours record this flow. Some of those were interpreted before the cruise as active pockmarks. Pore geochemistry and core analysis do not show any evidence of present-day gas seepage.

Off the east coast of South Island, New Zealand, the Bounty Fan lies in the most seaward axial deep of the Bounty Trough, a remnant continental rift. The north levee of the Bounty Channel was cored at Ocean Drilling Program (ODP) Site 1122 on Leg 181. The 617 m section, which is divided into three units and nine subunits, consists of a Quaternary fan turbidite sequence that transitions downward into a Pleistocene to Pliocene mixed turbidite to contourite facies, which unconformably overlies a Miocene contourite-pelagic succession. Petrographic analysis (point counts) of 55 fine to very fine sand samples across the cored interval shows them to be quartzofeldspathic with moderate mica and minor metamorphic lithic components (mean values = Q44F44L12, Qm50K3P47, Lm70Lv4Ls26, total%mica14). Mean recalculated parameters for Site 1122 units and subunits cluster on QFL, QmKP, and LmLvLs ternary plots with little compositional variation. Proportions of biotite, muscovite, chlorite, and various metamorphic lithic types also show little compositional variation among the units and subunits of Site 1122. Furthermore, there are no significant trends among thickness, grain size, composition, and depth of Site 1122 sand samples, except that thicker beds tend to contain slightly more metamorphic rock fragments. The generally homogeneous composition of Site 1122 sand indicates that it may have had a relatively uniform source back into the early Miocene. Thus, the up-section change from sandy contourite to turbidite deposits at Site 1122 is not reflected in sand composition. This suggests that the sand provenance remained constant while the depositional processes of sand at Site 1122 changed. Sand detrital modes at Site 1122 most closely match those of the Clutha River, especially in terms of QFL, QmKP, mica, and lithic proportions, suggesting that it was a major source of sand at Site 1122. However, admixing of sand from the Waitaki River and other sources cannot be completely ruled out.