Description: The transfer of sediment from the upper continental slope to rise is poorly documented along the southeast African passive margin. New swath bathymetric and sub-bottom data collected in the Natal Valley, southwest Indian Ocean, provide insight into the evolution of the Tugela canyon and fan system. Several distinct downslope changes in canyon morphology are noted. The canyon increases in relief and widens with depth. Basement outcrop is restricted to the head of the canyon becoming less prominent with depth. Step-like terracing of the canyon walls and floor becomes prominent in the mid-slope portions of the canyon and is related to a marked increase in the cross sectional asymmetry of the canyon profile. The contemporary Tugela canyon rests within a depression of the last phase of infilling. The canyon is the product of downslope erosion, and incision, caused by several phases of hinterland uplift in the mid Oligocene, mid Miocene and late Pliocene. Each phase was followed by pelagic infilling of the palaeo-canyon form. Downslope, the uplift phases are preserved in the cut-terraces and axial incisions within the main canyon thalweg. The contemporary canyon is a moribund feature, sediment starvation of the shelf area by current sweeping of the Agulhas current has decreased the material available for canyon incision and fan development. Additional current sweeping by the North Atlantic Deep Water current has stunted the development of the associated fan complex.

Description: The Mozambique Basin is one of the oldest extensional sedimentary basins developed along the eastern African margin. The basin hosts a continuous record of sediments since the Jurassic separation of Antarctica from Africa. The objectives of this study were to extend the regional stratigraphic framework north of the Zambezi Delta into the deep abyssal plains and review the early evolution of the Mozambique Basin using nine multi-channel seismic reflection profiles. We identify six major stratigraphic units that were deposited in Jurassic, Early Cretaceous, Late Cretaceous, Paleogene, Neogene and Quaternary times. Mesozoic sedimentation rates of 5-10 cm/kyr and 1-3 cm/kyr during the Paleogene are calculated in the deeper basin. The presence of shales in neighbouring wells on the shelf implies an euxinic environment in the rapidly subsiding basin until Early Cretaceous times. The Mesozoic sediments have a high seismic velocity that exceeds 4.5 km/s, except in a distinct Early Cretaceous low-velocity (3.7 km/s) zone that may indicate the presence of undercompacted, overpressured shales. In spite of the fact that the Zambezi catchment was much smaller in pre-Miocene times, the high Late Cretaceous sedimentation rates can be attributed to rapid denudation of the African continent after a major tectonic uplift episode at approximately 90 Ma. Increased sediment influx into the basin from the Zambezi in Late Cretaceous times resulted in the formation of an elongated submarine fan lobe into the Mozambique Channel north of Beira High. Strong north-south bottom currents commenced within the channel in Late Cretaceous times, forcing the aggradation of sediments on the southern flank of the lobe. In addition, we observe several current-controlled sediment deposits in the deeper basin that are influenced by north-south bottom currents. Low Paleogene sedimentation rates are attributed to a sediment-starved basin during a relative quiet tectonic phase onshore.

Description: During the RV Polarstern cruise ARK-XXIII-3 in the summer of 2008, seismic reflection and refraction data along an almost 1200 km long transect along 81�N latitude were acquired across the Amundsen Basin, Lomonosov Ridge, Makarov Basin, Mendeleev Ridge and parts of the Canada Basin. The seismic data are dominated by an unconformity/reflector band that is observed along the entire transect that separates a flat-lying well-stratified upper unit from the underlying sediment sequences. In our interpretation this reflector band spans a time interval from breakup of the Lomonosov Ridge from the Siberian/Barents shelves around 56 - 65 Ma to the top of the Oligocene. The velocity-depth functions indicate total sediment thicknesses ranging from 1200 to 2000 m on the Lomonosov Ridge, to 5500-6300 m within the deepest part of the Makarov Basin around 168�E, to 1000 e1500 m on the western flank of the Mendeleev Ridge, and, finally, to ~4000 m within the Canada Basin. The data show that stretched continental crust of the Lomonosov Ridge extends farther into the Makarov Basin than previously known. Horst and graben structures indicate that approximately 50% of the Makarov Basin along the 81�N transect is underlain by stretched continental crust. These structures most likely formed during a rift phase which is older than 56 Ma. Thick Mendeleev Ridge crust (up to 33 km) occupies the remaining portion of the basin. It is likely that the formation of this magmatic crust overprinted older oceanic crust during the Cretaceous Quiet Period (84e120 Ma).