Beschreibung: Sediment delivery to the abyssal regions of the oceans is an integral process in the source to sink cycle of material derived from the hinterland. How sediments are transported down-slope, and where they are deposited has implications for the mass balance of the upper lithosphere, hydrocarbon reserves, climate archives and sequence stratigraphic models. The Zambezi River, the largest in southern Africa, delivers vast amounts of material to the continental shelf, submarine Sofala/Zambesia Bank. The Sofala/Zambesia Bank acts as a staging area for this riverine input prior to its redistribution toward the abyssal plains of the Mozambique Channel. Much of this material is said to be directed into the submarine Zambezi Valley and Channel. Until this study, however, the sediment transfer routes between the Sofala/Zambesia Bank and abyssal plains of the Mozambique Channel have been quite poorly understood and remain unconstrained. The aim of this contribution is to better constrain sediment transport pathways to the abyssal plains using the latest, regional, high resolution multibeam bathymetry data available, taking into account the effects of bottom water circulation, antecedent basin morphology and sea level change. Results show that sediment transport and delivery to the abyssal plains is discreetly partitioned into southern, central and northern domains. This sediment partitioning is primarily controlled by changes in continental shelf and shelf break morphology under the influence of a dynamic anticyclonic inshore circulation system. However, changes in base level have an overarching control on sediment delivery to particular domains at various sea levels. A direct consequence of these controlling factors is limited sediment delivery to the submarine Zambezi Valley and Channel under present-day conditions, with increased activity envisaged during regression. Furthermore, the “on-off” switching of discrete domains along strike is a sequence stratigraphic concept generally not previously considered in the shelf-slope-abyssal continuum. The proposed sediment transport routes, under varied sea level scenarios, provide a framework which relates shallow to mid depth studies with those focused on the deep regions of the Mozambique Channel providing the first inclusive account of shelf to abyssal sediment transport in the region.

Beschreibung: Integrating geophysics with geology, and specifically geochronology, reveals the complex tectonic history of Dronning Maud Land, an important part of East Antarctica, and a crucial element for Rodinia and Gondwana reconstructions. We recognise three major tectonic provinces: a westernmost part with Kalahari, Africa, affinities and an easternmost part from about 35E with Indo-Antarctic affinities; sandwiched in between these two blocks, is an extensive region with juvenile Neoproterozoic crust (ca. 990-900 Ma), the Tonian Oceanic Arc Super Terrane (TOAST) that shows very limited signs of a pre-Neoproterozoic history. We have tested the spatial extent of the TOAST by a regional moraine study that confirm the lack of older material inland, though latest Mesoproterozoic juvenile rocks frequently do occur in the glacial drift and probably record a slightly earlier precursor of the TOAST inland. The TOAST records 150 Ma of almost continuous tectono-metamorphic reworking at medium- to high-grade metamorphic conditions between ca. 650 to 500 Ma. This long-lasting overprinting history is thought to record protracted accretion of ocean island arc terranes and the final amalgamation of East Antarctica along the major East African-Antarctic Orogen. There is no sign of significant metamorphic overprint immediately after the formation of TOAST. Therefore, these island arcs may have formed independent of or peripheral to Rodinia and may reveal major accretionary tectonics outboard of Rodinia.

Beschreibung: We present a comprehensive regional bathymetric data compilation for the southwest Indian Ocean (swIOBC) covering the area from 4°S to 40°S and 20°E to 45°E with a spatial resolution of 250 m. For this, we used multibeam and singlebeam data as well as data from global bathymetric data compilations. We generated the swIOBC using an iterative approach of manual data cleaning and gridding, accounting for different data qualities and seamless integration of all different kinds of data. In comparison to existing bathymetric charts of this region, the new swIOBC benefits from nearly four times as many data-constrained grid cells and a higher resolution, and thus reveals formerly unseen seabed features. In the central Mozambique Basin a surprising variety of landscapes were discovered. They document a deep reaching influence of the Mozambique Current eddies. Details of the N-S trending Zambezi Channel could be imaged in the central Mozambique Basin. Maps are crucial not only for orientation but also to set scientific processes and local information in a spatial context. For most parts of the ocean seafloor, maps are derived from satellite data with only kilometer resolution. Acoustic depth measurements from ships provide more detailed seafloor information in tens to hundreds of meters resolution. For the southwest Indian Ocean, all available depth soundings from a variety of sources and institutes are combined in one coherent map. Thus, in areas where depth soundings exist, this map shows the seafloor in so-far unknown detail. This detailed map forms the base for subsequent studies of e.g. the direction of ocean currents, geological and biological processes in the southwest Indian Ocean.

Beschreibung: The Baffin Bay between Greenland and Baffin Island (Canada) opened during the separation of Greenland and Canada in the Palaeocene and Eocene. The Melville Bay is situated in its northeastern part. The crustal composition of Northern and Southern Baffin Bay has been studied in detail: Southern Baffin Bay is underlain by oceanic crust with volcanic margins, while the margins of northern Baffin Bay are characterized by serpentinized mantle material. In contrast, the nature of crust in the deep, central Baffin Bay and the Melville Bay was still unclear due to a lack of deep seismic sounding lines. In 2010 a joint geophysical experiment in the Greenlandic part of Baffin Bay acquired seismic, magnetic and gravity data. We present three velocity and density models derived from seismic refraction and gravity data. Two of the three profiles are located within the Melville Bay and extend in a SW - NE direction from the deep sea area of central Baffin Bay to the shelf area of the Melville Bay. The third profile crosses the northern profile in the Melville Bay and extends in a N - S direction into the Northern Baffin Bay. The profiles in the Melville Bay can be divided in three crustal sections. The deep-sea area reveals a 3.5 - 7 km thick, 2-layered oceanic crust with increasing thickness towards the shelf and up to 6 km thick sediments. The crust is underlain by serpentinized upper mantle with velocities of 7.6 - 7.8 kms-1. A transition zone, which is affected by volcanism, connects the oceanic crust with stretched continental crust underneath the Melville Bay. Basement highs and deep sediment basins characterize the stretched and rifted continental crust. The Melville Bay Graben, the deepest rift basin in Melville Bay, contains up to 10 km thick, possibly metamorphosed sediments with unusually high velocities of up to 4.9 kms 1. Well-constrained reflections of the crust-mantle boundary can be found in many seismic sections indicating a maximum crustal thickness of ~ 26 km in the northern profile and ~ 32 km in the southern profile. In the southern part of the third, N-S extending profile, a 2-layered oceanic crust is covered by up to 5 km thick sediments. Underneath the shelf edge, the crust thickens towards the north in several steps and reaches a maximum thickness of ~ 40 km. The northern part of the profile is characterized by faulted end eroded basement, which crops out at the seafloor.

Beschreibung: The Alpha–Mendeleev ridge complex is a prominent physiographic and geological feature of the Arctic Amerasia Basin. The Alpha and Mendeleev ridges are, respectively, the eastern and western components of a continuous seafloor high that is approximately 2000 km long and 200–400 km wide. A surge of interest in the tectonic evolution of Arctic submarine features has led to a wealth of new geophysical data collected from the Alpha Ridge. Current interpretations of its origin vary but there is compelling evidence that the Alpha Ridge may have formed as an oceanic plateau during the Late Cretaceous. Geological samples are rare but most samples recovered indicate a genetic link with the High Arctic Large Igneous Province (HALIP). In August 2016, Canada’s Extended Continental Margin-United Nations Convention on the Law of the Sea Program dredged approximately 100 kg of volcanic rocks from the Alpha Ridge. The large size and pristine state of the samples enabled the first comprehensive study of a single eruptive event in the volcanic record of the Alpha Ridge. The dredge sample is a lapilli tuff containing vitric and basaltic clasts. Textural evidence and the coexistence of juvenile and cognate clasts suggest a phreatomagmatic eruption. The vitric fragments consist of sideromelane glass with abundant plagioclase microlites. Texturally, these basaltic glass lapilli display a fresh glassy core surrounded by Fe- and Ti-rich zones and a palagonite rim. Major and trace element analyses of glassy cores indicate remarkably uniform, mildly alkaline basaltic compositions. The plagioclase-bearing glass yielded a 40Ar/39Ar plateau age of 90.40±0.26 Ma (2σ error) which included 89% of 39 Ar released. We interpret this result to represent the eruption age of the plagioclase microlites and consequently, of the host basaltic glass lapilli in the tuff. Volatile species analyses by infrared spectroscopy on the fresh basaltic glass suggests that the melt was effectively degassed to shallow level. Assuming equilibrium degassing, the homogeneous resulting values of H2O total in the range 0.1 to 0.19 wt.% (1σ error) indicate subaerial or shallow eruption (surface to 80 m). The new 40Ar/39Ar age for the sample is consistent with a 40 Ar/39Ar age of 89±1 Ma obtained for a sample of tholeiitic basalt dredged from the central part of the Alpha Ridge, and with the range of ages reported for HALIP igneous rocks exposed onshore in the Canadian Arctic Archipelago (130-80 Ma). Our new data provide evidence for local emergence of the Alpha Ridge in the Late Cretaceous. A comparison the Alpha Ridge and Kerguelen Plateau–Broken Ridge Large Igneous Province (LIP) provides new insights on the episodic nature of LIP magmatism and variations in eruptive style through time.

Beschreibung: A new digital bathymetric model (DBM) for the Northeast Greenland (NEG) continental shelf (74°N–81°N) is presented. The DBM has a grid cell size of 250 m × 250 m and incorporates bathymetric data from 30 multibeam cruises, more than 20 single-beam cruises and first reflector depths from industrial seismic lines. The new DBM substantially improves the bathymetry compared to older models. The DBM not only allows a better delineation of previously known seafloor morphology but, in addition, reveals the presence of previously unmapped morphological features including glacially derived troughs, fjords, grounding-zone wedges, and lateral moraines. These submarine landforms are used to infer the past extent and ice-flow dynamics of the Greenland Ice Sheet during the last full-glacial period of the Quaternary and subsequent ice retreat across the continental shelf. The DBM reveals cross-shelf bathymetric troughs that may enable the inflow of warm Atlantic water masses across the shelf, driving enhanced basal melting of the marine-terminating outlet glaciers draining the ice sheet to the coast in Northeast Greenland. Knolls, sinks, and hummocky seafloor on the middle shelf are also suggested to be related to salt diapirism. North-south-orientated elongate depressions are identified that probably relate to ice-marginal processes in combination with erosion caused by the East Greenland Current. A single guyot-like peak has been discovered and is interpreted to have been produced during a volcanic event approximately 55 Ma ago.

Beschreibung: New high-resolution bathymetric and sub-bottom profiler data collected in the Southern Mozambique Channel along a grid of 16 parallel, non-overlapping lines show a large variety of bedforms which were formed by strong bottom currents. They are visually classified into four main microtopographic zones and several sub-zones which divide the study area into regions with (1) smooth seafloor, (2) undulating bedforms, (3) seamounts and islands, and (4) the Zambezi Channel. A smooth seafloor occurs on the Mozambican continental slope together with downslope mass-wasting processes, north and south of Bassas da India, on the eastern levee of the Zambezi Channel and in the Zambezi cone. Undulating bedforms of some kilometres wavelength and several tens of metres height cover most of the southern, central and northeastern study area. The most spectacular bedforms are numerous, closely spaced, giant erosional scours of up to ~450 m depth, more than ~20 km length and ~3 - 7 km width in the southwestern part of the study area. Here, northward flowing Antarctic Bottom Water (AABW) is topographically blocked to the north and deflected towards the east due to the shallowing bathymetry of the Mozambique Channel. SW-NE trending undulating bedforms aligned parallel to the deflected AABW and interpreted as small contourite mounds allow to trace the AABW flow path eastwards. An ~100 km long W-E trending channel indicates the northernmost extension of the AABW. NW-SE oriented undulating bedforms in the west, hummocky bedforms in the east and arcuate, cross-cutting features in-between reflect a completely different current regime in the central study area. Comparisons with LADCP sections show, that the western part lies in the range of deep-reaching anticyclonic Mozambique Channel eddies (MCEs), so that the undulating bedforms are again considered to be small contourite mounds aligned parallel to a part of the swirl. The cross-cutting features in the middle mark the eastern boundary of the MCE, where a northbound flow direction prevails. The hummocky bedforms in the east may have developed under the influence of seasonally variable cyclonic East Madagascar Current eddies pretending at least two different flow directions. The origin of arcuate bedforms, sediment ridges and circular or elongate depressions in the northeastern study area is not clear. Bottom currents which interact with the topography of the Bassas da India complex and the Zambezi Channel may contribute to their formation. All morphological features are draped with sediments indicating that the present-day current velocities are not strong enough to erode sediments. This agrees with published LADCP bottom-current velocities of 0.1 m/s. Hence, the microtopography must originate from a time when bottom-current velocities were stronger. Assuming a published sedimentation rate of 20 m/Myrs and a drape of at least 50 m thickness the microtopography may have developed during Pliocene times or earlier.

Beschreibung: Thick packages of drift-type sediments were identified in the northwestern and central part of the Fram Strait, mainly along the western Yermak Plateau flank, but also in the central, flat part of the Fram Strait. A large-scale field of sediment waves was found north of 80.5°, along the Yermak Plateau rise. This field separates two drift bodies, a deeper one towards west and a shallower one towards east. The drift bodies were deposited by bottom currents, most likely by the northbound Yermak Branch of the West Spitsbergen Current, but an influence of a southbound current on the westren drift body cannot be ruled out. Within the drift bodies and even more pronounced withing the sediment waves, a stratigraphic boundary is clearly visible. It separates a lower package of waves migrating upslope at a low angle of ~5° from an upper package with significantly increased wave crest migration at ~16.5°. Using the seismic network, this stratigraphic boundary could be tracked to ODP Leg 151, Site 911, where it corresponds to the lithostratigraphic boundary between units IA and IB dated to 2.7 Ma. The increase in wave-crest migration angle points at a shift towards higher sedimentation rates at 2.7 Ma. This corresponds to the intensification of the Northern Hemisphere glaciation with a major expansion of the Scandinavian, northern Barents Sea, North American and Greenland ice sheets. The Barents Shelf that was subaerially exposed and the expansion of the northern Barents Sea ice sheet (as well as Svalbard) are the likely sources for enhanced erosion and fluvial input along the pathway of the West Spitsbergen Current, resulting in higher sedimentation rates in the Fram Strait.