Search

Two-dimensional and three-dimensional multichannel seismic reflection data are utilized to examine previously unrecognized contourite depositional systems along the continental margin of Nova Scotia, Canada. Prior to this study these features were thought to be of limited extent in the study area. The new data show that contourite drifts are widespread with greatest drift development during the Late Miocene to Pliocene. Giant sediment waves form stacked, aggrading sequences of bedforms and their development is linked to pre-existing seafloor morphology. Small sediment drifts developed locally throughout the late Paleogene and Neogene, either southwest and down-current of seafloor obstacles or form channel fills. Major erosional pulses form regional seismic markers; first along the continental rise in the Early Oligocene, then along the continental slope during the Late Miocene and Pliocene. Three-dimensional seismic data show that erosion surfaces preserve along-slope amplitude anomalies, two-dimensional, low-relief sediment waves, and barchanoid bedforms. The geophysical evidence implies that a northeast-to-southwest, along-slope bottom current influenced Cenozoic depositional patterns throughout the study area. [ABSTRACT FROM AUTHOR]

The tectonic history of Amerasia Basin, Arctic Ocean, is not well known because of a paucity of data and complexities introduced by the Alpha–Mendeleev Ridge large igneous province. Makarov Basin, at the northern limit of Amerasia Basin and adjacent to Lomonosov Ridge, may provide a window into understanding the larger tectonic framework. The objective of this study is to decipher the sedimentary and tectonic history of northern Amerasia Basin by analysing the seismic stratigraphy, structure and morphology of Makarov Basin and surrounding regions (Alpha and Lomonosov ridges) of the central Arctic Ocean. The principal data sources for this study are a 400 km long multi-channel seismic line, extending from Alpha Ridge to the crest of Lomonosov Ridge via central Makarov Basin, and the Arctic bathymetric chart. The seismic record within Makarov Basin is divided into five seismic units. The first unit overlying basement hosts Late Cretaceous (minimum age) slope to base of slope sediments. Some of these sediments are interbedded with volcanic or volcanoclastic rocks with a minimum age of 89 Ma. Makarov Basin becomes isolated from proximal sources of sediments after the onset of rifting that separated Lomonosov Ridge from the Barents Shelf, which may have occurred as early as the mid-Late Cretaceous, and led to the creation of Eurasia Basin. Sediments are largely pelagic to hemipelagic as a result of this isolation. This deposition style also applies to the draped sedimentary strata on Alpha and Lomonosov ridges. The uppermost seismic units within Makarov Basin arejump-correlatedto the stratigraphic record of the ACEX drill site on top of Lomonosov Ridge to provide age control. This correlation shows that the 44.4–18.2 Ma hiatus documented in the drill core is not apparent in the basin. Inter-ridge correlations and the absence of an obvious planate surface on Alpha Ridge also suggest that sedimentation was uninterrupted on this ridge during the hiatus. Seismic data reveal a deep subbasin (~ 5 km thick) within Makarov Basin. This subbasin is immediately adjacent to Lomonosov Ridge within major bends in the general strike orientation of the ridge. The rhomboid shape of the deep subbasin, the straight and steep morphology of the Amerasian flank of Lomonosov Ridge and the presence of numerous sub-parallel ridges (e.g. Geophysicists and Marvin spurs) created by splay faulting are evidence of strike-slip (transtensional) tectonics. This interpretation supports the “rotational” model of opening of Amerasia Basin with a transform to transtensional margin at Lomonosov Ridge. As spreading continued, however, the tectonics became increasingly extensional perpendicular to Lomonosov Ridge. There is no evidence of major tectonic deformation in Makarov Basin beyond the late Paleocene. [ABSTRACT FROM AUTHOR]

Turbidity currents are fundamental marine sedimentary processes that deliver sediments from continental margins to deep ocean basins. They develop and maintain deep-sea channels that act as principal conduits for this sediment delivery. While turbidity current channels are frequently considered as analogous to river channel systems, there are distinct differences in the mechanisms that govern their formation. This is particularly true at high-latitudes, where glacial margin processes and Coriolis effects have direct consequences on the characteristics of channel-forming turbidity currents. Understanding the latitudinal controls that influence the structure of these channels is thus a key objective of this study. The geomorphology of the glacial-fed NP-28 Channel in the Amundsen Basin of the Arctic Ocean, the highest-latitude deep-sea channel on Earth, is assessed. Compilation of available bathymetry shows that the channel follows a low-gradient, low-sinuosity path roughly paralleling the base of Lomonosov Ridge. The channel has a broad cross-section comparable to other glacially-fed and tributary-fed deep-ocean channel systems. High-resolution subbottom profiles reveal intrachannel terraces and an incised channel thalweg that were likely formed through erosion by traction-dominated currents; stratified levees and sediment waves were likely deposited by overbank flows. Coriolis deflection of channel-filling currents is evident from consistent levee asymmetry along the entire channel path. Within the channel, the channel floor geometry suggests local dominance of both Coriolis and centrifugal forces at the base of the channel; the latter in particular where the channel is deflected by external bedrock. Overall, channel morphology is largely consistent with existing models of Coriolis force effects on turbidity currents at high latitudes. This influence of Coriolis force, in addition to the presumed glacial style of the sediment input and bedrock interaction with the channel path, are considered the major factors that affected channel morphology. [Display omitted] • Geomorphology of the highest-latitude submarine channel on Earth is presented. • Asymmetric levees are consistent with strong influence of Coriolis force of suspended currents. • Channel floor geometries are consistent with centrifugal and Coriolis-dominated basal currents. • Coriolis force, bedrock control and presumed glacial source are factors in channel geomorphology. [ABSTRACT FROM AUTHOR]