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Sedimentary processes in small, isolated oceanic basins that form adjacent to continental margins but detached from continents remain poorly understood. This work describes two such basins located in the southern Scotia Sea, the Protector and Pirie basins. We analysed multichannel seismic profiles to interpret morphostructural features and stratigraphy of these basins. Sedimentary stacking patterns and depocentre distribution illustrate basin development patterns. Basal units infill basement depressions formed by the submerged banks of thinned continental crust that abut the basin plains. These lower and middle deposits of the sedimentary record are interpreted as pre - and syn-rift deposits. The laterally extensive upper deposits are interpreted as post-rift deposits. These include five discrete units evident in seismic profiles. A prominent regional reflection referred to as Reflector-c , separates in these upper deposits two sets of seismic units that have recorded major shifts in the dominant sedimentary processes, stacking patterns and paleo-environmental conditions. The most important processes controlling deposition of the older units (those beneath Reflector-c), include down-slope gravity processes that infill depressions created by crustal thinning and seafloor spreading. These occurred under the coeval influence of Circumpolar Deep Water circulation. The major processes influencing younger units (those above Reflector-c) include bottom water circulation of the Circumpolar Deep Water and Weddell Sea Deep Water water masses, which coursed along bathymetric contours of the seafloor. The Reflector-c discontinuity developed concurrently with middle Miocene tectonic changes, which led to the opening and deepening of deep gateways in the South Scotia Ridge. These facilitated overflow of Weddell Sea Deep Water from the Weddell Gyre into the Scotia Sea. This overflow in turn forced the Circumpolar Deep Water northwards. Analysis of the Protector and Pirie basins shows that their tectonic evolution influenced regional deep water circulation patterns in an area that makes a significant cold water contribution to the global conveyor belt system. As a long-term factor controlling basin evolution and sedimentary processes, tectonics events in this region therefore influenced the present day climate system. These results further clarify our understanding of deep, isolated oceanic basins in terms their sedimentologic, climatologic and oceanographic significance. [ABSTRACT FROM AUTHOR]

A detailed morphologic and seismic stratigraphic analysis of the continental margin offshore of Adelaide Island on the Pacific Margin of the Antarctic Peninsula (PMAP) is described based on the study of a regular network of reflection multichannel seismic profiles and swath bathymetry. We present an integrated study of the margin spanning the shelf to the continental rise, establish novel chronologic constraints and offer new interpretations on tectonic evolution and environmental changes affecting the PMAP. The stratigraphic stacking patterns record major shifts in the depositional style of the margin that outline three intervals in its evolution. The first non-glacial interval (Early Cretaceous to middle Miocene) encompasses a transition from an active to a passive margin (early Miocene). The second glacially-influenced interval (middle to late Miocene) is marked by pronounced aggradational sedimentary stacking and subsidence. Ice sheets advanced over the middle shelf of the margin at the end of this second interval, while the outer shelf experienced rare progradational events. The third, fully glaciated interval shows clear evidence of glacially dominated conditions on the margin. This interval divides into three minor stages. During the first stage (late Miocene to the beginning of the Pliocene), frequent grounded ice advances to the shelf break began, depositing an initial progradational unit. A major truncation surface marked the end of this stage, which coincided with extensive mass transport deposits at the base of the slope. During the second progradational glacial margin stage (early Pliocene to middle Pleistocene), stacking patterns record clearly prograding glacial sequences. The beginning of the third aggradational glacial margin stage (middle Pleistocene to present) corresponded to an important shift in global climate during the Mid-Pleistocene Transition. Morphosedimentary characteristics observed along the margin today began to develop during the latest Miocene but did not become fully established until sometime during the interval between the end of the Pliocene and middle Pleistocene. Between these two time intervals, the northeastward lateral migration of the Marguerite Trough also played a critical role in margin evolution, as it controlled ice sheet drainage pathways across the shelf, which in turn influenced development of slope and rise morphologies. Areas offshore from Adelaide Island differ from other areas of the PMAP due to changes in sedimentary processes that resulted from migration of the trough. This study confirms that the PMAP represents an exceptional locality for decoding, reconstructing and linking past tectonic and climatic changes. The study area specifically records not only the most relevant changes in depositional style, but also the relative importance of persistent along- and down-slope sedimentary processes. Our study approach can be extended to other areas and integrated with additional techniques to understand the evolution and the global linkages of the entire Antarctic continental margin and the ice sheets. [ABSTRACT FROM AUTHOR]

The Scan Basin is the easternmost of the southern Scotia Sea basins. It is located in a complex tectonic setting, north of the boundary between the Scotia and Antarctic plates. In addition, Scan Basin is directly to the north of Bruce Passage, which connects the Scotia and Weddell seas through the northward overflow of the Weddell Sea Deep Water (WSDW). Scan Basin has been described as an isolated small oceanic basin, where the fan-shaped abyssal plain is bounded by Bruce and Discovery banks. Sedimentary processes involved in the development of the Scan Basin sediment record during the late Pliocene-Quaternary are discussed here, through the examination of the distribution and morphological and acoustic characteristics of erosional, depositional, gravitational, fluid-escape, and volcanic features in correlation to the geological and oceanographic setting. The abyssal plain reflects the action of high-energy bottom-current circulation along its western side and lower-energy bottom currents along the eastern side. In contrast, Discovery Bank reflects a highly dynamic interplay between bottom-current activity, mass-wasting processes, and processes linked to the water mass interfaces. Variations in the abyssal plain stratigraphy are associated with events that may be related to climate changes since the late Miocene, involving increased bottom-current circulation and variations in the interaction between the WSDW and the Antarctic Circumpolar Current. The Scan Basin sector is one example of a contourite depositional system developed downstream of a deep gateway exit, and its major depositional characteristics allow its classification as a contourite fan. These new findings contribute to clarifying the development of contourite fans in regions of significant bottom-water interchange. [ABSTRACT FROM AUTHOR]

Abstract: Identification of the pre-glacial, transitional and full glacial components in the deep-sea sedimentary record is necessary to understand the ice sheet development of Antarctica and to build circum-Antarctic sediment thickness grids for palaeotopography/-bathymetry reconstructions, which constrain palaeoclimate models. A ~3300km long Weddell Sea to Scotia Sea multichannel seismic reflection data transect was constructed to define the first basin-wide seismostratigraphy and to identify the pre-glacial to glacial components. Seven main seismic units were mapped: Of these, WS-S1, WS-S2 and WS-S3 comprise the inferred Cretaceous–Palaeocene pre-glacial regime (>27Ma in our age model), WS-S4 the Eocene–Oligocene transitional regime (27–11Ma) and WS-S5, WS-S6, WS-S7 the Miocene–Pleistocene full glacial climate regime (11–1Ma). Sparse borehole data from ODP Leg 113 and SHALDRIL constrain the ages of the upper three seismic units and seafloor spreading magnetic anomalies compiled from literature constrain the basement ages in the presented age model. The new horizons and stratigraphy often contradict local studies and show an increase in age from southeast to the northwest. The up to 1130m thick pre-glacial seismic units form a mound in the central Weddell Sea basin and in conjunction with the eroded flank geometry, allow the interpretation of a Cretaceous proto-Weddell Gyre bottom current. The base reflector of the transitional seismic unit has a model age of 26.6–15.5Ma from southeast to northwest, suggesting similar southeast to northwest initial ice sheet propagation to the outer shelf. We interpret an Eocene East Antarctic Ice Sheet expansion, Oligocene grounding of the West Antarctic Ice Sheet and Early Miocene grounding of the Antarctic Peninsula Ice Sheet. The transitional regime sedimentation rates in the central and northwestern Weddell Sea (6–10cm/ky) are higher than in the pre-glacial (1–3cm/ky) and full glacial regimes (4–8cm/ky). The pre-glacial to glacial rates are highest in the Jane- and Powell Basins (10–12cm/ky). Total sediment volume in the Weddell Sea deep-sea basin is estimated at 3.3–3.9×106 km3. [Copyright &y& Elsevier]

The Scotia Sea is a complex geological area located in the Southern Ocean which evolution is closely linked to the opening of the Drake Passage. Structural highs of continental nature derived from the former continental bridge between South America and the Antarctic Peninsula surround the abyssal plains of the Scotia Sea, restricting small isolated sedimentary basins along its southern margin. Morpho-structural and seismo-stratigraphic analyses of multichannel seismic reflection profiles, and additional geophysical data available in the region, have been conducted, decoding regional and global implications of the basins' evolution. The main aim of this work is to describe the stratigraphic evolution of the southern Scotia Sea basins, from their opening in the back-arc tectonic context of the Scotia Sea, to the last oceanographic changes which have carried on global climatic implications. The evolution of the south Scotia Sea occurred through two major tectonic stages registered in the sedimentary record of the region: 1) the end of the subduction in the northwest part of the Weddell Sea during the early Miocene, which shortened the back-arc subduction trench generating a major change in the regional tectonic field that determined the evolution of the southern basins towards two different types of passive margins: magma-poor and magma-rich; and 2) the full development of the southern Scotia Sea basins during the middle Miocene, that led to the opening of deep oceanic gateways along the South Scotia Ridge. Interplay among tectonics, oceanography and climate is proposed to control the regional sedimentary stacking pattern, with coeval changes globally identified. [ABSTRACT FROM AUTHOR]